Nanoporous polymers prepared by cyclotrimerization reaction of amine or nitro functionalized 4,4′diacetylbiphenyl were successfully introduced as active material in chemiresistive gas sensors for volatile organic compounds. Due to their different pore types and pore functionalization they exhibit different sensitivities and selectivities toward alcohols and ketones in the range of 100-3000 ppm. The amine functionalized polymers show the highest selectivities toward alcohols, whereas the nitro-functionalized show the highest toward ketones. Thus a differentiation of these VOCs was realized. Furthermore, the sensors exhibit for most of the VOCs limits of detection below 1 ppm and high sensitivities above 10^-3 ppm^-1. These enhancements in sensor performance are due to the high surface area of up to 680 m²/g. The alcohol vapor adsorption behavior of these materials was studied in detail using vapor physisorption experiments. The higher sensitivity of the microporous amine functionalized polymer correlates well with a higher vapor uptake as compared to the other porous polymers. Moreover, the different selectivities could be correlated to the swelling behavior of the porous polymer during vapor adsorption. Thus we were able to demonstrate that physisorption experiments of alcohol vapors provide useful/helpful mechanistic insights to understand the selectivity of polymer based gas sensors.