A single-element rotating-polarizer ellipsometer (psi-meter) was used for in situ characterization of the thermodynamic and kinetic behavior of poly-(methyl methacrylate), PMMA, thin films (1.2 μm) in solvent/nonsolvent binary mixtures of methyl ethyl ketone/isopropanol (MEK/IPA) and methyl isobutyl ketone/methanol (MIBK/MeOH). Thermodynamic effects were inferred from equilibrium behavior by the degree of swelling and polymer-solvent solubility. A sharp transition between complete solubility and almost total insolubility was observed in a narrow concentration range near 50:50 (by volume) solvent/nonsolvent for both MEK/IPA and MIBK/MeOH. In the insoluble regime, the polymer was found to swell up to three times the initial thickness. At 50:50 MEK/IPA, a temperature decrease from 24.8 to 18.4 °C caused a change from complete dissolution to combined swelling/dissolution behavior and rendered the PMMA film only 68% soluble. Kinetic effects were determined by dissolution and penetration rate measurements. A constant penetration velocity was observed for almost all compositions for both binary solvent mixtures with Case II transport assumptions providing good agreement with experimental results. For MEK/IPA, penetration rates increased with increasing MEK concentration. For MIBK/MeOH, however, a maximum was observed at 60:40 MIBK/MeOH.
The influence of processing and molecular parameters on the dissolution rate of poly‐(methyl methacrylate), PMMA, thin films (<1 μm) in methyl isobutyl ketone, MIBK, was studied in situ with a single‐element rotating‐polarizer ellipsometer (psi‐meter). Dissolution rates were highly sensitive to the molecular weight distribution, softbake cooling cycle, and dissolution temperature. The apparent activation energy for the dissolution of PMMA in MIBK varied from 25 to 43 kcal/mol depending upon softbake cooling rates and molecular weight distribution. The dissolution rate of air quenched, monodisperse
false(Mnormalw/Mnormaln<1.11false)
PMMA samples was found to vary with the molecular weight to the −0.98 power. For slowly cooled samples this constant was 85% higher, suggesting improved contrast with slow cooling. Polydisperse samples
false(Mnormalw/Mnormaln≈2false)
dissolved about twice as fast as monodisperse ones of the same number average molecular weight. Samples slowly cooled after softbaking and aged for 100h at room temperature or at 60°C showed no change in the dissolution rate with aging. However, the dissolution rate of samples cooled rapidly after softbaking and aged at 60°C decreased by as much as 25%.
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