Polymer blends of syndiotactic polystyrene based on metallocene catalyst

Abstract

A series of syndiotactic polystyrenes(SPS), which have different molecular weight, were polymerized using the metallocene/methylaluminoxane(MAO) catalyst systems in various polymerization temperatures. The used metallocene catalyst were $CpTiCl_3$(Cyclopentadienyl titanium trichloride) and $Cp^*TiCl_3$ (Pentamethyl cyclopentadienyl titanium trichloride) which are known to be moderate catalyst to polymerize SPS. The intrinsic viscosity (IV)-molecular weight relationship of SPS was established by using the Mark-Houwink-Sakurada(MHS) equation. The IV was measured in 1,2,4-trichlorobenzene at 140℃ and the weight averaged molecular weight from GPC was used. From the Log [η] vs. Log $\bar3MS_w$ plot due to MHS equation for SPS, the parameters, a and K, are determined using the linear regression analysis as bellow $[\eta] = 1.086\times 10^{-4}\bar{M}_w^{0.7115}$ This relationship, therefore, should be useful to determine molecular weight by measure of IV for the general SPS in the laboratory. To investigate the tacticity effect on the rheological and crystallization behavior, SPS ($Cp^*TiCl_3$/MAO catalyst, polymerized at 50℃, rrrr ＞ 99%) was blended with atactic polystyrene (APS) in the solution state. The rheological properties of SPS and SPS/APS blends were measured with the dynamic shear mode in the fully melt state and were compared with commercial atactic polystyrene (APS) in view of the tacticity effects. The storage (G) and loss modulus (G) of SPS/APS blends decreased with an increasing of APS content in the terminal region at the same temperature and frequency. To compare rheological properties of APS with those of SPS and SPS/APS blends in the fully-melted state, the shift factor ($a_T$) of APS was estimated in the higher temperature range ( ＞ $T_m$ of SPS) by using the Arrhenius-like equation. The shift factor of SPS/APS blends decreased by increasing APS contents at 285℃ and 300℃. The reason is that the syndiotactic chains have slower relaxation times du...