Synthesis and properties of ethylene-substituted styrene copolymers

The copolymerization of ethylene and substituted styrenes [RSt's; p-methylstyrene (MSt), p-tert-butylstyrene (BSt), 2-vinylnaphthalene (VN), and p-(tert-butyldimethylsilyloxy)styrene (BMSiOSt)] were investigated with dimethylsilylene(tetramethylcyclopentadienyl)(N-tert-butyl) titanium dichloride to yield the corresponding ethylene-RSt copolymers. The substituent on the styrene (St) monomers did not affect the monomer reactivity ratio. The effect of the substituent structure of RSt on the thermal and mechanical properties was studied with differential scanning calorimetry, dynamic mechanical thermal spectroscopy, and elongation testing. The glass-transition temperature (T _g) of the copolymers increased with increasing RSt content, and the order of T_g was as follows: BSt > VN > MSt = St. A copolymer with p-hydroxystyrene (HOSt) was successively synthesized by means of deprotection of the copolymer with BMSiOSt. The copolymer showed a much higher T_g than the other copolymers because of the hydrogen connection of its OH groups. The mechanical properties of the copolymer in the glass state, at a lower temperature than T_g, were almost independent of the nature of the RSt. The substituent of the St monomers affected the pattern of the stress-strain curve in the elongation testing in the amorphous state. An improvement in the shape memory effect was observed in poly(ethylene-co-BSt).