Theoretical Analysis of Properties of Ground and Excited States for Photodissociation of the C-O Bond in Polycarbonates

Photodegradation Pathways of Aliphatic Polyamide through Conical Intersection between Ground and Excited States

Time-dependent density functional theory studies were performed to investigate the photochemistry properties of the widely used aliphatic polyamide (APA), alias nylon, under ultraviolet radiation with N-ethylacetamide (NEA) being the model molecule. The characteristics of the transition molecular orbitals for the low-order excited states (ESs) of NEA were clarified, and the ES geometries related to the transition worthy of study were optimized. Our research proved that there is a conical intersection between the ground and excited states featured by the transition from the lone pair orbital to the σ antibonding orbital on the C-N bond within the peptide group or the N-C bond adjacent to the carbonyl group, and the C-N or N-C bond has the probability to be disrupted after internal conversion. These original quantum chemistry discoveries depict the C-N and N-C bond cleavage scheme that initiates the primary and secondary paths in the scission processes of the APA chain, respectively, which is helpful for giving new insight into the overall photodissociation mechanism of APA and designing advanced polyamide-based synthetic fibers.

Theoretical design of durable and strong polycarbonates against photodegradation

The photodegradation mechanism of polycarbonate (PC) was investigated by quantum chemistry, and a novel antidegradation molecular design using substituents was proposed. It was demonstrated that electron-withdrawing substituents in the phenyl moiety controlled bond alternation, leading to inhibition of the O-C bond cleavage in the carbonate moiety. These results provide a promising alternative for durable PC synthesis.