Radical Photopolymerization Of Acrylates Research Articles

Effect of UV-curing conditions on the polymer structures: a comparison between coating and adhesive

Radical photopolymerization of acrylate was carried out without a degassing process under conditions suitable for UV-curable coatings and UV-curable adhesives. We examined the differences in the resulting polymer structures obtained from the coating and adhesive by employing the same formulation. 2,2-Dimethoxy-2-phenylacetophenone was employed as a photoinitiator. The UV-curable coating yielded polymers terminated by either a hydroxyl group or a terminal carbonyl group as the main products. On the other hand, the UV-curable adhesive yielded a multitude of polymers that were terminated by disproportionation. In the latter case, some polymers underwent hydrogen abstraction from the polymer backbone, resulting in β-scission of the midchain radical to generate polymers with an α-substituted acryloyl group as the terminal group. We examined the differences between the resulting polymer structures in the cases of a coating and an adhesive employing the same formulation. The UV-curable coating yielded polymers terminated by either a hydroxyl group or a terminal carbonyl group as the main products, suggesting that bimolecular termination was strongly inhibited by oxygen. On the other hand, the UV-curable adhesive yielded a multitude of disproportionation products, whereas some polymers underwent hydrogen abstraction from the polymer backbone, resulting in β-scission of the midchain radical to generate polymers with an α-substituted acryloyl group.

Variations on the Benzophenone Skeleton: Novel High Performance Blue Light Sensitive Photoinitiating Systems

Newly developed benzophenone derivatives in combination with an iodonium salt (and optionally N-vinylcarbazole) or amines have been used as photoinitiating systems. Their abilities to initiate cationic photopolymerization of epoxides and/or radical photopolymerization of acrylates under very soft visible halogen lamp, LED and laser diodes irradiations have been investigated. One of them (BPD5) is particularly efficient for the cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure and leads to the formation of an interpenetrated polymer network IPN upon the house hold blue LED bulb exposure (1 min for getting tack free coatings). The performances attained with some derivatives are better than those obtained with camphorquinone, used as reference photoinitiator, highlighting their high initiating abilities. These systems can be useful to overcome the oxygen inhibition for very low light intensity. The photochemical mechanisms are studied by molecular orbital calcula...

Multicolor Photoinitiators for Radical and Cationic Polymerization: Monofunctional vs Polyfunctional Thiophene Derivatives

Thiophene and polythiophene derivatives have been prepared and used as photoinitiators upon visible light exposure. Their abilities to initiate, when combined with an iodonium salt (and optionally N-vinylcarbazole), a ring-opening cationic photopolymerization of epoxides and radical photopolymerization of acrylates under various different irradiation sources (i.e., very soft halogen lamp irradiation, laser diode at 405, 457, 473, 532, and 635 nm and blue LED bulb at 462 nm) have been investigated. These systems are characterized by a remarkable performance for purple to red light exposure. They are also particularly efficient for the cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure and lead to the formation of an interpenetrated polymer network IPN (30 s for getting tack-free coatings). Their migration stability is excellent in the cured IPNs. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, electron spin resonance spin trapping, and laser flash photolysis techniques.

Keggin‐Type Polyoxometalate ([PMo12O40]3−) in Radical Initiating Systems: Application to Radical and Cationic Photopolymerization Reactions

AbstractNew photoinitiating systems based on a polyoxometalate (POM) are proposed: phosphomolybdic acid in combination with silane, germane, or iodonium salt can be used to generate silyl, germyl, or phenyl radicals as well as silylium cations. The photochemical mechanisms are studied by steady‐state photolysis and electron spin resonance. The phosphomolybdic acid/silane/iodonium salt system can initiate either the radical photopolymerization of acrylates or the cationic photopolymerization of epoxides. The synthesis of interpenetrated polymer networks can also be carried out. The mechanical properties of the synthesized polymers are affected by the presence of POM in the matrix, as shown by their dynamic mechanical analysis (DMA).magnified image

Photopolymerization behavior and properties of highly branched polyester acrylate containing thioether linkage used for UV curing coatings

The highly branched polyester acrylate containing thioether linkage (HBAT) was synthesized using an “oligomeric A 2 + B 3” approach. The dithiol, 1,6-hexamethylene bis(3-mercaptopropionate) (HMBM), was prepared through the esterification between 1,6-hexanediol and 3-mercaptopropionic acid, and then underwent an amine-catalyzed thiol-Michael addition to the acrylic double bond of 1,6-hexamethylene diacrylate to obtain an oligomeric dithiol (oligomeric A 2), then further with trimethylolpropane triacrylate as a B 3 monomer. The molecular structure was characterized with FT-IR and 1H NMR spectroscopy. A broader molecular weight distribution from 1.74 to 2.75 was obtained for different oligomeric dithiol chains by GPC measurements. The photopolymerization kinetics study by photo-DSC analysis showed that the HBAT greatly reduced the oxygen inhibition in radical photopolymerization of acrylates in air. The maximum polymerization rate decreased along with the addition of HBAT into the UV curable resin (EB605) containing bisphenol A epoxy diacrylate and tripropylene glycol diacrylate due to the reduced double bond density and increased viscosity, whereas the final unsaturation conversion in cured film increased because of the longer spacer chain in HBAT compared to that in EB605 and the reduced crosslinking density by HBAT addition. The dynamic mechanical thermal analysis results showed that both the elastic modulus in the rubbery plateau and glass transition temperature of cured film decreased along with the incorporation of HBAT into EB605. The water swelling test and thermogravimetric analysis indicated that the thioether linkage in HBAT can greatly improve the water absorption resistance and oxidative stability of cured film.