Understanding microstructural heterogeneity in low and high molecular weight fractions of polydisperse polyisobutylene by SEC and NMR for its reactivity.

Heterogeneity in polymers is caused by broad distribution of different microstructures across the polymer chain length, which is responsible to generate polydispersity in complex polymeric materials. Combination of Size exclusion chromatography (SEC) and Nuclear magnetic resonance (NMR) spectroscopy were used to gain molecular weight distribution (MWD) and microstructural information respectively in polyisobutylene (PIB). The present study was aimed to develop an analytical method to understand in-depth microstructural compositions in narrow low and high molecular weight ranges of high polydispersive polyisobutylene (PDI = 5.1), by fractionating it using analytical SEC hyphenated with differential refractive index (dRI) detector. The quantitative estimation of chain microstructures including exo-, endo-, coupled-PIB, tri-and tetra-substituted olefinic end groups has been investigated in highly reactive PIB (HR PIB), unfractionated conventional PIB and it's SEC fractions by 1H NMR. The focus is to understand exo-coupled microstructures in a high PDI PIB. The high molecular weight fraction and low molecular weight fraction obtained using combination of three PLgel Mixed-B columns in series were essentially monodisperse with PDI ~ 1 hence, ideal for understanding exo-coupled microstructures. The analytical SEC fractionation procedure in combination of 1H NMR revealed important insights on compositional heterogeneities of high dispersive conventional PIB when compared to unfractionated material, which helps to establish the reactivity and properties of the polymer which helps in processing. [ABSTRACT FROM AUTHOR]