Reversible deactivation radical polymerization allows the synthesis of polymers with narrow molecular weight distribution (MWD). However, formation of dead chains is inevitable in the polymerization, leads to broader MWD than the one prepared by living anionic polymerization.

Polymer species in polystyrene prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization, nitroxide-mediated polymerization (NMP), and atom transfer radical polymerization (ATRP) were separated and characterized to study the MWD of the living and dead chains. To achieve chromatographic resolution of these polymer chains, a polystyrene with the different number of hydroxyl groups was prepared. The structures of fractionated polymer species were characterized using 1H nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS). The MWD of the living chains was as narrow as the Poisson distribution while the dead chains were responsible for broadening MWD of as-prepared polymers. This study is crucial to understand the MWD of polymers in RDRP and its mechanism.

In chapter 1, general introduction of this dissertation is briefly introduced.

In chapter 2, background knowledge of features, mechanism and MWD of RDRP, RAFT polymerization, NMP, and ATRP is described to study the MWD of living and dead chains in polystyrene.

In chapter 3, living and dead chains in polystyrene prepared by RAFT polymerization were separated by interaction chromatography. To achieve chromatographic separation of the polymer species, a polystyrene with distinctive end groups was synthesized using a designed RAFT agent (R-Z) with a hydroxyl group at both R and Z moieties and a thermal initiator (I-I) without hydroxyl group. The structures of fractionated two living chains (R-PS-Z and I-PS-Z originated from the RAFT agent and the initiator, respectively) and dead chains were characterized using 1H NMR spectroscopy and MALDI TOF MS. The MWD of the living chains, R-PS-Z was close to the Poisson distribution. On the other hand, the initiator (I-I) slowly dissociates with half-life time to generate the radicals, I? throughout the polymerization. Thus, the living chains, I-PS-Z have a broader MWD with low molecular weight tailing. In addition, as the [RAFT agent]/[initiator] ratio decreases, both the amount and the dispersity of the living chains, I-PS-Z increase while the dispersity of the living chains, R-PS-Z remains unchanged.

In chapter 4, different types of polymer chains generated during the NMP of styrene were separated, and their MWD was investigated. The living and dead chains were monitored during the reaction; specifically, two types of living chains derived from the initiation of the alkoxyamine (R-T), R-PS-T and the self-initiation of styrene D-PS-T, and dead chains presented in as-prepared PS. To distinguish between each polymer species, polar hydroxyl groups were introduced onto the T and R moiety of the alkoxyamine (one and two groups, respectively). Each living and dead chains was resolved according to the different number of hydroxyl groups on its chain-end using interaction chromatography. Molecular weight and MWD were measured using size exclusion chromatography and revealed a narrow MWD for the living chains, R-PS-T. Whereas, the situation is quite different for another living chains, D-PS-T. Self-initiation of styrene generates the new radical, D? throughout the polymerization that can initiate the polymerization. Thus, the living chains grown by the radical, D? from the self-initiation of styrene, D-PS-T have a lower Mn and a broader MWD with a long tail towards low MW.

In chapter 5, living and dead chains generated during the ATRP of styrene were separated, and their MWD was investigated. The polymer species were monitored during the reaction. To separate the living and dead chains, the bromine end group in the living chains was quantitatively converted to hydroxyl group by azidation and click reaction. Thus, the living chains with the polar chain-end compared with dead chains without the polar chain-end had different interaction strengths with the stationary phase of the interaction chromatography column, leading to their resolution. The MWD of the living chains was close to the Poisson distribution while dead chains had broad MWD, which were responsible for broadening MWD of as-prepared PS. This was also supported by performing the PREDICI simulation.