Raft Emulsion Polymerization Of Styrene Via Xanthate And The Synthesis Of Polystyrene-Block-Poly(N-Butylacrylate) Diblock Copolymer

This dissertation mainly researched the reversible addition-fragment chain transfer (RAFT) emulsion polymerization for styrene via isopropylxanthic disulfide (DIP) and the other three kinds of xanthates. The main contents are as follows:1. RAFT polymerization of the reactive monomer styrene mediated by DIP was investigation, using potassium persulfate (KPS) as the radical initiator. The well-defined PS homopolymers were synthesized via DIP, and the results of Gel Permeation Chromatography (GPC),1H NMR and Dynamic Light Scattering (DLS) showed that the polymerization was well-controlled by DIP, as illustrated by stepwise increase in molecular weight and relatively narrow molecular weight distribution of the final product. Moreover, DIP is rather a precursor of RAFT agent than an iniferter during the polymerization of styrene. Besides, the result of GPC,1H NMR, DLS, Differential Scanning Calorimeter (DSC) showed that we have successfully synthesized the PS-b-PnBA diblock copolymer which is well-defined by RAFT seeded emulsion polymerization via DIP.2. Three kinds of xanthates were synthesized: O-Ethyl-S-(2-oxo-2-phenylethyl) dithiocarbonate(CTA-1); O-Trifluethyl-S-(2-oxo-2-phenylethyl) dithiocarbonate(CTA-2); O-Ethyl-S-(1,3 diphenyl-3-oxo-propyl)dithiocarbonate(CTA-3), and then measured their chain transfer constant (Ctr1= 0.7; Ctr2= 0.9; Ctr3= 1.6), respectively. Controll of the free-radical polymerization of the styrene was achieved using a series of three xanthates as the RAFT agents. The influence of the nature of R leaving group and Z group was explored. It was found that the transfer ability of the xanthate is improved with increasing stability of R and its steric hindrance. When the electron-withdrawing power on the Z group is increased, the reactivity of polystyrene radicals towards the C=S bond is also increased. Both the chemical structure of R group and Z group have markedly effect on the Ctr values. Moreover, the higher Ctr values result in the lower molecular weight distribution. Besides, we have successfully synthesized the PS-b-PnBA diblock copolymer which is well-defined by RAFT seeded emulsion polymerization via CTA-3.