On demand shape memory polymer via light regulated topological defects in a dynamic covalent network

Wusha Miao,Weike Zou,Tao Xie,Qian Zhao,Chujun Ni,Ning Zheng,Binjie Jin

doi:10.1038/s41467-020-18116-1

Wusha Miao, Weike Zou + Show 5 more

Open Access

https://doi.org/10.1038/s41467-020-18116-1

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Abstract

The ability to undergo bond exchange in a dynamic covalent polymer network has brought many benefits not offered by classical thermoplastic and thermoset polymers. Despite the bond exchangeability, the overall network topologies for existing dynamic networks typically cannot be altered, limiting their potential expansion into unexplored territories. By harnessing topological defects inherent in any real polymer network, we show herein a general design that allows a dynamic network to undergo rearrangement to distinctive topologies. The use of a light triggered catalyst further allows spatio-temporal regulation of the network topology, leading to an unusual opportunity to program polymer properties. Applying this strategy to functional shape memory networks yields custom designable multi-shape and reversible shape memory characteristics. This molecular principle expands the design versatility for network polymers, with broad implications in many other areas including soft robotics, flexible electronics, and medical devices.

Highlights

The ability to undergo bond exchange in a dynamic covalent polymer network has brought many benefits not offered by classical thermoplastic and thermoset polymers
We aim to answer an intriguing question, that is, can the topological defects naturally present in real polymer networks be harnessed to enable a universal mechanism for topological isomerization? With this thought in mind, we hereafter illustrate such a topological isomerizable network (TIN) design and demonstrate its surprising benefit via construction of shape memory polymers (SMPs) with on demand shape-shifting versatility not offered by existing SMP
Our network was synthesized via photoinitiated radical polymerization between polyethylene glycol diacrylate (PEGDA, polyethylene glycol with Mn of 3350) and N-hydroxyethylacrylamide (Fig. 1a)

Summary

Introduction

The ability to undergo bond exchange in a dynamic covalent polymer network has brought many benefits not offered by classical thermoplastic and thermoset polymers. The use of a light triggered catalyst further allows spatio-temporal regulation of the network topology, leading to an unusual opportunity to program polymer properties Applying this strategy to functional shape memory networks yields custom designable multi-shape and reversible shape memory characteristics. The concept of topological isomerizable network (TIN)[29], by contrast, allows topological shifting within a “fully enclosed” solid material, that is, without participation of external reagents This isomerization mechanism typically requires highly delicate design to introduce network heterogeneity. To answer the first question, we realize that, besides inter-chain crosslinking, the universal topological features for real polymer networks are a range of defects including intra-chain cycles (loops), dangling chains, and free chains (sol) These defects affect the macroscopic mechanical and thermomechanical properties in a non-constructive way, but are statistically unavoidable[30,31]. We aim to answer an intriguing question, that is, can the topological defects naturally present in real polymer networks be harnessed to enable a universal mechanism for topological isomerization? With this thought in mind, we hereafter illustrate such a TIN design and demonstrate its surprising benefit via construction of shape memory polymers (SMPs) with on demand shape-shifting versatility not offered by existing SMP

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