Environmental Engineering Reference
In-Depth Information
The
atactic
grade of PS is a transparent resin with good moisture resistance
and moderate chemical resistance. Its brittleness, however, limits its
commercial uses. Therefore, in addition to this general-purpose grade, a
tougher grade of PS is made by polymerizing styrene with 5-10%
poly(buta-1,3-diene) rubber dissolved in the monomer. This tougher
product called High impact polystyrene (HIPS) is generally made
exclusively by continuous thermal polymerization.
Figure 3.14
shows the
microstructure of HIPS and compares it with a transmission micrograph
of a styrene-butadiene rubber (SBR) copolymer. Both show soft
microdomains of rubber dispersed in the styrene matrix. This toughened
low-costplastic,however,istranslucentduetolightscatteringbytherubber
microdomains dispersed in the bulk polystyrene matrix. It is best used for
structural applications that require low strength, good impact resistance
and machinability. Using new metallocene catalysts, stereoregular
(
syndiotactic
) grades of polystyrene can be synthesized. This syndiotactic
polymer has improved thermal and mechanical properties. Properties of
