Rotation of the polymer chain

Polar substituents such as chlorine increase the interchain forces and hinder free rotation of the polymer chain. Hence polydichlorostyrenes have softening points above 100°C. One polydichlorostyrene has been marketed commercially as Styramic HT. Such polymers are essentially self-extinguishing, have heat distortion temperatures of about 120°C and a specific gravity of about 1.40. 

A more direct method of studying rotation is to look for variation in the g or hyperfine (Section III,A,2) tensors as the temperature is changed. For certain peroxy radicals in polymers, considerable changes in the g tensor occur which can be correlated with both the onset of rotation of the polymer chain and also rotation about the C—O bond with increasing temperature (58, 59). Similar changes in the g tensor have been observed for ions formed by irradiation in frozen alcohols (60). Kazusaka et al. (61) have observed changes from an orthorhombic g tensor gt = 2.0266, g2 = 2.0097, g3 = 2.0042 at 77 K to an axial g tensor with gl = 2.007 and g = 2.018 at... 

When a polymer chain is placed in a flow field, the coil stretches out of its equilibrium state and rotates in the flow field. These conformation changes dramatically impact the global flow response of a polymer solution, beyond simply enhancing the viscosity of the solution. Shear thinning and viscoelasticity are two key behaviors observed in polymer solution flows. Rotation of the polymer chain in a shear flow leads to shear thinning, in which the viscosity decreases with increasing shear rate. The power law model is a simple model used to describe this behavior, where the viscosity is given by... 

If the carrier transport is much faster than the rotation of the polymer chain, i.e., r, Tr, T approaches to Tt- Then, we can evaluate the intrachain mobility of the carrier directly from the spectrum. The 2a component is given by... 

A still more intricate pattern of potential energy may be expected if the repeat units of the polymer chain carry other substituents, such as the phenyl groups in polystyrene, but these examples establish the general method for quantitatively describing the effects of steric hindrance on rotation. 

It has been shown [56] that if we measure the areas under the approach and retract curves of the force-distance plot we can get quantitative values of the resilience. Resilience is closely related to the ability of the polymer chain to rotate freely, and thus will be affected by rate and extent of deformation, as well as temperature. Different materials will respond differently to changes in these variables [46] hence, changing the conditions of testing will result in a change in absolute values of resilience and may even result in a change in ranking of the materials. Compared to more traditional methods of resilience measurement such as the rebound resiliometer or a tensUe/compression tester. 

Angle of rotation about one of the single bonds of the polymer chain (Chap. X). 

On the other hand, the moduli of as-spun fibers of polyarylates from Cl-HQ and l,2-bis(2-chlorophenoxy)ethane-4,4/-dicarboxylic acid (Cl-PEC) (Cl-HQ/ Cl-PEC), and Me-HQ and Cl-PEC (Me-HQ/Cl-PEC), were higher than those of Cl-HQ/PEC and Me-HQ/PEC. The reason for the higher moduli seemed to be the increased rigidity of the polymer chain caused by the restricted rotation of the ether linkage of Cl-PEC as a result of the steric hindrance of the Cl atoms. However, the moduli of polyarylates from fBu-HQ and Cl-PEC (fBu-HQ/Cl-PEC), and Ph-HQ and Cl-PEC (Ph-HQ/Cl-PEC), were lower than those of fBu-HQ/PEC and Ph-HQ/PEC, because the Cl atoms on the PEC units prevent... 

Conductance behavior is dependent on the material and what is conducted. For instance, polymeric materials are considered poor conductors of sound, heat, electricity, and applied forces in comparison with metals. Typical polymers have the ability to transfer and mute these factors. For instance, as a force is applied, a polymer network transfers the forces between neighboring parts of the polymer chain and between neighboring chains. Because the polymer matrix is seldom as closely packed as a metal, the various polymer units are able to absorb (mute absorption through simple translation or movement of polymer atoms, vibrational, and rotational changes) as well as transfer (share) this energy. Similar explanations can be given for the relatively poor conductance of other physical forces. 

Optical isomerism is possible whenever the substituents X contain centers of asymmetry polymers obtained from pure enantiomeric monomers are optically active. However, the specific rotation of the polymers is in general clearly different from that of the monomers. Optical isomerism is also possible when asymmetrically substituted carbon atoms are placed in the main chain (see Example 3-25). 

A low melting entropy is experienced if the intramolecular motions of the polymer are hindered, for example, the free rotation of chain segments. This is preferentially be done by stiffening of the polymer chain. Table 2.12 shows a selection of building blocks for temperature-resistant polymers. 

---