Graft Copolymerization Of Hydroxypropyl Methylcellulose In Emulsion

Graft copolymerization of ethyl acrylate(EA) onto hydroxypropyl methylcellulose(HPMC) was carried out by the use of potassium persulfate (KPS) initiator in aqueous medium. A mechanism, which resembled that of classic emulsion polymerization, was proposed. The extent of graft polymer formation was measured in terms of grafting percent and grafting efficient as functions of reaction temperature, monomer concentration, pre-interacting time and isopropanol(IPA). Grafting percent had maximum at temperature of 65 ℃ ,and grafting efficiency decreased as temperature increased. Longer pre-interacting time between KPS and HPMC and higher monomer concentration resulted in higher grafting percent and grafting efficiency. The effect of IPA on the extent of graft polymer formation was also examined. Stable high-solid-content emulsion was obtained in the presence of IPA. The formation of graft copolymers were confirmed by IR and DSC. The glass transition temperatures(Tg) of HPMC and PEA approached each other due to the improved compatibility with HPMC-g-PEA as a compatibilizer. The graft copolymers with low level of grafting percent exhibited bad mechanical properties due to poor compatibility. It was found that the extent of graft polymer formation on HPMC was appreciably reduced by the presence of DM. It was interpreted as due to the chain transfer effect of DM. An interesting discovery was the dramatically acceleration of decomposition of KPS, with the reaction rate showed 2-order with respect to the concentration of KPS and a half-time of less than 1min at 60℃ was observed.