Bonding at Compatible and Incompatible Amorphous Interfaces of Polystyrene and Poly(Methyl Methacrylate) Below the Glass Transition Temperature

Films of high-molecular-weight amorphous polystyrene (PS, M-w = 225 kg/mol, M-w/M-n = 3, T-g-bulk = 97degreesC, where T-g-bulk is the glass transition temperature of the bulk sample) and poly(methyl methacrylate) (PMMA, M-w = 87 kg/mol, M-w/M-n = 2, Tg-bulk = 109degreesC) were brought into contact in a lap-shear joint geometry at a constant healing temperature T-h, between 44degreesC and 114degreesC, for 1 or 24 hr and submitted to tensile loading on an Instron tester at ambient temperature.

The development of the lap-shear strength sigma at an incompatible PS-PMMA inter-face has been followed in regard to those at compatible PS-PS and PMMA-PMMA interfaces. The values of strength for the incompatible PS-PMMA and compatible PMMA-PMMA interfaces were found to be close, both being smaller by a factor of 2 to 3 than the values of or for the PS-PS interface developed after healing at the same conditions.

This observation suggests that the development of the interfacial structure at the PS-PMMA interface is controlled by the slow component, i.e., PMMA. Bonding at the three interfaces investigated was mechanically detected after healing for 24 hr at T-h = 44degreesC, i.e., well below Tg-bulkS of PS and PMMA, with the observation of very close values of the lap-shear strength for the three interfaces considered, 0.11-0.13 MPa.

This result indicates that the incompatibility between the chain segments of PS and PMMA plays a negligible negative role in the interfacial bonding well below Tg-bulk.