Surface Structures of Linear and Branched Alkyl-Side-Chain Polymer Coatings

Sum frequency generation (SFG) vibrational spectroscopy was utilized to investigate the surfaces and buried interfaces of release liners with hydrocarbon-side-chain-based release chemistries. Two release chemistries, RCA and RCB, both coated on poly(ethylene terephthalate) (PET) substrates, were studied. The hydrocarbon side chains of RCA were linear, while RCB had a mixture of linear and branched side chains. Evaluation of the SFG signals indicated a more upright average orientation for the methyl groups at the surface of RCB and a more reclined orientation for the methyl groups at the surface of RCA. Additionally, SFG data showed higher coverage of methyl groups on the surface of RCA compared with RCB. Assuming delta orientation distribution, the surface methyl group coverage of RCA was calculated to be approximately 40% higher. Calculations assuming Gaussian distributions of methyl group orientations suggested that the ratio of surface methyl coverage of RCA vs RCB could be higher still. Peel testing found a lower release force to separate a pressure-sensitive adhesive from RCA. In addition to better release performance, the relatively methyl-rich RCA surface was found to be more stable against heat and UV exposure. These desirable properties for RCA are attributed to the stability, low surface energy, and weakly interacting nature of the terminal methyl groups.