Synthesis of allyl acrylpimarate by microwave irradiation and phase-transfer catalytic reaction and its UV-curing reactions as a new monomer

The rosin molecules can improve the adhesion and mechanical properties of polymers. It may be introduced either directly or via active functional groups. The focus of this work has been to develop a new method for creating such active functional groups connected to the acrylpimarate molecule by a microwave irradiation and phase-transfer catalytic reaction with allyl chloride. The synthesized monomer was then polymerized under ultraviolet (UV) irradiation. A new polymerization monomer with two functional groups (two allyl groups) has been synthesized through Diels-Alder reaction using levopimaric acid (an important component of rosin) as raw material under microwave irradiation. The yield and gas chromatography on content of the allyl acrylpimarate monomer were 92.2% and 98.6%, respectively. Due to the steric hindrance in the original rosin molecules, two major allyl acrylpimarate isomers in a 1:4 ratio were observed in the monomeric products, as confirmed by two-dimensional nuclear magnetic resonance spectroscopy (2D NMR). UV-curing reaction of the synthesized monomer confirmed that its two functional groups led to a novel polymerization pathway compared with that of the monomer bearing only one allyl group. Conversion of the monomer reached 90% by using Michlers ketone as a photoinitiator. The cured film was composed of a three-dimensional cross-linked polymer due to the bifunctional monomer, and showed good performance in terms of thermal stability, hardness, and chemical resistance.