Interchain cohesion

Our results show for the first time the effect of antiplasticization-plasticization on polymer properties at the molecular level. These results provide experimental evidence for the assumptions of Robeson (20) and Kinjo (18) that attributed the changes in polymer properties with antiplasticization-plasticization to changes in the interchain cohesion of the polymer. 

The irregular intervals between linking amide units, 6 carbons between amide nitrogens staggered with the 10-carbon diacid units, confers a somewhat lower interchain cohesion to the product. As a result nylon 6,10 has a slightly lower melting point of 215°C. 

Structural and compositional factors, the most fundamental of which are chain stiffness and interchain cohesive forces. These factors will be discussed further in Section 6.B. 

A polymeric micelle is a macromolecular assembly that forms from block copolymers or graft copolymers, and has a spherical inner core and an outer shell (1). As shown in Fig. 1 in which an AB type block copolymer is used, a micellar structure forms if one segment of the block copolymer can provide enough interchain cohesive interactions in a solvent. Most studies of polymeric micelles both in basic and applied aspects have been done with AB or ABA type block copolymers... 

The diffusivity D is a kinetic parameter related to polymer mobility, while the solubility coefficient is a thermodynamic parameter which is dependent upon the strength of the interactions in the polymer-penetrant mixture. Chemical modifications of polymers affect the coefficients of diffusion and of solubility. Changes in material structure have a greater effect on diffusion coefficient, whereas the solubility coefficient depends mainly on the character of the low-molecular-mass compound. Permeability is determined by factors such as the magnitude of the free volume, and crosslinking which reduces the segmental mobility and the free volume and diminishes the permeability coefficient. A reduction of interchain cohesion and of crystallinity increases the permeability coefficient. The transition from the amorphous to the crystaUine state usually decreases the permeability. A decrease in crystallinity may increase the permeability. The permeability of polymers is determined primarily by the amount of the amorphous phase [62,300, 301]. 

Isoharic (constant pressure) and isochoric (constant volume) glass transitions in polymers were first observed for bisphenol A polycarbonate (62). A molecular dynamics study of such transitions in a model amorphous polymer has also been reported (63). This study shows that the glass transition is primarily associated with the freezing of the torsional degrees of freedom of polymer chains (related to chain stiffness), which are strongly coupled to the degree of freedom associated with the nonbonded Lennard-Jones potential (related to interchain cohesive forces). 

Structural and Compositional Factors. As was discussed at a sufficient level of detail earlier in this article, the major structural and compositional factors are chain stiffness and interchain cohesive forces. See the sections titled Key Physical Aspects, Fundamental Considerations, Quantitative Structure-Property Relationships, and Detailed Simulations. ... 

Within families of similar polymers, increasing chain stiffiiess and interchain cohesion increase the glass transition temperature. Copolymers may have one or multiple Tg s, depending on the ordering of monomers along the chain. The glass transition temperatures of eopolymers may be higher, lower, or in between those of the homopolymers of their eomonomers. 

Polyesters in general have less intermolecular cohesion (less interchain nonbonding interactions) than polyamides so that poly(ethylene terephthalate) (PET) is the only polyester, which is commercially useful as a fiber. This polymer can be prepared by direct polyesterification of terephthalic acid with 1,2-ethane diol (ethylene glycol), usually with the help of a strong acid catalyst... 

The cohesive energy Ecoij of a material is the increase in the internal energy per mole of the material if all of its intermolecular forces are eliminated [1,2]. The cohesive energy density ecoh> which is defined by Equation 5.1, is the energy required to break all intermolecular physical links in a unit volume of the material. In polymers, these physical links mainly consist of interchain interactions of various types, which will be discussed below. 

The fundamental equation of state central to GIM is a modified Lennard—Jones potential function which describes the interaction energy between adjacent polymers, E. This function has powers of 6 and 3 instead of the normal 12 and 6 because volume, V, is proportional to the square of the interchain separation distance, r. In a polymer, the chain length is significantly larger than r and is therefore assumed to be invariant. coh refers to the zero point cohesive energy and Vq is the zero point volume. 

The high cohesive energy density (H bonding) of PAs (Figure 4.2), which directs an efficient polymer interchain packing along with a rigid polymer backbone, results in poor processability and limits their applicability. 

The effects of chain stiflftiess and cohesive forces on the value of Tg are different from each other. The intrachain effect of the stiffness of individual chain segments is generally (hut not always) somewhat more important than the interchain effect of the cohesive (attractive) forces between different chains in determining the value of Tg. 

More recently, new quantitative structure-property relationships for Tg have been developed (1) they are based on the statistical analysis of experimental data for 320 linear (uncross-linked) polymers collected from many different sources, containing a vast variety of compositions and structural features. The Tg of the atactic form was used, whenever available, for polymers manifesting different tac-ticities. The Tg values of a subset of the polymers listed in this extensive tabulation are reproduced (with some minor revisions) in Table 1. (It is important to caution the reader here that these data were assembled from a wide variety of sources. Many different experimental techniques were used in obtaining these data.) The resulting relationship for Tg has the form of a weighted sum of structural terms mainly taking the effects of chain stiffness into account plus a term proportional to the solubility parameter S which takes the effects of cohesive interchain interactions in an explicit manner, as shown in equation (1) ... 

Table 12 lists the properties of this PI with those of PMDA-TFDB for comparison. In spite of the presence of electron-withdrawing -CF3 substituents, the maintained reactivity of TFDB is most likely based on the m a-substitution onto benzidine. If the (7r /i(7-substituted diamine counterpart was used, it must be difficult to obtain high molecular weight PAA in the conventional way because of its expected much lower reactivity. The transmission spectra of a series of TFDB-based Pis in Fig. 58 indicate how the 6FDA-TFDB polyimide film is optically transparent. A secondary positive effect of the -CF3 substituents in TFDB on the film transparency is the weakened intermolecular cohesive force due to lower polarizability of the C-F linkage. This functions negatively to interchain CTC formation. 

In addition to the well-established molecular relaxations, the TSC spectrum shows a weak / relaxation, ascribed to rotation of trace amounts of absorbed water, and a weak [3 relaxation, a dielectric signal that may correspond to translational mobility of charges, hindered sidechain motions, or even structural relaxation effects [see, e.g., Muzeau et al. (1995) Kalogeras (2004). The a relaxation has a peak at = 110 °C, near the DSC Tg (Kalogeras and Neagu 2004). The intrachain effect of the stiffness of individual chain segments is—at least in the case of PMMA and some other poly(n-alkyl metharylate)s— more important than the interchain effect of the cohesive (attractive) forces... 

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