Polystyrenes in channels

Polystyrenes (PS) with various stereosequences have been modeled in narrow cylindrical channels corresponding to those found in polymer-inclusion compounds (ICs), such as those formed with host cyclodextrins (CDs), where the polymers reside as guests. Isotactic (i) PS is found to fit in channels with narrower diameters (D) than syndiotactic (s) PS, when both adopt conformations permitted by the Yoon, Sundararajan, Flory RIS conformational model of PSs, while atactic (a) PS can be included in channels with D intermediate to those for i- and s-PS. In ICs formed with host gamma-CD and guest a-PS homopolymer and guest poly(epsilon-caprolactone) (PCL)-b-a-PS diblock copolymer it was observed that the a-PS homopolymer and the a-PS copolymer blocks were and were not included, respectively. Thus, it appears that a-PS is barely able to be threaded by gamma-CD, whose internal diameter is similar to 8 Angstrom. Because the channel conformers found for i- and s-PS have smaller and larger diameters, respectively, than those found for a-PS, we would expect i-PS to be complexed by gamma-CD, while s-PS might not. As a consequence IC formation with gamma-CD may provide a means to physically separate the stereoregular forms of polystyrene. In addition, only the mrm and rmr PS stereoisomers show channel conformations with significant probabilities, so we suggest that in situ polymerization of styrene monomer in the narrow channels of its IC formed with gamma-CD might produce a new stereoregular form of PS with regularly alternating m and r diads. (C) 2003 Elsevier Ltd. All rights reserved.