Dissimilar chains

Starting from simple statistical considerations concerning the coupling between similar or dissimilar chains, a model was constructed for the architecture of a class of IPN where interaction among phases occurs on a molecular level. It was shown(Equation 13) that the contributions to the modulus due to crosslinks are subject to linear additivity, while a square root additivity rule holds for the contributions due to entanglements. 

There are several types of collagen. In one type, two identical chains of one kind are coiled together with a third dissimilar chain to form the triple helix. Several of these triple helices associate to form 8-nm microfibrils (Fig 2-23D).199 Once synthesized, collagen is extensively modified and crosslinked. See Chapter 8. 

Each collagen molecule contains three polypeptide chains coiled around each other in a triple helix. These chains are called a-chains and are designated by Roman numerals according to the chronological order of their discovery. The three polypeptide chains may be identical or may consist of two identical chains and one dissimilar chain. 

Table 6. Effect of Dissimilar Chain Extenders In TPU Blends.

A different approach was used by Milner [326] in order to predict the phase diagram for asymmetric copolymer architectures (for example A2B, A3B etc. types of miktoarm stars). The free energy of the system can be calculated by summing the free energies of the polymer brushes existing on the two sides of the interphase. Milner described the effects of both chain architecture (i.e., number of arms) and elastic (conformational) asymmetry of the dissimilar chains, in the strong segregation limit, by the parameter... 

As for secondary processes that occur during grafting, their behavior in blends should also differ from that of homopolyolehns. In addition to side reactions typical of homopolymers, cross reactions between dissimilar chains are possible in blends. 

Wu, S., Entanglement, friction, and free volume between dissimilar chains in compatible polymer blends, J. Polym. Sci. Polym. Phys., 25, 2511-2529 (1987). 

Vhaliin a lipophosphoprotein present in egg yolk tr ether with Phosphovitin (see). It is present in a higher concentration than phosphovitin, but in contrast to this phosphorus-tich protein, V. contains only 1 % phosphate. M yolk, and in neutral salt solutions, V. exists as a dimer (M, 380,000 16-22% lipid). The monomer (JIf, 190,000) consists of two dissimilar chains (L, M, 31,000 Lj, M, 130,000) only L, contains phosphate. 

There are several factors that are either not included or assumed to be unimportant in the Stockmayer-Kennedy theory. Hydrodynamic interactions between two chains in a block copolymer are not included in the theory. This can be a serious omission, especially when dealing with low-molecular-weight diblock copolymers, such as the SI diblock copolymers considered above. Intermolecular (thermodynamic) interactions between chemically dissimilar chains are also neglected. Inclusion of such interactions can be important, especially when the chemical affinity between two chemically dissimilar chains is rather poor, such as the case in the SI diblock copolymers considered here. In Chapter 7, which discusses the rheology of miscible polymer blends, we pointed out the importance of the segmental interaction parameter in the prediction of the linear... 

Wu, S., Entanglements between dissimilar chains in compatible blends poly(methyl methracrylate) and poly (vinyhdine flouride). /. Polym. Sci.-Phys. (1987) 25, pp. 527-566 [50] Plazek,D. J., Tan, V, O Rourke, U. M. Creep behavior ofideaUy atactic and commercial poly(methyl methacrylate) Rheol Acta (1974) 13, pp. 875-884... 

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