Page 190 - Engineering Plastics Handbook

Thermoplastic Polyetherimide (PEI) 163

A crystalline polyetherimide derived from 3,3′-bis(4-aminophenoxy)-
biphenyl diamine (BP diamine) and pyromellitic dianhydride is also com-
mercially available [18]. The polymer structure is shown in Eq. (8.9). This
resin has two flexible ether linkages as well as the rigid PMDA-derived
−1
units. Viscosity is high [3000 to 10,000 P at 400°C (752°F) and 100 s ], but
the material may still be melt-processed. The T is ~250°C (482°F) and T m
g
is about 388°C (730°F). This PEI has sufficient symmetry—likely due to
the biphenyl and PMDAlinkages—that it will crystallize. The rate of crys-
tallization is relatively slow, so parts formed of this material often require
postmold annealing. Care must be taken to prevent distortion of the amor-
phous or semicrystalline parts during secondary heat exposure or in end
use. Like many polyimides, these resins show high strength and ignition
resistance. As molded, the parts may be transparent; crystallization results
in opacity. The crystalline PEI resin has excellent solvent resistance. The
BP diamine PMDA polymer has been melt-blended with BPADA-MPD
polyetherimide to form miscible systems [19].
O O

O O N N

O O
BP diamine PMDA
Equation 8.9 Biphenol diamine PMDA polyetherimide.

Another interesting commercial polyimide based on BPADA is an elas-
tomer made by replacing a portion of the MPD with a diamino dimethyl
siloxane [Eq. (8.10)]. This makes an elastomeric polyetherimide silicone
block copolymer that has a lower softening point [T = 165°C (329°F)].
g
The silicone polyetherimides have lower modulus and greater impact
resistance than the rigid BPADA-MPD polymer. This copolymer also has
good flame retardancy and—with the appropriate choice of short silicone
block length—can be made transparent [20–22].

O O O O
N N Si OSi N N
O O O O
O O m O O
n
Equation 8.10 Silicone polyetherimide copolymer.

A partial summary of commercial polyetherimide grade names and
their suppliers is listed in Table 8.1. Table 8.2 shows properties of some
of the commercial, fully amorphous, melt-processable thermoplastic poly-
imides listed in Table 8.1. They have high heat capability and excellent
strength [23].