Phosphorescence of naphthalene-labelled colloidal polymer particles. The α-methyl relaxation of one microphase in a multicomponent material

Abstract

Nonaqueous dispersions of poly(methyl methacrylate) (PMMA) particles, sterically stabilized with polyisobutylene (PIB), were prepared with naphthalene (N) groups covalently incorporated into the PMMA chains. These materials have a complex morphology of phase-separated PMMA and PIB microdomains, with the N groups in the PMMA microphases. The phosphorescence intensity and decay times of the N groups were measured as a function of temperature over the range 77–295 K for dispersions in methylcyclohexane and for freeze-dried powder samples. An Arrhenius treatment of the radiationlcss decay rate showed a change in slope at −35 °C. The activation energy for the radiationless decay process is 3.8 kcal/mol in the −35 – +22 °C temperature region, identical to that found for pure PMMA by nmr for chain motion associated with the a-methyl relaxation process. We believe that the phosphorescence experiment is sensitive to the diffusion of oxygen and other impurities in the sample. These rates increase as the temperature is raised, enhancing the rate of phosphorescence quenching. These experiments indicate that phosphorescence measurements on labelled samples are suitable for studying relaxation processes within individual microphases of a polyphasic composite material.