Intermolecular entanglement

All solutions were stored for 60 days before use. This delay was necessary for accurate results since Narkis (10) had already shown that poly(l-amidoethylene) solutions are not molecularly disperse until 54 days after preparation. These solutions age by losing intermolecular entanglements and becoming monomolecular solutions (10). Poly( 1-amidoethylene) solutions are known to lose viscosity with time (11). Several authors have attributed this viscosity loss to oxygen or radical degradation of the polymer (11), but Francois (12) has shown that changes in viscosity only... 

The viscosity behavior of poly[(a-carboxymethyl)ethyl isocyanide] may be studied in neutral organic solvents. The concentration dependence of its reduced specific viscosity in 1,2-dichloroethane is shown in Fig. 11. A linear dependence indicates that the coefficients of higher concentration terms of the usual virial equations are negligibly small—a case which should be found with molecules, such as stiff rods, that give few intermolecular entanglements in dilute solution. 

The critical concentration c (Bouldin) denoting the onset of intermolecular entanglements and c (Graessley), which describes the transition from a semi-dilute to a concentrated solution, are of no interest in the field under consideration due to the fact that the applied concentrations are far smaller in every case. 

In nondilute polymer solutions and melts, the polymer coils interpenetrate each other enough that the molecular motions of one chain are greatly slowed by the interfering effects of other chains. These interferences are attributed to intermolecular entanglements. 

The solution of a polymer in a good solvent, e.g. PS in toluene or PEA in methyl ethyl ketone (MEK), has a high viscosity because the chains are extended and undergo intermolecular entanglement. Solution in a poor solvent, e.g. PS in MEK or PEA in toluene, has a lower viscosity because the chains are coiled and undergo intramolecular rather than intermolecular entanglement. 

Conventional Linear ASTs. The increase in viscosity that occurs on neutralization of certain types of carboxylated copolymers in aqueous media is a well-known phenomenon, and the earliest theoretical descriptions of the process are still substantially accepted (28-30). In the generalized case for linear polymers forming true solutions, as pH is raised and carboxyl groups are neutralized, the polymer molecules become hydrated, and their molecular coils expand because of electrostatic repulsion of the carboxyl-anion charge centers. This coil expansion results in dissolution and an increase the polymer s hydrodynamic dimensions, which in turn increases intermolecular entanglement and resistance to flow. The increase in solution viscosity that occurs in this process is referred to as hydrodynamic thickening . 

Therefore, the conformation of the complex In the rapidly mixed system is presumed to consist of three structural parts the normal single helix (A), the side-by-side associated helices (B) and the entangled packet around Intermolecular junction (C). Thereby, the C part Includes the subsidiarily created junction by intermolecular entanglement In the complexatlon besides the authentic junction existing in uncomplexed amylose. The complex in the slowly mixed system Is composed of two structural parts for amylose with DP less than 1000 and three structural parts for higher DP amylose the normal single helix (A), a braided double helix (A ) and the entangled packet around Intermolecular junction (C). 

Real networks always contain molecular imperfections, such as pendant chains bound to the network at one end only, intramolecular loops formed by linking of two units of the same chain, and intermolecular entanglements. For an imperfect tetrafunctional network Hory [4,65] proposed a simple formula for correction for pendant chains... 

The Constrained Junction Fluctuation Model. The affine and phantom models are two limiting cases on the network properties and real network behavior is not perfectly described by them (recall Fig. 29.2). Intermolecular entanglements and other steric constraints on the fluctuations of junctions have been postulated as contributing to the elastic free energy. One widely used model proposed to explain deviations from ideal elastic behavior is that of Ronca and Allegra [34] and Hory [36]. They introduced the assumption of constrained fluctuations and of affine deformation of fluctuation domains. 

Composition of the Binary Solvent The composition of the binary solvent system used for making dope solution has been shown to have a great influence on the structure and properties of the fiber. The values of maximum draw ratio and tenacity are found to be influenced by the quality of solvent used for dry spinning. Draw-ability of the fibers increases at an optimum intermolecular entanglement of the polymer chains, which occurs at a particular solvent composition of 0 = 0.6 (40 60 chloroform toluene). 

Figure 9. Plot of log viscosity + constant vs. log MW + normalization constant for a series of synthetic polymers, illustrating the generic behavior of polymers with MWs above and below the critical DP required for intermolecular entanglement and network formation. (Reproduced with permission from reference 10. Copyright 1980 John Wiley Sons.)...

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