Effects of Physical Aging on Polarization-Induced Photodimerization in the Glassy Region of Poly(methyl methacrylate)

Abstract

ABSTRACT:Intramolecular photodimerization of the photochromic molecule 9-hydroxymethyl-10-[(l-naphthyl methoxy)-methyl]anthracene (HNMA) was investigated by ultraviolet-visible (UV-VIS) spectroscopy in the glassy region ofpoly(methyl methacrylate) (PMMA) under different aging conditions. The PMMA matrix was annealed for different time intervals in the glassy region after quenching from 140°C (37.8°C above the glass transition temperature (T 8 )). By following the photodimerization upon irradiation with linearly polarized light, it was found that the reaction kinetics of HNMA reflects the rearrangements oflocal free-volumes of the matrix. The maximum efficiency (I/max) of the reaction induced by linearly polarized light decreases with increasing aging time (t.). Under aging above 60°C, 'lmax decreased monotonously with aging time, whereas it did not change systematically for a PMMA aged at 40°C. The secondary relaxation of the PMMA matrix may thus play a key role in the aging process at low temperature. On the other hand, the reaction kinetics of HNMA can be well expressed by the sum of two exponential functions of irradiation time and a baseline. The two fractions of these decay processes are significantly affected by aging time whereas the influence on the two reaction rates is less remarkable. The baseline increases with increasing aging time, reflecting shrinkage of samples under aging. These experimental results are discussed in relation to the aging data obtained by other techniques such as dielectric relaxation and dynamic mechanical measurements.

Free Volume Determination of Azobenzene−PMMA Copolymer by a Pulsed Low-Energy Positron Lifetime Beam with in-Situ UV Illumination

“…There seems to be no reason to take into account the expansion of the free volume, which could indicate that the increase in the free volume leads to an increase in the fractions of [cis] r /([cis] u + [cis] r ) and [trans] r /([trans] u + [trans] r ) by roughly the same factor. Previous measurements indicate that the activation energy E a of azobenzene is relatively independent of the exact structure of the azobenzene moiety, often yielding values around 20 kcal, ,,, which is completely in agreement with our experimental data.…”

Polarized light-induced photoisomerization in glassy poly(methyl methacrylate) and local relaxation processes of the polymer matrix

“…Prior to the experiments, all the samples were dried at 170°C in vacuo over 48 h to remove residual solvent. Since it has been found that the physical aging process of the polymer matrix affects the optical anisotropy induced by linearly polarized light, 10,11 all the samples were prepared with the same thermal history prior to the experiments.…”

Photoinduced Reorientation of Azo Dyes Bonded to Polyurethane Studied by Polarized FT-IR Spectroscopy

“…These characteristics lead push-pull azo dyes to the prospect of the new optical functional materials utilizing the second-order nonlinear optical effect [2][3][4] or photoinduced anisotropy. [5][6][7][8] A polarized light-induced anisotropy has been observed in polymer films including photochromic molecules. Since the 1980s, this type of anisotropy has been studied in polymers doped with azo dyes for transient polarization holography by Todorov and co-workers.…”

“…The push−pull type of azo dyes has important characteristics, i.e., the larger polarity than that of azobenzene without substituent, and the fast thermal reisomerization from cis to trans forms, because of a large charge separation induced by D and A. These characteristics lead push−pull azo dyes to the prospect of the new optical functional materials utilizing the second-order nonlinear optical effect − or photoinduced anisotropy. − …”