Abstract Simultaneously improving the strength and toughness of polymer‐inorganic nanocomposites is highly desirable but remains technically challenging. Herein, a simple yet effective pathway to prepare polymer‐inorganic nanocomposite films that exhibit excellent mechanical properties due to their unique composition and structure is demonstrated. Specifically, a series of poly(methacrylic acid) x ‐ block ‐poly(benzyl methacrylate) y diblock copolymer nano‐objects with differing dimensions and morphologies is prepared by polymerization‐induced self‐assembly (PISA) mediated by reversible addition‐fragmentation chain transfer polymerization (RAFT). Such copolymer nano‐objects and ultrasmall calcium phosphate oligomers (CPOs) are used as dual fillers for the preparation of polymer‐inorganic composite films using sodium carboxymethyl cellulose (CMC) as a matrix. Impressively, the strength and toughness of such composite films are substantially reinforced as high as up to 202.5 ± 14.8 MPa and 62.3 ± 7.9 MJ m −3 , respectively. Owing to the intimate interaction between the polymer‐inorganic interphases at multiple scales, their mechanical performances are superior to most conventional polymer films and other nanocomposite films. This study demonstrates the combination of polymeric fillers and inorganic fillers to reinforce the mechanical properties of the resultant composite films, providing new insights into the design rules for the construction of novel hybrid films with excellent mechanical performances.

Dual Nanofillers Reinforced Polymer‐Inorganic Nanocomposite Film with Enhanced Mechanical Properties