Page 338 - Engineering Plastics Handbook

296 Engineering Plastics

by forming an aromatic dichloride intermediate which carries the struc-
tural features desired in the polymer to be produced [8, 9]. Next this aro-
0
matic dichloride is self-reacted in the presence of Ni , triphenylphosphine,
and zinc to form the polymer which contains biphenyl or terphenyl units
as part of the backbone repeat unit [10, 11]. This synthesis method is doc-
umented in the literature as applied to the synthesis of PPSF.
Oxidative coupling of aromatic compounds via the Scholl reaction has
been successfully applied to the synthesis of a polyarylethersulfone
[12]. High-molecular-weight polymer was obtained by treating 4,4′-
di(1-napthoxy)diphenylsulfone and 4,4′-di(napthoxy)benzophenone with
ferric chloride. Equimolar amounts of the Lewis acid were used to effect
the polymerization. This synthesis route is limited in scope and utility as
it is only applicable to naphthoxy-based monomers and other systems
that can undergo the Scholl reaction.

Properties

The three sulfone polymers that are most commonly used in commer-
cial applications have several structural commonalities that account
for the unique attributes of this family of resins. The key feature common
to all three sulfone polymers is the resonant diaryl sulfone group.
Because the sulfur is in its highest state of oxidation, the sulfone group
is in the para position, and due to the high bond dissociation energies
of the aromatic backbone, these polymers exhibit outstanding thermal
stability and resistance to oxidation. This feature can be realized both
during melt processing and in high-temperature end-use environments.
Sulfone polymers can be melt-processed at temperatures up to 400°C
without any significant degradation. They can be used in environments
anywhere between 150 and 190°C continuously for extended periods.
The ether linkage that is common to the sulfone polymers imparts chain
flexibility, which allows for mechanical toughness and attractive melt
rheological properties for thermoplastic fabrication. The chemical sta-
bility of the aromatic ether linkage and sulfone moieties contributes to
the resistance to hydrolysis and chemical attack by acids and bases.
Such behavior has allowed for the success of sulfone polymers in numer-
ous medical and food service applications. The aromatic nature of the
polymer backbones offers high strength and stiffness along with good
ductility even at elevated use temperatures. Although the sulfone resins
offer many common properties, they are quite different due to the vari-
ety of bisphenols that can be used to synthesize them. One particular
change that can be made is in the glass transition of the material. A list
of bisphenols and the T ’s of resulting polymers is shown in Table 13.2.
g
The backbone structure of a polysulfone is very closely tied to its phys-
ical properties [13].