The grafted 3,5-dimethylphenyl group remarkably improved the low temperature flexibility of a polyurethane (PU) copolymer. The rigid and blunt shape of 3,5-dimethylphenyl was designed to interrupt molecular interactions and to disturb the close contact between PU chains and, thus, to improve the flexibility at extremely low temperature, while maintaining high and reproducible tensile and shape memory properties at ambient temperature. The effect of the 3,5-dimethylphenyl group on the flexibility of PU was tested at $-30^{circ}C$ together with a linear PU, and the reason for the exceptional flexibility at low temperature is discussed.