Investigated Of Structure And Responsive Behavior Of Thermo-and Light-responsive Block Copolymer Films

In order to overcome the shortage of traditional polymers such as single function,poor weatherability and no stimuli-responsive property.The stimuli responsive polymers were broadly applied in daily lives,for example,temperature sensing alarm,pressure sensitive glass and so on.Responsive polymers are defined as polymers are able to respond to the external stimuli andshow its responsive behavior?the change of chemical or physical properties?spontaneously.According to the source,the external stimuli can be defined as light,heat,pH value,electricity and gas.Among them,the light and heat are easy accessed in our daily lives.For this reason,the light-and thermo-dual responsive polymers are broadly used in smart textiles,photosensitive switches,remote control equipment and so on.Thermo-responsive polymers are one kind of new responsive polymers.When the temperature is lower than its transition temperature?TT?,the thermo-responsive polymers are hydrophilic and can absorb water and swell.When the temperature is higher than TT,it switches to hydrophibic state.Thereby they shrink and repel water.If Thermo-responsive polymers are cross-linked to textiles,the textiles will obtain the switching ability of hydrophobicity according to the external temperature.Then such kind of smart textiles can be used for smart cleaning and so on.However,it is hard to satisfied the requirements for textiles in daily lives because the normal thermo-responsive polymers only have one TT.For example,in daily wear,textile is desired to be hydrophibic and porous state in a broad temperature range.Hence it is beneficial to enhance the air and moisture permeability.It will further improve the comfort of textiles.During washing process,the textile with hydrophilic state in a broad temperature range is required.Thus the cleaning performance will be enhanced during washing.Azobenzene is light-responsive.When illuminated with UV light,the apolar trans isomer azobenzene can be converted to polar cis one.This switching is reversible,meaning the azobenzene will turn back to trans state by visible light.Based on this special property,TT of the thermo-responsvie polymers containing azobenzene is able to vary according to the environment of applications?under UV light or visible light?spontaneously.Based on the above discussion,the random copolymer which is sensitive to the temperature and UV light were synthesized.The effect of azobenzene content on the TT was investigated in the copolymer aqueous solutions.Afterwards,the variation of hydrophobic and hydrophobic properties in the copolymer films were studied under different external stimuli.After cross-linking copolymer onto the cotton fabrics,the smart textiles with enhanced cleaning ability and comfort control can be realized.Simultaneously,block copolymer which is sensitive to the temperature and UV light were also synthesized.The mechanism of block copolymer responding to the single?temperature or UV light?and dual?temperature and UV light?external stimulihad been investigated.It is beneficial for the future design of sensors and switches based on the dual responsive copolymers.Random copolymer P?MEO₃MA-co-EGMA-co-AAAB?was synthesized by atom transfer radical polymerization?ATRP?with triethylene glycol methyl eater methacrylate?MEO₃MA?and poly?ethylene glycol?methacrylate?EGMA?which contained-OH groups in the end of the side chain and p-acrylamidoazobenzene?AAAB??molar ratio is 16.9?MEO₃MA?:2.1?EGMA?:1?AAAB??.Under visible light,the TT of P?MEO₃MA-co-EGMA-co-AAAB?aqueous solution was 38 ^oC with a concentration of 3 mg/mL.After illuminated with UV light,the TT of the copolymer aqueous solution was increased to 40-41^oC,which is 2-3 ^oC higher than the value undervisiblelight.Inaddition,thehydrophobicityof P?MEO₃MA-co-EGMA-co-AAAB?film was investigated in different external temperature and UV light.The copolymer film presented best hydrophilicity when the temperature was lower than TT and illuminated with UV light.The softness and stiffness of the cotton fabrics cross-linked with P?MEO₃MA-co-EGMA-co-AAAB?were studied and remained unchanged after cross-linking.The cleaning ability of the cotton fabrics cross-linked with P?MEO₃MA-co-EGMA-co-AAAB?can be prominently enhanced.For further understanding the influence of azobenzene on the moisture permeability of smart textiles.The amount of azobenzene was doubled in the copolymer.Themonomerswasforsynthesizingrandomcopolymer P?MEO₃MA-co-EGMA-co-AAAB?were triethylene glycol methyl eater methacrylate?MEO₃MA?,poly?ethyleneglycol?methacrylate?EGMA?and p-acrylamidoazobenzene?AAAB?with a molar ratio is 8?MEO₃MA?:1?EGMA?:1?AAAB?.It was synthesized by atom transfer radical polymerization?ATRP?as well.The test results showed that the TT shifted towards lower value after the copolymer aqueous was illuminated with UV light.This strange phenomenon was cause by the self-assemble behavior of copolymer in solution,which was confirmed by DLS measurements.And the FTIR-ATR measurements showed the UV light had a great influence on improving the hrdrophilicity of the copolymer.After cross-linking P?MEO₃MA-co-EGMA-co-AAAB?onto cotton fabrics,the ESR results show the swelling ratio increased after illuminated by UV light.The cross-linked cotton fabrics showed a comfort control ability when the temperature was increased.Block copolymer PMEO₅MA-b-PAzo2 was synthesized by RAFT polymerization with poly?ethylene glycol?methyl ether methacrylate?MEO₅MA?and azobenzene derivatives?Azo2?.By applying the white light interferometry,PMEO₅MA-b-PAzo2films absorbed water vapor molecules and swelled when the temperature was thermo-stated at 20 ^oC under water vapour atmosphere.During the swelling process,PMEO₅MA-b-PAzo2 film swelled rapidly in the beginning and reached an equilibrium state after 6095 s.When the external temperature was increased,the thickness of the film presented a shrinkage behavior.Moreover,the thinner film showed a more pronounced swelling and shrinkage.This phenomenon was related to the hydrophilic substrate.It attracted water molecules during the swelling process.In-situ neutron reflection measurements showed that the film absorbed water intensely and swelled under D₂O vapor atmosphere.Thus the water content in the film was dramatically increased.When a thermal stimulus?rapid increase of temperature from below TT to above TT?was performed on the swollen PMEO₅MA-b-PAzo2 film,it shifted from hydrophilic state to hydrophobic state.Hence the water molecules was repelled and the water content on the film was decrease.