Comparison of Absorption Kinetics of Ethanol and Butanol into Different Size Nanopores Present in Syndiotactic Polystyrene and Poly(P-Methylstyrene)

Abstract

The absorption kinetics of ethanol and butanol isomers diffused into the pores of the crystal units of syndiotactic polystyrene (sPS) and syndiotactic poly(p-methylstyrene) (sPPMS) cast from m-xylene was investigated by infrared spectroscopy. The OH stretching mode of these alcohols absorbed in the pores of sPS and sPPMS was observed at 3592 cm⁻¹, which does not correlate with the presence of hydrogen bonding. This finding indicates that the alcohol molecules are isolated from others in the small pores of the crystal units. The diffusion of ethanol into the pore of sPPMS was about ten times faster than that of sPS. The number of ethanol molecules included in the unit cell of the crystal was 3.9 and 7.6 for sPS and sPPMS at equilibrium. This corresponds to the incorporation of 1.9 and 3.8 ethanol molecules in one cavity in the crystal unit for sPS and sPPMS, respectively. Experiments probing the absorption of differently shaped butanol isomers showed that three of them were absorbed in the pores of both sPS and sPPMS, while tert-butanol was only absorbed by sPPMS. Apparently, only the pores of sPPMS are enough large to absorb tert-butanol. The diffusion coefficient of tert-butanol into the pore of sPPMS was about twenty-five times slower than that of n-butanol.

Keywords:

• Absorption nanopore
• Alcohol
• Syndiotactic poly(p-methylstyrene)
• Syndiotactic polystyrene

ACKNOWLEDGEMENT

Financial support from a research fund in 2009 from Ryukoku University and a grant from the High-Tech Research Center Program for private universities from the Japan Ministry of Education, Culture, Sports, Science, and Technology are gratefully acknowledged. We thank Prof. Guerra, Dr. P. Rizzo, and Dr. C. Daniel for useful discussion.