Controlled Synthesis,structure And Performance Of Stimuli-responsive Fluoro/silicon Copolymers

Stimulation responsive polymers is one kind of smart materials which are sensitive to external stimuli.When the stimulus signal is recognized,it will cause a reversible or irreversible change in the molecular structure or conformation,as well as the transformation behavior of bulk or liquid phase in the macromolecular system.The resulting polymer materials have important application in the fields of drug controlled release,nanocatalysis,chemical sensing and biotechnology.In this work,based on the low surface energy and high surface activity of fluorine/silicon copolymers,as well as the demand of special functional materials,some kinds of structure-controllable fluorine/silicon copolymers with stimuli responsive performance were prepared.And then,the humidity-responsive of copolymer films,the pH-responsive of electrospun copolymer membranes and the pH-responsive aggregation and dispersion behavior by the amphiphilic copolymers were studied.The detailed works are as follows:（1）Controlled synthesis,structure and properties of humidity-responsive fluorinated block copolymers.A series of well-defined PHFBMA-b-PMMA-b-PtBMA triblock copolymers with different compositions were synthesized via reversible addition-fragmentation chain transfer（RAFT）radical solution polymerization,using hexafluorobutyl methacrylate（HFBMA）,methyl methacrylate（MMA）and t-butyl methacrylate（tBMA）as the comonomers,azobisisobutyronitrile（AIBN）as the initiator,and2-cyanoprop-2-yl dithiobenzoate（CPDB）as the RAFT agent.And then,amphiphilic PHFBMA-b-PMMA-b-PMAA triblock copolymers were further obtained via the hydrolysis reaction.By the study of stimuli responsive performance of the amphiphilic PHFBMA-b-PMMA-b-PMAA triblock copolymers,the results showed that responsive performance of the copolymer films on the dry and wet states was mainly expressed through the movement of the fluorinzted segmentd and the hydrogen bonding force formed by the carboxyl group in the PMAA.But the partial crystallinity of the copolymer films inhibited the expression of responsive performance from the fluorinated segments.（2）PreparationandpH-responsivepropertiesofelectrospun polysiloxane-containing copolymer membranes.Based on the RAFT free radical polymerization and the electrospinning technology,a series of pH-responsive PDMS-b-PMMA-b-PDMAEMA triblock copolymers and their electrospun nanofiber membranes were successfully prepared.Then the wettability and pH-responsive performance in the buffer solution with different pH values were investigated.Scanning electron microscopy（SEM）was used to observe the changes of membrane morphology and video contact angle measurement（CAM）was used to investigate the wettability of electrospun membranes using buffer solutions with different pH values.It was found that the electrospun membrane had significant pH-response performance and could maintain the fiber morphology well within the range of pH=4.0 to pH=11.7.In addition,it was found that the electrospun membranes had better hydrophobic properties（caused by increased roughness）than the copolymer coating films.The pH-responsive performance of the obtained membrane was mainly due to the fact that in the acidic buffer solution,the interaction between-N（CH₃）₂ in PDMEMA segments and the free proton（H⁺）in the solution can transform-N（CH₃）₂⁺into-N（CH₃）₂⁺,which made the electrospun membrane more hydrophilic and accelerated the wetting rate.However,under the alkaline conditions,-N（CH₃）₂⁺was deprotonated to-N（CH₃）₂.So the electrospun membrane can show hydrophobic property for a long time（10 min）with the hydrophobic property of silicone segments and the roughness of electrospinning membranes.（3）pH-responsive aggregation and reversible dispersion behavior of gold nanoparticles（Au NPs）stabilized by well-defined amphiphilic copolymers containing poly（dimethylsiloxane）and poly（methacrylic acid）segments.Aseriesblockorrandomamphiphiliccopolymerscontaining poly（dimethylsiloxane）andpoly（methacrylicacid）segments（P（PDMS-MA）-b-PMAA and P（PDMS-MA）-co-PMAA）)were synthesized by the RAFT radical copolymerization of methacryloyl-terminated poly（dimethylsiloxane）（PDMS-MA）and tert-butyl methacrylate（tBuMA）and followed by a hydrolysis procedure.After the amphiphilic copolymers were dissolved and dropped it into an aqueous solution of chloro-auric acid and sodium borohydride（NaBH₄）,the amphiphilic copolymers could graft into the surface of Au NPs with thiol functional group at the copolymer chain-end,and then the functionalized Au NPs could exhibit high stability and the ability of pH-responsive.The results showed that the Au NPs can be stable for a long time and are not prone to aggregation because the amphiphilic copolymer chains were covered on the surface of Au NPs by chemical bonding.Moreover,the aggregation and dispersion of Au NPs can be well-controlled by the pH-responsive performance of carboxyl groups in acid or alkaline solutions.The results also showed that at pH=1.0 or pH=13.0,the aggregation and dispersion state of Au NPs can be reversibly converted with the change of pH value.By the control of pH value,the optical properties of the were also reversible and had a wide range of pH response.The aggregation to dispersion system of this work maybe has a broad application prospect in the fields of controlled catalytic reaction,controlled drug release and fluorescence photography.