Photochromic and fluorescent probe studies in glassy polymer matrices. 5. Effects of physical aging on bisphenol A polycarbonate and poly(vinyl acetate) as sensed by a size distribution of photochromic probes

Abstract

Multiple photochromic probes requiring different volumes to isomerize were used to monitor the effects of physical aging on Bisphenol-A polycarbonate (PC) glass. PC was found to possess a local free volume distribution that is more broad than those of polystyrene (PS) and poly(methyl methacrylate) (PMMA). Contrary to aging results in PS and PMMA, physical aging of PC affected the isomerization abilities of the smaller probes as well as the larger probes, and all probes are affected nearly equally. Physical aging in dry and wet poly (vinyl acetate) (PVAc) showed that absorbed water increases the fraction of local free volume sampled by azobenzene as would be expected in a plasticized system. Additionally, it was found that a local free volume distribution is difficult to determine with the photochromic technique in polymers such as PVAc that have glass transition temperatures near the experimental temperature. At temperatures near Te, the polymer has enough mobility to allow structural reorganization on the time scales required to reach the photostationary state, generally, 10-30 min. Therefore, the environments surrounding the probes change before the photostationary state is established, thereby making interpretation of the data difficult.

Microstructural evolution in polymerizations of tetrafunctional monomers

“…16). [11][12][13]. These results show, as expected, that as the critical volume required for isomerization increases, the fraction of probes that are mobile decreases dramatically.…”

Radical concentrations, environments, and reactivities during crosslinking polymerizations

“…Thus, it is highly desirable to characterize the structure of densely crosslinked polymers formed from the polymerization of multifunctional monomers; however, the fluorescent ro-'5) and photochromic probes [16][17][18][19][20][21][22], and various scattering techniques 23,24). In particular, the fluorescent and photochromic probing techniques have been most useful in characterizing the evolution of the polymer structure during polymerization.…”

“…fluorescent ro-'5) and photochromic probes [16][17][18][19][20][21][22], and various scattering techniques 23,24). In particular, the fluorescent and photochromic probing techniques have been most useful in characterizing the evolution of the polymer structure during polymerization.…”

Photochromic Polymers

“…27,28 One process, occurring at an early stage of the photoreaction, was found to be as fast as in a dilute solution and was followed by a much slower process. The contribution of the fast process decreases with physical aging [29][30][31][32] and increases with plasticization and with an increase in temperature.…”