CONFORMATIONS AND MOTIONS OF POLYETHYLENE AND POLY(OXYETHYLENE) CHAINS CONFINED TO CHANNELS

Inclusion compounds formed by linear polymers and host clathrates, such as urea and perhydrotriphenylene (PHTP), provide a unique environment for the included polymer chains. We have investigated the conformations and mobilities of isolated polyethylene (PE) and poly(oxyethylene) (POE) chains when confined to the channels of their inclusion compounds. This was achieved by a two-step procedure: (i) from all possible conformations available to the free polymer chain, those conformations which fit into the channels of their inclusion compounds were defined; (ii) a test was performed to determine whether or not it was possible to interconvert between these channel conformations while the polymer chains remained inside their channels. Though several PE and POE conformers with diameters appropriate to the channels in their urea and PHTP inclusion compounds (D = 5.25-5.50 Å) were found, it was not possible to interconvert between them without some portion of each polymer chain leaving the channel. This is in marked contrast to the behavior of trans-l,4-polybutadiene and isotactic trans-l,4-poly(penta-l,3-diene), which were previously found capable of conformational interconversions in their inclusion compounds with the same host clathrates. On the basis of a comparison of the channel conformers derived for PE and POE with X-ray diffraction studies of their urea and PHTP inclusion compounds, we conclude the following: PE, as it does in its pure crystalline phase, assumes the all-trans, planar zigzag conformation in both clathrates. (ii) POE in the PHTP clathrate adopts several extended conformations, some with a few gauche bonds, in addition to the all-trans conformer. (iii) In its inclusion compound with urea, only more compact conformations with significant gauche bond contents are permitted, (iv) The POE chains in both clathrates adopt conformations that are more extended than the …g±tt… conformer found in POE crystals, which does not fit in either clathrate channel. © 1990, American Chemical Society. All rights reserved.