Water-soluble microgels made by radical polymerization in solution

Abstract

The goal of this study was to prepare and characterize water-soluble, high-molecular-weight microgels. N-Vinylpyrrolidone (NVP) and vinylacetate (VAc) in combination with cross-linkers diethylene glycol dimethacrylate (DEGDMA) or diethylene glycol divinyl ether (DEGDVE) were copolymerized in solution to high conversion. Polymerization was performed in different solvents or solvent mixtures, with solubility parameters ranging from 16.0 to 47.6 J0.5cm−1.5, and at different initial monomer concentrations. In solvent mixtures with solubility parameters of 20–40 J0.5cm−1.5, macrogelation did not occur below a critical gelation concentration and microgels were formed. For NVP/VAc/DEGDMA (85.0/10.0/5.0 wt%, 84.8/12.9/2.4 mol%) and NVP/VAc/DEGDVE (85.0/10.0/5.0 wt%, 84.8/12.9/3.5 mol%) the critical gelation curves were determined. The molecular weights of the microgels depend on the solvent systems and the initial monomer concentration. Microgels of high molecular weight but low cross-linking density gave aqueous solutions with high viscosities. Increasing the amount of cross-linker to 20 wt% gave high-molecular-weight microgels with lower solution viscosity. Microgels with a monomer composition NVP/VAc/DEGDVE (65.0/15.0/20.0 wt%, 66.2/19.5/14.3 mol%) were prepared in ethanol at different monomer concentrations (3–20 wt%). The molecular weights were determined by a combination of field-flow fractionation and light scattering. By increasing the initial monomer concentration, the molecular weight and the molecular-weight distribution as well as the intrinsic viscosity increased. The exponent of the Mark–Houwink equation was 0.26.