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Abstract
The propagation polymer chains in RDRP can be isolated in the dormant form and be re-activated at chain ends to generate propagating radicals, which initiate subsequent chain extensions. Since the effect of remote substituents on kinetics decreases rapidly with their distance from the reaction site (chain ends), propagating radicals could be assumed to be only determined by the characteristics of terminal and penultimate units. Therefore, the chemical structure (substitution and stereochemistry) of dormant chain ends is crucial for the investigation of kinetics of RDRP. The investigation of stereochemical effect of dormant chain ends is challenging due to limited models which are highly accessible and able to represent long polymer chains. In this thesis, two ideal models (diastereomeric macro-RAFT agents with different chemical structures and two inherent diastereomers for each) were designed and prepared by single unit monomer insertion (SUMI) technology to examine their stereochemical effect on kinetics of RDRP. In the first work, diastereomeric CPDTC-Ane was synthesized by inserting the monomer anethole (Ane) into a trithiocarbonate, 2-Cyano- 2-propyl dodecyl trithiocarbonate (CPDTC) via SUMI. Two isolated diastereomeric oligomers, as the models for dormant polymer chains, were employed as initiators (chain transfer agents) for PET-RAFT (photoinduced electron/energy transfer reversible addition-fragmentation chain transfer) polymerization, respectively. Discriminatory photo-activation behavior was observed in separated diastereomer system with the consumption of Dia2 much faster than that of Dia1 under identical reaction conditions. However, such huge difference can be neutralized by chain transfer in mixed diastereomer system. The mechanistic insight into such interesting behavior was suggested with the aid of quantum chemical calculations. A bit more complicated system, diastereomeric CPDTC-St-PMI obtained by the insertion of two monomers (Styrene (St) and N-phenylmaleimide (PMI)) into CPDTC in proper sequence, was explored in the second work. Stereochemical effect on both initiation step and monomer addition step can be explored in the system of diastereomeric CPDTC-St-PMI due to the generation of diastereomeric radicals after photo-activation. Discriminatory kinetic behaviors were observed in both mixed and separated diastereomer systems, implying stereochemical effect still significantly affects kinetics in RAFT polymerization.