HYDROXY-TERMINATED POLYURETHANE PREPOLYMER HAVING LOW ALLOPHANATE CONTENT

Abstract

The present invention relates to hydroxy-terminated polyurethane prepolymers that consist to an extent of at least 90% by weight of the product of the reaction of hexamethylene 1,6-diisocyanate with butane-1,4-diol and have an allophanate content of ≤1.00 mol %, to a process for the production thereof, to compositions comprising such polyurethane prepolymers and to the use of said polyurethane prepolymers.

Claims

1. A hydroxy-terminated polyurethane prepolymer, consisting to an extent of at least 90% by weight of the product of the reaction of hexamethylene 1,6-diisocyanate with butane-1,4-diol, based on the total mass of the hydroxy-terminated polyurethane prepolymer, and that the allophanate content of the hydroxy-terminated polyurethane prepolymer is ≤1.00 mol % based on the sum total of all urethane and allophanate groups in the hydroxy-terminated polyurethane prepolymer, in each case determined by NMR spectroscopy.

2. The hydroxy-terminated polyurethane prepolymer according to claim 1, wherein the average degree of polymerization n of the hydroxy-terminated polyurethane prepolymer is within a range from 1.5 to 19, the average degree of polymerization being $n=\frac{x}{1-x},$ where x is the ratio of the NCO groups in the polyisocyanate monomers to hydroxy groups in the polyol monomers.

3. The hydroxy-terminated polyurethane prepolymer according to claim 1, consisting to an extent of at least 96% by weight, preferably to an extent of at least 97% by weight of the product of the reaction of hexamethylene 1,6-diisocyanate with butane-1,4-diol, based on the total mass of the hydroxy-terminated polyurethane prepolymer.

4. The hydroxy-terminated polyurethane prepolymer according to claim 1, wherein the allophanate content of the hydroxy-terminated polyurethane prepolymer is within a range from 0.25 mol % to 1.00 mol % based on the sum total of all urethane and allophanate groups in the hydroxy-terminated polyurethane prepolymer, determined by NMR spectroscopy.

5. The hydroxy-terminated polyurethane prepolymer according to claim 1, wherein the hydroxy-terminated polyurethane prepolymer has an average OH functionality, calculated from the functionalities of the monomers, of 1.8 to 2.1.

6. The hydroxy-terminated polyurethane prepolymer according to claim 1, wherein the ratio M.sub.w/M.sub.n of the hydroxy-terminated polyurethane prepolymer is within a range from 2 to 20 where M.sub.n is the number-average molar mass and M.sub.w the mass-average molar mass, in each case determined by gel-permeation chromatography, the sample being dissolved in a solution of potassium trifluoroacetate in hexafluoroisopropanol having a concentration of 2 mg/cm.sup.3 and using a polymethyl methacrylate standard.

7. The hydroxy-terminated polyurethane prepolymer according to claim 1, wherein the hydroxy-terminated polyurethane prepolymer has a melting point of >150° C., determined by differential scanning calorimetry in accordance with DIN EN 61006 (November 2004).

8. A process for producing a hydroxy-terminated polyurethane prepolymer according to claim 1, wherein at least hexamethylene 1,6-diisocyanate is reacted with butane-1,4-diol, optionally in the presence of a catalyst and/or auxiliaries and additives, the molar NCO/OH ratio being within a range from 0.6:1.0 to 0.95:1.0.

9. The process according to claim 8, wherein the reaction is carried out in a tubular reactor, the tubular reactor having at least one heat-transfer unit that continuously conducts away heat.

10. The process according to claim 8, wherein the process is solvent-free.

11. A composition comprising at least one hydroxy-terminated polyurethane prepolymer according to claim 1 and butane-1,4-diol.

12. The composition comprising at least one hydroxy-terminated polyurethane prepolymer according to claim 1 and at least one additive.

13. Use of a hydroxy-terminated polyurethane prepolymer according to claim 1 or of a composition according to claim 11 for the production of thermoplastic polyurethane and/or thermoplastic polyurethane dispersions.

14. A polymer obtained by the reaction of at least one hydroxy-terminated polyurethane prepolymer according to claim 1 or of a composition according to claim 11 with at least one chain extender.

15. An article comprising a polymer according to claim 14, a prepolymer according to claim 1, or a composition according to claim 11.

16. Use of a polymer according to claim 14 for the production of shaped bodies, films and/or fibres.

Description

[0084] The present invention is more particularly elucidated hereinbelow with reference to FIGS. 1, 2 and 3. In these figures:

[0085] FIG. 1 shows a preferred apparatus for the execution of the process of the invention,

[0086] FIG. 2 shows a further preferred apparatus for the execution of the process of the invention,

[0087] FIG. 3 shows a further preferred apparatus for the execution of the process of the invention.

EXAMPLES

[0088] The present invention is elucidated further by the examples that follow, but without being restricted thereto.

Colour Values

[0089] Colour values in the CIE-Lab colour space were determined with a Konica Minolta CM 2600d spectrophotometer with the D 65 illuminant, 10° observer, in accordance with DIN EN ISO 11664-1 (July 2011).

Allophanate Content

[0090] The allophanate concentration was determined by .sup.1H NMR spectroscopy (instrument: Bruker AV III HD 600, at a measurement frequency of 600.36 MHz, using the zg30 pulse program, with 64 scans, a relaxation delay (D1) of 6 s and TE of 354 K). For this, a sample of the polyurethane prepolymer was dissolved in deuterated dimethyl sulfoxide (DMSO-d6) at 80° C. and then measured. Spectra were evaluated using the MestReNova software. Firstly, a baseline correction (Whittaker smoother) was applied, which was followed by integration of the allophanate-specific protons of the CH.sub.2 group between 3.56 ppm and 3.66 ppm and of the urethane-specific protons of the O—CH.sub.2 group between 3.84 ppm and 4.04 ppm. The sum of the two integrals was then calculated and used to determine the proportion by percent of the allophanate signal, which corresponds to the molar proportion of the allophanate groups.

Gel-Permeation Chromatography

[0091] The molar masses of the polymers were determined by gel-permeation chromatography (GPC). For this purpose, the sample to be analyzed was dissolved in a solution of 3 g of potassium trifluoroacetate in 400 cubic centimetres of hexafluoroisopropanol (sample concentration about 2 mg/cubic centimetre). The respective GPCs were measured with the following components at a flow rate of 1 cubic centimetre/minute: [0092] Pump: 515 HPLC pump (Waters GmbH) [0093] Detector: Smartline 2300 RI detector (Knauer Wissenschaftliche Geräte GmbH) [0094] Columns: 1 pre-column, 1000 Å PSS PFG 7 μm, 300 Å PSS PFG 7 μm, 100 Å PSS PFG 7 μm in the sequence specified [0095] Degassing: PSS degasser (Polymer Standards Service GmbH) [0096] Injection volume: 100 microlitres [0097] Temperature: 23-25° C. [0098] Molar mass standard: Polymethylmethacrylate standard kit (PSS Polymer Standards Service GmbH)

Calculation of M.SUB.z .and M.SUB.w .and M.SUB.n

[0099] The centrifuge-average molar mass (M.sub.z) was calculated from the data obtained by the gel-permeation chromatography measurement with the aid of the following equation:

[00005]${\overline{M}}_z=\frac{{.Math.}_i{n}_i{M}_i^3}{{.Math.}_i{n}_i{M}_i^2}\mathrm{in}g/\mathrm{mol}$

[0100] where:

[0101] M.sub.i is the molar mass of the polymers of the fraction i, such that M.sub.i<M.sub.i+1 for all i, in g/mol, n.sub.i is the molar amount of the polymer of the fraction i, in mol.

[0102] The mass-average molar mass (M.sub.w) was likewise calculated from the data obtained by the gel permeation chromatography measurement with the aid of the following equation:

[00006]${\overline{M}}_w=\frac{{.Math.}_i{n}_i{M}_i^2}{{.Math.}_i{n}_i{M}_i}\mathrm{in}g/\mathrm{mol}$

[0103] where:

[0104] M.sub.i is the molar mass of the polymers of the fraction i, such that M.sub.i<M.sub.i+1 for all i, in g/mol, n.sub.i is the molar amount of the polymer of the fraction i, in mol.

[0105] The number-average molar mass (M.sub.n) was likewise calculated from the data obtained by the gel-permeation chromatography measurement with the aid of the following equation:

[00007]${\overline{M}}_n=\frac{{.Math.}_i{n}_i{M}_i}{{.Math.}_i{n}_i}\mathrm{in}g/\mathrm{mol}$

[0106] where:

[0107] M.sub.i is the molar mass of the polymers of the fraction i, such that M.sub.i<M.sub.i+1 for all i, in g/mol, n.sub.i is the molar amount of the polymer of the fraction i, in mol.

Differential Scanning Calorimetry (DSC)

[0108] Melting points were determined by DSC (differential scanning calorimetry) using a DSC 8500 (PerkinElmer, USA) in accordance with DIN-EN-ISO 11357-1. Calibration was effected via the melt onset temperature of octane, indium, lead and zinc. About 10 mg of substance was weighed into aluminium crucibles. The measurement was effected by two heating runs from −20° C. to +210° C. at a heating rate of 20 K/min with subsequent cooling at a cooling rate of 20 K/min. Cooling was effected by a compressor cooler. The purge gas used was nitrogen. The values reported are each based on evaluation of the 2nd heating curve.

I. Raw Materials Used

[0109] Hexamethylene 1,6-diisocyanate (HDI, purity ≥99% by weight) was obtained from Covestro Deutschland AG.

[0110] Butane-1,4-diol (BDO, purity ≥99% by weight) was obtained from Ashland.

Example 1

[0111] Hexamethylene 1,6-diisocyanate (HDI) was conveyed at room temperature from a holding tank to a static mixer by means of a pump (stream A). Butane-1,4-diol (BDO) heated to approx. 40° C. was likewise conveyed from another holding tank to the continuous mixer by means of a pump (stream B). The throughput of the HDI stream A and of the BDO stream B was monitored by mass flow meters. In the mixer 7, the HDI stream A and the BDO stream B were mixed/dispersed to form the HDI/BDO dispersion (stream C).

[0112] The HDI/BDO stream C is combined and mixed in a mixer in circulation with a prepolymer stream D heated to 182° C. (stream E). The temperature of the prepolymer stream D causes a reaction between HDI and BDO, which is maintained by further mixing in a temperature-controllable mixer, with the formation of prepolymers and with dissipation of the heat of reaction. The temperature-controllable mixer is heated/cooled with heat-transfer oil and has a heat-exchange surface area of at least 0.31 m.sup.2. The inflow temperature of the heating medium is approx. 180° C. An output stream is obtained from the temperature-controllable mixer in the form of a largely reacted HDI/BDO prepolymer stream having a temperature of 183° C. (stream E). The temperature-controllable static mixer was of similar construction to a Sulzer SMX reactor with internal crossed tubes. It had an internal volume of 2.2 litres and a heat exchange surface area of 0.31 square metres. Under the operating conditions, its heat-exchange capacity based on the product side was 78 watts per kelvin. Based on the total volume of the loop reactor of 4 litres, the heat-transfer coefficient was 19 kilowatts per cubic metre and kelvin. The amount of heat conducted away by the heat-transfer unit was approx. 890 watts. The ratio of heat-transfer surface area to total surface area was 0.655. The average OH functionality was exactly 2. Stream E is split at a branching point into two substreams F and G, substream F being fed back into the abovementioned mixer as prepolymer stream D by means of a pump, via pipelines heated to approx. 182° C. The mass flow of stream G corresponds to the mass flow of stream C. The mass flow of stream G was approx. 115 L/h. Substream G is collected in a 60 L drum and cooled. The resulting product is crystalline and white. The total amount of prepolymer produced is 50 kg. Colour index measurement gave an L value of 92.2, an a value of 0.7 and a b value of 1.7. The viscosity of the product at 190° C. was 0.7 Pa s.

[0113] In the inventive example, the following reactant streams were used:

TABLE-US-00001 kg/h mol/h Stream A HDI 4.367 25.965 Stream B BDO 3.000 33.289

[0114] The ratio of NCO groups in the polyisocyanate monomers to hydroxy groups in the polyol monomers was x=0.78. The degree of polymerization was n=3.55.

[0115] The allophanate content was determined to be 0.34%.

[0116] The average functionality of the monomers was 2.

[0117] M.sub.w was determined as 10810 g/mol, M.sub.n as 1404 g/mol, the ratio therefore being 7.7. M.sub.z was 28940 g/mol and the ratio

[00008]$\frac{{\stackrel{\_}{M}}_z}{{\stackrel{\_}{M}}_w}=2.68.$

[0118] The melting point was 175.5° C.

[0119] The heat conducted away in the tubular reactor was approx. 57% of the total enthalpy of reaction released therein.

Example 2

[0120] 1.49 kg/h of HDI was conveyed from holding tank 1 to the mixer 1 by means of a pump 1 (mzr-7255 annular gear pump from HNP). 2.00 kg/h of BDO was at the same time conveyed from holding tank 2 to the same mixer by means of a pump 2 (mzr-7205 from HNP). The mixing of the two material streams in the mixer was at room temperature. The mixer used was a Sulzer SMX, diameter 6 mm, ratio of length to diameter L/D=10. The mixture was subsequently fed into the reactor 1, which had been heated to 150° C. (model: CSE-X/8G, Form G, internal diameter=21.0 mm, length=1000 mm, from Fluitec). The resulting prepolymer with a HDI:BDO ratio of 0.4:1.0 was then mixed in mixer 2 (Sulzer SMX, diameter 6 mm, ratio of length to diameter L/D=10) at 121.44° C. with hexamethylene 1,6-diisocyanate from holding tank 3 (1.49 kg/h; pump 3: mzr-7255 annular gear pump from HNP). The mixture was subsequently fed into the reactor 2 (model: CSE-X/8G, Form G, internal diameter=21.0 mm, length=1500 mm, from Fluitec), which had been heated to 182° C. The dwell time in reactor 2 was 6.5 min. The pipelines from reactor 1 to reactor 2 and from mixer 2 were trace heated to approx. 180° C. The temperature increase in the second heat-transfer unit was 37.93° C. The average caloric temperature in the inflow to the first reactor was 25° C. The caloric temperature during the second HDI addition was 121.44° C., for which c.sub.p(HDI 2)=1750.27 J/(kg.Math.K) and c.sub.p(oligomer)=2000.00 J/(kg.Math.K). The complex viscosity of the product at 10 Hz and 190° C. was 0.15 Pa s. The average OH functionality was 2.

[0121] The ratio of NCO groups in the polyisocyanate monomers to hydroxy groups in the polyol monomers is x=0.8. The average degree of polymerization is n=4.

[0122] The allophanate content was 0.35%.

[0123] M.sub.w was determined as 4389 g/mol, M.sub.n as 1677 g/mol, the ratio therefore being 2.62. M.sub.z was determined as 8095 g/mol, the ratio therefore being

[00009]$\frac{{\stackrel{\_}{M}}_z}{{\stackrel{\_}{M}}_w}=1.84.$

[0124] The melting point was 173° C.

[0125] The heat conducted away in the tubular reactor was approx. 55% of the heat used.

Non-Inventive Example

[0126] A Teflon beaker equipped with a stirrer was charged with 35.11 g of butane-1,4-diol, blanketed with nitrogen and heated to approx. 180° C. 55.02 g HDI was then added dropwise, with stirring, such that the temperature of the reaction mixture did not exceed 200° C. (approx. 45 min). This was accompanied by a pronounced rise in the viscosity of the mixture. The remaining 9.71 g of HDI was then added and the reaction mixture stirred for a further 30 min for complete reaction of the HDI. This was accompanied by a gradual rise in temperature to 211° C. and a further increase in viscosity too. The product was then cooled to room temperature and measured. The allophanate content was 1.2%. However, the presence in the sample of gel particles that were insoluble in DMSO-d6 (crosslinking) suggests that the allophanate content is higher still. As a consequence of the gel particles, GPC was not carried out.

LIST OF REFERENCE SYMBOLS

[0127] (A) Polyisocyanate stream [0128] (B) Polyol stream [0129] (C) Mixture stream [0130] (D) Circulation stream [0131] (E) Prepolymer stream [0132] (1) Polyisocyanate reservoir vessel [0133] (2) First feed device [0134] (3) First mass flow meter [0135] (4) Polyol reservoir vessel [0136] (5) Second feed device [0137] (6) Second mass flow meter [0138] (7) First mixing device [0139] (8) Second mixing device [0140] (9) Temperature-controllable mixing device [0141] (10) Temperature-controllable feed device [0142] (11) First junction [0143] (12) Pressure-control valve [0144] (13) Three-way valve [0145] (14) Collecting vessel [0146] (15) Venting device [0147] (16) Extruder [0148] (17) Cooling device [0149] (18) Comminution device [0150] (19) Polyisocyanate line [0151] (20) Polyol line [0152] (21) Second junction [0153] (22) Circulation feed line [0154] (23) First junction [0155] (24) Circulation line [0156] (25) Prepolymer feed line