The effect of triplet sensitizers on the photoinitiated polymerization (cure) of a model acrylate monomer, isobornyl acrylate (IBOA), has been investigated. Time-resolved electron paramagnetic resonance (TR EPR) spectroscopy was employed to investigate the initiation of polymerization. Cure monitoring and photodifferential scanning calorimetry (photoDSC) were employed to follow the course of the polymerization. Thioxanthen-9-one (TX) and 2-isopropylthioxanthen-9-one (ITX) were found to be effective sensitizers of the photopolymerization, which was initiated by radicals produced from (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TMDPO) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO). TR EPR experiments demonstrated that the mechanism of sensitization involves T-T energy transfer from TX (or ITX) to TMDPO or BAPO followed by formation of radicals by R-cleavage of the photoinitiators. Direct photolysis of TMDPO and BAPO results in an absorptive chemically induced dynamic electron polarization (CIDEP) pattern due to the triplet mechanism (TM) of polarization of the substituted benzoyl and P-centered radicals produced by R-cleavage of the photoinitiators. TR EPR demonstrates that the same radicals were produced during direct and sensitized photolysis. However, a different CIDEP pattern is produced by photosensitization, namely an emissive/absorptive (E*/A) pattern. A TR EPR study of solutions containing phosphine oxide initiators and IBOA under direct and photosensitized conditions demonstrated that the polarized primary P-centered radicals add to the double bond of IBOA with the formation of polarized secondary radical adducts. Both primary and secondary radicals exhibit the same polarization pattern as the primary radical precursors, i.e., A in direct photolysis and E*/A in the presence of a sensitizer. The rate of polymerization of neat IBOA was followed by cure monitoring. In the presence of ITX the rate of cure increases significantly compared to direct photolysis of same. The heat evolved in the polymerization of IBOA photoinitiated (direct and sensitized) with TMDPO was monitored by photoDSC, and at early times was found to be higher in the sensitized photopolymerization. Time-intermittent UV irradiation allowed an estimation of the ratio of termination to propagation rate constants (k t /k p ) during dark periods of polymerization. The observed decrease of k t /k p with the progress of polymerization is discussed. The results suggest that photosensitization may provide a means of manipulating and controlling the parameters of photocuring of acrylates.

and OBz) in methanol, or methanol-tetrahydrofuran solution, yields in the majority of cases 3-substituted 2methoxy-3H-azepines. Substituted methyl 2-azidobenzoates (X-2-N,C6H,C0,Me; X = CI, OMe, NO,, Br.CO,Me, and C0,H) give the correspondingly substituted 2-methoxy-3-methoxycarbonyl-3H-azepines depending on the nature and position of the substituent group (X). In contrast, thermolysis of methyl o-azidobenzoate in alcohol solution gives mixtures of 3H-azepines and triplet nitrene derived products.

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Die Photolyse der o‐Azidobenzoesäure‐Derivate (I) in Alkoholen (II) führt abhängig von der Natur und Position des Substituenten Xhauptsächlich zu den substituierten 2‐Alkoxy‐3H‐azepin‐Verbindungen (III), deren NMR‐, UV‐ und massenspektroskopische Daten tabellarisiert sind.

Das aus dem Triazin (II) dargestellte Azid (Ia) wird zur Strukturbestätigung in das Hydrazon (Ib) übergeführt, das auch in unabhängiger Synthese aus (Ic) erzeugt wird und dessen Hydrolyse nicht zur erwarteten Verbindung (Ia), sondern zu dem Azin (V) und dem Azid (Id) führt.