Synthesis And Properties Of Double Temperature-sensitive Block Polymers Based On PEG-based Polymers

More and more attention is paid to stimuli responsive polymers, due to the widespread application and potential prospect in biomedical, tissue engineering, artificial muscle and drug carriers. Thereinto, temperature is the most common stimulus and various thermosensitive polymers have been widely investigated. With the development of the times, single stimulus-responsive polymers couldn't meet people's demand, during the past few decades, the double thermoresponsive block copolymers with two distinct phase transitions have been investigated, which provides a comparatively flexible design space for the thermoresponsive polymers.The monomers with oligo(ethylene glycol) side chains have been attracting a lot of attention as a new family of thermoresponsive monomers, especially 2-(2-methoxyethoxy) ethylmethacrylate (MEO2MA) and oligo (ethylene glycol) methyl ether methacrylate (OEGMA). The LCST of PMEO2MA with an average of two ethylene glycol repeating units has been reported to be 26?. However, corresponding temperature is higher (90?) for POEGMA because it has an average of nine ethylene glycol repeating units. And P(MEO2MA-co-OEGMA) is random copolymer of MEO2MA and OEGMA, the LCST of which could be accurately shifted toward higher temperature from 26? to 90? by rising the molar fraction of OEGMA units in the copolymer chains. These polymers with oligo (ethylene glycol) side chains display extremely sensitive and reversible phase separation. Meanwhile, MEO2MA and OEGMA are the analogues of the PEG, so they possess the good biological compatibility and widespread application. In addition, poly(ethylene glycol) (PEG) serves as a biomedical polymer material as a result of good water solubility and biocompatibility, approved by the US Food and Drug Administration (FDA). N-hydroxymethylacrylamide (HMAM) is a hydrophilic monomer, it can also be employed to adjust the LCST of the temperature responsive copolymer.According to the mentioned above, the two kinds of double thermoresponsive block copolymers were prepared by the MEO2MA, OEGMA, HMAM and PEG. Firstly, the ABC-type double thermoresponsive triblock copolymer PEG-b-PMEO2MA-b-P(MEO2MA-co-OEGMA) was designed and synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT), We studied the micellization and gelation of the copolymer solution emphatically; Secondly, the ABCBA-type double thermoresponsive block copolymer P(MEO2MA-co-HMAM)-6-PMEO2MA-b-PEG-b-PMEO2MA-b-P(MEO2MA-co-HMAM) was synthesized by atom transfer radical polymerization (ATRP). We studied the behavior of the copolymer solution emphatically. Specific works were as follows:1. The ABC-type double thermoresponsive triblock copolymer PEG-b-PMEO2MA-b-P(MEO2MA-co-OEGMA) was synthesized by RAFT. The chemical structures and molecular weight of the polymers were proved by 1H NMR, FT-IR and GPC; The thermoresponsive behaviors of the copolymer solution were investigated by the UV-vis spectrophotometer, the outcome illustrates that the LCSTs are influenced by the degree of polymerization of the thermosensitive blocks and the feed ratios of MEO2MA and OEGMA monomers; Dynamic light scattering (DLS) measurement was also performed to investigate the two-step self-organisation behaviour by measuring the aggregate particle size of the ABC-type triblock copolymer aqueous solution; Micellization of the copolymer solution was studied by the TEM, fluorescence probe technique and so on; Finally, thermo-induced sol-gel transition of the triblock copolymer was investigated by the test tube inverting method and dynamic rheological measurement, the outcome illustrates that concentration of triblock copolymer has an effect on the sol-gel transition temperature:the temperature would become lower with the increasing of concentration. 2. The double thermoresponsive block copolymer P(MEO2MA-co-HMAM)-b-PMEO2MA-b-PEG-b-PMEO2MA-b-P(MEO2MA-co-HMAM) was synthesized by ATRP. The chemical structures and molecular weight of the polymers were proved by 1H NMR, FT-IR and GPC; The thermoresponsive behaviors of the copolymer solution were investigated by transmittance measurement and DLS; The TEM was carried out to investigated the morphology of the micelles which were the spherical shape "core-shell" structure; The test results of fluorescence probe technique indicated that the temperature has an effect on the value of CMC; Finally, the diameter change of copolymer solution are investigated under the temperature induced, it demonstrated the heat-induced diameter change was reversible.