Silicon surface modification with trialkoxysilyl-functionalized star-shaped polymers

The synthesis of trimethoxysilane end-capped linear polystyrene (PS) and star-branched PS and subsequent silicon (Si) surface modification with linear and star polymers are described. Trimethoxysilane terminated PS was synthesized using sec-butyl lithium initiated anionic polymerization of styrene and subsequent end-capping of the living anions with p-chloromethylphenyl trimethoxysilane (CMPTMS). ¹H and ²⁹Si NMR spectroscopy confirmed the successful end-capping of polystyryllithium with the trimethoxysilane functional group. The effect of a molar excess of end-capper on the efficiency of functionalization was also investigated, and the required excess increased for higher molar mass oligomers. Acid catalyzed hydrolysis and condensation of the trimethoxysilane end-groups resulted in star-branched PS, and NMR spectroscopy and SEC analysis were used to characterize the star polymers. This is the first report of core-functionalized star-shaped polymers as surface modifiers and the first comparative study showing differences in surface topography between star and linear polymer modified surfaces. Surface-sensitive techniques such as ellipsometry, contact angle goniometry, and AFM were used to confirm the attachment of star PS, as well as to compare the characteristics of the star and linear PS modified Si surfaces. The polymer film properties were referenced to polymer dimensions in dilute solution, which revealed that linear PS chains were in the intermediate brush regime and the star-branched PS produced a surface with covalently attached chains in the mushroom regime.