Modifying a Polystyrene/Poly(methyl methacrylate) Interface with Poly(styrene-co-methyl methacrylate) Random Copolymers

• Published in: Macromolecules Vol. 30; no. 3; pp. 445 - 455
• Main Authors: Sikka, Mohan, Pellegrini, Nicole N, Schmitt, Edward A, Winey, Karen I
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.02.1997
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Surface properties; Strengthening; Solid solid interface; Mechanical properties; Methyl methacrylate polymer; Experimental study; Methyl methacrylate copolymer; Foil; Mechanism; Fracture toughness; Interface structure; Random copolymer; Interface properties; Morphology; Styrene polymer; Styrene copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma961302h

Joints of polystyrene (PS) and poly(methyl methacrylate) (PMMA) modified with ∼50 nm of poly(styrene-co-methyl methacrylate) random copolymer [P(S-ran-MMA)] were investigated. Copolymers having styrene compositions of f S = 0.48 and f S = 0.73 were used. Transmission electron microscopy reveals that the copolymers phase separate to form a distinct layer at the joint such that there is an interface with each homopolymer. Interfacial fracture toughness measurements, using the asymmetric double cantilever beam geometry, show a strong effect of the PS to PMMA sheet thickness ratio; that is, the phase angle influences the measured interfacial toughness. Reflection infrared spectroscopy on fracture surfaces indicates that the crack propagates at or near the PS/copolymer interface for all thickness ratios and for both copolymers. In-plane crazing was not observed in front of the crack tip for these systems. Rather, strengthening appears to be exclusively a consequence of oblique crazes in the more compliant PS sheet which form at 45° or 135° relative to the crack direction. Joints modified with P(S0.73-ran-MMA) exhibit denser oblique crazes than those modified with P(S0.48-ran-MMA), resulting in a higher measured fracture toughness at all sheet thickness ratios or phase angles.