Bimetallic Main-Group Catalysts for the Synthesis of Advanced Biocompatible, Biodegradable, and Sustainable Polymers

Biocompatible materials have gained increasing attention due to their broad applicability in biomedical, environmental, and industrial sectors. Among these, poly(lactic acid) (PLA) and its copolymers are especially notable for their biodegradability, sustainability, and tunable chemical and physical properties. This dissertation presents a systematic investigation into the synthesis of PLA and its copolymers with ε-caprolactone and other lactones. The work focuses on the design and synthesis of sterically tunable bimetallic ligands and the development of both neutral and cationic main-group bimetallic complexes, specifically dilithium and dizinc species. These complexes were employed as catalysts in the ring-opening polymerization (ROP) of lactide. Furthermore, both random and block copolymerizations of lactide with ε-caprolactone were carried out to achieve control over polymer microstructure and properties. In addition, this dissertation explores the synthesis of poly(o-phthalaldehyde), a stimuli-responsive polymer capable of depolymerizing to its monomer upon exposure to specific chemical triggers, with degradation behavior governed by the nature of the end-capping groups. First, binucleating aniline-based bis(pyrazolyl)alkane ligands were synthesized. Their corresponding neutral monoethyl monozinc complexes, as well as cationic μ-bridged dizinc complexes, were prepared and employed in the ring-opening polymerization of rac-lactide. The catalytic activity of these complexes was compared with that of cationic phenol-bridged dizinc analogues. Next, air-stable neutral and cationic dizinc halide complexes based on phenolic bis(pyrazolyl)alkane ligands were synthesized. The optimal complex demonstrated moderate activity in lactide polymerization and exhibited unique selectivity, enabling the formation of random copolymers of lactide and ε-caprolactone with an alternating tendency through a chemoselective transesterification process. Additionally, commercially available PLA was modified using various lactones to further tailor its properties. Finally, a series of μ-bridged dilithium HMDS (–N(SiMe3)2) complexes were synthesized using both symmetric phenol-based bis(pyrazolyl)alkane ligands and asymmetric derivatives incorporating an imine (Schiff base) arm. The symmetric dilithium complexes were employed in the polymerization of ortho-phthalaldehyde to produce poly(o-phthalaldehyde), a stimuli-responsive polymer capable of depolymerization under specific conditions. These complexes exhibited high catalytic activity, affording polymers with high molecular weights, improved control over polymerization, and a preference for trans-selectivity. In addition, a comprehensive computational study was conducted to elucidate the mechanism of the polymerization process.

Name thesis:degree_name

Doctor of Philosophy

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Houston

Year dc:date.issued

2025

Author dc:creator

• Naik, Pratyush Kumar 1996-

Advisor dc:contributor.advisor

• Comito, Robert J.

Committee members dc:contributor.committeemember

• Xu, Shoujun
• Carrow, Bradley P.
• Miljanic , Ognjen S.
• Bollini, Praveen

• Chemistry

Language dc:language.iso

English

Handle dc:identifier.uri

https://hdl.handle.net/10657/20719

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/20719