CA1064957A - Process for the preparation of polycarbonates - Google Patents
Process for the preparation of polycarbonatesInfo
- Publication number
- CA1064957A CA1064957A CA240,852A CA240852A CA1064957A CA 1064957 A CA1064957 A CA 1064957A CA 240852 A CA240852 A CA 240852A CA 1064957 A CA1064957 A CA 1064957A
- Authority
- CA
- Canada
- Prior art keywords
- diol
- transesterification
- evaporator
- stage
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G64/00—Macromolecular compounds obtained by reactions forming a carbonic ester link in the main chain of the macromolecule
- C08G64/02—Aliphatic polycarbonates
- C08G64/0208—Aliphatic polycarbonates saturated
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/42—Polycondensates having carboxylic or carbonic ester groups in the main chain
- C08G18/44—Polycarbonates
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G64/00—Macromolecular compounds obtained by reactions forming a carbonic ester link in the main chain of the macromolecule
- C08G64/20—General preparatory processes
- C08G64/30—General preparatory processes using carbonates
- C08G64/305—General preparatory processes using carbonates and alcohols
Landscapes
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Polyesters Or Polycarbonates (AREA)
- Polyurethanes Or Polyureas (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Linear aliphatic polycarbonates having terminal hydroxyl groups are produced by transesterification between a diol and diethyl carbonate, the transesterification being carried out in two stages:
(a) in the first stage, the reaction is carried out in the presence of a basic catalyst at a temperature below 150°C, and (b) in the second stage, the reaction is completed in a thin film evaporator, the heating medium supplied to the evaporator being at a temperature above 160°C.
The products obtained by this process are useful for the production of polyurethane elastomers which are resistant to hydrolysis.
Linear aliphatic polycarbonates having terminal hydroxyl groups are produced by transesterification between a diol and diethyl carbonate, the transesterification being carried out in two stages:
(a) in the first stage, the reaction is carried out in the presence of a basic catalyst at a temperature below 150°C, and (b) in the second stage, the reaction is completed in a thin film evaporator, the heating medium supplied to the evaporator being at a temperature above 160°C.
The products obtained by this process are useful for the production of polyurethane elastomers which are resistant to hydrolysis.
Description
1~649~;i7 The present inVention relates to a process for the preparation of linear aliphatic polycarbonates which have terminal hydroxyl groups and a number average molecular weight of from 500 to 3000, and the number of functional groups of which is greater than 1.95.
These oligomers, which will hereinafter be referred to as l'aliphatic polycarbonate-diolsl' have the following formula:
HO - A - (O - C - O - A)n- OH
in which A is a difunctional linear aliphatic or cycloaliphatic radical containing more than 4 carbon atoms.
~, The preparation of aliphatic polycarbonates by transesterification between a diol and a dialkyl carbonate is described in the works of CAROTHERS, VAN NATTA and HILL
(J. Am. Chem. Soc., 52, 314, 1930 and 55, 5031, 1933).
n HO-A-OH ~ n ROCOR H-~-OAOC-t- OR ~ (2n - 1) ROH
¦¦ RONa I n The reaction is carried out at an elevated tempera-ture (120 to 220C) in the presence oF strongly basic catalysts, ~o such as alkal~ metal alcoholates. This type of process is descri bed, in particular, in U.S. Patent 2,787,632.
As H. SCHNELL indicates in "Chemistry and Physics of Polycarbonates" (Wiley & Sons, 1964, page 15), it is imposs;ble to obtain polymers of high molecular weight by means of this process, since the presence of a basic catalyst leads, at the temperatures employed, to degradation of the polycarbonate.
Likewise, this process does no~ enable aliphatic carboxylate-diols having a sufficient number of functional groups, that is at least 1.95, to be prepared.
1~6 ~9 57 If, in the preparation of aliphatic polycarbonate-diols, an attempt is made to avoid the degradat;on reactions by carrying out the transesterification at a lower temperature (below 150C), the removal of the alcohol formed is incomplete and the product obtained contains a significant proport;on of unreactive terminal groups of the formula ROIlOA-.
U.S. Patent 2,210,817 described a technique which enables aliphatic polycarbonates of high molecular weights to be obtained. This technique consists of destroying the basic catalyst (when most of the alcohol has been removed by heating at 200C under reduced pressure) and of terminating the reaction under a high vacuum in the presence of traces of a carboxylic acid salt.
This procedure cannot be applied directly to the synthesis of aliphatic polycarbonate-diols by transesterifi-catlon between a diol and diethyl carbonate, principally for the following reasons:
(a) The reaction mixture always has a high content of hydroxyl groups, even at the end of transesterification.
Since these groups, in the presence o~ bases, catalyse degradat~on reactions, the temperature must not exceed 140C
(inskead of 200C), it is thus diPficult, i~ not impossible, to achieve a degree of forward reactlon higher than 99%, and (b) The second step is difficult to carry out because of the problem of regulating the molecular weight of the final product.
THE INVENTION
We have now found that it is possible to prepare aliphatic polycarbonate-diols having a satisfactory number of functional groups by transesterification between a diol and diethyl carbonate. According to the present invention, this ~64~357 process comprises two stages, in the first stage, the transesterification is carried out in the presence of a basic catalyst at a tempera-ture below about 150C, and in the second stage, the transesterification is com-pleted in a thin film evaporator, the heating medium supplied to the evaporator being at a temperature above about 160C.
The f;rst stage of the process is suitably carried out ;n a conventional reactor equipped with a stirrer and an effective distillation column which enables the ethanol formed to be separated from the diethyl carbonate. The alcoholate used as catalyst can be prepared by adding sodium to the previ-ously dried diol; from 0.1 to 0.5 g of sodium is preferably used per mol of diol. The temperature is preferably raised gradually from 90 to 140C and should at no time exceed 150C.
Dlst~llation is stopped when an amount of ethanol corresponding to 70 - 80% of the theoretical amount has been collected.
In the second stage, the reaction mixture resulting from the first stage is introduced into a thin Film evaporator.
The temperature of the heating medium in the double jacket of the evaporator is preferably from 190 to 250C. The product obtained is treated ~mmediately with an inorganlc acid, dis-solved in a water-imm~scible solvent and washed with pure water.
Aliphatic polycarbonate-diols having strictly two functional groups are of great value for the preparation of polyurethane elastomers which are resistant to hydrolysis.
In order that the invention may be more fully under-stood, the following example is given by way of illustration only.
~6~5~7 EXAMPLE
The following equipment was used:
a l lltre glass reactor equipped with an eff;cient stirrer, a thermometer and a distillation column, a double jacket distillation column packed with "Fenske" coils (useful length 5~0 mm, diameter 25 mm) equipped with a reflux head under manual control, and a stainless s~eel LEYBOLD thin film evaporator (heating surface area 200 cm2).
358.1 g of hexane-1,6-diol and 60 9 of anhydrous benzene were introduced into the reactor which was provided with a short distillation column, in order to remove water initially present in the hexanediol by azeotropic distillation.
When all the benzene had been d~stilled off, the temperature of the reaction medium was reduced to 70 - 80C and 0.6 g of sodium was added with stirring. After the latter had reacted completely, 304.3 g of diethyl carbonate were introduced. The reactor was equipped with the distillation column as first specified above and the mixture was heated whilst stirring vigorously.
When the temperature of the mass reached 95 - 100C, the ethanol began to distil. ReFluxing was re~ulated so that the temperature at the top oP the column was equal to 78.5 0.5C. The temperature of the reaction medium was raised gradually to 140C. Distillation was stopped when 197.5 g of ethanol had been collected. This distillation lasted for 30 minutes.
The reaction mixture was cooled rapidly to 60C and was introduced, at the rate of 0.9 litre/hour, into the thin film evaporator under a pressure of 10 mm Hg. The temperature of the heating fluid supplied the double jacket was 200C.
~ ~ 6 ~ S~
Under these conditions, the time taken for the pr~duct to pass throu~h the evaporator was approximately 80 seconds.
The non-volat;le product was collected and treated immediately with a slight excess of anhydrous hydrogen chloride, ~so as to ensure destruction of the basic catalyst).
The oligocarbonate was dissolved in 300 ml of dichloromethane and the organic phase obtained was washed once with 500 ml of water and dried over anhydrous sodium sulphate.
After removing the solvent by evaporation under reduced pressure, the product was stirred vigorously at 140 under
These oligomers, which will hereinafter be referred to as l'aliphatic polycarbonate-diolsl' have the following formula:
HO - A - (O - C - O - A)n- OH
in which A is a difunctional linear aliphatic or cycloaliphatic radical containing more than 4 carbon atoms.
~, The preparation of aliphatic polycarbonates by transesterification between a diol and a dialkyl carbonate is described in the works of CAROTHERS, VAN NATTA and HILL
(J. Am. Chem. Soc., 52, 314, 1930 and 55, 5031, 1933).
n HO-A-OH ~ n ROCOR H-~-OAOC-t- OR ~ (2n - 1) ROH
¦¦ RONa I n The reaction is carried out at an elevated tempera-ture (120 to 220C) in the presence oF strongly basic catalysts, ~o such as alkal~ metal alcoholates. This type of process is descri bed, in particular, in U.S. Patent 2,787,632.
As H. SCHNELL indicates in "Chemistry and Physics of Polycarbonates" (Wiley & Sons, 1964, page 15), it is imposs;ble to obtain polymers of high molecular weight by means of this process, since the presence of a basic catalyst leads, at the temperatures employed, to degradation of the polycarbonate.
Likewise, this process does no~ enable aliphatic carboxylate-diols having a sufficient number of functional groups, that is at least 1.95, to be prepared.
1~6 ~9 57 If, in the preparation of aliphatic polycarbonate-diols, an attempt is made to avoid the degradat;on reactions by carrying out the transesterification at a lower temperature (below 150C), the removal of the alcohol formed is incomplete and the product obtained contains a significant proport;on of unreactive terminal groups of the formula ROIlOA-.
U.S. Patent 2,210,817 described a technique which enables aliphatic polycarbonates of high molecular weights to be obtained. This technique consists of destroying the basic catalyst (when most of the alcohol has been removed by heating at 200C under reduced pressure) and of terminating the reaction under a high vacuum in the presence of traces of a carboxylic acid salt.
This procedure cannot be applied directly to the synthesis of aliphatic polycarbonate-diols by transesterifi-catlon between a diol and diethyl carbonate, principally for the following reasons:
(a) The reaction mixture always has a high content of hydroxyl groups, even at the end of transesterification.
Since these groups, in the presence o~ bases, catalyse degradat~on reactions, the temperature must not exceed 140C
(inskead of 200C), it is thus diPficult, i~ not impossible, to achieve a degree of forward reactlon higher than 99%, and (b) The second step is difficult to carry out because of the problem of regulating the molecular weight of the final product.
THE INVENTION
We have now found that it is possible to prepare aliphatic polycarbonate-diols having a satisfactory number of functional groups by transesterification between a diol and diethyl carbonate. According to the present invention, this ~64~357 process comprises two stages, in the first stage, the transesterification is carried out in the presence of a basic catalyst at a tempera-ture below about 150C, and in the second stage, the transesterification is com-pleted in a thin film evaporator, the heating medium supplied to the evaporator being at a temperature above about 160C.
The f;rst stage of the process is suitably carried out ;n a conventional reactor equipped with a stirrer and an effective distillation column which enables the ethanol formed to be separated from the diethyl carbonate. The alcoholate used as catalyst can be prepared by adding sodium to the previ-ously dried diol; from 0.1 to 0.5 g of sodium is preferably used per mol of diol. The temperature is preferably raised gradually from 90 to 140C and should at no time exceed 150C.
Dlst~llation is stopped when an amount of ethanol corresponding to 70 - 80% of the theoretical amount has been collected.
In the second stage, the reaction mixture resulting from the first stage is introduced into a thin Film evaporator.
The temperature of the heating medium in the double jacket of the evaporator is preferably from 190 to 250C. The product obtained is treated ~mmediately with an inorganlc acid, dis-solved in a water-imm~scible solvent and washed with pure water.
Aliphatic polycarbonate-diols having strictly two functional groups are of great value for the preparation of polyurethane elastomers which are resistant to hydrolysis.
In order that the invention may be more fully under-stood, the following example is given by way of illustration only.
~6~5~7 EXAMPLE
The following equipment was used:
a l lltre glass reactor equipped with an eff;cient stirrer, a thermometer and a distillation column, a double jacket distillation column packed with "Fenske" coils (useful length 5~0 mm, diameter 25 mm) equipped with a reflux head under manual control, and a stainless s~eel LEYBOLD thin film evaporator (heating surface area 200 cm2).
358.1 g of hexane-1,6-diol and 60 9 of anhydrous benzene were introduced into the reactor which was provided with a short distillation column, in order to remove water initially present in the hexanediol by azeotropic distillation.
When all the benzene had been d~stilled off, the temperature of the reaction medium was reduced to 70 - 80C and 0.6 g of sodium was added with stirring. After the latter had reacted completely, 304.3 g of diethyl carbonate were introduced. The reactor was equipped with the distillation column as first specified above and the mixture was heated whilst stirring vigorously.
When the temperature of the mass reached 95 - 100C, the ethanol began to distil. ReFluxing was re~ulated so that the temperature at the top oP the column was equal to 78.5 0.5C. The temperature of the reaction medium was raised gradually to 140C. Distillation was stopped when 197.5 g of ethanol had been collected. This distillation lasted for 30 minutes.
The reaction mixture was cooled rapidly to 60C and was introduced, at the rate of 0.9 litre/hour, into the thin film evaporator under a pressure of 10 mm Hg. The temperature of the heating fluid supplied the double jacket was 200C.
~ ~ 6 ~ S~
Under these conditions, the time taken for the pr~duct to pass throu~h the evaporator was approximately 80 seconds.
The non-volat;le product was collected and treated immediately with a slight excess of anhydrous hydrogen chloride, ~so as to ensure destruction of the basic catalyst).
The oligocarbonate was dissolved in 300 ml of dichloromethane and the organic phase obtained was washed once with 500 ml of water and dried over anhydrous sodium sulphate.
After removing the solvent by evaporation under reduced pressure, the product was stirred vigorously at 140 under
2 - 3 mm Hg for 30 minutes.
The aliphatic polycarbonate-diol obtained was in the form of a white wax which was soluble in the cold in the following solvents: toluene, dichloromethane, acetone and ethyl acetate.
The physico-chemical characteristics were as follows:
hydroxyl content: 0.75 equivalent/kg (acetylation method) acidity: 1.5 x 10 3 equlvalent/kg.
This polycarbonate was converted into a polyurethane reaction with d~phenylmethane dlisocyanate and butane-1,4-diol ("one shot" formulation), the molar ratio N~lO being equal to 0.95.
A film was produced by compression moulding of the polyurethane obtained, this film had a tensile strength of more than 400 kgf/cm2 (NFT Standard Specification 46,002).
The aliphatic polycarbonate-diol obtained was in the form of a white wax which was soluble in the cold in the following solvents: toluene, dichloromethane, acetone and ethyl acetate.
The physico-chemical characteristics were as follows:
hydroxyl content: 0.75 equivalent/kg (acetylation method) acidity: 1.5 x 10 3 equlvalent/kg.
This polycarbonate was converted into a polyurethane reaction with d~phenylmethane dlisocyanate and butane-1,4-diol ("one shot" formulation), the molar ratio N~lO being equal to 0.95.
A film was produced by compression moulding of the polyurethane obtained, this film had a tensile strength of more than 400 kgf/cm2 (NFT Standard Specification 46,002).
Claims (4)
1. A process for the preparation of a linear aliphatic polycarbonate-diol corresponding to the formula:
wherein A is a difunctional linear aliphatic or cycloaliphatic radical containing more than 4 carbon atoms, said poly-carbonate-diol having an average molecular weight of from 500 to 3000 and the number of functional groups being greater than 1.95, which comprises two stages:
in the first stage, the transesterification is carried out in the presence of a basic catalyst at a tempera-ture below about 150°C, and in the second stage, the transesterification is com-pleted in a thin film evaporator, the heating medium supplied to the evaporator being at a temperature above about 160°C.
wherein A is a difunctional linear aliphatic or cycloaliphatic radical containing more than 4 carbon atoms, said poly-carbonate-diol having an average molecular weight of from 500 to 3000 and the number of functional groups being greater than 1.95, which comprises two stages:
in the first stage, the transesterification is carried out in the presence of a basic catalyst at a tempera-ture below about 150°C, and in the second stage, the transesterification is com-pleted in a thin film evaporator, the heating medium supplied to the evaporator being at a temperature above about 160°C.
2. A process according to Claim 1, in which the basic catalyst is formed by adding sodium to the reaction mixture.
3. A process according to Claim 2, in which an amount of sodium used is from about 0.1 to about 0.5 g per mol of diol.
4. A process according to Claim 1, in which the heating medium supplied to the evaporator is at a temperature of from about 190°C to about 250°C.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7440838A FR2294199A1 (en) | 1974-12-11 | 1974-12-11 | PERFECTED PROCESS FOR PREPARING POLYCARBONATES IN TWO STAGES |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1064957A true CA1064957A (en) | 1979-10-23 |
Family
ID=9146037
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA240,852A Expired CA1064957A (en) | 1974-12-11 | 1975-12-01 | Process for the preparation of polycarbonates |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5183693A (en) |
| BE (1) | BE836535A (en) |
| CA (1) | CA1064957A (en) |
| DE (1) | DE2555805A1 (en) |
| DK (1) | DK558975A (en) |
| FR (1) | FR2294199A1 (en) |
| GB (1) | GB1476268A (en) |
| IE (1) | IE42097B1 (en) |
| IT (1) | IT1059855B (en) |
| LU (1) | LU73968A1 (en) |
| NL (1) | NL7513786A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4891421A (en) * | 1987-06-22 | 1990-01-02 | Dainippon Ink And Chemicals, Inc. | Processes for producing polycarbonate polyols |
| US6977290B2 (en) | 2003-01-31 | 2005-12-20 | Bayer Aktiengesellschaft | Process for preparing oligomeric aliphatic diols, polycarbonatediols based thereon and prepolymers thereof |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3717060A1 (en) * | 1987-05-21 | 1988-12-01 | Bayer Ag | POLYETHER-POLYCARBONATE-DIOLE, THEIR PRODUCTION AND USE AS STARTING PRODUCTS FOR POLYURETHANE PLASTICS |
| US5130384A (en) * | 1989-03-20 | 1992-07-14 | Reeves Brothers, Inc. | Calenderable thermoplastic polyurethane elastomer compositions containing millable linear polyurethanes |
| US5298303A (en) * | 1989-03-20 | 1994-03-29 | Reeves Brothers, Inc. | Fabric structure for severe use applications |
| US5001208A (en) * | 1989-03-20 | 1991-03-19 | Reeves Brothers, Inc. | Linear polyurethane elastomer compositions based on mixed polycarbonate and polyether polyols |
| US5096992A (en) * | 1989-03-20 | 1992-03-17 | Reeves Brothers, Inc. | Use of modified diisocyanates for preparing linear thermoplastic polyurethane elastomers having improved properties |
| US5110666A (en) * | 1991-05-06 | 1992-05-05 | Reeves Brothers, Inc. | Coated fabric structure for air bag applications |
| DE19513164A1 (en) * | 1995-04-07 | 1996-10-10 | Bayer Ag | Hydroxy-terminated polycarbonates based on high mol. cyclic dimer diols with and use in prodn. of polyurethanes stable against hydrolysis and oxidn. |
| DE19900554A1 (en) * | 1999-01-09 | 2000-07-13 | Bayer Ag | Process for the preparation of aliphatic oligocarbonate diols from dimethyl carbonate and aliphatic diols |
| DE10027907A1 (en) | 2000-06-06 | 2001-12-13 | Bayer Ag | Production of aliphatic oligocarbonate diols, useful in the production of plastics, fibers, coatings and adhesives, comprises reaction of aliphatic diols with dimethyl carbonate in a multi-stage process. |
| DE10130882A1 (en) | 2001-06-27 | 2003-01-16 | Bayer Ag | Process for the preparation of aliphatic oligocarbonate diols |
| US7112693B2 (en) | 2001-06-27 | 2006-09-26 | Bayer Aktiengesellschaft | Process for producing aliphatic oligocarbonate diols |
| DE10156896A1 (en) | 2001-11-20 | 2003-05-28 | Bayer Ag | Use of catalysts for the production of aliphatic oligocarbonate polyols |
| DE102004032419A1 (en) * | 2004-07-05 | 2006-01-26 | Bayer Materialscience Ag | Preparation of clear isocyanate prepolymers based on hexanediol ether carbonate |
| TWI761404B (en) | 2016-12-19 | 2022-04-21 | 德商科思創德意志股份有限公司 | Process for producing (cyclo) aliphatic polycarbonate polyols having low reactivity |
| EP4378972A1 (en) | 2022-11-30 | 2024-06-05 | Covestro Deutschland AG | (cyclo)aliphatic polycarbonate polyol composition |
-
1974
- 1974-12-11 FR FR7440838A patent/FR2294199A1/en active Granted
-
1975
- 1975-11-07 IE IE242975A patent/IE42097B1/en unknown
- 1975-11-18 GB GB4746875A patent/GB1476268A/en not_active Expired
- 1975-11-26 NL NL7513786A patent/NL7513786A/en not_active Application Discontinuation
- 1975-12-01 CA CA240,852A patent/CA1064957A/en not_active Expired
- 1975-12-09 IT IT7001875A patent/IT1059855B/en active
- 1975-12-09 LU LU73968A patent/LU73968A1/xx unknown
- 1975-12-10 DK DK558975A patent/DK558975A/en not_active Application Discontinuation
- 1975-12-11 JP JP50146950A patent/JPS5183693A/ja active Pending
- 1975-12-11 BE BE162658A patent/BE836535A/en unknown
- 1975-12-11 DE DE19752555805 patent/DE2555805A1/en not_active Withdrawn
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4891421A (en) * | 1987-06-22 | 1990-01-02 | Dainippon Ink And Chemicals, Inc. | Processes for producing polycarbonate polyols |
| US6977290B2 (en) | 2003-01-31 | 2005-12-20 | Bayer Aktiengesellschaft | Process for preparing oligomeric aliphatic diols, polycarbonatediols based thereon and prepolymers thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| GB1476268A (en) | 1977-06-10 |
| IE42097L (en) | 1976-06-11 |
| LU73968A1 (en) | 1977-07-01 |
| FR2294199A1 (en) | 1976-07-09 |
| BE836535A (en) | 1976-06-11 |
| IT1059855B (en) | 1982-06-21 |
| IE42097B1 (en) | 1980-06-04 |
| FR2294199B1 (en) | 1977-04-08 |
| NL7513786A (en) | 1976-06-15 |
| DE2555805A1 (en) | 1976-10-28 |
| DK558975A (en) | 1976-06-12 |
| JPS5183693A (en) | 1976-07-22 |
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