College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan, 030024, China.
School of Polymer Science and Polymer Engineering, University of Akron, 250 S Forge St, Akron, OH, 44325-0301, USA.
Macromol Rapid Commun. 2021 Jun;42(11):e2100072. doi: 10.1002/marc.202100072. Epub 2021 Mar 24.
A semi-crystalline, shape memory polymer (SMP) is fabricated by free radical cross-linking, polymerization, and grafting in a blend of n-octadecyl acrylate and polybutadiene (PB). Poly(n-octadecyl acrylate) (PODA) is a side-chain crystalline polymer, which serves as the structure-fixing network counterbalancing the elastically deformed, cross-linked polymer network. At a constant 50/50 ratio of monomer and polymer the amount of free radical initiator, dicumyl peroxide (DCP) is varied from 1% to 5% w/w PB. From swelling measurements and calculation of the cross-link density it is determined that DCP produces greater than one cross-link per DCP molecule. It is found that lower cross-linking efficiency is favorable for higher shape fixity. This lower efficiency is found to produce a higher degree of crystallinity of the PODA in the 2-5% DCP samples, which is determined to be the main driver of higher shape fixity of the polymer. A SMP with >90% fixity and 100% recovery at uniaxial strains from 34-79% is achieved. This material should be useful for mold processing of shape memory articles. This approach provides a method to decouple the elastomeric and thermoplastic portions of a SMP to convert commodity elastomers into SMPs and tailor the shape memory response.
一种半结晶形状记忆聚合物（SMP）是通过自由基交联、聚合和接枝在十八烷基丙烯酸盐和聚丁二烯（PB）的共混物中制备的。聚（十八烷基丙烯酸盐）（PODA）是一种侧链结晶聚合物，用作结构固定网络，平衡弹性变形的交联聚合物网络。在单体和聚合物的恒定 50/50 比例下，自由基引发剂二枯基过氧化物（DCP）的量从 PB 的 1%变化到 5%w/w。从溶胀测量和交联密度的计算可以确定，DCP 产生的交联数大于每个 DCP 分子的一个交联数。发现较低的交联效率有利于更高的形状固定性。在 2-5% DCP 样品中，发现较低的效率产生了更高程度的 PODA 结晶度，这被确定为聚合物更高形状固定性的主要驱动因素。在单轴应变从 34%到 79%的情况下，实现了>90%固定率和 100%恢复率的 SMP。这种材料应该对形状记忆制品的模具加工有用。这种方法提供了一种将 SMP 的弹性体和热塑性部分解耦的方法，将商品弹性体转化为 SMP，并调整形状记忆响应。
