Control of the Cell Structure of UV-Induced Chemically Blown Nanocellular Foams by Self-Assembled Block Copolymer Morphology

Abstract

A method to fabricate highly ordered nanocellular foam by incorporating the UV-induced chemical foaming technique with self-assembly of a block copolymer, poly(methyl methacrylate-block-tert-butyl acrylate) (PMMA-b-PtBA), was reported in our previous communication [Rattanakawin, P. ACS Macro Lett.2020, 9 (10), 1433–1438]. Cells with a size of a few tens of nanometers were successfully generated within the cylindrical PtBA-rich domains by heating the UV-irradiated self-assembled PMMA-b-PtBA. Here, we show how other self-assembled morphologies of PMMA-b-PtBA, such as lamellae and PMMA-rich cylinders, affect the formation of nanocellular foams. It is demonstrated that cells generated from the lamella templates are largely expandable compared to those from the cylindrical templates, mainly due to the increase in gas amount produced within the PtBA-rich domains. Meanwhile, the lamellar framework is no longer maintained and transformed into a microcellular structure when the foaming temperature is increased near the glass transition temperature of PMMA. We show that such a drastic change in cell structure may be mitigated by increasing the molecular weight of PMMA.