Ring-opening polymerization of vinylketene cyclicacetal

Abstract

To investigate further possibility of ring-opening polymerization behaviors of cyclic acetals, 4-Phenyl-2-propenylene-1, 3-dioxolane(P-PD) which is a phenyl-substituted vinylketene cyclic acetal was successfully synthesized by intramolecular cyclization reaction of 2-bromo-1-phenylethyl 2-butenoate and potassium hydride. P-PD was polymerized with radical and cationic initiators under various conditions. In the radical polymerizations, the polymer obtained with BPO as initiator at 78$^\circ$C was insoluble, because of gelation which may occur at this high temperature. However, when the polymerizations were carried out below 60$^\circ$C with AIBN, soluble high molecular weight polymers were obtained. DSC data indicated that the polymer had a glass transition at 42$^\circ$C and TGA showed that the polymer decomposed above 376$^\circ$C. The structure of the polymer was investigated with 1H-NMR, IR, and 13CNMR Spectrum and confirmed as $\delta$ -phenyl-substituted trans-$\alpha,\beta$ -unsaturated polycaprolactone. This results point out that polymerization proceeded via 1, 7-type ring-opening process cleanly without participation of vinyl- or butadienyl-type polymerization. These polymerization results suggest that butadiene and phenyl substituent contribute significantly to its radical polymerization. Butadiene moiety of the monomer accepts the propagating radical and transferred the resulting radical to ketal carbon. This is an essential step to undergo ring-opening of the acetal ring. The phenyl-substitution at the 4-position of P-PD stabilizes the rearranged radical, forming propagating species which is well studied polystyryl radical. This makes the monomer more prone to free radical ring-opening polymerization, determining the direction of ringopening process. Cationic polymerizations were also carried out with various cationic initiator such as $BF_3-Et_2O, AlCl_3, FeCl_3, ZnCl_2$, p-TsOH, $CH_3COOH$, and $I_2$. However, most of acids gave only insoluble pol...