Two-dimensional chromatographic characterisation of PS-b-PEO copolymers at the critical conditions of their corresponding homopolymers

[摘要] ENGLISH ABSTRACT: Block copolymers are very interesting materials but they are quite complex. During polymersynthesis only a certain amount of control can be enforced. As copolymers are made up of twoor more different homopolymer segments, and therefore have different end group possibilities,varying block lengths and block sequences, they have complex structures and are thereforedifficult to analyse.Different techniques exist by which polymers can be analysed to determine theaforementioned distributions. In order to achieve a complete characterisation of a polymerstructure, it is best to first use a separation technique to fractionate the polymer into morehomogeneous fractions, and then use identification techniques to analyse these fractions.Polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers were investigated usingliquid chromatography at the critical conditions (LCCC) of the copolymers' correspondinghomopolymers, two-dimensional liquid chromatography (2D-LC) and FTIR. The blockcopolymers were analysed using the established LCCC of PS but it was found that eventhough separation of PS homopolymer and copolymer was obtained, PS blocks of thecopolymers contributed to some extent to the retention of the PEO blocks.Some of the block copolymer samples were fractionated at the established criticalconditions of PS. These fractions were qualitatively and quantitatively analysed using FTIRspectroscopy. The settings for the 2D-LC analysis were established, using LCCC of PS as thefirst dimension and as the second dimension SEC, using DMF as eluent. DMF was a suitablesolvent to be used for the second dimension because PS, PEO and PS-b-PEO exhibited goodsolubility in this solvent. THF did not dissolve the block copolymers completely.The same solvent system as used for LCCC of PS was used for LCCC of PEO, but thecritical conditions correspond to a different solvent composition. The block copolymers wereanalysed using the established LCCC of PEO but it was found that even though separation ofPEO homopolymer and copolymer was obtained, the PEO blocks of the copolymerscontributed to some extent to the retention of the PS blocks. Some of the block copolymersamples were fractionated at the established critical conditions of PEO. These fractions werequalitatively and quantitatively analysed using FTIR spectroscopy. The settings for the 2D-LCanalysis were established, using LCCC of PEO as the first dimension and as the seconddimension SEC using DMF as eluent was used. Lastly, qualitative and quantitative analyses ofthe block copolymers were carried out using FTIR spectroscopy.

[发布机构] Stellenbosch University