Shape memory behavior and mechanism of poly(methyl methacrylate) polymer networks in the presence of star poly(ethylene glycol)

The shape memory poly(methyl methacrylate)/star poly(ethylene glycol) (PMMA/SPEG) networks and poly(methyl methacrylate)/linear poly(ethylene glycol) semi-interpenetrating networks (PMMA/LPEG semi-IPNs) were synthesized. The influence of two structural parameters for two network systems, the crosslinking density of the PMMA network and molecular weight of PEG, on the macroscopic properties of the polymer networks such as thermal properties, mechanical properties, dynamic mechanical properties and shape memory properties has been studied. The results showed that all samples for PMMA/SPEG networks had uniform deformation properties with recovery ratios above 98%. By contrast, PMMA/LPEG semi-IPNs showed poor recovery ratios. For two network systems, whereas the shape recovery speed decreased with increasing crosslinking density and molecular weight of PEG, the shape fixity ratio increased. The shape fixity ratio and shape recovery speed for PMMA/ SPEG networks is highly influenced by the two structural parameters of the networks, which have a negligible effect on its shape recovery ratio. It is proven that the embedding of the star-shaped structures greatly improved the shape recovery ratio and recovery speed of the PMMA/ SPEG networks with excellent mechanical properties compared to PMMA/LPEG semi-IPNs, which was caused by the star-shaped structures in the PMMA/ SPEG networks according to the tube model theory proposed by Edwards and the analysis of the creep properties of the materials.