Synthesis And Thermoresponsive Properties Of Polyacrylamide Derivatives

Polyacrylamide derivatives have unique temperature-sensitive properties in aqueous solution and have broad application prospects in the field of biomedicine.Temperature-sensitive polyacrylamide derivatives are receiving more and more attention.The thermoresponsive property of poly?N,N-diethylacrylamide??PDEAAm?has been studied using various its copolymers with poly?N,N-dimethylacrylamide??PDMAAm?.The B?C₆F₅?₃-catalyzed group transfer polymerization?GTP?was utilized for the precise synthesis of the statistical and di-,tri-and penta-block copolymers.The polymerization degree of all copolymers was ca.100 and their polydispersity was 1.05-1.26.The thermoresponsive property concerning with a coil-globule phase transition was estimated using the temperature of cloud point(T_cp)of aqueous copolymer solutions.For the statistical copolymer,the T_cp increased with the increasing DMAAm unit from 38.5 to68.0°C and no T_cp was observed for the copolymers with>75%of DMAAm.For the diblock copolymer,the T_cp increased with the increasing PDMAAm segment from 34.5 to44.5°C and the copolymer with the ratio of PDEAAm and PDMAAm segments of 10/90 did not showed the phase transition.For the tri-and penta-block copolymers,the copolymers consisting of the PDMAAm segment at both copolymer ends only exhibited the phase transition,such as the T_cps of 51.5 and 55.0°C for the tri-and penta-block copolymers,respectively.The phase transition behaviors of the block copolymer and the random copolymer were confirmed using DSC,DLS,NMR.For a multi-block copolymer in which the random copolymer and the hydrophobic monomer are at both ends,a multi-molecular aggregate having a large?R_h?is formed at a temperature greater than T_cp.For di-block copolymers,a temperature greater than T_cp will result in an intermediate hydrophobic,hydrophilic surrounding stable structure.For multi-block copolymers in which the hydrophilic monomer is at both ends,when the temperature is greater than T_cp,a structurally stable monomer which is hydrophilic around the intermediate hydrophobic layer is formed.