Polymethylene groups

Table I shows tensile properties of selected co-PEAs, all containing Lys(Bz) units at 25% of total di-amine monomers. The tensile property data showed that 8-Leu(6)o.75 -Lys(Bz)o.25 was the weakest of the co-PEA samples tested. Decrease in the length (y) of polymethylene groups in the diacid monomer I, or the incorporation of phenylalanine increased the tensile strength of the resulting co-PEAs. Following a general trend, shortening the polymethylene chain in the diol or diacid caused a decrease of film elasticity and increased the Young s modulus (2.5 GPa). The tensile strength can be further increased by processing conditions that induce molecular orientation...

Chemically Modified Waxes. Hydrocarbon waxes of the microcrystaHine, polyethylene, and polymethylene classes are chemically modified to meet specific market needs. In the vast majority of cases, the first step is air oxidation of the wax with or without catalysts (11). The product has an acid number usuaHy no higher than 30 and a saponification number usuaHy no lower than 25. An alternative step is the reaction of the wax with a polycarboxyHc acid, eg, maleic, at high temperature (12). Through its carboxyl groups, the oxidised wax can be further modified in such reactions as saponification or esterification. Oxidised wax is easily emulsified in water through the use of surfactants or simple soaps, and is widely used in many coating and poHsh appHcations. 

It is reasonable to consider that in an ester group the in-chain ether link —C—O—C— increases the chain flexibility compared with a polymethylene chain to decrease the heat of fusion. At the same time there will be some increase in interchain attraction via the carbonyl group which will decrease the entropy of fusion. Since these two effects almost cancel each other out there is almost no change in melting point with change in ester group concentration. 

With all six series of polyester illustrated in Figure 25.14, as the number of methylene groups in the repeating unit increases so the polymer becomes more like a linear polyethylene (polymethylene). Thus the melting points for five of the six classes are seen to converge towards that of the melting point of polymethylene. In the ca.se of the sixth class, the poly(alkylene adipates), there would appear no reason to believe that additional data on other specific members of the class would not lead to a similar conclusion. 

FFKM perfluororubbers of the polymethylene type, having all substituent groups on... 

Like the polymethylene hydrocarbons, acyclic carbohydrates and alditols tend to adopt the planar, zigzag conformation wherein all of the carbon atoms lie in the same plane. " However, non-bonded interactions between parallel hydroxyl groups in the 1,3 positions (sy/i-axial interaction) are the most highly destabilizing, and, in xylitol and ribitol, this... 

This analysis of hindrances to rotation is oversimplified even for a polymethylene chain. However, with the tacit assumption that only interactions between atoms or groups directly connected to the C—C bond under consideration affect the value of 0, the hindrance potential should be symmetrical about 0 = 0 regardless of the precise nature of the interactions. That is to say, the repulsion for an angle 0 should be the same as for —0. When this is true, the resultant of bond (3) in Fig. 74 (p. 400) averaged over all angles 02, each angle occurring with a probability proportional to can be resolved into two... 

The family of polymers that we refer to as nylons consists of molecules composed of amide groups alternating with short runs of methylene units. These molecules are also known as polyamides, which may be shortened to PA. The generic chemical structure of a nylon molecule is shown in Fig. 23.1. Variations on this basic structure include the length of the polymethylene sequences and the orientation of the amide groups relative to their neighbors. Figure 23.2 shows the chemical structures of nylon 6 and nylon 66, which are the two most common types of nylon. 

Nylon molecules contain short, non-polar, polymethylene sequences and polar amide groups. The ratio of the polar to non-polar components strongly influences the properties of the polymer. We can envisage a vast number of polymers that fall into the class of nylons, but... 

Fig. 13 Log EAZ-values for the formation of (O) catechol polymethylene ethers [2] and ( ) benzo-crown ethers [20] in 99% Me2SO at 25°C plotted against the number of single bonds, r, in the chain connecting the end-groups. (Data from Illuminati et al., 1981)...

The simple pictorial interpretation of the gem-dimethyl effect presented by Dale (1963, 1966) was based on the idea that the ease of cyclisation depends more on the conformation of the open-chain reactant than on the tension in a resulting strained ring. According to Dale (1963), a polymethylene chain tends to be straight zig-zag but, when substituted by a methyl group, it does not matter for the neighbouring C—C bond whether the chain itself or the methyl group continues in the trans-position hence the probability of a bent... 

In a model study aimed at elucidating the behavior of the polymers, Watanabe found that the dimer polymethylene diol diesters of type 7 (Figure 8.18) formed smectic phases.38 When the spacer between the two mesogenic units in the dimer had an odd number of methylene groups (diester 7 has nine methylenes in the spacer), then an intercalated tilted smectic structure with all anticlinic layer interfaces was formed. This structure is often termed SmC2 in the literature. As for the B6 phase, all of the layer interfaces in this structure are equivalent, and the X-ray layer spacing is less than half the fully... 

A wide variety of groups B separating the reactive sites have been employed. Apart from the aromatic ring shown for 100, a polymethylene chain and a bulky sugar alcohol derivative as in 102 have been used (174). 

Methoxy groups are also formed on the surface of silica by the action of diazomethane. This reaction was first described by Berger (232) and Ebert (233). Boehm and Schneider (1S8) found that methylation was somewhat incomplete when etheric diazomethane solutions were used. More methoxy groups were formed with gaseous diazomethane. However, polymethylene was formed as a by-product and explosions occurred occasionally. 

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