Synthesis of branched water-soluble vinyl polymers via oxyanionic polymerization

A range of new water-soluble branched vinyl polymers have been synthesized by the statistical copolymerization of 2-(dimethylaniino)ethyl methacrylate [DMA] with ethylene glycol dimethacrylate [EGDMA] under oxyanionic polymerization conditions (potassium benzyl alkoxide initiator, anhydrous THF, 50 degrees C). Advantages of using such living polymerization chemistry include (i) the ability to control the primary chain length simply by adjusting the comonomer/initiator molar ratio and (ii) the reduced probability of cross-linking due to improved control over the molecular weight distribution. In this study the mean degree of polymerization of the primary chains was fixed at 50, and the proportion of EGDMA branching agent was varied systematically. Gel permeation chromatography analysis indicated that soluble, high molecular weight DMA-EGDMA statistical copolymers were produced in most cases. The degree of branching increased monotonically as the proportion of EGDMA comonomer was increased, with Mark-Houwink alpha values as low as 0.25 being obtained. Using higher levels of EGDMA led to lower comonomer conversions; this is believed to be due to the increased solution viscosity rather than copolymerizability problems. No macrogelation was observed even at relatively high levels of EGDMA brancher (up to 25 mol %). In principle, more than one brancher per primary chain should be sufficient to cause cross-linking and hence macrogelation. Thus, this anomalous result was attributed to the relatively high probability of intramolecular cyclization of the EGDMA comonomer occurring under oxyanionic polymerization conditions. It is likely that complexation between the EGDMA comonomer and the potassium cation enhances this cyclization side reaction.