Investigating the Ductile Tensile Deformation of Poly(methyl methacrylate) Oriented Films Using Polarized FT-IR Spectroscopy and Birefringence

Hot-drawing induces chain orientation of glassy polymer films during tensile deformation, converting the fracture mode from brittle to ductile. Although the brittleness–ductility transition of oriented films has been explored, the mechanism is not fully understood. Here, employing poly(methyl methacrylate), PMMA, as the glassy polymer, the chain orientation and aggregation structures in PMMA oriented films integrated with cyanobiphenyl (CB) as a probe molecule (5 wt%) were investigated during tensile deformation by combining polarized Fourier-transform infrared (FT–IR) and birefringence (Δn) measurements with tensile tests. The polarized FT–IR data revealed the occurrence of a continuous PMMA-chain orientation in the pure PMMA oriented film during ductile deformation before and after reaching the yield point. Conversely, although the same PMMA orientation was observed in the PMMA/CB-oriented film, the CB orientation behavior was observed in three regions, namely Regions I, II, and III. As revealed by the Δn and FT–IR data, in I (before the yield point) and III (plastic deformation), the CB orientation was cooperative with the PMMA chain, and in II (after the yield point), the CB orientation relaxed without cooperativity, from. These results indicated the weakening of the glassy aggregation of PMMA, leading to the ductile tensile deformation of the oriented films.