Crystallinity polymer solubility

Bao, Z., et al. 1993. Conjugated liquid-crystalline polymers—Soluble and fusible poly(phenylene-vinylene) by the Heck coupling reaction. Macromolecules 26 5281. 

Polyoxyethylene. Synthetic polymers with a variety of compositionaHy similar chemical stmctures are as follows. Based on polarity, poly(oxymethylene) (1) would be expected to be water soluble. It is a highly crystalline polymer used in engineering plastics, but it is not water-soluble (see... 

A more interesting example is given with PVC and the polycarbonate of bis-phenol A, both slightly crystalline polymers. It is noticed here that whilst methylene dichloride is a good solvent and tetrahydrofuran a poor solvent for the polycarbonate the reverse is true for PVC yet all four materials have similar solubility parameters. It would seem that the explanation is that a form of hydrogen bonding occurs between the polycarbonate and methylene dichloride and between PVC and tetrahydrofuran (Figure 5.7). In other words there is a specific interaction between each solvent pair. 

In the case of crystalline polymers better results are obtained using an amorphous density which can be extrapolated from data above the melting point, or from other sources. In the case of polyethylene the apparent amorphous density is in the range 0.84-0.86 at 25°C. This gives a calculated value of about 8.1 for the solubility parameter which is still slightly higher than observed values obtained by swelling experiments. 

As is typical for crystalline polymers incapable of specific interactions with liquids, there are no solvents at room temperature but liquids which have a similar solubility parameter (8 = 22.4 MPa ) will cause a measure of swelling, principally in the amorphous region. ... 

Materials of these types have T s of some 290-300°C and some grades are claimed to be stable to about 400°C. Whilst resistant to hydrocarbons, halogenated hydrocarbons, ethers and acids the polymers are soluble in such materials as dimethylformamide, N-methylpyrrolidone and pyridine. Bases can cause stress cracking. These non-crystalline polymers are tough at temperatures as low as -46°C whilst at 260°C they have the strength shown by PTFE at room temperature. The polymers also exhibit excellent electrical insulation properties. 

Aromatic polyesters constitute an important class of main-chain liquid-crystalline polymers, but present the inconvenience of their reduced solubility and very high transition temperatures (sometimes not detected before the degradation of the sample). Their processability can be improved in several ways [2,3], e.g., reduction of the rigidity of the mesogen, lengthening of the spacer, or introduction of lateral substituents. 

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

Advanced computational models are also developed to understand the formation of polymer microstructure and polymer morphology. Nonuniform compositional distribution in olefin copolymers can affect the chain solubility of highly crystalline polymers. When such compositional nonuniformity is present, hydrodynamic volume distribution measured by size exclusion chromatography does not match the exact copolymer molecular weight distribution. Therefore, it is necessary to calculate the hydrodynamic volume distribution from a copolymer kinetic model and to relate it to the copolymer molecular weight distribution. The finite molecular weight moment techniques that were developed for free radical homo- and co-polymerization processes can be used for such calculations [1,14,15]. 

These opposing tendencies may defeat the purpose of the fractional precipitation process. The fractional precipitation of crystalline polymers such as nitrocellulose, cellulose acetate, high-melting polyamides, and polyvinylidene chloride consequently is notoriously inefficient, unless conditions are so chosen as to avoid the separation of the polymer in semicrystalline form. Intermediate fractions removed in the course of fractional precipitation may even exceed in molecular weight those removed earlier. Separation by fractional extraction should be more appropriate for crystalline polymers inasmuch as both equilibrium solubility and rate of solution favor dissolution of the components of lowest molecular weight remaining in the sample. 

The derivation of the quantitative relationship between this equilibrium temperature and the composition of the liquid phase may be carried out according to the well-known thermodynamic procedures for treating the depression of the melting point and for deriving solubility-temperature relations. The condition of equilibrium between crystalline polymer and the polymer unit in the solution may be restated as follows ... 

The curves of Figs. 133 and 134 may be regarded as plots of solubilities against temperature. It must be borne in mind however, that the dissolved phase is interspersed with the crystalline phase when polymer is present in excess of its solubility limit. Even in the more dilute solutions from which the crystalline polymer may settle out, the precipitate will contain some amorphous polymer and diluent. In short, these curves are useful primarily in defining the maximum amount of polymer which may be totally dissolved as a function of the temperature. 

According to Flory (10), the concept that proteins and carbohydrates are polymeric goes back to at least the work of Hlasiwetz and Habermann (11). In 1871 they proposed that these substances were made up of a number of species differing from one another with respect to the degree of molecular condensation. Flory also noted that Hlasiwetz and Habermann differentiate "soluble and unorganized" members of these substances, for example dextrin and albumin, from "insoluble organized" members, such as cellulose or keratin. This distinction is the precursor of the present day differentiation between non-crystalline and crystalline polymers. 

The third poly(aryl ether) surveyed as a coblock for polyimide copolymerization was poly(aryl ether ether ketone), PEEK, which is a highly crystalline polymer (40-50 % crystallinity) with a Tg of 145 °C and a Tj of 340 °C. However, PEEK is only soluble in diphenylsulfone at temperatures in excess of 300 °C or in strong acids [50]. This insolubility in organic solvents makes the synthesis and... 

Microcellnlar foams are reported to offer superior mechanical properties, while retaining the insulation properties of conventional foams. Low gas solubility resulting from the rigidity of the crystal lattice has precluded their production in semi-crystalline polymers, but a new process is said to have been experimentally proven in PP. Aspects covered include production difficulties, experimental details, results and conclusions. USA... 

Crystalline polymers exhibit the following basic properties They are opaque as long as the size of the crystallites or spherulites, respectively, lies above the wavelength of light. Their solubility is restricted to few organic solvents at elevated temperature. The following crystalline polymers have attained technical importance as thermoplastic materials polyethylene, polypropylene, aliphatic polyamides, aliphatic/aromatic polyamides, aliphatic/aromatic polyesters, poly-oxymethylene, polytetrafluoroethylene, poly(phenylene sulfide), poly(arylene ether ketone)s. 

The trans-poly-1,4-butadiene isomer is a harder and less soluble rigid crystalline polymer than the cis isomer. As shown by the skeletal structures for the trans isomer (Figure 1.11), chain extensions on opposite sides of the double bonds allow good fitting of adjacent polymer chains, and this, results in a rigid structure. In contrast, the os-poly-1,4-butadiene isomeric polymer units do not permit such interlocking of alternate units. Even so, chain... 

Crystalline polymers are less soluble below the Tm than amorphous... 

Crystalline polymers are much less soluble than amorphous polymers at temperatures below the melting point (Tm). Cross-linked polymers may swell but will not dissolve. 

The solubility of gases (Sg) in crystalline polymers, Sx, can be estimated from the extent of crystallinity,... 

Solubility. Cross-linking eliminates polymer solubility. Crystallinity sometimes acts like cross-linking because it ties individual chains together, at least well below T Thus, there are no solvents for linear polyethylene at room temperature, but as it is heated toward its Tm (135°C), it dissolves in a variety of aliphatic, aromatic, and chlorinated hydrocarbons. A rough guide to solubility is that like dissolves like, ie, polar solvents tend to dissolve polar polymers and nonpolar solvent dissolve nonpolar polymers. 

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