Thermal Annealing of High <i>cis</i>-1,4-Polybutadiene/Octadecyl Acrylate Blends as a One-Step Process for Fabricating Shape Memory Polymers
Sayan Basak, Juan Marin Angel, Kevin A. Cavicchi
Abstract
Blending molecular crystals with a cross-linkable elastomer is an inexpensive, formulation- and processing-friendly route to develop shape memory polymers (SMPs). In this work, a shape memory material consisting of thermally cross-linked, octadecyl acrylate (ODA)-grafted polybutadiene (PB) and free octadecyl acrylate was prepared. High-temperature (175 °C) annealing of a melt-processable blend of PB and ODA results in the ene grafting of a portion of the ODA onto the PB chains producing a side-chain crystalline polymer, while simultaneous cross-linking of the PB produces a cross-linked network. At ODA loadings of 0.66 ODA molecules:PB repeat unit (80 wt % ODA), materials with high shape fixity (>99%) and recovery (>99%) were prepared. Higher shape recovery was measured compared to previously reported peroxide cross-linked PB/ODA blends. Limited blooming of the free ODA was found on stored samples and during shape memory cycling, an improvement compared to other elastomer small molecule blends. These results are discussed in terms of the synthesis, structure, and physical properties of this blend system.