JPH04320952A - Method for measuring molecular weight of polymer - Google Patents

Abstract

PURPOSE:To enable productivity to be improved by heating a polymer measuring temperature difference of the polymer between two locations, and then calculating a molecular weight of the polymer corresponding to the temperature difference according to the temperature difference which is obtained previously and the molecular weight of the polymer. CONSTITUTION:Olefin and vinyl polymers are heated by a heating element such as a stainless sheathed heater. It can be preferably applied to the polymer of a ring opening polymerization such as polyoxyalkylene. Then, a temperature difference of the polymer between two locations which are thermally affected is measured by a temperature-sensing element such as a sensor. Then, a relationship between the temperature difference which is obtained previously and the molecular weight of the polymer allows the molecular weight of the polymer corresponding to the temperature difference to be estimated, thus enabling productivity to be improved since the molecular weight can be estimated on-line when the molecular weight data is needed in real time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the molecular weight of polymers.

0002

BACKGROUND OF THE INVENTION Generally, when measuring the molecular weight of a polymer, the viscosity average molecular weight (Mη) is used. The viscosity average molecular weight can be measured using a commercially available Ubelohde
) The viscosity of a diluted solution of the polymer is measured using a capillary viscometer, and the molecular weight is calculated from the results using a certain calculation formula depending on the type of polymer.

[0003] In order to carry out molecular weight measurement using such viscosity measurement, pretreatment of the sample, such as dilution and purification of the sample, is required, and as a result, the measurement requires 1 to 2 hours. Also, the temperature control during measurement is, for example, 30±0.
Strict control of the temperature at about 25° C. is required, and furthermore, there is a problem that measurement results may have large errors if one is not familiar with the measurement method. Therefore, in the polymerization process, etc.
After sampling and pretreating a sample from the reactor, it is necessary to measure the viscosity and determine whether or not a predetermined molecular weight has been reached based on the results. If the predetermined molecular weight has not been reached, it is necessary to proceed with the polymerization reaction again.

[0004] When using the conventional molecular weight measurement method using viscosity measurement as described above, time-consuming manual analysis is required, and errors occur due to differences in the measurement personnel and their skill level.
As a result, the reaction time will vary.

[0005]

SUMMARY OF THE INVENTION Therefore, in order to carry out efficient polymerization operations, it is necessary to provide a method for measuring the molecular weight of a polymer in a short time without error.

[0006]

[Means for Solving the Problems] The above-mentioned problem is to apply heat to a polymer by a heating element, and detect the temperature difference of the polymer at at least two locations that are subjected to different thermal effects due to the heating by the heating element by a temperature sensing element. The problem can be solved by a method for measuring the molecular weight of a polymer, which is characterized by calculating the molecular weight of the polymer corresponding to the temperature difference from the relationship between the temperature difference determined in advance and the molecular weight of the polymer. Served.

The present invention is based on the idea explained below. Generally, the dissipation of heat applied to a substance is greatly influenced by the flow properties of the substance, especially the viscosity. That is, a substance with high viscosity has a low heat transfer rate, and conversely, a substance with low viscosity has a high heat transfer rate. Therefore, by measuring the heat transfer properties of the polymer, the viscosity of the polymer can be measured, and the molecular weight of the polymer can be determined from the viscosity measured using the viscosity-molecular weight relationship determined in advance as in the past. can be estimated.

It has been known for a long time to estimate the viscosity of substances other than polymers from their heat transfer characteristics, and in this regard, see, for example, Japanese Patent Laid-Open No. 152943/1983. However, due to the heat transfer properties of materials,
Currently, there is no example of a method for measuring the viscosity of a substance being applied to a system containing a polymer, and it is also not known to estimate the molecular weight of a polymer from the obtained viscosity.

In practice, heat transfer properties are conveniently measured as the temperature difference formed by the balance between the amount of heat added and the dissipation of heat from the system. In addition, the viscosity is the heat transfer property (
It is merely a parameter that theoretically exists between the temperature difference (or temperature difference) and the molecular weight of the polymer, and in reality, the relationship between the temperature difference and the molecular weight can be directly determined.

Although the method of the present invention is a simple method, it has the excellent effect of being able to measure molecular weight with an accuracy comparable to that of the viscosity method, and temperature control during measurement is not required in the viscosity method. control accuracy (±0.25℃
) is not necessary, and a temperature of ±2 to 3°C is sufficient, and it can be used sufficiently for measuring the molecular weight of polymers, which requires high accuracy.

Polymers that can be measured according to the present invention include olefin-based (eg, polyethylene), vinyl-based (eg, polyvinyl chloride), and diene-based (eg, polybutadiene).
, ring-opening polymerization systems (e.g. polypropylene glycol), polycondensation/polyaddition systems (e.g. oligoester acrylate)
, petroleum resin type (e.g. C5 petroleum resin), fluorine-containing type (
For example, fluoroolefin telomer), silicone type (
Examples include polymers such as cyclic dimethylpolysiloxane) and polysulfide, which are not particularly limited, but can be preferably applied to synthetic organic polymers, particularly ring-opening polymers such as polyoxyalkylene. In addition, it is suitable for measuring the viscosity of low molecular weight substances (oligomers) having a molecular weight of up to about 2×10 4 .

[0012] Regarding polymers with extremely high viscosity, even if the molecular weight of the measurement part is accurate, it may not be possible to say that the molecular weight representative of the polymer has been measured from the viewpoint of homogeneity of the entire system. . Therefore, the viscosity of the polymer measured by applying the method of the present invention is 1000 poi
se or less is preferable.

[0013] In the present invention, the heating element is not particularly limited as long as it is an appropriate element that can uniformly apply heat to the polymer, such as a commonly used sheathed heater made of stainless steel. can be exemplified. In a particularly preferred embodiment, the sensor exemplified in JP-A-62-56849 is used as the heating element. In addition, applying heat to a polymer with a heating element means applying a certain amount of heat to a polymer over a certain period of time, that is, uniformly, using a heating element, and heating can be done temporarily or intermittently. There is no problem even if the heating is continuous.

[0014] In the present invention, the temperature sensing element is not particularly limited as long as it is a suitable element for measuring the temperature of a polymer, and examples thereof include a resistance temperature sensor. The reason for measuring the temperature of at least two polymers that are subject to different thermal influences is that the present invention measures heat transfer characteristics as a temperature difference, so it is important to measure the temperature of the polymer at at least two locations that are subject to different thermal influences. If so, the heat transfer characteristics cannot be measured as a temperature difference. Moreover, at least two locations means that at least one data is measured as a temperature difference. Therefore, it is also possible, for example, to measure the temperature at three or more locations, determine the temperature difference between them, and use, for example, the average value. Being thermally affected means that when the polymer is heated by a heating element, the temperature of the polymer at the measurement location is affected by the heating. Therefore, if the amount of heating is small, the polymer will not be affected by the heating at a position far from the heating element, so measuring the temperature of the polymer at such a location will not yield an accurate molecular weight.

[0015] Considering that temperature measurements may also have some degree of error, it is preferable to measure the temperature at two locations close to the heating element and separated by a suitable distance. Especially 1
It is preferable to measure the temperature of the polymer product immediately adjacent to the heating element. Therefore, in the most preferred embodiment, the heating element and the
Use an element that has two integrated temperature sensing elements. Such an element is, for example, a thermometer having a structure in which a minute current is passed through a resistor built in a stainless steel tube to generate heat, and the temperature of the generated resistor itself can be measured. It is sufficient to select at least two locations at which the temperature difference is to be measured so that the two locations have different temperatures, but preferably they are selected so that the temperature difference is large. These two
The distance between the points depends on the polymer to be measured and also on whether the fluid to be measured is stationary or flowing, but in general, it is about 20 to 30 mm in a static system, and about 20 to 30 mm in a fluid system. About 10 to 20 mm, for example about 10 mm, is sufficient.

The method of the present invention does not require any special operation other than measuring the temperature difference, and the molecular weight can be immediately estimated by an appropriate method from the relationship between the temperature difference and the molecular weight of the polymer obtained in advance. can.

Therefore, since the temperature can be measured in real time, the present invention can be applied not only when the polymer is in a static state in terms of molecular weight and fluidity, but also when it is in a dynamic state. method can be applied. For example, it can be applied even if the system is stirred or in a stationary state, or even if the molecular weight does not change, or even if the molecular weight is changing.

In the method of the present invention, in principle, it is necessary to determine the relationship between the viscosity and molecular weight of the polymer in advance, as in the conventional method. By determining the relationship between molecular weight and viscosity in advance using the temperature of the reaction system as a parameter, the actually obtained measured value can be corrected. As explained earlier, in reality, it is possible to directly determine the relationship between temperature difference and molecular weight, so it is necessary to determine in advance how the relationship between the two is affected by the temperature of the reaction system. is necessary. Therefore, it is necessary to determine in advance the relationship between the temperature difference and the molecular weight at a temperature close to the actual temperature of the molecular weight increasing system to be measured.

[0019] In this case, strictly speaking, there are two types of system temperatures because the measured temperatures are different at the two locations.
The temperature difference between the points is not large enough to affect the viscosity more than the measurement error, so the temperature of the system is, for example, 2.
The average temperature of the temperatures at the location may be used, or either one of the temperatures may be used.

The method of the present invention can be applied to any case in which it is necessary to estimate the molecular weight of a polymer, but it is particularly useful for estimating the molecular weight of the following operation in the polymerization process. In this case, it is necessary to make a judgment based on the following. Especially when molecular weight data is required in real time, molecular weight can be estimated online, allowing you to move on to the next operation without any time lag, leading to improved productivity.

Specifically, the relationship between the temperature difference between the sensors and the molecular weight at a given system temperature is determined in advance as a calibration curve, and by measuring only the temperature difference in the actual molecular weight increasing reaction, the molecular weight can be determined. calculate. Depending on the case,
To check the calibration curve, sample the reaction system at one point in the molecular weight increase reaction and measure the molecular weight using the conventional method to confirm that the system condition is the same as when the calibration curve was calculated. may be appropriate. for example,
Due to differences in raw material lots and differences in the amount of impurities contained in the raw materials, the checked points may not necessarily fall on the calibration curve. Even in this case, a predetermined calibration curve may be used depending on the desired specification of the designed molecular weight. In addition, if more precise control of molecular weight is required, if the reaction system is the same type for increasing molecular weight, move the previously determined calibration curve in parallel to the temperature difference direction so that the checked points are on it. It has been confirmed that even if the molecular weight is estimated from the measured temperature difference by using it as a new calibration curve, results with no practical problems can be obtained.

In particular, when increasing the molecular weight of a polymer with a low degree of polymerization whose molecular weight is known, or when measuring the molecular weight using a viscometer or the like more than once during polymerization, the shape of the calibration curve should be adjusted. If the calibration curve is moved and corrected as described above while maintaining the same, extremely accurate molecular weight measurement can be performed.

Furthermore, the present invention provides an element for heating the polymer,
Provided is a molecular weight measuring device comprising a temperature sensing element that measures the temperature difference of a polymer at at least two locations that are subjected to different thermal effects due to heating by a heating element. In a particularly preferred embodiment, the apparatus of the present invention has a data processing device into which the relationship between the molecular weight of the polymer measured in advance and the temperature difference is input, and which can immediately calculate the molecular weight from the actually measured temperature difference. Become.

Next, the present invention will be specifically explained based on examples. Example 1 A description will be given based on the stirring reaction tank (with jacket) shown in "Figure 1". 20 kg of an alcoholate compound in which 90% or more of the terminal OH groups of PPG (polypropylene glycol) were alkoxylated was charged into a stirring reaction tank 3 via a raw material receiving tank 1 and a raw material measuring tank 2. After the preparation was completed, the gas phase was replaced with N2, and at the same time, the temperature was raised to a predetermined temperature (130° C.) by the temperature control unit 6. After heating up,
The kinematic viscosity monitoring system (manufactured by JEOL Ltd.) 7 was activated and measurement of the temperature difference between the heated part and the non-heated part (temperature difference between two points in the reaction system) was started.

One sensor of this monitoring system has a resistor built in a stainless steel tube with a 400
This thermometer was designed to generate heat by passing a mA current through it, and measure the temperature of the generated resistor itself.The other sensor used was a normal resistance temperature detector separated by a distance of 10 mm.

Thereafter, a polyhalide, which is a molecular weight increasing reagent, is dropped in small quantities from the raw material measuring tank 2, and the temperature difference is sequentially measured by the kinematic viscosity monitoring system 7, and at the same time, the molecular weight (Mη) by the Ubbelohde method is measured. It was measured. A calibration curve was obtained by plotting the relationship between the measured temperature difference and Mη as shown in “FIG. 2”.

When a reaction similar to the above molecular weight increasing reaction is repeated, the molecular weight calculated from the temperature difference measured based on the obtained calibration curve is compared with the molecular weight Mη measured by the Ubbelohde method. It was found that the two coincided within an error range of approximately ±1% or less.

[0028] This shows that the molecular weight of a polymer can be accurately measured from the temperature difference with an accuracy equivalent to that of measurement by the Ubbelohde method. The molecular weight increasing reaction of the alcoholate compound (starting molecular weight M0 = 2400) was carried out by continuously dropping the molecular weight increasing reagent while monitoring the molecular weight using the calibration curve obtained as described above. When the molecular weight is calculated sequentially from the temperature difference using a calibration curve,
After about 1 hour, the desired molecular weight (8100) was reached, so dropping of the molecular weight increasing reagent was stopped. When the finally obtained polymer was measured by the Ubbelohde method, the molecular weight was 81.
It was 50.

Comparative Example 1 Molecular weight increasing reaction similar to the above example (starting molecular weight = 2
400, designed molecular weight = 8100) based on molecular weight measurement by Ubbelohde method. In the case of a molecular weight increasing reaction using only a conventional viscosity method, the molecular weight cannot be determined in real time, and therefore the molecular weight increasing reagent cannot be added dropwise continuously. It is not preferable for the molecular weight to be much larger than the designed molecular weight, and therefore, it is necessary to add the reagent in an amount slightly smaller than the estimated amount corresponding to the designed molecular weight (Mη=8100). Thereafter, unless the insufficient amount of the molecular weight increasing reagent is further added and reacted, a polymer having the desired molecular weight cannot be obtained accurately.

First, according to the conventional viscosity method, a slightly smaller amount of the molecular weight increasing reagent than the estimated amount corresponding to the designed molecular weight (Mη=8100) was added all at once. As a result of sampling and measuring the molecular weight 1 hour after addition, Mη = 7
It was 800. (This measurement took approximately 1.5 hours.)
Since this value was 300 less than the designed molecular weight of 8100, the molecular weight increasing reagent was added at once in an estimated amount equivalent to increasing the molecular weight by 300. After re-adding, the molecular weight was measured 30 minutes after sampling, and the results showed that Mη = 815.
0, and the reaction was completed. (Measurement time was approximately 1.5 hours.)

As described above, according to the conventional viscosity method, after measuring the molecular weight, it is necessary to judge based on the value whether or not to continue the reaction by adding the molecular weight increasing reagent again. It took a very long time to obtain the polymer. (The total time required was 4.5 hours.)

[
Example 2 Example 1 was carried out using an alcoholate compound in which 90% or more of the terminal OH groups of PPG were alkoxylated under different production conditions.
The molecular weight increasing reaction was carried out under the same conditions as above. As in Example 1, the relationship between the temperature difference and the molecular weight was measured by the Ubbelohde method.

[0033] The measurement results are shown in "Figure 3" together with the results of Example 1.
(The results of Example 1 are indicated by ○, and the results of Example 2 are indicated by △.) The relationship between the temperature difference and the molecular weight is the same as that between the temperature difference and the calibration curve obtained in Example 1. It did not fit the calibration curve, and there was a slight deviation. However, even in this case, it was found that by moving the calibration curve obtained in Example 1 parallel to the temperature difference direction, a calibration curve that best expressed the results obtained in Example 2 could be obtained. .

Therefore, if the types of polymers are the same, there is no need to create a new calibration curve.If the relationship between temperature difference and molecular weight is determined in advance as a calibration curve for a specific polymer, the molecular weight can be determined. If you measure the relationship between the temperature difference and the molecular weight of the conventional method at a certain point in an increase reaction, you can simply move the calibration curve in parallel in the direction of the temperature difference so that it passes through that measurement point. A calibration curve can be obtained.

[0035]

[Effects of the Invention] Since the method of the present invention can be carried out in real time, decisions in polymerization operations can be made much more easily than when conventional methods are applied, leading to improved productivity.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a reaction apparatus for carrying out a molecular weight increasing reaction using the method of the present invention.

FIG. 2 is a graph showing the results of Example 1.

FIG. 3 is a graph showing the results of Example 2.

[Explanation of symbols]

1... Raw material receiving tank, 2... Raw material measuring tank, 3... Stirring reaction tank, 4...
Stirring blade, 5...Discharge valve, 6...Temperature control unit, 7...Kinematic viscosity monitoring system.

Claims (2)

[Claims] Claim 1: Heat is applied to the polymer by a heating element, and the temperature difference of the polymer at at least two locations that are subjected to different thermal effects due to the heating by the heating element is measured by a temperature detection element, and a predetermined temperature is obtained. A method for measuring the molecular weight of a polymer, comprising calculating the molecular weight of the polymer corresponding to the temperature difference from the relationship between the difference and the molecular weight of the polymer. 2. The method for measuring the molecular weight of a polymer according to claim 1, wherein the heating element also acts as one of the temperature sensing elements.