||Microporous polymer networks are synthesized by organic sol-gel polymerization with multifunctional and tetrahedral monomers. The molecularly cross-linked polyurea networks can be prepared into a desired shape such as nanoparticle, film, or bulk with three-dimensionally interconnected pores ranging over multiple length scales. Thermal cleavage and rearrangement chemistry of urea bonds allows the network to generate hierarchical pores, mciropores and mesopores, via intra- and inter-particle sintering, which is able to improve the diffusibility of guest molecules. The resultant hierarchically porous networks exhibited excellent capacity and selectivity for CO2 adsorption even from low CO2 concentration sources. The thermal-treatment approach of porous polymer networks used here gives insights into the development of covalent organic networks for pore-based functionalities.