Segmented-chain polymer liquid

Linear chain polymers with repeating sequences of hard and soft segments Possibility of formation of liquid crystal polymers and thermoplastic elastomers... 

This treatment, resting essentially on the assumed approximate interchangeability of molecules of solvent and solute in the solution, cannot possibly hold for polymer solutions in which the solute molecule may be a thousand or more times the size of the solvent. The long chain polymer may be considered to consist of x chain segTneTits each of which is equal in size to a solvent molecule x is, of course, the ratio of the molar volumes of the solute and solvent. A segment and a solvent molecule may replace one another in the liquid lattice. In other respects the assumptions required are equivalent to those used above. The polymer solution differs from that containing an equal proportion of monomeric solute in the one important respect that sets of x contiguous cells in the lattice are required for accommodation of polymer molecules, whereas no such restriction applies to the solution of the monomeric solute. The situation is illustrated in Fig. 110. 

Fig. 110.—Segments of a chain polymer molecule located in the liquid lattice.

Three major topics of research which are based on phase transfer catalyzed reactions will be presented with examples. These refer to the synthesis of functional polymers containing functional groups (i.e., cyclic imino ethers) sensitive both to electrophilic and nucleophilic reagents a novel method for the preparation of regular, segmented, ABA triblock and (A-B)n alternating block copolymers, and the development of a novel class of main chain thermotropic liquid-crystalline polymers, i.e., polyethers. 

Polymer Melts. When a rigid, polarizable monomer forms wither a mainchtiin polymer with flexible segments in belween or a side-chain polymer with flexible segments between the rigid segments and the flexible main chain, liquid-crystal phases are usually viable. 

The expansion of a material on heating is a phenomenon that depends on internal - mostly intermolecular - forces. Bond lengths between atoms are virtually independent of temperature. This also holds for bond lengths between segments of a polymer chain. Polymer systems, therefore, have lower expansivities than related low-molecular liquids. 

Some examples of stiff-chain polymers able to form a liquid-crystalline phase in the solution are listed in Table l1. The ratio of the statistical segment length1 of a polymer chain, 1, to its width, d, (last column of Table 1) measures the degree of chain stiffness. For flexible macromolecules fid 1 stiff-chain macromolecules are those for which fid t> 1. 

The main part of the side group in these macromolecules consists of the alkoxy-benzoic acid moiety. This acid may form thermotropic liquid crystals. The investigation of the hydrodynamic properties of PPhEAA molecules in dilute solutions has revealed that the equilibrium rigidity of their main chains is relatively low (Table 12). Hence, since for all flexible-chain polymers, the shear optical coefficient An/Ar in PPhEAA solutions is independent of molecular weight the segmental anisotropy - tt2 and the anisotropy of the monomer unit Aa may be determined by use ofEq. (67). 

The genesis of the UCST curve for polymer-solvent systems is usually ascribed to enthalpic interactions between the mixture components, which are relatively insensitive to pressure for these constant density systems. The UCST curve can be modeled well with a liquid solution model that adequately accounts for specific interactions between the segments of polymer and the solvent. Examples of interactions are hydrogen bonding and polar interactions. The model also needs to account for the combinatorial entropy of mixing solvent molecules with the many segments that make up a single polymer chain (Prausnitz, 1969). 

The segments of a chain polymer molecule are located in a liquid lattice of coordination number However, the chain is not free to assume any configuration the first and last segments are tethered to the large protein fibers of connective tissue. This end-to-end length will vary linearly with tissue hydration. 

Sirigu, A., Segmented-chain liquid crystal polymers, in Liquid Crystallinity in Polymers, Ciferri, A., Ed. VCH, New York, 1991. 

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