Conformational Analysis of Poly(methylene-1,3-cyclopentylene) and Chain Conformation in the Crystalline Phase

Abstract

A conformational analysis for poly(methylene-1,3-cyclopentane) (PMCP) for different microstructures is presented. Independently of the microstructure of PMCP, extended conformations suitable for the disordered crystalline phase are geometrically and energetically feasible. However, strong restrictions to the conformational freedom, both of the rings and of the backbone, are required. The similarity between the experimental diffraction profiles of a PMCP sample and the Fourier transform calculations for isolated PMCP extended chains confirms that the crystalline phase of PMCP consists of parallel extended chains (configurationally and conformationally disordered) with a pseudohexagonal arrangement of the chain axes but with a nearly complete intermolecular rotational and translational disorder along the chain axes. The large increases of the entropy of melting with all the examined kinds of configurational order (cis or trans or isotactic) would be due to the related higher conformational order in the disordered crystalline phase.

Cyclopolymerization of Nonconjugated Dienes with a Tridentate Phenoxyamine Hafnium Complex Supported by an sp3‐C Donor: Isotactic Enchainment and Diastereoselective cis‐Ring Closure

“…It is interesting to note that the PMCP produced by achiral Cp 2 ZrCl 2 /MAO gives a microstructure of predominately cis ‐atactic rings ( σ = 0.86) with a T m of 189 °C 7. Given the lower T m s for the cis ‐enriched isotactic ( σ = 0.70–0.74) PMCPs produced by rac ‐ 1 , this supports the proposal that the melting temperature for PMCP is more dependent on the overall cis ring content than the tacticity of the polymer 36, 37…”

Cyclohexane Rings Reduce Membrane Permeability to Small Ions in Archaea‐Inspired Tetraether Lipids

“…These results are in contrast to reported computational studies suggesting that cyclopentane rings [41] in tethered lipids increased lipid packing. [7,42] Although the stereochemistry of the cyclopentane rings (cis versus trans)may account for the discrepancybetween our experimental results and the reported computational studies,c onformational analysis [43] and X-ray studies [44] of polymers containing multiple 1,3cyclopentane rings support that the energy of interstrand packing of these polymers is independent of the cis or trans configuration of the rings.N evertheless,t he results shown in Figure 1d emonstrate that any structural effects to the lipid through introduction of cis cyclopentane rings is not sufficient to significantly affect membrane leakage of small ions under the conditions used in these studies.…”

On Physical Properties of Tetraether Lipid Membranes: Effects of Cyclopentane Rings

“…The dominant conformational motion in cyclopentane is pseudorotational [ 68 ]. Pseudorotation is more restricted for the trans- isomer whereas several more orientations of the two substituents on the ring can be created for the cis -1,3-dialkyl cyclopentane ring [ 9 , 68 , 69 ]. Even though this study shows that the stereochemistry at the cyclopentane ring has a dramatic influence on membrane properties, more work is still required in order to explain why liposomes made of PLFE, which naturally occurs and contains trans -1,3-disubstituted cyclopentyl rings, can undergo the L α -to-Q II phase transition [ 48 , 49 ], while the synthetic trans BTL ( Figure 4 ) cannot [ 9 ].…”