OP-II-3

EXPERIMENTALPP-III-22We synthesized the RAFT agent (O-ethylxanthyl ethyl propionate) in ourlaboratory. Styrene, methyl and butyl acrylate monomers, initiator (sodiumpersulfate), purification column, and surfactant (sodium dodecyl sulfate) wereobtained from Sigma-Aldrich (USA). In the first stage, polystyrene and polybutylacrylate homopolymers were prepared with predetermined molecular weights.Emulsion polymerization was performed in a semi-batch reactor (at 60-80°C) with350 rpm agitation speed, water, a buffer solution and monomer. Experiments weredesigned to produce polymeric latex particles containing macro-RAFT agent with atargeted molecular weight. In the second stage remaining reagents were added tothe seed latexes from first stage to produce b-PBA-co-PSt. Monomer conversion wasdetermined gravimetrically, the PSD was measured using PL-PSDA (PL-DG2) wasmolar mass with PL-GPC120. 1 H-NMR spectra (Brüker AM400) was used to analysethe polymer structure and composition.RESULTS AND DISCUSSIONSExperimental data were compared with model predictions to confirm ourpostulated mechanism and the properties expected from the reactor. Low molecularweight polymers of butyl acrylate prepared in the first stage was used as thepolymeric RAFT agent to polymerize styrene in the second stage under batch andsemi-batch emulsion conditions to provide well-defined block copolymers (b-PBA-co-PSt) with narrow molecular weight distributions. The process was optimized byperforming semi-batch polymerization, in which the second monomer was graduallyadded to the reactor. This resulted in a block copolymer of high purity and relativelylow polydispersity as compared with that produced under batch conditions. Thechoice of block sequence is important in reducing the influence of terminated chainson the distributions of polymers that were obtained. We found that polymerizingstyrene first followed by the high active butyl acrylate monomer resulted in muchpurer block copolymer with low polydispersity as indicated by GPC and 1 H-NMRmeasurements.References[1]. Altarawneh, I.S., V.G. Gomes and M.S. Srour, (2008). Macromol Reaction Eng, 2(1): 58-79.[2]. Charmot, D. et al., (2000). Macromolecular Symposia, 150(Polymers in Dispersed Media): 23-32.[3]. Chiefari, J. et al., (1998). Macromolecules, 31(16): 5559-5562.481