Molecular Weight Distribution of Two Types of Living Chains Formed during Nitroxide‐Mediated Polymerization of Styrene

Different types of polymer chains generated during the nitroxide‐mediated polymerization of styrene are separated for the first time, and their molecular weight distribution (MWD) is investigated. Living and dead chains are monitored during the reaction; specifically, two types of living chains derived from the initiation of the alkoxyamine (RT) and the self‐initiation of styrene and dead chains present in the as‐prepared polystyrene (PS). To distinguish between each polymer species, different numbers of hydroxyl groups are introduced onto the T and R groups of the alkoxyamine (one and two groups, respectively). Each living and dead chains is resolved according to the distinct number of hydroxyl groups on its chain‐end using high‐performance liquid chromatography. Molecular structures of the fractionated PS are characterized using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and 1H nuclear magnetic resonance spectroscopy, and the results of which show two distinct initiation paths: one originating from RT and the other from the self‐initiation of styrene. Molecular weight and MWD are measured using size‐exclusion chromatography and reveal a narrow MWD for the living chains derived from RT. Contrastingly, a broad and skewed MWD is observed for the other living chains derived from the self‐initiation of styrene and the dead chains. Different types of polymer chains formed during the nitroxide‐mediated polymerization of styrene are separated and their molecular weight distribution (MWD) is investigated. The living chains derived from alkoxyamine have narrow MWD, while other types of living chains and dead chains resulting from self‐initiation of styrene and termination reactions, respectively, are responsible for broadening the overall MWD of the as‐prepared polystyrene.