Polyethylene phase diagram

Fig. 1 Polyethylene phase-diagram solid state NMR data solid lines) according to [13]...

The basis for the separation is that when two polymers, or a polymer and certain salts, are mixed together in water, they are incompatible, leading to the formation of two immiscible but predominantly aqueous phases, each rich in only one of the two components [Albertsson, op. cit. Kula, in Cooney and Humphrey (eds.), op. cit., pp. 451 71]. A phase diagram for a polyethylene glycol (PEG)-Dextran, two-phase system is shown in Fig. 22-85. Proteins are known to distribute unevenly between these phases. This uneven distribution can be used for the selective concentration and partial purification of the products. Partitioning between the two phases is controlled by the polymer molecular weight and concentration, protein net charge and... 

Recalling the previous assertion that efficient fractionation requires liquid-liquid phase separation, we conclude that nitrobenzene and amyl acetate should be satisfactory solvents from which to fractionate polyethylene by successively lowering the temperature and that the better solvent xylene should be avoided for this purpose. The character of the phase diagram may, in fact, be used as a criterion of the efficacy of a given solvent for fractionation (see Chap. VIII, p. 344). If the curve representing the precipitation temperature plotted against concentration rises monotonically, crystalline separation is clearly indicated if it passes through a maximum at a low concentration, liquid-liquid separation is virtually assured, and the solvent may be assumed to be a satisfactory one to use for fractionation. 

The morphologies of various copolymers composed of polyethylene oxide), PEO, and poly (1,2-butylene oxide), PBut, were recently reviewed by Ryan et al. [61]. The corresponding phase diagrams of PEO-fr-PBut, PBut-fo-PEO-fo-PBut and PEO-fo-PBut-fo-PEO melts are depicted in Fig. 11. In all phase diagrams the semi-crystalline lamellar phase was not attained because of the copolymers low melting points. 

The system polyethylene glycol (PEG)-dextran-water is still the most used and best-studied aqueous polymer two-phase system. A phase diagram for a typical two-phase system is shown in Fig. 10.12 for the PEG-dextran system. Both polymers are separately miscible with water in all proportions. As the polymer concentration increases, phase separation occurs, with the... 

Fig. 10.12 Phase diagram and phase compositions of the dextran-polyethylene glycol system D 48-PEG 4000 at 293 K. All values are % w/w.

Diphasic liquid systems used in CCC may have a wide variety of polarities. The most polar systems are the ATPS made by two aqueous-liquid phases, one containing a polymer, for example, polyethylene glycol (PEG), the other one being a salt solution, for example, sodium hydrogen phosphate. The less polar systems do not contain water there can be two-solvent systems, such as heptane/acetonitrile or dimethylsulfoxide/hexane systems or mixtures of three or more solvents. Intermediate polarity systems are countless since any proportion of three or more solvents can be mixed. Ternary phase diagrams are used when three solvents are mixed together. 

Figure 20 shows the phase diagram of polyethylene119). The existence range of the condis crystals increases with pressure and temperature. The enthalpy of the reasonably reversible, first order transition from the orthorhombic to the hexagonal condis phase of polyethylene is 3.71 kJ/mol at about 500 MPa pressure 121) which is about 80 % of the total heat of fusion. The entropy of disordering is 7.2 J/(K mol), which is more than the typical transition entropy of paraffins to their high temperature... 

Fig. 20. Phase diagram of polyethylene. The difference between folded and extended chain crystal melting temperatures is largely a size effect (1 kbar = 100 MPa). Curve based on data of Ref. I19>...

The orthorhombic and hexagonal phases of polyethylene crystallize independently in accordance with the phase diagram and kinetic competition during growth. 

Aboofazeli, R., Lawrence, C. B., Wicks, S. R., and Lawrence, M. J. (1994), Investigations into the formation and characterization of phospholipid microemulsions. Part 3. Pseudo-ternary phase diagrams of systems containing water-lecithin-isopropyl myristate and either an alkanoic acid, amine, alkanediol, polyethylene glycol alkyl ether or alcohol as cosurfactant, Int. J. Pharm., Ill, 63-72. 

Chiu, G. Mandelkern, L., "Effect of Molecular Weight on the Phase Diagram of Linear Polyethylene in 1-Dodecanol," Macromolecules, 23, 5356 (1990). 

In situ polymerisation does not however guarantee homogeneous blends as two phase regions can exist within the polymer/polymer/monomer three component phase diagram. In the case of vinyl chloride polymerisation with solution chlorinated polyethylene, the vinyl chloride has limited solubility in both poly(vinyl chloride) and chlorinated polyethylene. The phase diagram has the form shown in Fig. 3 The limit of swelling of vinyl chloride in the chlorinated polyethylene is A and the highest concentration of PVC prepared by a one-shot polymerisation is B. 

Fig. 3. The three component phase diagram for vinyl chloride, PVC and a chlorinated polyethylene is A and the highest concentration of PVC in a homogeneous blend prepared by a one-shot polymerisation is B...

DSC and complimentary thermal techniques such as temperature X-ray powder diffraction were used to determine the thermodynamic relationship of the six anhydrous polymorphs of tetracaine hydrochloride. ° The phase diagram of the polymorphic conversion of diflunisal in polyethylene glycol 4000 solid dispersions was obtained as a fimction of polymer content. ... 

These are prepared by rapid solidification of the fused melt of two components that show complete liquid miscibility but negligible solid-solid solubility. Thermodynamically, such a system is an intimately blended physical mixture of its two crystalline components. Thus, the X-ray diffraction pattern of a eutectic constitutes an additive composite of the two components. A phase diagram of a two-component system is shown in Fig. 1. Examples of this type include phenacetin-phenobarbital, chloramphenicol-urea, griseofulvin-sucdnic acid, paracetamol-urea, and the dispersions of giiseofulvin and tolbutamide in polyethylene glycol-(PEG-2000).[ ... 

The phase diagram given in Fig. 21 for darodipine-polyethylene glycol 6000 results from DSC experiments carried out by two techniques. The DSC of physical mixtures obtained by grinding were scanned just after the end of melting. After cooling a second scan at 5Kmin was performed. In the second technique the mixtures were dissolved in methanol and the solvent evaporated. With both techniques, the same results were obtained. 

Figure 1. Phase diagram for high-density polyethylene/hydrocarbon systems.

The phase diagram of polyolefins and hydrocarbon diluents is exemplified for high-density polyethylene in Figure 1. When the polymer-diluent mixture is heated, dissolution of the semicrystalline polymer takes place along the borderline 1 (turbidity curve) [43, 44], This line depends on the polymer (e. g., polyethylene, isotactic polypropylene), average chain length, and copolymer composition. 

The phase diagram (see Figure 1) shows that there are two solution processes a low-temperature process (below 100 °C) for the production of amorphous copolymers like ethylene/propylene elastomers (EPR or EPM) [2], and a high-tempera-ture process (far beyond 100 °C) for the production of semicrystalline homo- and copolymers like high-density polyethylenes (PE-HD), linear low-density poly-ethylenes (PE-LLD) and ethylene waxes [1, 3]. Polypropylenes (PP) cannot be made in high-temperature solution processes, except for propylene waxes. 

Proteins, like any other molecule, have a certain solubility limit, above which an aggregated state (either amorphous or crystalline) is thermodynamically favored. The solubility of a protein as a function of some variable like temperature, pH, or the concentration of a precipitant such as salt or polyethylene glycol (PEG) may be represented with a phase diagram (Figure 4). 

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