Forces Between Polymer Chains

Although bisphenol A polycarbonate is plasticized by a 30% concentration of dibutyl phthalate or dibenzyl sebacate (Table III), as has been reported (6, 7), a higher concentration is required for effectively plasticizing the polycarbonates of bisphenols I and II (Tables I and II). Perhaps the reason for this is the appreciably lower mobility of polymer chains containing bulky, three-dimensional, polycyclic structures than chains of the bisphenol A polycarbonate. So even though a plasticizer may weaken the secondary attraction forces between polymer chains,... 

Crystallinity is also favored by strong forces between polymer chains. In a nonpolar polymer such as polyethylene, the only forces holding the chains in place are van der Waals forces (see Section 2.5). Although these attractions are relatively weak, there are many of them, so their total force can be quite large. However, polymers with polar groups have stronger intermolecular forces and are more crystalline than nonpolar polymers, other factors being equal. 

For polymers k is of the order of 0.2Wm K This is much smaller than the 50Wm K for steel, due to the lack of free conduction electrons, and the weak forces between polymer chains. Steady-state conduction occurs through the foam-insulated wall of a domestic refrigerator the temperature at any point in the foam remains constant, however ... 

Chemical Cross-link The existence of a retaining force between polymer chains, brought about by covalent bonding. 

An existence of restraining force between polymer chains other than covalent braiding viz., entanglements, presence of microcrystaUinity, and glassy blocks in block copolymer. 

Figure 12.24 Using the Surface Forces Apparatus, the repulsive forces between polymer chains on both crossed cylinders, left, and one coated surface and one clean mica sheet, right, can be measured. Poly(ethylene oxide) anchors the nonadsorbing polystyrene chains to the mica, with toluene as the solvent.

A convenient practical measure of the intermolecular forces between polymer chains (hat might be used in selecting solvents for specific polymers is the solubility parameter. Solubility parameter 8 is related to the heat of vaporization, A//vap (cal/cm ), also a measure of the same intermolecular attractive force. The cohesive energy density c of a liquid is the energy needed to overcome intermolecular forces to separate the molecules from each other and is given by the expression... 

Thermal analysis using heated tip technology [115] has been reviewed by Price et al. [116], Wunderlich [117], Pollock and Hammiche [118], and Abad et al. [119]. Reviews on mechanical deformation of polymer films by nanoindentation [120] and AFM indentation [121] as well as in situ tensile deformation [122] have been published. A related area of force spectroscopy to extract intermolecular and intramolecular forces between polymer chains was reviewed by Hugel and Seitz in 2001 [123]. Bushan has written extensively on the use of SPM to study tribology [124], and frictional contrast has been discussed in reviews by Mate [125], Zasadzinski [126], and Feldman et al. [127]. Spatially localized adhesion studies using chemically modified AFM tips was reviewed in 2005 by Vezenov et al. [128] and Vancso et al. [129]. Characterization of polymer film surfaces [130,131], latexes [132,133], multiphase polymer blends [134, 135], and nanocomposites [136, 137] has also been reviewed. Authors from the laboratories of several manufacturers of industrial engineering polymers have published reviews on the application of SPM to characterization [138-140]. 

This is a much stronger plastic and has a higher melting temperature. Therefore HDPE can be used to make water pipes and containers that can be sterilised with boiling water. This demonstrates the importance of the intermolecular forces between polymer chains when considering the properties of polymeric materials. 

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