Synthesis of chain-end functionalized polyolefins and fluoropolymers and applications in nanocomposites.

摘要

In this thesis, we have demonstrated a very useful and simple method (one-pot polymerization process) for synthesis of chain end functionalized polypropylene. The chemistry involves a chain transfer reaction to a styrenic derivative (St-f), with or without hydrogen during propylene polymerization, using an Exxon-Hoechst C2-symmetric catalyst (rac-Me 2Si[2-Me-4-Ph(Ind)]2ZrCl2/MAO complex) or a Mitsubishi C1-symmetric catalyst (Me2Si(2-Me-Benz[e]Ind(2-Me-4-Ph-4HAzu)HfCl 2 with MAO or trialkylaluminum-treated clay). In the presence of the Exxon-Hoechst catalyst, the propylene propagating chain-end engages in a facile consecutive chain transfer reaction, reacting with St-f and then with hydrogen, with high catalytic activity under the proper reaction conditions. The polymer molecular weight is proportional to the molar ratio of [propylene]/[St-f]. A silane protecting group in St-NSi2 or St-OSi unit can be hydrolyzed in an acidic solution during the sample work-up step to obtain desirable i-PP polymers, such as i-PP with a terminal NH2 or OH group, in one pot. Despite the low concentration, the terminal functional group is very reactive and can serve as an active site for many applications. One example was shown in a chain extension reaction (coupling reaction) with polycaprolactone (PCL) in solution to form PP-b-PCL diblock copolymers that are very effective compatibilizers in PP/PCL polymer blends.; Unexpectedly, a Mitsubishi C1-symmetric catalyst exhibits significant polymerization activity even in the absence of hydrogen, indicating that the trialkylaluminum may participate in chain transfer to p-MS (p-methylstyrene) terminated propagating chains. In the case of polymerization using MAO as a cocatalyst at 55°C, the addition of hydrogen increases the activity and regulates the polymer molecular weight. The chain-end structure is solely terminal p-MS. When TEA (triethylaluminium) -treated clay is adopted as an activator and carrier at the optimal polymerization temperature of 75°C, the high concentration of hydrogen suppresses catalytic activity. The chain ends consist of predominately terminal p-MS and a small amount of unsaturated end groups. A higher p-MS concentration or introduction of hydrogen eliminates the undesirable unsaturated chain ends.; Furthermore, we also study a new chemical route to prepared side chain functionalized polyolefin, especially the desirable MA (maleic anhydride) -modified PE and PP polymers with well-controlled molecular structures. The chemistry involves a post-polymerization process using borane/O2 stable radical initiators to create polymeric radicals that are simultaneously stabilized by in situ formed *O-BR2 stable radicals. The dormant polymeric radicals do not undergo undesirable side reactions (crosslinking and degradation, etc.), but can react with maleic anhydride. Some MAH-modified PP polymers with high molecular weight and controlled MAH content have been obtained. They have been proven to be the effective compatibilizers to improve the interfacial adhesion in the PP/Nylon 11 blends. (Abstract shortened by UMI.)