Abstract
This paper investigates the photo-initiated cationic polymerization of diglycidyl ether of bisphenol A (DGEBA) modified with bisphenol A (BPA)/polyethylene glycol (PEG) hyperbranched epoxy resin. The relationship between curing behavior, rheological, and thermal properties of the modified DGEBA is investigated using photo-differential scanning calorimetry (DSC) and photo-rheometer techniques. It is seen that the addition of the hyperbranched epoxy resin can increase UV conversion (αUV) and reduce gelation time (tgel). After photo-initiation polymerization (dark reaction) occurred, a second exothermic peak in the DSC thermogram takes place: namely, the occurrence of curing reaction owing to the activated monomer (AM) mechanism. Consequently, the glass transition temperature decreased, and at the same time, UV intensity increased which was due to the molecular weight between crosslinking points (Mc). Furthermore, the radius of gyration (Rg) of the network segment is determined via small-angle X-ray scattering (SAXS). It is noted that the higher the Mc, the larger the radius of gyration proves to be, resulting in low glass transition temperature.
Highlights
In the electronics, coatings, and automotive industries, UV curing application is extensively used
The curing behavior and rheological property of the diglycidyl ether of bisphenol A (DGEBA) and D90H10 systems, using triarylsulfonium hexafluorophosphate salts acting as photoinitiator, were investigated via photo-differential scanning calorimetry (DSC)
Photo-DSC, photo-rheometer and small-angle X-ray scattering (SAXS) measurements were used to investigate the occurrence of the epoxy systems during UV curing and the final properties of the cured samples
Summary
Coatings, and automotive industries, UV curing application is extensively used This is because of the many advantages of UV curable resins, such as high reaction rate, good adhesion, curing at ambient temperature, and low energy consumption [1,2]. This single component, solvent free type of resin has high stability at any storage condition. Once a photoinitiator absorbs UV light, the photoinitiator is cleaved by UV light and changed into radicals and protonic acids or Brönsted acids. They can initiate cross-linking polymerization with a monomer. Crivello [3], one of the bestphoto-polymerization experts, proposed the overall mechanism of photolysis of a diaryliodonium salt Ar2 I+ MtX−
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