COMPOSITIONAL HETEROGENEITY EFFECTS IN HYDROPHOBICALLY ASSOCIATING WATER-SOLUBLE POLYMERS PREPARED BY MICELLAR COPOLYMERIZATION

An aqueous micellar radical copolymerization technique has been used t o prepare water-soluble copolymers of acrylic acid/styrene, acrylamide /styrene and acrylic acid/ethylphenylacrylamide. In this process, the hydrophobic monomer (1-2 mol% based on the monomer feed) is dispersed within surfactant micelles while the water-soluble monomer is dissolve d in the aqueous medium. This synthesis leads to block copolymers in w hich the number and length of the hydrophobic blocks vary with the deg ree of conversion. Kinetic studies have shown that the compositional h eterogeneity results from the balance between the values of the reacti vity ratios of the monomer pairs and the micellar effect inherent to t he technique. The latter always leads to an enhanced apparent reactivi ty for the hydrophobic monomer. It is shown that an optimization of th e process can be achieved which eventually corrects for the drift in t he average copolymer composition with conversion. The thickening abili ty of the hydrophobically modified water-soluble copolymers is directl y affected by the extent of their compositional heterogeneity. Analysi s of the data provides some criteria for selecting appropriate systems with good controllable theological properties.