Fractionation of Poly(vinyl methyl ether): Comparison of Two Large

Ind. Eng. Chem. Res. 2009, 48, 6943–6948

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Fractionation of Poly(vinyl methyl ether): Comparison of Two Large-Scale Fractionation Techniques Simona Morariu,†,‡ John Eckelt,*,†,§ and Bernhard A. Wolf† Institut fuer Physikalische Chemie der Johannes Gutenberg-UniVersitaet Mainz and Materialwissenschaftliches Forschungszentrum der UniVersitaet Mainz, Welder-Weg 13, D-55099 Mainz, Germany, and WEE-SolVe GmbH, Auf der Burg 6, D-55130 Mainz, Germany

The efficiencies of two large-scale fractionation techniques namely continuous polymer fractionation (CPF) and continuous spin fractionation (CSF) are compared. To this end, we used a commercially available sample of poly(vinyl methyl ether). Both methods are suitable to reduce the nonuniformity of the sample below 0.6. The results demonstrate that CSF has a better fractionation performance than the progenitor method, CPF. A further advantage is the three times higher throughput of CSF. 1. Introduction

2. Background

Since the beginning of polymer science, access to sufficiently large amounts of well-characterized polymers has been a problem. Especially, the availability of polymers with narrow molecular weight distribution is mandatory for basic research if one wants to study the influence of molecular weight on certain properties, like viscosity, durability, or compatibility. Nowadays materials with a defined molecular weight distribution gain also more and more industrial interest. The reason for this is that polymers are increasingly used in cosmetics/medicine or as high-duty materials for technical applications. As the polymers have to fulfill elaborate tasks, the requirements for the polymers are increasing. An example for the former field of application is hydroxyethyl starch (HES), and Novolak is an example for the latter field. HES represents a derivative of starch and finds application in medicine as a blood plasma expander. Its broad molecular weight distribution is a consequence of its biosynthesis. For the application as a blood plasma expander, it is necessary to remove chain material that is too long as well as molecular weight material that is too low: the long chains would be accumulated in the skin and lead to itching, while the short chains leave the body through the kidneys immediately and are therefore ineffective. Novolak is being used as a photoresistor for the production of miniaturized electrical circuits. In this case, it is necessary to remove the very low molecular weight material because these components limit the reduction in size. For only a few polymers is it possible to obtain material with the desired molecular weight and narrow molecular weight distribution. For some synthetic polymers, it is possible to achieve the desired product by means of living polymerization (e.g., anionic1 or atomic transfer radical polymerization (ATRP)2,3). However these methods are limited to certain polymers and due to the high cost to small amounts. For biopolymers, the molecular weight distribution is determined by the biological source. In order to achieve a desired molecular weight distribution, a separation of certain components out of a starting material is required. This separation process is called fractionation.

Many biopolymers and most synthetic polymers consist of very different species. Unlike low molecular weight compounds, which are normally made up of one kind of molecules only, polymers consist of molecules that are not identical. In the simplest case of linear homopolymers (identical monomeric units), those molecules differ in the chain length. The polymer exhibits a molecular weight distribution. With rising molecular complexity (chemically dissimilar monomeric units or nonlinear structures), additional modes of nonuniformity arise which might become important for technical applications. There are different kinds of analytical methods to determine the molecular weight of polymers like light scattering (LS), osmosis (OS), and ultracentrifugation (UC).4 These methods give access to different average values of the molecular weight namely the number average molecular weight Mn (OS; see eq 1), the weight average molecular weight Mw (LS; see eq 2), or the z-average molecular weight Mz (UC; see eq 3).

* To whom correspondence should be addressed. Tel.: +49 (0)61314813744. Fax: +49 (0)6131-883895. E-mail: [email protected]. † Universitaet Mainz. ‡ Current address: “Petru Poni” Institute of Macromolecular Chemistry, 41-A Grigore Ghica Voda Alley, 700487 Ias¸i, Romania. § WEE-Solve GmbH.

∑nM i

Mn )

i

i

(1)

∑n

i

i

∑nM i

Mw )

2 i

i

(2)

∑nM i

i

i

∑nM

3

∑nM

2

i

Mz )

i

i

i

(3)

i

i

where ni is the number of molecules of molecular weight Mi. The most powerful methods for the determination of molecular weights are gel-permeation chromatography (GPC)4,5 andsfor polymers with molecular weights that are not too highsmatrix-assisted laser deionization/ionization time-of-flight mass spectroscopy (MALDI-TOF).6 These methods give access to the whole molecular weight distribution of a polymer and therefore also to the nonuniformity U:

10.1021/ie900484g CCC: $40.75  2009 American Chemical Society Published on Web 07/09/2009

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U)

Mw -1 Mn

(4)

The nonuniformity represents a measure for the width of a molecular weight distribution. For polymers that consist of molecules with one chain length onlyse.g. proteinssthe nonuniformity is zero. As the difference in chain lengths of the single molecules rises, the nonuniformity increases. By removing low- and/or high-molecular weight material out off a starting materialsas is done by fractionationsthe nonuniformity is decreased. The fractionation of polymers is somewhat more difficult than for low molecular weight materials. The typical separation methods like distillation, fractional crystallization, or liquid-liquid extraction fail for polymers as their volatility is too low and many of them do not crystallize. The liquid-liquid extraction by means of incompletely miscible solvents is not applicable as the difference in solubility of molecules with dissimilar chain lengths is by far too small. The whole material would be found in one phase only. In almost all cases, it is mandatory to perform the separation of macromolecules in the dissolved state. A very powerful method is the preparative GPC which enables the access to different fractions in a single experiment. However, the amount of polymer that is fractionated in this manner does normally not exceed 1 g of polymer7 and scale-up for the production of several kilograms or tons per day is impractical or at least uneconomic. In order to fractionate large amounts, ultrafiltration8 can be used. However, this technique suffers from several fundamental drawbacks: Once a certain membrane is chosen, the molar mass at which the cut through the molecular weight distribution takes place is fixed. Further disadvantages are the fouling tendency of the membranes and the considerable amounts of solvent required due to the fact that the separation is normally performed with dilute polymer solutions. Large-scale fractionation techniques that avoid these drawbacks are based on liquid-liquid phase separation.9-12 Figure 1 shows how such a phase separation can be achieved for a binary system consisting of a polydisperse polymer and one solvent. The solvent power is reduced in such a manner that an initially homogeneous polymer solution (called feed, FD) demixes into a polymer rich phase (gel, GL) and a polymer lean phase (sol, SL). This can be achieved either through a change in temperature (route A) or in composition (route B) by adding pure solvent (extracting agent, EA) to the feed solution. In both cases the condition of the working point (WP) is reached which lies within the miscibility gap (shaded area). In daily life, binary systems are normally not used for fractionation because the miscibility gap is for a given polymer determined by the choice of the solvent. In many cases the fractionation would have to be performed at unsuitable temperatures or concentrations. Therefore ternary systems consisting of the polymer, a solvent, and a nonsolvent are normally used for practical reasons. Figure 2 shows a typical ternary phase diagram of such a system in the form of the so-called Gibbs phase triangle. It gives the whole composition range of a ternary mixture at a constant temperature. The pure components are located in the corners while the binary subsystems are given by the edges. Ternary mixtures are represented by points lying inside the triangle. The schematic phase diagram depicted in Figure 2 shows a typical representation as used for fractionation. The polymer and the solvent are at the given temperature miscible for the entire range of composition. The same is true for the mixtures of solvent and nonsolvent while polymer and nonsolvent exhibit a miscibility gap.

Figure 1. Schematic phase diagram of a binary system consisting of polymer and solvent. The miscibility gap below the cloud point curve is shaded. Indicated in the graph is how the compositions of the working point (WP) is reached either by cooling down a homogeneous feed solution (FD*, route A) or by adding the pure solvent (extracting agent, EA) to a concentrated feed solution (FD, route B). The system demixes into a polymer rich gel phase (GL) and a polymer lean sol phase (SL).

Figure 2. Schematic phase diagram of a ternary system consisting of polymer, solvent, and nonsolvent at constant temperature. The miscibility gap is shaded again. The composition of the working point is reached by adding the extracting agent (in this case, consisting of solvent and nonsolvent) to the feed solution. The system demixes into gel and sol phases.

Despite the increased complexity, the ternary system has the advantage that normally for every polymer a suitable solvent/ nonsolvent system can be found to enable operation at convenient temperatures. As indicated in Figure 2, the feed can be a ternary mixture and the extracting agent can consist of a solvent and nonsolvent. The working point lies inside the miscibility gap, and therefore, the mixture separates into the sol and gel phase. The phase separation leads to an enrichment of the long chain material contained in an initially broadly distributed polymer in the gel phase for enthalpic reasons, while the low molecular weight material accumulates in the sol phase due to entropic reasons. As a result of this fractionation, the compositions of the gel and of the sol phase do not lie on the cloud point curve of the starting material (cf. Figures 1 and 2). The efficiency of a fractionation is characterized by the required amount of solvent, the polymer throughput, the reduction of the nonuniformity within a single fractionation step, and the number of fractionation steps that are necessary to achieve the desired goal. The fractionation efficiency is mainly determined by the choice of the solvent/nonsolvent system and the location of the working point. Different fractionation tasks call for different strategies. For instance: If a sepparation calls for the removal of short chain material, comparatively high polymer concentrations can be chosen for the working point (located inside the miscibility gap), where the distance of this composition from the cloud point

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Figure 3. Scheme of a separation column as used for CPF. The feed enters the column in the middle while the extracting agent is added at the lower end. Within the column, the system demixes into two liquid phases. Due to higher density, the gel phase normally is accumulated at the lower end while the sol phase leaves the column at the top. The column is divided into two different temperature zones T1 and T2 in order to increase the fractionation efficiency as described in the text.

depends on the fraction of the total material that should be transferred into the sol phase. Suitable conditions for the removal of high-molecular weight material do normally require lower polymer concentrations for the working point. More generally, for practical purposes, one is interested finding a reasonable compromise between the fractionation efficiency, which increases with dilution, and the expenditure of solvent, which increases simultaneously. Two patented techniques, based on liquid-liquid phase separation, are continuous polymer fractionation (CPF)13,14 and continuous spin fractionation (CSF).15,16 The experimental setup of these two techniques will be briefly presented in the following sections. Continuous Polymer Fractionation. With CPF, the older method, the mixing of the feed and the extracting agent can, e.g., be performed in a thermostatted glass column or a mixer-settler extractor. Figure 3 shows the setup for a separation column. The feed enters the column at the middle while the extracting agent is pumped at the bottom into the column. The desired overall composition is reached inside the column and gel and sol separate due to differences in their densities. The gel phase is accumulated at the bottom while the sol leaves the column continuously at the top. As indicated in Figure 3, the separation column is normally divided into two different temperature zones. This offers the opportunity to increase the fractionation efficiency: At the inlet of the feed, the source phase gets directly in contact with the sol phase instead of the extracting agent. For this reason, some high molecular weight material which belongs, for thermodynamic reasons, to the gel phase enters the sol phase and is dragged along to the upper exit of the column. In order to transfer the high molecular weight material back again into the gel phase, the temperature in the upper zone is chosen in such a manner that the solvent power is lower. This means that, for a system that demixes upon cooling, T2 has to be lower than T 1. One of the drawbacks of this method lies in the limitation to low polymer concentrations of the feed. For high concentrations, the viscosity of the feed reduces the mobility of the polymer chains contained in the droplets of the source phase to such an extent that no equilibrium is reached when the droplets reach the bottom of the column. This implies that short chain material is retained in the gel phase and the fractionation efficiency

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Figure 4. Scheme of a mixer-settler extractor consisting of four mixer-settler units. The sol phases enter the mixing vessels of the preceding unit while the gel phases enter the following mixer.

becomes poor. In principle, this problem can be solved by means of filling the column with carrier material (e.g., glass beads) to increase the residence time. However, this procedure increases the probability of backdamming dramatically. For this reason, the polymer concentration is limited to small values on the order of few weight percents only. Higher polymer concentrations can be handled by using a mixer-settler extractor. A mixer-settler unit consists of a vessel which mixes the feed and extracting agent vigorously followed by a settling vessel that allows the sol and gel phase to separate by gravity. The liquids are then removed separately from the end of the settler. In order to increase the fractionation performance, several mixer-settler units can be combined in a row (cf. Figure 4). In this case, the gel phase enters the following mixing vessel while the sol phase enters the preceding mixer vessel in a kind of countercurrent extraction. Such a set of mixer-settler units is a powerful method for liquid-liquid extractions. However, when applying it to the fractionation of polymers the small differences in the densities of the coexisting phases and the large differences in their viscosity make its use problematic. Continuous Spin Fractionation. CSF overcomes the limitation of low polymer concentrations and low flows by using spinning nozzles, like they are applied in the fiber industry. The feed is pressed through the nozzle in order to produce a large number (one spinning nozzle has about 1000 holes) of very thin threads with diameters in the range of 60-100 µm. Because of the Rayleigh instability,17 these threads break up immediately into tiny droplets of typically 50 µm diameter with a high surface to volume ratio. Due to the short distances of transportation, the more soluble component can leave the droplets much faster and equilibrium conditions are reached immediately. A scheme of a typical CSF setup is shown in Figure 5. It mainly consists of a mixing vessel into which the extracting agent is pumped freely and the feed is pumped through a spinning nozzle. From this container, the mixture is continuously transported into a device that allows macroscopic phase separation. In the simplest case, this is a column in which the phases separate due to their difference in density. In case of densities of the coexisting phases that are too similar or if high throughputs are desired, continuously working centrifuges can be used. Even with a laboratory-scale device of rather low capacity, it is possible to reach polymer throughputs on the order of 10-100 g/h. It is obvious that modifications, like the use of more spinning nozzles, a suitable mixing vessel, and a centrifugal separator to detach sol and gel, make virtually any size of fractions accessible. In this paper, we compare the efficiencies of the two most promising methods: the older CPF (performed

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Figure 6. Fractionation scheme as used for CPF (mixer-settler device): (solvent) toluene, (nonsolvent) petroleum ether. The distribution of the PVME into the two arising phases is indicated in weight percent for every step.18

Figure 5. Scheme of a typical apparatus suitable for CSF. Feed (FD) and extracting agent (EA) are transported by means of two precision pumps at the rate required to realize the desired working point (cf. Figure 1 and 2). The feed is spun through a spinning nozzle into a vigorously stirred vessel. The two-phase mixture produced in this manner is transferred into a column where one phase (normally the polymer rich gel phase) sediments and leaves at the lower end, whereas the other phase (normally the polymer lean sol phase) exits at the upper end. The differential molecular weight distributions of the initial polymer and the two obtained fractions are depicted in the insets.

by means of a separation column and a mixer-settler array) and the more recently developed CSF. For this purpose, we have chosen a commercially available sample of poly(vinyl methyl ether) (PVME) which we have already fractionated by means of CPF.18 3. Experimental Section 3.1. Materials. Poly(vinyl methyl ether) (Lutonal M40, in 70 wt % ethanol) was kindly donated by BASF, Ludwigshafen, Germany. According to gel-permeation chromatography (GPC) measurements, the weight average molecular weight Mw ) 50.5 kg/mol and the number average molecular weight Mn ) 18.1 kg/mol lead to a nonuniformity U ) Mw/Mn - 1 ) 1.79. Ethanol (EtOH) and n-hexane (n-hex) were used as the solvent and nonsolvent for the fractionation of PVME, while tetrahydrofuran (THF) served as the eluent for GPC measurements. All solvents were of p.a. grade and were obtained from Carl Roth GmbH, Karlsruhe, Germany, except n-hexane which was obtained from Fisher Scientific, Schwerte, Germany. 3.2. Methods. Gel-Permeation Chromatography. These experiments were carried out in THF at room temperature (Columns: PSS SDV gel, 102, 104, 105 nm, supplied by Polymer Standards Service (PSS), Mainz, Germany. Detectors: RI detector (Shodex RI-71) and UV detector (Spectra-Physics 200)). Polystyrene (PS) standards served for calibration. The molar mass resulting for PVME from GPC were obtained by means of universal calibration using the following Kuhn-MarkHouwink parameters for THF: KPS ) 0.0136 mL/g, aPS ) 0714 (at 25 °C);19 KPVME ) 0.0135 mL/g, aPVME ) 0.739 (at 30 °C).20 All samples were filtered through 0.45 µm Millipore membrane filters Membrex 13 PET (membraPure, Bodenheim, Germany) before injection. Continuous Spin Fractionation. The starting polymer solution (feed) and the extracting agent were pumped with precision pumps (Ismatec BVP, allowing an accurate flux control) from their storage tanks into a mixing vessel under vigorous stirring. The feed is pressed through a spinning nozzle consisting of tantalum with 800 holes of 90 µm diameter each. The twophase system arising from this procedure in the mixing vessel

Figure 7. Fractionation scheme as used for CPF (separation column): (solvent) toluene, (nonsolvent) petroleum ether. The distribution of the PVME into the two arising phases is indicated in weight percent.18 Table 1. Operating Conditions of the Continuous Polymer Fractionation by Means of a Mixer-Settler Extractor starting material run 1 Lutonal M40 run 2 gel 1 run 3 gel 2

comp FD comp EA flux FD flux EA (PVME/TL/PLE) (TL/PLE) (g/min) (g/min) 28/32/40 30/31/39 30/31/39

20/80 20/80 20/80

1.2 1.1 1.1

3.8 4.2 7.2

Table 2. Operating Conditions of the Continuous Polymer Fractionation by Means of a Separation Column starting material run 1 Lutonal M40

comp FD comp EA flux FD flux EA (PVME/TL/PLE) (TL/PLE) (g/min) (g/min) 30/25/45

13/87

2.0

4.0

is pumped (Ismatec BVP pump) into a thermostatted container with a volume of 10 L, to allow for complete macroscopic phase separation. 4. Results and Discussion The fractionation of PVME by means of CPF as reported in the literature was performed using a separation column as well as a mixer-settler device consisting of four mixer-settler units.18 The authors used two different Lutonal M40 charges for the fractionation with nonuniformities of 1.4 (mixer-settler device) and 1.1 (separation column), respectively. Toluene (TL) was used as the solvent while petroleum ether (PLE) with a boiling range from 60 to 80 °C served as the nonsolvent. The fractionation schemes of these two procedures are shown in Figures 6 and 7 while the important parameters like the compositions of FD and EA and their fluxes are collected in Tables 1 and 2. In case of a mixer-settler device, the authors needed three fractionation stepssusing the obtained gel fraction as the starting material for the following stepsin order to reduce the nonuniformity from 1.4 to a value below 0.6. The overall yield was in this case around 40 wt % of the initial material. When using a separation column, the authors achieved the same goal (nonuniformity below 0.6) with only one fractionation step. They came to the conclusion that the fractionation efficiency of the

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Two fractionation steps were necessary to achieve a PVME sample with a nonuniformity below 0.6 using the gel phase of the first step as starting material for the second step. 5. Conclusions

Figure 8. Phase diagram of the ternary system PVME/EtOH/n-hexane at room temperature. The inhomogeneous region is shaded. Indicated are the compositions of feed, extracting agent, and working point as well as the obtained sol and gel phases by means of CSF.

Figure 9. Fractionation scheme as used for CSF: (solvent) EtOH, (nonsolvent) n-hexane. The distribution of the PVME into the two arising phases is indicated in weight percent for every step. Table 3. Operating Conditions of the Continuous Spin Fractionation starting material run 1 Lutonal M40 run 2 gel 1

comp FD comp EA flux FD flux EA (PVME/EtOH/n-hex) (EtOH/n-hex) (g/min) (g/min) 20/80/0 4/33/63

0/100 0/100

9.1 13.2

38.0 13.9

CPF is somewhat higher for a separation column than for a mixer-settler device. Also, the throughputs achieved on the laboratory scale were for a separation column higher than for the mixer-settler device (36 g polymer/h for the column, 20 g polymer/h for the mixer-settler device). The authors claim that the main advantages of the separation column are the ease with which a second temperature reflux zone can be established and the less complicated technical performance. The main advantages of the mixer-settler device lie in the possibility to handle larger viscosities of the gel phase (i.e., lower consumption of solvent) and the tolerance with respect to smaller differences in the densities of the coexisting phases plus the fact thatsin the case of an interruptionsthe experiment can be restarted where is was interrupted. The fractionation of PVME by means of CPF was performed about 12 years before the fractionation by means of CSF. Meanwhile, BASF provided the PVME in ethanolic solution (ca. 70 wt %). Therefore, ethanol was used as a solvent instead of toluene for the actual fractionation. In this case, the supplied solution had only to be diluted down to manageable concentrations (ca. 20 wt %). n-Hexane served as the nonsolvent. The resulting phase diagram is shown in Figure 8. Indicated is the region on immiscibility (shaded area), the compositions of FD and EA (pure n-hexane) as used for the first fractionation step, the location of the working point, and the composition of the coexisting phases. In order to enable a comparison of the two fractionation techniques, the PVME sample was fractionated with the same goal: reducing nonuniformity below 0.6. The applied fractionation scheme is depicted in Figure 9. The significant parameters of the fractionation are collected in Table 3.

The experiments have shown that both large-scale methods, CPF and CSF, are well suitable for the fractionation of PVME. In comparison with the older CPF, the newer CSF has several advantages that make this technique more economic. First of all, the fractionation efficiency is higher for CSF than for CPF. This leads to a reduced number of fractionation steps necessary to achieve the desired nonuniformity. For CSF, the number of required steps was two while, for CPF, three steps (mixer-settler device) were necessary. The fact that only one step was required in the case of CPF using a separation column is not very surprising as the nonuniformity of the starting material was 1.1, i.e. much lower than for CSF where a sample with U ) 1.79 was used. Normally, the largest reduction in nonuniformity is achieved in the first fractionation step, where the starting material still has a broad molecular weight distribution. The narrower the molecular weight distribution gets, the more difficult it becomes to reduce the nonuniformity further. As both techniques are based on the same thermodynamic principles, the higher efficiency has to be explained by kinetics. In the case of CSF, the thermodynamic equilibrium is reached practically instantaneously due to the short distances that must be overcome to transport the components of higher solubility out of the source phase. Moreover the average lifetime of the initially formed droplets is considerably larger for CSF than for CPF, which means that the available time might in the latter case not suffice for the establishment of equilibrium. For CPF, the amount of polymer that was fractionated per hour was 20 g (mixer-settler device) and 36 g (separation column), respectively, while 109 g of PVME could be fractionated per hour by means of CSF. These data also show that an scaling up is much easier for CSF than for CPF. In the case of CPF, the dimensions of the separation column and the settling vessels have to be adjusted to the desired fluxes in order to guarantee long enough residence times for equilibration. In the case of CSF, only the mixing vessel and the number of spinning nozzles have to be scaled up andsif necessary because of insufficient density differencessan adequate centrifugal separator has to be used. In addition to its higher efficiency, CSF overcomes some drawbacks and combines some advantages of the different CPF methods. For example, the problem of backdamming that limits the polymer concentration in the case of the separation column to low values is not present in the case of CSF. In case of an interruption, CSF can be restarted easily while the separation column has to be refilled. Acknowledgment The authors are thankful to BASF for the donation of the PVME sample. The financial support of the DFG (436 RUM 113/24/1-1) is gratefully acknowledged. The spinning nozzle was kindly donated by the Lenzing AG, Austria. Literature Cited (1) Szwarc, M. Living Polymers and Mechanisms of Anionic-Polymerization. AdV. Polym. Sci. 1983, 49, 1. (2) Coessens, V.; Pintauer, T.; Matyjaszewski, K. Functional Polymers by Atom Transfer Radical Polymerization. Prog. Polym. Sci. 2001, 26, 337.

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(3) Patten, T. E.; Matyjaszewski, K. Atom Transfer Radical Polymerization and the Synthesis of Polymeric Materials. AdV. Mater. 1998, 10, 901. (4) Elias, H. G. Macromolecules; Wiley VCH Verlag GmbH: Weinheim, 2008. (5) Barth, H. G.; Boyes, B. E.; Jackson, C. Size-Exclusion Chromatography. Anal. Chem. 1994, 66, R595. (6) Nielen, M. W. F. Maldi Time-of-Flight Mass Spectrometry of Synthetic Polymers. Mass Spectrom. ReV. 1999, 18, 309. (7) Tung, L. H.; Moore, J. C. In Fractionation of Synthetic Polymers; Tung, L. H., Ed.; Marcel Dekker: New York, 1977. (8) Peinemann K. V.; Nunes S. P. Membrane Technology; Wiley-VCH: Weinheim, 2001. (9) Tung, L. H. Fractionation of Synthetic Polymers; Marcel Dekker: New York, 1977. (10) Francuskiewicz, F. Polymer Fractionation; Springer: Berlin, 1994. (11) Cantow, M. J. R. Polymer Fractionation; Academic Press: New York, 1967. (12) Koningsveld, R.; Kleintjens, L.; Geerissen, H.; Schu¨tzeichel, P.; Wolf, B. A. In ComprehensiVe Polymer Science; Allen, G., Ed.; Pergamon Press: Oxford, 1989. (13) Wolf, B. A.; Geerissen, H.; Roos, J.; Amareshwar, P. Verfahren zur kontinuierlichen Fraktionierung Von Polymeren im technischen Maβstab. Deutschland DE3242130.3A1, 1982.

(14) Wolf, B. A. CPF: Continuous Polymer Fractionation. Makromol. Chem., Macromol. Symp. 1992, 61, 244. (15) Eckelt, J.; Haase, T.; Loske, S.; Wolf, B. A. Spinning process and apparatus for the technical fractionation of oligomers and polymers. Chem. Abs. 2002, 139, 134096. (16) Eckelt, J.; Haase, T.; Loske, S.; Wolf, B. A. Large Scale Fractionation of Macromolecules. Macromol. Mater. Eng. 2004, 289, 393. (17) Rayleigh, J. W. S. On the Instability of Jets. Proc. Lond. Math. Soc. 1879, 10, 4. (18) Petri, H.-M.; Stammer, A.; Wolf, B. A. Continuous Polymer Fractionation (CPF) of Poly(vinylmethylether) and a new [η]-M-Relation of Methylethylketone. Macromol. Chem. Physic 1995, 196, 1453. (19) Kurata, M.; Tsunashima, Y. In Polymer Handbook, 4th ed.; Brandrup, J., Immergut, E. H., Grulke, E. A., Ed.; John Wiley & Sons: New York, 1999. (20) Bauer, B. J.; Hanley, B.; Muroga, Y. Synthesis and Characterization of Poly(Vinylmethyl Ether). Polym. Commun. 1989, 30, 19.

ReceiVed for reView March 24, 2009 ReVised manuscript receiVed June 25, 2009 Accepted June 28, 2009 IE900484G