DISTRIBUTION AND MOTION OF TRIFLUOROMETHANESULFONATE ANIONS IN POLY(P-HYDROXYSTYRENE) AND POLYSTYRENE FILMS STUDIED BY MULTIPLE-QUANTUM NMR

The degree of ammonium trifluoromethanesulfonate (triflate) salt aggregation in polystyrene (PS) and poly(p-hydroxystyrene) (PHOST) films was quantified using F-19 multiple-quantum (MQ) nuclear magnetic resonance (NMR) spectroscopy. The dispersion and diffusivity of photosensitizers containing triflate anions in polymer thin films affect the performance of chemical amplification resists. A low salt loading in PHOST films produced predominately dispersed anions, while both dispersed anions and salt aggregates coexist in films with higher loadings. In three films with high salt loadings, the maximum dispersed salt in PHOST films is 9.1 +/- 2.0% w/w. The 10% w/w triflate salt in PS film has an aggregate fraction of 0.13 as compared to 0.29 for the same salt loading in PHOST. However, the 8.7 +/- 2.0% w/w dispersed salt in this PS film falls within the range observed for the remaining PHOST films. In addition, the dispersed anions are less rotationally hindered in the PS film than in the PHOST films. In the PHOST films as well as the bulk triflate salt, oscillations are observed in the zero and two quantum intensities, indicating that the anions do not rotate isotropically at room temperature. These oscillations are absent in the PS film, indicating isotropic motion of the anion. An interaction between the salt anion and hydroxyl groups in PHOST could account for the rotation hindrance observed in the PHOST films, while its absence in PS would allows the anion to rotate isotropically. These differences in salt dispersion and mobility correspond to the observed variation in the T(g) upon salt addition. A large plasticization effect (-23-degrees-C) is observed in PHOST. The specific interaction between the salt anion and the hydroxyl group in PHOST may influence its free volume, configuration entropy, the degree of hydrogen bonding between the polymer chains, and degree of aggregate formation. Lack of such an interaction in PS may result in improved packing on the molecular level, corresponding to the observation of a small degree of antiplasticization (+5-degrees-C). Finally, the growth rate of the higher order MQ coherences indicates that the salt aggregates in both types of films have interanion spacings similar to the bulk salt.