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Copolymers of maleic anhydride (MA or 0) with styrene (ST or 1) and copolymers of citraconic anhydride (CA or 0) with ST(1) were prepared with a radical initiator at 50°C in CC1₄ (the dielectric constant ε =2.24) and in highly polar N,N-dimethylformamide (DMF, ε=36.7). ¹³C NMR spectroscopy was used to determine the ST(1) centred triad mole fractions (Fₒ₁ₒ, Fₒ₁₁+₁₁ₒ)and F₁₁₁) and the mole fraction of the cis/trans linkage configuration at the cyclic anhydride units (Fcis and Ftrans). Non-linear least squares (NLLS) minimisation techniques was applied for the examination of the applicability of various copolymerisation models; the terminal model, the penultimate unit effect model, the complex participation model, the complex dissociation model and the so-called "comppen" model. The triad distribution data and the overall copolymer composition were used for the NLLS examination of the copolymerisation models, in combination with the test functions a and b. For both MA-ST copolymers and CA-ST copolymers, the copolymerisation models which incorporated a participation of the complex were most consistent with the data; for the MA-ST copolymers, the complex participation model, while for the CA-ST copolymers the comppen model showed the best fit. |
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