Synthesis Of Block Copolymer Latex Via RAFT Emulsion Polymerization

Reversible addition fragmentation chain transfer (RAFT)polymerization is one of the most important controlled living radical polymerization (CLRP) methods. RAFT water-emulsion polymerization,as one of recent developed of RAFT polymerization method, is very important for both academia and industry because of its fast polymerization rate and environmental friendly product and process. The products of RAFT water-emulsion polymerization can be used directly as water-based paint and ink. In this dissertation, RAFT water-emulsion polymerization is studied to prepare block copolymer latex without using organic solvent and surfactant. Firstly, bi-block copolymer surfactant was synthesized and used for synthesis of multi-block copolymer latex based on the study of emulsification property of synthesized bi-block copolymer surfactant. The latex films prepared from the prepared multi-block copolymer latex have not only excellent mechanical property and transparency, but also can be transferred from hydrophilicity to hydrophobicity after post-heating treatment; therefore, the newly developed copolymers have wide application potential because of their special properties. The main research contents in this dissertation are summarized as follows.1.After screening RAFT agents, RAFT polymerization was applied to prepare amphiphilic block copolymer and RAFT emulsion polymerization was studied by using prepared amphiphilic block copolymer as polymeric surfactants. Firstly, hydrophilic poly acrylic acid(PAA) was prepared as first block via RAFT polymerization and five amphiphilic polymeric surfactants were synthesized via polymerization of PAA with monomer of St, BA, HFBA, EA or TFEA which can prepare hydrophobic block. Then self-assembly induced nucleation RAFT emulsion polymerization of St, BA, HFBA, EA and TFEA were studied by using the prepared five amphiphilic polymeric surfactants. And the copolymerization of AA with TFEA was studied thoroughly. Several amphiphilic ABA tri-block copolymeric surfactants,PAA-b-PTFEA-b-PAA and AB di-block copolymeric surfactants,PAA-b-PTFEA were prepared and their property as surfactant were compared. It has been found and proved that ABA tri-block copolymer is better than AB di-block copolymer as a surfactant via comparing their Critical Micelle Concentration(CMC) value, HLB (Hydrophilic Lypophilic Balance) value and surface tension at CMC since ABA tri-block copolymers have higher surface activity, more stable micelle forming ability and better ability for self-assembly induced nucleation RAFT emulsion polymerization. This new finding is extremely important for self-assembly induced nucleation RAFT emulsion polymerization when ABA tri-block copolymer was used as surfactant.2.Bi-functional RAFT agent was used in RAFT emulsion polymerization and several ABA tri-block copolymers were synthesized successfully via two-step RAFT emulsion polymerization without using surfactants. PAA-b-PHFBA-b-PAA, as a representative of triblock copolymers were characterized and proved to have symmetrical structure and controllable molecular weight and molecular weight distribution;therefore, the preparation process of PAA-b-PHFBA-b-PAA tri-block copolymers is under control of RAFT polymerization mechanism. The film forming process of tri-block copolymer latex was also studied and a film forming mechanism was proposed. The mechanism was confirmed and the reason for film surface changing from hydrophilicity to hydrophobicity was explained via characterization and testing of FTIR,water contact angle (WCA), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) before and after heating treatment. The mechanical property measurement of hydrophobic film showed that the synthesized tri-block copolymers behave as an elastomer material with high elongation at break and very low permanent set when soft block is longer than rigid block. Star structure polymer was also prepared by using AB di-block copolymer and film casted from its latex also has very good optical and mechanical properties.3.ABCBA penta-block copolymer was prepared by introducing B block via a surfactant and solvent free, one-pot RAFT emulsion polymerization process. The prepared penta-block copolymer latex particle was proved to have three layers' core-shell structure. The forming mechanism of the three layers' core-shell latex particle was proposed and confirmed by TEM image. The mechanism for film forming and transferring from hydrophilicity to hydrophobicity was proposed after the study on casted film forming process and relationship between film structure and hydrophilic or hydrophobic properties. The performance of ABCBA penta-block elastomer had been improved by optimizing the structure of B block or C block. ABCBA penta-block terpolymer showed much better performance as an elastomer when HFBA and BA was copolymerized to replace PHFBA as C block with increased segment flexibility.