Structural evidence for a complex participation in the alternating copolymerization of citraconic (alpha-methylmaleic) anhydride with styrene in N,N-dimethylformamide

The C-13 DEFT NMR spectra of semi-alternating copolymers of citraconic (alp ha-methylmaleic) anhydride (CA) and styrene (ST) prepared in a very polar s olvent, N,N-dimethyformamide (DMF), with AIBN show that more than 50 % of t he linkage configuration at the cyclic CA units is in cis configuration. Si nce the cis linkage configuration may result when the electron donor-accept or complex formed between the comonomers is involved in the propagation, it is considered that, in very polar DMF, a participation of the complex is t he driving force for the copolymerization.