- Chromatographic examination of the chemical composition and sequence distribution of copolymers from ethyl and benzyl diazoacetate
- Journal of Chromatography A
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- Document type
- Faculty of Science (FNWI)
- Van 't Hoff Institute for Molecular Sciences (HIMS)
Polymers, especially copolymers, are highly complex samples and, therefore, require various setups for their thorough characterization. In this work, one- and two-dimensional chromatographic approaches were applied to characterize two homopolymers and two dissimilar copolymers prepared by rhodium-mediated carbene polymerization using ethyl and benzyl diazoacetate as the monomers: poly-(EA-ran-BnA) and poly((EA)b-(BnA-ran-EA)b). Different strategies of synthesis suggested that poly-(EA-ran-BnA) was an approximately 1:1 random copolymer and that poly((EA)b-(BnA-ran-EA)b) was a block-type copolymer of which the (BnA-ran-EA)b block is dominated by BnA. The hydrodynamic volume of the investigated polymers turned out to be comparable, i.e. size exclusion chromatography (SEC) did not separate them. Temperature-gradient interaction chromatography was not feasible and one-dimensional (solvent-)gradient-elution liquid chromatography (GELC) suffered from coelution problems. Pyrolysis-gas-chromatography (Py-GC-MS) experiments allowed determining the monomer ratio. SEC with UV and refractive-index detection indicated the presence of molecular-weight-dependent chemical heterogeneity for the poly((EA)b-(BnA-ran-EA)b) copolymer. This finding was confirmed with off-line SEC//Py-GC-MS. Only a comprehensive two-dimensional GELC × SEC setup enabled the separation of high-molecular-weight material of the less-retained homopolymer from low-molecular-weight copolymeric material. In this way it was possible to detect some high-molecular-weight homopolymeric material in one of the copolymers.
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