Page 304 - Engineering Plastics Handbook

264 Engineering Plastics

other diamines without methylene carbons, such as ODA, are used for
the injection-molding grades.

Other polyamide-imide chemistries
Other direct one-pot syntheses are known and have been cited in the lit-
erature but are not practiced commercially. One example involves the
formation of a diacid containing internal di-imide groups from the reac-
tion of TMA and a diamine. The amide bond is then condensed in a
second step in the same pot with additional diamine, using pyridine, tri-
phenylphosphite, and lithium chloride in NMP [14]. This amide conden-
sation may also be completed by the addition of a thionyl chloride/NMP
complex to the diacid in the presence of an acid acceptor [15].
Alternatively, other methods use a di-isocyante, such as MDI, to react
with the diacid-dimide [16]. This defined architecture allows microstruc-
tured polymers to be synthesized which can be useful in membrane and
other specialty applications.
Most commercial PAIs, including the Torlon family, have glass tran-
sition temperatures in the range of 275 to 280°C. Lower and higher
glass transition temperatures are possible by modifying the structure
of the diamine or di-isocyanate. Incorporating more flexible units, such
as monomers with ether bonds, will reduce the glass transition tem-
perature T , while stiffer units, such as diaminodiphenylsulfone, will
g
increase it [17].

Applications Using Polyamide-imides

Polyamide-imides have outstanding properties. Fortunately, they are
commercially available in many different forms. Torlon polyamide-imide
compounded grades can be processed via injection molding and extru-
sion into intricate parts and standard shapes and geometries. Coatings
and adhesives may be formulated using Torlon polyamide-imide pow-
ders. Alternatively, polyamide-imide solutions manufactured via the
isocyanate process may be used directly in coating applications, such as
wire enamels and other industrial coatings. Because of their properties,
polyamide-imide powders can be used as a toughening, wear-resistant,
high-strength additive in other thermoplastics and fluoropolymer parts
and systems. Individual parts may be easily machined from compression-
molded or injection-molded ingots or extruded rod and plate stock.
Polyamide-imides, due to their high relative cost compared to common
engineering plastics such as nylon and polycarbonate, are used when the
application conditions require the property benefits of these materials
and where lesser polymeric materials would fail. In addition to this, they