Tetrahydrofuran (THF), a common organic solvent for polymers, is often stabilized with butylated hydroxytoluene (BHT) due to THF forming peroxide compounds.  In prior work we have shown that solutions of 996 kg/mol poly(methyl methacrylate) (PMMA) dissolved at a concentration of 15.0 mg/mL in THF and spun-cast onto Si substrates produces thin nanoporous films unlike smooth films prepared from other solvents such as toluene and chloroform. In this study, we examined the effect of the interaction between BHT and THF on the PMMA films by varying the concentration of BHT present in the THF solutions from 0 - 5000 ppm. The influence of BHTs molecular structure was then examined by replacing the BHT with analogous compounds phenol and p-cresol in THF. Solutions also prepared with toluene and BHT were tested to determine if the films produced using BHT alone caused microstructural changes. Optical microscopy of the films exhibits color variation which may be due to opalescence caused by porosity variations in the films. All films were examined using tapping mode atomic force microscope (AFM) imaging in air. While the toluene/BHT and the THF/phenol solutions produced smooth films, the p-cresol solution exhibited some areas of porous structure similar to the THF/BHT solutions. This suggests the importance of both the tertiary butyl and methyl groups in BHT in order to produce the micro/nanoporous structure formation of PMMA. Varying concentrations of BHT appears to have a direct effect on the porosity of the films, although this may be dependent on the presence of water in the THF, as anhydrous THF reproduced these results with less reliability. We are in the process of performing molecular dynamic (MD) simulations on the solvent and inhibitor solutions to better determine the origin of the micro/nanoporous film structure and thus understand the molecular  interactions resulting in the film morphology.

Understanding the impact of BHT inhibitor on the microstructure of spun-cast nanoporous films of PMMA exhibiting high surface areas

ACS Spring 2022

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