Highly Swelled Networks in Polymer Particles; an Application of Exponential Series Method

Abstract

The direct energy transfer method was used to trace swelling phenomena in rubbery network of glassy polymer panicles. Fluorescence measurements were carried out in poly(vinyl acetate) particles which were prepared by dispersion polymerization in isooctane using a copolymer of 2-ethylhexyl methacrylate as a steric stabilizer. These reactive particles were treated with 2–(1 -naphthyl)ethanol to produce particles specifically labelled in the stabilizer phase. Energy transfer experiments were carried out on the N-labelled particles doped with a hydrocarbon soluble anthracene derivative which dissolved exclusively in the rubbery poly(2-ethylhexyl methacrylate) (PEHMA) phase. Donor fluorescence decay profiles were measured, and the data were fitted to the Klafter-Blumen (KB) model for energy transfer on fractal. The exponential series method was used to obtain the lifetime distributions and the inverted KB equation was applied to interpret the results. The finding that the effective dimensionality d = 2 for this energy transfer process was interpreted in terms of a crossover in a restricted geometry if PEHMA was present in the form of interconnected long viggle threads. This idea was supported by our data that swelling agents for PEHMA, such as hexadecane, are also taken up by the particle from the pentane solution. Experiments on these particles yield d values that increase with increasing hexadecane until d becomes equal to 3.0. Further swelling measurements were performed with the cyclohexane as a swelling agent. We found that energy transfer kinetics obeyed the Stem-Volmer type of relation in the highly swollen, nonrestricted PEHMA phase.

Key Words:

• Direct energy transfer method
• Fluorescence
• graft copolymer.