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In the synthesis of polyurethane acrylate, hydroxyl acrylate reacts with NCO groups to introduce acryloyloxy groups, which are generally present at the chain ends of polyurethane prepolymers.
Suitable hydroxy acrylates can be divided into the following categories according to the number of functional groups:
1. Monofunctionality: hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA), hydroxybutyl acrylate (HBA);
Generally speaking, monofunctional UV monomers have greater odor, volatility, and irritation, such as HEA and HPA. Hydroxyl methacrylate has an additional methyl group on the carbon of the double bond, so its odor and skin irritation are reduced, but its reactivity is also reduced. The polyurethane acrylates made with hydroxy methacrylate end-capping is slightly higher in hardness than hydroxy acrylates, but the curing rate is worse. Compared with HEA and HPA, HBA is much less irritating. HBA has two structures: 2-HBA and 4-HBA. In comparison, the performance of 4-HBA is better.
Since the photocuring rate of acrylate is much faster than that of methacrylate, most of them use hydroxy acrylate. The reactivity of isocyanate and alcohol hydroxyl group is: primary alcohol > secondary alcohol > tertiary alcohol, so most of them use HEA (primary alcohol) to react with isocyanate, while HPA and HBA are rarely used.
2. Difunctionality: trimethylolpropane diacrylate (TMPDA);
TMPDA is a difunctional TMPTA, in which one of the acrylic double bonds of TMPTA is converted into a hydroxyl group. This monomer is almost impossible to find a manufacturer on the market. Generally, manufacturers with monomer production qualifications will produce it for their own use. And because it is difficult to accurately control the reaction of the hydroxyl group, the final TMPDA is not pure, but a mixture containing TMPTA. TMPDA can be used to synthesize tetrafunctional, hexafunctional, or even higher-functional polyurethane acrylates.
3. Trifunctionality: pentaerythritol triacrylate (PET3A);
PET3A is generally used to produce high-functionality polyurethane acrylates. The resulting high-functionality resins have the characteristics of fast curing rate, high hardness and high wear resistance.
4. Dipentaerythritol pentaacrylate (DPHA);
In the esterification process of DPHA, a part of hydroxyl groups can be reserved by controlling the degree of esterification. Due to the different processes of different manufacturers, the final DPHA also exists in the form of a mixture. DPHA can be used to synthesize polyurethane acrylates with ten or higher functionalities. The products have higher cross-linking density and better wear resistance. However, due to the large double bond content, the cured film is prone to cracking during light curing.
The above are the commonly used hydroxyl acrylates in the synthesis process of polyurethane acrylates. As a manufacturer of photocurable resins, Bossin specializes in the research and development, production, sales and technical services of new photocurable materials. New and old customers are welcome to call for consultation.
