Aminopolymers confined within mesoporous supports have shown promise as materials for direct capture of CO2, from ambient air. In spite of this, relatively little is known about the energetics of CO2, binding in these materials, and the limited calorimetric studies published to date have focused on materials made using molecular aminosilanes rather than amine polymers. In this work, poly(ethylenimine) (PEI) is impregnated within mesoporous SBA-15, and the heats of CO2, adsorption at 30 degrees C are investigated using a Tian-Calvet calorimeter with emphasis on the role of PEI loading and CO2, pressure in the compositional region relevant to direct capture of CO2, from ambient air. In parallel, CO2, uptakes of these materials are measured using multiple complementary approaches, including both volumetric and gravimetric methods, and distinct changes in uptake as a function of CO, preskre and amine loading are observed. The CO2, sorption behavior is directly linked to textural data describing the porosity and PEI distribution in the materials.