Shape memory elastomers from reactive monomer/polymer blends

Shape memory polymers (SMPs) can memorize a programmed ‘temporary shape’ and return to their initial shape under an external stimulus. Most SMPs contain two structure-spanning, solid networks; a permanent elastic network that is strained during programing to drive shape recovery; and a temporary network that fixes the programmed shape. An interesting route to fabricate SMPs is by blending an elastomer and a crystalline small molecule, where the elastomer forms the permanent network, and the small molecule crystal forms the temporary network. However, a drawback of this approach is the blooming and expulsion of the small molecule during programming and recovery. To address this issue, blends of polybutadiene and octadecyl acrylate (ODA) have been investigated, where the ODA can either be grafted to the PB through an ene-reaction or undergo simultaneous polymerization, grafting and crosslinking with the PB using a peroxide free radical initiator. It will be demonstrated that the side-chain crystallization of the ODA produces shape memory polymers with high shape fixity and recovery ratios (> 95%) with processing compatible with molding operations. The structure-property relationships between the physical parameters and shape memory properties are discussed.