VINYLCYCLOPROPANONE CYCLIC ACETAL SYNTHESIS, POLYMERIZATION, STRUCTURE OF THE POLYMER AND MECHANISM OF THE POLYMERIZATION

Synthesis and radical polymerization of a few hybrid monomers between vinylcyclopropane and cyclic ketene acetal (vinylcyclopropanone cyclic acetals, 1-vinyl-4,7-dioxaspiro[2,4]heptane (1a), 1-vinyl-4,9-dioxasp iro[2.6] nonane (1b), 1-vinyl-5-phenyl-4,7-dioxaspiro[2.4]heptane (1c) , and 1-vinyl-6,7-benzo-4,9-dioxaspiro[2.6]nonane (1d)) were carried o ut. 1a-d were prepared by the reaction of 1,1-dichloro-2-vinylcyclopro pane with corresponding diols in the presence of a base. Radical polym erization of 1 was carried out in the presence of an appropriate initi ator (3 mol % vs monomer) at 60-120-degrees-C. Polymers which were sol uble in n-hexane, methanol, chloroform, ether, and tetrahydrofuran (TH F) were obtained as pale yellow transparent viscous oils, except for t he polymerizations of 1a and 1b with DTBP at 120 -degrees-C, in which they were obtained as gelled polymers insoluble in common organic solv ents. Structures of the polymers obtained were determined by H-1 NMR a nd IR spectra referring to those of model compounds of double ring-ope ned units. Poly(1a) was determined to consist mainly of a single ring- opened unit. On the other hand, poly(1b) was determined to consist mai nly of a double ring-opened unit. 1c, which has the structure of pheny l-substituted la, afforded a double ring-opened unit in addition to a single ring-opened unit. 1d, which has a structure of benzo-substitute d lb, afforded mainly a double ring-opened unit. Calculation of two-ce nter energies with the semiempirical molecular orbital method (PM3) wa s carried out to examine the mechanism of the radical ring-opening pol ymerization of 1. Results of the examination of two-center energies ag reed well with the selectivity in the bond cleavage of the cyclopropan e ring of 1. Moreover, it was confirmed that the higher the polymeriza tion temperature becomes, the more thermodynamically superior path pro ceeds, from the comparison of the formation energies of the various ra dical intermediates. The volume shrinkages of 1c and 1d were 8.86 and 3.15% in the polymerization with DTBP at 120-degrees-C, respectively, which were regarded as the smallest ones for a radically polymerizable monomer.