Controlling Volume Shrinkage in Soft Lithography through Heat-Induced Cross-Linking of Patterned Nanofibers

When poly(isopropylidene diallylmalonate) rich in threo-disyndiotactic sequences (st(rich)-2) was utilized as a cross-linkable ink for microcontact printing, the resultant submicrometer-scale patterns featuring 700 and 300 nm wide stripes were successfully insolubilized while maintaining their high dimensional integrity by heat-induced cross-linking with elimination of CO(2) and acetone. In sharp contrast, although the thermal properties and reactivities of a polymer rich in threo-diisotactic sequences (it(rich)-2) and a polymer having low stereoregularity (2(low)) are little different from those of st(rich)-2, the patterns printed with these reference polymers collapsed considerably upon heating as a result of a volume shrinkage effect. The striking difference between st(rich)-2 and the other two polymers most likely arises from the nanofiber-forming character of st(rich)-2, where the printed stripes are porous and much less affected by the volume shrinkage of individual nanofibers.