Shape memory polymers with high and low temperature resistant properties.

Xinli Xiao,Wenbo Zhang,Xueying Qiu,Fenghua Zhang,Yang Hu,Yanju Liu,Jinsong Leng,Shen Zhang,Deyan Kong

doi:10.1038/srep14137

Abstract

High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to −150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed.

Highlights

Vast deterioration in shape memory performance after the thermal cycling
The shape memory effect of SMP is generally explained by dual-state mechanism, in which the molecular chains are regarded as the reversible phase, and the nodes of macromolecule segments attributed to physical or chemical crosslinks are regarded as the permanent phase[1,5,43] SMPs with Tg lower than 110 °C are mainly composed of polymers with flexible main chains, while SMPs with high Tg are all characteristic of the rigid chains comprising phenyl rings and flexible linkages[26,27,28,29,30,31]
The shape memory polyimide here is obtained by polycondensation of bis phenol A dianhydride (BPADA)/ODA, where the isopropylidene and ether linkage within the backbone provide some flexibility to the highly aromatic polyimide structures, and the molecular chains act as reversible phase

Summary

Introduction

Vast deterioration in shape memory performance after the thermal cycling (unpublished work of our group). We report new shape memory polyimide samples with adjustable Tg ranging from 229 to 243 °C, which show excellent thermal cycling resistant properties. Molecular weight has great influence on the physical properties of polymer[39,40,41], and high molecular weight is necessary to form physical crosslinks as the permanent phase of thermoplastic shape memory polyimide[27]. Thermoset shape memory polyimide samples are fabricated, and the influence of covalent crosslinking on their physical properties are studied. The possible mechanism of high temperature shape memory effects of the polyimide based on chain flexibility, molecular weight and crosslink density is proposed. The shape memory polyimides possess thermal cycling resistant properties, and the possible reason is discussed

Methods

Results

Conclusion