Synthesis Of Amphiphilic Block Copolymers By Raft Polymerization And Their Sol-gel Transition

The self-assembly of block copolymers has been applied to various fields and subjects due to its high designability and functionality.The temperature-sensitive sol-gel transition caused by the self-assembly and its application in industry has become one of the increasingly popular research fields.This unique sol-gel transition is especially suitable for biomedical field.The aqueous dispersion of copolymer can easily load the drug in a fluid sol state and release the drug in a gel state.The gel state is an excellent carrier for sustained release drugs.1.Synthesis of poly(N,N-dimethylacrylamide)-b-poly(diacetone acrylamide)-b-poly(N,N-dimethylacrylamide)by a simple two-step reversible addition-fragmentation chain transfer(RAFT)polymerization.The amphiphilic triblock copolymer can be readily dispersed in water,and this dispersion is critical for its lower critical solution temperature(LCST)type sol-gel transition.Comparison of copolymers with same composition and different structures found that only the ABA type triblock copolymer has this LCST-type sol-gel transition.The sol-gel transition process was monitored by dynamic light scattering(DLS),transmission electron microscopy(TEM)and rheology.The results show that the LCST characteristics of the ABA copolymer are due to the sphere-worm transition in the self-assembled structure near the transition point.The loading and controlled release of the copolymer gel against paracetamol drugs were further determined.Sustained release behavior was also studied using the Rigter-Peppas model.2.The thermal response of ABA-type triblock copolymer was studied by variable temperature 'H-NMR test and Fourier transform infrared spectroscopy(FTIR).It was found that the sphere-worm transition of the triblock copolymer was affected by the solubility change of PDAAM(B block),mainly depending on the hydrogen bond association inside the PDAAM.It was also found that the length of PDMAA block(B block)and the length of PDMAA block(A block)and the dispersion concentration of copolymer has a regulatory effect on the LCST temperature.3.The relationship between the self-assembly morphology of ABA triblock copolymer and the length of hydrophilic/hydrophobic block was studied in detail.It was found that the hydrophilic block mainly plays a role in controlling the diversity of morphology.The length of the hydrophobic block can regulate the transition of the sphere-worm-vesicle order-order transition within a certain range.The phase diagrams were constructed for the results of different morphological structures caused by the length of each block,which facilitated the targeted preparation of specific morphological structures.