High-conversion copolymerizations of methyl methacrylate (MMA) and divinylbenzene (DVB) in aqueous emulsion have been carried out using sodium dodecyl sulfate as the emulsifier and potassium persulfate as the conventional free radical initiator. Various thiols have been investigated in order to inhibit cross-linking and hence favor the formation of branched products. Hexanethiol (HT) and benzylthiol (BT) have been found to be particularly effective. Use of appropriate levels of BT allow mole feed ratios of MMA/DVB up to 100/20 to be employed in producing highly branched products without cross-linking. Typically DVB/BT mole ratios of ≤1 ensure that cross-linking is avoided. Perhaps most remarkably of all no organic solvent is required in producing these branched products, whereas analogous polymerization feed compositions under bulk or aqueous suspension polymerization conditions lead inevitably to cross-linked products irrespective of the level of chain transfer agent used. The molar mass and branching architecture of the products have been characterized by 1H NMR and MALS/SEC analyses, and the complete incorporation of DVB residues as branching units has been confirmed.

Poly(vinyl alcohol) (PVOH) is a ubiquitous synthetic polymer that finds widespread application in biological and medical products through to personal, domestic, and industrial products. The currently available range of materials all have linear backbone architectures with interesting solubility, rheological, and interfacial properties. The latter might be significantly broadened if complementary polymers with branched backbone architectures could be synthesized, especially if the methodology involved only minor changes from that currently practiced. We have now synthesized branched PVOHs via conventional free radical copolymerization of vinyl acetate (VAc) and triallyl-triazine-trione (TTT), in 2-isopropoxy ethanol (IPE) solvent in the presence of appropriate thiol free radical chain transfer agents, followed by alcoholysis of the so-formed branched poly(vinyl acetates)s (PVAc)s with methanol. Balancing the mole ratio of TTT to thiol allows high conversion to branched materials to be achieved while inhibiting cross-linking and gelation of the products. The branch points derived from the TTT comonomer have been shown to be conserved during the alcoholysis step, and extensive characterization of the PVAc precursors and the derived PVOHs using multiple detector size exclusion chromatographic (SEC) instrumentation has confirmed the highly branched nature of both groups of polymers. Final confirmation of the branched architecture of the PVOH samples has been made by reacetylation of some samples, in effect to regenerate their PVAc precursors. SEC analysis of the latter has indeed shown these to be architecturally very similar to the original precursor PVAcs. This novel methodology for synthesizing branched PVOHs involves relatively minor adjustments to the currently used industrial process for linear PVOHs and so offers good prospects for scale-up and exploitation.

No abstract