Page 680 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Selected Topics 643

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain poly-
mers, including synthetic polypeptides, are known to change shape on application of electric current,
temperature, and chemical environment. For instance, selected bioelastic smart materials expand in
salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides
and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent
adhesion growth between surgically operated tissues, and in controlled drug release where the material
is designed to behave in a predetermined matter according to a specific chemical environment.

Most current efforts include three general types of smart materials: piezoelectric, magnetostrictive

(materials that change their dimension when exposed to a magnetic field) and shape memory alloys
(materials that change shape and/or volume as they undergo phase changes). Conductive polymers and
liquid crystalline polymers can also be used as smart materials since many of them undergo relatively
large dimensional changes when exposed to the appropriate stimulus such as an electric fi eld.
New technology is being combined with smart materials called micromachines, machines that

are smaller than the width of a human hair. Pressure and flow meter sensors are being investigated
and commercially manufactured.
As with so many areas of polymers smart materials have our imagination as the limit.

19.9 HIGH-PERFORMANCE THERMOPLASTICS
Engineering plastics are also referred to as high-performance thermoplastics or advanced thermo-
plastics. An engineering plastic is simply one that can be cut, sawed, drilled, or similarly worked
with. Along with the ability to be worked with, high-performance thermoplastics generally also can
o
be used at temperatures exceeding 200 C. These materials are also referred to as high-temperature
thermoplastics. As the advantages of polymeric materials become evident in new areas, the property
requirements, including thermal stability, will increase causing the polymer chemist to seek new
materials or “old” materials produced in new ways to meet these demands.
Table 19.2 contains some of the new advanced thermoplastics that are currently available.

TABLE 19.2
Advanced High-Temperature Thermoplastics and Applications
Heat Defl ection
Material Temperature, C Properties
o
Poly(arylene carbonates) — Leaves no degradation residue
Polyamide-imides 280 Good wear and good friction and solvent
resistance
Polyanilines 70 Electrical conductor
Polyarylates (Aromatic polyesters) 175 Good toughness, UV stability, fl ame retarder
Polybenzimidazoles 440 Good hydrolytic, dimensional, and compressive
stability
Polyetherimides 220 Good chemical, creep, and dimensional stability
Polyethersulfones 200 Good chemical resistance and stability to
hydrolysis
Polyimides 360 Good toughness
Polyketones 330 Good chemical resistance, strength, and stiffness
Poly(phenylene ether) 170 Often alloyed with polystyrene

Poly(phenylene sulfide) 260 Good dimensional stability and chemical
resistance
Polyphenylenesulfone 260 Good chemical resistance
Polyphthalamide 290 Good mechanical properties
Polysulfone 175 Good rigidity

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