Monomers, thermal behavior

One of the complexities in the direct study of the PMR cure is the superposition of monomer isomerization on the polymerization chemistry of interest. To ensure our ability to dissect these two kinds of processes, we first studied the thermal behavior of each of our model compounds in the absence of any polymer forming process in dilute solution. 

Interestingly, it should not be assumed that a polymer will be useless above its ceiling temperature. A dead polymer that has been removed from the reaction media will be stable and will not depolymerize unless an active end is produced by bond cleavage of an end group or at some point along the polymer chain. When such an active site is produced by thermal, chemical, photolytic, or other means, depolymerization will follow until the monomer concentration becomes equal to [M]c for the particular temperature. The thermal behavior of many polymers, however, is much more complex. Degradative reactions other than depolymerization will often occur at temperatures below the ceiling temperature. 

Prior to the polycondensation, the thermal behavior of the salt monomers was investigated in some detail. Figure 1 shows the DTA and TG curves of salt monomer 12PMA consisting of dodecamethylenediamine and pyromellitic acid, which are typical for the aliphatic-aromatic salt monomers (see Eq. 5, X=12, Ar=PM, and R=H) [24]. 

Very recently, Placek and Szocs have reported the ESR study of radicals generated in monomer-free PMMA at low temperatures by y-irradiation They have shown the thermal behavior of several types of radicals above 100 K [45]. There is no essential difference of spectral assignment between their results and the present ones, except that they incorrectly assigned the singlet spectrum due to the anion radical as being due to acyl-type radicals. 

The latest vinylferrocene monomer / -C5H4CH202CC(CH3) = CH2 rj -C5H4CH = C(CN)C02Et Fe 15 that undergoes radical polymerization has been prepared as shown in Scheme 10-3 [17] Copolymerization of the monomer with methyl methacrylate produced copolymer 16, via radical initiation using AIBN in benzene. The ethyl a-cyanoacrylate moiety on the ferrocene remained intact through the polymerization process. The thermal behavior of 16 was similar to that of polymethyl methacrylate glass transition temperature, 7 120 °C, melt transition... 

In general, pyrolysis of poly(methacrylic acid derivatives) have a thermal behavior similar to those of the corresponding poly(acrylic acid derivatives). However, the amount of monomer is typically higher for the methacrylic series. 

Finally, we performed similar experiments for the various copolymers. As shown in Figure 12 for one of the copolymers, despite a large (70%) decrease in excimer intensity, the thermal behavior is qualitatively identical, and an Arrhenius plot of the monomer intensity data. Figure 13, gives the same activation energy, vl30-150cm . ... 

Characterization. Infrared spectra of bisdichloromaleimide monomers and polymers in KBr pellets were recorded, using a Perkin-Elmer 180 spectrophotometer. Elemental analyses were provided by Huffman Laboratories. Mass spectra were recorded at 70 eV on a Hewlett-Packard MS 5980 instrument by the direct inlet procedure. A DuPont 990 thermal analyzer was used to evaluate thermal behavior of bisdichloromaleimide monomers and polymers. Reduced viscosity of the polymers was determined in DMF at 30°C with a Cannon viscometer. Thermal polymerization was studied by heating a known weight of the material from room temperature to the desired temperature in a glass tube. The extent of curing was evaluated by extraction with DMF at room temperature. 

Table 1. Mesogen Monomers and Their Thermal Behaviors...

Flame-retardant textiles are textiles or textile-based materials that inhibit or resist the spread of fire. Factors affecting flammability and thermal behavior of textile include fiber type, fabric construction, thermal behavior of textile polymer and its composition as well as the presence or absence of flame additives. On the other hand, flame-retardant additives can be classified by their chemical composition or by mode of action, i.e., gas phase action or by the formation of protective barrier [49, 50]. Moreover, flame-retardant functional finishes of cellulose-based textiles can be accomplished by [i] using inorganic phosphates, (ii) with organophosphorous compounds, [iii) with sulfur-derivatives or (iv) by grafting flame retardants monomers [49,50]. 

A more detailed study of thermal behavior using both differential thermal (DTA) and thermogravimetric (TGA) analysis gave results that indicate a different aspect of thermal stability (Table 7.4). In ordinary PVC, HCl is eliminated at about 300 C, with depolymerization at about 450-460 C. The latter endotherm was found to be unchanged by the presence of monomer, stabilizer, or plasticizer or by irradiation. However, the dehydrochlorination endotherm (Thci) was quite sensitive to all these factors. The addition of plasticizer and stabilizer alone raised irradiation of such controls had no further effect. In the presence of polyfunctional monomer. 

TG-DTA-MS has obvious synthetic polymer applications. TA-MS has been appHed to study the thermal behavior of homopolymers, copolymers, polymeric blends, composites, residual monomers, solvents, additives, and toxic degradation products. In the latter context, FICl evolution from heated polyfvinyl chloride) materials is readily quantified by TA-MS and such data are of major significance in the design of fire-resistant polymeric materials. Pyrotechnic materials have been studied by TA-MS. A complex sequence of thermal events relates to the decomposition of these materials involving interactions between the nitrocellulose, perchlorate, and metal components with periodic release of carbon dioxide and oxygen. Only by EGA is it possible to rationalize the thermal behavior of such materials. TA-FTIR has also been applied extensively to study the thermal characteristics of synthetic polymers... 

While they are not strictly functionalized polyethylenes, our model ethylene/propylene copolymers represent our first success at making precise microstructures through the use of symmetric a,o>diene monomers. They also demonstrate the effect of regularly spaced pendant groups (the methyl group) on the thermal behavior of polyethylene, and serve as a basis for comparison of the functionalized models that follow. 

The PCN monomer was prepared by reaction of cyanamide with phenylisocyanate in alkaline solution at 15-18°C according to the literature [40]. The crude white powdered product was purified by recrystallization from an acetone-petroleum ether mixed solvent. The resulting colorless fine needles of phenylcarbamidonitrile melted at 134-136°C. Figure 5 shows its thermal behavior in differential scanning calorimetry (DSC, Dupout 1090) a sharp endothermic melting point peak appears... 

Polybenzimidazoles are a class of thermally stable polymers, typically condensed from aromatic bis-o-diamines and dicarboxylates. The namesake polymer repeat unit, which contains a 1,3-dinitrogen heterocycle, is benzimidazole. As a monomer, benzimidazole, has a melting point of 170°C and a boiling point of >360°C. Benzimidazole s hydrocarbon analog, indene, has a melting point of -2°C and a boiling point of 183°C. With only a molecular weight difference of 2, the differences in thermal behavior between benzimidazole and indene foretells some of the unusual thermal characteristics to be found in benzimidazole polymers. 

The initiation of the polymerization with y-radiation from a Co source was studied by Usmanov et al. [460,484,485]. Polymerization was carried out by irradiation of the monomer, in both liquid and gaseous phase, with the use of y-rays at 38 °C. The dose rates were lOrad/s and 0.5Mrad/s. Impurities such as acetylene greatly inhibited polymerization. Oxygen influenced the kinetics, a factor that confirms a free-radical mechanism. Liquids such as difluoroethane, benzene, and carbon tetrachloride reduced the polymerization rate and caused low-molar-mass polymer. On studying the thermal behavior of PVF it was found that the polymers obtained by y-ray initiation in bulk were the most crystallized and had the lowest degree of irregularity in the polymer chain. Nearly no branches were found in contrast to the chemically initiated polymers produced in suspension [482,484]. 

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