Construction Of Stimuli Responsive Shape Memory Gel Carrier And Its Controlled Catalysis Performance

The design and synthesis of intelligent and controllable catalysts has come to be one of the research hotspots with the development of modern catalytic technology.As a class of smart materials,shape memory polymers?SMPs?are able to adopt a temporary shape and recover their "remembered" permanent shape when exposed to an external stimulus.The shape memory polymer is used as the carrier of the metal nanoparticle catalyst,which can avoid the agglomeration of the metal nanoparticles,and impart catalytic intelligent controllability.In various stimulus signals,light is particularly appealing because it allows remote and non-contact irradiation at ambient temperature,which can be delivered instantaneously to the stimulus-responsive system without any diffusion limitations.In this paper,a combination of metal nanoparticles and photosensitive shape memory hydrogel was used to prepare a photosensitive double-layer shape memory hydrogel with shape memory and controlled catalytic characteristics.Inspired by the amazing thoughts published in the literature,a novel photoresponsive shape memory reactor with controllable catalytic performance has been designed in the present work.A double-layer shape memory hydrogel was fabricated.A light sensitive monomer,cinnamic acid hydroxyethyl methacrylate?CAM?,was copolymerized with acrylamide to produce the photoresponsive layer and polyacrylamide formed the supporting layer without any light sensitivity.Ag nanoparticles,formed via the in situ reduction of AgNO₃,were dispersed in the photoresponsive layer and act as the catalyst.It is known that cinnamic moieties are able to carry out efficient photoreversible cycloaddition reactions when exposed to light irradiation??>260 nm or?<260 nm?by acting as molecular switches.Subsequently,if the double layer hydrogel is forced into a new shape and then irradiated with UV light at?>260 nm,the change in the morphology resulting from segmental movements under external stress can be fixed through the formation of new light-sensitive crosslinks in the photoresponsive layer.Under this condition,reactants in solution find it difficult to permeate into the photoresponsive layer to come in contact with the Ag nanoparticle catalyst because of the higher degree of crosslinking in the polymer network.Therefore,the catalytic reaction is greatly hindered.However,if irradiated with UV light at?<260 nm,the photoresponsive crosslinks were reversibly cleaved.As a result,the fixed temporary shape recovers to the original permanent shape.At the same time,an enhanced catalytic activity is also induced by the lowered crosslinking around the Ag nanoparticles.They show relatively high shape fixity ratios of 98%the shape recovery ratios were determined to be 90%.After50 min,the conversion under light irradiation atl>260 nm?40.15%?was much lower than that under light irradiation atl<260 nm?83.21%?.So,in principle,the catalytic performance of the smart hydrogel can be effectively regulated using an external light stimulus through shape change and recovery.This strategy may be valuable in applications under ambient conditions,especially when catalytic reactors with predetermined shapes are needed.