Influence Of Chain Flexibility On The Properties Of Thermoresponsive Polymers And Hydrogels

Thermoresponsive polymers have gained enormous attention over last decade because of their various potential applications. In order to stuy the relationship between the structure and the thermoresponsive behavior of polymers, we have designed and synthesized two series thermo-responsive polymers with different chain flexibility: flexible chain thermo-responsive polymers and semi-rigid chain thermoresponsive polymers. And we further studied the aqueous solution properties of those polymers. Then, two kinds of hydrogels with different crosslinking degree were synthesized on the bases of those corresponding polymers. The relationship between the chain flexibility and properties of those hydrogels were investigated by a systematic comparision.(1) Two series of thermo-responsive polymers with different chain flexibility were synthesized via reversible addition- fragmentation chain transfer(RAFT) polymerization successfully, i.e., poly((N-(2-hydropropyl) pyrrolidone) methacrylate)(P(2-HPPMA), poly(Bis(N-(2-hydropropyl) pyrrolidone) 2-vinylterephthalate)(P(2-HPPVTA). The results reveal that the chain flexibility has a strong influence on the thermoresponsive behaviors of polymers. The cloud point of the flexible chain polymer P(2-HPPMA) system decreased monotonically with the Mn increased. While the trend of cloud point of aqueous P(2-HPPVTA) solution was different. At the beginning, the cloud point decreased when the Mn increased. And it increased monotonically with the increasing of the molecular weight when the Mn was greater than 1.0×104 g·mol-1.(2) Two series of thermo-responsive hydrogels with different crosslinking degree were synthesized by using N,N’-methylene acrylamide(MBA) as the crosslinker, i.e., P(2-HPPMA) thermo-responsive hydrogels, P(2-HPPVTA) thermo-responsive hydrogels. Based on the investigation o f the equilibrium swelling ratio, swelling kinetics, deswelling kinetics and volume phase transition temperature of the hydrogels, it was found that the P(2-HPPVTA) hydrogels had higher swelling ratio and deswelling rate than P(2-HPPMA) hydrogels at the same crosslinking degree. But the P(2-HPPMA) hydrogels had a higher swelling rate than the P(2-HPPVTA) hydrogels. The volume phase transition temperature o f the P(2-HPPVTA) hydrogels showed a monotonous decrease with the increase of the crosslinking degree, while the P(2-HPPMA) hydrogels remain the same level at about 57 oC.