Synthesis Of Ultra-High Molecular Weight Poly Methyl Methacrylate

Poly(methyl methacrylate) (PMMA) is a very important transparent polymer material. The inherent low heat resistance, abrasion resistance and organic solvent resistance of ordinary PMMA limit its service temperature and cause low anti-abrasive and anti-impact properties of PMMA. PMMA creeps under continuous high load, resulting in stress cracking at room temperature. The heat resistance, abrasion resistance and impact resistance of PMMA increase with the increase of molecular weights of PMMA. Ultra-high molecular weight PMMA is tough and abrasive-proof at high temperature and can still maintain its mechanic strength and anti-impact strength at temperature over 200℃.Currently, ultra-high molecular weight PMMA is generally produced by suspension polymerization or plasma polymerization at low temperature. However, a large quantity of water containing disperse and stabilizer agents is used as continuous phase in suspension polymerization, leading to low productivity, great emission of wastewater and high cost of handling. Special equipments such as radio-frequency generator are required in plasma polymerization. The PMMA prepared from plasma polymerization often has a wide molecular weight distribution and is prone to cross-linking, consequently decreasing the solubility, toughness and impact resistance of PMMA.This work is focused on the development of new catalyst for the synthesis of ultra-high molecular weight PMMA by bulk polymerization. The thesis is designed to mainly cover following aspects:1) MMA is polymerized via traditional free radical polymerization, radical polymerization in the presence of chain transfer agent, and silane-initiated polymerization mediated by transition metal catalyst. The effects of metal catalysts, initiators, additive agents, reaction temperature and solvents on the molecular weights of PMMA are investigated. The results show these polymerizations could hardly produce PMMA with molecular weight over 1 million Dalton and molecular weight distribution lower than 1.5.2) A high efficient catalyst system with AlCl3 as a main catalyst and dicyclopentadienylplatinum chloride as a cocatalyst is developed. PMMA with a weight-average molecular weight of 1.37×106, number-average molecular weight of 1.06×106 and molecular weight distribution of 1.3 is prepared at 70℃ by the catalyst.3) Gel permeation chromatography, nuclear magnetic resonance spectroscopy and differential scanning calorimetry are employed to characterize the ultrahigh molecular weight PMMA. The PMMA is found to have an atactic structure with a glass transition temperature of 110.7℃.