Study On Synthesis Of Diblock Copolymer By RAFT Living Polymerization And Application To Emulsion Polymerization

Two RAFT agents, 1-phenylethyl dithiobenzoate (PEDB) and cumyl dithiobenzoate (CDB), were synthesized and their structures were determined by 1H NMR spectrums. The preparation route and purification technique was studied. A process of preparing St block RAFT polymer first, followed by introducing AA polymer segment as the second block was determined in preparation of PSt-PAA diblock copolymer. The bulk polymerizations of styrene were carried out with AIBN as initiator and two RAFT agents as chain transfer agents, respectively. The kinetics, molecular weight and its distribution were studied in details. The studies on kinetics show that the polymerization rate decreases with increasing in concentration of RAFT, but with decreasing in AIBN concentration and lowering in the reaction temperature. The polymerization conforms to pseudo-first-order kinetic behavior for both St/CDB and St/PEDB bulk system. The GPC analysis shows that the molecular weight determined consists with the theoretical values when the monomer conversion is below 35%. The diblock copolymers of PSt-PAA were prepared in solution using the PSt precursors as polymeric RAFT agents. The structure of block copolymer was verified by IR spectrum. The studies on GPC suggested that molecular weight distribution becomes narrower as the second monomer was added. When the AIBN and PSt concentrations increase simultaneously, the molecular weight of polymer gets higher slightly and the molecular weight distribution becomes broader. Block copolymers of PSt-PAA were used for the emulsion polymerization of St. The preparation route and process of emulsion was studied. It order to prepare stable emulsifier-free emulsion, potassium carbonate was charged to neutralize carboxylic acid with the molar ratio of K2CO3 to carboxylic acid being 2:1. The emulsification of the block copolymer was more facilitated when acetone was added. The emulsifier-free emulsion polymerization rate increases significantly when reaction temperature is raised. The emulsion polymerization is carried out with micelle nucleation mechanism when the diblock contains 8 AA and 18 St. And minisuspension polymerization is carried out when the diblock contains 90 AA and 18 St. The particle diameter of the final latex is 181.21nm and the index of diameter distribution is 0.075 when using the diblock with 8 AA and 18 St structure. The factors influenting the final latex particle number (Np) of the emulsion polymerization were discussed. The structure and concentration of diblock copolymer, the concentration of initiator, the concentration of K2CO3 and the polymerization reaction temperature all affect on Np. Np increases with the concentration of block copolymer increasing. But Np is not influenced prominently by the concentration of initiator. Np slightly increases when the temperature varies from 70℃ to 80℃. Np continuously decreases as concentration of K2CO3 increasing.