Entanglement physical

The overlap concentration c is that concentration where contacts between the polymer chains occur, c depends on molecular weight the higher M is, the smaller is c. At c > c, the polymer chains form an entanglement (physical) network with elastic properties. It can be destroyed by adding solvent. 

P. van Loock and A. Fumsawa. Detecting genuine multipartite continuous-variable entanglement. Physical Revew A 2003 May 29 67(5) 052315(13). 

Solvents exert their influence on organic reactions through a complicated mixture of all possible types of noncovalent interactions. Chemists have tried to unravel this entanglement and, ideally, want to assess the relative importance of all interactions separately. In a typical approach, a property of a reaction (e.g. its rate or selectivity) is measured in a laige number of different solvents. All these solvents have unique characteristics, quantified by their physical properties (i.e. refractive index, dielectric constant) or empirical parameters (e.g. ET(30)-value, AN). Linear correlations between a reaction property and one or more of these solvent properties (Linear Free Energy Relationships - LFER) reveal which noncovalent interactions are of major importance. The major drawback of this approach lies in the fact that the solvent parameters are often not independent. Alternatively, theoretical models and computer simulations can provide valuable information. Both methods have been applied successfully in studies of the solvent effects on Diels-Alder reactions. 

The foregoing equations all express the multiphase viscosity as a function of the solids content, without any recourse to liquid parameters. A more realistic portrayal of the physical situation would include the fluid dynamic picture that compensates for entanglement and absorbed liquids carried along with the solid phase, thus effectively decreasing the liquid volume. An equation applicable to this case is [24] ... 

Interaction with plurivalent cations via ligand exchange mechanism is one more rather widely applied crosslinking technique. The network bonds of ionic or donor-acceptor nature are located, with respect to lifetime, between the truly covalent crosslinks and physical entanglements. Generally speaking, gelation in these systems is reversible. 

The results of these four groups of investigators present, at least for the present author, a bewildering and scarcely understandable diversity in the interactions of furan with arenediazonium ions. Where is the physical organic or theoretical chemist who will accept the challenge to unravel this entanglement It is not surprising to... 

The model was tested against solution polymerization data for MMA reported by Schulz and Haborth (11). The minimization of error in fitting the model to the data resulted in negative values for a. This is physically unrealistic, and suggests that the model needs modification. Further work is intended which will refine the choice of initial condition for application of the model and/or change the inverse dependency of on entanglement density to power greater than unity. 

In Equation 1, t is a thermal vibration frequency, U and P are, respectively activation energy and volume whereas c is a local stress. The physical significance and values for these parameters are discussed in Reference 1. Processes (a)-(c) are performed with the help of a Monte-Carlo procedure which, at regular short time intervals, also relaxes the entanglement network to its minimum energy configuration (for more details, see Reference 1). 

Through physical interactions such as entanglements, electrostatics, and crystallite formation... 

Simple physical entanglements can be sufficient to produce a structurally stable gel if the polymer has a sufficiently great molecular weight and if the polymer is of only modest hydrophilicity. In this case, the polymer will swell in water without dissolving, even in the absence of covalent cross-links. Poly(2-hydroxyethyl methacrylate) (PHEMA) is a prominent example of this type of hydrogel when uncross-linked, it will dissolve in 1,2-propanediol but only swell in water. 

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