JPH0794504B2 - Ethylene-α-olefin copolymer and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention has a broad molecular weight distribution and high strength ethylene-α-
The present invention relates to an olefin copolymer and a method for producing the same.

<Prior Art> Ethylene-α-olefin copolymers are also called linear low-density polyethylene (including so-called VLDPE, but hereinafter referred to as LLDPE), and are low-chain branched polymers obtained by radical polymerization under high pressure and high temperature. It is characterized by superior strength and heat resistance as compared to high density polyethylene. However, general LLDPE with a narrow molecular weight distribution has a problem that the load is high during melt extrusion, and LLDPE with a low melt flow rate (hereinafter referred to as MFR) such as hollow film formation and thick film molding such as heavy bags.
When using LDPE, there was a drawback that molding was particularly difficult. Therefore, LLDPE having a wide molecular weight distribution is commercially available for such molding applications. However, the LLDPE having a wide molecular weight distribution has lower strength than the LLDPE having a narrow molecular weight distribution and is not satisfactory at present.

LLDPE is obtained by copolymerizing ethylene and an α-olefin in the presence of a transition metal catalyst such as a Ziegler catalyst. Known LLDPE manufacturing processes include a gas phase method, a slurry method, a solution method, and a high pressure bulk method, all of which are industrially operated. Among them, the high-pressure bulk method is used for the LLDP in the radical polymerization low-density polyethylene manufacturing plant.
Since E can be produced and it is not necessary to have an inert solvent in the system, generally the residence time is short and the volumetric efficiency of the reactor is high, the produced polymer discharged from the reactor is in a molten state. This is a process with many advantages, such as the ability to pelletize without applying heat. JP-A-52-125590, JP-A-54-26889, JP-A-54-52192, and JP-A-55-90512 disclose polyethylene having a wide molecular weight distribution by a high pressure bulk method (specifically, Has proposed a method for producing an ethylene homopolymer). However, by these methods, it is difficult to control the melt flow rate ratio (MFR ratio) and the melt expansion ratio of LLDPE to predetermined values at the same time, and the molecular weight distribution is not wide enough.
There were many unsatisfactory points such as low strength and complicated process.

<Problems to be Solved by the Invention> The object of the present invention is, in view of the current situation as described in the description of the prior art, without reducing the strength that is the characteristic of LLDPE as much as possible, and has a wide molecular weight distribution and excellent workability. Provide LLDPE,
Another object of the present invention is to provide a method for producing such LLDPE by a high pressure bulk method, which has many economical advantages.

<Means for Solving Problems> The present invention is that a copolymer of ethylene and an α-olefin having specific physical properties does not have a decrease in strength, which is a characteristic of LLDPE, and exhibits good processability. The present invention has been completed as a result of extensive studies on the heading and its manufacturing method, and is characterized by having the following requirements.

That is, (1) ethylene having a melt flow rate of 0.1 to 100 g / 10 minutes, a melt flow rate ratio of 35 or more and a melt expansion ratio of 1.35 or less, and 0.5 to 40% by weight of 4 to 10 carbon atoms. (2) a reaction system comprising at least two reaction zones, and the temperature of each reaction zone is in the temperature range of 130 to 350 ° C. under a pressure of at least 400 bar, In addition, ethylene and an α-olefin having 4 to 10 carbon atoms are present in the presence of a Ziegler type catalyst so that the following conditions 1 and 2 are satisfied with respect to the temperature difference between the reaction zones and the production rate of the copolymer in the reaction zones. A method for producing an ethylene-α-olefin copolymer, which comprises copolymerizing with ethylene.

Condition 1: The temperature of each reaction zone is T ₁ , T ₂ , ...
... T _i , T _{i + 1} ... T _n (where n ≧ 2), T _i
-At least one set of reaction zones satisfying T _{i + 1} ≥ 40 ° C is present.

Condition 2: When the temperature of the reaction zone of the group having the largest T _i −T _{i + 1} among the reaction zone groups satisfying the condition 1 is T _h and _TL , the reaction zone having a temperature of T _h or higher. The ratio M _h / M _L of the sum M _h of the production amount of the copolymer in the above and the sum M _L of the production amount of the copolymer in the reaction zone where the temperature is T _L or less is 20/80 to 80/20. It is related to that.

The ethylene-α-olefin copolymer (LLDPE) of the present invention
Is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms. As the α-olefin, butene-
1,4-methylpentene-1, hexene-1, octene-1, decene-1 and the like, which have 4 to 10 carbon atoms
Since those of the above range are preferable, the range of this range is used in the present invention. These α-olefins may be copolymerized not only in one kind but also in two or more kinds.

The density (according to JIS K6760) of LLDPE of the present invention is 0.945 g
/ cm ³ or less, preferably in the range of 0.88 to 0.940 g / cm ³ , particularly 0.90 to 0.935 g / cm ³ . Density 0.94
When it is higher than 5 g / cm ³ , the strength is poor and the characteristics of LLDPE are lost. The copolymerization ratio of the α-olefin is slightly different depending on the type of the α-olefin, but in order to obtain a copolymer having the above density, it is usually 0.5 to 40% by weight, preferably 1.0 to
30% by weight.

MFR is measured in accordance with JIS K6760, especially
Since it is preferably in the range of 0.1 to 100 g / 10 minutes, the range is set in the present invention. LLDPE with a low MFR has an extremely high load during melt extrusion when the molecular weight distribution is narrow, and is used in applications where high strength is required. It has a high biological value and is particularly preferable.

In the present invention, the MFR ratio (hereinafter referred to as MFRR) means JIS K72
2 measured according to 10 conditions 7 and 4 respectively
It is the ratio of two MFR values. The MFRR value directly corresponds to the shear stress dependence of melt viscosity, but is proportional to the breadth of the molecular weight distribution for linear polymers. The MFRR of LLDPE of the present invention is 35 or more, preferably 40 or more. If the MFRR is less than 35, the load during melt extrusion will be high and the workability will be poor.

Melt expansion ratio (hereinafter referred to as SR) is a value obtained by dividing the diameter of a rod-shaped extruded product extruded according to the method described in JIS K6760 and cooled and solidified in the air at a position 5 mm from the diameter of the orifice of the melt indexer. Is. SR corresponds to the elastic properties of the melt, ie the melt elasticity.

The SR of the LLDPE of the present invention needs to be 1.35 or less, preferably 1.30 or less, more preferably 1.25 or less, and particularly preferably 1.20 or less. If SR is greater than 1.35, the strength, particularly impact strength, is poor and the characteristics of LLDPE are not fully exhibited.

Therefore, the essence of the LLDPE of the present invention is that the MFRR value corresponding to the breadth of the molecular weight distribution is large, and the SR value corresponding to the melt elasticity is small, the mechanism is not yet clear, but for this reason the processability It is presumed that it gives a molded product which is excellent and has excellent strength. Such LLDPEs have never been offered.

The LLDPE of the present invention is a low-density polyethylene obtained by a radical polymerization method, a copolymer of ethylene and a polar vinyl monomer such as an ethylene vinyl acetate copolymer or an ethylene acrylic acid copolymer, or a Ziegler polymerization method. It can also be used as a mixture with high density polyethylene, polypropylene, ethylene propylene rubber, ethylene butene-1 rubber, and other known polymer substances. In addition, known compounding agents such as weathering stabilizers, antioxidants, antistatic agents,
It is possible to mix antifogging agents, slip agents, lubricants, release agents, antiblocking agents, dyes, pigments, inorganic or organic fillers, etc., if necessary.

The LLDPE of the present invention is a film of various thicknesses by an inflation method or a casting method, a hollow container such as a bottle or a bag-in-box by a blow molding method, a pipe for water or gas by an extrusion molding method, an electric wire or a steel pipe, etc. It can be suitably processed into shoes and the like, and a molded product having excellent physical properties can be obtained. In addition, known molding methods such as injection molding and foam molding can be applied.

Next, the ethylene-α-olefin copolymer (LL
DPE) is a reaction system consisting of at least two reaction zones,
At a pressure of at least 400 bar, the temperature in each reaction zone is 130
To 350 ° C., and ethylene and α-having 4 to 10 carbon atoms so as to satisfy the following conditions 1 and 2 with respect to the temperature difference between the reaction zones and the proportion of the copolymer produced in the reaction zones. It can be obtained by copolymerizing with an olefin in the presence of a Ziegler type catalyst. Conditions 1 and 2 are: Condition 1: The temperature of each reaction zone is T ₁ , T ₂ , ...
... T _i , T _{i + 1} ... T _n (where n ≧ 2), T _i
-At least one set of reaction zones satisfying T _{i + 1} ≥ 40 ° C is present.

Condition 2: When the temperature of the reaction zone of the group having the largest T _i −T _{i + 1} among the reaction zone groups satisfying the condition 1 is T _h and _TL , the reaction zone having a temperature of T _h or higher. The ratio M _h / M _L of the sum M _h of the production amount of the copolymer in the above and the sum M _L of the production amount of the copolymer in the reaction zone where the temperature is T _L or less is 20/80 to 80/20. That is.

The density of the produced ethylene-α-olefin copolymer is
The desired value can be controlled by controlling the amount of α-olefin supplied to the reaction system.

The MFR of the copolymer is adjusted by changing the absolute value of the temperature of each reaction zone within the range of 130 to 350 ° C while satisfying the above-mentioned condition 1 which defines the relative relationship of the temperature of each reaction zone. be able to.

In the present invention, the Ziegler type catalyst is a periodic table of elements.
It is preferable to use a catalyst composed of a compound of a group IVb and / or a group Vb transition metal element and a compound of a group IIb and / or group IIIa metal element of the periodic table. Compounds of transition metal elements include titanium, zirconium, hafnium,
A halide such as vanadium, an alkoxide or the like can be used. In addition, such compounds of transition metal elements and the periodic table of elements such as magnesium chloride and aluminum chloride
A complex with a halide of a group IIa and / or group IIIa typical metal element can also be preferably used. Periodic table of the elements
As the compound of the group IIb and / or group IIIa metal element, a hydride of zinc and / or aluminum and / or an organometallic compound can be preferably used.
Examples of these Ziegler type catalysts include JP-A-49-97088, JP-A-49-97089, JP-A-50-50487, JP-A-52-103485, JP-A-54- No. 26889, JP-A-5
4-146285, JP-A-56-99209, JP-A-57-131
It is specifically described in JP-A-208, JP-A-57-145106, JP-A-58-27706, JP-A-58-65708, and JP-A-59-133210.

The temperature of each reaction zone is in the temperature range of 130 to 350 ° C., and it is necessary to satisfy the following condition 1 regarding the temperature difference between the reaction zones. That is, when the temperature of each reaction zone is T ₁ , T ₂ , ... T _i , T _{i + 1,} ... T _{n in} order from the highest temperature (where n ≧ 2), T _i −T _{i + 1} It is necessary that there be at least one set of reaction zones satisfying ≧ 40 ° C. The above requirement regarding the temperature of the reaction zone is essential to the present invention, and if this requirement is not satisfied, LLDPE having a sufficiently wide molecular weight distribution cannot be obtained. More preferably, T _i −T _{i + 1}
The presence of at least one set of reaction zones satisfying ≧ 60 ° C. and the presence of at least one set of reaction zones satisfying T _i −T _{i + 1} ≧ 80 ° C. are particularly preferred.

The temperature of each reaction zone depends on the ethylene and α fed into the reaction zone.
The temperature and / or the feed amount of the unreacted monomer fluid containing olefin and / or the mixed fluid containing the unreacted monomer and the copolymer, the temperature of the external cooling or heating medium of the reaction zone, and the reaction zone A desired temperature can be controlled by controlling the amount of the Ziegler type catalyst fed.

Further, regarding the amount of the copolymer produced in each reaction zone, the following condition 2 is satisfied, that is, the reaction zone of the group having the largest T _i −T _{i + 1} among the reaction zone groups satisfying the condition 1 when the temperature T _h, T _L, a, the amount sum of the copolymer in the reaction zone sum M _h and the temperature of the product weight of the copolymer is less than T _L in the reaction zone temperature is more than T _h M the ratio M _h / M _L with _L is required to be 20/80 to a 80/20.

The above requirement regarding the production amount of the copolymer in the reaction zone is essential to the present invention, and if this requirement is not satisfied, LLDPE having a sufficiently wide molecular weight distribution cannot be obtained. M _h
/ M _L more preferably from to no 30/70 70/30,
It is particularly preferably 40/60 or 60/40. The amount of copolymer produced in each reaction zone depends on the enthalpy of the fluid fed into and discharged from the reaction zone, the amount of heat added to or removed from the outside of the reaction zone, and the copolymer unit. It can be known from the heat of polymerization per mass by taking the heat balance.

The amount of the copolymer produced in each reaction zone depends on the amount of heat added to or removed from the outside of the reaction zone and the enthalpy of the fluid fed into the reaction zone, particularly ethylene and α.
It can be set by changing the temperature and feed rate of the unreacted monomer fluid consisting of olefin.

In order to meet the above two conditions, the reaction system must have at least two reaction zones, but the reaction zones can be frozen in series and / or in parallel.

This reaction is carried out continuously, using two or more reactors,
Each reactor can be used as one reaction zone, but in a reactor that conducts the copolymer at a low temperature, the viscosity of the fluid is high, so the agitation power is large and the reactor or recovery system can be used next. It is easy to transfer Therefore, the reaction system preferably has at least one reactor composed of at least two reaction zones.

One of the preferred embodiments of the stirred reactor is a reactor having a stirrer with one or more partition plates mounted on the shaft. The partition plate is preferably attached horizontally to the stirring shaft in terms of stirring power. Another preferred embodiment is
It is a reactor in which one or more partition plates are attached to the reactor wall.

FIG. 1 shows one embodiment of a reactor that can be preferably used in the present invention, and it will be specifically described.

The unreacted monomer fluid of ethylene and α-olefin in a predetermined ratio is pressurized by the compressor 1 to a predetermined pressure. The compressed unreacted monomer fluid flows through the flow control valve 2,
Two partition plates 9 and 10 which are controlled to a predetermined temperature in three channels through 3 and 4 and are horizontally attached to the shaft 8 of the stirrer.
Is fed into each reaction zone of a vertical cylindrical reactor 14 divided into three reaction zones 11, 12, 13. The Ziegler type catalyst dispersed or dissolved in the inert solvent is pressurized by pumps 15, 16 and 17 for every three channels and injected into each channel of the unreacted monomer fluid. It is also possible to inject the catalyst directly into each reaction zone. The catalyst supplied to each reaction zone may be the same or different. The temperature of each reaction zone is controlled to a predetermined temperature by adjusting the amount of catalyst injected. The mixed fluid of the unreacted monomer and the produced copolymer is introduced into the separator 19 from the bottom of the reactor through the pressure reducing valve 18, and is separated into the unreacted monomer and the produced copolymer. The separated unreacted monomer is recompressed and reused.

<Examples> Examples are shown below to more specifically describe the present invention, but the present invention is not limited thereto.

Example-1 Each reaction zone of a vertical cylindrical reactor with a stirrer having three reaction zones divided into equal volumes by two partition plates mounted perpendicularly to the stirring shaft was adjusted to 50 ° C. An equal amount of a mixed gas of ethylene and butene-1 was continuously fed. The mixing ratio of ethylene and butene-1 was adjusted so that the density of the product would be a desired value. In addition, the temperature of the first and second reaction zones was adjusted to 160 by continuously feeding the Ziegler type catalyst into each reaction zone and adjusting the amount of feeding.
The temperature of the third reaction zone was kept at 260 ° C. Where T ₁
= T _h == 260 ° C. and T ₂ = T ₃ = _TL = 160 ° C., so T ₁
Satisfies −T ₂ = 100 ≧ 40 ° C. The pressure in each reaction zone was kept at 1000 bar. The mixed fluid composed of the copolymer and the unreacted monomer produced in the first and second reaction zones moves from the gap between the inner wall of the reactor and the partition plate to the second and third reaction zones, respectively, The mixed fluid was continuously taken out from the lower part of the third reaction zone through the pressure reducing valve. The average residence time of the fluid in the reactor is 50 seconds. The copolymer produced in the first and second reaction zones was 35% of the total produced copolymer. Therefore, M _h / M _L = 65/35.

The content of butene-1 in the obtained copolymer was 7.2% by weight, M
FR is 2.4g / 10min, density is 0.921g / cc, MFRR is 46, SR is 1.17
Met. Its tensile impact strength was 310 kg · cm / cm ² , and its tensile strength was 200 kg / cm ² .

Example-2 The procedure of Example 1 was repeated, except that the flow rate of the mixed gas fed into the third reaction zone was reduced to 2/5 times that of Example. First
The copolymer produced in the second reaction zone was 44% of the total produced copolymer.

The butene-1 content of the obtained copolymer was 6.4% by weight, MFR
Was 1.5 g / 10 minutes, the density was 0.922 g / cc, the MFRR was 53, and the SR was 1.19. It had a tensile impact strength of 400 kg · cm / cm ² and a tensile strength of 230 kg / cm ² .

Comparative Example-1 The procedure of Example 1 was repeated, except that the temperatures of the first and second reaction zones were changed to 220 ° C and the temperature of the third reaction zone was changed to 240 ° C. That is, T ₁ = T _{h =} = 240 ° C., T ₂ = T ₃ = T = 220
Since the temperature was ° C, T ₁ -T ₂ = 20≤40 ° C, and the conditions were not satisfied. The copolymer produced in the first and second reaction zones was 60% of the total produced copolymer.

The butene-1 content of the obtained copolymer was 7.0% by weight, MFR
Was 2.5 g / 10 minutes, density was 0.920 g / cc, MFRR was 28, and SR was 1.15.

It has a tensile impact strength of 340 kgcm / cm ² and tensile strength of 210 kg.
It was / cm ² .

Example-3 The same as Example-1 except that the temperature of the second reaction zone was changed to 220 ° C and the flow rate of the mixed gas fed into the second reaction zone was reduced to 1/2 times that of Example-1. Carried out. The copolymer produced in the first reaction zone is 21% of the total produced copolymer.

The content of butene-1 in the obtained copolymer was 8.0% by weight, M
FR is 2.5g / 10min, density is 0.919g / cc, MFRR is 41, SR is 1.16
Met.

It has a tensile impact strength of 310 kgcm / cm ² and a tensile strength of 220 kg.
It was / cm ² .

Comparative Example-2 Example-1 except that the temperature of the second reaction zone was changed to 240 ° C.
It carried out similarly to. The copolymer produced in the first reaction zone is 17% of the total produced copolymer.

The butene-1 content of the obtained copolymer was 8.3% by weight, MFR
Was 4.1 g / 10 minutes, the density was 0.918 g / cc, the MFRR was 34, and the SR was 1.17.

It has a tensile impact strength of 270 kgcm / cm ² and tensile strength of 170 kg.
It was / cm ² .

Example 4 Ethylene and hexene-1 were used as the mixed gas fed into each reaction zone.
Example 2 was carried out in the same manner as in Example 2 except that The copolymer produced in the first reaction zone is 43% of the total produced copolymer.

The hexene-1 content of the obtained copolymer is 11.4% by weight,
MFR 1.1g / 10min, density 0.917g / cc, MFRR 59, SR 1.1
Was 5.

It has a tensile impact strength of 850 kg ・ cm / cm ² and a tensile strength of 310 kg.
It was / cm ² .

Example-5 The temperature of the mixed gas fed into the first and second reaction zones was adjusted to 25
C., the flow rate of the mixed gas fed into the third reaction zone was changed to 1/5 of that in Example-1, and the temperature of the mixed gas was changed to 7
Example 1 was repeated except that the temperature was changed to 0 ° C. First
And the copolymer produced in the second reaction zone is 53% of the total copolymer produced.

The butene-1 content of the obtained copolymer was 5.9% by weight, MFR
Is 0.72g / 10 minutes, density is 0.923g / cc, MFRR is 62, SR is 1.20
Met.

It has a tensile impact strength of 450 kgcm / cm ² and a tensile strength of 260 kg.
It was / cm ² .

Example 6 The temperature of the mixed gas fed into the first and second reaction zones was adjusted to 25
C., the temperature of the first and second reaction zones was changed to 180.degree. C., and the mixed gas was not fed into the third reaction zone.
It carried out like Example 1. The copolymer produced in the first and second reaction zones is 66% of the total produced copolymer.

The butene-1 content of the obtained copolymer was 6.0% by weight, MFR
0.69g / 10min, density 0.923g / cc, MFRR 55, SR 1.18
Met.

It has a tensile impact strength of 490 kgcm / cm ² and tensile strength of 270 kg.
It was / cm ² .

Reference example-1 MFR 1.2g / 10min, density 0.921g / cc, MFRR 53, SR 1.3
8 commercially available LLDPE (a copolymer of ethylene and 7.8 wt% butene-1 according to the results of carbon 13 nuclear magnetic resonance spectroscopy) has a tensile impact strength of 220 kg · cm / cm ² and a tensile strength of 200 kg / It was cm ² .

When this is compared with the tensile impact strength and tensile strength of the copolymer of ethylene and butene-1 obtained in Example 2 in which MFR, density, MFRR are close, and SR is as small as 1.19, the copolymer of the present invention has high strength, It can be seen that the impact strength is particularly excellent.

<Effects of the Invention> By the manufacturing method disclosed in the present invention, which satisfies each condition, MFRR35 or more, SR1.35 or less ethylene-α-
An olefin copolymer can be obtained, and the copolymer has a wide molecular weight distribution and excellent processability while maintaining the strength characteristic of LLDPE.

[Brief description of drawings]

FIG. 1 is one embodiment of the reactor. 1 ... Compressor, 2,3,4 ... Flow rate control valve 5,6,7
...... Heat exchanger, 8 …… Stirring shaft, 9,10 …… Partition plate, 11,
12, 13 …… Reaction zone, 14 …… Vertical cylindrical reactor, 15,16,
17 …… Pump, 18 …… Pressure reducing valve 19 …… Separator

Front Page Continuation (72) Inventor Riki Konaka 5-1 Anezaki Kaigan, Ichihara-shi, Chiba Sumitomo Chemical Co., Ltd. (72) Inventor Yukio Naito 5-1 Anesaki Kaigan, Ichihara-shi, Chiba Sumitomo Chemical Co., Ltd. (72) Inventor Hisao Tanaka 1-5 Anezaki Kaigan, Ichihara-shi, Chiba Sumitomo Chemical Co., Ltd. (72) Inventor Naohiro Nakama Yokkaichi, Mie 3-5-8 (72) Inventor Toru Takahara Yokkaichi City, Mie Prefecture 3-5-8

Claims (2)

[Claims] 1. The melt flow rate measured according to JIS K6760 is 0.1 to 100 g / 10 minutes, and the melt flow rate ratio (JI
According to Condition 7 and Condition 4 of S K7210, the ratio of two melt flow rates measured respectively is 35 or more and the melt expansion ratio (extruded according to the method described in JIS K6760), and the solid extruded rod is cooled and solidified in air. Ethylene and 0.5 to 40% by weight of α-olefin having 4 to 10 carbon atoms, characterized in that the diameter at the position of 5 mm from the tip of the object divided by the diameter of the orifice of the melt indexer is 1.35 or less. Copolymer of. 2. A reaction system comprising at least two reaction zones, at a pressure of at least 400 bar, the temperature of each reaction zone being in the temperature range of 130 to 350 ° C., and the temperature difference between the reaction zones and It is characterized in that ethylene and an α-olefin having 4 to 10 carbon atoms are copolymerized in the presence of a Ziegler type catalyst so that the following conditions 1 and 2 are satisfied with respect to the production ratio of the copolymer in the reaction zone. Melt flow rate measured according to JIS K6760 is 0.1-100g / 10
Min, melt flow rate ratio (ratio of two melt flow rate values measured according to JIS K7210 condition 7 and condition 4, respectively) is 35 or more and melt expansion ratio (JIS K676
Ethylene having a diameter of 5 mm from the tip of the extrudate extruded in the air cooled and solidified in accordance with the method described in 0 divided by the diameter of the orifice of the melt indexer) to be 1.35 or less and 0.5 to 40 A method for producing an ethylene-α-olefin copolymer, which is a copolymer with wt% of an α-olefin having 4 to 10 carbon atoms. Condition 1: The temperature of each reaction zone is T ₁ , T ₂ , ...
... T _i , T _{i + 1} ... T _n (where n ≧ 2), T _i
-At least one set of reaction zones satisfying T _{i + 1} ≥ 40 ° C is present. Condition 2: When the temperature of the reaction zone of the group having the largest T _i −T _{i + 1} among the reaction zone groups satisfying the condition 1 is T _h and _TL , the reaction zone having a temperature of T _h or higher. the ratio M _h / M _L of the sum M _L of the amount of the copolymer in the reaction zone sum M _h and the temperature of the product amount is less than T _L of the copolymer is to not 20/80 80/20 in .