The effect of pendant tertiary butyl group on the shape recovery of polyurethane copolymer under freezing

The effect of the pendant tertiary butyl group on the shape recovery and tensile properties of a polyurethane (PU) block copolymer was investigated. The pendant tertiary butyl group was designed to interrupt molecular interactions and to disturb the close contact between PU chains through its bulky structure and, thus, to improve the shape recovery at subzero temperatures, while maintaining high and reproducible tensile properties and the shape recovery at ambient temperature. The attachment of the tertiary butyl group did make a difference in the phase separation of the hard and soft segments in the PU structure, as determined from the results of infrared and differential scanning calorimetry. The crosslink density and the intrinsic viscosity experienced an unusual increase with the tertiary butyl content due to partial crosslinking by the grafting reagent. Shape recovery and retention were reproducible after performing repeated shape memory tests. Finally, the effect of the tertiary butyl group on the shape recovery at −10°C was compared with that of linear PU, and the reason for the remarkable flexibility is discussed.