Borosiloxane oligomers for improving adhesion of addition-curable liquid silicone rubber with epoxy resin by surface treatment

The purpose of this study is to improve the interfacial adhesion property between epoxy resin (EP) and addition-curable liquid silicone rubber (AL-SR). A novel surface treatment agent, borosiloxane oligomers (BSiO), was synthesized, and the major chemical structure was evaluated by gel permeation chromatography, Fourier transform infrared spectra, nuclear magnetic resonance spectroscopy (²⁹Si- and ¹¹B-NMR), and thermogravimetric analysis. BSiO served as surface treatment agent for EP to improve interfacial adhesion characteristics of EP and AL-SR. The adhesion strength between EP and AL-SR was measured by pull-out test, and the results indicated that the adhesion strength increased from 0.02 MPa for EP/AL-SR to 0.18 MPa for BSiO-EP/AL-SR with the failure mode from EP posts dislodgement for EP/AL-SR to rubber breakage for BSiO-EP/AL-SR. Furthermore, adhesive mechanism was analyzed and concluded that the improvement of adhesion characteristics of EP/AL-SR through the oligomers surface treatment was a result of chemical and physical bonding. The BSiO acted as binder by reacting with amino groups on EP surface through the active epoxy groups and absorbing electron clouds of phenyl groups of AL-SR chains through the boron atoms. This feature makes BSiO a superior candidate to improve the adhesion and reduce the dislodgement or exfoliation of silicone rubber or other materials possessing electron-rich groups on the molecular chains from EP in the future.