Page 164 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Polycondensation Polymers 127

TABLE 4.9
General Physical Properties of PPO

o
Heat-deflection temperature (1,820 kPa; C) 100
o
Maximum resistance to continuous heat ( C) 80
Crystalline melting point ( C) 215
o
–5
o

Coefficient of linear expansion (cm/cm- C, 10 ) 5.0
Compressive strength (kPa) 9.6 × 10 4
Flexural strength (kPa) 8.9 × 10 4
Impact strength (Izod: cm-N/cm of notch) 270
Tensile strength (kPa) 5.5 × 10 4
Ultimate elongation (%) 50
Density (g/mL) 1.1
The Noryl trade name covers a variety of PPO-intense materials, the most important being with
polystyrene. While the methyl groups discouraged good interactions between PPO chains, the aro-
matic character positively interacts with the phenyl group on the polystyrene, and the methyl groups
interact positively with the aliphatic polystyrene backbone. Unlike most polymer mixtures, the com-
bination of PPO and polystyrene forms a miscible blend. These blends and alloys with polystyrene
raise the heat distortion temperature to over 100°C, allowing production of materials that can be
boiled. Combinations with PS, in particular high impact polystyrene (HIPS), are more easily pro-

cessed and the PPO imparts needed flame resistance. The PS adds flexibility and lowers the melting
point. The combinations also offer good hydrolytic stabilities and electrical properties, and they are
relatively light weight. Noryl is widely used in switch boxes because of its good electrical resistance.

It can also be modified by addition to glass and other mineral fillers and are especially adaptable
to metallizing.
Aliphatic polyethers are also referred to as polyacetals. Polyoxymethylene (POM), precipitates
spontaneously from uninhibited aqueous solutions of formaldehyde and was isolated by Butlerov
in 1859. Staudinger, in the 1920s and 1930s, experimented with the polymerization of formalde-

hyde but failed to produce chains of sufficient length to be useful. While pure formaldehyde readily
polymerized, it also spontaneously depolymerizes, un-zippers. In 1947, DuPont began a program
to make useful polymers from formaldehyde since formaldehyde is inexpensive and readily avail-
able. After 12 years, they announced the commercialization of the polymer from formaldehyde,
POM, under the trade name of Delrin. The “secret” was capping the end groups by acetylation of
the hydroxyl end groups, thus preventing the ready unzipping of the polymer chain (Equation 4.79).
POM has a T of −75°C and a T of 180°C. General physical properties are given in Table 4.10.
m
g
R
O
Capping (4.79)
H O
R O OH
H
O R
Celanese came out a year latter with a similar product under the trademark of Celcon. Celanese
circumvented DuPont’s patent on the basis of employing a copolymer variation that allowed enhanced
stabilization against thermal depolymerization (Equation 4.80). The copolymer has a T of 170 C.
o
m
O O
H + R O H (4.80)
O
H

9/14/2010 3:38:27 PM
K10478.indb 127 9/14/2010 3:38:27 PM
K10478.indb 127