Abstract
This study aims to prepare poly(methyl methacrylate)-co-poly(dimethylsiloxane) urethane （PMMA-co-PDMS urethane）graft copolymers which possess improved toughness and thermal stabilities compared with neat PMMA. Confirmed by IR、NMR、GPC、Soxhlet extraction and swelling measurement, slightly cross-linked PMMA-co-PDMS urethane graft copolymers based on MMAs and PDMS urethane-methacrylate macromonomers with two various diisocyanates: 2,4-toluene diisocya-nate (2,4-TDI) and m-xylene diisocyanate (m-XDI) have been synthesized. The results measured by DMA、DSC、visible spectrometer and frequency-shift in IR spectra show that the structural difference in the diisocyanates affect the compa-tibility of PDMS-urethane and PMMA segments. The strength of hydrogen bonding between urethane and ester groups is close to that between urethanes. Consequently, PDMS-urethane is miscible with PMMA in 2,4-TDI system. However, the strength of hydrogen bonding between urethane and ester groups is smaller than that between urethanes, which causes phase separation in m-XDI system. The copolymer containing 3.75 phr macromonomer in m-XDI system presents maximum impact strength（from 13.02J/m to 22.21J/m）. However, the impact resistance behavior of the copolymers in 2,4-TDI system is independent of the content of macromonomer existing in the copolymer. The morphological features on the fracture surface show that soft rubbery microdomains composed of PDMS-urethane toughen PMMA in m-XDI system. On the other hand, by PDMS-urethane segments in 2,4-TDI system the improvement on the impact strength of copolymer is insignificant, since PDMS-urethane and PMMA segments in 2,4-TDI system show a uniform phase. Both copolymers of 2,4-TDI and m-XDI systems exhibit better thermal stabilities than those of neat PMMA. After analyzing the residuals of the decomposed copoly-mers, it was proposed that PDMS in the copolymers trap free radicals generated from the thermal decomposition of the copolymer to reduce the rate of thermal decomposi-tion of copolymer. In addition, the cross- linking structure can also reduce the evapora- tion of volatiles from the thermal decomposition process of the copolymer.