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 due to their rotational hindrance and also more have interaction with each other. In the LogG vs. LogG plot, SPS containing samples had slopes smaller than 2 and this trend was vivid in SPS. Thus one can say that even though this system is chemically homogeneous, it is inhomogeneous in tacticity. Further work on molecular dynamics remains untouched.
The nonisothermal crystallization from the melt state, the morphology and the recrystallization behaviors of SPS/APS blends have been analyzed by differential scanning calorimetry (DSC), optical microscopy, and wide angle x-ray diffractometry (WAXD) to investigate the effect of the atactic chain on the crystallization behavior of the syndiotactic chain. It was observed that increasing APS content causes a decrease in the dynamic crystallization peak temperature($T_c$) of SPS but does not change the enthalpy of crystallization ($ΔH_c$) and the enthalpy of melting ($ΔH_m$). To further investigate the influence of APS on the crystallization of SPS, the crystalline structure and the reheated melting exotherm have been studied for crystallized samples with several pre-cooling rates. The SPS spherulites are more opened as more APS is added due to the presence of APS in the interfibrillar region of the SPS spherulites, and some APS chains are also found in the front region of the SPS spherulites. The WAXD pattern of the crystalline SPS exhibits a β′-form, which is not altered with the addition of APS and with the increasing cooling rates. The prominence of the lower melting endotherm with the addition of the APS in the DSC thermogram is due to the predominant hindrance effect of the APS chains on the recrystallization of SPS over the effect of supercooling. From the comparison of the WAXD patterns of the SPS/PPO (poly 2,6-dimethylphenylene oxide) blend system, we concluded that APS is immiscible with SPS in the molecular chain scale even in the melt state, while PPO is miscible with SPS.
The mechanical and morphological properties of SPS/LCPs blends were investigated. To give a synergistic effect on the mechanical properties of SPS/LCPs blends, two LSPs (Vectra A950 and Rodlan LC-3000) which have largely different melt viscosity were used as a dispersed phase in the SPS matrix. In the DMA(Dynamic mechanical Analyzer) experiment, the dynamic modulus of SPS/LCPBL(Vectra A950/Rodlan LC-3000 (50%/50%)) blends at 50℃ increased as the LCPBL content increased and it shows the higher values than that of the additive rule with LCPH in the lower LCPBL content region (~20wt.%). The tensile strength (TS) and elongational mudulus (MD) had the same trend with the dynamic modulus. In the morphological investigations, the LCPs domains are more finely dispersed and smaller domains were detected in the SPS matrix in the lower LCPBL content blends. From the morphological result, the drastically increases of dynamic modulus, TS, and MD of SPS/LCPBL seems to be due to the synergistic effect of two different LCPs domains.
The nucleating agent effects on the nonisothermal crystallization of SPS were investigated utilizing DSC, programmed cooling/heating procedure. The crystallization temperature peak($T_c$),the crystallization rate parameter (CRP), enthalpy of crystallization and melting, and the recrystallization behavior were compared in the organic (SPS-MILLAD) and inorganic (SPS-TALC) nucleating agents contained SPS. The effect of SPS-MILLAD was more prominent than that of SPS-TALC on the nucleation of SPS, except the trend in $T_c$. It could be explained by that the temperature where the MILLAD acts as a nucleating agent should be lower than that of TALC, because the TALC is solid state in the region of crystallization of SPS.
