Aromatic homopolymer

As briefly outlined in the introductory section, configurational and ensemble averages for an adequate description of EET in an aromatic homopolymer have not been solved so far. From a more qualitative point of view, however, the concepts of diagonal disorder and dispersive excitation energy transport - as applied to condensed... 

The neady symmetrical composition of SBI-PC (T = 230° C) makes birefringence disappear iu homopolymers, but the material becomes very britde due to the blocking of the free rotation of the aromatic rings, which puts its technical appHcation iu question. Only a copolymerization with 80 wt BPA-PC reaches sufficient levels of impact resistance but T is lowered to 170°C and birefringence iucreases to 80% of that of BPA-PC (195,196). In contrast, TMC-PC as a homopolymer already has sufficient impact resistance at a T of 238°C and a birefringence of 83% of that of BPA-PC (195,205) (Table 7). 

Vulcanizates of ECH homopolymer and ECH—EO copolymer are resistant to ASTM oils, aUphatic solvents, and aromatic-containing fuels, showing low swell after exposure. The polymers do not harden after exposure to these fluids, although plasticizer may be extracted. Overall, these polymers offer a good balance of heat, ozone, and fuel resistance over a broad temperature range. 

As it will be shown the presence of an aromatic amino group in the macromolecule of modified PAN offers new possibilities for graft copolymers without the formation of a homopolymer. 

Aromatic polyesters that do not contain any flexible structural units are often nonmeltable or extremely high melting polymers that cannot be processed. Copolymerization is a way to obtain processable wholly aromatic polyesters The Tm versus copolyester composition curve is a U-shaped curve exhibiting a minimum that is generally well below the Tm of corresponding homopolymers. Liquid crystalline aromatic polyesters, for instance, are usually copolymers.72 An example is Ticona s Vectra, a random copolyester containing 4-oxybenzoyl and 6-oxy-2-naphthoyl units in ca. 70 30 mol ratio. This copolymer melts at ca. 

C and is easily processable, whereas the homopolymers do not melt before the onset of thermal degradation, at temperatures as high as 500°C.73,74 Varying copolymer composition permits the adjustment of melting temperature and of other properties (e.g., solubility) to desired values. This method is frequently used for aliphatic and aromatic-aliphatic polyesters as well. 

The range of properties of polymers can be greatly extended and varied by copolymerization of two or more monomers. The effects of radiation on copolymers would be expected to show similarities to the homopolymers, but major differences from linear relationships are often experienced. Aromatic groups in one monomer frequently show an intramolecular protective effect so that the influence of that monomer may be much greater than its mole fraction. The Tg of a copolymer is normally intermediate between the homopolymers, except for block copolymers, and this can cause a discontinuity in radiation degradation at a fixed temperature. 

Modern life and civilization opened the way to other important practical applications of heterocycles, for example dyestuffs, copolymers, solvents, photographic sensitizers and developers, and in the rubber industry antioxidants and vulcanization accelerators. Some of the sturdiest polymers, such as Kevlar, have aromatic rings. Melamines (2,4,6-triamino-substituted s-triazines) are monomers with numerous applications as both homopolymers and copolymers. Scheme 9 shows a few examples of compounds with various applications in our daily life, having in common the same building block, the aromatic s-triazine. 

Several wholly aromatic polyesters are available. As expected, they are more difficult to process, stiffer, and less soluble, but are employed because of their good high-thermal performance. Ekonol is the homopolymer formed from p-hydroxybenzoic acid ester (structure 4.51). Ekonol has a Tg in excess of 500°C. It is highly crystalline and offers good strength ... 

The general correlations of structure and properties of homopolymers are summarized in Table 2.13. Some experiments which demonstrate the influence of the molecular weight or the structure on selected properties of polymers are described in Examples 3-6 (degree of polymerization of polystyrene and solution viscosity), 3-15, 3-21, 3-31 (stereoregularity of polyisoprene resp. polystyrene), 4-7 and 5-11 (influence of crosslinking) or Sects. 4.1.1 and 4.1.2 (stiffness of the main chain of aliphatic and aromatic polyesters and polyamides). 

Basu et al. (2004) reported a series of amphiphilic homopolymers in which the hydrophUic moiety is a carboxylic acid moiety and the hydrophobic moiety can be based on either an alkyl chain or an aromatic ring (Chart 2.7). These polymers self-assemble into either micelles or reverse micelles, depending on the solvent environment. Figure 2.7 represents the formation of a micellar assembly in a polar... 

When MCA is copolymerized with MMA, the resulting copolymer etches faster than PMMA, consistent with the PMCA and MCN/MCA results. Incorporation of MCA, a monomer with a-chlorine, has the effect of decreasing plasma etch resistance, as is observed for the MCA homopolymer. Sensitization by chlorine appears to be general (see Tables I, III, and VI), except for the case where the chlorine is Incorporated onto the aromatic side chain group. This effect was observed previously by Taylor and Wolf for other polymer systems. ( ) The C-Cl bond strength is lower than that for C-H and C-F, and there is much evidence that this bond can be easily cleaved, even in the solid state. (, ) This weaker side chain group leads to lower dry-etch resistance. 

Copolymers. Studies of the radiation sensitivities of amino acid homopolymers highlight the protective effect of aromatic substituents in the amino-acid side-... 

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