Preferential Organization Of Methacrylate Monomers And Polymer Thin Films At The Air Interface Using Femtosecond Sum Frequency Generation Spectroscopy

Monitoring and understanding monomer conformational changes as substituents are varied is an important step in investigating in situ polymerization and controlling the polymerization process as well as regulating the functionality of polymer surfaces to provide efficient polymer coatings. In this study, the preliminary stage involves characterization of the interfacial structures of methacrylate-based functional monomers and their polymer thin films at the air-liquid interface using femtosecond sum frequency generation spectroscopy (FSFGS). By varying the substituted ethyl group of the methacrylate monomers with hydroxy (-OH), chloro (-CO, and phenoxy (-OPh), the alphamethyl (alpha-CH3), alkene-methylene (alkene-CH2), and methylene (CH2) groups are observed to have preferential surface ordering toward the air interface. A peak positioned at similar to 3000 cm(-1) was observed in the spectrum of the 2-hydroxyethyl methacrylate (HEMA) monomer and assigned to alkene-CH2 group. This functional group signifies that the pure monomer has not undergone polymerization. However, the SFG spectra of the polymer versions of these monomers revealed that for the poly(2-hydroxyethyl methacrylate), the alpha-CH3 group dominated the surface; in both poly(2-chloroethyl methacrylate) and poly(2-phenoxyethyl methacrylate), the alpha-CH3 and CH2 groups were both segregated at the interface. These observations of the conformational changes of the monomer units and polymer thin films indicated that substitution of the ethyl group of the methacrylates affected the behavior of the interfacial molecules.