Polyamide glass transition temperature

This type of adhesive is generally useful in the temperature range where the material is either leathery or mbbery, ie, between the glass-transition temperature and the melt temperature. Hot-melt adhesives are based on thermoplastic polymers that may be compounded or uncompounded ethylene—vinyl acetate copolymers, paraffin waxes, polypropylene, phenoxy resins, styrene—butadiene copolymers, ethylene—ethyl acrylate copolymers, and low, and low density polypropylene are used in the compounded state polyesters, polyamides, and polyurethanes are used in the mosdy uncompounded state. 

In the area of moleculady designed hot-melt adhesives, the most widely used resins are the polyamides (qv), formed upon reaction of a diamine and a dimer acid. Dimer acids (qv) are obtained from the Diels-Alder reaction of unsaturated fatty acids. Linoleic acid is an example. Judicious selection of diamine and diacid leads to a wide range of adhesive properties. Typical shear characteristics are in the range of thousands of kilopascals and are dependent upon temperature. Although hot-melt adhesives normally become quite brittle below the glass-transition temperature, these materials can often attain physical properties that approach those of a stmctural adhesive. These properties severely degrade as the material becomes Hquid above the melt temperature. 

As is commonly the case with crystalline polymers the glass transition temperature is of only secondary significance with the aliphatic polyamide homopolymers. There is even considerable uncertainty as to the numerical values. Rigorously dried polymers appear to have TgS of about 50°C, these figures dropping towards 0°C as water is absorbed. At room temperature nylon 66 containing the usual amounts of absorbed water appears to be slightly above the T ... 

Gellation catalysts, 224, 227-236 Gel permeation chromatography (GPC), 385-386, 490 Gels, urethane, 205 Glass-fiber-filled polyamides, 136 Glass transition temperature (7)), 3, 266, 267... 

TDI isomers, 210 Tear strength tests, 242-243 TEDA. See Triethylene diamine (TEDA) Telechelic oligomers, 456, 457 copolymerization of, 453-454 Telechelics, from polybutadiene, 456-459 TEM technique, 163-164 Temperature, polyamide shear modulus and, 138. See also /3-transition temperature (7)>) Brill temperature Deblocking temperatures //-transition temperature (Ty) Glass transition temperature (7) ) Heat deflection temperature (HDT) Heat distortion temperature (HDT) High-temperature entries Low-temperature entries Melting temperature (Fm) Modulu s - temperature relationship Thermal entries Tensile strength, 3, 242 TEOS. See Tetraethoxysilane (TEOS)... 

Diamantane-based polymers are synthesized to take advantage of their stiffness, chemical and thermal stability, high glass transition temperature, improved solubility in organic solvents, and retention of their physical properties at high temperatures. All these special properties result from their diamantane-based molecular structure [90]. Polyamides are high-temperature polymers with a broad range of applications in different scientific and industrial fields. However, their process is very difficult because of poor solubility and lack of adequate thermal stability retention [90]. Incorporation of 1,6- or... 

PTT, with three methylene units in its glycol moiety, is called an odd-numbered polyester. It is often compared to the even-numbered polyesters such as PET and PBT for the odd-even effect on their properties. Although this effect is well established for many polycondensation polymers such as polyamides, where the number of methylene units in the chemical structures determines the extent of hydrogen bonding between neighboring chains and thus their polymer properties, neighboring chain interactions in polyesters are weak dispersive, dipole interactions. We have found that many PET, PTT and PBT properties do not follow the odd-even effect. While the PTT heat of fusion and glass transition temperature have values between those of PET and PBT, properties such as modulus... 

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. 

The dipole associated with the maleimide unit, which is located in the plane of the maleimide cycle and perpendicular to the C - C bond taking part to the chain backbone. The motion of this resultant dipole implies a rotation of the rigid maleimide unit around the local chain axis. This structure is, in some way, analogous to that encountered with iso-phthalic units in aryl-aliphatic polyamides (Sect. 6) where the zso-phthalic rings only undergo small amplitude oscillations but no flips at temperatures below the glass transition temperature. Thus, it is unlikely that the maleimide dipole could be involved in the transition motions of CMIMx copolymers. 

Adhesion studies of epoxy resins modified with high modulus and high glass transition temperature thermoplastics have shown adhesion can reach or even exceed that of the unmodified resin. The use of flexible polyamides or flexible epoxides resulted in shear strength increases in epoxy systems employed by Cunliffe et al. [144],polyethersulfones [18,145],polyetherimides [109,146,147], and polyetherketones [148-150]. 

For the same purpose, a composition consisting of Bisphenol A copoly (carbonate-terephthalate) and BPA/DC was reinforced with polyamide fibers. After crosslinking at 270 °C, a glass transition temperature of 212 °C was obtained [39]. The same di-cyanate monomer was added to polycarbonate in order to decrease the brittleness [40]. 

However, the incorporation of the solvent in the cured resin will significantly lower the glass transition temperature and thermal resistance. When cured at room temperatures, these solutions give properties more similar to those of the polyamide curing agents, but they do have the advantage of low viscosity and adjustable cure rate. 

Aside textile and packaging applications the use of PET (Poly(ethylene Terephthalate) for structural applications is rather limited compared to equivalent polymers such as polyamides. Two main reasons can be given. Firstly, the high sensitivity of PET toward hydrolysis and its slow crystallisation kinetics constrain its processing. Secondly, its low glass transition temperature constrains its use if amorphous, whereas its weak impact resistance if semicrystalline constrains its use when crystallised. The industrial objective of this work deals with the latter of these points increasing the impact resistance of semi-crystalline PET. 

The dependence of microhardness on the glass transition temperature for some commercial polymers is presented in Fig. 3.11. The polymers used for the plot in Fig. 3.11 are summarized in Table 3.2. Only non-crystallizable polymers have been selected. For the crystallizable ones, for which there are no reliable evidence for the presence of a completely amorphous phase, as is the case for example with polyamide 6 (PA6), the Hg value obtained by extrapolation to zero crystallinity is used. In this way we attempt to avoid the very strong effect on H of even small amounts of the crystalline phase. 

Account for the differences in glass transition temperatures among the polyesters and polyamides listed in Exercise 2.19. 

The 1,2,4,5-tetrasubstitution pattern confers a symmetrically opposed pair of dipoles on the molecule which, in turn, inposes enhanced crystallinity and accounts for its high melting point compared to the other tetramethyl benzenes prehnitene and isodurene (MP -6°C and -24°C respectively(4)). One use of durene and its derivatives, therefore, is to increase the crystallinity of polymers. For example, consider the glass transition points of polyamides if a polyamide is made from a diamine and, say, sebacic acid, durene diamine raises the glass transition temperature of the polymer more than 40°C above that produced by 1,4-diaminobenzene (5). 

Figure 6.26. Predicted melting temperature (Tm) and glass transition temperature (Tg), for aliphatic polyesters -[(CH2)k-COO-]n and polyamides -[(CH2)k-CON(H)-]n. All calculations were performed in absolute temperature units (K), although the results are shown above in °C.

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