Anionic syntheses of terminally functionalized ethylene oligomers

Anionic Syntheses of Terminally Functionalized Ethylene Oligomers

DAVID E. BERGBREITER,* J. R. BLANTON,t R. CHANDRAN, M. D. HEIN, K.-J. HUANG, D. R. TREADWELL, and

S. A. WALKER,* Department of Chemistry, Texas A & M University, College Station, Texas 77843

Synopsis

Synthetic procedures for preparation of terminally functionalized linear ethylene oligomers are described. The preferred synthetic method is anionic oligomerization of ethylene with n-butyllithium-tetramethylethylenediamine and electrophilic substitution of the living oligomer so- formed. Conditions and procedures for subsequent chemistry to elaborate the end groups of these oligomers are described. These procedures afford strictly linear ethylene oligomers which contain a wide variety of end groups and which range in molecular weight from lo00 to 4500 (M,) . The product oligomers were characterized spectroscopically as toluene-ct, solutions at 110°C using multinuclear NMR, FT-IR, fluorescence, and W-visible spectroscopies as appropriate. Alterna- tive stepwise approaches to such oligomers are also discussed.

INTRODUCTION

Terminally functionalized polymers including comparatively low molecular weight oligomers of poly(ethy1ene glycol), various condensation polymers, polystyrene, and polyolefins have been of interest and are of continuing current interest in a number of applications of functional Such oligomers can be of interest in materials science as polymer additives and are also of interest in their own right as catalysts, reagents, or catalyst supports. In the case of derivatives of condensation polymers, such low molecular weight species can be synthesized by stepwise methods.' Low molecular weight peptides for instance are conveniently synthesized by stepwise approaches using methodology pioneered by Mer~ifield.~.~ Syntheses of well- defined oligomers of the other sorts of polymers mentioned above which allow for manipulation of both the end groups of the product and of the oligomer's microstructure can be more difficult. In general, control of the molecular size of oligomers and polymers such as polystyrene, poly(ethy1ene glycol), polybutadiene, and polyisoprene can be achieved by anionic polymerization. Both high functionalization efficiencies and control of the end group in the case of the hydrocarbon polymers is possible using literature procedures to'elec- trophilically trap the intermediate living polymer or to chemically modify end-functionalized polymers formed in such an anionic polymerization. As a

*To whom correspondence should be addressed. 'Present address: Department of Chemistry, The Citadel, Charleston, SC 65345. * NIH MARC Pre-doctoral Fellow, 1986-1989.

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 27, 4205-4226 (1989) 0 1989 John Wiley & Sons, Inc. CCC 0887-624X/89/124205-22$04.00

4206 BERGBREITER ET AL.

result, such syntheses are very useful as routes to materials for studies of polymer blend morphology and in other applications. In this paper, we describe related electrophilic substitutions and end group transformations of linear ethylene oligomers prepared by anionic oligomerization. The procedures we describe can be used to obtain good yields in conversion of end groups based on NMR spectroscopy (up to 90% conversion of end groups). More importantly for our purposes, the procedures we describe can be used to quantitatively modify various end groups so as to incorporate spectroscopic probes and reactive groups suitable a catalysts or catalysts ligands.

Our group has actively been exploring applications of low molecular weight polyethylene and polyethylene derivatives as catalysts, ligands and as polymer addi t i~es .~- '~ In our work, we have developed a variety of reactions which have proven to be practical and useful for preparation of terminally functionalized linear ethylene oligomers. Specifically, we have found that anionic oligomerization of ethylene using n-butyllithium-tetramethylethylenediamine as an initiator, electrophilic quenching of the resulting living oligomer and subsequent functional group chemistry is a versatile route leading to these functional oligomers. Of particular concern in our applications of functionalized ethylene oligomers was the need to quantitatively convert all functionalized termini into spectroscopically or catalytically useful groups. In such cases it was important that an adequate loading of functionality be present so that the penultimate solution of oligomer or blend of oligomer in polyethylene would have a sufficient concentration of functionality for useful catalysis or spectroscopic analysis. Typically this means that a loading of at least 0.2 mmol/g of functionality must be present on the starting oligomer. Further, we needed to be able to prepare a wide range of derivatives. As discussed below, this has proven to be possible based on 'H-NMR spectroscopic analysis of the oligomeric products of our reactions. We were less concerned about the presence of CH,-terminated ethylene oligomers (such species would be inert in the catalytic and the synthetic applications we were most concerned with). We also briefly explored stepwise approaches to such oligomers. This paper summarizes the synthetic chemistry we have developed in the course of this work and describes a number of synthetic procedures which should be useful in making various end-functionalized oligomers. As noted above, anionic polymerization is a well established route to

hydrocarbon polymers of butadiene, isoprene and styrene. Such reactions are practiced commercially. The importance of these reactions and the importance of block copol_ymers of polystyrene has resulted in considerable synthetic work. Many examples of electrophilic substitution of living oligomers and polymers of these monomers have been de~cribed.'~.'~ However, there are significant differences between the intermediates in these procedures and the intermediates in anionic oligomerization of ethylene. First, the intermediate organolithium reagents in polybutadiene, polyisoprene and polystyrene anionic polymerizations are all allylic or benzylic. These lithium reagents are resonance-stabilized. I t is thus easier to initiate these polymerizations. In addition, the resonance-stabilized intermediates in these polymerizations are less basic and less reactive toward weak carbon acids than are the intermediates in anionic polymerization of ethylene. Second, polymerizations of these dienes or styrene are homogeneous. Both the intermediate living oligomers

FUNCTIONALIZED ETHYLENE OLIGOMERS 4207

and polymers and the product polymers are soluble. In contrast, the product ethylene oligomers and the intermediate growing ethylene oligomers are both insoluble at 25°C once they reach a degree of polymerization of ca. 40.

Anionic polymerization of butadiene followed by hydrogenation of the product polybutadiene is presently one of the most common routes to ethylene 01igomers.~* 15, l6 However, there are some disadvantages to this method. Depending on the a-basicity of the solvent used in the polymerization, polybutadiene oligomers are varying mixtures of 1,2-polybutadiene and 1,4- p01ybutadiene.l~ Inevitably there is some 1,2-polybutadiene even with hydrocarbon solvents. Thus, the fully hydrogenated polymer always contains some ethyl branching and is, in effect, an ethylene-butene copolymer. Anionic oligomerization of ethylene in contrast yields strictly linear oligomers.

RESULTS AND DISCUSSION

Anionic oligomerization of ethylene has been reported previo~s ly . '~-~~ How- ever, i t has been of comparatively little interest because it is not a feasible route to high molecular weight polymers a t low ethylene pressures. Anionic polymerizations at high pressures of ethylene do however lead to high molecular weight material.17 We have observed that such oligomerizations of ethylene to form polyethylene-like macromolecules are initially homogeneous reactions [eq. (l)]:

(1) n-BuLi

heptane

CH2=CHz n-C,H,~CH2CH2fnCH2CHzLi

1

These oligomerizations require an activated alkyllithium initiator such as n-BuLi-TMEDA. Unlike the more reactive butadiene, isoprene and styrene monomers, ethylene is simply too unreactive to readily form oligomers in the absence of TMEDA.21 When n-BuLi-TMEDA was added to an ethylene- saturated heptane solution under a 30 psig ethylene atmosphere there was an immediate mildly exothermic reaction. This reaction continued for about sixty minutes. At this point, a precipitate of oligomer 1 formed. Subsequent anionic polymerization was then a heterogeneous reaction and was markedly slower. As a result, polymerization to yield very high molecular weight materials is not practical. Nonetheless, we have found that further polymerization past the precipitation point followed by electrophilic substitution in combination with subsequent synthetic transformations is a viable method to prepare terminally functionalized ethylene oligomers containing many different sorts of functional groups with 40-200 ethylene groups. While the product oligomers prepared in this way cannot be charactreized by conventional GPC at room temperature (these oligomers, like polyethylene, are insoluble in all solvents at 25"C), the presence of functional groups at the chain terminus makes NMR analysis feasible. Nearly any functional group that one might wish to introduce at the end of an ethylene oligomer will shift the adjacent methylene protons far enough away from the large -CH2CHz-- signal to permit easy detection and integration of the end group relative to an internal standard using a 200 or 400 MHz 'H-NMR spectrometer. End group analysis by


TABLE I The Effect of Initiator Concentration on Lithiated Ethylene Oligomer M, a

n-BuLi-TMEDA Precipitation time Oligomer yield (mmol) (fin) Oligomer M,, (9)

19.2 9.6 4.3 1.7

67 53 66 54

926 940

1119 992

10.5 6.0 3.7 1.6

"Oligomerizations were carried out at 25°C under a 30 psi ethylene atmosphere in heptane. bOligomer molecular weights were determined by 'H-NMR spectroscopy in toluene-d, using

1,1,2,2-tetrachloroethane 8s an internal standard and integrating the -CH, groups produced by protonation of living oligomer 1 with CH,CH,OH versus this standard and versus the -CH,- signal.

H-NMR spectroscopy is thus a simple way to determine oligomer molecular weight. At the same time, NMR spectroscopy provides useful information about the success of various synthetic reactions. Such NMR spectra were obtained in toluene-d, a t 100-110°C. The only difficulties encountered in these analyses were in cases where the terminal group on the oligomer was oxygen-sensitive. For example, in the case of the diphenylphosphine terminated oligomers discussed below, it was essential to degas the toluene-d, before dissolving the oligomer to avoid inadvertent oxidation of the functional #YOUP*

These anionic oligomerizations are initially rapid. When the initiator n-BuLi/TMEDA mixture was added to an ethylene-saturated heptane solution under a 30 psi ethylene atmosphere, an exothermic reaction ensued. This rapid phase of the reaction continues for about 60 min until a white precipitate forms. Quenching these reactions after 24 h with ethanol and analysis of the M,, of the product oligomers (see Experimental Section) from these protonations showed that the H-terminated oligomers formed had a molecular weight (M,) of ca. 950. Studies of this oligomerization with varying amounts of initiator n-BuLi-TMEDA showed that the precipitation occurred a t the same time regardless of the amount of oligomer formed and that the molecular weight of the products was similar even when the amount of initiator varied over a greater than 10-fold range (Table I). Changing the amount of initiator only changed the amount of final oligomer produced. These results suggest that precipitation occurred when the oligomer reached a particular size and that the molecular weight of oligomer only depended on the time allowed for the oligomerization. As noted above, the rate of oligomerization based on consumption of ethylene beyond the precipitation point was slower. While extended polymerization times could be used under these conditions to obtain oligomers with molecular weights of up to 4500, these oligomerizations required more than 1 week. Most commonly, we used 2-4 day oligomerizations to prepare oligomers with molecular weights (M,) in the range of

The product ethylene oligomers produced by the reaction in eq. (1) are strictly linear with no branching. Such oligomerizations have several advan- tages as synthetic routes to polyethylene-like materials. Side reactions such as chain transfer are chemically precluded by the low acidity of the saturated

1

1500-2500.


hydrocarbon oligomer and of the heptane solvent. In addition, anionic polymerization of ethylene is experimentally simple and affords a readily deriva- tized living oligomer. These oligomerizations could also be carried out with conventional inert atmosphere techniques since our uses of these oligomers were unaffected by the presence of either low molecular weight material or H- terminated oligomers which could result from inadvertent termination due to adventitious protonation.

There are also some inherent disadvantages with anionic oligomerizations like eq. (1). First, oligomers 1 with n > 40 are insoluble a t room temperature. While these lithiated ethylene oligomers are soluble a t higher temperatures, the known thermal instability of the intermediate alkyllithium reagents above 100°C limits the temperature at which such reactions can be carried out.,, The product oligomer's size is thus practically limited to about M, < 5000 for reasonable reaction times. Second, the reactivity of alkyllithium reagents like 1 and especially TMEDA complexed alkyllithium reagents like those in eq. (1) precludes the use of any solvents other than hydrocarbon solvents. Even solvents as weakly acidic as toluene and benzene are metalated under these conditions and thus behave as proton donating chain terminators. Thus, most other solvents including aromatic solvents and ether solvents are best not used, a t least during the oligomerization process.

Although n-BuLi-TMEDA was the preferred initiator, other alkyllithium reagents were also used to initiate these oligomerizations. For example, tert- butyllithium was successfully used and seemed to give results much like those using n-butyllithium. There were some minor differences in that the initiator derived end group was in these cases a sharp singlet in the 'H-NMR spectrum of the product. Otherwise the two initiators were equivalent. The use of less reactive lithium reagents such as phenyllithium did not work. While PhLi-TMEDA should have been reactive enough to initially add to ethylene, we speculate that the benzylic CH, necessarily produced in this reaction subsequently quenched the growing living oligomer before it reached the precipitation point. We also briefly examined the possibility that we could incorporate alkenes other than ethylene. Bicyclo[2.2.l]hept-2-ene was selected as a candidate internal alkene because it does not have acidic allylic C - H ' s and because as a strained alkene it is known to react with some alkyllithium reagents.,l However, oligomerizations in the presence of a 10-fold excess of this alkene (relative to initiator) failed to form any cooligomer. Metalation of TMEDA by alkyllithium reagents was another possible side reaction during this chemistry. However, we did not see any evidence of this product other than the presence of some proton terminated oligomer. If this reaction were occurring, i t was of minor importance and was not distinguished from other adventitious protonations which we believe occurred. Our NMR analyses did not detect any TMEDA-derived end groups in the product oligomers. On this basis, we exclude any significant initiation by metalated TMEDA. However it should be noted that while incorporation of nitrogen species and initiation by aryllithium reagents was unsuitable for these slow low pressure oligomerizations, different results have been reported for anionic ethylene polymerizations carried out a t slightly higher temperatures and much higher pressures.17

Given this information about the available sizes of 1 and the most feasible routes for its formation, we turned our attention to developing useful chemistry with 1 and products derived from this lithiated oligomer. Derivatization


of the living oligomer 1 was carried out in several ways, all of which relied on the chemical similarity of 1 and an alkyllithium reagent. In some cases [eqs. (2)-(5)], electrophilic substitution of 1 led directly to products of interest, e.g., ligands for homogeneous catalysts or phase transfer catalysts.

1. cop n-C4Hg( CH&H2jnCH2CH2Li n-C,HgfCH,CH,j~CH,CH2C02H (2)

1 2 CIPPh,

n-C4H9f CH&H2-fnCH2CH2Li n-C4Hg( CH2CH2-)-,CH&H2PPh2 (3) 1 3

? 9

(4)

4

5

In these examples, the oligomeric lithium reagent 1 reacted readily with both sp2-hybridized carbon electrophiles and with a phosphorus electrophile and thus mimicked the reactivity of n-butyllithium with these same electrophiles.

Carboxylic acid formation by CO, quenching of 1 [(eq. (2)] has proven to be one of the most useful reactions for introducing functional groups in these oligomers. This reaction can be complicated by formation of ketone by reaction of the intermediate lithium carboxylate with 1. This side product was not easy to detect as a contaminant of 2. However, it was readily distinguished by IR spectroscopy (v c=o = 1710 cm-') after formation of carboxylic acid esters or amides from 2. Formation of this ketone side product was avoided by ensuring that the carboxylation of 1 with CO, is carried out a t - 78°C.

The need to use temperatures of ca. 100°C to dissolve these products also affected the outcome of these reactions. For example, the reaction of 1 with pyridine [eq. (5)] presumably proceeded by initial formation of a polyeth- ylenedihydropyridine. However, no effort was made to avoid contact with air during the work-up and cleanup of the product oligomer so oxidation with atmospheric oxygen occurred. This oxidation accounts for isolation of. the observed aromatic product and parallels known chemistry for alkyllithium reagents reacting with ~yridine.,~ In other cases, air oxidation is less desirable. For example, solutions of 3 that were not degassed readily formed polyethylene diphenylphosphine oxide.


Yields in these electrophilic substitution reactions typically ranged from 30-80% with loadings on the oligomers in the range of 0.1-0.6 mmol of functional groups/g. Yields in successive steps in multi-step reactions on functionalized oligomers were however much higher. In all cases described here, conditions were developed so that the end group conversions were quantitative by 'H-NMR spectroscopy. 'H-NMR spectroscopic analysis using hexamethyldisiloxane or 1,1,2,2-tetrachloroethane as internal standards showed that the M, of the functionalized chains was in the range 1500-2500. In calculating these molecular weights, we corrected for the amount of non-functionalized chains by integrating the CH, signals in addition to the signals for the functionalized chain ends. These electrophilic substitutions were good, general reactions. However, there are occasions in which extensions of this chemistry appears failed. For example, we have not been successful in reactions of 1 with cyclopent-2-enone. In this particular example enolization by the solid lithium reagent 1 presumably occurred instead of the desired 1,2-addition by 1 to the carbonyl

While alkyllithium reagents are often poor carbon nucleophiles for carbon-carbon bond formation with alkyl halides, these reagents react readily with benzyl halides to form carbon bonds to the benzyl carbon. This reaction, which has precedent as a titration procedure for analysis of residual base in alkyllithium reagent chemistry,25 was successfully applied to oligomers like 1. This reaction can be effected with various groups on the aromatic ring. Halides and ethers both were used successfully [eqs. (6) and (7)]. Thus, the nucleophilic substitution by 1 at the benzylic carbon is faster than either metalation of the aromatic ring or metal-halide exchange.

1 3

BrCH, O - O C H ,

1 >

/ \ n-C4H t CH $HZ CH -0- Br (6)

6

7

While the above routes to terminally functionalized ethylene oligomers work well in many cases, multistep reactions are also feasible. For example, hydroxy terminated ethylene oligomers were conveniently prepared either by reduction of the carboxylic acid terminated oligomer 2 with borane-dimethyl sulfide or by the reaction of 1 with ethylene oxide [eq. (8) or (9)].

1. BH3.S(CH,), n-C4 Hg 3- CH2CH2 jnCH2CH2C02 H 2. H202 . OH-, CH30H ' n-C4H9(CH2CH2*~cH20H (8)

0 8 2 / \

1.H2C-CH,

1 8

n-C, H, $. CH2CHz-)nCH2CHz Li 2. H,O+ ' n-C,H,f CH2CH,J;;r,CH,OH (9)


While the two-step process of formation of 2 followed by reduction to form 8 was only an alternative to the direct formation of 8 from a living oligomer, other terminally functionalized oligomers are only available through multistep processes. In many cases, we needed such functionalized oligomers as catalyst ligands, as catalysts or as spectroscopically labeled oligomers. Thus, we have developed a variety of conditions suitable for such multistep transformations as discussed below.

Synthetic transformations of carbonyl groups are well established transformations in organic chemistry and were easily extended to oligomers like 2. For example, direct esterification of 2 with methanol or ethanol was achieved simply by heating 2 in toluene in the presence of acid and methanol or ethanol [eq. (lo)]. Alternatively, the carboxyl group could first be activated by formation of an acid chloride. Addition of an alcohol and a base like pyridine to consume any HC1 generated was an alternative route to form an ester. While this reaction did lead to esters, the acid chloride 10 was more useful as a precursor of amides. Acid chloride 10 was used to make a variety of carboxylic acid amides from a variety of amines including 11,12, and 13.

13

Carboxylic acid derivatives of terminally functionalized ethylene oligomers were also prepared starting with hydroxy terminated oligomers 8 and the amine terminated oligomer 23 whose synthesis is discussed below. For example, carboxylic acid esters were conveniently prepared by reaction of the polyethylene alcohol with solutions of acid chlorides such as 14,16, and 18. In this manner, we have attached a variety of UV-visible and fluorescent labels at the termini of these ethylene oligomers.

In these reactions, as in the other multistep reactions discussed in this paper, we have generally found model reactions using the appropriate deriva-


tive of octadecane to be useful as examples of the chemistry of these oligomers a t 100°C. While some reactions can be successfully carried out with suspensions of these ethylene oligomers and a soluble reagent, we have been most successful when the derivatization is carried out under conditions where the oligomers are in solution. Because of the insolubility conferred on these oligomers by their polyethylene-like alkyl groups, such solubility can only be attained by heating the reaction mixture up to 90-llO°C in solvents like toluene or dibutyl ether or to higher temperatures in mixed solvents. Thus, when developing a new derivatization procedure for an oligomer like 8, we have found it to be useful to first carry out a similar reaction under the s u m conditions using octadecanol. Since we can easily monitor the success of the reaction using the low molecular weight substrate using ambient temperature NMR, GC, HPLC, and TLC, we can easily adjust the reaction's conditions so as to best achieve the desired results when the reaction is extended to the oligomer. The 'H-NMR spectrum of the octadecyl derivative also provides us with a good model for what the 'H-NMR spectrum of the polyethylene derivative will look like.

Transformation of the hydroxy-terminated oligomer 8 into an oligomer with a leaving group was accomplished two ways. First, 8 was transformed into a chloro-terminated oligomer 20 by treatment with triphenylphosphite and benzyl chloride [eq. (18)].26 Second, reaction of 8 with methanesulfonyl chloride and triethylamine in hot toluene was used to prepare the methanesul- fonate ester of 8 [eq. (19)].27 While either of these oligomers could be used as substrates for subsequent nucleophilic substitutions, we found the mesylate synthesis to be more convenient and it was therefore used in the chemistry described below.

c l c o e ""0 - &H(CH,)2

* (15) 14 n-C, H, f CH,CH2 jnCH2CH,CH,0H

15

CH2CH2CH2COCI

n-C,Hgf CH2CH2jnCH2CH2CH20H 16 P

8

17


0 n-C,H,( CH2CH2-f,CH2CH,CH,0H i8

> 8

n-C, H, f CH2CH2-)-,CH,CH,CH,0COCH20 0 (17) 19

C6H5CH2CI

n-C,Hgf CH2CH,jnCH,CH,CH,0H (C6H50)3P ~ n-C4Hg( CH,CH2-)-,CH2CH,CH2C1 8 toluene, 100°C 20

CH3S02CI (CH3CHZ )3N

8 toluene, 100°C

n-C, Hg ( CH2CH,jnCH,CH2CH,0H

(19) n-C4Hg( CH2CH,-)-,CH&H,CH2OSO,CH,

21

Introduction of amino groups a t the terminus of these oligomers was accomplished by a classical series of reactions as is shown in eq. (20). The hydroxy terminated oligomer 8 was first converted into the mesylate 21. Having made the oligomer terminus into an electrophilic group, sodium phthalimide was added. Heating then produced the desired polyethylene phthalimide. At this point the reaction proved to be somewhat different than its soluble analog. Hydrazine and butyllithium were both tried as reagents to cleave the phthalimide group and to generate the desired free amino group. However, neither .of these reactions were successful. However, a two step process using first alkali and then sulfuric acid did successfully effect removal of the phthalimide protecting group and generated the desired amine.

n-C4 Hg ( CH,CH, jnCH2CH,CH,0H CH&QCI, (CH~CHZ )3N 0 * 8 toluene, 100°C xylene, DMF, 160°C

120°C, 24 h d’ 22

Other nucleophilic substitution reactions a t the terminus of these oligomers were successful as well. For example, lithium diphenylphosphide anion reacted readily with the mesylate derivative of 8 to form the equivalent of what we


were able to obtain directly from 1 with a ClPPh, quench. Similarly, the potassium salt of carbazole reacted with the mesylate derivative of 8 to form the fluorescent carbazole terminated oligomer 24.

K +

n-C, H, -t CH2CH2 -)-,CH,CH,CH,OH C H ~ O Z C I , (CHsCHz )3N b

8 toluene, l00OC

Conversion of the hydroxy terminated oligomer 8 into a hindered phosphite group was more of a problem. While conversion of alcohols into phosphites can be accomplished readily by a number of procedures a t 25"C, these same procedures with 8 necessarily had to be carried out a t ca. 100°C. Under these conditions, we typically obtained mixtures of phosphorus containing products which were unusable as ligands for transition metals. Alternative classical routes to phosphites which involved reaction of alcohol with a chlorodi- alkylphosphite or with phosphorus trichloride were not useful. These procedures involving the reaction of the oligomeric alcohol 8 with ClP(OR), or PCl, formed only modest or small amounts of phosphite a t best. More commonly a major product was a polyethylene dialkylphosphonate. For example, using chlorodiethylphosphite, 8 and triethylamine the major polyethylene product was 25.

n-C,Hgt CH,CH,* ,CH,OPO( OEt), 25

The best procedure for this transformation required a deprotonation of 8 with n-butyllithium to form a lithium alkoxide followed by exchange with excess triarylphosphite [eq. (22)].

e x c w (ArO),P

100°C. toluene R 26

-o.h=Q R = H, - CH, or C,H,

Both direct and multi-step reactions of 1 were useful in forming organometallic derivatives of polyethylene. For example, using bromobenzene terminated ethylene oligomers i t was possible to generate a reactive organolithium terminus on these oligomers. Metal halide exchange on the bromoben-

4216 BERGBREITER E T AL.

zene terminated oligomer 6 generated the lithiated oligomer 27 which could then be quenched with various electrophiles. We found this procedure to be a useful way to generate triarylphosphine terminated oligomers for use as ligands. In these reactions, CIPPh, was used as an electrophile to quench the lithiated oligomer 27 as a means of forming a triarylphosphine ligand 28.

n-C4H9fCH2CH2*1cH2 O B r n-BuLi , n-C4HgfCH&H,J;;T-icH,

6 27

(23) CIPPh, n-C4Hgf CH,CH,J;;?-lCH, 0 PPh,

28

We have also used 1 and derivatives of 1 as precursors to less reactive metalated ethylene oligomers. For example, reaction of 1 with alkyltin chlorides 29 yielded ethylene oligomers terminated with triorganotin groups and with alkyl tin halide groups. These tin-containing polyethylene derivatives were characterized by 'H- and "%n-NMR spectroscopy and by ICP analysis of acid digested samples of these oligomers.

n-C4Hg+ CH,CH,---f;;T,CH,Li CL+IsnR3-; n-C4Hg( C H 2 C H , ~ l C H , S n C l , R 3 - x 1 29

29a, n = 1 , R = n-Bu 29b, n = 1, R = C6Hs 29c, n = 1, R = oligomer 29d, x = 2, R = oligomer 29e, n = 0, R = C,H,

Terminally functionalized oligomers like these were also useful in synthesis of block cooligomers. Two examples are shown below. In the first example, we introduced a polystyrene block onto 1 directly using styrene as the electrophile to quench the living alkyllithium oligomer [eq. (25)]. Although this reaction had to be carried out heterogeneously because 1 is insoluble at 25"C, we were able to add an average of 8 styrene units onto 1 under our reaction conditions. We also used poly(ethy1ene glycol) derivatives to make higher molecular weight block cooligomers using the acid chloride terminated oligomer 10.

n-C4H,( CH,CH,J;;?-,CH,Li 1 . r *

1 2. COB 3. H30i


H 3 0 i - CH,(CH,CH,),+ ,,,CH,CO,H or CH,(CH,CH, ),+ ,,,CH,CH,OH

Scheme 1

As shown by the chemistry above, anionic oligomerization of ethylene is a useful alternative to anionic polymerization of butadiene followed by hydrogenation for formation of terminally functionalized ethylene oligomers. Dur- ing the course of this work, we also investigated an alternative, stepwise syntheses using a polymer immobilized, terminally functionalized hydrocarbon. Stepwise synthesis of oligomers of condensation polymers is a well-established method which works for simple polymers as well as for more complex biopolymers such as peptides and nucleosides. However, we are unaware of any examples where a Merrifield type approach has been used for polymers in which the backbone contains only carbon-carbon bonds. When we originated this aspect of our project, we thought that this approach might be useful in that we could drive reactions to completion with excess reagents and avoid repetitive product purifications required in a typical stepwise organic synthesis in solution.

The general approach we attempted is shown in Scheme 1. In this chemistry, we started with a terminally functionalized carboxylic acid, ll-iodoundecanoic, which was bound to 1% divinylbenzene crosslinked polystyrene containing 1.25 meq of ClCH,-/g polymer through an ester bond. Then a Grignard reagent derived from 11-chlorooundecene was added to methylcop- per(1) to form a cuprate reagent which was added to this polymer-bound i~dide.~ ' ,~ ' The product of this nucleophilic substitution was a polymer-bound alkene which was hydroborated and oxidized. While the product polymer- bound alcohol could be converted into a polymer-bound mesylate, appreciable


hydrolysis occurred during the oxidation of the intermediate borane. Separate experiments with a polystyrene-bound mesylate showed that repeated cou- plings with copper(1) reagents could be successful. However, while repetition of this operation 10 times could have yielded a strictly monodisperse version of the oligomers derived from 1, the experimental problems with unwanted hydrolysis of intermediates, the difficulties of removing by-product copper salts from the coupling reactions and other experimental problems which resulted in poorer yields of these reactions as the chains used became larger doomed this approach. The alternative segment approach used successfully to minimize similar problems in peptide synthesis was also unsuccessful.30 In this approach, two pieces of intermediate length, e.g., a C,, derivative, would be coupled. Unfortunately, such intermediates are too insoluble and too crys- talline to react as desired. At best, we were able to combine these strategies to make small amounts of a C,, difunctionalized carboxylic acid which we were unable to further elongate.

One alternative successful stepwise synthesis strategy leading to ethylene oligomers has been described.31 In this chemistry, olefin metathesis of large terminal alkenes is used to generate successively larger internal alkenes which are then isomerized stoichiometrically to terminal alkenes using a bis(cyc1o- pentadieny1)zirconiumhydridochloride reagent. Repetition of this process the desired number of times would yield a final product alkene which should be essentially monodisperse. Solubility and thermal instability problems of the intermediate organometallic compounds which plagued our approach using organocopper(1) chemistry may not hinder this approach based on this literature report. However, this procedure is still more lengthy and tedious com- pared with the simpler alternative of anionic oligomerization.

In summary, anionic oligomerization of ethylene and subsequent electrophilic substitution of the intermediate living oligomer is a useful route to a variety of terminally functionalized linear ethylene oligomers. With modest effort, it is possible to develop and modify reaction conditions to introduce a wide variety of functional groups a t the terminus of such oligomers.

EXPERIMENTAL

General Methods

Ethylene and carbon dioxide were obtained from Matheson Co. Other chemicals and reagents were obtained from Aldrich Chemical Co. Hydrocar- bon and ethereal solvents were distilled under nitrogen from sodium benzophenone ketyl immediately prior to use. Other solvents used were reagent grade and were generally not further purified. Tetramethylethylenediamine was distilled from potassium metal and stored

under nitrogen until use. Nitrogen was purified by passage through a calcium chloride drying tower. The ethylene used was reagent grade and used without further purification. Thionyl chloride was purified according to a literature method.32 Styrene was purified by a procedure described by C011man.~~ All glassware was dried in an oven at 13OOC overnight prior to use. Magnetic stirring or shaking on a wrist-action shaker was generally used for agitation of reactions. Syringes and stainless steel cannulae were utilized to transfer


water-and air-sensitive solvents and reagents.34 The column for GPC analysis was a 30 cm long by 7.8 mm in diam and packed with ful!y porous, highly crosslinked styrene-divinylbenzene copolymer (Waters, 500 A Styragel). GPC carried out with degassed toluene a t room temperature showed that the suspensions of linear precipitated oligomers were not contaminated by low molecular weight species other than solvent (RI detection). Infrared spectra of polymer powders (i.e., polyethylene or entrapment-functionalized polyethylene) were taken using thin translucent discs prepared by a pressed-disc technique. IR spectra were recorded on a Pye Unicam SP3-200 or IBM Model 32 FT IR spectrometer a t room temperature. Band positions are reported in cm-'. 'H-NMR spectra were obtained using a Varian XL-200, Gemini 200, or XL-400 MHZ NMR spectrometer a t 25°C or a t higher temperatures when elevated temperatures were necessary to keep the polymer or oligomer in solution. Chemical shifts are reported relative to TMS. Using the reaction conditions described, conversion of one functional group into another as described below was quantitative by 'H-NMR spectroscopy. Under the conditions reported we could detect no starting material by 'H-NMR spectroscopy (> 95% conversion). Number average molecular weights were generally determined by 'H-NMR spectroscopy usi'ng 1,1,2,2-tetrachloroethane and hexamethyldisiloxane as internal standards. M,, values were determined by H-NMR integration of the areas of the end methyl groups versus 1,1,2,2-

tetrachloroethane or hexamethyldisiloxane internal standards.

1

Preparation of Lithiated Ethylene Oligomer (1)

A dry 500-mL Fisher-Porter pressure bottle equipped with 2 magnetic stirring bar was connected to a multiple-use (vacuum, nitrogen and ethylene) pressure line through a pressure coupling. This bottle was then evacuated and purged with nitrogen 3 times. Dry heptane (250 mL), 6.2 mL of 1.6N n-butyllithium in hexane, and 2 mL of N, N, N , N-tetramethylethylenediamine were added successively by syringe. The bottle was pressurized with ethylene to 30 psig and the oligomerization was carried out a t this pressure. The reaction was initially homogeneous and slight warming of the pressure bottle was detectable. After about 30 min, 1 precipitated. Depending on the desired size of the final product, the oligomerizations was continued for varying lengths of time. Typical times ranged from 36-48 h. This living oligomer was not itself characterized but rather was converted by electrophilic substitution reactions to the desired terminally functionalized ethylene oligomers described below.

Preparation of Carboxyl Terminated Ethylene Oligomer (2)

The suspension of oligomer 1 in heptane was cooled to -78°C using a dry ice-acetone bath. Any ethylene in the reactor was evacuated and dry CO, was introduced. The resulting suspension was then allowed to stir under 30 psi of CO, while the reaction mixture warmed to room temperature. After stirring at room temperature for several hours, the product suspension was poured into 10% HC1. Filtration through a coarse fritted funnel yielded the crude product as a white powder. This product was then worked up one of two ways. Most commonly, the product was added to a glass thimble in a jacketed Soxhlet extractor and extracted with hot toluene for 1-2 days. Extraction was facili-


tated by attaching a trap to the apparatus to remove any water. The final product was then recovered by cooling the hot toluene solvent to precipitate 2. Filtering and vacuum drying yielded the final product. A typical yield was 15 g of product oligomer with yields in multiple runs ranging from 10-20 g. The M , of this product was usually determined by esterification with CH,OH/H+CH,CH,OH/H+ and subsequent 'H-NMR analysis using tetrachloroethane or hexamethyldisiloxane as an internal standard. Percent conversion of end groups varied between 40-90% based on 'H-NMR end group analysis of derivatives of 2.

Preparation of Polyethylenediphenylphosphine

This alkyldiphenylphosphine ligand was prepared in three ways. First, it was prepared from 1 and ClPPh, according to a procedure we have previously de~cribed.~ Second, this phosphine was prepared by reaction of LiPPh, with the methane sulfonate ester of polyethylene alcohol. In a typical procedure, the mesylate derived from 8 was suspended in an 4 : 1 (vol/vol) mixture of dry toluene and THF and LiPPh, (prepared from the reaction of lithium metal and ClPPh,) was added by forced siphon using a cannula. The red color of the LiPPh, solution discharged rapidly initially but then persisted as the rest of the LiPPh, solution was added. After the addition was complete the mixture was heated first to 60°C for 2 h and then to 90°C for 16 h. A slight orange color persisted throughout the reaction. After cooling to room temperature, 20 mL of CH,OH was added to quench any unreacted LiPPh, and the solid product was isolated by suction filtration. Starting with 5 g of mesylated polyethylene, 4.6 g of product was isolated having 31P-NMR (xylene, 100°C) 6 - 14.3 (major and 26.5 (minor). The later peak was due to 10-20% of phosphine oxide. Loading of the polymer estimated from its 'H-NMR spec- trumgand was 0.4 mmol of -PPh,/g of oligomer. The oligomer was estimated to have a M, of 2100 by end group analysis. Percent conversion of end groups in this case was 84% by 'H-NMR spectroscopy (the balance of 16% of the oligomers were terminated with -CH, groups). Third, an analog of 1 was prepared using tert-butyllithium as an initiator. This product, which contained a tert-butyl end group, had a number average molecular weight of 1795.

Polyethylene-bound benzo-15-crown4

This crown ether derivative was synthesized and characterized as previously described."

Preparation of 2-Polyethylenepyridine

To a 500-mL Fischer-Porter pressure flask equipped with a magnetic stir bar, 200 mL of heptane distilled from sodium benzophenone ketyl was introduced by syringe under a positive pressure of nitrogen. To this flask 2 mL of TMEDA was added by syringe immediately followed by 10 mL of a 1.5M solution of n-butyllithium in hexanes. The flask was pressurized to 30 psi with ethylene and allowed to stir for 72 h. The polymerization was quenched with 3.5 mL of pyridine. The solution was heated to 95°C and stirred for 24 h. The solution was cooled to room temperature and the oligomer isolated by vacuum filtration. A jacketed Soxhlet extraction with toluene was used to remove any insoluble materials present in the oligomer. The oligomer was isolated by


vacuum filtration and dried under reduced pressure for 24 h. 'H-NMR (C,H,, HMDS, 105°C) 6 0.9 (t), 1.3 (br s), 2.72 (t), 6.68 (pair of d), 6.8 (d), 7.15 (pair of t), 8.4 (d). From end group analysis by 'H-NMR using 1,1,2,2-tetrachlorethane as an internal standard the number average molecular weight of 5 was calculated to be 2800 g/mol and the number of functional groups present was calculated to be 0.19 mmol/g of oligomer. In this case 53% of the oligomers were functionalized with pyridine residues with the balance of 47% of the oligomers being terminated by -CH, groups.

Preparation of Phenyl Substituted Ethylene Oligomers

Reactions of 1 with benzyl halides were all carried out in a similar manner. We have previously described a typical procedure." Extensions of this procedure have successfully used benzyl bromide, benzyl chloride, 4-bromo(bromomethyl)benzene, and 4-methoxy(bromomethyl)benzene as electrophiles. Characterization of 7 has been described.12 Phenyl-terminated and 4- bromophenyl-terminated ethylene oligomers were characterized by 'H-NMR spectroscopy; (toluene-d,, 110°C) 6 2.53 (t) and 6.8-7.2 (m, obscured by residual H in toluene-d,), loading of 0.2 mmol of -C,H,/g of oligomer; and 2.6 (m) and 7.0-7.3 (m, obscured by residual H in toluene-d,), loading of 0.27 mmol of - C,H,Br /g of oligomer, respectively.

Preparation of Hydroxyl Terminated Ethylene Oligomer

The hydroxy oligomer 8 was prepared either by reduction of the acid 2 or by quenching of 1 with ethylene oxide. The procedure used for the reduction has been described previou~ly.~ The reaction of 1 with ethylene oxide was carried out by addition of ethylene oxide gas to a suspension of 1 in heptane a t 0°C. This suspension was then allowed to warm to room temperature for 24 h. The reaction mixture was quenched by adding a toluene solution of p-toluenesulfonic acid and the resulting precipitate of crude oligomer was recovered by suction filtration. This precipitate was washed 3 times with aqueous acetone-HC1 and then dried. The final waxy solid was dissolved and precipitated from toluene 3 times and finally filtered hot to remove any toluene insoluble impurities. The final product had IR and 'H-NMR spectra like those previously described for 812 produced by reduction of 2. The loading of 8 prepared by the ethylene oxide route was 0.3 mmol of -CH20H/g of oligomer.

Esterification of Carboxylic Acid Terminated Ethylene Oligomers

Addition of excess methanol or ethanol and a catalytic amoufit of an acid such as sulfuric acid or HC1 to a toluene suspension of 2 followed by heating to 110°C for 8 h yielded a solution of ester 9a or 9b. Cooling this solution to room temperature precipitated the oligomer which was characterized by H-NMR spectroscopy and by F'l-IR spectroscopy, IR (thin film, 9a and 9b),

1740 cm-' and 'H-NMR (C,D,, 110°C) 6 (9a) 3.6 (s); (9b) 3.8 ((I)

1

Preparation of Chlorocarbonyl Terminated Ethylene Oligomer 11

The acid 2 (1 g) was added to a 100-mL, three-necked round-bottomed flask equipped with a magnetic stirrer. The flask was purged with argon and 30 mL of toluene was added. Heating up to 100°C produced a solution which was


treated with 3 mL of thionyl chloride. After 16 h reflux, the toluene was removed by distillation to yield the crude acid chloride 11. This product was generally used without purification in subsequent reactions. The crude product could be characterized by IR, v c=o = 1804 cm-'.

Preparation of Carboxamide Terminated Ethylene Oligomers

The procedure for formation of 11 is representative. The acid chloride 10 prepared as described above was suspended in 30 mL of toluene and heated to reflux a t which point it dissolved. Then 3 mL of diisopropyl amine was added to the solution. The reaction was allowed to reflux for 24 h. The solution was cooled to precipitate the product 11 which was recovered by filtration. This crude solid was rinsed with ether and then dried under reduced pressure for 24 h. The product formed had 'H-NMR (C,D,, HMDS, 105°C) S 0.9 (t), 1.4 (br s), 1.7 (t), 2.85 (t), 3.45 (m); IR (thin film) 1670 cm-'. From the 'H-NMR the molecular weight was calculated to be 2636 g/mol and the number of functional groups was calculated to be 0.18 mmol/g of oligomer. Oligomer 12 was prepared in a similar manner and characterized by 'H-NMR (toluene-d,, 105°C) 6 0.9 (t), 1.3 (broad s), 2.18 (t), 2.53 (t), 3.23 (t), 3.33 (t), and 7.7-8.2 (m) and IR (KBr pellet) 1650 and 1464 cm-'. The loading of 12 was 0.16 mmol/g and the M, was 2927 g. Both oligomer 11 and 12 had 47% of their end groups as carboxamide groups with 53% of their end groups as -CH, groups.

Esterification of Hydroxy Terminated Ethylene Oligomers

The preparation of 15 is representative. To a lW-mL, 3-necked, round-bottomed flask equipped with a magnetic stir bar was added 2 g of 8 and 0.5 g of N, N-dimethyl-p-aminobenzeneazobenzoyl chloride. The flask was purged with argon for 10 min and then 50 mL of toluene and 1 mL of pyridine were added. After heating this mixture up to reflux for 24 h, the solution was cooled and the precipitated crude 15 was collected by filtration. After suspending the crude 15 in aqueous sodium carbonate to remove any pyridinium salts, 15 was placed in a jacketed Soxhlet apparatus and extracted with hot toluene. The resulting toluene solution was cooled, a precipitate again collected and extracted yet again this time with THF to remove any soluble or any excess methyl red. This second extraction was terminated once the THF extraction solvent was free of methyl red based on W-visible spectroscopy. The product 15 had IR (pressed pellet) 1710 cm-' and 'H-NMR (toluene-d,, 1lOOC) S 0.9 (t), 1.3 (broad s), 2.5 (s),.4.2 (t), 6.6 (d), 7.9 (d), and 8.1 (d). Oligomer 15 has a M, of 1746 g/mol and a loading of 0.39 mmol of azo dye/g of oligomer (68% of end groups as ester groups, 32% as -CH, groups). Oligomer 17 was prepared in a similar manner and characterized by IR and 'H-NMR spectroscopy; IR (KBr pellet) 1736 cm-'; 'H-NMR (C7DB, 105°C) 6 0.9 (t), 1.7 (br s), 3.2 (t), 4.0 (t), 7.6 (d), 7.75 (m), 7.9 (m), 8.2 (d). The loading of 17 was 0.12 mnmol/g and the M, was 1654 g/mol. Oligomer 19 was prepared in a similar manner and characterized by IR and 'H-NMR spectroscopy; IR (KBr pellet) 1732 cm-'; H-NMR (C7D,, 105°C) 6 0.9 (t), 1.3 (broad s), 1.7 (s), 4.0 (t), 4.2 (s), 5.75 (s),

6.5 (s), 6.6 (d), and 6.9 (d). The loading of 19 was 0.24 mmol/g and the M, was 2021 g/mol.

1


Formation of Chloro Terminated Ethylene Oligomer 26

Hydroxy terminated ethylene oligomer 8 (1 g, 0.4 mmol), 15 mL of benzyl chloride (130 mmol), and 2 g (6.4 mmol) of triphenylphosphite were placed in a round-bottomed flask equipped with a stirring bar and condenser. This mixture was then heated with stirring to 160°C for 48 h. The resulting red-brown solution was cooled and filtered and the solid product washed with dilute sodium hydroxide, water, and 95% ethanol. After drying at 60°C under vacuum for 24 h 0.91 g of products were obtained having IR (thin film) 1457, 1262, and 801 cm-' (the vOH peak of 8 was gone) and 'H-NMR (toluene - d,, 105°C) 6 0.9 (t), 1.35 (broad s), 3.2 (t). The calculated M, was 2445 and the loading was 0.36 mmol of - C1 /g of oligomer (88% of end groups as - CH $31, 12% as -CH,).

Formation of Amine Terminated Ethylene Oligomer

Amine terminated oligomers were prepared both by multistep nucleophilic substitutions and by reduction of carboxamides. For example, polyethylene diisopropylamine was prepared from a sample of 12 by reduction in the following manner. To a 250-mL, round-bottomed three-necked flask was added 0.9 g of polyethylene diisopropyl amide and the flask was purged with argon. Addition of 100 mL of toluene and heating to reflux produced a solution of 12 which was allowed to react with 1 mL of neat BH,.S(CH,), complex. The reaction mixture was heated at a reflux for 24 h after which time the heat was removed and the oligomer precipitated. The oligomer was isolated by vacuum filtration and rinsed with diethyl ether and dried overnight in vacuo. The product so formed had 0.14 mmol of amine groups/g of oligomer and a M, of 2720; 'H-NMR (toluene-d,) S 0.9 (t), 1.4 (broad s), 2.4 (t), and 2.95 (q).

An -NH, terminated ethylene oligomer was prepared by a classical Gabriel amine synthesis starting with polyethylene mesylate. Polyethylene mesylate (1.3 g) was placed in 52 mL of a 1 : 1 (v/v) mixture of xylene and dimethylformamide along with 0.26 g (1.4 mmol) of potassium phthalimide in a 250-mL round-bottomed flask equipped with a stirring bar and reflux condenser.@This mixture was heated with stirring at 160°C for 40 h, cooled, filtered, and washed first with dilute NaOH and then with water until the water washings were neutral. After finally washing with 95% ethanol it was dried under vacuum at 80°C for 24 h to yield 1.1 g of product oligomer 22 having 0.45 mmol of phthalimido groups/g of oligomer; IR (KBr pellet) 1714 and 1637 cm-'; 'H-NMR (toluene-d,, 105°C) 6 0.9 (t), 1.3 (broad s), 3.52 (t), 6.87 (s), 7.0 (q), 7.4 (q). The oligomer 22 (1.2 g) was then suspended in 24 mL of xylene and 20% aqueous KOH and heated to 120°C for 24 h. The intermediate oligomer formed from this alkaline hydrolysis was isolated by filtration after cooling the xylene/KOH-H,O mixture and suspended in a 1 : 1 (v/v) mixture of water and fresh xylene. After addition of 9.6 mL of conc. H,SO,, the reaction was heated to reflux for 12 h. Cooling yielded a solid oligomer which after isolation by filtration was further treated with 1 g of KOH/40 mL of methanol a t 70°C for 1 h. This yielded the final oligomer 23 which was washed with water and 95% ethanol and dried to yield 1.1 g of product having 'H-NMR (toluene-d,, 105°C) S 0.9 (t), 1.3 (broad s), and 2.53 (t). The

4224 BERGBREITER E T AL.

H-NMR spectrum of this oligomeric amine was nearly the same as that for octadecylamine. The presence of tin amino group in this oligomer was further established by synthesis of a methanesulfonamide derivative by reaction of 23 with methanesulfonyl chloride. The sulfonamide had 'H-NMR (toluene-d,, 105°C) S 0.9 (t), 1.3 (broad s), 2.3 (s), and 2.7 (q) and IR (KBr pellet) 3290, 1320, and 1148 cm-'.

1

Formation of Carbazole Terminated Ethylene Oligomer(24)

Potassium carbazole was first prepared by the reaction of 5.6 g of KOH and 16.7 g of carbazole by azeotropic removal of water using xylene. The resulting solid potassium carbazole was isolated by filtration and dried. Then 1.2 g of this potassium carbazole, 1 g of polyethylene mesylate, 20 mL of a 1 : 1 (v/v) mixture of toluene and DMF were heated to 110°C for 24 h. The precipitate which formed on cooling was isolated by filtration and washed with THF in a Soxhlet apparatus for 16 h. After drying, 0.24 g of oligomer 22 was obtained. The product oligomer has a M, of 2095 and a loading of 0.22 mmol of carbazole/g of oligomer: IR (KBr pellet) 3049, 2950, 1630, 1600, 1485, 1474, 1341, 1326, 1240, 803, 748, and 719 cm-'; 'H-NMR (toluene-d,, 105°C) S 0.9 (t), 1.3 (broad s), 3.9 (t), and 7.1-7.9 (m).

Preparation of Tin Containing Ethylene Oligomers

Tin was introduced onto the end of ethylene oligomers in several ways. First, 1 could be quenched with excess dibutyltin dichloride by adding dibutyltin dichloride to a -78°C suspension of 1 and then allowing the reaction mixture to warm to room temperature with stirring for 8 h. The product oligomer was isolated by filtration and purified by dissolution precipitation and then by hot extraction with toluene from any insoluble impurities. The product formed in this case was polyethylenedibutyltin chloride. This trialkyltin chloride was not readily characterized by 'H-NMR spectroscopy because of the low electronegativity of tin. However, ICP analysis for tin from an acid digested sample showed that some tin had been introduced at a level of 0.07 mmol of SnBu,Cl/g of oligomer based on comparison of the "%n-NMR signal for the oligomer 29a a t 6 137.2 versus the Sn signal of a known amount of Bu ,Sn. Similar procedures using diphenyltin dichloride, tin tetra- chloride, and triphenyltin chloride yielded oligomers 29b, a mixture of oligomer 29c and 29d and oligomer 29e which were characterized by "%n-NMR: 29b, S - 74.1,O.ll mmol SnPh,Cl/g of oligomer; 29c and 29d, 6 139.2 and 119.6, a 1 : 1 mixture with a total tin loading of 0.11 mmol/g of oligomer; and 29e, S - 102.2, a tin loading of 0.136 mmol/g of oligomer. These loadings estimated by "%n-NMR spectroscopy were minimum values. Subsequent acid digestion of these oligomers and ICP analysis for tin showed the actual loadings to be substantially higher.

1'9

Digestion of Polymer Samples

The procedure used was a modification of S h a n i n a ' ~ . ~ ~ To a 20-mL quartz crucible was added 0.2 g of the polymer sample and 4 mL of conc. H,SO,. The polymer mixture was gently heated on a hot plate until the polymer sample


was completely decomposed. Then, 10 mL of conc. HNO, was added dropwise to the decomposed polymer sample, followed by further heating on the hot plate for an additional 24 h with occasional shaking. A brownish homogeneous solution was finally obtained after this acidic digestion. After cooling this solution to 25"C, the solution was diluted with distilled water in a 25-mL volumetric flask and analyzed for tin content by atomic absorption spectroscopy by the Agricultural Analytical Services Laboratory at Texas A & M University. A blank tin analysis using the same amount of reagents excluding the polymer sample was also carried out. These analyses showed that the mixture of oligomers 29c and 29d contained 14.1 x lop6 mmol of Sn/g of oligomer corresponding to 0.58 mmol of Sn/g of oligomer.

Preparation of Polystyrylmethyl l-Iodoundecanoate

A round-bottomed flask was equipped with a stirring bar, 6.8 g (20 mmol) of l-iodoundecanoic acid,29 and 100 mL of ethanol. A 10% aqueous solution of cesium hydroxide was added to the resulting solution until a pH of 10 was attained. The solvent was removed by rotary evaporation until a gummy solid formed. The flask was then placed under vacuum for 12 h to facilitate the removal of the remaining solvent. The solid was dissolved in DMF and added to 20 g of 1% crosslinked Merrifield resin (1 meq of Cl-/g of polymer) that was swollen in DMF. The resulting mixture was heated for 48 h a t 140°C with stirring. Samples of the polymer were removed periodically and analyzed by infrared spectroscopy. After the reaction was shown to be complete, the reaction mixture was cooled to room temperature and the polymer was isolated by filtration. The yellow solid was washed with twice with 200 mL of THF, three times with 200 mL of MeOH : THF (1 : l), once with 200 mL of water, twice more with 200 mL of THF, and twice with 200 mL of ether. Upon drying the yellow solid in uacuo, 25 g of polymer was obtained. IR(KBr), 1735 cm-'; ',C-NMR (CDCl,) 6 145-120 ppm (broad), 43-49 (broad), 36,32,31,28, 25, and 7.

General Procedure for Coupling Reactions Using Cuprates and Polystyrene-Bound Substrates

A suspension of the polystyrene bound iodide, polystyryl methyl 1- iodoundecanoate, was treated with a cuprate derived from ll-undecenylmag- nesium chloride and a copper(1) salt at 0°C. The resulting suspension was allowed to warm to room temperature and stirred for 2 h and then quenched with aqueous NH,Cl. However, since the blackish polymer still evidently contained copper salts, it was recovered and washed in a Soxhlet apparatus until the color was complete removed (ca. 4 days). After the copper salts had been removed, the pendant double bond on the polymer bound ester was successfully hydroborated. However on alkaline-hydrogen peroxide oxidation, significant amounts of hydrolysis of the growing oligomer occurred.

Support from National Science Foundation (DMR-8605941), the Petroleum Research Fund administered by the American Chemical Society and the Robert A. Welch Foundation for this research is gratefully acknowledged.


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Received November 28, 1988 Accepted April 25, 1989

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Anionic syntheses of terminally functionalized ethylene oligomers