Photopolymerization and photodegradation of polymers after long-term UV light exposure

Over the past two decades, research into photostimulated processes in polymeric materials has gained new momentum, driven both by the growing demand for functional polymers with controllable properties and the need to understand their long-term stability under operational conditions. Current approaches combine the development of new materials, such as photopolymerization systems for 3D printing and biosensing, with a deep fundamental study of the mechanisms of photoinduced changes, including the role of free volume and the dynamics of molecular motions. UV light irradiation is known to affect materials, and possibly change their properties in certain conditions due to the existence of ‘subthreshold radiation effects’. Polymerization reactions may also need light exposure to happen, this is photopolymerization, and UV light exposure is a very good way to start these reactions. However, UV light can degrade the polymer if it is exposed to it for a prolonged period of time. In this case, the newly formed polymer will undergo changes in its network structure, which can change its properties. A combination of positron annihilation lifetime spectroscopy (PALS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) and electron paramagnetic resonance (EPR) spectroscopy in complementary with computer modeling using recurrence analysis, was used to obtain information on the network properties of polymer matrix based on acrylated epoxidized soybean oil (AESO) and vanillin dimethacrylate (VDM) with and without a photoinitiator (2,2-dimethoxy-2-phenylacetophenone) (DMPA) according to the proposed light on/off protocol in view of long-term UV light exposure.