Quartz crystal microbalance gravimetry measurements of the sorption of trimethylaluminum into polystyrene and poly(methyl methacrylate)

The sorption behavior of metalorganic species into polymers is important in various gas-phase processes including vapor phase infiltration (VPI) which is used to transform organic polymers into organic-inorganic hybrid materials and area-selective deposition where various organic layers are used to prevent vapor deposition. In this work, we use in situ quartz crystal microbalance (QCM) gravimetry to measure the long-term mass uptake of TMA into polystyrene (PS) and compare it with that of poly (methyl methacrylate) [PMMA]. While TMA infiltration into PMMA, PS, and PMMA-PS copolymers is widely studied, a direct investigation of TMA's long term sorption behavior into pure PS has not previously been reported. During a 17.5 h TMA exposure step, PMMA is found to sorb 0.67–0.83 ng of TMA per nanogram of polymer while PS is found to sorb only 0.02 ng per nanogram polymer. These results clarify that the mechanism for low TMA infiltration into PS is a lack of sorption rather than rapid out-diffusion of the precursor. This result has implications ranging from designing impermeable layers for selective area deposition to predicting mass transport during vapor infiltration into ordered block copolymers. Here, the poor sorption of TMA into PS is utilized in a demonstration to pattern inorganic infiltration into PET films.