Poly(methacrylic acid) Grafts Grown from Designer Surfaces: The Effect of Initiator Coverage on Polymerization Kinetics, Morphology, and Properties

Poly(methacrylic acid) (PMAA) films,were photografted by iniferter-mediated polymerization from self-assembled monolayers (SAMs) of initiator molecules immobilized on Au via disulfide linkages and mixed with disulfide alkanes. The influence of initiator coverage on the growth rates of film thickness, surface morphology, and nanoscale mechanics was studied. Film thickness was measured by ellipsometry and atomic force microscopy (AFM), whereas mechanical performance was assessed by AFM compression force. Remarkably, the film thickness growth rate by ellipsometry did not show any significant variation with initiator coverage. However, surface morphology visualized by AFM showed clear influences of the composition of the initiating SAW which directly affected the rate of termination reactions. To investigate the early stages in the grafting process, polymerization was performed in situ using a quartz crystal microbalance with dissipation monitoring setup (QCM-D). The mass increment during the photografting was evaluated using concentrated and diluted SAMs of the initiator. A remarkably higher number of grafted chains in the case of concentrated SAMs was observed. By comparing this result with the AFM measurements on the obtained films, we recognized a broader chain length distribution, consequent to termination reactions in dense systems, to influence the surface morphology of the layers.