Polyethylene weak interactions

It has been outlined by several authors that the single macromolecule may be irreversibly bound because of the large number of weakly interacting segments. The first papers on the construction of polymer-coated silica adsorbents involved the physical adsorption of water-soluble polymers. Polyethylene oxides [28, 29] and poly-/V-vinylpyrrolidone [30] are examples of the stationary phases of this type. 

Several theoretical studies have been carried out on a phenomenological basis to justify the idea that a dynamic slip can indeed occur [43-45]. New experimental techniques and theoretical treatments must be developed to reveal the molecular origin of dynamic slip and characteristic time scales governing the dynamic processes in the melt/wall interfacial region. Our own experiments on polyethylenes [27-29] have persistently indicated that slip, either through chain desorption on weakly interacting surfaces or interfacial chain disentanglement... 

New properties arise when the molecular sizes increase to the dimensions of the phase, as for example in the case of a typical polyethylene of 500,000 Da. It has a contour length of 2.8 pm and can easily cross microphase boundaries. This ttaversing of the surface makes neighboring phases interact sttongly, in contrast to the weak interactions by intermolecular forces (see Fig. 1.5). 

Concentration-independent diffusion results when inert gases diffuse in most polymers (Crank and Park, 1968 Duda and Vrentas, 1971) at sorbed concentrations of <0.2 wt%. In addition, this behavior is observed for water diffusing in some hydrophobic polymers, such as polyethylene and polypropylene (Rehage et al., 1970). Thus, only weak interactions exist between penetrant and polymer. 

A recent example of the composition dependence of Xsc for a weakly interacting blend PE/dPE of hydrogenated and deuter-ated polyethylene and for a weakly interacting copolymer blend HPB(97)/DPB(88) of hydrogenated and deuterated statistical copolymer of linear and branched C4 units derived from polybutadienes (PB) with vinyl content percentages indicated, is presented in Figure 12. Marked composition dependence only occurs at the composition boundaries. 

Some vinyl silanes were found to act feasibly as weakly interacting comonomers. Functional copolymers with ethylene and vinyl-Si(CH3)3, aUyl-Si(CH3)3,3-butenyl-Si(CH3)3, 4-pentenyl-Si(CH3)3, 5-hexenyl-Si(CH3)3 or 7-octenyl-Si(CH3)2Ph as comonomers were polymerized [23-25]. The short trialkylsilane monomers suffered from the electroific influence of sihcon, which led to poor polymerization performance. In these cases, the chain end of the S3mthesized polyethylene-co-allyl-Si (CH3)3 consisted of reactive allyhc silane groups and therefore the functionality and reactivity of these copolymers was higher than the weakly interacting trimethylsUane moiety can provide. Also it was found that the phenylene group in... 

The forces which contribute to complex formation between PE and proteins are mainly coulombic ion-ion, ion-dipole and dipole-dipole interaction. It has been reported that the interaction between proteins and non electrical charged polymers like the polyethylene glycol family involves very weak interaction forces of the type Van der Waals, judging by the low interaction heat involucrated in the interaction [5]. Pico et al. [48] found enthalpic changes associated to the... 

The way in which these factors operate to produce Type III isotherms is best appreciated by reference to actual examples. Perhaps the most straightforward case is given by organic high polymers (e.g. polytetra-fluoroethylene, polyethylene, polymethylmethacrylate or polyacrylonitrile) which give rise to well defined Type III isotherms with water or with alkanes, in consequence of the weak dispersion interactions (Fig. S.2). In some cases the isotherms have been measured at several temperatures so that (f could be calculated in Fig. 5.2(c) the value is initially somewhat below the molar enthalpy of condensation and rises to qi as adsorption proceeds. In Fig. 5.2(d) the higher initial values of q" are ascribed to surface heterogeneity. 

The majority of physisorption isotherms (Fig. 1.14 Type I-VI) and hysteresis loops (Fig. 1.14 H1-H4) are classified by lUPAC [21]. Reversible Type 1 isotherms are given by microporous (see below) solids having relatively small external surface areas (e.g. activated carbon or zeolites). The sharp and steep initial rise is associated with capillary condensation in micropores which follow a different mechanism compared with mesopores. Reversible Type II isotherms are typical for non-porous or macroporous (see below) materials and represent unrestricted monolayer-multilayer adsorption. Point B indicates the stage at which multilayer adsorption starts and lies at the beginning of the almost linear middle section. Reversible Type III isotherms are not very common. They have an indistinct point B, since the adsorbent-adsorbate interactions are weak. An example for such a system is nitrogen on polyethylene. Type IV isotherms are very common and show characteristic hysteresis loops which arise from different adsorption and desorption mechanisms in mesopores (see below). Type V and Type VI isotherms are uncommon, and their interpretation is difficult. A Type VI isotherm can arise with stepwise multilayer adsorption on a uniform nonporous surface. 

Nonpolar molecules such as ethane H(CH2CH2)H and polyethylene (CH2CH2) are attracted to each other by weak London or dispersion forces resulting from induced dipole-dipole interactions. The temporary dipoles in ethane or along the polyethylene chain are due to instantaneous fluctuations in the density of the electron clouds caused by constant motion of electrons about the nucleus with the homogeneity upset by similar electron movement about the other nucleus. The energy of these forces is about 2 kcal per mole of repeating unit in nonpolar and polar polymers alike, and this force is independent of temperature. These dispersion forces are the major forces present between chains in many elastomers and soft plastics. 

Schreiber and co-workers have noted very persistent history effects in linear polyethylenes (69). Fractions which have been crystallized from dilute solution required times of the order of hours in the melt state at 190° C in order to attain a constant die swell behavior upon subsequent extrusion. The viscosity on the other hand reached its ultimate value almost immediately. The authors concluded from this result that different types of molecular interactions were responsible for elastic and viscous response. However, other less specific explanations might also suffice, since apparent viscosity might be relatively intensitive to the presence of incompletely healed domain surfaces, while die swell, requiring a coordinated motion of the entire extrudate, might be affected by planes of weakness. It would... 

Adsorption of block copolymers onto a surface is another pathway for surface functionalization. Block copolymers in solution of selective solvent afford the possibility to both self-assemble and adsorb onto a surface. The adsorption behavior is governed mostly by the interaction between the polymers and the solvent, but also by the size and the conformation of the polymer chains and by the interfacial contact energy of the polymer chains with the substrate [115-119], Indeed, in a selective solvent, one of the blocks is in a good solvent it swells and does not adsorb to the surface while the other block, which is in a poor solvent, will adsorb strongly to the surface to minimize its contact with the solvent. There have been a considerable number of studies dedicated to the adsorption of block copolymers to flat or curved surfaces, including adsorption of poly(/cr/-butylstyrcnc)-ft/od -sodium poly(styrenesulfonate) onto silica surfaces [120], polystyrene-Woc -poly(acrylic acid) onto weak polyelectrolyte multilayer surfaces [121], polyethylene-Wocfc-poly(ethylene oxide) on alkanethiol-patterned gold surfaces [122], or poly(ethylene oxide)-Woc -poly(lactide) onto colloidal polystyrene particles [123],... 

The properties of elastomeric materials are greatly influenced by the strong inter-chain, i.e., intermolecular forces which can result in the formation of crystalline domain. Thus the elastomeric properties are those of an amorphous material having weak inter-chain interaction and hence no crystallisation. At the other extreme of polymer properties are fibre-forming polymers, such as Nylon, which when properly oriented lead to the formation of permanent crystalline fibres. In between these two extremes is a whole range of polymers, from purely amorphous elastomers to partially crystalline plastics, such as polyethylene, polypropylene, polycarbonate, etc. 

Figure 3.28 shows the P-T diagram for four polyethylene-low molecular weight hydrocarbon mixtures. The cloud point pressures decrease substantially with increasing carbon number, or conversely polarizability, as a result of increased dispersion interactions between polyethylene and the solvent. Free volume differences between polyethylene and the hydrocarbons also decrease as the carbon number is increased. Even though ethane and ethylene have virtually identical polarizabilities, the cloud point curve with ethane is at a much lower pressure than that with ethylene, since the quadrupole moment of ethylene enhances ethylene-ethylene interactions relative to ethylene-polyethylene interactions because polyethylene is a nonpolar polymer. The two cloud point curves for polyethylene with propane and propylene are virtually identical. Evidently, the quadrupole moment for propylene is weak enough that propylene-propylene polar interactions do not substantially influence the strong dispersion interactions between polyethylene and each of these two solvents of virtually identical polarizabilities. 

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