Poly(lactic acid) (PLA)-block-poly(norbornene) (PNB) copolymers which bear photocrosslinkable cinnamate side-chains are synthesized by combining the ring-opening metathesis polymerization (ROMP) of norbornenes with the ring-opening polymerization (ROP) of lactides. Highly porous 3D scaffolds with tunable pore sizes ranging from 20 to 300 µm are fabricated through liquid–solid phase separation. Scaffolds with an average pore size around 250 µm, which are under investigation as bone grafting materials, are reproducibly obtained from freeze-drying 5% w/v benzene solutions of PLA-b-PNB copolymers at −10 °C. As a demonstration of the impact of photocrosslinking of cinnamate side-chains, scaffolds are exposed to UV radiation for 8 h, resulting in a 33% increase in the compressive modulus of the polymeric scaffold. The foams and the methodology described herein represent a new strategy toward polymeric scaffolds with potential for use in regenerative medicine applications.