Chain rigidity solution properties

The solution properties of dendrigraft polybutadienes are, as in the previous cases discussed, consistent with a hard sphere morphology. The intrinsic viscosity of arborescent-poly(butadienes) levels off for the G1 and G2 polymers. Additionally, the ratio of the radius of gyration in solution (Rg) to the hydrodynamic radius (Rb) of the molecules decreases from RJRb = 1.4 to 0.8 from G1 to G2. For linear polymer chains with a coiled conformation in solution, a ratio RJRb = 1.48-1.50 is expected. For rigid spheres, in comparison, a limiting value RJRb = 0.775 is predicted. 

Other structural variations on the rigid-rod PBZXs have encompassed a variety of changes that affect the backbone geometry. Deviation from 180° para-catenation has been investigated by a number of researchers for improved processability. Solution properties are of particular interest in an effort to determine concentration effects on the ability to form liquid crystalline solutions. Most notable backbone deviations have been the ABPBT, ABPBO and ABPBI systems which are characterized by catenation angles of 162°, 150°, and 150° respectively. They are classified as extended chain systems because of the unrestricted rotation between the repeat units. The polymer backbone can... 

Unfortunately, this procedure is not possible for various classes of polymers with moderate equilibrium chain rigidity shown in Fig. 23 since for all of them the dependence of [n]/[7j] on M cannot be expressed by a universal function A = A (x). The fact that for these polymers the experimental dependences A (x) differ greatly from Curve III in Fig. 23 implies that the dynamo-optical properties of their molecules cannot be described in terms of the theory of kinetical rigid chains. Presumably, flow birefringence in solutions of these polymers is related, to a certain extent, to the kinetic flexibility of their chains. 

As already indicated, (p. 170) the dispersion of the Kerr effect in the range of radio frequencies is a characteristic property of rigid-chain polymer solutions. This can be seen in Figs. 59-61 which show frequency dependences of EB for solutions of polj chlorohexyl isocyanate)s, cellulose earbanilate and ladder polychlorophenylsiloxane. Similar dependences have been obtained for poly(butyl isocyanate) various cellulose ethers and esters and ladder polysiloxanes ... 

The values of S obtained in this manner (Table 14) and those obtained by other methods (Tables 1 and 9) are close to each other within experimental error whereas the values of mo (Table 14) and the values that could be expected taking into account the structure of the main chain of tl se polymers are in reasonable agreement This means that equilibrium dielectric properties of rigid-chain polymer solutions can be adequately described in terms of the model of a worm-like chain according to Eqs. (86) and (87). 

The material considered in this review show that the molecules of r id-chain polymers exhibit a number of characteristic (sometimes even unique) propertfes many of which cannot be observed in flexible-chain polymers. The FB and EB of rigid-chain polymer solutions can serve as effective methods of studying these properties. 

Many properties of polymer solutions are well explained in terms of the freely-jointed-chain model. The present work constitutes a part of a program of study of polymer chains in solution which are partially rigid (or partially flexible). 

Comparison of the values of C for the polymers with a flexible C-C or Si-O-Si backbone (as occurs in siloxane polymers) of about 6-10 with the value for the rigid-rod polymer of 125 demonstrates the fundamental difference in the solution properties of the latter polymer which has a highly extended conformation characteristic of liquid-crystal polymers. Equation (1.5) also shows that for a real chain the value of Rq would be expected to increase as the half power of the number of repeat units, i.e. the degree of polymerization, DP. ... 

Many cellulose derivatives form lyotropic liquid crystals in suitable solvents and several thermotropic cellulose derivatives have been reported (1-3) Cellulosic liquid crystalline systems reported prior to early 1982 have been tabulated (1). Since then, some new substituted cellulosic derivatives which form thermotropic cholesteric phases have been prepared (4), and much effort has been devoted to investigating the previously-reported systems. Anisotropic solutions of cellulose acetate and triacetate in tri-fluoroacetic acid have attracted the attention of several groups. Chiroptical properties (5,6), refractive index (7), phase boundaries (8), nuclear magnetic resonance spectra (9,10) and differential scanning calorimetry (11,12) have been reported for this system. However, trifluoroacetic acid causes degradation of cellulosic polymers this calls into question some of the physical measurements on these mesophases, because time is required for the mesophase solutions to achieve their equilibrium order. Mixtures of trifluoroacetic acid with chlorinated solvents have been employed to minimize this problem (13), and anisotropic solutions of cellulose acetate and triacetate in other solvents have been examined (14,15). The mesophase formed by (hydroxypropyl)cellulose (HPC) in water (16) is stable and easy to handle, and has thus attracted further attention (10,11,17-19), as has the thermotropic mesophase of HPC (20). Detailed studies of mesophase formation and chain rigidity for HPC in dimethyl acetamide (21) and for the benzoic acid ester of HPC in acetone and benzene (22) have been published. Anisotropic solutions of methylol cellulose in dimethyl sulfoxide (23) and of cellulose in dimethyl acetamide/ LiCl (24) were reported. Cellulose tricarbanilate in methyl ethyl ketone forms a liquid crystalline solution (25) with optical properties which are quite distinct from those of previously reported cholesteric cellulosic mesophases (26). 

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