LAUSR

Five types of palladium‐loaded mesoporous silica nanoreactors with varying pore sizes and structures (Pd@MCM41‐3, Pd@SBA15‐7, Pd@SBA15‐10, Pd@DMSNs‐15, and Pd@DMSNs‐20, where the numbers at the end represent the corresponding pore sizes of the mesoporous silicas) are synthesized and employed in Suzuki–Miyaura polymerization. The influence of pore size and structure on the molecular weight and molecular weight distribution of conjugated polymers is investigated by confining this step‐growth polymerization within the nanopores. Experimental results demonstrate that narrowly distributed conjugated polymers with a dispersity (Ð) as low as 1.17 are obtained in these nanoreactors, in stark contrast to those produced through conventional methods (Ð = 2.05). Notably, as the pore size of the nanoreactors increases, a gradual rise in molecular weight from 1.7 to 6.7 kDa is observed, indicating effective control over molecular weight through this confined polymerization technique. Theoretical analysis and computational simulations further reveal that the probability of each species participating in step‐growth polymerization decreases with increasing chain length, resulting in a species distribution curve that closely matches the gel permeation chromatography trace of each polymeric product.