SK288062B6 - Process for separation of multicomponent synthetic polymers - Google Patents

Abstract

It is described a process for separation of multicomponent synthetic polymers with a barrier process. As mobile phase is used a mixture of strong and weak solvent in the composition of 70/30 h./Wt. dimethylformamide / toluene, wherein barriers apply at the sample of mixture of macromolecules, at first with a higher concentration of the weak solvent and later with barrier of the weak solvent alone.

Description

Technical field

The invention relates to a process for separating multi-component synthetic polymers according to their composition, independently of their molar mass.

BACKGROUND OF THE INVENTION

The properties of synthetic rubbers and plastics depend on the molecular characteristics of the macromolecules that make up them, on the mutual arrangement of the macromolecules, and on the type and amount of impurities such as stabilizers, antioxidants, plasticizers, fillers, colorants, etc.

The molecular characteristics of the macromolecules are the molar mass (M), the chemical structure (e.g., their composition and functionality) and the physical architecture (e.g., their linearity / branching / cyclic structure, stereoregularity or cis-trans isomerism). The molecular characteristics of the polymers are determined by various physicochemical methods, in particular chromatography, spectroscopy including mass spectrometry, and nuclear magnetic resonance (NMR).

Without exception, all synthetic polymers have a non-uniformity in molecular characteristics with a defined distribution around average values. If a macromolecular substance simultaneously has more than one distribution of molecular characteristics (molar mass distribution is always present), it is referred to as a complex polymer or a complex polymer system (Berek, D .: Progr. Polym. Sci. 25, 2000, p. 873) . These include e.g. blends of polymers, various types of copolymers, stereoregulated polymers, derivatized polymers, etc. Most physicochemical methods of measuring polymer properties provide average values for their molecular characteristics.

In order to determine the distribution of molecular characteristics, the polymers need to be separated. Presently, liquid chromatography methods are used for the separation of polymers and more recently, especially for the lower molar masses, also mass spectrometry methods. Liquid chromatography methods are dominated by gel permeation chromatography (GPC) (Berek, D., Rubin, M., Marcinka, K., Dressler, M .: Gel Chromatography, Science, Bratislava, 1983), also known in the Anglo-Saxon literature as size exclusion chromatography. GPC separates the polymers according to the size of their joints in solution and provides accurate values of mean molar mass (MMM) and their molar mass distribution (MMD) for macromolecules whose size in solution is a blowing of exclusively molar mass and branching. For the vast majority of complex polymers, the size of the macromolecules in solution is a blowing not only of molecular weight, but also of other molecular characteristics, e.g. the chemical composition of the components of the polymer or copolymer mixture. For this reason, the MMM and MMD values of the complex polymers obtained by GPC are not absolute values. This is only indicative data, suitable for assessing tendencies (growth - decline in MMM, widening - narrowing MMD). In the case of multi-component polymer blends containing macromolecules of similar size, it is usually not possible to make such orientation closures from GPC measurements. The components of the mixture in this case elute together from the GPC column, they are not separated. Therefore, the components of the polymer mixture need to be separated from each other regardless of their molar mass before each component is separated according to the size of its macromolecules. Combined methods of coupled methods of polymer HPLC are used to separate the components of complex polymers [Berek, D .: Progr. Polym. Sci. 25, 2000, p. 873]. Combining these last methods online with GPC is called two-dimensional liquid chromatography of polymers (2-D polymer HPLC) (Berek, D .: Progr. Polym. Sci. 25, 2000, p. 873, Berek, D .: Two-Dimensional Liquid Chromatography of Synthetic Macromolecules, IN: Chi-san Wu, ed., Handbook of Size Exclusion Chromatography and Related Techniques, M. Dekker, New York, 2004).

Several combined methods of HPLC polymers have been proposed (reviewed in Berek, D .: Progr. Polym. Sci. 25, 2000, p. 873). These associate the exclusive (entropy) GPC separation mechanism with the interactive (enthalpy) macromolecular separation mechanisms. In the development of combined HPLC polymer methods, it is important to identify experimental conditions such that the elution of macromolecules from the liquid chromatography columns is as little as possible dependent on the molar mass of the sample. In this way, separation (virtually) is ensured exclusively according to the desired molecular characteristic - e.g. in the case of polymer blends, this is the composition of the components.

The most commonly used combined method of HPLC polymers is liquid chromatography under critical enthalpy interaction conditions (LC CC) (Berek, D .: Progr. Polym. Sci. 25, 2000, p. 873). It compensates for the exclusive and interactive mechanism of separation, and the macromolecules with a certain chemical composition are eluted from the LC CC column independently of their molar mass. Macromolecules of different composition are eluted from the column either in the exclusion or until their MMM is not too high - in an interactive mechanism and thus separated from the LC CC of the eluted macromolecules. The disadvantages of LC CC include high sensitivity to small changes in experimental conditions (Berek, D .: Macromol. Symp. 110, 1996, p. 33), significant expansion of chromatographic zones, impossibility to work with high M polymers, low sample yield (Berek, D (Russ, A .: Chem. Pap. 60, 2006, p. 249) and the ability of the method to usually separate only two different polymers.

Another popular combined polymer HPLC method utilizes elution of macromolecules in the eluent composition gradient (Berek, D., Kubin, M., Marcinka, K., Dressler, M., Gel Chromatography, Science, Bratislava, 1983). In the Anglo-Saxon literature, this method is often referred to as eluent gradient polymer HPLC (EG HPLC). At the beginning of the experiment, the sample components are retained by the enthalpy interaction on the packing at the entrance to the column, from where they are eluted successively in a gradient of increasing elution force of the mobile phase. In this case too, it is possible to create experimental conditions such that macromolecules of different compositions are eluted irrespective of their molar mass. Under optimal conditions, EG HPLC provides narrow chromatographic zones and allows separation of more than two different types of polymers. A general disadvantage of EG HPLC polymers is the limited repeatability and reproducibility of the mobile phase gradient and problems with sample recovery that can be irreversibly retained in the column (Berek, D., Russ, A .: Chem. Pap. 60, 2006, p. 249).

A third group of combined polymers of HPLC polymers is liquid chromatography under liquid enthalpy interactions (LC LC). (Berek, D .: Progr. Polym. Sci. 25, 2000, p. 873) LC LC utilizes a large difference in the elution rate of small eluent and macromolecule samples from a porous packed column. Small molecules penetrate into the pores of the cartridge and their path is extended. Macromolecules are partially or completely excluded from the pores of the packed bed and are transported through the column rapidly. Suitably selected small molecules delivered to the column in front of the macromolecules promote enthalpy interactions of macromolecules in the column and selectively inhibit their rapid elution, forming a certain non-permeable barrier. Therefore, such procedures are also called barriers. Under optimized conditions, LC LC provides narrow, focused peaks because the macromolecules of the sample accumulate at the leading edge of the barrier. Further, the elution of the polymer does not depend on its molecular weight and the method works reliably even at very high molecular weights of the sample. LC LC polymer separation rates are very high, typically a few minutes. LC LC procedures are very robust in most cases, i. j. little sensitive to changes in experimental conditions. This simplifies the identification of a suitable chromatographic system for solving a given separation task and increases the repeatability and reproducibility of measurements (Šnauko, M., Berek, D .: J. Chromatogr. A, 1094, 2005, p. 42). To date, LC LC procedures have been used to separate binary polymer mixtures (Šnauko, M., Berek, D .: J. Separ. Sci. 28, 2005, p. 2094). A single barrier was used that selectively slowed the elution of one type of polymer while the other eluted rapidly in the exclusion mechanism. SUMMARY OF THE INVENTION The present invention is based on the use of a series of barriers with different compositions and thus with a different ability to block rapid elution of polymers of different compositions. This can be used for the rapid and efficient separation of multi-component polymer blends, particularly for separating the parent homopolymers from the block copolymers.

Block copolymers of type A-B consist of macromolecules, where A denotes a polymer chain composed of one type of monomer units and B denotes a chain composed of another type. Both chains are bound by chemical bonding (Lazzari, M., Liu, G., Lecommandoux, S., Block Copolymers in Nanoscience, Wiley, New York, 2007). Block copolymers present an important challenge for research, especially since they have found widespread application in technological practice as surfactants, polymer blend compatibilizers, function carriers, etc. Their production is estimated to be hundreds of thousands of tonnes per year worldwide. Research and production are about how to produce block copolymers and how to characterize them. Generally, the block copolymers are formed by first preparing block A and, at the end (or ends), polymerization of block or blocks B. In particular, methods of anionic polymerization or controlled free-radical polymerization are used. In either case, the polymerizations exhibit breakdowns: Either polymerization B on the already formed block A does not start or polymerization B starts independently of block A. In both cases, homopolymers A or B - or both - appear in the system in addition to copolymer A - B. . The homopolymers present in the block copolymers are called parent homopolymers. These are, at best, ballast, a loss of material. Often, however, the presence of homopolymers significantly reduces the technological quality of the block copolymers. Therefore, it is understandable to determine the concentration and to determine the molecular characteristics of the parent homopolymers in block copolymers in order to optimize their synthesis and utilization. For such analysis, the parent homopolymers A and B need to be separated from the block copolymers A-B. The use of conventional methods for such separation (eg gradual precipitation or gradual dissolution) is time consuming (tens of hours) and often poorly effective (differences in solubility) components A or B and A - B are usually small) and the homopolymers are occluded in the copolymer. Therefore, GPC is usually used for this purpose, although the selectivity of exclusive separation is in most cases insufficient to completely separate A or B from A - B. This is particularly pronounced when one of the blocks is short and the other long. In such a case, the size of the long blocks and the corresponding parent homopolymer is similar to the size of the macromolecules of the whole copolymer. Insufficiently separated chromatographic peaks are mathematically deconvolved, but the results obtained are poorly accurate. When the parent homopolymers in the copolymers are less than about 5%, GPC fails completely.

The above problems of separation of multi-component polymer blends, including separation of parent homopolymers from block copolymers, are solved by the present invention.

SUMMARY OF THE INVENTION

The subject of the invention is the application of tandem of two or more barriers in LC LC systems. Each of the barriers retains one component of the complex polymer system. Ideally, the LC LC system is selected such that one polymer is not retained at all, i. j. to freely wash out in the GPC mode. Then, n-1 barriers are needed to distribute the n-component mixture. Typically, two barriers are used to completely separate the three-component blend of polymers as well as to separate both parent homopolymers from the block copolymer. The realization of the necessary chromatographic equipment is unpretentious, since it only requires the inclusion of an additional metering valve in conventional liquid chromatography - between the original sample metering valve and the chromatography column. This metering valve is used to convey zones of liquids that act as barriers. Moreover, the search for suitable experimental conditions requires only a basic knowledge of the nature and role of enthalpy interactions of macromolecules in a given chromatographic system. Examples of embodiments of the invention are shown on the separation of a three-component blend of different polymers and, in a single step, practically unenforceable separation of the two parent homopolymers A and B from the block copolymer A-B. These examples demonstrate the potential of the invention. polymer components having a different chemical composition or physical architecture.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 shows the separation of polystyrene, poly (methyl methacrylate and poly (ethylene oxide) in one step by means of a two-barrier LC LCD (details in the text).

In FIG. 2 is a schematic representation of the course of separation of three polymers by LC LC using two barriers.

a) Situation at the moment of injection of barrier # 2 and sample. Barrier # 1 is already passing through the column.

b) Situation in approximately one third of the experiment. Homopolymer A elutes in the secreted (GPC) mode, i. j. he is not detained. Barrier # 2 released the copolymer, but barrier # 1 detained it. Homopolymer B is retained by barrier # 2.

In FIG. 3 shows the separation of the PS-b-PMMA copolymer from its parent PS and PMMA homopolymers in one step by means of a two-barrier LC LCD.

In FIG. 4 shows the separation of the PPO-b-PEO copolymer from its parent PPO and PEO homopolymers in one step by means of a two-barrier LC LCD.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Separation of a three-component mixture of homopolymers with similar molar masses. An example is a fast (<3 min.) And effective (at baseline) separating the polystyrene (PS) (M ~ 37,000 g.mol ^1), poly (methyl methacrylate (PMMA) (M ~ 36 000 g.mol ¹⁾ and poly ( Ethylene oxide) (PEO) (M ~ 50,000 g / mol ¹ ) The average molar masses of the polymers are similar and their molar mass distributions are relatively broad - these are industrial polymers - such a mixture cannot even be theoretically separated by GPC. adsorption of macromolecules on the surface of unmodified silica gel (Silpearl, Sklámy Votice, Czech Republic) with a pore diameter of 5 nm Eluent is a mixture of a strong solvent that prevents adsorption of PMMA and PEO (desorli) dimethylformamide (DMF) and weak PMMA adsorption PEO (adsorli) -toluene PS is not adsorbed onto silica gel from pure solvents and mixtures thereof The mobile phase has a composition of 70/30 w / w DMF / toluene This composition has been chosen so that Three polymers eluted in GPC mode The experiment temperature was 30 [deg.] C. Dose concentration of polymers: 1 + 1 + 1 mg / ml. Two tandem barriers (200 μΐ each) of 100% toluene and toluene / DMF (90/10% w / w) were used. Bariéra č. 1 (toluene) was dosed 36 seconds before the sample, barrier no. 2 immediately before the sample solution. The elution rate was 1 ml / min. ¹ . Schematically, the process shown in FIG. 1. The result of the separation, the chromatogram, is shown in FIG. 2. In this case, unlike FIG. 1, the retention volume of the samples increases from left to right. The example illustrates the high rate and efficiency of separation. The chromatographic peaks obtained are narrow. For barrier-retained polymers, the width of the peaks over a wide range does not depend on the sample volume dosed. This is important for preparative and two-dimensional separations.

Example 2

Separation of the block copolymer of polystyrene and poly (methyl methacrylate) in PS-b-PMMA from its parent homopolymers PS and PMMA. It is a commercial sample of Polymer Laboratories, Varian, Church Stretton, United Kingdom, batch no. 29120-31. Its reported MMM is 140,000 g / mol ¹ and the percentage of PS blocks is 76.6% by weight. That is, PMMA blocks should have an M ~ 33,000 g / mol * and PS blocks, an M ~ 107,000 g / mol *. The column used was as in Example 1. The eluent used was a mixture of toluene (adsorli for PMMA, desorli for PS) and tetrahydrofuran (THF - desorli for both polymers) 50/50 w / w. The temperature of the experiment was 30 ° C. Dosing volume V; was 20 µL, the sample concentration was c, 1 mg / ml. A tandem of two barriers, each with a volume of 200 μΐ, was used. Bariéra č. 1 (cf. FIG. 1) contained pure toluene. She was holding the block copolymer. After 36 s. the barrier no. 2, which contained 82 wt. % toluene. The chromatogram obtained is shown in FIG. 2. PS eluted without enthalpy trap, in GPC mode. This was followed by a copolymer which was not retained by barrier no. 2, but was detained on barrier no. 1. Finally, PMMA, retained by barrier no. 2. FIG. 2, both homopolymers appear beside the prevailing copolymer. As can be seen, the separation is very fast and the chromatographic zones are narrow. This creates the prerequisites for two-dimensional liquid chromatography, where the second dimension may be an on-line GPC column. This example shows that the commercial sample is not pure, as claimed by the manufacturer, but contains a significant amount of PMMA in addition to a small amount of the homopolymer PS. So far, it has not been possible to separate these ingredients quickly and accurately.

Example 3

The separation of the PPO-b-PEO block copolymer of polypropylene (PPO) and polyethylene oxide (PEO) is shown in FIG. 4. This is a laboratory sample (Dr. S. Carlotti, University of Bordeaux, France). Chromatography column - as in Example 1. The eluent used was a mixture of toluene (adsorli for both PPO and PEO) and dimethylformamide (DMF) (desorli for both PPO and PEO) of 80/20 w / w. The temperature of the experiment was 30 ° C. Dosing volume v; was 20 μΐ and the dose concentration Cj was 1 mg.mľ *. A tandem of two barriers was used, each having a volume of 200 μΐ. Bariéra č. 1 contained pure toluene. She was holding the block copolymer. After 36 seconds, the barrier no. 2, which contained 90 wt. % toluene. Bariéra č. 2 retained the PEO homopolymer. PPO eluted in the GPC mode, not restrained by any of the barriers. This was followed by a block copolymer retained by the toluene barrier and finally a PEO homopolymer retained by the barrier was eluted from the column.

Claims (3)

PATENT CLAIMS A process for separating multicomponent synthetic polymers by means of a barrier process, characterized in that a mixture of macromolecules of different chemical composition is fed into a column packed with porous silica gel and washed with a mobile phase consisting of a mixture of a strong solvent and a weak solvent of 70/30 w / w. dimethylformamide / toluene, which, in the absence of barriers, ensures free elimination of all components of the separated mixture, while the sample is gradually treated with barriers that selectively retain the individual components of the mixture by first acting through a barrier containing an increased concentration of weak solvent of 90 / 10 w / w. toluene / dimethylformamide and subsequently the sample is treated with an even more effective barrier of the weak solvent itself. The separation process according to claim 1, wherein the strong solvent is dimethylformamide. The separation method of claim 1, wherein the weak solvent is toluene.