Macroscopic and microscopic shape memory effects of block copolymers prepared via ATRP

Arbitrarily Reconfigurable and Thermadapt Reversible Two-Way Shape Memory Poly(thiourethane) Accomplished by Multiple Dynamic Covalent Bonds

The fabrication of a single polymer network that exhibits a good reversible two-way shape memory effect (2W-SME), can be formed into arbitrarily complex three-dimensional (3D) shapes, and is recyclable remains a challenge. Herein, we design and fabricate poly(thiourethane) (PTU) networks with an excellent thermadapt reversible 2W-SME, arbitrary reconfigurability, and good recyclability via the synergistic effects of multiple dynamic covalent bonds (i.e., ester, urethane, and thiourethane bonds). The PTU samples with good mechanical performance simultaneously demonstrate a maximum tensile stress of 29.7 ± 1.1 MPa and a high strain of 474.8 ± 7.5%. In addition, the fraction of reversible strain of the PTU with 20 wt % hard segment reaches 22.4% during the reversible 2W-SME, where the fraction of reversible strain is enhanced by self-nucleated crystallization of the PTU. A sample with arbitrarily complex permanent 3D shapes can be realized via the solid-state plasticity, and that sample also exhibits excellent reversible 2W-SME. A smart light-responsive actuator with a double control switch is fabricated using a reversible two-way shape memory PTU/MXene film. In addition, the PTU networks are de-cross-linked by alcohol solvolysis, enabling the recovery of monomers and the realization of recyclability. Therefore, the present study involving the design and fabrication of a PTU network for potential applications in intelligent actuators and multifunctional shape-shifting devices provides a new strategy for the development of thermadapt reversible two-way shape memory polymers.

Synthesis and Self-Assembly of Poly(N-Vinylcaprolactam)-b-Poly(ε-Caprolactone) Block Copolymers via the Combination of RAFT/MADIX and Ring-Opening Polymerizations

Well-defined amphiphilic, biocompatible and partially biodegradable, thermo-responsive poly(N-vinylcaprolactam)-b-poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by combining reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerizations (ROP). Poly(N-vinylcaprolactam) containing xanthate and hydroxyl end groups (X–PNVCL–OH) was first synthesized by RAFT/macromolecular design by the interchange of xanthates (RAFT/MADIX) polymerization of NVCL mediated by a chain transfer agent containing a hydroxyl function. The xanthate-end group was then removed from PNVCL by a radical-induced process. Finally, the hydroxyl end-capped PNVCL homopolymer was used as a macroinitiator in the ROP of ε-caprolactone (ε-CL) to obtain PNVCL-b-PCL block copolymers. These (co)polymers were characterized by Size Exclusion Chromatography (SEC), Fourier-Transform Infrared spectroscopy (FTIR), Proton Nuclear Magnetic Resonance spectroscopy (¹H NMR), UV–vis and Differential Scanning Calorimetry (DSC) measurements. The critical micelle concentration (CMC) of the block copolymers in aqueous solution measured by the fluorescence probe technique decreased with increasing the length of the hydrophobic block. However, dynamic light scattering (DLS) demonstrated that the size of the micelles increased with increasing the proportion of hydrophobic segments. The morphology observed by cryo-TEM demonstrated that the micelles have a pointed-oval-shape. UV–vis and DLS analyses showed that these block copolymers have a temperature-responsive behavior with a lower critical solution temperature (LCST) that could be tuned by varying the block copolymer composition.