Page 275 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology En012c-604 July 26, 2001 16:2

784 Polymers, Thermally Stable

area of increasing importance for PPS is as a thermoplastic exhibitingthehigheststability.Nevertheless,onlytwoma-
matrix for advanced structural composites using carbon- terials (XI,R = CH 3 and R = C 6 H 5 ) have demonstrated
or glass-fiber reinforcement. Blends of PPS with other useful commercial application as thermoplastic molding
systems such as Bisphenol-A/Polysulfone, nylon-6,6 and products of intermediate heat resistance.
high-density polyethylene (HDPE), using glass fiber rein- The utility of the ether-link in thermally stable car-
forcement, have been recorded. bocyclic polymers has proved most effective, applica-
Individually, PPS with carbon fiber reinforcement is tionally, when combined with other flexibilizing units.
under investigation in advanced (aerospace) structures. Poly(phenylene ether sulfones) (XII and XIII) have typi-
Complex shapes such as I-beams and C-channels have cally been produced by polyetherification or polysulfony-
been manufactured from laminates incorporating unidi- lation processes:
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rectional, offaxis (90 , +/−45 ) and fabric reinforcement.
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The lower interlaminar fracture toughness (G IC ) of epoxy
2
2
(0.1 kJ/m ) and polysulfone (0.63 kJ/m ) compared with
2
2
that of PPS (1.3 kJ/m ) and PEEK (1.4–2.4 kJ/m ) has
been ascribed to the bonding efficiency of PPS and PEEK
to the carbon fiber reinforcement due, it is suggested, to
the development of transcrystalline regions at the fiber
surface in the latter two systems.
A very recent development has been the use of rigid-
rod LCPs to reinforce thermoplastics such as PPS (and
PEEK). Using a novel mixing process, a blend of 10–20%
LCP with PPS is extruded or blow-molded into film or
tape. It is claimed that the dynamic torsional properties of
LCP/PPS films are higher than for carbon fiber reinforced
PPS.

E. Poly(Phenylene Ether), Poly(Phenylene Ether
Sulfones), Poly(Phenylene Ether Ketone)

The ether-link is frequently used to promote an added flex- Weight loss (Fig. 6) and property retention data at
ibility to inherently rigid polymer chains without incurring elevated temperature (Fig. 7) indicate continuous-use
too radical a reduction in thermal/thermo-oxidative stabil- temperature for thermoplasts (XII, Polymer 200P and
◦
ity. This approach, particularly effective in the heteroaro- XIII, Astrel 360) of 175 and 200 C, respectively. Ta-
matic series of polymers to be discussed later, has also ble IV indicates tensile strength retention versus tem-
characteristically enhanced the low-temperature flexibil- perature for carbon fiber reinforced poly(ethersulfone),
ity of the aliphatic fluoroalkylene chain in, for example, while Table V compares tensile strength retention at var-
PTFE [poly(tetrafluoroethylene)] to produce fluoroether ious temperatures of typical glass fiber reinforced ther-
elastomers with specialized application. moplastics. Poly(phenylene ether ether ketone) (XIV,
Carbocyclic poly[phenylene ethers (oxides)] (XI) are PEEK) is commercially produced via a polyetherification
produced from substituted phenols by oxidative, free- reaction:
radical, or replacement reactions.

Thermal and thermo-oxidative stability decrease both
with type and extent of substitution in the nucleus (H >
C 6 H 5 > CH 3 > CH 3 O > OH > SO 3 H > SO 2 Cl);
poly(1,4- phenylene ether) (XI,R = H) with a decomposi-
tion temperature (TGA/ITGA); air and nitrogen) of 570 C
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