Synthesis,Characterization And Properties Of Thermoresponsive Copolymers Based On N-isopropyl Acrylamide And N-ethyl Acrylamide

A thermoresponsive polymer based on N-isopropylamide(NIPAM)has a low critical solution temperature(LCST)very close to body temperature.This provides a great base for its application in biomedical field.While lots of research exists on NIPAM,the incorporation of N-ethylacrylamide(NEAM)as a comonomer has not been studied in depth,and the further study on this kind of polymer by LCST adjustment may open up a new application range for this kind of materials.The grafting of biopolymers to p NIPAM is a rarely explored type of study,mostly focused on chemical cross-linking.However,physical cross-linking based on hydrogen bonds has not been further studied,and the development of these structures may be applied to a new generation of drug carriers,since its viscosity can be adjusted appropriately.Firstly,a series of NIPAM and NEAM random copolymers with different monomer ratios were synthesized by free radical polymerizatione,for which the phase transition behavior of the aqueous polymer solution was studied by UV-vis spectrophotometry and conventional calorimetry.Rheological studies extend this work,with experiments focusing on understanding LCST phase transitions and mechanical properties.LCST of random copolymers increases with the increase of NEAM content.It can be concluded from calorimetry and rheology tests that the presence of NEAM will lead to "soft transition" and LCST transitions are slow.Secondly,block copolymers with different monomer proportions were synthesized by the method of free radical polymerization.After the specific analysis of molecules and structures,the phase transition and mechanical properties of polymer aqueous solution were studied by dynamic light scattering test and rheological temperature scanning.When the content of NIPAM sequence was high enough,the NIPAM sequence collapse would limit the interaction of NEAM sequences,resulting in the decrease of two LCSTs of block copolymer with the increase of NEAM sequences content.Finally,two series of polymers,carboxymethyl cellulose(CMC)and mixed solution of water and water-methanol were blended.The phase transition of the blends was detected by calorimetry analysis and rheological temperature scanning.The different effects of NEAM monomer and CMC on phase transition temperature were compared with the results of polymer aqueous solution.In addition,the mechanical properties of blends were further studied by rheological dynamic frequency scanning(DFS)and dynamic strain scanning(DSS).Combined with the above studies,the competition between the hydrogen bonds involved in LCST and physical cross-linking is explained.The presence of CMC not only increases the viscosity of polymer solution,but also improves the thermal stability of the whole blend system.In terms of phase transition temperature,for random copolymers,the influence of NEAM content on LCST was greater than content of CMC.In the study of block copolymers,the influence of NIPAM sequence content on LCST was also greater than CMC.Because of the conosolvency effect caused by the water-methanol mixture,there were no gelation in p NIPAM blends.The presence of ethyl groups in NEAM can promote the interaction between-NH and =O and water,affect the hydrogen bond between CMC and-OH group,and have a negative effect on gelation.Therefore,the presence of NEAM in the copolymers help to increase LCST and reduce physical cross-linking.