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The monomer unit triad sequence distribution and the cidtrans linkage configurations at the cyclic maleic anhydride (MA) units in the copolymers of styrene (ST) and MA prepared in CCI, with AIBN at 50°C were quantitatively determined by 13C DEPT NMR spectroscopy. So much as 61 % of the linkages at the MA units were found to be in cis configuration, which was considered to be formed by a participation of the 1 : 1 electron donor-acceptor complex formed between ST and MA in the propagation step. The mole fraction of the cis configuration was found to be proportional to the mole fraction of alternating triad sequences when the monomer unit sequences approach to be completely alternating. This supported the proposal that, in alternating and semi-alternating copolymerizations, the alternating sequences were formed mainly by the addition of the complex. The equilibrium constant of the complexation in CCI, at 23°C was determined to be 0,21 L/mol.

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The monomer unit sequence distribution and the cis/trans linkage configurations of maleic anhydride units in maleic anhydride (Ma)-styrene (St) copolymers prepared in N,N-dimethylformamide with N,N'-azobisisobutyronitrile at 5OoC over a wide range of Ma monomer feed mole fractions were determined using DEPT I3C-NMR spectroscopy. It was found that when the Ma feed mole fraction is more than 0.4, the monomer unit sequence becomes almost alternating and the mole fraction of the cis linkages at the Ma units in the copolymer attain a nearly defined maximum value of 0.54 f 0.06.

Styrene (ST or 1) and maleic anhydride (MA or 0) were copolymerized in carbon tetrachloride (CCl 4 ) and in N,N-dimethylformamide (DMF) with a wide range of MA mole fraction in the feed (f 0 = 0.01 to 0.90) at 50 8C. The DEPT 13 C NMR subspectra of methylene carbon of ST(1) units were used to determine the ST(1) centered triad mole fractions (F 010 , F (011 + 110) , F 111 ). Non-linear least squares (NLLS) curve fitting was used to fit the theoretical equations of the five copolymerization models, namely, the (1) terminal, (2) penultimate unit effect, (3) complex participation, (4) complex dissociation and (5) comppen models, to these experimental data in order to calculate the sum of squares (SS) and the reactivity ratios. The complex participation model is indicated as the model providing the best fit by the smallest SS values calculated from F 010 data and by the variation pattern of the test functions a and b for both copolymerization systems. The F test for SS of F 010 data can only show an improvement of fit of the complex participation model over the penultimate unit effect model with less than 90% probability confidence for the MA + ST/CCl 4 system and with 97.5% probability confidence for the MA + ST/ DMF system. This is consistent with the result obtained from the "order grade matrix" method reported previously.