Reversible Actuation of Thermoplastic Multiblock Copolymers with Overlapping Thermal Transitions of Crystalline and Glassy Domains

Abstract

Polymeric materials possessing specific features like programmability, high deformability, and easy processability are highly desirable for creating modern actuating systems. In this study, thermoplastic shape-memory polymer actuators obtained by combining crystallizable poly(εcaprolactone) (PCL) and poly(3S-isobutylmorpholin-2,5dione) (PIBMD) segments in multiblock copolymers are described. We designed these materials according to our hypothesis that the confinement of glassy PIBMD domains present at the upper actuation temperature contribute to the stability of the actuator skeleton, especially at large programming strains. The copolymers have a phase-segregated morphology, indicated by the well-separated melting and glass transition temperatures for PIBMD and PCL, but possess a partially overlapping T m of PCL and T g of PIBMD in the temperature interval from 40 to 60 °C. Crystalline PIBMD hard domains act as strong physical netpoints in the PIBMD−PCL bulk material enabling high deformability (up to 2000%) and good elastic recoverability (up to 80% at 50 °C above T m,PCL ). In the programmed thermoplastic actuators a high content of crystallizable PCL actuation domains ensures pronounced thermoreversible shape changes upon repetitive cooling and heating. The programmed actuator skeleton, composed of PCL crystals present at the upper actuation temperature T high and the remaining glassy PIBMD domains, enabled oriented crystallization upon cooling. The actuation performance of PIBMD-PCL could be tailored by balancing the interplay between actuation and skeleton, but also by varying the quantity of crystalline PIBMD hard domains via the copolymer composition, the applied programming strain, and the choice of T high . The actuator with 17 mol% PIBMD showed the highest reversible elongation of 11.4% when programmed to a strain of 900% at 50 °C. It is anticipated that the presented thermoplastic actuator materials can be applied as modern compression textiles.

Two-Way and Multiple-Way Shape Memory Polymers for Soft Robotics: An Overview

“…For several years, chemically cross-linked polymer networks have been considered to be a necessary condition for the two-way SME in order to prevent the flowing of the polymer above T m . However, some thermoplastic polymers, i.e., class (iii), have been shown to feature the two-way SME under stress-free condition [142][143][144][145][146]. Thermoplastic polymers may be reprocessed and reused, thereby avoiding the synthesis of a new polymer.…”

Linear Shape Memory Polyester with Programmable Splitting of Crystals

“…Lendlein et al developed thermoplastic SMP actuators, which were obtained by combining crystallizable poly( ε ‐caprolactone) (PCL) and poly(3S‐isobutylmorpholin‐2,5‐dione) (PIBMD) segments in multiblock copolymers. [ 30 ] In this system, the crystalline PIBMD hard domains provided the permeant crosslinks, while the crystallization and melting of PCL actuation domains were used to achieve pronounced reversible shape changes. Such design generally requires multiblock copolymers with distinct separation between the fixed and switching phases.…”

Thermoplastic Polyolefin Elastomer Blends for Multiple and Reversible Shape Memory Polymers

“…The chemical cross-linking is a clear drawback for reprocessing and recycling. In the recent years, there have been a few works demonstrating that thermoplastic polymers could also yield RSME, such as poly­(ethylene-co-methacrylic acid), polyurethane, , ethylene/1-octene diblock copolymer, and poly­(3S-isobutylmorpholin-2,5-dione)-polycaprolactone copolymer . The physical cross-links in the thermoplastic polymers help to keep the permanent shapes, instead of the chemical cross-links in the thermoset polymers.…”