Flexible-chain polymers viscosity

Low viscosity ratios far below unity are necessary for the fibrillation of LCPs in resin melts, even for LCPs having good spinnability [18]. Furthermore, even for blends of flexible-/flexible-chain polymers, viscosity ratios far below unity (0.01) generated fibrils of a minor phase in an envelope of composition from 10% fo 40% after differenf mixing times [21]. 

In a comparison study of the values of flow birefringence An and the viscosity t of a polymer solution it is often possible to simplify the experimental procedure so as to avoid the determinations of the characteristic values of [n] and [tj] by determining the quantity An/g (i - tjq) at finite solution concentration instead of the ratio [n]/[7j]. Here is the viscosity of the solvent and the value of g(rj - t o) - At characterizes the effective shearing stress in solution introduced by the dissolved polymer. Many experimental data show that for a flexible-chain polymer in the absence of the macroform effect the ratio An/At, which may be called the shear optical coefficient , is independent of solution concentration, and, also, over a wide range of molecular weights, of chain length ... 

The expoimental data on the non-steady state Ken effect of flexible-chain polymers dissolved in solvents with moderate viscosities reveal that at frequences up to lO Hz no dispersion of B is observed (just as in solutions of low molecular weight substances and monomers). This is also an indication of mutually independent orientation of single monomer units in the electric field which is only sightly related to the structure and conformation of the polymer chain as a whole. 

We have thus considered relatively simple irreversible phenomena in the solution of flexible chain polymers. Through use of the segment distribution functions several different theories are reviewed in a somewhat unified way. It is clear now what will be our next task to improve the existent theories. Apart from the transport phenomena discussed in this paper, however, there are more complicated cases. For instance, treatment of the concentration dependence of the specific viscosity requires further development. We hope to discuss such cases in the near future. 

For calculation of the intrinsic viscosity [rj] of PSD solutions in tetra-hydrofuran Mark-Kuhn-Houwink equation fractal variant (the Eq. (10)) was used, where the constant c(a) is accepted equal to 2.91. and values, received experimentally, are adduced in Table 24 and value for PSD was calculated as follows. As it is known through Ref [1], for flexible-chain polymers, having a l, Huggins constant can be determined according to the Eq. (174), from which it follows that the condition cc l is fulfilled for the values k 0.55. The Table 24 data showed that the last... 

In comparison to the behavior of flexible chain polymers we note that the viscosity dependence on y is similar. However, for flexible chain polymers of similar molecular weight, n is not highly y dependent. Hence, at processing conditions, n of LCP can be two to three orders of magnitude lower than that of flexible chain isotropic systems. Furthermore, isotropic polymer systems which exhibit pseudoplastic behavior at such low shear rates usually have values of Po two to three orders of magnitude higher than the values of r measured at low y for LCP. 

Whereas orientation and texture generated in flow take long periods of time (minutes) to relax, the stresses are found to relax in a matter of several seconds. In Figure 18 we have plotted shear stress versus time on cessation of flow. Here we see that the shear stress (it is plotted in Figure 18 as the reduced time dependent viscosity, n"/n ) relaxes faster with increasing y. However, by 7 = 10.0, it relaxes to zero in a time of less than 2 seconds. The normal stresses, which are plotted in figure 19 relax slower than the shear stresses which is what is observed for flexible chain polymers. The key point is that the time for the stresses to relax is much faster than would be expected based on a relaxation time determined from the flow curve or the time for relaxation of orientation. 

In Figure 3 we have presented the stress growth curves at 275°C obtained at several different shear rates. The ppearance of the first peak occurs at y values of about 1.0 sec." whi]. e the second peak appears at values of y of about 5.0 sec.". In flexible chain systems stress overshoot occurs at values of y similar to the reciprocal of the loni gst relaxation time (t). Based on the shear dependence of viscosity, t should be at le st 100 sec. and hence for shear rates of the order of 0.01 sec.", overshoot should be observed. Howeyer, we observe that values of y must be of the order of 1.0 sec." before overshoot is observed. Hence, we cannot associate the- overshoot with the relaxation processes which occur in flexible chain polymers. 

Blends based on longitudinal PLCs and flexible chain polymers have been the subject of many reports. A comprehensive list is not given here, but emphasis is placed on a few of the early papers [56-63]. The components of the blends should phase separate and the PLC are oriented during the processing and form a reinforcing, often fibrous component. The low viscosity of the nematic PLC components makes the blends readily processable. 

Cox and Merz [C20] have made the remarkable experimental observation that the non-Newtonian shear viscosity function of flexible chain polymers has the same form as the complex viscosity-frequency function, i.e.. 

Nakajima et al. [N2] and later researchers found that the Cox-Merz [C19] rule mentioned earlier for flexible chain polymer melts is not valid for filled polymer melts or elastomer. Generally, one has the inequality r (o) > r](7). The complex viscosity is considerably larger. 

The viscosity reduction in flexible chain polymers by addition of small amounts of liquid-crystalline polymers can, therefore, be reflected in the processing parameters. 

The dependence of no Ro polymer concentration c and molecular weight M provides another means to compare the properties of the pol3rmers studied here with the more familiar behavior of flexible chain polymers. For the latter, for example, the viscosity of concentrated solutions is given by the relational... 

The viscosity of PES decreases with an increase in shear rate. PES as a polymer consists of semi-rigid molecular chains which have a strong affect on rheological behavior. Hence, a decrease in the degree of apparent viscosity of PES is less than that of a flexible-chain polymer, but higher than a rigid-chain polymer, with increase in shear rate. 

The dependence of the intrinsic viscosity on the temperature for two polymers, PMBH and PM-12, in different solvents is shown in Fig. 3.6. The experiment shows that in solvents where the size of the macromolecules is smaller (less than the value of [q], curves 4-6), an increase in the temperature is accompanied by an increase in [q] and consequently the size of the macromolecules, as for flexible-chain polymers with improvement of the thermodynamic quality of the solvent The temperature coefficient of the viscosity for these dependences is positive and equal to din [q]/dT = 0.0064 0.(XX)4. On the contrary, in solvents where the intramolecular interaction causes the large size of the molecules— PMBH and PM-12 in chloroform—an increase in the temperature results in a decrease in [q], which is characterized by a negative temperature coefficient of the viscosity d In [q]/dT, whose average value for the dependences [Tj] = f(J) shown in Fig. 3.6 (curves 1-3) is 0.0030 0.0002. A similar decrease in the viscosity, characterized by a negative coefficient dln[q]/d7 of similar... 

Fig. 9.1. Generalized concentration dependence of the viscosity of solutions of polymers (the different points correspond to different polymers, where the most flexible-chain polymer is polycaproamide and the most rigid-chain polymer is poly-p-benzamide).

The transition from a power dependence with p 1 to a dependence with P 4.2 takes place for concentrations of 0.2-0.7%. This transition is usually correlated [20,21] with the formation of a fluctuation network of contacts. The value of P in this region is slightly lower than for solutions of flexible-chain polymers (5-6) this was previously indicated in [18, 23] and theoretically predicted in [25, 52]. A stronger dependence of t (c) with an exponent of 6.0 is observed for c > 6.5%. Similar figures were found in the literature 6.8 [17] and 5-8 [87], but for the entire range of c between c and c. Near c, heterophase fluctuations with random orientation of the macromolecules apparently have the determining effect on the rate of the increase in the viscosity with an increase in the concentration [69]. Traces of mesophase woe also found for c 0.5-1.0% lower than c, and an increase in the order parameter is mentioned in [25] beginning with c > 8/9 c. ... 

The viscosity of the mixture is thus almost equal to the viscosity of the LC components, which could not only indicate specific fiber formation of the disperse phase but also its emergence in the surface layers of flow. Practical grounds for a significant decrease in the viscosity of a macromolecular isotropic thamoplastic and the system as a whole arise as a result. We find that ultrathin fib of the LC polymer are also fibrillated, but in the matrix of a flexible-chain polymer. This protects the system from macrodecomposition to some degree and causes an increase in the strength of the matrix. Substances of the isotropic matrix-LC fibrils type can be considered composite materials with their characteristic mechanisms of intensification of the physical-mechanical properties. 

With increasing c, chain entanglements enforce reptational motion among the chains, requiring modification of equation (204). This effect occurs when cMocl > pM, where is a number characteristic of the flexible-chain polymer. In this range of concentration, rj is far greater than and the viscosity can be represented... 

Conformation of single-chain molecules, that is, statistical size and shape, is the most basic issue in polymer science in relation to excluded-volume effects and hydrodynamic interactions in flexible chain polymers. The M dependence of Rg, Aj, and Rh (traditionally related to intrinsic viscosity) has been a central issue, which can be measured by static and dynamic light scattering. These properties as well as the particle scattering... 

WOCI4 is combined with Ph Sn (ratio WOCI4 Plx Sn = 1 2) in 1,4-dioxane/benzene to afford poly(phenylacetylene) efficiently, whose reaches 1.1 x 10 ([77] 1.23 dL g ) and whose m-content is 7i% High polymer yields can be achieved even in the case of a high monomer/catalyst ratio, 1260. The viscosity index, a, of poly(phenylacetylene) formed by this catalyst was determined to be 0.61, indicating a sufficiently flexible chain. 

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