Synthesis of Alkali-Soluble Resins by Catalytic Chain Transfer Polymerization and Their Use as Stabilizers in Emulsion Polymerizations

Abstract

The effects of alkali-soluble resins (ASRs) as colloidal stabilizers in emulsion homopolymerizations of butyl acrylate (BA) and butyl methacrylate (BMA) have been investigated using ASRs synthesized by catalytic chain transfer (CCT) solution/emulsion polymerization. All ASRs were copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA), prepared using 20 wt% MAA in the comonomer mixture. The CCT agents bis(boron difluorodimethylglyoximate) cobaltate(II) (CoBF) and bis(boron difluorodiphenylglyoximate) cobaltate(II) (CoPhBF) were synthesized using a standard method. The chain transfer constant of CoBF and CoPhBF in MMA bulk polymerization was found to be 30,000 and 40,000, respectively. Investigation of the effects of different components (oxygen, azobisisobutylnitrile and MAA) on the CCT agent was carried out using UV-vis spectroscopy to provide fundamental information to guide selection of ASR synthesis conditions. It was found that oxygen does not have a significant effect on deactivation of CoBF, while azobisisobutylnitrile and methacrylic acid can lead to complete disappearance of the Co(II) signal in the UV-vis spetrum. In order to prevent batch-to-batch variation, several large-scale ASR syntheses (3.5 kg) using 15, 20 and 40 ppm CoBF (by weight to monomer) were carried out by CCT solution polymerization. ASRs of similar molar masses were dissolved together in isopropanol and re-precipitated to produce sufficient ASRs to be used throughout the project. Characterization of the ASRs by nuclear magnetic resonance (NMR) spectroscopy confirmed that each ASR chain contains a terminal C=C bond. In order to facilitate comparison of the effect of the terminal C=C bond in BA and BMA emulsion polymerizations, portions of the as-prepared solution CCT ASRs were hydrogenated. The reduced CCT ASRs are of similar molar mass distribution and acid number to their unsaturated counterparts. Hence, the only difference between the CCT ASRs and reduced CCT ASRs is the C=C bond terminal functionality in the former. For ASR synthesis by CCT emulsion polymerization, continuous feeding of CoBF was implemented to compensate for the loss of CCT agent during the polymerization. MMA CCT emulsion polymerization with feeding of CCT agent was investigated as a model for the subsequent ASR syntheses. It was found that instantaneous molar mass of the PMMA produced with feeding of MMA and CoBF decreased at the start of the reaction and increased after ~40% conversion. The results are explained in terms of CoBF partitioning and the continuous change in volume ratio between particle/monomer phase and the aqueous phase. Latex CCT ASRs were successfully synthesized by CCT emulsion polymerization using 100, 200, 250 and 300 ppm CoBF (by weight to monomer). For the latex ASRs prepared using 200, 250 and 300 ppm CoBF, each polymer chain was confirmed by NMR to have one terminal C=C bond while for the ASR with 100 ppm CoBF, ~73% of the ;chains possess terminal a C=C bond. Use of the ASRs in emulsion homopolymerizations of BA/BMA were investigated in detail and interpreted via a hypothesis based on theory for micellar and homogeneous nucleation. All reactions with reduced CCT ASRs were found to undergo a nucleation-growth process. For BA reactions with CCT ASRs, a second crop of particles were nucleated in the later stage of reaction without ASR feeding, while in BMA reactions with CCT ASRs, a nucleation-growth process was observed. These results were explained using the different chemistry reaction of CCT ASRs with acrylates and methacrylates. It was proposed that in BA reactions using CCT ASRs, particles are first nucleated from the copolymers formed by reaction between the CCT ASR molecules and the BA oligomeric radicals in the aqueous phase, while later in the reactions, particles are nucleated from radical entry into ASR aggregates. In the BMA reactions with CCT ASRs and all reactions with reduced CCT ASRs, it was proposed that particles are only nucl

Date of Award	1 Aug 2014
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Peter Lovell (Supervisor)