Determination of the Composition of Statistical Copolymers by Liquid Chromatography Under Limiting Conditions of Adsorption

Abstract

Liquid chromatography under limiting conditions of adsorption (LC LCA) was applied to determine the composition of statistical poly(styrene-methyl methacrylate) (PS/ MMA) copolymer standards. Two series of copolymers were prepared and characterized. The first series varies with respect to the styrene/methyl methacrylate ratio in the copolymer, at a constant molar mass (220,000 i 30,00Og/mol), while the second has molar masses from 20,000 to 250,000 g/mol at a molar styrene fraction of 0.5 f 0.02. The copolymers were fractionated using size exclusion chromatography (SEC) and LC LCA.In the case of LC LCA, two different ratios of THF to n-hexane were employed. Low and high LC LCA were differentiated according to the composition of the binary eluent, the lowest n-hexane content corresponding to low LC LCA. The influence of the molar mass on the peak distance, defined as the difference of retention volume between SEC and LC LCA, was negligible in the studied range compared to composition effect. A calibration curve was subsequently established and correlated the peak distance to the copolymer composition. The application range of the calibration curve was found to vary with the percentage of n-hexane contained in the eluent and corresponded to 0.1 -0.4 and 0.2-0.6 molar fraction of styrene for low and high LC LCA, respectively. Using these calibration curves, the P(S/MMA) copolymer composition distribution calculation was estimated for one sample. Therefore, the limiting condition method can be coupled on-line or off-line with SEC to perform a simultaneous characterization of the compositions and molar mass distributions.

Dilute Solution Characterization of Statistical Poly(styrene-co-methylmethacrylate) Polymers as Applied to Liquid Chromatography under Limiting Conditions of Adsorption

“…In the case of the solvent employed in the SEC study, such as THF and a mixture of THF and n-hexane, the experimental radius of gyration analysis corroborates liquid chromatographic observations. [2] …”

“…While it is certainly not unusual that A 2 varies with composition, we should note that both THF and toluene are poorer solvents for PS than for PMMA, as has been evidenced by recent LC LCA experiments. [1,2] The LC LCA experiments of Sauzedde and Hunkeler [2] also reveal the strongest dependence of solvency over the same range of styrene contents. Therefore, the virial coefficient data, while somewhat noisy, seem to reflect the general solution behavior of such copolymers.…”

“…Chromatography under limiting conditions of adsorption (LC LCA) is a new method that has been developed to overcome this problem and to perform a simultaneous determination of copolymer molar mass and composition as well as their distributions. [1,2] For the purpose of separately studying molar mass and composition effect on the elution using LC LCA, two series of statistical poly(styrene-co-methyl methacrylate) polymers have been employed.…”

Liquid Chromatography under Critical and Limiting Conditions: A Survey of Experimental Systems for Synthetic Polymers

“…Blends of polymers and structurally different macromolecules, i.e., cyclic versus linear versus branched and even with different tacticity, have been separated. Graft copolymers has been studied [43,117] as well as random copolymers [111,153,154] (Fig. 13).…”

Determining the Polydispersity in Chemical Composition and Monomer Sequence Distribution in Random Copolymers Prepared by Postpolymerization Modification of Homopolymers

“…Kawai et al and Teramachi et al attempted to measure the PCC in poly[styrene- co -(methyl methacrylate)] copolymers via HPLC. Several other groups have also used various HPLC variants, including size exclusion chromatography (SEC) and temperature rising elution fractionation, to determine the PCC of RCPs. − However, none of these techniques has been able to quantify the PCC in random copolymers. Several factors may have likely contributed to this difficulty, including a broad PMW, which contributes significantly to the broadness in the HPLC curves and makes determination of PCC very challenging, if not impossible.…”