Controllable Preparation And Application Of PDMS Microgel And Gel Based On Photo Induced Radical Polymerization

Polydimethylsiloxane(PDMS),as a kind of silicone material,is known for its excellent physicochemical properties including biocompatibility,high elasticity,air permeability,optical transparency,high temperature resistance and high hydrophobicity.PDMS can be prepared as microgel and gel which possess cross-linked network,controllable three-dimensional structure,adjustable mechanical properties and responsiveness to external stimuli,and they are widely used in energy storage,coating,catalysis,antifouling coating,drug delivery and sensing.Nowadays,the commonly used approach for preparing PDMS gel materials(such as microgel and bulk gel)is thermally induced polymerization.In contrast,photoinduced polymerization has the characteristics of high polymerization efficiency,low energy consumption,and environmental friendliness.Besides,photo-induced living radical polymerization is distinguished at spatial and temporal control.However,to a heterogeneous system(PDMS microgel),the obstruction of light penetration and refraction will result in a non-uniform radiation distribution,which in turn affects the polymerization rate and particle uniformity.On this basis,a flow reactor was first designed in this paper to improve the uniformity of microgel particles and their contact efficiency with light,leading to the increase of polymerization rate.Subsequently,reversible addition-fragmentation chain transfer(RAFT)polymerization was introduced into the preparation of PDMS microgel.Compared with polymer network prepared through traditional free radical polymerization,its counterpart formed by RAFT polymerization is more uniform.Given that dormant polymer chains in the network can be reactivated,it will be convenient to conduct post modification,benefiting the synthesis of PDMS microgel and gel with various properties.Finally,the method of preparing PDMS gel via photoinduced RAFT polymerization was successfully applied to photocuring 3D printing.The resolution and precision of the printed product were also studied,providing a theoretical basis and technical support for the further achievement of the additive manufacturing of PDMS materials.The details are as follows:(1)The flow reactor with a flexible tubular reactor and a rod-shaped light source was designed and assembled.Through feeding continuously the ultrasonically dispersed PDMS miniemulsion into photoreactor using a syringe pump,the microgel product was then collected to analyze its crosslinking degree,particle size,swelling and shrinkage.To study the effect of the residence time on the crosslinking degree and particle size,we regulated the time of the PMDS miniemulsion resident in the photoreactor by adjusting the injection speed.Also,the generality of applying continuous streamer reactors to monomers with different viscosities was investigated by changing the molecular weight of PDMS monomers.(2)Based on the flow reactor described above,visible light induced RAFT polymerization was introduced into the preparation of microgel,and therefore,an "active" PDMS microgel synthesis system was established.The eosin and RAFT reagent were added into the PDMS polymerization system,and the effects of different residence time on the size and crosslinking degree of the microgel were studied.The spatial and temporal control of photo-induced RAFT polymerization was verified by on-off experiment.Based on the observation of swelling and shrinking behavior of microgel particles,the uniformity of the cross-linked network and its ability to carry dyes were investigated.A functional fluorescent monomer was used to study the activity of PDMS microgel through post modification.(3)Considering the excellent oxygen resistance and high polymerization rate of PDMS microgel prepared by visible light induced RAFT polymerization,we employed photo-induced RAFT polymerization to prepare PDMS gel,of which the mechanical properties were characterized and tested.And for the first time,photo-induced RAFT polymerization was used for photocuring 3D printing of PDMS gel materials,and the effects of different printing parameters on the accuracy and resolution of printed products were investigated.