Low viscosity, high molecular weight polyether polyol and preparation method thereof

Abstract

The present invention belongs to the field of polyether polyol synthesis, and specifically relates to low-viscosity, high-molecular-weight polyether polyol and its preparation method. It is prepared by the following steps: using a small-molecule diol as an initiator, under the action of an alkali metal catalyst, using propylene oxide as a polymerization monomer, heating reaction, neutralization, dehydration, and filtration to obtain a low-molecular-weight polyether polyol; using a low-molecular-weight polyether polyol as an initiator, under the action of a double metal cyanide catalyst, using propylene oxide as a polymerization monomer, and preparing a medium-molecular-weight polyether polyol through induction and polymerization. Using a medium-molecular-weight polyether polyol as an initiator, under the action of a double metal cyanide catalyst, using propylene oxide as a polymerization monomer, and preparing a high-molecular-weight polyether polyol through pre-induction, induction, and polymerization; the high-molecular-weight polyether polymerization stage of the present invention adds a pre-induction process, which effectively improves the activation rate of the catalyst, and the prepared polyether polyol has a low unsaturation value and low viscosity.

Description

Technical Field

[0001] The invention belongs to the field of polyether polyol synthesis, and in particular relates to low-viscosity, high-molecular-weight polyether polyol and a preparation method thereof. Background Art

[0002] Silane-modified polyether adhesive (MS adhesive) is a new generation of building sealant developed after silicone adhesive (SR) and polyurethane adhesive (PU). MS adhesive has good bonding properties to metal, non-metal, plastic, wood and other building substrates. Secondly, MS adhesive has better weather resistance and durability than silicone adhesive and polyurethane adhesive. Moreover. The VOCs emission of MS adhesive is much lower than that of silicone adhesive and polyurethane adhesive, and it is a green and environmentally friendly product. High-end MS adhesive prepared by allyl alcohol polyether (Zhongyuan Chemical Process, Sanyo Chemical Process) has high tensile strength, high elongation at break, excellent performance, and a high proportion of use in adhesives. Domestic MS adhesive synthesis adopts Wacker process, firstly, the polyether polyol is chain extended with isocyanate group to enhance the tensile properties of polyether polyol, and then the polyether is capped with aminosilane containing isocyanate group. The MS adhesive synthesized by this process is a low-end product, and its tensile properties and elongation at break are lower than those of foreign products. The performance of MS glue prepared by using high molecular weight polyether polyol with a molecular weight exceeding 18000g / mol is close to that of high-end MS glue from abroad.

[0003] At present, the synthesis of high molecular weight polyether polyols used for MS glue in China all uses DMC as a catalyst. During the synthesis process, as the molecular weight increases, the side reactions gradually increase and the viscosity increases sharply, so it cannot be used for the synthesis of MS glue. Therefore, low-viscosity, high-molecular-weight polyether polyols have become a key factor restricting the development of high-end MS glue. Patent CN103635506A mentions the use of low-molecular-weight polyether polyols containing active hydrogen to synthesize low-viscosity, high-molecular-weight polyether polyols. This process has three shortcomings: first, the polymerization stage of the process requires 15-23h to complete, and the production efficiency is low; second, the long polymerization time of the process leads to an increase in side reactions and the formation of a large number of unsaturated polyethers; finally, the equipment requirements of the process are high, and high-speed grid stirring is required, which increases the production cost. Patent CN108070082A provides a method for preparing a low-viscosity high-molecular-weight polyether polyol, which first induces a bimetallic catalyst in an oligomer, then adds an epoxide and a small molecule initiator to the polymerization system at the same time, and obtains a polyether polyol after degassing. This patent still has some shortcomings. First, the initial catalyst concentration is too high during the polymerization induction process, resulting in the presence of extremely high molecular weight polyether tailing. Secondly, the continuous addition of small molecules is very small and difficult to control. At the same time, excessive addition of small molecules causes the molecular weight distribution D value of the high molecular weight polyether polyol to increase to 1.364, and the molecular weight distribution becomes wider. Since DMC catalysts are not easy to catalyze small molecule initiators, the introduction of small molecules leads to excessive side reactions in the polymerization process. The experimental test shows that the unsaturation value of the polyether increases to 0.0278 mol / kg (Comparative Example 4). Furthermore, when small molecules are used as initiators, the "construction ratio" of the polyether is large, the initiator occupies a very small volume in the reactor, and the temperature fluctuation range is large in the initial stage of polymerization, resulting in poor quality of the polyether and unstable reaction activity. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a low-viscosity, high-molecular-weight polyether polyol, which has low viscosity, low unsaturation, and a molecular weight of 17000-23000 g / mol. The molecular weight is a theoretical calculated value, molecular weight = 56100 × 2 ÷ hydroxyl value.

[0005] The invention also provides a preparation method thereof, which is divided into three stages. The "building ratio" of each stage is appropriate, the molecular weight is stable and increases regularly, and the finally prepared high molecular weight polyether polyol has low viscosity and low unsaturation value.

[0006] The method for preparing the low-viscosity, high-molecular-weight polyether polyol of the present invention is prepared by the following steps:

[0007] Step 1: Preparation of low molecular weight polyether polyols:

[0008] Using a small molecule diol as an initiator, propylene oxide as a polymerization monomer, and heating the reaction under the action of an alkali metal catalyst to synthesize a crude polyether with a molecular weight of 400-1000 g / mol, and then neutralizing it with an acidic reagent such as phosphoric acid or sulfuric acid, dehydrating it, and filtering it to obtain a low molecular weight polyether polyol;

[0009] Step 2: Preparation of medium molecular weight polyether polyols:

[0010] The low molecular weight polyether polyol is used as an initiator, under the action of double metal cyanide (DMC) catalyst, propylene oxide is used as a polymerization monomer, and a medium molecular weight polyether polyol with a molecular weight of 4000-8000 g / mol is prepared through an induction process and a polymerization process.

[0011] Step 3: Preparation of high molecular weight polyether polyols:

[0012] The medium molecular weight polyether polyol is used as an initiator, and propylene oxide is used as a polymerization monomer under the action of a double metal cyanide (DMC) catalyst to prepare a high molecular weight polyether polyol with a molecular weight of 17000-23000 g / mol through three processes of pre-induction, induction, and polymerization; the viscosity of the high molecular weight polyether polyol is 16000-35000 mPa·s;

[0013] Among them, the prepared high molecular weight polyether polyol with a molecular weight of 18000g / mol (generally referred to as high molecular weight polyether polyol with a theoretical molecular weight of 17000-19000g / mol) has a viscosity of 16000-19000mPa·s; the high molecular weight polyether polyol with a molecular weight of 20000g / mol (generally referred to as high molecular weight polyether polyol with a theoretical molecular weight of 19000-21000g / mol) has a viscosity of 23000-28000mPa·s; the high molecular weight polyether polyol with a molecular weight of 22000g / mol (generally referred to as high molecular weight polyether polyol with a theoretical molecular weight of 21000-23000g / mol) has a viscosity of 32000-35000mPa·s.

[0014] The small molecule diols in step 1 include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, diethylene glycol, dipropylene glycol, 1,4-butanediol, etc., preferably 1,2-propylene glycol.

[0015] The alkali metal catalyst in step 1 includes sodium hydroxide, potassium hydroxide, cesium hydroxide, potassium alcoholate, sodium alcoholate, etc. Potassium hydroxide is preferred.

[0016] The content of the alkali metal catalyst in step 1 is 1000-4000ppm based on the mass of the low molecular weight polyether polyol; the temperature of the heating reaction in step 1 is 85-130°C.

[0017] The dosage of the double metal cyanide (DMC) catalyst in step 2 is 15-40ppm of the mass of the medium molecular weight polyether polyol; the temperature of the induction process and the polymerization process in step 2 is 130-160°C; the dosage of propylene oxide in the induction process of the high molecular weight polyether polyol in step 2 is 10-20% of the mass of the low molecular weight polyether polyol initiator.

[0018] The dosage of the double metal cyanide (DMC) catalyst in step 3 is 40-150 ppm based on the mass of the high molecular weight polyether polyol.

[0019] The pre-induction temperature in step 3 is 30-90°C; the pre-induction time is 0.5-15h. The pre-induction reagent in the pre-induction process in step 3 is an epoxy compound, including propylene oxide, ethylene oxide, butylene oxide, 2,3-butylene oxide, isobutylene oxide, pentyl oxide, 2,3-pentyl oxide, hexyl oxide, 2,3-hexyl oxide, 3,4-hexyl oxide, heptane oxide, octane oxide and other epoxy compounds; the amount of epoxy compound in the pre-induction process in step 3 is 0.5%-3% of the mass of the molecular weight polyether polyol in the initiator; the pre-induction process is completed, and the epoxy compound used in the pre-induction process is removed by reduced pressure vacuum.

[0020] The temperature of the induction process and the polymerization process in step 3 is 130-160° C.; the amount of propylene oxide used in the induction process of the high molecular weight polyether polyol accounts for 3-15% of the initiator of the medium molecular weight polyether polyol.

[0021] In the polymerization process of the high molecular weight polyether polyol described in step 3, the rate of addition of propylene oxide gradually decreases as the reaction proceeds: after the pre-induction and induction processes are completed and the polymerization process begins, 40% of the total mass of propylene oxide is added to the reaction vessel in 1-2 hours, 40-80% of the propylene oxide is added to the reactor in 2-3 hours, and 80-100% of the propylene oxide is added to the reactor in 2-3 hours.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention divides the synthesis process of high molecular weight polyether polyol into three steps. Compared with the polymerization time of 15-23 hours in the process of the prior art, the present invention can shorten the polymerization process of medium molecular weight polyether and high molecular weight polyether to less than 10 hours in total, thereby improving the polymerization efficiency.

[0024] (2) The high molecular weight polyether polymerization stage of the present invention adds a pre-induction process, which effectively improves the activation rate of the catalyst, and the prepared polyether polyol has a low unsaturation value and low viscosity. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the embodiments.

[0026] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0027] Example 1

[0028] The method for preparing the low-viscosity, high-molecular-weight polyether polyol is prepared by the following steps:

[0029] Step 1: Preparation of low molecular weight polyether polyols:

[0030] 300g of 1,2-propylene glycol and 1.6g of potassium hydroxide were added to a 5L autoclave, and the air in the autoclave was replaced with nitrogen. The temperature was raised and the pressure was reduced to dehydrate. 1300g of propylene oxide was added at 107.5±22.5℃, and the pressure during the addition process was less than 0.4MPa to obtain a crude low molecular weight polyether polyol with a molecular weight of 400g / mol. Then 8.2g of 70wt.% phosphoric acid aqueous solution and 68g of deionized water were added to remove potassium ions from the crude polyether, and potassium phosphate was adsorbed with an adsorbent, dehydrated and filtered to obtain a low molecular weight polyether polyol. The amount of catalyst potassium hydroxide used was 1000ppm according to the theoretical value of 1600g for synthesizing low molecular weight polyether. The theoretical value is the sum of the mass of 1,2-propylene glycol and the mass of propylene oxide, that is, the sum of the added reaction raw materials. The calculation method of the following catalyst amount is the same as here.

[0031] Step 2: Preparation of medium molecular weight polyether polyols:

[0032] Into a 5L high-pressure reactor, 300g of the above 400g / mol low-molecular-weight polyether polyol was added, and 0.0462g of a bimetallic catalyst DMC was added at the same time. The temperature was increased and the reduced pressure was reduced to dehydrate. 30g of propylene oxide was added at 145±15°C to induce the reaction. After the reaction was initiated, 2750g of propylene oxide was added at 145±15°C. The pressure during the addition process was less than 0.4MPa. The polymerization time was 2h. After the polymerization, a medium-molecular-weight polyether polyol with a molecular weight of 4000g / mol was obtained.

[0033] Step 3: Preparation of high molecular weight polyether polyols:

[0034] Add 600g of the above-mentioned medium molecular weight polyether polyol with a molecular weight of 4000g / mol to a 5L reactor, add 0.075g of bimetallic catalyst DMC at the same time, heat up and reduce pressure to dehydrate, add 3g of propylene oxide at 30°C for pre-induction reaction, after pre-induction for 0.5h, remove the epoxy compound in vacuum, add 30g of propylene oxide at 145±15°C to induce and initiate the reaction, after the reaction is initiated, add 1250g at 145±15°C for polymerization reaction: first, add 500g of propylene oxide to the reactor within 1h, then add 500g of propylene oxide to the reactor within 2h, and finally add 250g of propylene oxide to the reactor within 2h, the pressure during the addition process is less than 0.4MPa, and after the polymerization is completed, a high molecular weight polyether polyol with a molecular weight of 18000g / mol is obtained. The polymerization time in all the following tables is the sum of the polymerization time in step 2 and step 3.

[0035] The basic indicators of the obtained high molecular weight polyether polyol are shown in Table 1 below:

[0036] Table 1 Basic indicators of high molecular weight polyether polyols in Example 1

[0037]

[0038] Example 2

[0039] The method for preparing the low-viscosity, high-molecular-weight polyether polyol is prepared by the following steps:

[0040] Step 1: Preparation of low molecular weight polyether polyols:

[0041] 300g of 1,2-propylene glycol and 7.9g of potassium hydroxide were added to a 5L autoclave, and the air in the autoclave was replaced with nitrogen. The temperature was raised and the pressure was reduced to dehydrate. 2860g of propylene oxide was added within the range of 107.5±22.5℃, and the pressure during the addition process was less than 0.4MPa to obtain a low molecular weight polyether crude product with a molecular weight of 800g / mol. Then 20.3g of 70% phosphoric acid and 115g of deionized water were added to remove potassium ions from the crude polyether, and potassium phosphate was adsorbed by an adsorbent, and dehydrated and filtered to obtain a low molecular weight polyether polyol.

[0042] Step 2: Preparation of medium molecular weight polyether polyols:

[0043] Into a 5L high-pressure reactor, 300g of the above low-molecular-weight polyether polyol was added, and 0.0675g of a bimetallic catalyst DMC was added at the same time. The temperature was increased and the reduced pressure was reduced to dehydrate. At 145±15°C, 37.5g of propylene oxide was added to induce the reaction. After the reaction was initiated, 1912.5g of propylene oxide was added at 145±15°C. The pressure during the addition process was less than 0.4MPa. The polymerization time was 2h. After the polymerization, a medium-molecular-weight polyether polyol with a molecular weight of 6000g / mol was obtained.

[0044] Step 3: Preparation of high molecular weight polyether polyols:

[0045] Add 600g of the above-mentioned medium molecular weight polyether polyol with a molecular weight of 6000g / mol to a 5L reactor, and add 0.243g of a bimetallic catalyst DMC at the same time, heat up and reduce pressure to dehydrate, add 15g of propylene oxide at 60°C for pre-induction process, and remove the epoxy compound in vacuum after 8h of pre-induction. Add 54g of propylene oxide at 145±15°C to induce and initiate the reaction. After the reaction is initiated, add 1496g of propylene oxide at 145±15°C for polymerization: first, add 598.4g of propylene oxide to the reactor within 1.5h, then add 598.4g of propylene oxide to the reactor within 2.5h, and finally add 299.2g of propylene oxide to the reactor within 2.5h. The pressure during the addition process is less than 0.4MPa. After the polymerization, a high molecular weight polyether polyol with a molecular weight of 20000g / mol is obtained. The basic indicators of the obtained high molecular weight polyether polyol are shown in Table 2 below:

[0046] Table 2 Basic indicators of high molecular weight polyether polyols in Example 2

[0047]

[0048] Example 3

[0049] The method for preparing the low-viscosity, high-molecular-weight polyether polyol is prepared by the following steps:

[0050] Step 1: Preparation of low molecular weight polyether polyols:

[0051] 300 g of 1,2-propylene glycol and 15.8 g of potassium hydroxide were added to a 5L autoclave, the air in the autoclave was replaced with nitrogen, the temperature was raised and the pressure was reduced to dehydrate, 3650 g of propylene oxide was added within the range of 107.5±22.5°C, and the pressure during the addition process was less than 0.4 MPa, to obtain a low molecular weight polyether crude product with a molecular weight of 1000 g / mol. Then 27.3 g of 70% phosphoric acid and 150 g of deionized water were added to remove potassium ions from the crude polyether, and potassium phosphate was adsorbed with an adsorbent, dehydrated and filtered to obtain a low molecular weight polyether polyol.

[0052] Step 2: Preparation of medium molecular weight polyether polyols:

[0053] Into a 5L high-pressure reactor, 300g of the above low-molecular-weight polyether polyol was added, and 0.099g of a bimetallic catalyst DMC was added at the same time. The temperature was increased and the reduced pressure was reduced to dehydrate. At 145±15°C, 60g of propylene oxide was added to induce the reaction. After the reaction was initiated, 2120g of propylene oxide was added at 145±15°C. The pressure during the addition process was less than 0.4MPa. The polymerization time was 2h. After the polymerization, a medium-molecular-weight polyether polyol with a molecular weight of 8000g / mol was obtained.

[0054] Step 3: Preparation of high molecular weight polyether polyols:

[0055] 600g of the above-mentioned medium molecular weight polyether polyol was added to a 5L reactor, and 0.354g of a bimetallic catalyst DMC was added at the same time. The temperature was raised and the pressure was reduced to dehydrate. 18g of propylene oxide was added at 90°C for pre-induction reaction. After 15h of pre-induction, the epoxy compound was removed in vacuum. 90g of propylene oxide was added at 145±15°C to induce and initiate the reaction. After the reaction was initiated, 1670g of propylene oxide was added at 145±15°C for polymerization: first, 668g of propylene oxide was added to the reactor for 2h, and then 668g of propylene oxide was added to the reactor within 3h, and finally 334g of propylene oxide was added to the reactor within 3h. The pressure during the addition process was less than 0.4MPa. After the polymerization was completed, a high molecular weight polyether polyol with a molecular weight of 22000g / mol was obtained. The basic indicators of the obtained high molecular weight polyether polyol are shown in Table 3 below:

[0056] Table 3 Basic indicators of high molecular weight polyether polyols in Example 3

[0057]

[0058] Comparative Example 1

[0059] Compared with Example 1, Comparative Example 1 does not have a pre-induction process, and the remaining processes are the same.

[0060] The preparation method of the polyether polyol is prepared by the following steps:

[0061] Step 1: Preparation of low molecular weight polyether polyols:

[0062] 300 g of 1,2-propylene glycol and 1.6 g of potassium hydroxide were added to a 5L autoclave, the air in the autoclave was replaced with nitrogen, the temperature was raised and the pressure was reduced to dehydrate, 1300 g of propylene oxide was added at 107.5±22.5°C, and the pressure during the addition process was less than 0.4 MPa, and a low molecular weight polyether polyol crude product with a molecular weight of 400 g / mol was obtained. Then 8.2 g of 70 wt.% phosphoric acid aqueous solution and 68 g of deionized water were added to remove potassium ions in the crude polyether, and potassium phosphate was adsorbed with an adsorbent, and the low molecular weight polyether polyol was obtained by dehydration and filtration.

[0063] Step 2: Preparation of medium molecular weight polyether polyols:

[0064] Into a 5L high-pressure reactor, 300g of the above 400g / mol low-molecular-weight polyether polyol was added, and 0.0462g of a bimetallic catalyst DMC was added at the same time. The temperature was increased and the reduced pressure was reduced to dehydrate. 30g of propylene oxide was added at 145±15°C to induce the reaction. After the reaction was initiated, 2750g of propylene oxide was added at 145±15°C. The pressure during the addition process was less than 0.4MPa. The polymerization time was 2h. After the polymerization, a medium-molecular-weight polyether polyol with a molecular weight of 4000g / mol was obtained.

[0065] Step 3: Preparation of high molecular weight polyether polyols:

[0066] Add 600g of the above-mentioned medium molecular weight polyether polyol with a molecular weight of 4000g / mol into a 5L reactor, and add 0.075g of a bimetallic catalyst DMC at the same time. Heat and reduce pressure for dehydration, add 30g of propylene oxide at 145±15°C to induce and initiate the reaction. After the reaction is initiated, add 1250g at 145±15°C for polymerization: first, add 500g of propylene oxide into the reactor within 1h, then add 500g of propylene oxide into the reactor within 2h, and finally add 250g of propylene oxide into the reactor within 2h. The pressure during the addition process is less than 0.4MPa. After the polymerization, a high molecular weight polyether polyol with a molecular weight of 18000g / mol is obtained.

[0067] Compared with Example 2, Comparative Example 2 does not have a pre-induction process, and the remaining processes are the same.

[0068] Compared with Example 3, Comparative Example 3 does not have a pre-induction process, and the remaining processes are the same.

[0069] The basic indicators of the high molecular weight polyether polyol obtained in the comparative example are shown in Table 4 below:

[0070] Table 4 Basic indicators of high molecular weight polyether polyols in comparative examples

[0071]

[0072] It can be seen from the above table that the pre-induction process can effectively improve the activation rate of the catalyst, and the prepared polyether polyol has a low unsaturation value and low viscosity.

[0073] Comparative Example 4

[0074] According to Example 8 in patent CN108070082A, polymer polyether polyol is synthesized:

[0075] A polyether polyol with a number average molecular weight of 2000 g / mol and 0.0798 g of a DMC catalyst were put into a reactor, 30 g of propylene oxide was added, and the DMC catalyst was initiated at 125±10°C. 1844 g of propylene oxide and 6.0 g of a small molecule propylene glycol initiator were continuously added to the reactor, and the addition time was 12.6 hours. After aging, the polyether polyol was degassed in vacuum to obtain the polyether polyol.

[0076] Table 5 Basic indicators of high molecular weight polyether polyol of comparative example 4 and polyether polyol of example 2

[0077]

[0078] Comparative Example 5

[0079] According to Example 3 in patent CN111518268A, polymer polyether polyol is synthesized:

[0080] 500 g of propylene glycol polyoxypropylene ether with a number average molecular weight of 4000 g / mol was mixed with 0.033 g of phosphoric acid at 800 rpm for 5 min, 0.83 g of DMC catalyst was added, and the mixture was mixed and stirred at 2000 rpm for 10 min, and then all the materials were added into the reactor. Control the system vacuum degree at 10 kPa, continue to evacuate for 10 minutes, then introduce nitrogen into the system until the pressure reaches 300 kPa, repeat this three times to complete the replacement; raise the temperature to 120°C, introduce nitrogen and start the vacuum pump to control the system pressure to <10 kPa, continue for 2 hours, complete the gas stripping dehydration, and introduce nitrogen into the system to normal pressure; raise the temperature to 135°C, add 50 g of propylene oxide, complete the induction when the pressure drops and the temperature rises, maintain 135°C, and continuously introduce 200 g of propylene oxide within 1 hour to obtain a polyether homogeneous liquid containing 1100 ppm of active catalyst and the number average molecular weight of the polyether polyol intermediate being 6000 g / mol, cool to 25°C, add 2905 g of propylene oxide and set aside.

[0081] In another reactor, add 600g of propylene glycol polyoxypropylene ether with a number average molecular weight of 4000g / mol, and after displacement and gas stripping dehydration, heat to 145°C, and continue to add the above polyether homogeneous liquid containing active catalyst into the reactor for 5 hours; then add 1245g of propylene oxide for 2 hours. Maintain the reaction temperature, and after aging for 30 minutes, remove the unreacted propylene oxide to obtain a polyether polyol with a molecular weight of 20000g / mol.

[0082] Table 6 Basic indicators of high molecular weight polyether polyol of comparative example 5 and polyether polyol of example 2

[0083]

[0084] This shows that the properties of the high molecular weight polyether polyol synthesized in Example 3 of patent CN111518268A are not as good as those of Example 2 of the present invention.

Claims

1. A method for preparing a low-viscosity, high-molecular-weight polyether polyol, characterized in that: Prepared by the following steps: Step 1: Preparation of low molecular weight polyether polyols: Using a small molecule diol as an initiator, propylene oxide as a polymerization monomer, and heating the reaction under the action of an alkali metal catalyst to synthesize a crude polyether with a molecular weight of 400-1000 g / mol, and then neutralizing, dehydrating, and filtering to obtain a low molecular weight polyether polyol; Step 2: Preparation of medium molecular weight polyether polyols: The low molecular weight polyether polyol is used as an initiator, under the action of a double metal cyanide catalyst, and propylene oxide is used as a polymerization monomer, and a medium molecular weight polyether polyol with a molecular weight of 4000-8000 g / mol is prepared after an induction process and a polymerization process respectively; Step 3: Preparation of high molecular weight polyether polyols: The medium molecular weight polyether polyol is used as an initiator, and propylene oxide is used as a polymerization monomer under the action of a double metal cyanide catalyst, and three processes of pre-induction, induction, and polymerization are respectively carried out to prepare a high molecular weight polyether polyol with a molecular weight of 17000-23000 g / mol; the viscosity of the high molecular weight polyether polyol is 16000-35000 mPa·s; The dosage of the double metal cyanide catalyst in step 2 is 15-40ppm of the mass of the medium molecular weight polyether polyol; the temperature of the induction process and polymerization process in step 2 is 130-160°C; the dosage of propylene oxide in the induction process of the medium molecular weight polyether polyol in step 2 is 10-20% of the mass of the low molecular weight polyether polyol initiator; The dosage of the double metal cyanide catalyst in step 3 is 40-150 ppm based on the mass of the polymer polyether polyol; The pre-induction temperature in step 3 is 30-90° C. and the pre-induction time is 0.5-15 h. The pre-induction reagent in the pre-induction process of step 3 is an epoxy compound; The amount of the epoxy compound used in the pre-induction process in step 3 is 0.5%-3% of the mass of the molecular weight polyether polyol in the initiator; the pre-induction process is completed, and the epoxy compound used in the pre-induction process is removed by vacuum reduction; The temperature of the induction process and the polymerization process in step 3 is 130-160° C. The amount of propylene oxide used in the induction process of the high molecular weight polyether polyol is 3-15% of the initiator of the medium molecular weight polyether polyol; In the polymerization process of the high molecular weight polyether polyol in step 3, the rate of addition of propylene oxide gradually decreases as the reaction proceeds: 40% of the total mass of propylene oxide is added to the reaction vessel in 1-2 hours, 40-80% of the propylene oxide is added to the reactor in 2-3 hours, and 80-100% of the propylene oxide is added to the reactor in 2-3 hours.

2. The method for preparing a low-viscosity, high-molecular-weight polyether polyol according to claim 1, characterized in that: The amount of the alkali metal catalyst used in step 1 is 1000-4000ppm based on the mass of the low molecular weight polyether polyol; the temperature of the heating reaction in step 1 is 85-130°C.

3. A low viscosity, high molecular weight polyether polyol, characterized in that: The method is prepared by any one of claims 1 to 2.

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