Reaction photo-induced polymerization

Dual Photo/Thermal Initiation Studies. A series of studies were performed using reactive formulations containing both a photoinitiator and a thermal initiator dissolved in the Derakane resin. The objective of these studies was to investigate a dual cure strategy in which the heat liberated by the photo-induced polymerization leads to the production of additional active centers by the dissociation of a thermal initiator. In this way, the dual cure strategy could offer both the temporal control of the start of the reaction afforded by the photopolymerization, as well as enhanced reaction rate and completeness of cure provided by the thermal initiation. 

As early as 1965 Licari and Crepean (20) reported the photo-induced polymerization of epoxide resins by diazonium tetra-fluoroborates for use in the encapsulation of electronic components and the preparation of circuit boards. The use of these materials in coatings was pioneered by Schlesinger and Watt (21-23). When irradiated with UV light, these materials produce BF3, fluoroaromatic compounds, and nitrogen (Reaction 42) ... 

The development of satisfactory adhesive bonding capabilities for rapid high-energy electron or photo-induced polymerization reactions involving free radical intermediates is of prime importance for commercial utility and requires knowledge of the following concepts ... 

Schiff-base or imine bonds are also available as pH-sensitive crosslinkers. Because imine bonds are degradable at weakly acidic pH values, endosome-specific dissociation can be achieved by imine-based crosslinking. A simple imine-based crosslinker, glutaraldehyde, has been used to stabilize a DNA delivery system [111]. Photo-induced polymerization [112], epoxide reaction [113], and Michael addition [114] have also been reported as crossUnking methods. However, because... 

Since the optical transitions near the HOMO-LUMO gap are symmetry-forbidden for electric dipole transitions, and their absorption strengths are consequently very low, study of the absorption edge in Ceo is difficult from both an experimental and theoretical standpoint. To add to this difficulty, Ceo is strongly photosensitive, so that unless measurements arc made under low light intensities, photo-induced chemical reactions take place, in some cases giving rise to irreversible structural changes and polymerization of the... 

Reaction Mechanism of Vinyl Polymerization with Amine in Redox and Photo-Induced Charge-Transfer Initiation Systems... 

A substantial number of photo-induced charge transfer polymerizations have been known to proceed through N-vinylcarbazole (VCZ) as an electron-donor monomer, but much less attention was paid to the polymerization of acrylic monomer as an electron receptor in the presence of amine as donor. The photo-induced charge-transfer polymerization of electron-attracting monomers, such as methyl acrylate(MA) and acrylonitrile (AN), have been recently studied [4]. In this paper, some results of our research on the reaction mechanism of vinyl polymerization with amine in redox and photo-induced charge transfer initiation systems are reviewed. 

The polymerization proceeds under photo- [49,50],X-ray [51], and y-ray [52] irradiation in the dark in vacuo, in air, or even in water or organic solvent as the dispersant (nonsolvent) for the crystals, similar to the solid-state polymerization of diacetylene compounds [ 12]. The process of topochemical polymerization of 1,3-diene monomers is also independent of the environment surrounding the crystals. Recently, the thermally induced topochemical polymerization of several monomers with a high decomposition and melting point was confirmed [53]. The polymer yield increases as the reaction temperature increases during the thermal polymerization. IR and NMR spectroscopies certified that the polymers obtained from the thermally induced polymerization in the dark have a stereoregular repeating structure identical to those of the photopolymers produced by UV or y-ray irradiation. 

Detailed studies on the decomposition of organic peroxides are of fundamental interest and of high importance in polymerization reactions. The time-scales of intermediate radical formation and of their subsequent decomposition determine process parameters such as the initiator efficiency in radical polymerizations. An improved understanding of the mechanism and dynamics of photo-induced fragmentation is achieved by systematic investigations in which quantum-chemical calculations are carried out in conjunction with highly time-resolved experiments. 

Previously reported photo-induced M(CO)e-catalysed reactions of olefins and dienes include isomerizations, hydrogenations, and polymerizations. Recently two groups have reported that irradiation of W(CO)e in CC14 causes the metathesis of olefins, e.g. of pent-2-ene (reaction 64).203>204... 

The role of the isomers of 2,4,6-trimethyl-l,3,5-trithiane as co-initiators in benzophenone-induced photopolymerizations was pursued by studying the primary photochemical reactions by nanosecond laser-flash photolysis <2001JPH133> it was found that the polymerization efficiency of the co-initiator did not follow the efficiency of photo induced formation of the initiating radicals however, detailed mechanisms of the various stages of polymerization were proposed <1998JPH21, 1999MM2173, 2001JPH133>. 

By a technique which interposed a rotating sector between a source of UV radiation and a dilatometer bearing a monomer, variations in the rotational speed of the sector and size of the opening, controlled bursts of radiation strike the monomer and induce polymerization. From the frequency of exposure and the effect on the polymerization many of the kinetic constants were evaluated. In this connection it should be noted that vinyl acetate exhibits virtually no absorption of UV radiation at 290-300 nm. On the other hand, acetaldehyde has an extinction coefficient of 14 at 290 nm and an extinction coefficient of 15 at 300 nm. Therefore acetaldehyde can act as a photo-sensitizer for the polymerization of vinyl acetate at wavelengths above 299.8 nm [23]. At 366 nm, 2,2 -azo-bisisobutyronitrile has been used as a sensitizer [29,180]. Azobicyclohexane carbonitrile is a UV sensitizer suitable for use with a 124 watt mercury arc at 25°C which does not produce a dark reaction in rotating-sector experiments. Its absorption peak is at 350 mn with an extinction coefficient of 16 [181]. 

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