-f*3 612 HYDID INOflAIC-ORAUZC POLYMERS DERIVD FROM 11ORAMOFUNCTIONRL PHOSPNRZEMES(U) VERMONT UNIVBURLINGTON DEPT OF CHEMISTRY C W ALLEN 24 JUL 67 TR-?

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R&T Code 413C012-01

TECHNICAL REPORT NO. 7

Hybird Inorganic-Organic Polymers Derived from

Organofunctional Phosphazenes

by

Christopher W. Allen

Accepted for publication

in

A.C.S. Sym.Ser., "Inorganic and Organometallic Polymers".

University of Vermont D T ICDepartment of Chemistry

Burlington, VT 05405 ELECTEJUL 31197

July 24, 1987 S 0Reproduction in whole or in part is permitted for any purpose of theUnited States Government.

This document has been approved for public release and sale; its

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Technical Report No. 7

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University of Vermont

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Hybrid Inorganic-Organic Polymers Derived from Organofunctional Phosphazenes

12. PERSONAL AUTHOR(S)

Christopher W. Allen

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16 SUPPLEMENTARY NOTATION

Accepted for publication in ACS Symp. Ser.: Inorganic and Organometallic Polymers

7 COSATI CODES IlI.UBJECT TERMS (Continue on reverse if necessary and identify by block number)

r:!L) GROUP SUB-GROUP Cyclophosphazenes / Thermal decompositionVinyl polymerization /Monomer reactivity/

! - .,- ." CT (Continue on 'reverse if necessary and identify by block number)1 nCarbon chain polymers with pendant inorganic ring systems can be prepared by homo-

or copolymerization-reactions of cyclophosphazenes with olefinic exocyclic groups. The re-sulting polymers and copolymers exhibit flame retardancy and have a large number of reactivesites for further synthetic transformations. In alkenylpentafluorocyclotriphosphazenes thereactivity of the olefinic center may be mediated by placement of an electron donatinggroup on the olefin or by the phosphazene. A broad range of homo--and copolymers have beenprepared from vinyloxyphosphazenes. These materials undergo facile thermal decomposition.The volatile products of these processes have been identified and some insight has beengained into the kinetics and mechanism of the polymer thermolysis reactions. K...

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HYBRID INORGANIC-ORGANIC POLYMERS DER:VEDFROM ORGANOFUNCT IONAL PHOSPHAZENES

by

Christopher W. AllenDepartment of Chemistry, University of Vermont

Burlington, VT 05405

Carbon chain polymers with pendant inorganic ring

systems can be prepared by homo- or copolymeri-Accession For zation reactions of cyclophosphazenes with olefinic

NTIS GRA&I exocyclic groups. The resulting polymers and copo-

DTIC TAB lymers exhibit flame retardancy and have a large

Unannounced number of reactive sites for further synthetic

Justification transformations. In alkenylpentafluorocyclotri-phosphazenes the reactivity of the olefinic center

By may be mediated by placement of an electron

Distrlbution/ donating group on the olefin or by placing an insu-

lating function between the olefin and the phospha-

Availability Codes zene. A broad range of homo- and copolymers have-IAvail and/or been prepared from vinyloxyphosphazenes. These

Dist /Special materials undergo facile thermal decomposition.

The volatile products of these processes have beenidentified and some insight has been gained into

the kinetics and mechanism of the polymer ther-molysis reactions.

OINTRODUCTION

PECDThe primary approach to the development of main group inorganicpolymer chemistry has been in the preparation, characterizationand utilization of polymers with an inorganic backbone which may,

or may not, be protected by organic substituents (la). Importantmembers of this class of materials which are discussed in thisvolume and elsewhere include,

R R'

LAB) n Ia. LCHCH 2 )n lb.

R (AB) xR 2

R 2AB:R 2SiR 2Si; SS; R 2SiO; R 2PN; SN x = 2-4

124'0I11 ZO N

poly(siloxanes), poly(phosphazenes) and more recently poly-(silanes), poly~carbosilanes) and poly(silazanes). Our approachhas been to invert the roles of the organic and inorganic enti-ties thereby producing polymers with carbon chain backbones andinorganic substituents (ib). Vinyl polymers with transitionmetal substituents have been studied extensivelywIth mostinterest being shown in metallocene derivatives. Inorganicmain group entities as substituents on carbon chain polymers havereceived sporatic study with the most interes being shown inacyclic substituents involving organosilanes. Vinyl carboranescan also be polymerized and copolymerized jo polymeric specieshaving the boron cluster as a substituent. Our primary focushas been on the use of organofun~tional cyclophosphazenes as pre-cursors to the desired polymers. We have conducted a systematicstudy of the effect of variation of both the phosphazene and ole-finic components within the general structure of an organofunc-tional phosphazene (2). These studies have allowed for both anunderstanding of the polymerization behavior of this novel classof monomers and the incorporation of certain of the useful pro-perties, such as flame retardency, of the phosphazenes into tra-ditional organic polymers.

R

X E-C=CH2 X=CI,FR=Me,OEt ,OMe

S*Y=N,KOX 2N

N N E=OC 6H4

Y2

ALKENYL PHOSPHAZENES

We intially demonstrated that our basic approach was feasibleby preparing copolymers (3; R=Me) of 2-(propenyl)pentafl o5o-cyclotriphosphazene (4) and styrene or related monomers.'The copolymers, which have good solubility and thermal stability,do not burn or produce smoke when exposed to a flame. Nucleo-philic substitution reactions of the types which are well knownin phosphazene chemistry can be carried out on the phosphazenemoiety in these copolymers thus allojing for the preparation of abroad spectrum of related materials. However, the strongelectron withdrawing nature of the N P F unit transforms thepropenyl group into a highly polar ole~iR which undergoes qqm-petitive anionic addition in the course of its preparation"' a~dserves as a termination site in the copolymerization reaction.'

Ph

[CRCH2 ) (CH 2 n2

F

P 3

N N

FF N 2

The electron deficient nature of the olefin can be mediated intwo ways eithqI by placement of an electron donating substituenton the olefin or by insulating the olefin from the phosphazenering by other groups. The introduction of an alkoxy function asthe electron donating group on the olefin leads to 2-(l-ethoxyvinyl)pentafluorocyclotriphosphazene, N9P3F5 C(OEt)=CH2 (5).I Acomparison of the 3C nmr chemical shifts of the olefinic B-carbon in 4 and 5 gives evidence for a significant reduction inthe olefin polarity by addition of the electron donating ethoxyfunction. The change in olefin polarity is also demonstrasted bythe absence of anionic addition to the olefinic center in 5.Facile copolymerization of 5 with styrene or methylmethacrylateoccurs to yield materials (e.g. 3; R=OEt) with higher degrees ofphosphazene incorporation but properties similar to the copoly-mers derived from 4. The use of an aryl group as an insulatingfunctionl3,14 is exemplified in a-methylstyrylphosphazenes suchas the meta and para isomers of N3P3F5C6H4C(CH3)=CH2 (6) whichalso have been induced t undergo copolymerization with styreneand methylmethacrylate. These later compounds have the highestdegree of phosphazene incorporation into copolymers which we haveyet observed. Reactivity ratio and Q,e calculations show that,in general, (i.e., in 4,5,6) the phosphazene moiety exhibits avery strong electron withdrawing effect without any significantmesomeric interaction. Thus, the model of the electronic struc-ture of the olefinic center in alkenylphosphazenes which arisesfrom quantitative studies of reactivity in copolymerization reac-tions is very similar to that deduced from spectroscopic studiesof arylphosphazenes.9

Further examination of these reactivity and Q,e data allowfor a clear understanding of the polymerization behavior and howit is modified by the phosphazene. Although most systems arebest described by the terminal model, the reactivity patternsexhibited in the copolymerization of a-methylstyryl penta-fluorocyclophosphazene (6) with methylmethacrylate can only byquantitatively fit by a pennltimate model. 14

9$

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In order to obtain homowolymers from the organofunctionalphosphazenes, monosubstituted rather than 1,1-oisubstituted cle-fins of the type described above, are required. The styrenederivative, N P F C H4CH-CH=, was prepared from the phenylmethylether derivatvj, N p4C H4 COMe)=CH,, via hyd:ostannatlin andsubsequent B-eliminatoA of the tri lkyltin methoxide.Polymerization of the styryl phosphazene lead to a high molecularweight polymer with pentafluorocyclotriphosphazene units at thepara position of each phenyl group (7; E=C H X=F). The TGA ofthis material shows a significant retentioA O involatilematerial to over 1000S, suggesting the intriguing possibility

(CHCH2 )n

E X

N N 7II IX2P N X

of using the pyrolysis of polymers of type lb as a new route to

ceramic solids.

VINYLOXYPHOSPHAZENES

In an attempt to generate convenient routes to organofunctionalphosphazenes which could undergo homopolymerization reactions,we explored the reactions of lithium enolates, particularlythat of acetaldehyde, with halophosphazenes which leads to theeries of organofvnctional monome$N3PaCl6 n OCH=CH W5,16n=1-6), N3P3 F6 n (0CH=CH2 )n(n=l-5) 7 and N4P4C18_n (0H=CH2)n(n=1,2).18 In these systems, an oxygen atom acts as the insu-lating function between the phosphazene and the olefin. Other,related monomers, can be prepared by nucleophilic substitutionreactions with, for example alkoxide ions, of the chlorine atomsin N 3 P COCHCH (8). The appropriate monosubstituted deriva-tive (A=l5 in magy cases has been polymerized by radical ini-tiation to yield the linear high polymer with a cyclophos azenemoiety as part of each repeating unit, e.g. 7; E=O, X=Cl.However, not all of the vinyloxyphosphazene monomers will undergoradical po}lmerization; those with amino substituents are unreac-tive. The C nmr data indicate that these species electronicallyresemble vinyl ethers (which do not undergo radical polymeriza-tion) whereas the reactive derivatives resemble vinyl acetate.These data demonstrate an excellent example of electronic effecttransmission in cyclophosphazene systems.

The large number of reactive sites per monomer unit in thesehighly functionalized polymers has allowed for further synthetic

transformations based on the chemistry of the phosphazene unitthereby allowing preparation of the amino substituted polymers byreaction of 7 (E=O, X=Cl) with the appropriate amine. The broadrange of vinyloxyphosphazene monomers which are available allowfor the formation of copolymers of two different organofunctionalphosphazene monomers. Consequently, we can apply polymerizationreactivity studies to directly explore differences in chemicalbehavior based on changes in substituent, ring size, etc. of theinorganic monomer. We have prepared a series of copolymers of 8and Its tetrameric analog, N4P4Cl 7OCH=CH2 and shown that 8 hasthe greater reactivity in this system. In a joint study withDr. van de Grampel of the University of Groningen, we haveexplored the copolymerization of 8 with a vinyloxycyclophospha-(thia)zene.20

As opposed to the alkenylphosphazene polymers, the viny-loxychlorophosphazene polymers are thermally labile undergoing anexothermic decomposition via HCl elimination as low as 100followed by a more complex endothermic process at higher tem-peratures. The first step represents a mild thermal cross-linkingreaction with low weight loss. The solid state kinetics of thisfirst step have been measured. The activation energy for thefirst step is greater for the tetramer than for the trimer deri-vative. Since this is the reverse of the behavior observed fordisplacement reactions of the (NPCl2)3 and (NPCl2)48 , it impliesthat the barrier is primarily associated with the chain reorgani-zation energy needed to bring the phosphorus-chlorine bond inproximity with a carbon-hydrogen group. After the exothermiccross-linking step, there is a second process which appears toresult in the elimination of oxobridged phosphazene dimers, e.g.(N3P3C15 )20 and, by implication, to build an oxo cross-link bet-ween the polymer chains. Copolymerization with organic monomerssuggest a similarity of behavior between the vinyloxyphosphazeneand vinylacetate. The thermal lability of the polymers con-taining the vinyloxyphosphazene is even more pronounced in thecopolymers. In order to overcome some of these problems a largerinsulating function was sought. The reactions of 2-hydroxyethylmethylmethacrylate with N3P3CI6 leads toN3P3Cl5OCH2CH20C(O)C(CH3) = CH2 which undergoes radical or ther-mal homo and copolymerization which if not carefully controlledis accompanied by extensive cross-linking.

EXTENSIONS TO OTHER SYSTEWS

Our studies have convinced us that this approach to hybridorganic-inorganic polymers is a valuable one leading to a widevariety of new, interesting, materials. In addition to newphosphazenes, we are now expanding our studies to the preparationof pentamethylvinylcyclotriborazene polymers and we are investi-gating various silicon containing systems.

- . pU ~

ACKNOIALEDGE kENT S

This work was supported in part by the Office Of Naval Resear'Ch;collaborative efforts with Dr. van de Crampel are supported, inpart, by a NATO travel grant.

LITERATURE CITED

1. Pittmann, Jr., C.U.; Rausch, M.D., Pure Appl. Chem., PureAppl. Chem., 1986, 58, 617.

2. Dzhardimalieva, G.I.; Zhorin, V.A.; Ivkva, I.N.1 Pomogailo,A.D.; Enikopolyan, N.S., Doki. Akad. Nauk SSSR, 1986, 287,654.

3. Billingham, N.C.; Jenkins, A.D.; Kronfli, E.B.; Walton,D.R.M. 3. Polym. Sci., Polym. Chem. Ed., 1977, 15, 683;Lakshmana Rao, V.; Babu, G.N., J. Macromol. Sci., Chem.,1983, A20, 527; Ledwith, A.; Chiellini, E.; Solaro, R.,Macromolecules, 1979, 12, 240; Carbonaro, A.; Greco, A.;Vassi, I.W., Eur. Polym. J., 1968, 4, 445; Tumanova, I.A.;Semenov, O.B.; Yanovsky, Yu. G., Inter. 3. Polym. Mater.,1980, 8, 225.

4. Wright, 3.R., Kingen, T.J., 3. Inorg. Nucl. Chem. 1974, 36,3667; Klingen, T.3., ibid, 1980, 42, 1109.

5. Allen, C.W., 3. Polym. Sdi., Polym. Symp., 1983, 70, 79.6. Dupont, 3.G., Allen, C.W., Macromolecules., 1979, 12, 169.7. Allen, C.W.1 Dupont, 3.G., Ind. Eng. Chem. Prod. Res. Dev.,

1979, No. 18, 80.8. Allcock, H.R., Phosphorus-Nitrogen Compounds; Academic Presst

New York, 1972; Allen, C.W. , "Cydlophosphazenes and RelatedCompounds" in The Chemistry of Inorganic Rings, Ed. I. Haiducand D.B. Sowerby, Academic Press, in press.

9. Allen. C.W.; White, A.3., Inorg. Chem., 1974, 13, 1220;Allen, C.W., 3. Organometal. Chem., 1977, 125, 215; Allen,C.W.; Green, J.C., Inorg. Chem., 1980, 19, 1719.

10. Allen, C.W.; Bright, R.P.; Ramachandran, K., ACS Symp. Ser.,Phosphorus Chemistry, 1981, 171, 321.

11. Allen, C.W.; Bright, R.P., Inorg. Chem. 1983, 22, 1291.12. Allen. C.W.; Birght, R.P., Macromolecules, 1986, 19, 571.13. Shaw, J.C.; Allen, C.W., Inorg. Chem., 1986, 25, 4632.14. Allen, C.W.; Shaw, J.C., Phosphorus and Sulfur, 1987, 30, 97.15. Allen, C.W.; Ramac-handran, K.; Bright, R.P.; Shaw, J.C.,

Inorg. Chim. Acta, 1982 64, L1095.16. Rarnachavidran, K.; Allen, C.W., Inorg. Chem. 1983, 22, 1445.17. Allen, C.W.; Bright, R.P., Inorg. Chim. Acta 1985, 99, 107.18. Brown, D.E.; Allen, C.W., Inorg. Chem., 1987, 26, 934~.19. Allen, C.W.; Ramachandran, K.; Brown, D.E., Inorg. Syn., in

press.20. van de Grampel, J.C.; Jekel, A.P.; Dnathatzhreyan, K.; Allen,

C.W.; Brown, D.E., Abstract 319, 193rd American ChemicalSociety Meeting, Denver, April, 1987.

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