Partially constrained recovery of (meth)acrylate shape-memory polymer networks

The purpose of this study was to characterize the partial strain recovery of a thermoset shape-memory polymer under a constraining stress. Three polymer networks were synthesized from tert-butyl acrylate and poly(ethylene glycol) dimethacrylate (PEGDMA) solutions. The molecular weight and the weight fraction of the PEGDMA crosslinking monomer was altered systematically to maintain a constant glass transition temperature (Tg = 54 degrees C) but tailorable rubbery moduli, which varied by almost an order of magnitude for the three polymer networks (E?r' = 1.811.3 inverted perpendicular MPa). The shape-recovery behavior of the polymers under a constraining stress was characterized for programming temperature below (20 degrees C) and above (70 degrees C) the Tg. The experiments revealed a peak in the recovered strain for samples programmed at 20 degrees C. Recovered strain scaled linearly with the constraining stress by the rubbery modulus. The work performed by the shape-memory polymer networks was observed to be primarily a function of constraining stress and crosslinking density, while programming temperature had a relatively mild influence; however, the efficiency of the shape-memory effect was shown to be a function of constraining stress and programming temperature, but was independent of crosslinking density. Maximum work efficiencies (up to 45%) were observed for programming temperature of 70 degrees C. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012