JPH07316228A - Dispensing method for polyethylene with narrow molecular weight distribution - Google Patents

Abstract

PURPOSE:To dispense polyethylene with a narrow-molecular weight distribution in a amt. simply, conveniently, efficiently, and accurately by coating a filler packed into a fractionation column with a sample and utilizing the difference in solubility by solvents to thereby change the ratio of a good solvent to a poor solvent in steps. CONSTITUTION:Polyethylene with a narrow mol.wt. distribution is dispensed by coating a filler packed into a fractionation column with a sample dissolved in a good solvent, keeping the temp. in the column at lower than the b.p. of the good solvent, transferring a solvent mixture of the good solvent with a poor solvent into the column at a rate of 1.0-10.0ml/min, and changing the ratio of the good solvent to the poor solvent in the solvent mixture in steps. Thus, a relatively large amt. (gram-unit) of the sample can be fractionated by mol.wt. and dispensed efficiently and accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for collecting polyethylene having a narrow molecular weight distribution. More specifically, the present invention relates to a method of separating a relatively large amount (gram unit) of polyethylene for each molecular weight and efficiently and accurately collecting the separated polyethylene.

[0002]

2. Description of the Related Art A calibration curve is necessary when calculating the molecular weight and molecular weight distribution of a polymer by the GPC (gel permeation chromatography) method, but when a calibration curve is prepared using a standard sample, a calibration curve is required. A wide range of samples with narrow molecular weight distribution is required. A large number of standard samples of polystyrene are commercially available, but a small number of standard samples of polyethylene are not available.

Therefore, it is necessary to prepare a standard polyethylene sample. However, unlike polystyrene, which is close to monodisperse (Mw / Mn is 1.1 or less) by living polymerization, polyethylene has to have a narrow molecular weight distribution sample by separating a sample having a wide molecular weight distribution.

[0004]

However, in the conventional method, since the amount of polyethylene sample having a narrow molecular weight distribution that can be collected at a time is small, the analysis means is limited. Therefore, the analysis sample is used as an analysis means that requires a large amount of sample (gram unit), such as a nuclear magnetic resonance device, an X-ray diffraction device, a light scattering device, a viscoelasticity measurement device, a tensile test device, and an impact test device. It was impossible to do.

Polymers are generally heterogeneous mixtures of any or all of the molecular species such as molecular weight, chemical composition, molecular structure, etc., and the quality of the polymer generally depends on these molecular species. Therefore, when characterizing a polymer, fractionation by molecular weight fractionation is an effective method for reducing the influence of the molecular weight among them.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for easily and efficiently collecting a large amount of polyethylene having a narrow molecular weight distribution in large quantities.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, completed the present invention. That is, according to the present invention, the packing material packed in the fractionation column is coated with the sample, and the difference in solubility depending on the solvent is utilized to stepwise change the composition ratio of the good solvent and the poor solvent to narrow the molecular weight distribution. This is a method for fractionating polyethylene, and according to the present invention, a relatively large amount (gram unit) of polyethylene can be fractionated by molecular weight, and fractionation can be carried out efficiently and accurately.

The present invention will be described in more detail below.

The fractionation column used in the method of the present invention is packed with an appropriate packing material which is usually used depending on the components to be fractionated. The filler is not particularly limited as long as it is insoluble in the solvent and inert, but generally particle size of sea sand, diatomaceous earth, glass beads, etc. is 50
Those having about 400 mesh are preferably used.

The shape and size of the separation column are not particularly limited, but for example, the diameter is 10 to 50 m.
A cylindrical stainless steel column with m and a length of 100 to 1000 mm is preferably used.

In this method, the sample is coated on the packing material, the combination of the good solvent and the poor solvent, the gradient of the solvent composition, the flow rate,
Column temperature is an important factor.

The coating of the sample on the filler produces a thin polymer layer uniformly on the surface of the filler in order to obtain a temperature of 1 ° C. /
Gradual cooling of min or less is preferable.

The good solvent is not particularly limited, but p-xylene (boiling point: 138 ° C.) and tetralin (boiling point: 207) in which polyethylene dissolves at a temperature not higher than the boiling point of the solvent.
C.), ortho-dichlorobenzene (boiling point; 180.degree. C.), trichlorobenzene (boiling point; 218.degree. C.) and the like are preferable.

The poor solvent is not particularly limited, but has a boiling point higher than that of the good solvent and is freely soluble in the good solvent, such as ethylene glycol monoethyl ether (ethyl cellosolve) (boiling point: 162 ° C.), ethylene. Glycol monobutyl ether (butyl cellosolve) (boiling point; 1
71 ° C.) and the like are preferable.

In the present method, one kind of each of these good solvent and poor solvent is selected as a mixed solvent, and p-xylene having a boiling point of 138 ° C. and ethylene glycol monoethyl ether (ethyl acetate having a boiling point of 162 ° C. are selected according to the combination of boiling points. Cellosolve)
Alternatively, a combination of ethylene glycol monobutyl ether (butyl cellosolve) having a boiling point of 171 ° C. is common.

The gradient of the solvent composition is appropriately selected according to the molecular weight and the molecular weight distribution of polyethylene to be subjected to molecular weight fractionation and is not particularly limited, but it is good because fractionated samples having different molecular weights are fractionally collected. When the mixing ratio of the solvent and the poor solvent is 50/50 or more, a gradient of the solvent composition of about 10% or less, further about 5% or less is preferable.

The flow rate of the mixed solvent sent to the fractionation column is 1.
It is 0 ml / min to 10.0 ml / min, preferably 5.0 ml / min to 8.0 ml / min. If the flow rate is less than 1.0 ml / min, it takes time to separate and is not efficient, and recrystallization may occur in the pipe during the separation, causing clogging and stopping the separation thereafter. There is. On the other hand, when the flow rate exceeds 10.0 ml / min, the molecular weight distribution is widened and sufficient molecular weight fractionation cannot be performed.

In the present method, the composition ratio of the good solvent and the poor solvent and the column temperature are particularly important for obtaining a polyethylene sample having a narrow molecular weight distribution. The temperature, solvent composition and flow rate in each step can be controlled by, for example, a system computer.

In the present method, in order to carry out sufficient molecular weight fractionation, the column temperature is set within the range below the boiling point of the good solvent used, preferably about 10 to 20 ° C. lower than the boiling point (for example, p-xylene ( 12 at boiling point; 138 ° C)
Keep constant at any temperature (in the range of 0 to 135 ° C),
The composition ratio of the mixed solvent of the good solvent of p-xylene and the poor solvent of ethylene glycol monoethyl ether (ethyl cellosolve) is changed stepwise in the range of 0/100 to 100/0 (volume ratio) and sent to the separation column. This elutes the sample coated on the packing material in the fractionation column.

When the column temperature is lower than 115 ° C., the composition (crystallinity) causes separation, and the molecular weight distribution is widened, which is not preferable. When the boiling point of a good solvent (for example, p-xylene, etc.) becomes higher or higher, the solvent boils and the sample comes out of the packing material, sufficient elution due to the molecular weight is not performed, and the relationship between the molecular weight and the solvent composition is reversed. Or the intended molecular weight component cannot be collected due to a sudden change in the molecular weight.

In this method, a sample (2,6-tert-butyl-p-) dissolved in a good solvent (for example, p-xylene) is used.
Antioxidant such as cresol is added to the sample solution at 0.05
(adding about wt%) is sent to the separation column, and then the packing material in the column is coated by lowering the temperature. Then, the solvent in the column is replaced with a poor solvent (for example, ethylene glycol monoethyl ether (ethyl cellosolve)). After the solvent replacement, the temperature inside the column is raised to a temperature below the boiling point of the good solvent used. After the temperature inside the column is kept constant at that temperature, the amount of the good solvent of p-xylene in the mixed solvent transferred into the column is increased stepwise to send it to the separation column while changing the composition ratio, and separate each separation fraction from the effluent. To get
Respective precipitation fractions are obtained by reprecipitation in methanol, filtering and drying to obtain a polyethylene sample having a narrow molecular weight distribution.

An apparatus for carrying out the present method is, for example, the apparatus shown in FIG. The main configuration of this device consists of two pumps, a thermostat, a column in the thermostat, a fraction collector and an infrared detector. Interactions are automatically sorted by system computer control.

The method is mainly composed of two steps. The sample solution in which the sample is dissolved in a good solvent is sent from the sample injection part to the separation column, and the sample is coated with the filler in the separation column by lowering the temperature (first step).

After replacing with the poor solvent, the sample coated on the packing material in the fractionation column is eluted (second step) by sending it to the fractionation column while changing the composition ratio of the good solvent and the poor solvent stepwise. , Fractionated samples are collected in the fraction collector.

By the above method, polyethylene having a narrow molecular weight distribution of Mw / Mn of 2.1 or less can be collected.

[0026]

The present invention is described in detail below with reference to examples, but the present invention is not limited to these.

Using the apparatus shown in FIG. 1 described above, the following conditions and the temperatures shown in Table 1 (110 ° C., 120 ° C., 130 ° C.) were used.
℃, 140 ℃, high density polyethylene (HDP
E) 7300A (Made by Tosoh MFR = 0.05 g / 10
min, density = 0.951 g / cm ³ ).

Solvent: A mixed solvent of p-xylene / ethylene glycol monoethyl ether (ethyl cellosolve), the composition ratio of which was changed stepwise in the range of 0/100 to 100/0 (volume ratio).

Separation column: diameter 21.4 mm, length 60
0 mm Filler: Sea sand 290 g Table 1 summarizes the results of molecular weight fractionation. The molecular weight and the molecular weight distribution were measured by the GPC method (gel permeation chromatography) under the following conditions.

Equipment: Waters 150C ALC / G
PC column: Tosoh GMHHR-H (S) (7.8 mmI)
D × 30 cm × 3) Solvent: Ortho-dichlorobenzene (ODCB) Flow rate: 1.0 ml / min Injection concentration: 40 mg / 50 ml ODCB (injection volume 30
The column elution volume was calibrated by the universal calibration method using standard polystyrene manufactured by Tosoh Corporation.

[0031]

[Table 1]

From the results in Table 1, it can be seen that the fractionation of HDPE by this method has a remarkable effect of fractionation of the molecular weight, and a sample having a narrow molecular weight distribution is obtained.

On the other hand, it is understood that when the column extraction temperature is lower than 115 ° C., fractionation due to composition (crystallinity) occurs and the molecular weight distribution broadens, which is not preferable. Further, when the boiling point of the good solvent of p-xylene is around or higher, the solvent is boiled and the sample is removed from the packing material, sufficient elution due to the molecular weight is not carried out, and the molecular weight is changed suddenly. It turns out that can't be collected.

Reference Example As a commercially available polyethylene standard sample, NBS (Nati
(Bureau Standards), but the weight average molecular weight is at most Mw = 119,
600 (Standards Reference M
1184), which is very expensive.
Table 2 shows the published and measured values.

[0035]

[Table 2]

[0036]

As is clear from the above description, according to the method of the present invention, 1) a relatively large amount (gram unit) of a sample can be fractionated by molecular weight, and fractionation can be performed efficiently and accurately. In addition, 2) this device has the effect of being able to perform automatic fractionation by controlling the mutual operations of the pump, the constant temperature bath, the fraction collector, the infrared detector and the like by a system computer.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an example of an apparatus used in the present invention.

Claims (2)

[Claims] 1. A sample is coated on a packing material packed in a fractionation column, and the difference in solubility depending on the solvent is utilized,
A method for fractionating polyethylene having a narrow molecular weight distribution, which comprises fractionating polyethylene by stepwise changing the composition ratio of a good solvent and a poor solvent. 2. The packing material packed in the fractionation column is coated with a sample dissolved in a good solvent, and thereafter, the inside of the fractionation column is maintained at a temperature lower than the boiling point of the good solvent, and in the fractionation column,
1.0ml / min-1 of mixed solvent of good solvent and poor solvent
A method for fractionating polyethylene having a narrow molecular weight distribution, characterized in that polyethylene is fractionated by transferring at 0.0 ml / min and stepwise changing the composition ratio of a good solvent and a poor solvent in the mixed solvent.