Post-polymerization modification offers a facile and effective tool for adapting polymer properties. However, it has not been applied to poly(propylene carbonate) (PPC) as traditional PPC lacks sufficient functional groups along the polymer chain. In the present work, for the first time, hydroxyl-functionalized PPC has been prepared and used to construct PPC-brush and cross-linked polymer gels through post-polymerization modification approach. PPC-brushes in the form of PPC-graft-poly(PEOMA) were obtained with controllable brush length and brush density via “grafting from” a PPC-macroinitiator which was synthesized from esterification reaction of PPC-OH with 2-bromoisobutyryl bromide. PPC permanent networks in the form of dioxane gels were prepared by cross-linking PPC-OH with 4,4′-diphenylmethane diisocyanate (MDI). Rheological measurement of the gels showed that the cross-linking density scales linearly with the hydroxyl group density in PPC-OH. This work not only offers a facile strategy to realize the post-modification of PPC but also spurs the devising of innovative biodegradable materials with tailored molecular architectures.