Poly polarity

Just as de l ati es of methAiolphenols can be obtained by joint reactions of phenols with formaldehyde and ariou.s polar compounds, complex resiiis can be obtained when the polar compounds are di- or poly-polar. Thk may be illustrated by the formation of amine-resins from phenol, formaldehyde, and non-aromatic primary amines as described by Harmon and Meig. This reaction is contrasted below with a similar reaction in olv-ing a secondary amine which is monopolar. 

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... 

The cured polymers are hard, clear, and glassy thermoplastic resins with high tensile strengths. The polymers, because of their highly polar stmcture, exhibit excellent adhesion to a wide variety of substrate combinations. They tend to be somewhat britde and have only low to moderate impact and peel strengths. The addition of fillers such as poly (methyl methacrylate) (PMMA) reduces the brittleness somewhat. Newer formulations are now available that contain dissolved elastomeric materials of various types. These mbber-modifted products have been found to offer adhesive bonds of considerably improved toughness (3,4). 

Polymer Ferroelectrics. In 1969, it was found that strong piezoelectric effects could be induced in the polymer poly(vinyhdene fluoride) (known as PVD2 or PVDF) by apphcation of an electric field (103). Pyroelectricity, with pyroelectric figures of merit comparable to crystalline pyroelectric detectors (104,105) of PVF2 films polarized this way, was discovered two year later (106.)... 

Synthesis and Properties. Several methods have been suggested to synthesize polyimides. The predominant one involves a two-step condensation reaction between aromatic diamines and aromatic dianhydrides in polar aprotic solvents (2,3). In the first step, a soluble, linear poly(amic acid) results, which in the second step undergoes cyclodehydration, leading to an insoluble and infusible PL Overall yields are generally only 70—80%. 

Poly(phenylquinoxaline—arnide—imides) are thermally stable up to 430°C and are soluble in polar organic solvents (17). Transparent films of these materials exhibit electrical insulating properties. Quinoxaline—imide copolymer films prepared by polycondensation of 6,6 -meth5lene bis(2-methyl-3,l-benzoxazine-4-one) and 3,3, 4,4 -benzophenone tetracarboxyUc dianhydride and 4,4 -oxydianiline exhibit good chemical etching properties (18). The polymers are soluble, but stable only up to 200—300°C. 

Polymer—polymer iacompatibiHty encapsulation processes can be carried out ia aqueous or nonaqueous media, but thus far have primarily been carried out ia organic media. Core materials encapsulated tend to be polar soHds with a finite degree of water solubiHty. EthylceUulose historically has been the sheU material used. Biodegradable sheU materials such as poly(D,L-lactide) and lactide—glycoHde copolymers have received much attention. In these latter cases, the object has been to produce biodegradable capsules that carry proteias or polypeptides. Such capsules tend to be below 100 p.m ia diameter and are for oral or parenteral administration (9). 

Heat-reactive resins are more compatible than oil-soluble resins with other polar-coating resins, such as amino, epoxy, and poly(vinyl butyral). They are used in interior-can and dmm linings, metal primers, and pipe coatings. The coatings have excellent resistance to solvents, acids, and salts. They can be used over a wide range of temperatures, up to 370°C for short periods of dry heat, and continuously at 150°C. Strong alkaUes should be avoided. 

N-Alkylpyrroles may be obtained by the Knorr synthesis or by the reaction of the pyrrolyl metallates, ie, Na, K, and Tl, with alkyl haUdes such as iodomethane, eg, 1-methylpyrrole [96-54-8]. Alkylation of pyrroles at the other ring positions can be carried out under mild conditions with allyhc or hensylic hahdes or under more stringent conditions (100—150°C) with CH I. However, unless most of the other ring positions are blocked, poly alkylation and polymerisation tend to occur. N-Alkylation of pyrroles is favored by polar solvents and weakly coordinating cations (Na", K" ). More strongly coordinating cations (Li", Mg " ) lead to more C-alkylation. 

Dynamic membranes are concentration—polarization layers formed in situ from the ultrafiltration of coUoidal material analogous to a precoat in conventional filter operations. Hydrous zirconia has been thoroughly investigated other materials include bentonite, poly(acryhc acid), and films deposited from the materials to be separated (18). 

Poly(vinyhdene chloride) also dissolves readily in certain solvent mixtures (82). One component must be a sulfoxide or A/,Al-diaIk5lamide. Effective cosolvents are less polar and have cycHc stmctures. They include aUphatic and aromatic hydrocarbons, ethers, sulfides, and ketones. Acidic or hydrogen-bonding solvents have an opposite effect, rendering the polar aprotic component less effective. Both hydrocarbons and strong hydrogen-bonding solvents are nonsolvents for PVDC. 

Solubility. Poly(vinyl alcohol) is only soluble in highly polar solvents, such as water, dimethyl sulfoxide, acetamide, glycols, and dimethylformamide. The solubiUty in water is a function of degree of polymerization (DP) and hydrolysis (Fig. 4). Fully hydrolyzed poly(vinyl alcohol) is only completely soluble in hot to boiling water. However, once in solution, it remains soluble even at room temperature. Partially hydrolyzed grades are soluble at room temperature, although grades with a hydrolysis of 70—80% are only soluble at water temperatures of 10—40°C. Above 40°C, the solution first becomes cloudy (cloud point), followed by precipitation of poly(vinyl alcohol). 

All these elastomers, especially poly(ethylene- (9-butylene) and poly(ethylene- (9-propylene), are nonpolar. The corresponding block copolymers can thus be compounded with hydrocarbon-based extending oils, but do not have much oil resistance. Conversely, block copolymers with polar polyester or polyether elastomer segments have Htde affinity for such hydrocarbon oils and so have better oil resistance. 

Fig. 11. In a system of water and hydrocarbon a nonionic emulsifier with a poly(ethylene glycol) chain as the polar part dissolves in the aqueous phase at low temperatures (a) and in the oil phase at high temperatures (c). At an intermediate temperature (b) three isotropic Hquid phases may be found.

It has, however, been possible to find solvents for some polar crystalline polymers such as the nylons, poly(vinyl chloride) and the polycarbonates. This is because of specific interactions between polymer and solvent that may often occur, for instance by hydrogen bonding. 

In the case of polar polymers the situation is more complex, since there are a large number of dipoles attached to one chain. These dipoles may either be attached to the main chain (as with poly(vinyl chloride), polyesters and polycarbonates) or the polar groups may not be directly attached to the main chain and the dipoles may, to some extent, rotate independently of it, e.g. as with poly(methyl methacrylate). 

When dipoles are directly attached to the chain their movement will obviously depend on the ability of chain segments to move. Thus the dipole polarisation effect will be much less below the glass transition temperature, than above it Figure 6.4). For this reason unplasticised PVC, poly(ethylene terephthalate) and the bis-phenol A polycarbonates are better high-frequency insulators at room temperature, which is below the glass temperature of each of these polymers, than would be expected in polymers of similar polarity but with the polar groups in the side chains. 

Poly(vinyl chloride) has a good resistance to hydrocarbons but some plasticisers, particularly the less polar ones such as dibutyl sebacate, are extracted by materials such as iso-octane. The polymer is also resistant to most aqueous solutions, including those of alkalis and dilute mineral acids. Below the second order transition temperature, poly(vinyl chloride) compounds are reasonably good electrical insulators over a wide range of frequencies but above the second order transition temperature their value as an insulator is limited to low-frequency applications. The more plasticiser present, the lower the volume resistivity. 

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