Chromatographic investigations of macromolecules in the critical range of liquid chromatography: 11. Polymer blend separation using a reversed stationary phase1Part 10: cf. Pasch and Rode[16]1

Separation and characterization of functional poly(n-butyl acrylate) by critical liquid chromatography

The separation of functional poly(n-butyl acrylate) (PnBA) polymers based on the number of end-groups under critical liquid chromatography (LC) conditions has been studied using a bare-silica column. The (near-) critical solvent compositions for non-, mono-, and difunctional (telechelic) carboxyl-PnBAs were determined in normal-phase LC, using mixtures of acetonitrile, acetic (or formic) acid, and dichloromethane of varying composition. Some formic or acetic acid had to be added to the mobile phase to elute PnBA polymers with carboxyl end-groups. The critical solvent compositions obtained were not exactly the same for non-, mono-, and difunctional PnBA polymers. These were unusual experimental observation, but they were in agreement with theoretic predictions. Nevertheless, low-molecular-mass PnBA samples were successfully separated according to the carboxyl functionality at (near-) critical conditions. With the aid of mass spectrometry (MS), the (near-) critical separation of low-molecular-mass PnBA polymers was confirmed to be mainly based on the carboxyl functionality. Calibration curves for evaporative light-scattering detection (ELSD) were used for quantitative analysis of carboxyl-functional PnBA polymers. The results proved that nearly ideal functionalities (average number of carboxyl end-groups per molecule up to 1.99) were achieved for telechelic PnBAs prepared by one-step reversible addition-fragmentation chain-transfer (RAFT) polymerization of PnBA.

Quantitative Characterization of a Polystyrene/Poly(α-methylstyrene) Blend by MALDI Mass Spectrometry and Size-Exclusion Chromatography

The use of coupled size-exclusion chromatography and MALDI mass spectrometry for quantitative measurement of the composition of technical polymer blends at the molecular level is described. The method is illustrated with a model binary blend consisting of polystyrene and poly(alpha-methylstyrene), both polymers having similar molecular weights and polydispersities. The proposed MALDI data treatment allows determination of the chemical composition of the blend, the molecular weights of the constituents, and the distributions of the homopolymers.

Endgroup-based separation and quantitation of polyamide-6,6 by means of critical chromatography

Polyamide-6,6 is a polycondensation product from the two monomers adipic acid and 1,6-hexamethylenediamine. Depending on the reacted amount of these monomers, different ratios of amine and carboxylic acid endgroups can be formed. Besides linear chains, cyclic polyamides will also be formed. Using critical chromatography, polyamide-6,6 can be separated independently of molar mass. Retention is based solely on endgroup functionality. It is demonstrated that high-molecular-mass polyamide-6,6 (Mw approximately 20,000-30,000) can be separated using this approach. The separation was optimized by using different parameters, such as percentage modifier, temperature and pressure. The concentration of phosphoric acid was used for selective retention of the different endgroup functionalities. Using this property, a new method called critical gradient chromatography was performed where the mobile phase changes from a weak to a strong solvent with respect to the endgroup functionality, while retaining the critical conditions of the backbone unit. Quantification using UV detection is discussed.

Separation and quantification of the linear and cyclic structures of polyamide-6 at the critical point of adsorption

The linear and cyclic structures of polyamide-6 were separated by liquid chromatography at critical conditions (LCCC) and identified with different mass spectrometric (MS) techniques and quantitated by LCCC with evaporative light-scattering detection (ELSD). Electrospray ionization MS was not suitable to identify the higher cyclic structures. For this purpose, matrix-assisted laser desorption ionization time-of-flight MS performed better and cyclic and linear structures were oligomerically resolved and separately identified in the mass spectrometer. The highest cyclic structure present and detected was the cyclic pentacontamer. It could be demonstrated that cyclic and linear oligomers follow different ionization and fragmentation routes/patterns. Quantification with ELSD of the components separated by LCCC using a universal calibration curve or an iterative procedure was developed. An area correction to account for different peak widths of coeluting components improves precision and accuracy of the calibration curve and improves quantitation accuracy for the samples analyzed. With these corrected values, no molecular mass dependency was observed for the cyclic and linear structures. Under critical conditions, the linear and cyclic structures of polyamide-6 were separated, identified and quantified.