Study On Synthesis Of Block Copolymers And Their Properties And Applications In Solution

Molecular design, synthesis and properties of block copolymers with well-difined structure have been subjects of numerous studies. In the last decade, the development of living/controlled free radical polymerization has provided control over molecular architectures for a variety of monomers, allowing the easy synthesis of block copolymers with well-defined molecular weights and narrow molecular weight distributions. The techniques mainly include Initiator-transferagent-terminator (Iniferter), atom-transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer polymerization (RAFT). RAFT polymerization is probably the most versatile tool of the prominent living/controlled free radical polymerization techniques to synthesize polymers with complex architecture ranging from block to star, as it is tolerant of a wide range of functionality in the monomer and solvent. The main works and results in this paper are described as follows:1) Synthesis of RAFT agents.Synthesis of 1-Phenylethyl dithiobenzoate (PEDB) by Grignard reagent method, and an easier synthesis of S,S′-Bis(α,α′-dimethyl-α″-acetic acid) trithiocarbonate (BDATC) were reported. FTIR, 1H NMR and 13C NMR were both used to determine the stuucture of the two different RAFT agents.2) The study on synthesis of PMMA-b-PS by RAFT miniemulsion polymerization and their self-assemblyPoly (methyl methacrylate)-b-polystyrene block copolymers and the corresponding PMMA homopolymer with controlled molecular weight were synthesized in miniemulsion system by using reversible addition-fragmentation chain transfer polymerization. The structure and the composition of these copolymers were characterized by means of FTIR, 1H NMR and GPC. Their self-assembly in mixed solvent tetrahydrofuran/cyclohexane (THF/CYH) was studied. The effects of different weight ratios of PMMA homopolymer to block copolymer and different THF contents in mixed solvent on the micellar morphology were both discussed. Detailed micelle structural information was extracted from transmission electron microscopy (TEM). The morphological changed from well-structured spherical micelles to irregular micelles when changing the weight ratio of PMMA homopolymer. The studies of the effect of different THF contents in the mixed solvent on the micellar morphology indicated thatincreasing the THF content lead to the formation of larger micelles. 3) Synthesis of PVP-b-PMAA block copolymer and its effect on morphologies control of CaCO₃A novel double-hydrophilic block copolymer (DHBC) poly (vinyl pyrrolidone)-block-poly (methacrylic acid) (PVP-b-PMAA) was synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. The structure of the resulting copolymer was characterized by 1H NMR, and the molecular weight of the copolymer was 28800 which determined by gel permeation chromatography (GPC), and the molecular weight distribution index was 1.42. A systematic study of morphological control of calcium carbonate (CaCO₃) has been performed by using the PVP-b-PMAA block copolymer. It was found that with the concentration of block copolymer increasing, the morphologies of CaCO₃ particles were changed from layered to aggregate. When concentration of block copolymer was 1.0 g/L, some cavities were observed in the aggregated crystals.4) Synthesis of PS-b-PAA and its effect on morphologies control of CaCO₃Amphiphilic block copolymer polystyrene-block-poly (acrylic acid) was synthesized via RAFT by using BDATC as chain transfer agent. The synthesis of CaCO₃ crystals in PS-b-PAA aqueous solution was discussed. Spherical particles were obtained by varing the concentration of the copolymer. The FTIR,XRD,SEM were both used to characterized the structure and mophology of the CaCO₃ crystals. The results show that the obtained CaCO₃ crystals were both calcite, while the spherical crystal changed from smooth-surface into coarse-surface along with the concentration of the copolymer increasing from 0.1 g/L to 1.0 g/L.