Complexation of microgel particles with small ester molecules as a function of the ionic content of the monomer feed composition

Abstract

Water-soluble, polyacrylate, internally cross-linked latex particles (microgels) form complexes with small ester molecules. The association is more favourable as the carboxy group content of the microgels increases; it does not vary significantly with the content of the ethylene dimethacrylate cross-linking co-monomer present in the monomer feed in the range 2–30 mol%. The binding of the ester to the polymer is not electrostatic, as the positively charged ester 4-nitrophenyl 4-trimethylammoniobenzoate iodide is only marginally better bound than is the neutral 4-nitrophenyl acetate to the same polymer under similar conditions. The second-order rate constant for the reaction of the ester with hydroxide ion in the ester–polymer adducts is more than an order of magnitude smaller than that for reaction of hydroxide ion with the free ester; this effect also occurs with polymers prepared from neutral monomers.

The large acceleratory effects observed previously for reactions of functions attached to microgels might arise partly from partitioning of substrate into the latex particle to produce a more concentrated solution local to the reactive group.