The effect of allophanate crosslinking according to the NCO/OH molar ratio on the shape memory properties of polyurethane was investigated. Shape memory polyurethanes were polymerized with the variation of NCO/OH ratio keeping the content of total hard segment constant. The result of DSC and DMA showed that the glass transition temperature (T_g) of the soft segment in polyurethane slightly increased as the NCO/OH ratio varied from 1 to 1.2, but decreased at 1.3. In thermomechanical cycling test, as the NCO/OH ratio was changed from 1 to 1.2, the residual strain was decreased, the stress at maximun strain was maintained, and the recovery stress measured at reheating step was increased However, the enhancement of shape memory properties was not found at NCO/OH = 1.3

NCO/OH 몰비에 따른 allophanate 가교 형성이 폴리우레탄의 형상기억 성질에 미치는 영향을 검토하였다. 형상기억 폴리우레탄은 hard segment의 함량을 일정하게 하고 NCO/OH비를 변화시켜 중합되었다. DSC와 DMA 측정결과, 폴리우레탄에서의 soft segment의 유리전이온도가 NCO/OH비가 1에서 1.2로 변함에 따라 약간 증가함을 나타냈으나, NCO/OH비가 1.3인 경우는 오히겨 감소하였다. 열비계적 반복실험에서는 1에서 1.2로 NCO./OH비가 증가함에 따라 잔류변형이 감소하였고 최대변형률에서 응력이 유지되었으며, 재가열과정에서 측정된 회복력이 증가하였다. 반면에 NCO/OH비가 1.3인 경우, 형상기억 성질의 향상이 보이지 않았다.

Keywords: shape memory; polyurethane; allophanate crosslinking; NCO/OH molar ratio; thermomechanical cycling test