Methyl methacrylate copolymers, brittle-ductile

Figure 11. Brittle-ductile behavior of a series of methyl methacrylate/ethyl acrylate copolymers.

ZYLAR series of alloys of brittle polymer, ductile polymer and rubbery polymer are available from Novacor Chemicals, Inc. The components are brittle polymer, styrene (70 wt%) and methyl methacrylate (30 wt%) (Novacor s NAS30) ductile polymer, block copolymer derived from styrene (75 wt%) and butadiene (25 wt%) and rubbery polymer, a tapered polymer derived from styrene (43 wt%) and butadiene (57 wt%). No specific gamma stabilizers were added to these polymer alloys. 

Poly(vinyl chloride) (PVC) homopolymer is a stiff, rather brittle plastic with a glass temperature of about 80°C. While somewhat more ductile than polystyrene homopolymer, it is still important to blend PVC with elastomer systems to improve toughness. For example, methyl methacrylate-butadiene-styrene (MBS) elastomers can impart impact resistance and also optical clarity (see Section 3.3). ABS resins (see Section 3.1.2) are also frequently employed for this purpose. Another of the more important mechanical blends of elastomeric with plastic resins is based on poly(vinyl chloride) as the plastic component, and random copolymers of butadiene and acrylonitrile (AN) as the elastomer (Matsuo, 1968). On incorporation of this elastomeric phase, PVC, which is ordinarily a stiff, brittle plastic, can be toughened greatly. A nonpolar homopolymer rubber such as polybutadiene (PB) is incompatible with the polar PVC. Indeed, electron microscopy shows... 

Figure 12.32 Plot of brittle stress at about — 180 °C against a line joining yield-stress values at —20 °C (o), respectively, for various polymers. Line A divides polymers that are brittle unnotched from those that are ductile unnotched but brittle notched, and line B divides polymers that are brittle notched but ductile unnotched from those that are ductile even when notched. PMMA, poly(methyl methacrylate) PVC, poly(vinyl chloride) PS, polystyrene PET, poly(ethylene terephthalate) SAN, copolymer of styrene and acrylonitrile CA, cellulose acetate PP, polypropylene N, nylon 6 6 LDPE, low-density polyethylene POM, polyoxy-methylene PB, polybutene-1 PC, polycarbonate PTFE, polytetrafluoroethylene. (Reproduced with permission from Vincent, Plastics, 29, 79 (1964))...

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