- ? 12C AND 14N SOLID STATE NMR CHARACTERIZATION OF I/1ARAMID-COUTRINING NYLON-6 (U) UNIVERSITY OF SOUTHERNMISSISSIPPI HATTIESBURG DEPT OF POLYNE

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OFFICE OF NAVAL RESEARCHGoUContract N00014-86-K-0659

ITechnical Report No. 7

13C AND 15N SOLID STATE NMR CHARACTERIZATION OF ARAMID-CONTAINING NYLON-6 POLYMERS SYNTHESIZED BY IN SITU POLYMERIZATION

OF CAPROLACTAM WITH BENZOYL CAPROLACTAM DERIVATIVES

by

Douglas G. Powell, Allison M. Sikes and Lon J. Mathias

Prepared for Publication in

Polymer Preprints, in press

DTICELECTE

Department of Polymer Science DEC 1 41987University of Southern Mississippi

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it. TITtsE (include Wrifny Classolicarsonj"C andi 'N Solid State NMR Characterization of Aramid-Containing Nylon-6 Polymers

Synthesized by in situ Polymerization of Caprolactam with Benzoyl Caprolactam Derivative12. PERSONAL AUTHOR(S)

l3a, TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (Yoar.?Aonth.ay S. PAGE COUNTTechnical FROM TO 12/1/87

16. SUPPLEMENTARY NOTATION

Polymer Preprints, in press.

11. COSATI CODES 18. SUBJECT TERMS (Continue an rovers@ if necessary and identify by black number)FIEL IGROUP. SUB-GROUP

19. ABSTRACT (Continue an reverse it necessary and identify by Wlok number)

0 Copolyamides were prepared by in situ polymerization from TAIp-Aminobenzoylcaprolactam and caprolactam systems initiated with sodium TAB,3 0hydride. The microstructure of the copolymers as determined by i 3 C~ow~eElsolution NMR varied from alternating to blocks of aliphatic and/orfco~taromatic units depending on the reaction conditions and the ratio of---"

PO~~m the comonomers. The solid-state CP/MAS 13C NMR were consistent with-- -- -solution studies. Detailed interpretation was difficult due to largerthiontl-linewidth and number of resonances. Natural abundance CP/MAS, 1 5N~llebility Codelspectra were found to less complicated. Based on these results and 15N Avealland/or_

studies with model amides, 15N CP/MAS, was shown to be a useful Speolaltechnique for probing copolymer composition and microstructure.

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13C AND 1 N SOLID STATE NMR CHARACTERIZATION OFARAMID-CONTAINING NYLON-6 BY IN SITU POLYMERIZATION

WITH BENZOYL CAPROLACTA-M3MIVATIVES

Douglas . Powell. Allison M. Sikes, and Lon J.Mathia,Department of Polymer Science

University of Southern Mis-;issiprpiHattiesburg. Miss;is:-ippi 39406 0076

INTRODUCTION

Polyamides and arramids are two important structurij mati," ial,: fst4, for" th ,t-i[

_* toughness, high modulus, and tensile strength.' They ar, ct-remilly u.ed in a wid

varioty of applications as structural plastics ,ind t:. ri'.it,rc. ing 1 b, :. i~i ;iig~ l

performance composites.

Natural abundance "NX NMR spectroscopy ha!, i)n u5Cd to t j3Ja terizc

polyamides in solutionl.1,a4 . 1N NM1R spectroscopy has scvvral advntag; ()-'er

"'C NMR including larger spectral width and simpler spectra. Charmcterizjtic;a 0

polyamides by solution 1N NMR is, however, hampered by the limited solubility of

many polyamides, especially homo- and copolymers containing aromatic moiutios.

Polyamide nitrogens are subject to large chemical shift changes in the solvents

needed to dissolve them., 7 Moreover, solution studies cannot duplicate the

0crystalline structure or hydrogen bonding in solid polyamides.

Recently, polyamic acid precursors to polyimides have been characterized by

solid state 'IN CP-MAS NMR.8 We had previously prepared and characterized

several aliphatic/aromatic copolyamides based on caprolactam and several N benzoyl

caprolactam initiators." (Figure 1) We have compared these results with 11N C11--

MAS NMR data to evaluate the usefulness of the latter technique for polyamide

microstructure characterization. In this paper we present the Ir N CP MAS NMR

results for several copolyamides along with model amides used for chemical shift

assignments.

EXPERIMENTAL

Caprolactam homo- and copolymers were prepared as previously described.', "

Model amides were purchased from Aldrich Chemical Company and used as received.

'IN solid state CP-MAS measurements were made on a Bruker MSL 200 NMR

spectrometer equipped with a Bruker MAS solids accessory. Measurements were

made in a 4.7T field corresponding to 1H and 'IN frequencies of 200.13 and 20.287

MHz, respectively. Cross-polarization was performed using a 5 ps 1H pulse and a

contact pulse of ] to 5 ms to meet the Hartmann-Hahn condition. MAS rotor

speeds were 3.0 to 3.2 lHz. Sample temperature was maintained at 300K. Spectral

widths were 25 Klz. Between 20,000 and 50,000 scans were acquired for each

sample with a delay of 3 s between scans. Chemical shifts are reported relative to

"NHNOs (NO. = 0 ppm; "NH, = -353.5 ppm) as an external standard. Solution16 N measurements were made using an inverse-gated decoupling technique with a

87 12 8 102S , € . .. . . , .. ,, q y , ,~ . . , , ,,,,-

.pulse width of 25 ps. All solution spectra were obtain.d in concciitratod ,;uljfuric

acid solvent. lLNHjNOz, dissolved in D?.O was used as the refeerence (NH' = 3.5

PPm)'by inserting a tube containing the solution coaxially into the !;aiii.

RESULTS AND DISCUSSION

"N chemical shifts of model amides and polyamides arc listed in "l]b ,. i.

expected, the chemical shifts of the solid samples are approximately :Xo ppn, up1 i,

of the solution resonances. Protonation of the amide carbonyl causes kj:pre,.-Ji0 ;,i,

shifts in 'IN resonances depending on the pha of the amide and E.rivent icidiy.

Typical linewidths at half height were 8-10 ppm.

The solid-state chemical shifts of di-functional initiated and star initiated

nylon-6 are similar to wholly linear nylon 6 although the star pic:yntkr i; insolubh:

in concentrated HZSO4. We were disappointed to find that nitrogens on the

initiator species were not visible in the spectrum. The low concentration of

initiator (<1%) makes this technique inadequate without 1"N onrichment in the

initiator. With atom enrichment, determination of the number of imide sitis

consumed would give the efficiency of initiation as well as confirm the synthesis of

a star polymer.10

Figure 2 shows the 'IN CP-MAS spectra of a previously prepared copolymer of

p-aminobenzoic acid and caprolactam with alternating aliphatic and aromatic units.

This copolymer consists of only two types of amide nitrogens in equal proportions.

The resonances at -240.6 and -261.3 show equivalent areas consistant with tiie

alternating copolymer structure. Comparison with the model acetanilide (-241.5)

indicates the downfield resonance is due to the aromatic substituent on the

nitrogen. N-methyl benzamide, however, lies well upfield of any other resonances

in the Table. It is apparently a poor model for an aliphatic substituted amide in

the copolymer. A possible explanation is that the methyl group of these, modcls

cannot duplicate the effects of an aliphatic chain on the nitrogen resonance. These

."neighboring residue effects" have also been recognized in solution "\ experimeiht.

as well.' - & The solution 'IN spectrum of the copolymer in sulfuric acid is also

shown and is consistant with the solid state spectrum with the exception of large

chemical shift changes.

Figure 3 shows a series of copolymers synthesized under conditions :Jightly

different than those for the alternating copolymer. By altering conditions it, was

found that blocks of aromatic units could be generated in situ and incorporated into

novel copolymers. Figure 3a shows a copolymer containing blocks of p-benzamid(:

with few caprolactam units. The downfield shift of the 16N resonanc. is consistcnt

with nitrogen in a deshielding environment between an aromatic ring and carbonyl

group. This shift also compared favorably with the N spectrum of fully aromatic

2

Sd

azid 20% ararmid units, re& pecti ,i .% , %vit n t , r nm.i ri,.o, bi- ,.: ( proia"L; n I

The upfield shift is consistant with the of jiiyo, G !_,p,.clt r. '.hwn in .

copolymer peak, however, is 5-6 ppm downifield (A the - . ,j .

surprising that the presence of the aramid spt ci-; c ,tics .u :;l i I c v,:n i ,c

the concentration is too low for the aramid 'IN r'(.soalhc,.!: to i): -;eei,

"N NMR of these samples gave a chemical shift identihal tO iht 01 th. it.' i011 (G

homopolymer.

The presence of two crystal forms of nylon-6 iE well kn-ow % ard l- l ,',-

been previously characterized by IR and x-ray." , ' Figures 4a and ic show th,

"N NMR of a and -y crystal forms of nylon-G, respectivule, whih -.l, hu :,

mixture that is predominately ae . Although 1"C and "N chemical shifti, have ueO,

reported to be conformationally dependent,. ' the "'C CP-M:\; ,hcmical silifts were

identical for both crystal forms. It is clear that "tN solid state NMR is a better

tool for differentiating the two crystal forms. Moreover. th, tlbe c-onicai -;hifi,;

correlate well with observed nylon--6 resonances seen in the copolymer; in lit,.-urc_-.

Tie 'N solid state NMR clearly shows that the nylon--G ble. k!; in t,-o M4 I.'m,-!:;

are mostiy of the -y form.

SUMMARY AND CONCLUSION

Natural abundance 1'N NMR of solids has been demonstrated a:. ,i

characterization tool for polyamides. Anisotropies and crystal forms cin be

examined in the solid phase which are not pren;ent in solution. "N Ci' .M.'S XVI

provides a new method for determining the crystal structuro of nN lo -G. "ihe

greater sensitivity of nitrogen to its environment in solid state NMR coriapar,d to

carbon opens up a broad area for study of crystalline polyamides. Potential also

exists for characterization of peptides and other nitrogen containing (eryvstaiiilo

materials using 16N CP-MAS NMR to complement traditional X-ray analysi.s.

ACKNOWLEDGEMENT

We gratefully acknowledge the Department of Defense grant iur purhasa:i 1g t,

solid state NMR, and the Office of Naval Research and ICI Amcuri, s for , oi

5 our work on composites.

I. G. Odian, "Principles of Polymerization," 21d ed.. Chap. 1. Jo, ii il.y illi, s ,flInc., New York, 1981.

2. Kricheldorf, H.R.;-ull, W.E. Makromol. Che_. 1981. 182, i177; .lti,_.oc' .1980, 13, 87.

p 1 ,_

3. Kricheldorf, H.R. Makromol. CheM., 1978, 179, 2687.

3

Lo

-4. 1h'richeidoi'1. 1..:Joshi, S.\. J. L . 56c.: 1'l(,v. Chur-n. 1-d., 1982. 20. Z27,'J

5. hriciholdorf, I.R.. Schillirng, G. NFJkromol. Chcrn., 1978. 179, 2667.v

6. hricnuldorl, iH.li. Ma1krcmol. Churnm.. 1978, 179, 2675.

.Spiinger- \erlag . ije!'lilJ, 196J*1. p. J171 58.

8. Weber, W .1.; Murphy, P.D. Preprints of* the PISL8] i)iv% iiori cA *\( Fall 3 9'27-57, 341.

9. Mathias, L.J.; Moore, D.R.; Smith, C.A. J. I'oivm. Sc6.: Purit A: L4vII i 1 ___j

1987. 25, 2699.__- _

10. Mathias, L. J.; Sikes, A. M. "Chemistry, Properties, anci Applications; uf'Crosslinking Systems," A. C. S. Symposium Series, in press.

11. Holmes, D.R.; Bunn, C.W.; Smith, D.J. J. Poly. Sci., 1955, 17. 159.

12. Arimoto, H. 3. Poly. Sci. Part A. 1964. 2, 2283.

13. Shoji, A.; Ozaki. T.; Fujito, T.; Deguchi. 1\.; Ando, 1. Macromolecules. 1987, 2?0,2441.

4

TABLE I

CP MNAS ,_'ii

N-methyl benzamide -2-o3.3 -226.

Acetanilide -241.9 -Z

poly(p-benzarnide) -248.5

Alternating copolymer --240.G, -261.3 WL

Nylon--6 (annealed) --261 .7)

3-Arm star nylon-6 --258.422.

Nylon-6 (quenched) -256.7. -261.1

5

LIST OF FIGURES

Figure 1: h) f,, nti h-s-is' of aii i i~l.t i aI ab ic blo Ii ano c4ij iid ij. (UPA l'

b) ,; ithesi; of rl4 N 1 - f.) E~tai'p irl~ tj!;;llp tl i Ilkill(t iona; ~ I~'

Fig ure 2: ', kU \'AS !;114'( ti Um (l PpezF tracce and q .h I * j'cl uia .. *

of polly (p - i ,efzamiide-alt-capr-oingdc) ait-Irnla!j Ig '~YIl

Figure 3: " N Ci'- MAD INIMI ,;Pt~ctj-a of bilk C0pkA)xnClrS 0 CcsPl'Ui. hll1 b2lk t)

aminobenzoic acid: a) 80-90 mole% aromatic corisloomer-; 1)) 1() mole]( X

aromatic comonomer; c) 20 mole % aromatic comxoxiomcr; d) inylon- 6

homopolymei-

* Figure 4: 1"N CP-MAS NNMR OF Nylon-6 homopolymer crystal forms: a) mainly-

gamma nylon-6; b) predominately alpha nylon-6; c) alpha nylon-6

6

a) MIN .~~ .0 . H 0 t

14 Na

A

in n

b) Ho

0 NANlA

,

CH ajNH-

0.1.

-210 -229 -230 -240 -250 -260 -270 -280pp"

a

A~t t ~w~fvVW

/0I

~J.

0* d

t,. .- I el 21 -221 -241 -.21 1 -2811

PP

0

a.

4

*1'

0

b

0

I * I * I *

-229 -249 -269 -289PPM

0,

.1

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*~0 .0 0 0. V... V,. 0V