Star-shaped polyhedral oligomeric silsesquioxane (SPOSS)-based multi-arm poly(ε-caprolactones) (PCLs) with various arm lengths were synthesized by ring opening polymerization of ε-caprolactone. Increasing the PCL arm lengths was observed to increase the melting temperature and also the melt crystallization temperature in SPOSS-PCLs. Star-shaped POSS-PCL polyurethanes (SPOSS-PUs) were then prepared by cross-linking SPOSS-PCLs with hexamethylene diisocyanate (HMDI) and their shape memory (SM) behaviour was determined. For this purpose two cyclic thermo-mechanical testing concepts with similar programming (deformation and shape fixing) but different recovery strategies (free strain versus fixed-strain constrained stress recovery) were used and the synthesized polymers were systematically investigated around the crystallization and melting temperatures of PCL. SPOSS-PU with the highest POSS content exhibited remarkable cycles-averaged (N = 2–5) shape fixities and strain recoverabilities of 98% and stress recoverabilities close to 100%. The main structural factors that were expected to reduce the SM performances with increasing PCL arm lengths were a lowering of cross-link density (content of octasubstituted POSS) and an increase in chain flexibility/molecular mobility.
通过
ε-己内酯的环开聚合反应,合成了具有不同臂长的星形多面体寡聚倍半
硅氧烷(
SPOSS)基多臂聚(
ε-己内酯)(PCL)。研究发现,增加PCL的臂长可以提高
SPOSS-PCL的熔融温度和熔融结晶温度。然后,通过六
亚甲基二异氰酸酯(
HMDI)与
SPOSS-PCL交联,制备了星形POSS-PCL聚
氨酯(
SPOSS-PU),并确定了其形状记忆(SM)特性。为此,我们使用了两种循环热力学测试概念,它们具有相似的编程(变形和形状固定),但不同的恢复策略(自由应变与固定应变约束应力恢复),并对合成的聚合物进行了系统研究,围绕PCL的结晶和熔融温度。POSS含量最高的
SPOSS-PU表现出显著的循环平均(N = 2-5)形状固定性和应变恢复性(98%),应力恢复性接近100%。随着PCL臂长的增加,预计会降低SM性能的主要结构因素是交联密度(八取代POSS的含量)降低和链柔性/分子流动性增加。