Abstract
Thermoset polymers show favorable material properties, while bringing about environmental pollution due to non-reprocessing and unrecyclable. Diels–Alder (DA) chemistry or reversible exchange boronic ester bonds have been employed to fabricate recycled polymers with covalent adaptable networks (CANs). Herein, a novel type of CANs with multiple dynamic linkers (DA chemistry and boronic ester bonds) was firstly constructed based on a linear copolymer of styrene and furfuryl methacrylate and boronic ester crosslinker. Thermoplastic polyurethane is introduced into the CANs to give a semi Interpenetrating Polymer Networks (semi IPNs) to enhance the properties of the CANs. We describe the synthesis and dynamic properties of semi IPNs. Because of the DA reaction and transesterification of boronic ester bonds, the topologies of semi IPNs can be altered, contributing to the reprocessing, self-healing, welding, and shape memory behaviors of the produced polymer. Through a microinjection technique, the cut samples of the semi IPNs can be reshaped and mechanical properties of the recycled samples can be well-restored after being remolded at 190 °C for 5 min.
Highlights
Polymeric material is conventionally categorized as thermoset or thermoplastic, which is based on whether the material flows at elevated temperatures
When dynamic covalent bonds are activated at high temperatures, the rapid exchange reactions provide a rearrangement of the networks, enabling the polymer to be deformed, processed, and recycled, the shape can be fixed by quenching the exchange reactions at low temperatures [6,7]
Based on associative exchange mechanisms, polymer networks characterize a constant value of chemical bonds, and cross-links do not depolymerize at high temperatures [8]
Summary
Polymeric material is conventionally categorized as thermoset or thermoplastic, which is based on whether the material flows at elevated temperatures. Thermoplastic polymer with reprocess ability, can flow when heated, which permits extrusion, injection, and molding, whereas normally it exhibits poor chemical and solvent resistances, low mechanical strength, and low dimensional stability at high temperatures To combine both merits of thermoset and thermoplastic polymers, covalent adaptable networks (CANs) are explored; these can provide a stimulus responsive (such as temperature, light, electric, pH, moisture, and chemicals) to the polymer with fantastic properties such as shape memory, repairing, crack healing and stress relief [3,4,5]. We demonstrate the synthesis of semi IPNs by a sequential reaction approach using P(St-co-FMA), boronic ester crosslinker and TPU elastomer, along with the high compatible networks. Mini twin screw injection molding machine (WLG10G, Shanghai Xinshuo Precision Machinery Co., Ltd., Shanghai, China) as a reprocessing equipment, obtained sample particles were put into the barrel, post-processing was performed at 190 ◦C, and the samples were repeated for three cycles
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