On-line extraction of polymers, oligomers, additives and monomers by multiple solvents on packed HPLC columns

Extn. of monomers, additives, oligomers, and polymers from a blend is very time-consuming and labor intensive. Using a special guard column and multi-solvent gradient liq. chromatog. (HPLC), the extn. and anal. can be performed in one ste

Critical retention behavior of homopolymers

The isocratic retention behavior of a homopolymer at a specific temp. and varying solvent compns. can be divided into three modes: exclusion mode, transition mode (crit. conditions) and adsorption mode. Under crit. conditions (a specific non-solvent/solvent compn. at a specific temp.) the retention of a homopolymer is independent of the molar mass. The crit. conditions depend upon the temp., the type of polymer and the type of non-solvent/solvent mixt. A difference in the crit. conditions between polystyrene stds. and polybutadiene stds. was found. No significant influence of different types of column packing on the crit. solvent compn. was noticed. The exact mechanism of the retention of a polymer under crit. condition is not clear yet. In order to det. the crit. conditions, a new method has been developed. The method can be easily performed on existing equipment. The method contains a different setup of the data acquired by isocratic HPLC than methods described in literature. Therefore, less expts. need to be performed to det. the crit. conditions compared to the current method. The newly developed method is more efficient than the methods described in the literatur

Critical retention behavior of homopolymers

The isocratic retention behavior of a homopolymer at a specific temp. and varying solvent compns. can be divided into three modes: exclusion mode, transition mode (crit. conditions) and adsorption mode. Under crit. conditions (a specific non-solvent/solvent compn. at a specific temp.) the retention of a homopolymer is independent of the molar mass. The crit. conditions depend upon the temp., the type of polymer and the type of non-solvent/solvent mixt. A difference in the crit. conditions between polystyrene stds. and polybutadiene stds. was found. No significant influence of different types of column packing on the crit. solvent compn. was noticed. The exact mechanism of the retention of a polymer under crit. condition is not clear yet. In order to det. the crit. conditions, a new method has been developed. The method can be easily performed on existing equipment. The method contains a different setup of the data acquired by isocratic HPLC than methods described in literature. Therefore, less expts. need to be performed to det. the crit. conditions compared to the current method. The newly developed method is more efficient than the methods described in the literatur

Monitoring of originated polymer in pure monomer with gradient polymer elution chromatography (GPEC)

The anal. of the amt. of polymer in pure monomer with cloudpoint measurements gives only a qual. answer. Now by use of a liq. chromatograph and gradient elution a fully automated detn. the amt. of polymer can be measured and an impression of the molar mass can be achieve

Ester-functionalized polycarbonates obtained by copolymerization of ester-substituted oxiranes and carbon dioxide: A MALDI-ToF-MS analysis study

Two ester-functionalized cyclohexene oxide monomers (3,4-cyclohexene-oxide-1-carboxylic acid methyl ester (1) and 3,4-cyclohexene-oxide-1-carboxylic acid phenyl ester (2)) could be copolymerized with CO2 using the ß-diketiminato zinc catalyst (EtBDI)ZnOEt (EtBDI = 2-(2,6-diethylphenyl)amido-4-(2,6-diethylphenyl)imino-2-pentene) under mild conditions. MALDI-ToF-MS microstructure analyses of the formed aliphatic polycarbonates revealed the occurrence of chain transfer reactions to both monomer and polymer as a result of zinc-catalyzed transesterifications. As a consequence, branched and cyclic polymer structures were formed, which limited the molecular weight development and led to an increase in the polydispersity. The zinc catalyst is also capable of transesterifying carbonate functionalities, albeit that the transesterification rate is considerably lower than that for ester functionalities and only becomes visible at high conversion. This was supported by independent catalytic transesterification reactions of esters and carbonates. Transesterification of carbonate functionalities at the end of the polymerization reaction might explain the observed bimodal behavior for the intrinsically living ß-diketiminato zinc catalyst

Recycling gradient-elution liquid chromatography for the analysis of chemical-composition distributions of polymers

Synthetic polymers typically show dispersity in molecular weight and potentially in chemical composition. For the analysis of the chemical-composition distribution (CCD) gradient liquid chromatography may be used. The CCD obtained using this method is often convoluted with an underlying molecular-weight distribution (MWD). In this paper we demonstrate that the influence of the MWD can be reduced using very steep gradients and that such gradients are best realized utilizing recycling gradient liquid chromatography (LC↻LC). This method allows for a more-accurate determination of the CCD and the assessment of (approximate) critical conditions (if these exist), even when high-molecular-weight standards of narrow dispersity are not readily available. The performance and usefulness of the approach is demonstrated for several polystyrene standards, and for the separation of statistical copolymers consisting of styrene/methyl methacrylate and methyl methacrylate/butyl methacrylate. For the latter case, approximate critical compositions of the copolymers were calculated from the critical compositions of two homopolymers and one copolymer of known chemical composition, allowing for a determination of the CCD of unknown samples. Using this approach it is shown that the copolymers elute significantly closer to the predicted critical compositions after recycling of the gradient. This is most clear for the lowest-molecular-weight copolymer (Mw = 4.2 kDa), for which the difference between measured and predicted elution composition decreases from 7.9% without recycling to 1.4% after recycling

Silica-grafted diethylzinc and a silsesquioxane-based zinc alkyl complex as catalysts for the alternating oxirane-carbon dioxide copolymerization

A novel zinc silsesquioxane complex ([(c-C5H9)7Si7O11(OSiMePh2)]2Zn4Me4 (1)) has been used as a model compound for silica-grafted zinc catalysts in the copolymerization of cyclohexene oxide and CO2. Complex 1 exists as a dimer in the solid state and is moderately active in the copolymerization, and polycyclohexene carbonates have been obtained with a carbonate content of 79-98%. Polymerizations with ZnEt2-treated silica particles resulted in polymer particles with n and w values and carbonate contents comparable to those of the polymers obtained with 1. It was further demonstrated that CO2 consumption can be followed online by monitoring the decrease of system pressure during the reaction. CO2 consumption has been interpreted in relation to both polycarbonate and cyclic carbonate formation. These measurements represent the intrinsic kinetics of this reaction, which appear to be directly related to CO2 pressure