Page 188 - Engineering Plastics Handbook

Thermoplastic Polyetherimide (PEI) 161

The BPADA-MPD polymer is most conveniently processed as a fully
polymerized polymer melt. All amide-acid groups have been closed to imide
linkages, and no volatile species are liberated on heating (assuming the
polymer has been adequately dried to remove a small amount of absorbed
water).
BPADA-MPD PEI is soluble in some polar aprotic solvents, such as
N-methyl pyrrolidinone, dimethyl formamide, or dimethyl acetamide,
as well as solvents such as chloroform, anisole, and dichlorobenzene
[11]. If melt processing is not desired, thermoplastic PEI resin can
also be cast into film, or solution-blended with other ingredients.
Since the materials are fully polymerized, only the removal of solvent,
rather than dehydration or chemical curing, is needed to form a
molded component.
Polyetherimides are amorphous polymers with excellent dimensional
stability. They are transparent with useful optical properties [12], but all
thermoplastic polyetherimides are a yellow amber color (as are almost all
polyimides). The yellowness index (YI) of a 3.2-mm (0.130-in) BPADA-
MPD PEI injection-molded part is usually > 50.
PEI resins do not have outstanding impact strength, but they do have
the practical toughness to be used in a variety of applications, including
serving trays and freezer-to-oven cookware [13]. Additionally, PEI resins
have good electrical insulating properties with stable dielectric constant
and dissipation factor over a range of temperatures [14,15]. Furthermore,
these materials have good inherent resistance to ignition and, in large fire
situations, may give reduced heat release and low smoke in some formu-
lations [16]. While PEI resins have good flame-retardant (FR) character-
istics, testing of all articles using PEI resins in actual end-use conditions
is strongly recommended to ensure FR performance and compliance with
all codes and regulations.

Other Thermoplastic Polyetherimides
BPADA has been polymerized with a wide variety of other diamines and
other dianhydrides to produce a family of polymers and copolymers. Chief
among these is the polymer of BPADA with p-phenylene diamine (PPD),
as shown in Eq. (8.6). This PPD resin has a slightly higher T than the
g
MPD resin and also has much better solvent resistance. Removal of the
MPD-derived kink from the PEI chain makes the resin much less solu-
ble, but symmetry is not so high as to allow for crystallization under most
conditions. The presence of the three flexible links—two ether groups
and an isopropylidene linkage—still allows for melt processability. The
T is raised slightly to 227°C (441°F), and solvent resistance is much
g
improved versus the BPADA-MPD polymer.