Stability thermooxidative

Since the utility of these materials is improved by the incorporation of these reactive functionalities without severely decreasing other favorable properties such as thermooxidative stability and solvent resistance the chemistry of the isoimide isomerization and acetylene crosslinking reactions is of considerable interest. Previous work in our laboratory has shown that these materials, when loaded with metal powders, provide a convenient and effective method of optimizing the electrical conductance and thermal stability of aluminum conductor joints. 

Sundar and Keller have reported the synthesis of linear boron-silicon-diacetylene polymers (31) (Fig. 21) using phenylboron dichloride (PBD) as the source for boron.50 The compositions of the thermally stable boron-silicon-diacetylene copolymers 31a-d are summarized in Figure 21. These polymers were observed to possess exceptional thermooxidative stabilities. 

L. Rychla and J. Rychly, New concepts in chemiluminescence at the evaluation of thermooxidative stability of polypropylene from isothermal and non-isothermal experiments. In A. Jimenez and G.E. Zaikov (Eds.), Polymer Analysis and Degradation, Nova Science Publishers, New York, 2000 p. 124. 

It has been determined from X-ray diffraction measurements that polycarbonate containing Bisphenol AF moiety are all amorphous.6 The (Tg) of poly(carbonate)s increases with an increase in hexafluoroisopropylidene unit from 149°C for Bisphenol A poly(carbonate) (3) to 169°C for Bisphenol AF poly(carbonate) (2) (Table 9.3).6 Thermooxidative stability is also improved by the introduction of fluorine atoms into the isopropylidene units. The 10% weight-loss temperature (DT10) increases from 429 to 460°C and the residual weight (RW) at 500°C goes from 37 to 57% by perfluorination of the isopropylidene units. 

The thermooxidative stability is improved by increasing the hexafluoroiso-propylidene unit content.12 The DTi0 in air is raised from 363°C for Bisphenol A poly(formal) (6) to 398°C for Bisphenol AF poly(formal) (7), and the RW at 500°C is increased from 48 to 73%.12... 

Thermooxidative stability of the fluorine-containing poly(ether ketone) (11) and poly(sulfide ketone) (13) from 15 is very high. The 5% weight-loss temperatures (DT5) are 391 and 436°C for poly(ether ketone) and poly(sulfide ketone) analogues having no fluorine atoms, whereas those of poly(ether ketone) (11) and poly(sulfide ketone) (13) are higher than 500°C. 

The solubility, water and oil repellency, thermal and thermooxidative stability, and Tg are enhanced and crystallinity and water absorption are decreased by introducing hexafluoroisopropylidene units, rather than units ofisopropylidene, into polymer backbone of aromatic condensation polymers. 

Using Differential Scanning Calorimetric and Roentgen-phase analyses methods it has been established that synthesized polymers are amorphous systems. Thermal (phase) transformation temperatures of synthesized polymers have been determined. Thermooxidation stability of the synthesized polymers has been studied. There was shown that their thermooxidation stability exceeded the analogical characteristic of polyorganocarbosiloxanes. 

To improve the processability of PPQ, appropriate phenylquinox-aline oligomers were end-capped with acetylenic groups using 3-(3,4-diaminophenoxy)phenylacetylene (43) or 4-(3- and 4-ethynyl-phenoxy)benzil (44, 45) (Eq. 10). The processability was improved but at the sacrifice of the thermooxidative stability. In general, cured acetylene-terminated heterocyclic polymers are less stable in a thermooxidative environment than the parent linear polymer. 

In industrial practice temperature stability of a polymer means that it is able to maintain its mechanical properties up to a certain temperature and over a certain time period. Depending on the environmental conditions under which the thermal stability is measured one ftuther differentiates between two cases physical thermostability if the thermal treatment occurs in inert atmosphere and chemical thermostability if the thermal treatment is done, e.g., in the presence of air (thermooxidative stability). 

Replacing the hydrogen in 68 with a phenyl group leads to the secondary acetylenic monomer 70. It was believed that this disubstituted acetylene would suppress the reaction of acetylene with itself and insure that there was an acetylene functionality available for reaction with the o-quinodimethane at 200 °G The DSC of 68 showed the presence of a single exothermic peak at 263 °C which the authors felt was adequate evidence for the occurrence of a Diels-Alder reaction between the acetylene and benzocyclobutene. Unfortunately they did not report on any control experiments such as that between diphenylacetylene and simple benzocyclobutene hydrocarbon or a monofunctional benzocyclobutene in order to isolate the low molecular weight cycloaddition product for subsequent characterization. The resulting homopolymer of 68 had a Tg of 274 °C and also had the best thermooxidative stability of all of the acetylenic benzocyclobutenes studied (84% weight retention after 200 h at 343 °C in air). 

Somewhat greater improvements were found in the thermooxidative stability of the fluorinated materials, though the effect for most part was still only moderate with the greatest difference found to be about 40°C. These stability improvements were most notable when comparisons were made at the 2% index, and (in contrast to the anaerobic results) often became less pronounced at the 5 and 10% weight loss indexes. 

PFMB can be used to prepare aromatic polyimides that display solubility in ketone, ether, and polar aprotic solvents. This unusual solubility can be utilized in die facile preparation of thin films that display anisotropy in their structures and properties. The anisotropy in the optical properties of the films makes them promising candidates for use as compensation layers in liquid-crystal displays. Their low dielectric constants and CTEs in combination with their outstanding thennal and thermooxidative stabilities make diem candidates for dielectric layers in microelectronics applications. 

A PFMB-based polyimide (BPDA-PFMB) can be used to prepare fibers with mechanical properties comparable to those of commercial PPTA fibers. However, owing to superior thermooxidative stability, the fibers retain their properties for much longer periods of time when subjected to isothermal aging in air at elevated temperatures. In fact, BPDA-PFMB fibers retain their properties under these conditions better than any other available high-performance fiber. 

Polyphenylquinoxalines (PPQ) are easier to make than the polyquinoxalines and offer superior solubility, processibility, and thermooxidative stability (65). The PPQs exhibit excellent high temperature adhesive, composite, and film properties. However, to increase the use temperature of PPQs, acetylene... 

Triallyl cyanurate (TAC) and triallyl isocyanurate (TAIC) are used as crosslinking agents for methacrylates and UP resins to improve heat and solvent resistance as well as thermooxidative stability. 

In contrast to the preceding examples, polybenzimidazole (PBI 12a) resins couple an outstanding thermooxidative stability with a pronounced affinity for the active Mo complexes (241-243). 

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