One polymer in another

A block copolymer is expected to be superior to a graft copolymer in stabilizing dispersions of one polymer in another because there will be fewer conformational restraints to the penetration of each segment type into the homopolymer with which it is compatible. Similarly, diblock copolymers might be more effective than triblock copolymers, for the same reason, although tri- and multiblock copolymers may confer other advantages on the blend because of the different mechanical properties of these copolymers. 

The shear flow is inefficient for dispersing one polymer in another if they significantly differ in viscosity, especially when the viscosity ratio X 3.8. The elongational field is more proficient and rapid. On all accounts, viz. ... 

The properties of polymer mixtures depend on the method by which they are obtained and are determined by many factors by sizes of particles of the dispersed phase, by their shape and number in bulk, and by the thermodynamic affinity of the components for one another [19]. Linear polymers blend either in the course of their mutual dissolution or, in two-phase systems, under conditions of thermodynamic incompatibility of the components, when the dispersion is forced. The mixtures formed can be compatible (forming true solutions of one polymer in another), incompatible (representing a typical colloid system), quasicompatible (characterized by microscopic homogeneity at a level above heterogeneity on the molecular level), or pseudocompatible (with a strong adhesion interaction on the boundary) [106]. 

Although miscible blends of polymers exist, most blends of high-molecular-weight polymers exist as two-phase materials. Control of the morphology of these two-phase systems is critical to achieve the desired properties. A variety of morphologies exisL such as dispersed spheres of one polymer in another, lamellar structures, and co-continuous phases. As a resnlL the properties depend in a complex maimer on the types of polymers in the blend, the morphology of the blend, and the effects of processing, which may orient the phases by shear. 

In the discussion above, the limited solubility of one polymer in another was ascribed to the unusually low entropy of mixing. In a block copolymer, cone chain portion is attached to another, end on end. It is interesting to note the miscibility characteristics and morphology of these materials. 

The equations given above are usually referred to in books dedicated to polymer mixtures. However, the validity of these approaches is questionable, because the theory for regular solutions is used as a base for the theoretical consideration of polymer mixture and the solutions of one polymer in another. 

As was illustrated in Example 7.3c, AS for the dissolution of one polymer in another is extremely small. For this reason, the true solubility of one polymer in another is relatively rare, although many more examples have come to light in recent years. When such solubility does occur, it generally results from strong interactions (e.g., a large, negative AH), most often hydrogen bonds, between the polymer pairs. Polymer-polymer miscibility has been extensively reviewed [20,21]. 

Ignition will occur when both combustible gases and oxygen are available in sufficient quantity above the ignition temperature. The amount of oxygen required for ignition varies from one polymer to another. For example, in tin... 

To the left of the peak where the tubules have shorter lengths, c, i is less than Cii so the net flux is from i-mers to (i — l)-mers. To the right of the peak, the distribution of polymer length falls off, and c, i is greater than Cj. Therefore, the net flux will be in the opposite direction. The combined action of these fluxes wiU result in the broadening of the peak distribution. Eventually, the peak will completely disappear due to the relationships among the concentrations of each polymer species. In this respect, the initial polymer-protomer equilibrium is maintained by the balanced rates of protomer addition and loss from polymer ends, and the protomers will scramble or diffuse from one polymer to another. Indeed, even after the polymer length redistribution reaches its thermo-... 

Since radical polymerizations are generally carried out at moderately high temperatures, most of the resulting polymers are highly atactic. This does not mean that there is a complete absence of syndiotacticity. There is a considerable difference in the extent of syndiotacticity from one polymer to another. Thus, methyl methacrylate has a much greater tendency toward syndiotactic placement than vinyl chloride. Whereas the poly(vinyl chloride) produced at the usual commerical polymerization temperature ( 60°C) is essential completely atactic, that is, (r) (m) 0.5, this is not the case for poly(methyl methacrylate). The polymerization of MMA, usually carried out at temperatures up to 100°C, yields polymers with appreciable syndiotacticity—(r) is 0.73 at 100°C. The difference is a consequence of the fact that MMA is a 1,1-disubstituted ethylene, leading to greater repulsions between substituents in adjacent monomer units. 

Experimental data on branched polystyrenes were used to test the theory. There are some discrepancies in particular the parameter A varies from one polymer to another, especially for comb-shaped polymers y> also varies. It is suggested that the reason for the discrepancies in A may be the failure of the assumption of a Gaussian distribution of segment density. 

Values of Mc (and Me and Mc ) are found to vary widely from one polymer to another, although the variations are much smaller (ca 50%) when comparisons are made in terms of r., the number of chain bonds per molecule at Mc. Fox and Allen (245) have pointed out that the variations are reduced still... 

One advantage of this method is that the enzyme is in contact with any particular substrate molecule for a short time only, and so can be used in cases in which the enzyme slowly hydrolyzes or chemically transforms the ligand. Another advantage is that some available gels are able to distinguish between the size of one polymer and another, so that, for example, the binding of a tRNA (Mr = 25 000) to an aminoacyl-tRNA synthetase (Mr = 100 000) may be measured. 

Figure 3.16 Ionic electrical conductivity for solutions of lithium triflate in solid poly[fc (methoxyethoxyethoxy)phosphazene] ( MEEP ) is believed to occur following coordination of the etheric side groups to Li+ ions, cation-anion separation, ion transfer from one polymer to another as the polymer and side groups undergo extensive thermal motions. From Shriver and Farrington, Chem. Eng. News, 1985, 42-57 (May 20). Reprinted by permission of the American Chemical Society.

Another practical approach to the question of moldability, especially in comparing one polymer with another, is the use of a standard spiral mold cavity and the measurement, under prescribed molding conditions, of the spiral length filled (7). 

This article discusses size and charge data for nanoparticles produced in both batch and continuous processes from two different polymer systems. In both systems, a polyanionic solution is atomized into a swirling bath of polycationic solution, forming nanoparticles as the solutions come together. This method of mixing solutions used to produce the nanoparticles is often referred to as titration (sequential addition of one polymer into another). Different ratios of polyanion to polycation were used to vary the composition of the nanoparticles, which were then evaluated for their size and charge. 

In some cases of the titration of one polymer with another one (polymers are complementary, i.e. they contain groups, which are capable to interact specifically, e.g. poly(acrylic add) and the copolymer of N-vinylpyrrolktone and acrylic add) no inflection point on the titration curves were observed. Therefore, the titrations do not indicate the interaction in PAA-VP/AA system, in contrast to systems composed of poly(methacrylic acid) and the copolymer N-vi nylpyrrolidone and acrylic add221 (Fig. 2). Apparently, subtle differences in the chemical structure of components predetermine the possibility or impossibility of complex formation, which is an evidence for a high selectivity of the polymer-polymer interactions. Even when one of the components is a low molecular compound (Fig. 1, curve 1), complex formation is not observed. Interpolymer complexes can be divided into several types, due to the kind of the dominating interaction ... 

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