Strain dihedral angle deformation

Cyclodecene is the smallest cycloalkene, which can accommodate a trans double bond without significant deformation of bond angles and/or dihedral angles. The strain energies and structures of smaller fraws-cycloalkenes have been the subjects of considerable research over the years. 

The absence of significant change in the distribution of the backbone dihedral angles upon plastic deformation of glassy BPA-PC has been experimentally observed. Utz [30] and Utz et al. [31] compressed specifically labeled samples uniaxially and in plane strain to strains of —0.68 and found, by solid-state NMR, that the distributions of the torsion angle pairs (f>2 and (f>4 (or and (f>s) do not change perceptibly. 

The volume of the atomistic box initially remains constant because the volume of the system is kept constant during deformation under both uniaxial extension and pure shear. At strains greater than ef 0.07, the volume of the atomistic box grows gradually with the strain and there are sharp increases at several points where sudden drops in the stress in the atomistic box are observed. No considerable change in the distribution of the backbone dihedral angles is observed during deformation up to the system strain 0.2. 

The reason for the extremely high modulus of oriented polyethylene in comparison to typical specimens ( 1 GPa for injection-molded high density polyethylene [24]) is simple. The tensile deformation of isotropic samples at low strains principally involves the distortion of molecules whose trajectories approximate to a random coil, which is largely accommodated by bond rotation. This requires much less force than the molecular stretching required to extend the all-trans configuration, which involves bond elongation and an increase in the C—C—C dihedral bond angle. 

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