RADICAL RING-OPENING POLYMERIZATION OF NOVEL VINYLCYCLOPROPANES DESIGNED AS LOW SHRINKAGE MONOMERS - STRUCTURE OF THE POLYMER, MECHANISM OFTHE POLYMERIZATION, AND VOLUME CHANGE ON THE POLYMERIZATION

Synthesis and radical polymerization of new vinylcyclopropane derivati ves, 1,1-bis(ethoxycarbonyl)-2-isopropenylcyclopropane (4a) and ethoxy carbonyl)-2-isopropenyl-2-methylcyclopropane (4b), were carried out. 4 a and 4b were prepared by treating 1,4-dibromo-2-butene derivatives an d diethyl malonate with sodium ethoxide. The radical polymerization of 4 was carried out in the presence of an appropriate initiator (3 mol % vs monomer) at 60-120 degrees C. The polymers which were insoluble i n methanol/water (volume ratio = 80:20), were obtained as transparent solids. The conversion of 4a in the polymerizations in both bulk and c hlorobenzene was 95-99%. On the other hand, the conversion of 4b was 4 0-48%. From the detailed analyses of H-1 and C-13 NMR spectra of the p olymers obtained, poly(4a) was determined to consist of 1,5-ring-opene d units in cis and trans configurations in the main chain and a cyclob utane-containing unit. The content ratio of poly(4a) in the trans conf iguration to that of the cis configuration increased as the polymeriza tion temperature was raised. Poly(4b) was determined to consist of a 1 ,5-ring-opened unit in the trans configuration and a cyclobutane-conta ining unit. MM and MO calculations were carried out to examine the dif ference in the selectivity of radical ring-opening polymerizations of 4a and 4b. The results of examination of the conformation of 4 and act ivation energy in the addition reaction of the trimethylmethyl radical to 4 agreed well with the selectivity in the configuration of the mai n chain of the polymers. The degrees of volume shrinkage on the polyme rization of 4a and 4b were 10.4 and 10.2%, and the T-g's of 4a and 4b were 24 and 3 degrees C, respectively.