The ability of terminal model kinetics to predict copolymer microstructure was tested for the styrenemethyl methacrylate system copolymerized at 40 O C at various fractions of monomers. NMR studies (in the accompanying paper) showed that previous peak assignments of the spectra of statistical styrenemethyl methacrylate copolymers were incorrect. The peak areas obtained for all copolymers were described in terms of triad sequences and were also adequately predicted by the terminal model utilizing reactivity ratios calculated from a nonlinear least squares fit to the copolymer composition data determined by 'H NMR. The nonterminal model behavior of the kinetics of the rate of polymerization described elsewhere can be successfully modeled by the 'restricted" penultimate model of Fukuda et al. We show that all current data can also be explained by various "bootstrap" or monomer-polymer complex models. Further model discrimination awaits new independent experimental results.
IntroductionThe kinetic model that is most widely used to model free radical copolymerizations is the terminal model, also known as the Mayo-Lewis model.' For most copolymer systems the copolymer composition has been shown to be well fitted by the terminal model equation.2 Recently, however, there have been numerous reports of the inability
The -methyl proton NMR resonances of the three different configurational methyl methacrylate centered triad sequences of alternating styrene-methyl methacrylate (SMMA) copolymers have been reassigned. Literature assignments are inconsistent with data and each other. Selective decoupling experiments were carried out in the present study to assign the carbon NMR resonances of the -methyl groups of alternating styrene-methyl methacrylate copolymers. Subsequently, the carbon resonances of the aromatic Cl and -methyl literature assignments of the statistical SMMA copolymers have been reconsidered and reassigned in terms of configurational triad sequences.
The 400 MHz proton NMR spectra of butyl acrylate (BA)—methyl methacrylate (MMA) copolymers prepared by free radical polymerization in solution at 323 K were used for the determination of the reactivity ratios. The reactivity ratios rM and rB calculated by the error‐in‐variables method are 2.279 and 0.395, respectively. The methoxy region of the MMA proton signal resonance was found to be sensitive for MMA‐centred sequences and a new assignment is proposed. The coisotacticity parameter σBM was calculated using a non‐linear least‐squares procedure with relative error estimation based on the new assignment and was found to be 039. The carbon‐13 NMR spectra of the BA‐MMA copolymers, in particular the carbonyl signal resonances, are sensitive for MMA‐and BA‐centred configurational sequences. The same assignment is used as for the ethyl acrylate—methyl methacrylate copolymer.
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