Green construction of highly tunable micro-nano porous polymers based on polymethylmethacrylate /polyvinylidene fluoride self-assembly system and ultra-low pressure CO2 foaming

Abstract

The green construction of micro-nano porous polymers with great potential still faces extreme challenges, including polluting solution blending processes, the use of exogenous nucleating agents, high saturation pressure and even chlorofluorocarbon foaming gas. It is urgent to establish a cleaner and flexible method for managing the nucleation and growth of cells. Hence, a novel approach for manufacturing micro-nano porous polymers via ultra-low pressure CO₂ foaming of polymethylmethacrylate (PMMA)/polyvinylidene fluoride (PVDF) blends was proposed in this work. In this approach, the self-assembly behavior of PVDF macromolecular chains was manipulated through CO₂ absorption process to dominate cell nucleation and regulate cell growth. It was found that as the absorption pressure increases, the phase morphology of PVDF changes from amorphous particles to bundle-like crystals. As the PVDF content increases, it transitions from groove-like microcrystals to bundle-like crystals, and finally to granular crystals. The self-assembled PVDF microphase can reduce the nucleation barrier and significantly increase the nucleation density. Furthermore, the miscible PVDF prolongs the cell growth and effectively increases the expansion ratio through plasticization. By this method, porous polymers with both small cell size and high expansion ratio can be obtained. Moreover, highly expanded microporous polymers with an expansion ratio of 25.6 can also be prepared under ultra-low pressure of 1.7 MPa. These findings provide a new route for green construction of highly tunable micro-nano porous polymers.