Acrylonitrile and Glycidyl Methacrylate Copolymers: Nuclear Magnetic Resonance Characterization A. S. Brar* and Kaushik Dutta Department of Chemistry Indian Institute of Technology, Delhi Hauz Khas, New Delhi 110 016, India Received February 6, 1998; Revised Manuscript Received May 8, 1998 ABSTRACT: Copolymers containing acrylonitrile (A) and glycidyl methacrylate (G) units of different compositions were synthesized by free radical solution polymerization. The reactivity ratios were estimated by Kelen Tudos and nonlinear error in variable methods. The triad sequence distributions in terms of A- and G-centered triads have been obtained from 13 C{ 1 H} NMR spectroscopy. The complete spectral assignments in terms of compositional and configurational sequences of the overlapping carbon and proton spectra of these copolymers were done with the help of distortionless enhancement by polarization transfer (DEPT), two-dimensional proton-detected heteronuclear correlation (inverse- HETCOR), and total correlated spectroscopy (TOCSY) experiments. The Monte Carlo simulation was used to study the effect of the fractional conversion on the triad fractions. Introduction Acrylonitrile-based copolymers have many commer- cial applications. 1 The need for functional polymers for several specialty applications demands the synthesis of these materials with well-controlled structures and topologies. 2,3 The copolymers based on the glycidyl methacrylate belong to the potential class of functional polymers. The interest in these copolymers is largely due to the ability of the pendent epoxy group to enter into a large number of chemical reactions, 4,5 thus offering the opportunity for chemical modification of the parent copolymer for various applications. The knowl- edge of microstructure is essential to understand the macroscopic characterization of the polymers. Two- dimensional NMR spectroscopy has been used for determining the compositional 6-8 and configurational 9-11 sequences of the polymers. The microstructure of poly- (glycidyl methacrylate) and its copolymers with alkyl acrylates, N-vinylpyrrolidione, vinyl acetate, etc. have been investigated by many workers. 12-14 The micro- structure of acrylonitrile copolymers with alkyl meth- acrylates has been reported earlier. 15a-e To the best of our knowledge the microstructure of acrylonitrile/gly- cidyl methacrylate (A/G) copolymers has not been reported so far. In this paper, we report the copolymerization mech- anism of industrially important acrylonitrile/glycidyl methacrylate copolymers prepared by solution polym- erization. The overlapping carbon-13 NMR spectra of the A/G copolymers were assigned without ambiguity, with the help of DEPT experiments. The methine, methylene, and R-methyl carbon signals of the A/G copolymers were sensitive to compositional and con- figurational sequences. The various compositional/ configurational sequences were assigned to triad, tetrad, and pentad sequences with the help of the inverse- HETCOR (HSQC) and DEPT experiments. 2D inverse- HETCOR and TOCSY (low mixing time) experiments were used for complete assignments of the overlapping and broad proton spectra of the A/G copolymers. The reactivity ratios of the comonomers were estimated using the Kelen Tudos 16 (KT) and nonlinear error-in- variable 17 (EV) methods. The triad sequence distribu- tion in terms of A and G units were obtained from the 13 C{ 1 H} NMR spectra of the copolymers. The Monte Carlo (MC) simulation method 18 was used to study the effect of the triad fraction as a function of fractional conversion. Experimental Section Acrylonitrile (GSC) and glycidyl methacrylate (Merck) were distilled under reduced pressure and stored below 5 °C. A series of A/G copolymers containing different mole fractions of acrylonitrile in the feed were prepared by solution polym- erization using benzoyl peroxide as initiator. The percent conversion was kept around 5-6% by precipitating the co- polymers in methanol. The copolymers were further purified from the DMSO/methanol system. The copolymer composition was calculated from the percent nitrogen of the copolymers. The C, H, and N analyses were done on a Perkin-Elmer 240C elemental analyzer instrument. NMR experiments were performed in DMSO-d 6 on a Bruker DPX-300 spectrometer at a frequency of 300.13 and 75.7 MHz for 1 H and 13 C{ 1 H} NMR spectra, respectively. DEPT meas- urements were carried out in DMSO-d6 at 100 °C using the standard pulse sequence with a J modulation time of 3.7 ms (JCH ) 135 Hz) with 2 s delay time. The two-dimensional proton-detected heteronuclear chemical shift correlation ex- periment (inverse-HETCOR) was recorded in DMSO-d 6 at 100 °C using the standard pulse sequence. 19 A total of 32 scans were accumulated with a relaxation delay of 2 s for each of the 512 t1 experiments. The two-dimensional homonuclear total correlation spectroscopy (TOCSY) spectrum was recorded at 4 ms mixing time in DMSO-d6 at 100 °C. A total of 32 scans were accumulated with a relaxation delay of 2 s for each of the 512 t1 experiments. The details of the Lorentzian shape curve fitting have been described elsewhere. 7 All regression converged to  2 < 1. Results and Discussion Monomer Reactivity Ratios. The copolymer com- position of acrylonitrile/glycidyl methacrylate (A/G) copolymers were determined from the percent nitrogen in the copolymers using the following equation: * To whom all correspondence should be addressed. F A ) M G N M G N + 1400 - M A N 4695 Macromolecules 1998, 31, 4695-4702 S0024-9297(98)00184-3 CCC: $15.00 © 1998 American Chemical Society Published on Web 07/10/1998