Unidirectional Fracturing of Super Engineering Plastic Films

Polyamideimides and polyimides are prepared based on chemical imidization using aromatic diamine, diacid anhydride, and diacid chloride as monomers, with the precursor polyamic acid remaining in part, to produce mechanically unique films through convection drying. The resulting films are colorless and transparent and exhibit unidirectional fracture behavior. These films do not break when bent in the direction of the air contact surface but easily break when bent in the opposite direction. A cross‐sectional electron microscope image of the broken film shows that the film consists of a double layer. After examining both sides of the film through various spectroscopic and gel permeation chromatography analyses, it is found that the residual polyamic acid undergoes both hydrolytic and thermal decomposition, exclusively on the air contact surface. Later, the polymer film is laminated with two sheets of glass through UV curing of commercial acryl resin. Because of the unidirectional fracture characteristics of the film, the laminated glass does not completely break when subjected to bending toward the air contact surface but easily breaks (without fragments) in the opposite direction, indicating its potential application in safety glasses suitable for emergency escapes.