Chains polyphenylene oxide

Aromatic cyclic chains are more stable than aliphatic catenated carbon chains at elevated temperatures. Thus linear phenolic and melamine polymers are more stable at elevated temperatures than polyethylene, and the corresponding cross-linked polymers are even more stable. In spite of the presence of an oxygen or a sulfur atom in the backbones of polyphenylene oxide (PPO), polyphenylene sulfide (PPS), and polyphenylene sulfone, these polymers are... 

Amide urethane, and ester groups in the polymer chain, such as those present in nylons and polyesters may be hydrolyzed by acids to produce lower-molecular-weight products. Polyacetals are also degraded by acid hydrolysis, but ethers, such as polyphenylene oxide (PPO), are resistant to attack by acids. 

Other macromolecules are formed by condensing their monomers to form a repeat functional group (e.g., esters, amides, ethers) interspersed by alkyl chains, aromatic rings, or combinations of both. These condensations are characterized frequently, although not always by the loss of some by product (e.g., water, alcohol). The methods of formation of these polymers are far more varied than those of addition polymers. Examples of condensation polymers are (a) poly(esters), (b) poly(urethanes), (c) poly (carbonate), and (d) polyphenylene oxide). 

Kambour et al. performed extensive studies on the mechanisms of plasticization [18-25]. The correlation observed between the critical strain to craze and the extent of the glass-transition temperature (Tg) depression speaks strongly in favor of a mechanism of easier chain motion and hence easier void formation. In various studies on polycarbonate [19,24], polyphenylene oxide [20], polysulfone [21], polystyrene [22], and polyetherimide [25], Kambour and coauthors showed that the absorption of solvent and accompanying reduction in the polymer s glass-transition temperature could be correlated with a propensity for stress cracking. The experiments, performed over a wide range of polymer-solvent systems, allowed Kambour to observe that the critical strain to craze or crack was least in those systems where the polymer and the solvent had similar solubility values. The Hildebrand solubility parameter S [26] is defined as... 

Spin relaxation in dilute solution has been employed to characterize local chain motion in several polymers with aromatic backbone units. The two general types examined so far are polyphenylene oxides (1-2) and aromatic polycarbonates (3-5) and these two types are the most common high impact resistant engineering plastics. The polymer considered in this report is an aromatic polyformal (see Figure 1) where the aromatic unit is identical to that of one of the polycarbonates. This polymer has a similar dynamic mechanical spectrum to the impact resistant polycarbonates (6 ) and is therefore an interesting system for comparison of chain dynamics. 

Figure 11.13 illustrates the effect of dioctyl phthalate on the clusters and matrix of polyphenylene oxide ionomer. As stated in Section 11.15.4, dioctyl phthalate, DOP, influences both the matrix polymer and ionic clusters. But the intensities of these effects are different. Up to about 10 wt% DOP, the matrix Tg rapidly decreases (DOP preferentially plasticizes polymer chains). Above 10 wt%, the Tg of both matrix and clusters decreases at similar rates. 

Techniques for chloromethylating polyarylether sulfones, polyphenylene oxide, phenolic resins, and model compounds were described recently [191]. When the subsequent products are cmiverted to quaternary amines, there is a decrease in the quatemization rate with increase in degree of substitutimi. This may be due to steric effects imposed by restricted rotation of the polymeric chains [191]. This phenomenon was not observed in quatemization of poly(chloromethyl styrene). The chloromethylation reaction of a polysulfone with chloromethyl ether, catalyzed by stannic chloride, can be illustrated as follows ... 

Another complication is that thin dense membrane films have been shown to decline in permeation properties over extended periods of time (10000hours) even without external stresses. The rate of ageing effect becomes greater the thinner the film [37]. This loss over extended time is presumably due to cast membrane films slowly reorienting polymer chains to achieve equilibrium properties with reduced free volume. The thin dense films used in these studies (0.4-25 pm) approach the same order of thickness as the active layer of cast asymmetric films at less than 2000 A (0.2 pm). The property appears common in that it was reported in this paper with polysulfone, polyphenylene oxide and polyimide... 

LC polyesters belong to the class of thermotropic main-chain LCPs, which also comprises polymers such as polycarbonates, polyethers, polyphenylenes, polyester-imides, polymers containing azo- or azo V-oxide linking groups, some cellulose derivatives, and polypeptides such as po 1 y (y - be n zy 1 -1. - g 1 u tamate). Both from the academic and industrial points of view, polyesters are by far the most important representatives of this class of polymers. 

The first conducting polymers (named ICPs for intrinsically conducting polymers, or ECPs for electroactive conducting polymers) were discovered in the seventies by McDiarmid, Heeger, and Shirakawa [1] who showed that unsaturated conjugated polymers (polyacetylene, polyphenylene) became conductive when doped, corresponding to the chemical oxidation of the ethylene or polyphenyl carbon chain. 

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