This study introduces a “ship‐in‐a‐bottle” technique to impregnate porous supports with amines via a straightforward in situ polymerization process. Specifically, alkylamines—tris(2‐aminoethyl)amine (TAEA) and tetraethylene pentamine (TEPA)—are crosslinked with epoxides—trimethylolpropane triglycidyl ether (TMPTE) and 1,3‐butadiene diepoxide (BDE)—within the pores of the metal–organic framework (MOF) Cr‐BDC (also MIL‐101(Cr), where BDC = 1,4‐benzenedicarboxylate), producing four distinct MOF‐polymer composites. These composites are subsequently evaluated for their efficacy in postcombustion carbon capture, examining metrics such as CO2 capacity, CO2/N2 selectivity, isosteric heat of CO2 adsorption, kinetic breakthrough times, and cyclability. Among the composites, Cr‐BDC‐TAEA‐BDE (branched‐linear) demonstrates the most promising results, achieving a CO2 capacity of 2.2 mmol g−1 at 0.15 bar and 313 K, a CO2/N2 selectivity of 301, and an isosteric heat of CO2 adsorption of −110 kJ mol−1. This composite also exhibits superior breakthrough performance, with N2/CO2 separation times of 103 and 143 min per gram under dry and humid conditions, respectively. Furthermore, the four MOF‐polymer composites are subjected to up to 100 temperature swing adsorption/desorption cycles (at 313 and 393 K, respectively), revealing minimal amine leaching or degradation over time. Notably, the composites also show significantly enhanced cyclability compared to Cr‐BDC impregnated with amines without epoxide crosslinking agents; this indicates that crosslinking inhibits amine leaching.