Abstract
Size Exclusion Chromatography is traditionally carried out in either aqueous or non-polar solvents. A system to present molar mass distributions of polymers using methanol as a mobile phase is presented. This is shown to be a suitable system for determining the molar mass distributions poly(N-isopropylacrylamide)s (PNIPAM); a polymer class that is often difficult to analyze by size exclusion chromatography. DOSY NMR was used to provide intrinsic viscosity data that was used in conjunction with a viscometric detector to provide absolute calibration. Then the utility of the system was shown by providing the absolute molar mass distributions of dispersed highly branched PNIPAM with biologically functional end groups.
Highlights
Polymer molar mass distributions are often obtained by size exclusion chromatography (SEC)
In this work we report SEC carried out in methanol and we apply this to the analysis of the molar mass distributions of a range of well studied amphiphilic polymers based on the N-isopropyl acrylamide as the main repeat unit
With this in mind we have prepared a series of linear PNIPAMs, which were analyzed both by SEC, with viscometric detection with THF as eluent, to get their absolute molar masses, and DOSY NMR in deuterated methanol to determine their intrinsic viscosities in this solvent
Summary
Polymer molar mass distributions are often obtained by size exclusion chromatography (SEC). Intrinsic viscosity of the standard has been obtained from capillary viscometry but it is necessary to relate the average molar mass and average intrinsic viscosity from the same point on the distribution This is usually achieved by using samples with very narrow dispersity so that the various means converge. DOSY provides the facility to obtain average intrinsic viscosities [25] that can be directly related to the average molar mass from the same position on the distribution provided by SEC; both DOSY and SEC provide log distributions with separation provided by the distribution of hydrodynamic volume (VH) With this in mind we have prepared a series of linear PNIPAMs, which were analyzed both by SEC, with viscometric detection with THF as eluent, to get their absolute molar masses, and DOSY NMR in deuterated methanol to determine their intrinsic viscosities in this solvent. The use of DOSY NMR to provide the standards with known VH allows for simple calibration of the SEC in terms of the distribution of VH or hydrodynamic radius (RH)
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