Abstract
In this work, epoxy acrylate resin (EA) based on the industrial-grade bisphenol A-based epoxy resin (Ep6) and acrylic acid (AA) has been synthesized in order to develop hybrid resin comprising both epoxide group and reactive, terminal unsaturation. Obtained epoxy acrylate prepolymer was employed to formulate photocurable coating compositions containing, besides the EA binder, also cationic or radical photoinitiators. Hence, when cationic photoinitiators were applied, polyether-type polymer chains with pending acrylate groups were formed. In the case of free radical polymerization, epoxy acrylates certainly formed a polyacrylate backbone with pending epoxy groups. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Therefore, photopolymerization behavior of synthetized hybrid resin with various photoinitiators was determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) methods, and properties of cured coatings were investigated. The performance of the following type of photoinitiators was tested in the cationic photopolymerization: diaryliodonium cations or triarylsulfonium cations, and the following type of photoinitiators were used to induce free radical photopolymerization: α-hydroxyketones, acylphosphine oxides, and their mixtures. Lastly, the basic physicomechanical properties of cured coatings, such as tack-free time, hardness, adhesion, gloss, and yellowness index, were evaluated. Some structural factors and parameters of cationic and radical photoinitiators and photopolymerization mechanisms affecting the epoxy acrylate hybrid coatings performance are discussed.
Highlights
The polymerization of multifunctional monomers or oligomers by UV curing has become a widely used technology that has found many industrial applications due to its unique advantages
The addition reaction of acrylic acid (AA) to the epoxy resin was carried out in order to obtain a hybrid resin containing both epoxy and acrylic groups in the molecule, which will be used in the further part of the research to monitor the course of cationic and radical photopolymerization with the use of various photoinitiators
An epoxy acrylate resin based on the industrial-grade bisphenol Abased epoxy resin and acrylic acid have been synthesized in order to develop hybrid resin comprising both epoxide group and reactive, terminal unsaturation
Summary
The polymerization of multifunctional monomers or oligomers by UV curing has become a widely used technology that has found many industrial applications due to its unique advantages. Many applications result from the high speed of curing by UV radiation and the high efficiency of the process This solution exhibits a few other advantages; it is environmentally friendly with the possibility of adjusting parameters (from brittle to very flexible films), curing at ambient temperature, and adjusting the properties of the final product to the needs [4,5]. Compared to traditional coatings (e.g., solvent-based coatings), UV-curable coatings provide energy savings and low volatile organic compounds [6,7,8]. This is believed to be the most effective method to rapidly convert a solvent-free liquid resin into a solid polymer at ambient temperature. The cross-linking polymerization of the resins is intense, sometimes within a fraction of a second, creating a dense three-dimensional polymer network that exhibits excellent resistance to organic solvents, chemicals, and heat [4,6]
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