Intrinsic porosity in polymeric materials arises from the formation of a continuous network of interconnected voids and is a direct consequence of the shape and rigidity of the molecular building blocks. To obtain well-defined pores with narrow size distributions, the polymerization of rigid and sterically hindered monomers must not interfere with the pore formation and should avoid the use of additives that may occupy voids. Polydiacetylenes can be generated by the topochemical polymerization of diacetylene-bearing molecules favorably arranged in crystals, gels, thin films, or vesicles. Polydiacetylene formation in amorphous materials has been sparsely studied because higher-order self-assembled structures are assumed to be required for the topochemical polymerization of 1,3-butadiyne to occur. In this study, a bulky hexachlorocyclotriphosphazene core (N3P3Cl6) was functionalized with six diacetylene-containing alkyl chains and successfully converted to an intrinsically porous multifunctional polydiacetylene. The successful formation of the polydiacetylene was confirmed by Raman spectroscopy, and the porous structure of the resulting materials was verified by X-ray diffraction and Brunauer–Emmett–Teller surface area measurements. This investigation revealed a significant change in the porous structure after polymerization, leading to a 5-fold increase in specific surface area. Overall, the topochemical polymerization of diacetylenes is a promising strategy for the preparation of functional materials, which is shown to be compatible with rather amorphous phases of bulky molecules. The results obtained from this investigation give access to a range of porous polydiacetylene materials for potential applications in organic electronics, gas adsorption, and other related fields.