1.3.1 Solution polymerization
The reaction of isocyanate and hydroxyl groups in the synthesis of urethane acrylates is strongly exothermic, and the exothermic problem of the reaction can be controlled by the addition of a suitable solvent.


Commonly used solvents are ethyl acetate, butyl acetate, toluene, xylene, and the like. The solvent is used, the reaction is easy to control, the viscosity of the system is low, and the conversion rate is high.


However, the solvent is toxic, the removal is difficult, the shrinkage rate of the cured film is high, the curing speed of the system is low, the excellent performance of the prepolymer to the coating film is weakened, and the modern environmental protection development requirements are not met, and this method will be gradually replaced.


1.3.2 Bulk Aggregation
Bulk polymerization refers to the reaction of only a monomer and a small amount of initiator in the absence of a solvent, and the product has high purity, simple post-treatment and environmental protection.


The disadvantage is that the viscosity of the system is large during the reaction, the reaction heat is not easy to control, and the thermal polymerization side reaction of the unsaturated double bond is prone to occur.


Peng Wei used isophorone diisocyanate (IPDI), polypropylene glycol (PPG) and pentaerythritol triacrylate (PETA) as raw materials to synthesize PUA resin by bulk method. The synthesis route and reaction conditions were studied. PUA cured film with excellent mechanical properties and chemical resistance.


1.3.3 Sol-gel polymerization
The organic/inorganic hybrid materials prepared by the sol-gel technique have unique advantages, and their film-forming properties, optical properties and mechanical properties are excellent, and have become a research hotspot in the field of composite materials.


Yang Zehui et al. prepared silica sol using tetraethyl orthosilicate (TEOS) and prepared UV-curable urethane acrylate/epoxy acrylate/nano-silica hybrid material with KH-570 as silane coupling agent. ,


Studies have shown that the thermal weight loss and thermal decomposition temperature of hybrid materials are nearly double that of pure resin systems.