Preparation And Characterization Of Multi Responsive Silicone-polyethylene Glycol Multiblock Copolymers

Polyethylene glycol(PEG)is biocompatible,non-toxicand temperature reponsive.Copolymerization of PEG with other monomers can change its temperature responsiveness and increase its application range.We synthesized multiblock copolymers P(APDS-PEGDA)with polyethylene glycol diacrylate(PEGDA)and diaminopropyl tetramethyldisiloxane(APDS)as monomers,and synthesized block copolymer P(AD-OEGA)with methoxy polyethylene glycol monoacrylate(OEGA)and diaminopropyl polydimethylsiloxane(AD)as monomers.The luminescence and phase transition behaviors of the two copolymers in water were characterized,the low critical dissolution temperature(LCST)of the copolymers was determined,and the fluorescence properties and temperature response of the copolymers were studied.The structures of copolymers P(APDS-PEGDA)and P(AD-OEGA)were characterized by FTIR and NMR.The effects of monomer ratio,pH,salt concentration,carbon dioxide and organic solvent on LCST and fluorescence properties of two copolymer aqueous solutions were investigated.The results showed that with the increase of the content of APDS or AD in copolymer,the LCST of copolymer P(APDS-PEGDA)solution decreased from 38℃ to 26℃,the LCST of copolymer P(AD-OEGA)solution decreased from over 80℃ to 39℃.The copolymer P(APDS-PEGDA)with a molar ratio of 1/1 of APDS and PEGDA was denoted as P6,and the copolymer with a molar ratio of 1/2 of AD and OEGA was denoted as OP 1.With the increasing of copolymer concentration,LCST of P6 solution decreased from 40℃ to 32℃,while LCST of OP1 solution decreased from more than 80℃ to 63℃,and the fluorescence intensity of both of them increased gradually.With the increase of pH from 3 to 11,the LCST of P6 solution decreased from more than 80℃ to 27℃,and the fluorescence intensity decreased gradually.The LCST of OP1 solution decreased from more than 80℃ to 63℃ with little change in fluorescence intensity.With the increase of NaCl concentration,the LCST value of P6 solution decreased from 38℃ to 25℃,and the LCST value of OP1 solution decreased from 63℃ to 55℃,and the fluorescence intensity of both P6 and OP1 solutions increased gradually.The LCST of P6 solution gradually increased from 38℃ to 64℃,and that of OP1 solution gradually increased from 63℃ to 71℃ with the increase of CO2penetration time.With the increase of acetonitrile volume fraction in the solution,LCST of P6 solution decreased from 38℃ to 25℃,and LCST of OP1 solution decreased from 63℃ to 53℃,and the fluorescence intensity of both of them increased gradually.With the increasing volume fraction of dimethylformamide in solution,LCST of P6 solution increased from 38℃ to more than 80℃,LCST of OP1 solution increased from 63℃ to more than 77℃,and the fluorescence intensity of both decreased sharply.Obviously,copolymers P(APDS-PEGdA)and P(AD-OEGA)do not have any conjugated chromophore in the traditional sense,and their fluorescence emission should be caused by the aggregation of oxygen atoms in polyethylene glycol,and the greater the concentration of oxygen atoms,the stronger the fluorescence intensity.The LCST of copolymer solution is related to the interaction between copolymers and copolymers and water.The greater the interaction between copolymers,the greater the clustering degree of copolymers,ultimately resulting in lower LCST and higher fluorescence intensity of copolymers.When the external environment changed,the LCST value and fluorescence intensity of copolymer P(AD-OEGA)changed less,because copolymer P(AD-OEGA)had a longer hydrophobic chain segment and a smaller proportion of ethylene glycol chain segment,which reduced the influence of external factors.