Fragment Parameters for the Calibration of Molecular Weights of Rod-Like Oligomers/Polymers by Gel Permeation Chromatography
Date Issued
2015
Date
2015
Author(s)
Chen, Chih-Chun
Abstract
Gel permeation chromatography (GPC) offers a powerful tool to determine number average molecular weight (Mn) and weight average molecular weight (Mw), of a polymer, from which polydispersity (PDI) of the polymer is obtained. Polystyrenes are commonly used as the reference in GPC analyses. What GPC measures is the hydrodynamic volume of a polymeric sample which is closely related to the shape of the polymeric molecules. Thus, when the molecular shape or hydrodynamic radius of a polymer is different from that of polystyrene references, the deviation of molecular weights of polymers from the exact values is frequently observed. This is particularly true for rod-like polymers such as oligo/polythiophenes that exhibit larger intrinsic viscosity than that for highly folded polymers. A set of new empirical parameters ci of commonly used fragments including a range of different substituted thiophenes, benzenes, pyridines, ethylenes, ethynylenes as well as butadienes for the calibration of the inflated Mn data obtained by GPC measurements for rod-like oligomers/polymers has been established. The parameters, ci, are ranging from 0.16 to 1.18, and they are obtained by adjusting the slopes of the plots of Mn versus the real molecular weights, Mr, for a series of oligomers and polymers to approximately 1. The calibrated molecular weights, Mc, are calculated based on equation, Mc = [ciFi]Mn, where Fi indicates the fragment fraction for the corresponding fragment ci in an oligomer/polymers, and match nicely with Mr of oligomers/polymers. More than 84% of calculated Mc values are within 12% deviating from the real molecular weights, Mr.
Subjects
GPC
molecular weight calibration
Type
thesis
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