JPS5856530B2 - Manufacturing method of polyurethane elastomer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyurethane elastomer having excellent stretch recovery properties, particularly a polymer for polyurethane elastic fibers (spandex fibers).

In recent years, demand for spandex fibers has increased significantly.

Most of these fibers are mainly manufactured by reacting an intermediate polymer having an incyanate group at the end with a polyfunctional active hydrogen compound to obtain an elastic body, which is then spun.

It also has greater strength and durability than natural rubber.

However, when the load is removed after being stretched to a certain length, spandex fibers have a disadvantage that their recovery properties are inferior to those of natural rubber.

Spandex fibers obtained by using polytetramethylene glycol as a soft segment usually have poor recovery properties due to crystal orientation due to elongation.

Furthermore, the deformation of the hard segment due to elongation also reduces the elongation recovery property.

In order to improve such elongation recovery properties, if a polyester with a low secondary transition point is used as the soft segment of spandex, orientation due to elongation can be suppressed to some extent.

Japanese Patent Publication No. 3922682 discloses a spandex fiber made of a linear polymer containing polyester segments.

That is, it is a spandex fiber consisting of linear polyester units, symmetrical aromatic diisocyanate units, and units constructed using diamines or water.

Also, the original patent application for this publication, Japanese Patent Publication No. 42-1362,
Publication No. 9 describes a method for producing the above-mentioned spandex fiber.

This publication states that symmetric aliphatic diamines are preferred as diamines.

Polymerization reactions are generally carried out by solution polymerization, but when symmetrical diamines are used as so-called chain extenders, they tend to have poor solution stability, resulting in polymer precipitation from the polymer solution.
This results in drawbacks such as the polymerization solution exhibiting a gel-like appearance.

In order to prevent this, at least the equivalent molar amount of diamine is used for the prepolymer containing terminal incyanate groups. This results in the disadvantage of reduced stability.

Using side chain-containing diamines as chain extenders solves the gelation problem, but even with such side chain-containing diamines, if the chain length of the hard segment becomes large, the polymer solution will deteriorate when the polymer solution is left for a long time. An apparent increase in viscosity can be seen.

When shearing force is applied to this polymer solution, the viscosity appears to decrease.

When such a thixotropic property is exhibited, it becomes difficult to prepare a polymer solution and then move it to the next step.

Furthermore, elastic fibers obtained from such polymer solutions have insufficient elongation recovery properties.

The present inventors conducted intensive research to obtain a polyurethane elastomer with excellent stretch recovery properties and solution stability, and as a result, arrived at the method of the present invention.

That is, the present invention uses a polyester having a melting point of 40'C or less and a molecular weight of 1,500 to 7,000 and having a terminal hydroxyl group.
Symmetrical aromatic diisocyanate and -NCO group/-〇H
When producing an intermediate polymer by reacting at a molar ratio of groups -2 to -4, the following formula [(mol of aromatic diincyanate) (mol of polyester)] x a where a is 0.05 to 0.30 Produce an intermediate polymer by adding water in a molar amount represented by
Next, the obtained intermediate polymer was reacted with a diamine in an amount equivalent to 0.70 to 0.96 equivalents based on the equivalent of the remaining incyanate group in the intermediate polymer, and the general formula The aromatic group R/ is a polyester residue obtained by removing the hydroxyl group from a polyester having a terminal hydroxyl group, a molecular weight of 1,500 to 7,000, and a melting point of 40° C. or lower. R〃 represents a divalent organic group.

It is characterized by obtaining a substantially linear polymer containing segments represented by:

According to the method of the present invention, by using specific amounts of polyester as the soft segment and water and diamine as the hard segment, the hard segment can be formed by the following formula, where R2H" represents the same group as above.

Elastic fibers obtained by dry spinning a polymer obtained from such a structure consisting of two types of segments represented by the following are characterized by significantly improved elongation recovery properties.

That is, when the ratio of the two types of segments constituting the bird segment is within the range of the present invention, the elongation recovery rate after leaving the fiber under 500% elongation for 24 hours and then leaving it in a non-tensioned state for 10 minutes (described later) is at least 80% or more.

On the other hand, elastic fibers obtained by dry spinning a polymer produced in the same manner without adding water during intermediate polymer production showed an elongation recovery rate of only 75% or less as a result of a similar test. .

Furthermore, elastic fibers obtained by dry spinning a polymer produced in the same manner by adding water beyond the scope of the present invention show an elongation recovery rate of only about 70% in similar tests. .

Furthermore, when the amount of water added is reduced to such a level that the addition of diamine is almost unnecessary, that is, the elongation recovery rate of elastic fibers obtained by dry spinning a polymer prepared using only water as a chain extender. It is only about 75%.

Only by using water and diamine in a specific ratio as described above can an elastic body having an excellent elongation recovery rate be obtained.

Furthermore, the solution of the elastic body obtained by the method of the present invention does not gel or exhibit thixotropy, has good stability, and has many advantages in industrialization, such as no problem of viscosity reduction.

The polyester used in the present invention can be obtained by reacting a divalent carboxylic acid, its ester or acid halide with a molar excess of glycol.

Polyesters can also be made into copolymers, such as copolyesters, by using one or more acids and/or one or more glycols.

Copolymerization components are useful for changing the melting point of polyester, its crystallinity, etc.

Preferred glycols include alkylene glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, decamethylene glycol, neopentyl glycol, and fats such as cyclohexanediol and cyclohexane dimetatool. Examples include cyclic glycols.

These glycols can be aliphatic, cycloaliphatic or aromatic.
A polyester having a hydroxyl terminal group can be obtained by reacting an excess mole of glycol with a derivative having an ester-forming ability such as a polyhydric acid, its ester or acid halide.

Preferred acids include, for example, succinic acid, adipic acid,
Examples include speric acid, azelaic acid, sebacic acid, isophthalic acid, and hexahydroisophthalic acid.

The polyester or copolyester must have a melting point below 40'C in combination with an acid and a glycol.

When the melting point exceeds 400C, the elongation recovery rate of the resulting polyurethane elastic body at low temperatures decreases.

In the polymerization of polyester, terminal carboxyl groups often remain, but it is preferable to reduce the number of such carboxyl groups as much as possible.

A polyurethane elastomer produced by the method of the present invention using a polyester with a high acid value has the disadvantage of reduced hydrolysis resistance.

Polyester has poor hydrolysis resistance, and in particular it is difficult to obtain a useful elastic body for fibers, but by reducing the acid value as much as possible, the hydrolysis resistance can be significantly improved.

The carboxyl group of the polyester used in the present invention is preferably at most 10 equivalents, and particularly preferably at most 5 equivalents, per 106 g of polyester.

Elastic fibers obtained using such polyesters do not have any practical problems with hydrolysis even if they have a fine denier.

Further, the molecular weight of the polyester is 1,500 to 7,000, preferably 2,000 to 6,000.

Further, as the aromatic diisocyanate used in the present invention, a symmetrical aromatic diisocyanate is selected.

Preferred diisocyanates include, for example, P-phenylene diisocyanate, m-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate,
Examples include 4,4'-isopropylidene diphenyl diisocyanate.

These compounds may also contain other substituents.

A particularly preferred diisocyanate is 4,4'-diphenylmethane diisocyanate.

Aliphatic diisocyanates require harsh conditions for reaction due to their low reactivity, and asymmetric aromatic diisocyanates are unsuitable for producing elastic fibers because they deteriorate the thermal performance of the fibers when made into fibers. .

In the present invention, when the polyester and diisocyanate are reacted to obtain an intermediate polymer, the reaction is carried out in the presence of water.

The added water reacts with the isocyanate groups to form hard segments.

The amount of water added is the molar amount represented by the following formula: [(moles of aromatic diisocyanate) - (moles of polyester)]×a where a = 0.05 to 0.30.

When the amount of water added deviates from the range of the present invention, either below the lower limit or exceeding the upper limit, the elongation recovery rate decreases.

By adjusting the amount of water added within the range of the present invention, the elongation recovery rate of elastic fibers can be significantly improved.More surprisingly, the polymer solution obtained by the method of the present invention has no thicuntropy. It should have good fluidity without exhibiting any viscosity.

Of course, it will not become gel-like. The intermediate polymer is usually prepared by heating a mixture of polyester and diisocyanate compound.

The invention is of course carried out by adding water to the mixture.

In this case, a tertiary amine, a tin compound, etc. may be added as a catalyst.

However, in a more preferred embodiment of the invention, the intermediate polymer is prepared in solution.

Due to the addition of water, some of the hard segments are formed during the preparation of the intermediate polymer, which increases the viscosity of the intermediate polymer;
This is because it may become difficult to stir or transfer to the next step.

The solvent used in this case is preferably the same as that used in the next chain extension reaction.

Suitable solvents include, for example, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, N,N,N',N'
Examples include -tetramethylurea, and N,N-dimethylformamide and N,N-dimethylacetamide are particularly preferred.

Furthermore, the intermediate polymer is N,N-dimethylformamide, N,
When prepared in a solvent such as N-dimethylacetamide, the reaction temperature is low and the reaction rate can be increased.

The amount of solvent is preferably such that the concentration of the intermediate polymer is 30 to 90% by weight.

The reaction temperature is preferably 30 to 90°C.

A catalyst such as a tertiary amine or a tin compound may be added during this reaction.

The molar ratio of diisocyanate and polyester used in the preparation of the intermediate polymer is -NCO group/-OH group = 2 to 4, preferably in the range of more than 2.5 and less than 3.5.

When the molar ratio is less than 2, the chain of the soft segment is seen to be elongated.

Moreover, if the molar ratio exceeds 4, the length of the hard segment becomes large, and when it is made into an elastic fiber, the deformation of the hard segment during elongation becomes large, resulting in a disadvantage that the elongation recovery property decreases.

The intermediate polymer thus obtained is chain-extended with a diamine to produce a polyurethane elastomer.

Examples of diamines that can be used include ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,2-diaminopropane, cyclohexanediamine, piperazine, etc., but from the viewpoint of elongation recovery rate, solution stability, and other physical properties, Preferred is 1,2-diaminopropane.

Usually, the chain extension reaction is carried out by a solution polymerization method.

Examples of the solvent used at this time include N,N-dimethylformamide, N,N-dimethylacetamide, N
-Methylpyrrolidone, dimethyl sulfoxide, N, N,
Examples include N,N'-tetramethylurea.

Further, it is preferable that the diamine be diluted with the same solvent used in the chain extension reaction and then added.

The amount of diamine added should correspond to 0.70 to 0.96 equivalents relative to the equivalents of incyanate groups remaining in the intermediate polymer.

The amount of incyanate groups remaining in the intermediate polymer is
For example, it can be quantified as follows.

That is, a certain amount of intermediate polymer is collected, a certain amount of di-n-butylamine solution is added thereto to react with incyanate groups, and then excess di-n-butylamine is added using an appropriate acid solution.
It can be determined by neutralizing butylamine.

If more than 1 equivalent of diamine is added to the incyanate group equivalent obtained in this way, not only will the viscosity increase abnormally around 1 equivalent, but the viscosity of the polymer will decrease u-fL due to the excess diamine. However, it has the disadvantage that it deteriorates.

In the present invention, the addition of diamine is stopped when the polymer solution reaches a predetermined viscosity.

If inocyanate groups remain in the polymer solution after addition of the diamine, a monofunctional compound that reacts with the isocyanate groups can be added to stabilize the polymer solution.

The polymer solution thus obtained is stable and has excellent fluidity.

In particular, in order to obtain a polymer useful for elastic fibers, it is necessary to adjust the content of soft segments to 75 to 94% by weight in the polymer.

Polymers containing more than 94% by weight polyester soft segments are too soft to be suitable for forming useful elastic fibers.

Further, a polymer having a content of less than 75% by weight is insufficient as an elastic fiber due to its low elongation at break.

The stretch recovery of elastic fibers is also influenced by the molecular weight of the polymer.

The intrinsic viscosity of the polymer is expressed as ■=βin ηsp/c, and is usually ■−0.8 to 3. OdV&, preferably ■-1,
0-3,0 d17g.

The polymer solution thus obtained is wet or dry spun to form elastic fibers.

Dry spinning is suitable for obtaining elastic fibers with excellent stretch recovery properties.

Dry-spun elastic fibers can be made into more suitable fibers by heat treatment or drawing steps.

In addition, we can form films, sheets, tubes, belts, packing, etc. by dry molding from polymer solutions, as well as paper,
It can also be applied to cloth-like sheets for applications such as synthetic leather.

Furthermore, it is useful as a protective coating for glasses, bottles, etc., or as an adhesive, a coating agent for magnetic tape, an ink binder, etc.

In addition, in order to stabilize the elastic body, it is also possible to add effective amounts of stabilizers such as antioxidants and ultraviolet absorbers, and other additives within a range that does not impede desirable physical properties.

The present invention will be explained below with reference to Examples, but it goes without saying that the present invention is not limited to the Examples.

In addition, parts in the examples mean parts by weight, and the intrinsic viscosity is N,
It was measured using N-dimethylacetamide as a solvent at a temperature of 30°C and is expressed by the formula: -1inηsp/c.

Moreover, the strength was expressed in grams per denier.

The elongation recovery rate is the recovery after 10 minutes when the fiber is left in a constant elongated state for a certain period of time in an atmosphere of 20°C and 65% humidity, and then the fiber is brought to a non-tensioned state. is the fiber length before elongation, and the fiber length when stretched.

It is expressed as

The solvent and polyester used in the examples were all dried to a water content of 30 pp [Il or less].

Example 1 292 parts of adipic acid, 124 parts of ethylene glycol, and 181 parts of 1,4-butanediol were charged into a No. 11 flask and heated at 210° C. under atmospheric pressure for 2 hours in a nitrogen atmosphere.

Next, 0.02 part of titanyl ammonium oxalate and 0.025 part of triphenyl phosphite were added, and the pressure was gradually reduced at 210°C, and the pressure was reduced to 0.2 Hg in 2 hours.
Heating was continued for an additional 2 hours under a pressure of mmHg.

A copoly(ethylene-butylene) adipate having a melting point of 32 DEG to 35 DEG C. and having 680 equivalents of hydroxyl groups and 4.8 equivalents of carboxyl groups per 106 g of polymer was obtained.

100 parts (0,0342 mol) of this copolyester
．． 21.4 parts (0,0856 moles) of 4'-diphenylmethane diisocyanate and 0.09 parts (0,005 moles) of water
mol) into a flask for polymerization, add N, without stirring,
80 parts of N-dimethylacetamide was added to form a homogeneous solution.

Next, this solution was heated to 50° C. and reacted for 60 minutes to obtain an intermediate polymer.

The amount of residual incyanate groups in the obtained intermediate polymer was quantified and found to be 4.60×10 −4 equivalent NCO/g.

Next, 220 parts of N,N-dimethylacetamide was added to make a homogeneous solution, which was then cooled to 10°C, and 3.2 parts (0,0432 mol) of 1,2-diaminopropane was added to 30 parts of N,N-dimethylacetamide. The dissolved solution was added over 30 minutes.

The intrinsic viscosity of the obtained polymer was 1.28 dl/g.

Next, this polymer solution was dry-spun by a conventional method to obtain 28
A multifilament of 0 denier/15f was obtained.

The strength of the obtained fiber is 0.96g/d% elongation 650%,
The stress at 300% elongation was 0.11 g/d.

Furthermore, the elongation recovery rate was 98% when the material was held under 500% elongation for 10 minutes in an atmosphere with a temperature of 20° C. and humidity of 65%, and then left under no tension for 10 minutes.

In addition, when held under 500% elongation for 24 hours in the same atmosphere and then left under no tension for 10 minutes, the elongation recovery rate was 9.
It was 6%.

Furthermore, after the fiber was immersed in water at 80° C. for 120 hours, the strength was measured to be 0.68 g/d, and the strength retention rate was 70.8%.

Example 2 404 parts of sebacic acid and 156 parts of neopentyl glycol were placed in a 17 flask and heated in a nitrogen atmosphere at 2100C under atmospheric pressure for 2 hours.

Next, 0.02 part of titanyl ammonium oxalate and 0.025 part of triphenylphosphite I were added, and the mixture was heated at 220°C.
The pressure was gradually reduced.

Depressurize to 0.3 mrttHg in 2 hours, 0.3 mrttHg
Heating was continued for an additional 4 hours at a pressure of mHg.

Polymer 106. per g, 570'x amount of hydroxyl groups and 4
．． Melting point 25-27° with 2 equivalents of carboxyl groups
Polyester C was obtained.

Conopolyester/l/100 parts (0,0287 mol) and 20 parts of 4°4'-diphenylmethane diincyanate (
o, osoo moles) and 0.18 parts of water (0,0100
Put 11 parts of mol) into a flask for polymerization, and add N to the flask without stirring.
, N-dimethy)Ld,) 80 parts of remamide was added to form a homogeneous solution.

Next, this solution was heated at 45° C. and reacted for 90 minutes to obtain an intermediate polymer.

Next, 220 parts of N,N-dimethylformamide was added to make a homogeneous solution, which was then cooled to 8°C.

A solution of 2.75 parts (0,0371 mol) of 1,2-diaminopropane dissolved in 30 parts of N,N-dimethylformamide was added thereto over 30 minutes.

The intrinsic viscosity of the obtained polymer was 1.3 dl/9.

Next, this polymer solution was dry-spun using a conventional method to obtain 280%
A multifilament of d/15 f was obtained.

The strength of the obtained fiber was 1.01 g/d, the elongation was 680%,
The stress at 300% elongation was 0.1 (1/d).

Furthermore, when the elongation recovery rate was measured using the same method as in Example 1, the elongation recovery rate after being held at 500% elongation for 10 minutes was 96%, and the elongation recovery rate after being held at 500% elongation for 24 hours was 94%. %Met.

Further, when this fiber was immersed in water at 80° C. for 120 hours, the strength was measured, and it was found to be 0.81 g/d, and the strength retention rate was 80.2%.

Comparative Example 1 100 parts of the copolyester obtained in Example 1 (0,034
2 moles) and 21.4 parts (0,0856 moles) of 4,4'-diphenylmethane diisocyanate were placed in a 14-polymerization flask, and while stirring, 80 parts of N,N-dimethylacetamide was added to form a homogeneous solution.

This solution was heated to 50°C and reacted for 45 minutes to obtain an intermediate polymer.

Next, 220 parts of N,N-dimethylacetamide was added to make a homogeneous solution, and then 1.

Cooled to ℃.

Then, a solution of 3.73 parts (0,0504 mol) of 1,2-diaminopropane dissolved in 30 parts of N,N-dimethylacetamide was added over 30 minutes.

The intrinsic viscosity of the obtained polymer was 1.35 dl19.

Next, a multifilament of 280 d/15 f was obtained in the same manner as in Example 1.

The strength of the obtained fiber was 0.95.9/d, and the elongation was 750.
%, the stress at 300% elongation is 0.12. It was p/d.

Furthermore, when the elongation recovery rate was measured using the same method as in Example 1, the elongation recovery rate after being held at 500% elongation for 10 minutes was 85%, and the elongation recovery rate after being left at 500% elongation for 24 hours was 74%. %Met.

The apparent viscosity of the obtained polymer solution was 20°C at 20°C.
The viscosity was 50 poise, but the apparent viscosity after standing for U hours was 2.
It was 4500 poise at 0°C.

However, after applying a shear force to this solution, it was measured again and found to be 2200 poise at 20°C.

Example 3 292 parts of adipic acid, 93 parts of ethylene glycol, and 135 parts of 1,4-butanediol were placed in a No. 11 flask and heated at 190° C. under atmospheric pressure for 16 hours in a nitrogen atmosphere.

Then, at the same temperature, the pressure was reduced to 0.1 m in 2 hours.
The pressure was reduced to mHg and the mixture was heated under the same conditions for 24 hours.

A copolyester having a melting point of 30 to 33°C and having 710 equivalents of hydroxyl groups and 18.2 equivalents of carboxyl groups per 106 g of polymer was obtained.

Using this copolyester, a polymer solution (intrinsic viscosity: 1.25 d i/i ) was obtained in the same manner as in Example 1, and a multifilament of 280 d/15 f was obtained by dry spinning.

The strength of the obtained fiber was 0.94 g/d, the elongation was 660%, and the stress at 300% elongation was 0.10 g/d.

The elongation recovery rate was also good. However, this fiber
When the strength was measured after being immersed in water at a temperature of 120 hours, it was 0.29 g/d, and the strength retention rate was 30.9%.

As described above, tahouri urethane elastic fibers made of polyester with a high acid value are inferior in hydrolysis resistance to polyurethane elastic fibers obtained using polyester with a low acid value, and are subject to limitations in terms of use.

Example 4 292 parts of adipic acid, 11 parts of ethylene glycol, and 158 parts of 1,4-butanediol were placed in a No. 11 flask and heated at 210°C under nitrogen atmosphere for 2 hours under atmospheric pressure.

Next, 0.02 part of titanyl ammonium oxalate and 0.025 parts of triphenylphosphite hO were added, the pressure was gradually reduced to 210°C, the pressure was reduced to 0.2 mmHg over 2 hours, and the mixture was further heated under the same conditions for 3 hours.

A copolyester having a melting point of 28 DEG to 30 DEG C. was obtained, having 388 equivalents of hydroxyl groups and 2.8 equivalents of carboxyl groups per 106 parts of polymer.

100 parts (0,0195 mol) of this copolyester
．． 15 parts of 4'-diphenylmethane diisocyanate (0
,0600 mol) and 0.11 part (0,0061 mol) of water were placed in a flask for polymerization, and while stirring, N,N
- 80 parts of dimethylformamide was added to form a homogeneous solution.

Next, this solution was heated to 50° C. and reacted for 75 minutes to obtain an intermediate polymer.

Next, 220 parts of N,N-dimethylformamide was added,
A few parts (0,0
A solution of 310 mol) of 1,2-diaminopropane dissolved in 30 parts of N,N-dimethylformamide was added over 30 minutes.

The intrinsic viscosity of the obtained polymer was L46 dl/g.

Next, this polymer solution was dry-spun using a conventional method to obtain 40%
A multifilament of d/3 f was obtained.

The obtained fiber had a strength of 1.13 g/d and an elongation of '11.
The stress at 0% and 300% elongation was 0.13 g/d.

The elongation recovery rate of this fiber was measured in the same manner as in Example 1.

The elongation recovery rate after holding for 10 minutes under 500% elongation was 91%.
The elongation recovery after holding for 24 hours under 500% elongation was 85%.

Further, when the strength of the fiber was measured after being immersed in water at 80° C. for 120 hours, it was found to be 0.94 g/d, and the strength retention rate was 83.2%.

The fibers obtained by the method of the present invention not only have useful properties for woven and knitted fabrics, but also have excellent performance particularly suitable for uses such as strings.

Furthermore, since it has a low secondary transition point, it is extremely suitable for use at low temperatures.

Example 5 In the same manner as in Example 1, the value of a in the formula below indicating the molar amount of water added was varied. Under 500% elongation, 2
The elongation recovery rate after holding for 4 hours was determined.

[(Mole of aromatic diisocyanate) (Mole of polyester)] ×a According to the present invention, a fiber having excellent stretch recovery properties was obtained.

Comparative Example 2 100 parts of the copolyester obtained in Example 1 (0.03
42 mol), 21.4 parts (0,0856 mol) of 4,4' diphenylmethane diisocyanate, and 0.01 part of dibutyltin dilaurate were placed in a flask for polymerization, and 6
The mixture was heated to 0'C and reacted for 30 minutes to obtain an intermediate polymer.

Next, 240 parts of N,N-dimethylformamide was added to make a homogeneous solution, which was then cooled to 10°C, and 3.99 parts (0,0539 mol) of 1,2-diaminopropane was added to N,N-
A solution in 50 parts of dimethylformamide was added over 30 minutes.

The solution viscosity of the obtained polymer was 18,000 poise at 25°C, but after 16 hours it was 520 poise at 25°C.

Claims (1)

[Scope of Claims] 1. A molecular weight compound having a melting point of 40°C or lower and having a terminal hydroxyl group.
When producing an intermediate polymer by reacting a symmetrical aromatic diisocyanate with a polyester of 500 to 7000 at a molar ratio of -NCO groups/-OH groups of -2 to 4, the following formula [(moles of aromatic diisocyanate) (Mole of polyester)]×a where a is 0.05 to 0.30 Add water in a molar amount shown to produce an intermediate polymer,
Next, the obtained intermediate polymer is reacted with a diamine in an amount equivalent to 0.70 to 0.96 equivalents based on the equivalent of the residual incyanate group in the intermediate polymer to obtain the general formula % formula %) where , R is a symmetrical aromatic group R' is a polyester residue obtained by removing the hydroxyl group from a polyester having a terminal hydroxyl group, a molecular weight of 1500 to 7000, and a melting point of 400C or less, R
represents a divalent organic group. 1. A method for producing a polyurethane elastomer, which comprises obtaining a substantially linear polymer containing segments represented by: 2 The proportion of polyester segments in the polymer is 7
The method for producing a polyurethane elastic body according to claim 1, wherein the content is 5 to 94% by weight. 3. The method for producing a polyurethane elastomer according to claim 1 or 2, wherein the polyester has a carboxyl group content of 10 equivalents/106 g (polyester) or less. 4. The method for producing a polyurethane elastomer according to claim 1, wherein the diamine is 1,2-diaminopropane. 5. The method for producing a polyurethane elastomer according to claim 1, wherein the aromatic diisocyanate is 4,4'-diphenylmethane diisocyanate. 6. The method for producing a polyurethane elastomer according to claim 1, wherein the intermediate polymer is produced in a solvent inert to incyanate groups.