| Poly(methyl methacrylate) (PMMA) is a transparent polymeric material possessing many desirable properties. However, the glass temperature (Tg) and heat-deformation temperature (HDT) of PMMA are relatively low, which limits its applications. In order to improve Tg and HDT of PMMA organic glass, a series of MMA copolymer organic glasses were prepared through batch bulk polymerization and by incorporating of different kind of cyclic monomers, monomers containing groups which can form hydrogen-bonding interactions with MMA, and crosslinking agents. In addition, the light transmittance, the water absorption and the impact strength of modified organic glasses were investigated.Firstly, methyl methacrylate (MMA)-isobornyl methacrylate (IBMA), MMA-dicyclopentanyl methacrylate (DPMA), and MMA-pentafluorophenyl methacrylate (PFPMA) copolymers were synthesized by bulk polymerization using azobisisobutyronitrile (AIBN) as an initiator. The structure and properties of modified organic glasses were measured by using differential scanning calorimetry (DSC),1H nucleat magnetic resonance (1H NMR), ultraviolet-visible spectrophotometer (UV-vis) and pendulum impact testing. Incorporation of cyclic rigid structure into the copolymers would reduce the chain flexibility and restrain the molecular chain movement. The results indicated that Tg was increased with the increase of IBMA, DPMA or PFPMA contents in MMA copolymers, due to increasing amounts of cyclic moiety in the copolymer backbone. IBMA was found to be the best modified monomer, and Tg of copolymer prepared with MMA/IBMA molar ratio of 80/20 was 139℃. Moreover, the light transmittance of copolymers was closed to that of PMMA. The moisture absorption of copolymers was reduced due to the hydrophobicity of cyclic group. The notched impact strength of modified organic glasses was decreased as IBMA and DPMA introduced into polymer chains because of the brittleness of IBMA polymer and DPMA polymer. MMA-IBMA copolymer with MMA/IBMA molar composition of 80/20 and MMA-DPMA copolymer with MMA/DPMA molar composition of 70/30 exhibited good comprehensive performance with higher Tg, lower moisture absorption and good transparency.Secondly, effects of α-methacrylic acid (MAA) and methacrylamide (MAAM) on the structure and properties of MMA-IBMA copolymers (MMA/IBMA molar with fixed at 90/10) and MMA-DPMA copolymers (MMA/DPMA molar with fixed at 70/30) were investigated. It was found that Tg was increased with the increase of MAA or MAAM contents in MMA copolymers, due to strong hydrogen bonding interactions of carboxyl or amide group. Respectively, Tg was increased by 9℃ and 5℃ as 5 mol% MAA or 5 mol% MAAM was incorporated into MMA-IBMA copolymer. For MMA-DPMA copolymerss, Tg was increased to 148℃ as 10 mol% MAA incorporated into copolymers. Besides, the high light transmittance of trepoymers was observed. The moisture absorption was increased upon increasing the MAA or MAAM content in the terpoymers, and the moisture absorptions of terpolymers were closed to that of PMMA, due to hydrophobic character of the cyclic group in IBMA and DPMA. It was also found that the impact strength was increased with the increase of MAA or MAAM content. The organic galsses with MMA/IBMA/MAA molar ratio of 85/10/5 or MMA/DPMA/MAA molar ratio of 65/30/5 possessed good comprehensive performance.Finally, effects of crosslinking of MMA copolymers (MMA/IBMA/MAA=85/10/5 or MMA/DPMA/MAA=65/30/5) with ethylene glycol methacrylate (EGDMA), triallyl isocyanurate (TAIC) and allyl methacrylate (AMA) on the structure and properties of organic glass were studied. It was indicated that Tg of copolymers could be further increased by crosslinking. The gel fractions of crosslinked organic glass were all above 93%. EGDMA was found to be the best crosslinking agent, and Tg was increased by 5℃ and 9℃ for MMA-IBMA-MAA and MMA-DPMA-MAA copolymers, respectively. Furthermore, the crosslinking agents barely had effect on light transmittance, moisture absorption, and impact strength.The above results would provide a good instruction for preparation of organic glasses with high Tg and HDT... |
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