A Strategy for Developing Novel Structural Polyurethanes and Functional Materials. Controlled/Living Free-Radical Polymerization of Acryloyl Azide under 60Co γ-ray Irradiation

Photo-Iniferter RAFT Polymerization

Light-mediated polymerization techniques offer distinct advantages over polymerization reactions fueled by thermal energy, such as high spatial and temporal control as well as the possibility to work under mild reaction conditions. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a highly versatile radical polymerization method that can be utilized to control a variety of monomers and produce a vast number of complex macromolecular structures. The use of light to drive a RAFT-polymerization is possible via multiple routes. Besides the use of photo-initiators, or photo-catalysts, the direct activation of the chain transfer agent controlling the RAFT process in a photo-iniferter (PI) process is an elegant way to initiate and control polymerization reactions. Within this review, PI-RAFT polymerization and its advantages over the conventional RAFT process are discussed in detail.

Acryloylnitrenes: Spectroscopic Characterization, Spin Multiplicities, and Rearrangement to Vinyl Isocyanates

The simplest acryloylnitrene, CH₂═CHC(O)N (1b), and two halogenated derivatives, CH₂═CFC(O)N (2b) and CH₂═CBrC(O)N (3b), were generated through the 266 nm laser photolysis of the corresponding azide precursors in solid N₂-matrices at 15 K. The IR spectroscopic characterization of these new acylnitrenes is supported by ¹⁵N-labeling and quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) level of theory. For the three nitrenes 1b, 2b, and 3b, two conformers exhibiting syn and anti configurations between the C═C and C═O bonds with respect to the C-C bonds have been identified. Consistent with the CBS-QB3 calculated singlet-triplet energy gaps (ΔE_ST < 0 kcal mol^-1), the IR spectral analysis suggests that all these acryloylnitrenes adopt oxazirine-like structures with closed-shell singlet spin multiplicity. Upon subsequent green light (532 nm) irradiation, these acryloylnitrenes rearrange to form vinyl isocyanates CH₂═CXNCO (X = H, F, Br), for which the IR spectra have also been obtained. According to the calculations on the α,β-fluorinated acryloylnitrenes at the CBS-QB3 level, their spin multiplicities can be switched from singlet CH₂═CFC(O)N (ΔE_ST = -0.86 kcal mol^-1) to triplet CF₂═CFC(O)N (ΔE_ST = +0.61 kcal mol^-1), whereas CFH═CFC(O)N is magnetically bistable due to a rather small ΔE_ST (+0.09 kcal mol^-1).