polycarbonate

pol·y·car·bon·ate

P0421000 (pŏl′ē-kär′bə-nāt′)n. Any of a group of thermoplastics that are linear polyesters of carbonic acid, especially those derived from bisphenol A and phosgene, characterized by high-impact strength, light weight, and flexibility, and used as shatter-resistant substitutes for glass.

polycarbonate

(ˌpɒlɪˈkɑːbəˌneɪt; -nɪt) n (Elements & Compounds) any of a class of strong transparent thermoplastic resins used in moulding materials, laminates, etc

pol•y•car•bon•ate

(ˌpɒl iˈkɑr bəˌneɪt, -nɪt)

n. a synthetic thermoplastic resin, a linear polymer of carbonic acid, used for molded products, films, and nonbreakable windows. [1930–35]

polycarbonate

[¦päl·i′kär·bə·nət] (organic chemistry) [OC₆H₄C(CH₃)₂C₆H₄OCO]_xA linear polymer of carbonic acid which is a thermoplastic synthetic resin made from bisphenol and phosgene; used in emulsion coatings with glass fiber reinforcement.

Polycarbonate

a polyester of carbonic acid and dihydroxy compounds of the following general formula:

Polycarbonates may be aliphatic, mixed, or aromatic, depending on the nature of A and A′. Only aromatic polycarbonates have gained practical importance; they are produced commercially by interphase polycondensation, phosgenation of aromatic dihydroxy compounds in a pyridine medium, or transesterification of diaryl carbonates (for example, diphenylcarbonate) by aromatic dihydroxy compounds. The most commonly used dihydroxy compound is 4,4′ -isopropylidenediphenyl, also called dian or bisphenol A. Polycarbonates based on the bisphenol A have the formula

These polycarbonates are thermoplastic linear polymers (molecular weight, 35,000–70,000) that are characterized by very high impact strength (250–500 kilojoules per sq m, or kilograms-force per cm per sq cm [kgf.cm/cm²]), yield strength (strength in flexure, 77–120 meganewtons per sq m [MN/m²], or 770–1,200 kgf/cm²), and very good dielectric properties (dissipation factor, 0.0009 at 50 hertz). Polycarbonates are optically transparent, cold-resistant (stable at temperatures slightly below – 100°C), and self-extinguishing; they dissolve in most organic solvents such as methylene chloride and chloroform, and are resistant to acids, salt solutions, and oxidizing agents.

Polycarbonates are processed by all the standard methods used for thermoplastic resins (for example, injection molding, extrusion, and compression molding). They are used in the preparation of films, fibers, and various products in many sectors of industry, mainly in electric engineering. In 1973, world production of polycarbonates (mainly in the Federal Republic of Germany, the USA, and Japan) was 100,000 tons.

REFERENCES

See references under .

O. V. SMIRNOVA

polycarbonate

A category of plastic materials used to make myriad products, including CDs and DVDs.

polycarbonate

(pŏl″ē-kăr′bĭ-nāt, -nĭt) [″ + ″] A transparent polymer used to manufacture eye protectors, shields, and other medical devices.

Polycarbonate

A very strong type of plastic often used in safety glasses, sport glasses, and children's eyeglasses. Polycarbonate lenses have approximately 50 times the impact resistance of glass lenses.Mentioned in: Eye Glasses and Contact Lenses

index of refraction

The ratio of the speed of light in a vacuum or in air, c, to the speed of light in a given medium, v. Symbol: n. Hence,n = c/vThe speed of light in a given medium depends upon its wavelength. Consequently, the index of refraction varies accordingly, being greater for short wavelengths (blue) than for longer wavelengths (red). The index of refraction forms the basis of Snell's law, which quantitatively determines the deviation of light rays traversing a surface separating two media of different refractive indices. Syn. refractive index. Plural: indices. See dispersion; law of refraction; gradient-index lens; high index lens; speed of light; refractometer.

Table I3 Refractive indices of some transparent media at selected wavelengths
spectral line	G	F	D	C	A
Origin	Calcium	Hydrogen	Sodium	Hydrogen	Oxygen
wavelength (nm)	430.8	486.1	589.3	656.3	759.4
aqueous or vitreous humour	1.3440	1.3404	1.3360	1.3341	1.3317
crystalline lens	1.4307	1.4259	1.4200	1.4175	1.4144
spectacle crown	1.5348	1.5293	1.5230	1.5204	1.5163
dense flint	1.6397	1.6290	1.6170	1.6122	1.6062

Table I4 Index of refraction n of various media for sodium light (λ = 589.3)
air	1.00
water (at 20ºC)	1.333
spectacle crown glass	1.523
flint glass (dense)	1.62
flint glass (extra dense)	1.65-1.70
titanium oxide glass	1.701
calcite crystal
ordinary ray	1.658
extraordinary ray	1.486
quartz crystal
ordinary ray	1.544
extraordinary ray	1.553

diamond	2.42
Canada balsam	1.53-1.54
CR-39	1.498
polycarbonate	1.586
silicone rubber	1.44
CAB	1.47
PMMA	1.49
HEMA	1.43
hydrogel polymer
20% water content	1.46-1.48
75% water content	1.37-1.38
eye
tears	1.336
cornea	1.376
aqueous humour	1.336
crystalline lens (average effect)	1.42
vitreous humour	1.336

plastic

Various organic or synthetic materials (e.g. CR-39, HEMA, polymethyl methacrylate, polycarbonate, etc.) that can be transformed into solid shapes to make spectacle frames, contact lenses, ophthalmic lenses, etc. and can be made to have good optical surfaces, high light transmission and refractive indices and dispersions similar to that of crown or flint glass. See acetone; index of refraction; plastic spectacle frame.