| dc.description.abstract | Syndiotactic polystyrene (sPS) possesses special properties that are different from atactic and amorphous polystyrene such high crystallinity, faster crystallization rate then isotactic polystyrene (iPS) and exhibit potential as an engineering plastic.
This research focuses on the copolymerization of styrene with α-methylstyrene（α-Mst）and para-methylstyrene（p-Mst） using CpTiCl3 catalyst and the effects of methyl substitution position on the crystallization behaviors of sPS. In the sPS-co-(?-methyl styrene) system, ? substituted methyl increases the steric hindrance for monomer incorporation and causes a reduced polymerization activity, as a results the reactivity ration is much lower than polystyrene leading to a random copolymer whereα-Mst monomer is almost isolated. In the sPS-co-(para-methyl styrene) system, the para-substituted methyl group do not create the same hindrance asα-Mst, instead it stabilized the activated reaction intermediate and facilitated the monomer incorporation. As a result, the reactivity ratio is much higher and the copolymer bears longer p-Mst block length. Crystallization kinetic studies revealed that the difference of microstructure has dramatic effects on the crystalliztion behavior. For the poly(styrene-co-alfa methyl styrene) (sPS/PAMS) system, α-Mst has increased chain stiffness with increasingα-Mst content in polymer. This decreases the crystallization rate with more ?-form crystalline modifications. For the poly(styrene-co-para-methyl styrene) (sPS/PPMS) system, long block of p-Mst unit is excluded from the crystallite and also reduces the crystallization rate. The non-crystallizable p-Mst block improves the segmental mobility during crystallization and instead of yielding ?-form crystalline modifications, it gives more perfect ?” crystalline modification. Crystallization kinetic study shows both comonomer increases the values of nucleation parameter, Kg, the fold surface energy,σe and the work of chain folding, q when compared with sPS homopolymer. However, for (sPS/PAMS) they increase with increasingα-Mst, but for (sPS/PPMS) system, rapid incense is found with 2-3 mole % of p-Mst, but decrease afterwards when p-Mst is higher than 5 mole%. | en_US |