Sum Frequency Generation Vibrational Spectroscopic Studies on a Silane Adhesion-Promoting Mixture at a Polymer Interface

Sum frequency generation (SFG)vibrational spectroscopy was used to probe the interface between poly- (ethylene terephthalate)with deuterated ethylene glycol subunits (d4-PET)and a silane adhesion-promoting mixture (SAPM)comprised of (3-glycidoxypropyl)trimethoxysilane (ç-GPS)and a methylvinylsiloxanol (MVS). Such a mixture has been found to improve the adhesion of an addition-curing silicone elastomer to a range of plastic and metal substrates. Our results demonstrated that at the interface between d4-PET and a SAPM with a ç-GPS/MVS ratio of 1:1 (w/w), the silane molecules not only segregated to the interface but also the methoxy headgroups likely adopted a greater net orientational order along the surface normal than at the d4-PET/ç-GPS interface. The effects of varying the silane/siloxane ratio and using different siloxane oligomers on interfacial structures were also examined. This study provides unique molecular-level insights into the prerequisite conditions for adhesion of curable silicone adhesives.