Normal-phase (temperature gradient) interaction chromatography – A powerful tool for the characterisation of high molecular weight chain-end functionalised polymers

Abstract

We report here, for the first time, quantitative analysis of end-group functionalisation and the extent of end-group modification of polymers with molar mass up to 200,000gmol−1, using a combination of isothermal and temperature gradient interaction chromatography. At such high molecular weights, other common analytical techniques such as MALDI-ToF-MS and NMR spectroscopy are simply unable to offer any quantitative insight into the end-group functionality of polymers. Thus, normal phase isothermal interaction chromatography (NP-IIC) has been used to characterise a series of polystyrene samples, with identical molar mass (c. 90,000gmol−1), each carrying a single chain-end functionality of varying polarity, introduced via a series of end-group transformation reactions – from silyl-protected alcohol→primary alcohol→alkyl bromide. It is shown that the polarity of the functional group dictates the elution volume of the polymers and that NP-IIC could be used to monitor the quantitative end-group transformation. Thus, rather than estimating the success of the transformation reaction from the very small peaks observed in 1H NMR spectra, NP-IIC gives clear chromatographic peaks, whose retention volumes change dramatically only as a consequence of each new chain-end functional group. We also describe the analysis, by a combination of normal phase isothermal and temperature gradient interaction chromatography, of a series of linear polybutadiene samples of varying molar mass (28,000–200,000gmol−1) each carrying a single primary alcohol functionality at the chain-end. The primary alcohol functionality enabled the separation of functionalised and non-functionalised polymers, which eluted at different retention volumes despite identical molecular weights. It is all the more remarkable that complete (baseline) resolution can be achieved for two polymers with an identical molar mass (<200,000gmol−1), which differ only in that one sample is functionalised with a single primary alcohol group.