Nanofiltration and sorption of organic solvents in poly(1-trimethylsilyl-1-propyne) samples of different microstructures

Abstract

For two PTMSP samples synthesized on various catalytic systems (TaCl5/TIBA and NbCl5) and having different chain configurations (the ratio of cis/trans units is equal to 50/50 or 63/37 for PTMSP/Ta and PTMSP/Nb, respectively), sorption and organic solvent nanofiltration (OSN) behavior is studied. Equilibrium sorption (a homological series of linear alcohols C1-C10, diols and ketones for PTMSP/Ta and a homological series of linear alcohols C1-C10 for PTMSP/Nb) and equilibrium swelling of polymers in the above solvents are estimated. Nanofiltration of dilute ethanol solutions of three dyes (Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R) is studied for the PTMSP/Ta sample, and the resultant nanofiltration characteristics of this sample are compared with the earlier data on PTMSP/Nb. Analysis of the experimental results on sorption and swelling of the PTMSP/Ta samples makes it possible to conclude that PTMSP contains sorption sites which are able to coordinate two hydroxyl groups. Structure of the PTMSP/Ta and PTMSP/Nb samples is studied by the methods of vibrational IR spectroscopy and quantum chemistry. The nature of sorption sites in PTMSP is likely to be related to an exceptionally high polarity of the C=C and Si-C bonds in the repeat polymer units. Computational simulation for the model composed of five PTMSP units in the presence of ethanol monomer shows that, in this system, a complex with ΔE = 18 kJ/mol is formed. Nanofiltration studies indicate that, for the PTMSP/Ta sample, the permeability coefficient of ethanol and overall flux of dye-containing ethanol solutions are nearly two times lower than those for PTMSP/Nb. For both PTMSP samples, dye retention increases in the following order: Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R, and this tendency agrees with the increase in the partition coefficients of the above dyes. For the PTMSP/Ta sample, dye retention of Solvent Blue 35 and Safranine O dyes with molecular masses of 350 g/mol appears to be lower than that of the PTMSP/Nb samples. Sorption and nanofiltration behavior of PTMSP/Ta and PTMSP/Nb can be reasonably explained in line with the existing approaches which treat glassy amorphous polymers as microheterogeneous systems containing structural regions with different ordering of polymer chains, and the observed difference in their sorption behaviour and membrane characteristics can be explained by the fact that packing of polymer chains in the PTMSP/Ta is more loosened as compared with that of the PTMSP/Nb sample.