Page 310 - Handbook of Plastics Technologies

ELASTOMERS

4.102 CHAPTER 4

The polystyrenic segments, with molecular weights of 5000 to 8000, form glassy ag-
gregates on cooling with many of the properties of polystyrene itself. The upper glass
transition temperature of such TPEs based on styrene is thus close to that for polystyrene
(100 to 110°C). On cooling from the molten state to temperatures below the hard-segment
T , the styrene-derived segments coalesce to form domains that act both as reinforcing
g
filler and as cross-links since the ends of the rubbery chains (D) are bound therein. Di-
block (S-S) copolymers are not TPEs, because the D-segments cannot be supporting
chains, each having only one of its ends restrained in the glassy domain.

FIGURE 4.39 Cost/performance for thermoset rubbers and TPEs.

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