High-conversion polymerization of fluorescence probes. 1. Polymerization of methyl methacrylate

Abstract

The effect of polymerization of methyl methacrylate on the fluorescence intensities of a series of donor-acceptor molecules ([p-()VJV-dialkylamino)benzylidene]malononitriles) has been investigated. The fluorescence of the probes increases gradually (1.5 times) as conversion increases to 60%. Further increase in conversion causes a sharp increase in fluorescence (20-40 times), reaching a limiting value at the limiting conversion. This sudden rise in the fluorescence occurs when the polymerization approaches the glassy state. In this region, mobility becomes restricted and internal molecular relaxation of the probes becomes controlled by the microscopic free volume provided by the polymer. This leads to a decrease in the nonradiative rate and consequently to an increase in fluorescence. Bulk polymerization of methyl methacrylate was carried at 50, 70, and 90 °C in the presence of the fluorescent probe. A correlation between the limiting fluorescence yield and the limiting conversion was found. It is assumed that these results reflect the influence of free volume on the molecular relaxation of the probes.

Kinetic study of epoxy curing in the glass fiber/epoxy interface using dansyl fluorescence

“…The advantage of using such a small amount is that no perturbation is introduced into the system. In general, the f uorescent emission changes when polarity and/or rigidity variations occur in the system where the chromophore is immersed [11][12][13][14][15]. Some studies propose that an enhancement in the microviscosity of the medium leads to a decrease in the nonradiactive decay rate and consequently an increase in the fluore cence quantum yield [13].…”

“…In general, the f uorescent emission changes when polarity and/or rigidity variations occur in the system where the chromophore is immersed [11][12][13][14][15]. Some studies propose that an enhancement in the microviscosity of the medium leads to a decrease in the nonradiactive decay rate and consequently an increase in the fluore cence quantum yield [13]. Other authors use the increase of the fluore cent intensity that comes from the chemical changes of the f uorophore [14,15].…”

Studies of polymerization of acrylic monomers using luminescence probes and differential scanning calorimetry

“…A class of probes called molecular rotors was em ployed for the first time by Loufty ( 1,2), to follow the progress of a series of methacrylate polymerizations. It was reported that the rotational relaxation of the probes is sensitive to free volume, which affects the microscopic mobility and the fluorescence intensity.…”

Spectroscopic investigation of cyanovinyl-diethylaniline dyes in solutions

“…The electronic excitation of these dyes is accompanied by a large increase in the polarity due to changes in the charge distribution (internal charge transfer) [8][9][10][11][12][13][14][15][16][17][18][19][20]. The ground-state and excited-state dipole moments, // g and H e , of some dicyanovinyl-alkylaniline dyes were determined in refs.…”

“…The ground-state and excited-state dipole moments, // g and H e , of some dicyanovinyl-alkylaniline dyes were determined in refs. [8,12,19,20] by measurement of spectral absorption and emission shifts in various solvents. For the dye /^(N,N-dimethylamino)-benzylidene malonitrile which is very similar to DCVA values of /* g =8.7 D and /* c =24 D were measured [ 8 ].…”