Spin probe studies of nonsolvent penetration into polymer particle formed from poly(vinyl acetate) and poly(2‐ethylhexyl methacrylate)

Nonaqueous dispersion (NAD) of poly(vinyl acetate) (PVA c ) particles sterically stabilized by poly(2‐ethylhexyl methacrylate) were examined by ESR spectroscopy after introduction of a trace quantity of a spin probe, 3‐carbomoyl‐2,2,5,5‐tetramethyl 3‐pyrolin‐1‐yloxy. ESR spectra were monitored as a function of temperature from ‐160 to 100°C. In spite of the complex morphology of the particle, it is found that the behavior of the probe in the NAD was essentially identical to that in a pure PVA c matrix. Solvent penetration into (NAD) particles were studied. These colloidal particles were exposed to a dilute solution of the spin probe, and the bimodal distribution of the ESR spectra of this probe molecule were carefully monitored as a function of time. Fickian‐type diffusion of spin probes into the particles was observed and a spherical model was employed to obtain the diffusion coefficients ( D ) in various solvents. D values were found around 10 –15 cm 2 /s and were interpreted as the parameter, inversely proportional to the apparent viscosity of the environment inside the PVA c particle. The maximum amount of diffused solvent molecules ( M ∞ ) into the PVA c particle was found inversely proportional to polymer‐solvent interaction through the solubility parameters. © 1993 John Wiley & Sons, Inc.