【作者】 王国成；

【导师】 范志强； 程时远；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2005， 博士

【摘要】 本文采用球形高效负载Ziegler-Natta催化体系（TiCl₄-MgCl₂/AlR₃/二苯基二甲氧基硅烷（Diphenyl Dimethoxy Silane,DPDMS））合成等规聚苯乙烯（iPS）,研究了聚合温度、助催化剂用量和种类、外给电子体用量、单体浓度及氢气压力等条件对催化效率及产物结构的影响;采用溶液成膜、从玻璃态升温等温结晶,对不同分子量及分子量分布的等规聚苯乙烯的结晶性能进行了研究;通过对丙烯预聚产物的粒子形貌分析,确定了适宜的预聚合条件,并通过预聚合工艺合成了球形聚乙烯和苯乙烯-乙烯共聚物;用正辛烷和二甲苯为溶剂分别对两种不同聚合工艺制备的共聚物进行了分级,各级分经过逐步降温等温结晶（step-wise crystallization）后,用DSC分析了其结晶熔融行为,结合FTIR对各级分的组成进行了分析;通过热台偏光显微镜（PLM）、示差扫描量热法（DSC）、广角X射线衍射（WAXD）等对苯乙烯-乙烯共聚物结晶行为进行研究,并对其等温和非等温结晶动力学进行了分析;用电子拉力机和DMTA分析了共聚物的拉伸性能和动态力学性能,并对共聚物磺化改性,表征了其表面极性的变化。结果表明: 1、该催化体系对苯乙烯的等规聚合活性较高,催化效率最高可达7700gPS/gTi.h,通过多个Schulz-Flory最可几分布对产物的分子量分布曲线拟合分峰,结果发现AlEt₃能使产物中低分子量部分含量增加,Al（i-Bu）₃则倾向于形成高分子量的活性中心。体系中加入氢气不仅能显著提高催化效率,而且使iPS的分子量分布显著增宽。 2、对等规聚苯乙烯的DSC分析发现,iPS晶体熔融过程中出现两个吸热峰:退火峰与熔融峰,其中退火峰对应的温度随退火温度的增加而升高但与退火时间无关。在相同条件下等温结晶,随着分子量分布的增加,晶核密度减小,球晶尺寸逐渐增大。在分子量分布较窄和较宽的情况下,iPS球晶内部晶片主要是edge-on取向,但在分子量分布适中时,在不同结晶温度下,可同时观察到edge-on与flat-on取向的晶片。通过对AFM相图的分析,球晶内部晶片厚度约为25±10nm,说明晶片取向是edge-on或类似edge-on。 3、在丙烯预聚合研究中,发现在Al/Ti=80～100、Si/Ti=5～10、聚合温度40～50℃、适中的搅拌速度下可得到粒子形貌为球形且粒径较均匀的预聚物粒子。丙烯预聚合时间在10～15min时,可以得到较高的乙烯聚合活性、较大的球形聚乙烯粒子且粒径较均匀。加入适量H₂可小量提高乙烯聚合的活性,同时可以调节聚乙烯的分子量及分子量分布。通过丙烯预聚—乙烯聚合—苯乙烯聚合、丙烯预聚—苯乙烯聚合—乙烯聚合以及苯乙烯预聚—乙烯聚合等三种聚合工艺合成苯乙烯-乙烯共聚物,其中第一种工艺的产物中苯乙烯含量极低,第二种工艺产物中苯乙烯含量有所增加,第三种工艺制备的产物中苯乙烯含量最高。更多还原

【Abstract】 Isotactic polystyrene （iPS） and styrene-ethylene copolymers （PES） were synthesized with spherical MgCl₂-supported Ziegler-Natta catalytic system consisted of titanium tetra- chloride, diisobutyl o-phthalate （DIBP） as internal electron donor, triisobutyl aluminium as cocatalyst and diphenyl dimethoxy silane as external electron donor. The effects of polymerization temperature, cocatalyst, external electron donor, monomer concentration and pressure of molecular hydrogen on the synthesis of iPS were investigated. The crystallization behavior of iPS films with various molecular weight distributions prepared from solution and isothermally crystallized from glassy state were revealed by atomic force microscopy （AFM） and transmission electron microscopy （TEM）. The pre-polymerization in the preparation of PES was studied by the particle morphology of propylene pre-polymerization and the PES were fractionated with octane and xylene as solvent by temperature gradient elution fractionation method （TGEF）. The crystallization behavior of PES and its fractions were investigated by differential scanning calorimetry （DSC）, polarized light microscopy （PLM） with hot-stage and wide angle X-ray diffraction （WAXD）. The tensile and dynamic mechanical properties of PES were characterized to verify the conclusions on its structure and crystallization. The sulfonation of PES was carried out and the contact angle between the PES films and alcohol were obtained to characterize the level of the modification. The results are follows.1. The catalytic efficiency of isospecific polymerization of styrene is far above the values of the reported in references;particularly it can be 7700 gPS/gTi.h under the suitable conditions. The curves of iPS molecular weight distribution can be fitted with several Schulz-Flory most-probable distributions and the results show that the fraction of lower molecular weight in the product increases when triethyl aluminium is used as cocatalyst. On the contrary, the high molecular weight products can be obtained with triisobutyl aluminium as cocatalyst. The introduction of molecular hydrogen results in higher catalytic efficiency and broader molecular weight distribution.2. There appear two peaks in the DSC endotherm of iPS, called annealing peak and melting peak, respectively. The temperature of annealing peak increases with the rising temperature of isothermal crystallization. With the increasing of iPS molecular weight distributions, the nucleation density increases and the size of iPS spherulites decrease, at the same crystallization temperature and time. The lamellar thickness in the spherulites is about 25 ± lOnm, larger than the typical value of polymer lamellar thickness. The orientations of lamellae are all edge-on in the spherulites with narrow and broad molecular weight distributions, while both the edge-on and flat-on lamellae can be observed in the sample with medium molecular weight distribution.3. The uniform spherical particles of polypropylene pre-polymerized can be obtained under the conditions that Al/Ti molar ratio is 80-100, Si/Ti molar ratio is 5-10, and the temperature is 40-50 °C. With the pre-polymerization process for 10 ¹5min, the uniform large polyethylene particles are yielded with high catalytic efficiency. The catalytic efficiency can be enhanced and the molecular weight and molecular weight distribution can be controlled when the molecular hydrogen is introduced during the ethylene polymerization. The styrene-ethylene copolymers can be obtained with three polymerization technologies with different orders of the monomers introduction. The styrene content in PES is relatively higher with styrene pre-polymerization technology.4. The PES can be fractionated effectively with octane as the extraction solvent by temperature gradient elution fractionation method. The components in the copolymers are identified as three major types based on the thermal behaviors and FT-IR and 13C-NMR spectrum: high styrene content and short ethylene sequence copolymer, ethylene-predominant copolymer and highly molecular weight copolymer containing multi-ethylene segments.5. The spherulitic growth rates and melting points of PES decreased with the increase of styrene content, and the unit cell dimensions of the orthorhombic crystals of copolymers are larger than that of pure polyethylene. The peak in the WAXD curve corresponding to （200） reflections disappears gradually and the peak corresponding to （110） reflections is weakened with the increasing of styrene content.The crystallinites of PES, however, are larger than that of pure PE under the same crystallization conditions, which is correlated to the nucleation rate after the insertion of styrene unit in the polyethylene chains. Both isothermal and non-isothermal crystallization kinetics show the overall crystallization rate of PES with higher styrene content is larger than that of low styrene-content copolymer.6. The tensile strength and elongation at break of PES prepared with styrene pre-polymerization technology are larger than that of pure polyethylene. On the contrary, the tensile strength of PES prepared with propylene pre- polymerization is decreased with the increase of styrene content and the elongation at break is less than that of PE. There appears a new weak peak in the dynamic mechanical thermal analysis of PES, which corresponds to the irregular structure due to the insertion of styrene units. The contact angle between the PES films and alcohol is reduced for the sulfonation of copolymers.更多还原