Biomedical Engineering Reference
In-Depth Information
Chapter 2
Synthesis and Processing of PEEK for
Surgical Implants
Steven M. Kurtz Ph.D.
2.1 Introduction
PEEK used in biomedical applications. Readers with
an interest in PEEK composites may wish to skip
ahead to Chapter 3, which covers blending of PEEK
with additives.
Polyaryletheretherketone (PEEK) is a challenge to
synthesize and convert into surgical implants. The
polymer is chemically inert and insoluble in all
conventional solvents at room temperature. Indeed,
PEEK can only be completely dissolved using fairly
esoteric solvents, such as diaryl sulfones
[1]
.
Although inertness and insolubility are desirable for
a biomaterial, these attributes constrain the synthesis
and manufacture of PEEK.
Fabrication techniques for polyaryletherketone
(PAEK) polymers have undergone constant refine-
ment since the preparation of polyetherketoneketone
(PEKK) was first described in the 1960s
[1
e
3]
.
Although many of the details associated with
synthesis and processing of PAEKs are proprietary to
resin and stock material suppliers, it is important to
understand the steps used in the manufacture of raw
materials, because these techniques can substantially
impact the properties and quality of the stock shapes
and molded implant components
[4]
. Consequently,
this chapter summarizes the principal steps used to
synthesize and fabricate PEEK implant components.
Early studies on PEEK processing tend to
emphasize the fabrication of PEEK composites,
using carbon and glass fibers
[4]
. This chapter is
focused on the synthesis and processing of neat,
unfilled PEEK polymer. We begin by outlining the
two main synthesis routes for contemporary
PEEK. As a high-temperature thermoplastic, PEEK
can be processed using a variety of commercial
techniques, including injection molding, extrusion,
and compression molding. This chapter provides an
overview of the methods for processing unfilled
2.2 Synthesis of PAEKs
As noted previously, the polymerization of aryl-
etherketones is a complex and challenging process
due to the insolubility of PAEKs in typical solvents.
Furthermore, the solvents and high temperatures
necessary to carry out successful polymerization of
PEEK, such as benzophenone or diphenylsulfone
above 300
C, necessitate dedicated plant facilities
with rigorous safety procedures (
Fig. 2.1
). Because
of the precautions necessary to carry out safe poly-
merization, the reactions are typically carried out in
batches, as opposed to in a continuous process. All
these challenges contribute to the higher cost in
producing PAEK polymers, when compared with
other thermoplastics.
Historically there are two main routes involved in
the production of PAEKs. The first method involves
linking aromatic ether species through ketone
groups, whereas a second method involves linking
aromatic ketones by an ether bond. The first method
involves an electrophilic reaction and Friedel Crafts
acylation chemistry, and the second route involves
a nucleophilic displacement reaction.
2.2.1 Electrophilic Routes to PAEK
Polymers
The inherent solvent resistance and propensity to
reach high crystallinity levels prevents PAEK
