Functionality and structure of polymers. II. Photodimerization of polymer‐bound anthryl groups and thermal dissociation of the photodimers

Abstract

Anthryl groups bound to various polyesters and polyesterurethanes as side groups were photodimerized in solid state in a nitrogen atmosphere. The rate of photodimerization is strongly affected by polymer structure as observed in the photodimerization of dilute solutions. The results revealed the importance of segment mobility rather than local concentration of anthryl groups. Temperature effects on the rate of photodimerization indicated that the rate jumped above the glass transition temperature (Tg). A definite difference in photodimerization behavior was apparent between polyesters and polyesterurethanes. Anthryl groups in polyesters were to some extent photodimerized at Tg, whereas polyesterurethanes did not react at all. Hydrogen bonding in polyesterurethanes restricted the movement of anthryl groups and consequently additional energy was required to liberate them and allow photodimerization to proceed. The anthryl groups can be recovered from the photodimerized polymers by heating to 80–100°C. The activation energy of thermal dissociation of the photodimer depends to a great extent on polymer structure. These results were interpreted as being due to the strain brought about by photodimer formation exhibited this dependence. The photodimerization–thermal dissociation cycle was reversible (reversibility: 95–100% under nitrogen). A novel principle of reversible photomemory, based on dry unit processes that consisted of image recording above Tg, fixation of image by cooling below Tg, and image erasure at elevated temperature, was proposed.

Photocure properties of high‐heat‐resistant photoreactive polymers with cinnamate groups

“…Photoreactive polymers have a certain degree of mobility to perform the photoreaction in the solid state, and photopolymers with rigid chain are less reactive. 17,18 Similar results were observed in the thermal curing reaction of YX-4000H epoxy resin systems with different phenolic hardeners, in which the conversion rate of YX-4000H epoxy resin systems increased with bulky phenolic hardeners. 19 This implies that there are decreases in the molecular interactions between biphenyl groups in accordance with the increase in distance between the biphenyl epoxy resin units.…”

Photocrosslinkable Star Polymers: Precursors for Model Polyelectrolyte Networks

“…This value is typical for the dissociation of photodimers, as both species absorb UV light, leading to a photosta- tionary state. [32,33] However, as a consequence of the long irradiation times, side reactions take place, which are responsible for the resonance signals at d = 4.2-5.4 ppm. Generally, the long irradiation times are not surprising, as it is well known, that the [4p + 4p] cycloaddition of anthryl derivatives shows a low quantum yield (b X 0.001-0.005).…”

“…While excimer formation of anthracene derivatives is observed fairly common in the solid state, [31,36] only few examples of this phenomenon in solution have been described. [32,38] The fluorescence of three star polymers with different molecular weight have been examined in detail (St 3 -PMAA 14 -Na, St 3 -PMAA 45 -Na, St 3 -PMAA 75 -Na). To increase the difference in polarity between hydrophilic and hydrophobic segments, the sodium salts of the respective stars have been analyzed.…”

Photobleaching of oligoanthrylenes in the film state

“…According to the literature [9], the kinetics of the phototransformation were investigated by plotting ln(A,/A) vs. irradiation time (Fig. 2b).…”