Controllable preparation and characterization of the thermosensitive block polymers

Two kinds of triblock copolymers based on N-isopropylacrylamide (NIPAAm) and ethyl acrylate(EA), PEA(n)-PNIPAAm(m)-PEA(n) (BAB type) and PNIPAAm(m)-PEA(n)-PNIPAAm(m) (ABA type) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Thermosensitive block polymer of PEA(n)-PNIPAAm(m)-PEA(n) (BAB type) and PNIPAAm(m)-PEA(n)-PNIPAAm(m) (ABA type) self-assembly form flower coronal and dendritic micelles in water solution with hydrophobic PEA as the core and hydrophilic PNIPAAm as the shell, respectively. Critical micelle concentration (CMC) can be obtained by measuring the surface tension of the copolymer. The study reveals that CMC of micelles are significantly affected by the monomer weight ratios of EA/NIPAAM in block copolymer and block in the order. The higher the content of the hydrophilic block, the smaller the copolymer CMC, and ABA-type with respect to the BAB-type has a smaller CMC value. Particle size of self-assembled micelles decreased first and then rapidly increased with the temperature increasing, surfactant SDS significantly affects the particle size of the polymer. By measuring the light transmission ratio of the copolymer solution, the effect of the lower critical solution temperature (LCST) in the salt solution was investigated, and it was also found that the higher content of the hydrophilic block, the higher LCST of copolymer.