Microporous polynorbornenes bearing carbocyclic substituents: Structure-property study

Abstract

Four sets of polymers from norbornene-type monomers with various carbocyclic groups were prepared to perform the structure-property study and to evaluate the effect of main- and side-chains on the porosity of resultant polymers. As monomers, norbornenes with phenyl-, cyclohexyl-, norbornyl-, and framed carbocyclic-groups were designed and synthesized using the Diels-Alder reaction in good yields. All these monomers were involved in ring-opening metathesis and vinyl-addition polymerization to form polymers with various structure of main-chains. The porosity was investigated with help of low temperature nitrogen adsorption/desorption method, and the sorption of H2, CO2, CH4 were also assessed for the most promising synthesized polymers. The obtained polymers exhibited large BET surface areas (up to 740 m2/g), while CO2 and H2 uptake reached 3.0 and 0.18 mmol/g, correspondingly. The porosity of polymers was shown to be determined by the nature of both backbones and side-chains, and it seems that the influence of side-chains is the main one. The largest values of BET surface areas were achieved for polynorbornenes with framed carbocyclic groups. At the same time, vinyl-addition polynorbornenes, which have more rigid main-chains, also provided larger BET surface areas compared to isomeric metathesis ones. Therefore, new valuable relationships between polymer structure and its porosity were established, and an efficient strategy to readily available soluble microporous polymers from norbornene derivatives was suggested. The combination of comparatively simple synthesis, high porosity and solubility in organic solvents can be considered as a key advantage of the synthesized polymers.