trans-4-Acryloyloxyazobenzene/Vinylidene Chloride Copolymers. Nuclear Magnetic Resonance Characterization

Abstract

ABSTRACT:trans-4-Acryloyloxyazobenzenelvinylidene chloride (A/V) copolymers of different monomer concentrations were prepared by solution polymerization using benzoyl peroxide as initiator. The copolymer composition was determined from the quantitative 13 C{'H} NMR spectrum. The carbonyl carbon of A-and the quaternary carbon of V-centered resonances were used for determining the sequences in terms of the distribution of A-and V-centered triads. The sequence distribution of A-and V-centered triads determined from 13 C{'H} NMR spectrum of the copolymer is in good agreement with triad concentration calculated from statistical model. The comonomer reactivity ratios, determined by both Kelen-Tiidos (KT) and nonlinear error in variables (EVM) method are rA =0.36±0.03, rv = 1.02±0.06; rA =0.37 and rv= 1.04, respectively. 13 C Distortionless enhancement by polarization transfer (DEPT) spectrum was used to differentiate the resonance signals of methine (A) and methylene carbon signals of A-and V-units. Assignments to the methinc and methylene resonance signals have been assigned up to the tetrad levels using 2D HSQC experiments. The geminal coupling in the methylene and methine proton region is shown in the 2D TOCSY spectrum.KEY WORDS 13 and trans-4-methacryloyloxyazobenzene/menthyl methacrylate copolymer. 14 The chiroptical properties and photochromic behavior of the copolymers were reported by AI tomare e t a!. 15 To the best of our knowledge, the detailed microstructure study of trans-4-acryloyloxyazobenzenejvinylidene chloride (A/V) copolymers have not been reported so far. In this work, we report the stereochemical structure and sequence distribution of (A/V) copolymers by one and two-dimensional NMR spectroscopy. The 1 H NMR spectrum of copolymer is complex and hasTo whom all correspondence should be addressed. 1224been interpreted with the help of 2D heteronuclear single quantum correlation (HSQC) NMR spectroscopy. The reactivity ratios of the comonomers have been calculated using Kelen-Tiidos (K T) 16 and the non-linear Error in Variable Model (EVM) 17 methods, using the compositional data. The A-and V-centered triad sequence distribution obtained from 13 C{ 1 H} NMR spectrum and are compared with those calculated from the first order Markov model using reactivity ratios determined from the EVM 18 method. EXPERIMENTALThe details of the copolymerization process and NMR measurements are explained in our earlier publications. 19 · 20 RESULTS AND DISCUSSION Reactivity Ratios DeterminationThe copolymer composition of the A/V copolymers were determined from the quantitative 13 CCH} NMR spectra using the inverse gated decoupling pulse program with 8 s as delay time. Table I shows the comonomers mole fractions in the feed and in the copolymer. The initial estimate of the reactivity ratios was done by the KT method. The values of the terminal model reactivity ratios obtained from the KT plot are r A= 0.36 ± 0.03 and rv = 1.02 ± 0.06. These values along with the copolymer data were used to calculate the reactivity rat...