Stepwise stereocomplex assembly of isotactic poly(methyl methacrylate) and syndiotactic poly(alkyl methacrylate)s on surfaces

Isotactic (it-) poly(methyl methacrylate) (PMMA) and syndiotactic (st-) poly(ethyl methacrylate) (PEMA) and poly(propyl methacrylate) (PPMA) were synthesized by anionic polymerization in toluene at -78 degreesC with t-C4H9MgBr and t-C4H9Li/(C2H5)(3)Al, respectively, as initiators/coordinators. Combined it- and st-polymers were assembled by the alternate immersion of a 9 MHz quartz-crystal microbalance (QCM) as a substrate into their acetonitrile solutions at ambient temperature. QCM analysis showed constant growth of the assembly except in the first two steps. The assembled ratios between st-PEMA and st-PPMA with it-PMMA (st-/it-) were 2.5 x 0.4 and 1.8 x 0.5, respectively, indicating stepwise stereocomplex formation. The static contact angle of the assembly at each step and its reflection absorption spectrum also implied complex formation. The amount of stereocomplex assembled was significantly affected by the st-polymer concentration and its molecular weight. Atomic force microscopy observation showed the assemblies to have a molecularly smooth surface.