Polyethers thermal transitions

Figure 6. Thermal transition temperatures (T = melting, = isotropization) versus n, the number of methylene units in the polymers containing 4,4 -dihydroxybiphenyl for 1) polyethers ( ) esters (A) T, (A) T. (data from reference 25).

Table 1. Properties and Thermal Transitions of 2,4 TDI Based Polyether Polyurethanes and Polyether Polyurethaneureas...

C—S—C) in the main chain. The new polyethers prepared either by new heteroarylene activated or by aromatic activated systems have good melt processability. The thermal stability and glass transition temperature of bisphenol-A based new polymers are shown in Table 10. 

Much attention has been paid to the synthesis of fluorine-containing condensation polymers because of their unique properties (43) and different classes of polymers including polyethers, polyesters, polycarbonates, polyamides, polyurethanes, polyimides, polybenzimidazoles, and epoxy prepolymers containing pendent or backbone-incorporated bis-trifluoromethyl groups have been developed. These polymers exhibit promise as film formers, gas separation membranes, seals, soluble polymers, coatings, adhesives, and in other high temperature applications (103,104). Such polymers show increased solubility, glass-transition temperature, flame resistance, thermal stability, oxidation and environmental stability, decreased color, crystallinity, dielectric constant, and water absorption. 

Most of the liquid crystalline main-chain polymers synthesized are polyesters. For the present study where isothermal phase transition kinetics studies should be performed, this was a less suitable alternative since they undergo thermally induced reactions, i. e. transesterifications, and for this reason instead polyethers were chosen. Polyethers also have other advantages like lower transition temperatures and higher solubilities. 

Organometallic polyurethanes containing backbone polyether units have been reported.184,185 The incorporation of ferrocenyl segments into the backbone of polyurethanes enhanced thermal stability.186 There have been a number of studies on the incorporation of ferrocenyl units into the backbone of polyesters 101.187-191 A number of polymers of this class exhibited liquid crystalline properties.189-192 The thermal stability and glass transition temperatures of these polymers decreased with an increase in the length of the alkyl chains. 

Additional TMDSC study of other vinyl polysiloxane, polyether and polysulfide impression materials is important to verify if the polymer transitions shown in Figures 16 to 19 generally exist in different products and to investigate the effects of other temperature modulation conditions. Complementary research on correlations with clinically relevant mechanical properties of the elastomeric impression materials is needed to verify if these thermal analyses have useful predictive power. Interestingly, when compared at apparently similar viscosities, the reported values of the elastic modulus [3] are highest for the vinyl polysiloxane silicone impression materials, intermediate for the polyether impression materials, and lowest for the polysulfide impression materials, in reverse order to the relative values of Tg fovind in our thermal analyses [45]. Our X-ray diffraction and scanning electron microscopic study [47] of these impression materials has shown that they contain substantial amounts of crystalline filler particles in the micron size range, which are incorporated by manufacturers to achieve the clinically desired viscosity levels. Tliese filler particles should have considerable influence on the mechanical properties of the impression materials. 

Noryl, for example, is composed of polystyrene, an inexpensive polymer, and polyfphenylene oxide) or PPO, a relatively expensive polyether. For the most, the properties of Noryl are additive. For example, Noryl has poorer thermal stability than the polyether alone, but is easier to process. Its single glass transition temperature increases with increasing polyether content. In terms of tensile strength, however, the polyblend is synergistic. 

The polyether sulfones are amorphous and have high glass transition temperatures of between 190 and 290° C. They have good creep behavior, dielectric properties, and thermal and hydrolytic resistance. They are suitable for use in engineering parts, electrical components, as pan and saucepan coatings, and also for the removal of salt from seawater when used in membrane form as sulfonated products. 

If we consider the ester groups as being part of the mesogen, then the transition temperatures for the polyesters are shifted with two more carbons to the right side of Figure 7. This will depress the transition temperatures and enlarge the mesophase thermal stability range for the polyethers even more. For the polyester with seven methylene units in the spacer, the data... 

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