Liquid crystalline elastomers programmed with light-activated bond exchange allowing controlled shape change.

Free-radical polymerizations are used for a wide range of applications but are detrimentally impacted by the presence of oxygen. Zinc phthalocyanines have been previously used as singlet oxygen generators to excite radical-consuming ground-state triplet oxygen into its less reactive singlet state prior to photoexcitation of a photoinitiator. We report for the first time that polymerization can be achieved via irradiation of UV band of phthalocyanine and that photosensitization and photoinitiation can be independently achieved via irradiation of its two distinct absorption bands to reduce oxygen inhibition and initiate polymerization without the need for additional treatment. We propose a mechanism for this unique photoinitiation phenomenon and verify its feasibility via computational and experimental approaches. This new class of dual-photosensitive molecules shows promising utility in applications that are adversely impacted by the presence of oxygen, such as coatings and stereolithography.

Amine−peroxide redox polymerization (APRP) has been highly prevalent in industrial and medical applications since the 1950s, yet the initiation mechanism of this radical polymerization process is poorly understood so that innovations in the field are largely empirically driven and incremental. Through a combination of computational prediction and experimental analysis, we elucidate the mechanism of this important redox reaction between amines and benzoyl peroxide for the ambient production of initiating radicals. Our calculations show that APRP proceeds through S N 2 attack by the amine on the peroxide but that homolysis of the resulting intermediate is the rate-determining step. We demonstrate a correlation between the computationally predicted initiating rate and the experimentally measured polymerization rate with an R 2 = 0.80. The new mechanistic understanding was then applied to computationally predict amine reductant initiators with faster initiating kinetics. This led to our discovery of N-(4-methoxyphenyl)pyrrolidine (MPP) as amine reductant, which we confirmed significantly outperforms current state-of-the-art tertiary aromatic amines by ∼20-fold, making it the most efficient amine−peroxide redox initiator to date. The application of amines with superior kinetics such as MPP in APRP could greatly accelerate existing industrial processes, facilitate new industrial manufacturing methods, and improve biocompatibility in biomedical applications conducted with reduced initiator concentrations yet higher overall efficiency.

Semicrystalline crosslinked thiol–ene networks achieved rapid polymerization kinetics, and mechanical properties substantially improved from the linear thiol–ene thermoplastic.