Rigid-chain polymers attractive forces

Polymers that exhibit liquid crystallinity, either in the melt or in their solutions, usually consist of comparatively rigid structures that confer high extension on the molecular chains. Intermolecular attractive forces also may contribute to the stabilization of the LC state. Polarizability of the molecules and then-constituent groups are the molecular feature that is required to render the intermolecular force. Anisotropy of the polarizability tensors of the interacting molecules confers a corresponding anisotropy on the dispersive attractions between molecules. On this account, parallel molecular alignment may be energetically favored [1-3]. 

ROLE OF THE ATTRACTIVE FORCES OF THE UNITS IN NEMATIC ORDERING OF A SOLUTION OF RIGID-CHAIN POLYMERS... 

A number of aspects of the role of the attractive forces of units in nematic ordering of a solution of rigid-chain polymers was defined in [57-59], but the mechanisms of partial flexibility of the polymer chain remained the most common within Ae framewoik of the analysis (cf 1.3). 

The structural characteristics that are most important to determining the properties of polymers are (1) the degree of rigidity of the polymer molecules, (2) the electrostatic and van der Waals attractive forces between the chains, (3) the degree to which the chains tend to form crystalline domains, and (4) the degree of cross-linking between the chains. Of these, cross-linking is perhaps the simplest and will be discussed next. 

In natural rubber the attractive forces between neighboring polymer chains are relatively weak, and there is little overall structural order. The chains slide easily past one another when stretched and return, in time, to their disordered state when the distorting force is removed. The ability of a substance to recover its original shape after distortion is its elasticity. The elasticity of natural rubber is satisfactory only within a limited temperature range it is too rigid when cold and too sticky when warm to be very useful. Rubber s elasticity is improved by vulcanization, a process discovered by Charles Goodyear in 1839. When natural rubber is heated with sulfur, a chemical reaction occurs in which... 

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