Effect of crystallinity and flexibility on the photodegradation of polyurethanes

Abstract

Using fluorescence spectroscopy and gel content measurement, the photolysis of simple polyurethanes based on methylene 4,4′‐diphenyldiisocyanate (MDI) is shown to depend on both the flexibility and crystallinity of the polymer. Polyurethane films based on MDI and 1,12‐dodecanediol (MDI‐12) can be either annealed or quenched to yield a semicrystalline (as measured by DSC and X‐ray diffraction) or amorphous film, respectively. In the case of the quenched (amorphous) film, photolysis yields an ortho photo‐Fries product whereas the annealed (semicrystalline) film does not. Similarly, for a given photolysis time the annealed film generates a lower extent of crosslinked gel. In addition, photolysis of amorphous polyurethane films derived from MDI and ethylene oxide oligomers shows that for relatively inflexible polymers with only three ethylene oxide segments, little or no ortho photo‐Fries rearrangement products are generated upon photolysis. In contrast, photolysis of more flexible polyurethane films with approximately 13 ethylene oxide linkages yields the ortho photo‐Fries product. Apparently, for aromatic diisocyanate based polyurethanes, the extent and mechanism of degradation is directly dependent on the crystallinity and main‐chain flexibility of the polymer.

Degradation and stabilization of polyurethane elastomers

“…The flexibility of the HSs can be adjusted by altering the length of ChEx used, the crystallinity, and the temperature during photoageing. The photodegradation of aromatic PUs will become less efficient with the use of shorter ChExs, higher crystallinity of the HSs (which can be achieved by annealing), and a temperature that is below the Tg, all of which can decrease the flexibility of HSs [169,170]. Again, the increased stiffness and crystallinity of the polymer chains may inhibit the oxygen diffusion that is required for photooxidation.…”

Photochemistry and photopolymerization activity ofp-nitroaniline in the presence ofN,N-dimethylaniline as a bimolecular photoinitiator system

“…(l), RP' and @Pd, respectively, and the values of these kinetic parameters determined experimentally from SEC measurements, Rexp and @exp, could be ascribed to chaintransfer processes during LA photopolymerization. It is known that the basicity of the amine plays an important role in the ability of these compounds to behave as chaintransfer agents [31,32]. The characteristics of the lauryl polyacrylate samples prepared using these photoinitiators are similar for all the members of the family, with the exception of IpNA.…”

Biobased Epoxy Resin with Inherently Deep-UV Photodegradability for a Positive Photoresist and Anticounterfeiting

“…The amorphous state allows more space for photoscission reactions to occur. On the other hand, the molecular packing (crystallization/amorphism) can possibly affect the energy state of molecules under light irradiation, affecting the occurrence of reactions. ,− …”