Stabilizer-free dispersion copolymerization of maleic anhydride and vinyl acetate. II. Polymerization features

The polymerization features of the novel stabilizer-free dispersion copolymerization of MAn and VAc were studied. It was found that the dispersion copolymerization of MAn/VAc is a fairly rapid process, which starts from a slow Solution polymerization (below 10% conversion, Stage I) and follows a drastic increase of polymerization rate (10-80% conversion, Stage II) due to the known gel effect. Such process was accompanied by the increase Of Molecular weight Of the copolymer formed (fin from 1.2 x 10(4) to 3.8 x 10(4) mol(-1)) and the broadening of the molecular weight distribution ((M) over bar (W)/(M) over bar (n) from 2.4 to 8.0). E-a of Stage I was determined to be 76.7 kJ (.) mol(-1), while the value of Stage II was 64.7 kJ (.) mol(-1). The lower Ea in Stage than that in Stage I suggests that there exists a shift of polymerization locus from the Solution phase to the particle phase. Moreover, we found that the initial rate of polymerization increased with monomer concentration as well as initiator concentration, followup the relationship (R-p)(i)proportional to[MAn + VAc](0)(0.92) (.) [BPO](0)(0.57) This further implies that the dispersion copolymerization mainly proceeds as a solution polymerization in the very early stage.