Adhesion of two flat substrates covered with polymer brushes was performed to understand the effect of molecular weight distribution (MWD) and graft density. Polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(n-butyl methacrylate) brushes with various number-averaged molecular weight (Mn), MWD, and graft density were prepared by surface-initiated atom transfer radical polymerization from silicon wafers. Two polymer brush substrates were jointed in a 1 cm2 contact area using 5 μL of toluene, and pressed under a reduced pressure for 3 h at 408 K. Two substrates covered with PS brush having larger MWD than Mw/Mn = 1.20 were successfully jointed by thermal press to afford 1.2 MPa of the lap shear adhesion strength, as shown in Figure 1. In contrast, PS brush with narrower MWD than Mw/Mn = 1.20 gave lower adhesion strength than 0.1 MPa. Neutron reflectivity measurement revealed chain mixing structure at the interface between opposite polymer brushes with broad MWD, that induced strong adhesion strength. Similar results were obtained by PMMA brush substrates.

Interfacial adhesion by polymer brushes with large molecular weight distribution

ACS Spring 2022

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