The effect of pressure ranging from ambient atmosphere to 28.5 MPa on the free radical polymerizations of methyl methacrylate (MMA) in carbon dioxide (CO 2 ) was investigated and discussed. The poly (methyl methacrylate) (PMMA) with high molecular weight was synthesized at quite high conversion of MMA in the polymerization at or below 9.2 MPa, as compared to those polymerized under 11.8-28.5 MPa. A phase transition behavior of MMA-CO 2 binary mixture from homogeneous state to vapor-liquid equilibrium (VLE) state was observed below 10.51 MPa. In such a VLE system, almost all MMA was found to exist in the liquid phase with higher concentration than that in homogenous system. Thus, the fast polymerization rate of MMA and high molecular weight of PMMA could be related to the VLE state of MMA/CO 2 under low pressure. Similar phenomena were also observed in the polymerization systems of styrene and vinyl acetate in CO 2 , respectively.

A series of castor oil-based polyurethane (PU)/poly (methyl methacrylate-butyl methacrylate-styrene) (PA) grafted interpenetrating polymer networks (IPNs) were prepared. The effect of composition of the IPNs on the damping, thermal and mechanical properties were studied systematically. PU/PA (60:40, weight ratio) IPNs with methyl methacrylate/butyl methacrylate/styrene (MMA/BMA/St = 80/10/10, weight ratio). In the paper castor oil (CO) was used as PU’s branch units, the damping properties affected by the branch units ratio (ρ) were studied. Mechanical tests showed the tensile strength of the IPNs was improved after increasing the ρ value and PA content. The thermal stability was improved by incorporating heterocyclic imide rings into the PU molecular chains using isocyanate reacting with pyromellitic dianhydride (PMDA). It was found that the IPN composition with ρ value = 0.2 and PU/PA = 60:40 would be useful as structural damping materials, having tanδ values higher than 0.3 for a temperature range of 102°C (5.0-106.9°C).