Synthesis And Study On Morphology Of Amphiphilic Diblock Copolymer Pnipam-b-PS

Amphiphilic diblock copolymer has attracted much attention of world-wide scholars in polymer science due to its unique property and potential applications in many fields such as surface modification of medical materials and drug carriers. In consideration of the increasing demand of functional materials, the successful preparation of amphiphilic diblock copolymers with bicontinuous morphology by self-assembly is of great significance.In this study, RAFT macro-transfer agents and diblock copolymer Poly(N-isopropylacrylamide)-b-polystyrene were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization by adopting PEPDTA as chain transfer agent. The characteristics of RAFT "living"/ controlled polymerization of PS-PEPDTA, PNIPAM-PEPDTA under certain condition were studied. Proton nuclear magnetic resonance (1H-NMR) spectroscopy,gel permeation chromatography (GPC) and intravenous drip contact angle (CA) test were performed respectively to characterize the structure and purity,molecular weight and distribution and hydrophilic/hydro-phobic property of homopolymers. In addition, diverse methods were employed for the preparation of diblock copolymer PNIPAM-b-PS, such as one-pot method and two-pot method, different feeding sequences of two monomers. The characteristics of RAFT polymerization of styrene (St) as the second monomer were also investigated. The 1H-NMR and Frontier infra-red spectroscopy were combined for the analysis of structure and composition; HPLC characterization was used to confirm the narrow distribution of diblock copolymer; besides, the surface property and morphological behavior of diblock copolymer were explored. The specific contents were as followes:(1)PEPDTA was synthesized by nucleophilic addition of carbodithioic acid and styrene.1H-NMR spectroscopy verified its purity and allowed its application as chain transfer agent in the preparation of block copolymer.(2)Through the comparision of monomer conversion into RAFT macro-transfer agents under various molar ratios of chain transfer agent to initiator, it was demonstrated that the monomer conversion was higher when the molar ratio was 3:1. The relationships between monomer conversion and reaction time,ln([M0]/[M]) and reaction time of RAFT macro-transfer agents, and the relationship between Mn,PDI and monomer conversion of PNIPAM-PEPDTA were ideal to fit in with the feature on RAFT controlled radical polymerization.(3)Through the comparision of monomer conversion into diblock copolymer by one-pot method and two-pot method respectively, it was shown that the final conversion was higher and purification was relatively simple by one-pot method. The relationship between conversion and polymerization time with the addition of styrene as the second monomer after the polymerization of PNIPAM-PEPDTA by one-pot method corresponded well with the intrinsic conclusions of RAFT living radical polymerization.(4)The purity and composition, molecular weight and distribution of homopolymer PNIPAM-PEPDTA and diblock copolymer PNIPAM-b-PS were analyzed by 1H-NMR and GPC; Furthermore, the morphology and surface hydrophilic/hydrophobic property of the copolymer film have been studied by transmission electron microscopy (TEM), swelling percent (SP) and contact angle test (CA). The results of SP and CA showed that the film had affinity to both water and organic solvents, indicating that the PNIPAM-b-PS diblock copolymer may form biocontinous microphase structure, which allowed both water and hydrophobic organic solvents to penetrate from the surface into deep internal sections of the film.