Loading...
Please wait, while we are loading the content...
Similar Documents
Fluorescence technique for studying the sol-gel transition in the free-radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate 0
| Content Provider | Semantic Scholar |
|---|---|
| Author | Yllmaz, Y. |
| Copyright Year | 2001 |
| Abstract | The steady-state fluorescence technique was used to study the free-radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate in the absence and presence of toluene at 75°C. A sol-gel phase transition was observed and monitored by an excited aromatic molecule during the gelation of the above system. Bond percolation theory was employed to quantify the results. The critical exponent and gel point were found to be around 0.45 and 0.36 both in bulk and solution polymerization. The fluorescence and phosphorescence intensities of aromatic molecules are affected by both radiative and non-radiative processes [ 11. If the possibility of perturbation due to oxygen is excluded, the radiative probabilities are found to be relatively independent of environment and even of molecular species. Environmental effects on non-radiative transitions which are primarily intramolecular in nature are believed to arise from a breakdown of the Born-Oppenheimer approximation [2]. The role of the solvent in such a picture is to add the quasi-continuum of states needed to satisfy energy resonance conditions. The solvent acts as an energy sink for rapid vibrational relaxation which occurs after the rate limiting transition from the initial state. Birks et al. studied the influence of solvent viscosity on the fluorescence characteristics of pyrene so* Corresponding author. lutions in various solvents and observed that the rate of monomer internal quenching is affected by solvent quality [ 3 1. Weber and co-workers reported the solvent dependence of energy trapping in phenanthrene block polymers and explained the decrease in fluorescence yield with static quenching, caused by the solvent induced trapping states [ 41. As the temperature of the liquid solution is varied, the environment about the molecule changes and much of the change in the absorption spectra and fluorescence yields in solution can be related to the changes in solvent viscosity. A matrix that changes little with temperature will enable one to study molecular properties themselves without changing environmental influence. Poly (methyl-methacrylate) (PMMA) has been used as such a matrix in many studies [ 5 1. Recently we reported the viscosity effect on the low frequency, intramolecular vibrational energies of excited naphthalene in swollen PMMA latex particles [ 6 1. 0009-2614/94/$07.00 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://web.itu.edu.tr/okayo/pdf/94onder.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
