Ether chain, flexible

Poly(ethylene oxide). Although AH j is more than double that of polyethylene, the effect is offset by an even greater increase for AS j. The latter may be due to increased chain flexibility in the liquid caused by the regular insertion of ether oxygens along the chain backbone. 

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. 

The presence of ether linkages in the polymer molecule imparts chain flexibility, lowers glass transition temperature, and enhances solubility while maintaining the desired high temperature characteristics [192]. Recently, polyether imines were prepared by the reaction of different diamines with 4,4 -[l,4-phenylene bis(oxy)] bisbenzaldehyde [184]. The polymers synthesized by the solution method were yellow to white in color and had inherent viscosities up to 0.59 dl/g in concentrated H2SO4. Some of these polyimines can be considered as... 

A crystal structure of BOBCalixC6 [82] was made possible by the fact that the compound can be crystallized from certain solvents (Figure 4). As so often is the case for crown ethers, the flexible polyether chain twists in upon itself, and the cavity does not exist until a guest species such as Cs+ ion is present. 

The most well-known member of this class is the polyether, polyethylene oxide, whose complexes with lithium perchlorate have been used commercially in lithium batteries.60-62 The good solvating power of polyethylene oxide is attributed to an optimal spacing of the electron-donating ether oxygens along a flexible backbone that allows multiple contacts between the polymer backbone and cations. When this distance is decreased, as in polymethylene oxide, chain flexibility is greatly reduced when it is increased, as in 1,3-polypropylene oxide, the distance between... 

Ether (-C-0-C-) Chain flexibility, oxidative/hydrolytic stability (unless in Lewis acidic media), soluble in polar solvents (for small substituents)... 

Polyetherimide has a chemical structure based on repeating aromatic imide and ether units. High performance strength characterisitics at elevated temperatures are provided by rigid imide units, while the ether linkages confer the chain flexibility necessary for good melt processing and flow. 

It is well known that the connection of oligo(alkylene ether) chains into a calamitic rigid rod at the terminals destabilizes the thermotropic meso-phases [8]. However, mesomorphic properties can be obtained by molecules with extended rigid rod segments as a result of the microphase segregation between the polar flexible oligo(alkylene oxide) ethers and rigid rod seg-... 

As mentioned earlier, UV-curable resin formulations are very attractive for fiber coating because of the rapid cross-linking rates that are achievable. Most commonly, epoxy- or urethane-acrylate resins are employed (18-22), and viscosity and cross-link density are controlled through the addition of reactive diluents. With these systems work has focused on producing low modulus, low T properties (20-22) through the incorporation of appropriate chemical constituents to enhance higher chain flexibility, for example, ether linkages. 

Chain flexibility is determined by the ease with which rotation occurs about primary valence bonds. Polymers with low hindrance to internal rotation have low Tg values. Long-chain aliphatic groups — ether and ester linkages — enhance chain flexibility, while rigid groups like cyclic structures stiffen the backbone. These effects are illustrated in Table 4.1. Bulky side groups that are stiff and close to the backbone cause steric hindrance, decrease chain mobility, and hence raise Tg (Table 4.2). 

It was observed that the TBAPP-based polyimides derived from dianhydrides BPDA and BTDA were soluble in polar aprotic solvents. The high solubility of TBAPP-based polyimides was possibly governed by the structural modification through the incorporation of the flexible isopropylidene, increasing the overall chain flexibility, and methyl substituted arylene ether groups into the polyimide structure. It has been verified that polyimide derived from diamine DAM3 (Table 2.4) had less solubility than that derived from diamine TBAPP. This result clearly demonstrated that the tetramethyl substituents on the phenylene unit effectively improved the polymer solubility. It has been reported that methyl... 

Poly(sulfo-l,4-phenylene), or poly(p-phenylene sulfone), with the monomeric unit -(-SO2 —C6H44-> has a very high melting temperature of 520° C, and so can only be worked with difficulty. Products of good processability were only obtained after introducing ether groups which make the polymer chains flexible. 

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