Enthalpy-assisted interactive SEC and its application to separate cyclic SI diblock copolymer from linear SIS triblock copolymer precursor.

Abstract

At present, both synthetic and natural polymers play an essential and ubiquitous roles in everyday life, because of their broad range of properties. Their large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, viscoelasticity, etc. Moreover, the distributions in-clude molecular weight distribution, chemical composition distribution and end group distribution will take place during the polymerization, resulting in difficulty in estab-lishing the correct connection between the molecular weight and its properties.1 Therefore, a novel technology Liquid chromatography (LC) which is believed to be a promising tool, has been widely studied over the years to solve those problems. In this thesis, the works based on liquid chromatogram and some applications are pre-sent. In chapter 1, the fundamental concepts of modern LC method for separa-tion of polymer will be discussed. It could be explicitly divided in to three main cate-gories: a) separations governed by entropy change, i.e. size exclusion chromatogram; b) separation controlled by both enthalpy and entropy changes, but dominated by changes in enthalpy, i.e. interaction chromatography; c) separation governed by no changes in free energy where enthalpic and entropic contributions compensated with each other, i.e. interaction chromatography under critical condition. In the early peri-od, it was quite common to use only one specific method to carry on the analysis of the polymerized polymers. This, however, will bring about some insufficient infor-mation. Instead of that, in this study, the enthropic effect was introduced to the tradi-tional GPC to provide an improved method with better resolution. Furthermore, with implementation of this so-called interactive SEC, it also provided an opportunity to separate cyclic SI diblock copolymer from its linear SIS triblock copolymer precur-sor. In chapter 2, the synthesis, characterization and separation of pure cyclic polystyrene from its linear precursor are introduced. Further exploration with using the interactive SEC analysis will exhibit the advantages over the traditional SEC anal-ysis both in resolution and efficiency. In chapter 3, the application of the interactive SEC on isolating ring-shape SI (polystyrene-block-polyisoprene) diblock copolymer from linear SIS (polystyrene-block-polyisoprene-block-polystyrene) triblock copolymer is illustrated.