RADICAL RING-OPENING POLYMERIZATION OF ALPHA-CYCLOPROPYLSTYRENES - POLYMERIZATION BEHAVIOR AND MECHANISTIC ASPECTS OF POLYMERIZATION BY THEMOLECULAR-ORBITAL METHOD

Synthesis and radical polymerization of substituted alpha-cyclopropyls tyrenes [1-(4-substituted phenyl)-1-cyclopropylethylene; 3a (X = OMe), 3b (X = H), and 3c (X = Cl)] were carried out. 3a-c were prepared by the Wittig reaction of the corresponding cyclopropyl aryl ketones. The radical polymerization of 3 was performed in the presence of an appro priate radical initiator (3 mol % vs monomer) at 60-120-degrees-C. The molecular weight of the polymer obtained decreased while the conversi on of the monomer increased, as the polymerization temperature rose. T he structure of the polymer was determined to consist only of the unit formed by selective 1,5-ring-opening polymerization. The ratio of the observed rates of polymerization was estimated to be 3c:3a:3b = 2.0:1 .6:1. The effect of a para substituent on the rate of polymerization w as not the same as that of para substituted styrenes. The electron den sity of vinyl beta-carbon of 3 decreased in the following order: 3a > 3b > 3c, being the same as that of para substituted styrenes from C-13 NMR analysis and molecular orbital calculation. The rate of polymeriz ation was suggested to be affected by the polarity of the monomers (3) . The dipole moment as an index of polarity well explained the order o f the rate of polymerization. 3 showed shrinkage similar to those of c ommon cyclic monomers with similar molecular weights; 7.23-8.56%. This value was consistent with the occurrence of the selective radical rin g-opening polymerization of 3. T(g) of the polymers (4) obtained was l ower by 94-102-degrees-C than corresponding poly-(para-substituted sty rene)s.