A theoretical study of the interfaces between aluminium and poly(ethylene terephthalate), polycaprolactone,and polystyrene: Illustration of the reactivity of aluminium towards ester groups and phenyl rings

The interfaces between aluminium and poly(ethylene terephthalate), poly(ε-caprolactone), and polystyrene are investigated theoretically in order to assess the reactivity of aluminium towards the functional groups (i.e., ester functions and phenyl rings) present at the surface of the polymers. The theoretical approach consists in performing quantum-chemical calculations on small molecular model systems interacting with a few Al atoms. The geometric structures of the organometallic complexes are optimized and their stabilities and changes in charge densities due to Al bonding are evaluated. The results are compared to experimental X-ray photoelectron spectroscopy data collected during the early stages of interface formation following aluminium deposition on the polymer surfaces. In agreement with experimental data, it emerges from this study that aluminium interacts strongly wirth both polyesters by forming covalent bonds with the carbon and oxygen atoms of the ester functions. The attack of the poly(ethylene terephthalate) phenyl rings occurs only for high metal coverage and does not hamper the interaction with the ester sites. Furthermore, our theoretical investigation has confirmed, on one hand, that the aluminium/polystyrene interactions are weak, and on the other hand, the absence of strong reactions at the interfaces between aluminium and saturated hydrocarbon polymers.