POLYURETHANE COVERINGS HAVING REDUCED WATER ABSORPTION AND USE THEREOF

Abstract

The invention relates to coverings made of polyurethane having reduced water absorption and the use thereof.

Claims

1. An outer shell composed of polyurethane, wherein the polyurethane is obtained from: A) a polyol component consisting of: A1) 5% to 90% by weight of at least one polyether carbonate polyol (PEC) having a number-average molecular weight (M) of 600 to 6000 Da and a number-average functionality of 2 to 3; A2) 10% to 95% by weight of at least one further polyol having a number-average molecular weight of 200 to 6500 Da selected from the group consisting of polyether polyols having a number-average functionality of 2 to 8, polyester polyols having a number-average functionality of 2 to 3, and polycarbonate polyols having a number-average functionality of 2 to 3; A3) 2% to 20% by weight of aliphatic alkanediols having number-average molecular weights of 62 to 500 Da; A4) 0% to 10% by weight of short-chain aliphatic polyamines and/or aliphatic amino alcohols having number-average molecular weights of 60 to 1200 Da and a functionality of 2; A5) catalysts; and A6) optionally auxiliaries and/or additives; where the sum total of A1), A2), A3), A4), A5) and A6) is 100% by weight of component A); and B) an isocyanate component consisting of: B1) at least one isocyanate selected from the group consisting of polyisocyanates from the diphenylmethane series, polyisocyanate mixtures from the diphenylmethane series, and reaction products thereof with at least one polyol component having a number-average molecular weight of 140 to 500 Da and a number-average functionality of 2 to 3, having NCO contents of 10% to 28% by weight NCO; or B2) at least one isocyanate selected from the group consisting of aliphatic polyisocyanates and reaction products thereof with at least one polyol component having a number-average molecular weight of 140 to 500 Da and a number-average functionality of 2 to 3, having NCO contents of 10% to 28% by weight NCO; wherein the index is 90 to 115.

2. The outer shell composed of polyurethane as claimed in claim 1, wherein the polyurethane is obtained from: A) a polyol component consisting of: A1) 13% to 75% by weight of at least one polyether carbonate polyol (PEC) having a number-average molecular weight of 800 to 4500 Da and a number-average functionality of 2 to 3 and a proportion of incorporated CO.sub.2 in the range from 14% to 25% by weight, based on the total mass of the PEC, and based on alkylene oxides selected from the group consisting of 70% to 100% by weight of propylene oxide and 0% to 30% by weight of ethylene oxide; A2) 23% to 85% by weight of at least one further polyol having a number-average molecular weight of 200 to 6500 Da selected from the group consisting of 70% to 100% by weight of polyether polyols having a number-average functionality of 2 to 8, 0% to 30% by weight of polyester polyols having a number-average functionality of 2 to 3, and 0% to 30% by weight of polycarbonate polyols having a number-average functionality of 2; A3) 2% to 20% by weight of alkanediols having number-average molecular weights of 62 to 500 Da; A4) 0% to 10% by weight of short-chain aliphatic polyamines and/or aliphatic amino alcohols having number-average molecular weights of 60 to 1200 Da and a functionality of 2; A5) catalysts; and A6) optionally auxiliaries and/or additives; where the sum total of A1), A2), A3), A4), A5) and A6) is 100% by weight of component A); and B) an isocyanate component consisting of: B1) at least one isocyanate selected from the group consisting of polyisocyanates from the diphenylmethane series, polyisocyanate mixtures from the diphenylmethane series, and reaction products thereof with at least one polyol component having a number-average molecular weight of 140 to 500 Da and a number-average functionality of 2 to 3, having NCO contents of 10% to 28% by weight NCO; or B2) at least one isocyanate selected from the group consisting of aliphatic polyisocyanates and reaction products thereof with at least one polyol component having a number-average molecular weight of 140 to 500 Da and a number-average functionality of 2 to 3, having NCO contents of 10% to 28% by weight NCO; wherein the index is 90 to 115.

3. An outer shell for encasing sheets, slabs, tiles, laminates, wooden boards, metal plates and cables comprising the outer shell as claimed in claim 1

4. An outer shell for encasing sheets, slabs, tiles, laminates, wooden boards, metal plates and cables comprising the outer shell as claimed in claim 2.

Description

EXAMPLES SECTION

A) Methods and Equipment

[0063] Hydroxyl numbers (OHN) were determined according to DIN 53240; December 1971.

[0064] Acid numbers were determined according to DIN EN ISO 2114 (June 2002).

[0065] Viscosities were determined at the temperature specified in each case according to EN ISO 3219 in the October 1994 version.

[0066] The proportion of CO.sub.2 incorporated in the resulting polyether carbonate polyol (CO.sub.2 incorporated) and the ratio of propylene carbonate to polyether carbonate polyol were determined by .sup.1H NMR (Bruker DPX 400, 400 MHz; pulse program zg30, relaxation delay d1: 10 s, 64 scans). Each sample was dissolved in deuterated chloroform. The relevant resonances in the .sup.1H NMR (based on TMS=0 ppm) are as follows:

[0067] Cyclic carbonate (which was formed as a by-product) resonance at 4.5 ppm, carbonate resulting from carbon dioxide incorporated in the polyether carbonate polyol (resonances at 5.1 to 4.8 ppm), unreacted propylene oxide (PO) with resonance at 2.4 ppm, polyether polyol (i.e. without incorporated carbon dioxide) with resonances at 1.2 to 1.0 ppm.

[0068] The molar proportion of the carbonate incorporated in the polymer, of the polyether polyol and of the unreacted PO (propylene oxide) are determined by integration of the corresponding signals.

[0069] Further details are given in detail in WO 2014/033 071.

[0070] B) Commercially Available Starting Materials:

[0071] Isopur Schwarzpaste N black paste from ISL-Chemie GmbH+Co. KG.

[0072] Irganox 1135: alkyl 3,5-bis(isobutyl)-4-hydroxybenzene- 1-propionate, antioxidant from BASF.

[0073] Tinuvin B75: light-stabilizing additive from BASF

[0074] Fomrez UL28: dimethylbis[(1-oxoneodecyl)oxy]stannane; catalyst from Chemtura Vinyl

[0075] Additives GmbH

[0076] Dabco 33LV: 33% by weight of triethylenediamine in dipropylene glycol, catalyst from Air Products

[0077] Desmorapid VP.PU 20AK36: tin catalyst from Bayer MaterialScience

[0078] Desmophen 4050E: amine-based tetrafunctional polyether polyol from Bayer MaterialScience with a hydroxyl number of about 625 mg KOH/g and a viscosity at 25 C. of about 19 000 mPas

[0079] Desmophen L2830: bifunctional polyether polyol with predominantly primary hydroxyl groups from Bayer MaterialScience with a hydroxyl number of 26-30 mg KOH/g and a viscosity at 25 C. of 790-930 mPas

[0080] PET 5168T: bifunctional polyether polyol with predominantly primary hydroxyl groups from Bayer MaterialScience with a hydroxyl number of about 28 mg KOH/g and a viscosity at 25 C. of about 1000 mPas

[0081] Polyether V2725: trifunctional polyether polyol with predominantly primary hydroxyl groups from Bayer MaterialScience with a hydroxyl number of about 28 mg KOH/g and a viscosity at 25 C. of about 1500 mPas

[0082] Desmophen 4011T: trifunctional polyether polyol from Bayer MaterialScience with a hydroxyl number of 525-575 mg KOH/g and a viscosity at 25 C. of about 1540-2060 mPas

[0083] Polyether L800: bifunctional polyether polyol from Bayer MaterialScience with a hydroxyl number of about 515 mg KOH/g and a viscosity at 25 C. of about 80 mPas

[0084] PET 3973Y: trifunctional polyether polyol with predominantly primary hydroxyl groups from Bayer MaterialScience with a hydroxyl number of about 28 mg KOH/g and a viscosity at 25 C. of about 1100 mPas

[0085] Desmophen C XP 2716: linear aliphatic polycarbonatediol having terminal hydroxyl groups from Bayer MaterialScience with a molecular weight of about 650 g/mol and a viscosity at 25 C. of about 4100 mPas

[0086] Desmodur E 305: aliphatic polyisocyanate having terminal NCO groups from Bayer MaterialScience with a molecular weight of about 650 g/mol and a viscosity at 25 C. of about 4000 mPas

[0087] Desmodur PA 09: modified diphenylmethane 4,4-diisocyanate from Bayer MaterialScience with an NCO content of 24.0%-25.0% by weight and a viscosity at 25 C. of 375-575 mPas

[0088] Desmodur 481F44: aliphatic polyisocyanate from Bayer MaterialScience with an NCO content of about 21% and a viscosity at 20 C. of about 9015 mPas

[0089] Desmodur XP2489: aliphatic polyisocyanate from Bayer MaterialScience with an NCO content of about 21.00.5% and a viscosity at 23 C. of about 22 5002500 mPas

[0090] Arcol Polyol 1004: PET 1004: bifunctional polyether polyol from Bayer MaterialScience for preparation of polyurethanes with a hydroxyl number of about 260 mg KOH/g and a viscosity at 25 C. of about 220 mPas

[0091] Butane-1,4-diol: from Acros

[0092] Ethylene glycol: from Acros

[0093] Diethylene glycol: Sigma Aldrich

[0094] Propylene carbonate (cPC): from Acros

[0095] Indrosil 2000: separating agent from Indroma Chemikalien

[0096] IPDA: isophoronediamine from Evonik

[0097] DMC catalyst: was prepared as described in example 6 of WO 01/80994 A1

C) Preparation of Polyester Polyols, PES-C

Preparation of the Polyester Polyol 1 (PES C-1):

[0098] In a 2 liter four-neck flask (equipped with mechanical stirrer, 50 cm Vigreux column, thermometer, nitrogen inlet, column head, distillation system and vacuum membrane pump), 602 g of adipic acid (4.122 mol, corresponding to 52.45% by weight) and 546 g (5.147 mol, corresponding to 47.55% by weight) of diethylene glycol were heated to 200 C. under a nitrogen blanket over the course of 60 min, in the course of which water of reaction was removed by distillation. After 3 hours, 20 mg of zinc dichloride dihydrate (corresponding to 20 ppm based on the end product) were added and the reaction was continued. After a total reaction time of 5 hours, the pressure was reduced gradually to 15 mbar over the course of 1 hour. Over the course of further reaction, the acid number was monitored. After a total reaction time of 33 hours, the reaction was ended. The acid number was 0.42 mg KOH/g.

Analysis of the Polyester:

[0099] Hydroxyl number: 112.2 mg KOH/g

[0100] Acid number: 0.42 mg KOH/g

[0101] Viscosity: 170 mPas (75 C.)

Preparation of the Polyester Polyol 2 (PES C-2) :

[0102] In a 2 liter four-neck flask (equipped with mechanical stirrer, 50 cm Vigreux column, thermometer, nitrogen inlet, column head, distillation system and vacuum membrane pump), 638 g of adipic acid (4.366 mol, corresponding to 55.14% by weight) and 519 g (4.892 mol, corresponding to 44.86% by weight) of diethylene glycol were heated to 200 C. under a nitrogen blanket over the course of 60 min, in the course of which water of reaction was removed by distillation. After 3 hours, 20 mg of zinc dichloride dihydrate (corresponding to 20 ppm based on the end product) were added and the reaction was continued. After a total reaction time of 5 hours, the pressure was reduced gradually to 15 mbar over the course of 1 hour. Over the course of further reaction, the acid number was monitored. After a total reaction time of 35 hours, the reaction was ended. The acid number was 0.37 mg KOH/g.

Analysis of the Polyester:

[0103] Hydroxyl number: 56.7 mg KOH/g

[0104] Acid number: 0.37 mg KOH/g

[0105] Viscosity: 540 mPas (75 C.)

[0106] Preparation of the polyester polyol 3 (PES C-3) :

[0107] In a 2 liter four-neck flask (equipped with mechanical stirrer, 50 cm Vigreux column, thermometer, nitrogen inlet, column head, distillation system and vacuum membrane pump), 657 g of adipic acid (4.498 mol, corresponding to 56.57% by weight) and 505 g (4.756 mol, corresponding to 43.43% by weight) of diethylene glycol were heated to 200 C. under a nitrogen blanket over the course of 60 min, in the course of which water of reaction was removed by distillation. After 3 hours, 20 mg of zinc dichloride dihydrate (corresponding to 20 ppm based on the end product) were added and the reaction was continued. After a total reaction time of 5 hours, the pressure was reduced gradually to 15 mbar over the course of 1 hour. Over the course of further reaction, the acid number was monitored. After a total reaction time of 40 hours, the reaction was ended. The acid number was 0.67 mg KOH/g.

Analysis of the Polyester:

[0108] Hydroxyl number: 26.6 mg KOH/g

[0109] Acid number: 0.67 mg KOH/g

[0110] Viscosity: 2930 mPas (75 C.)

TABLE-US-00001 TABLE 1 Overview of polyester polyols PES C-1 to C-3 Example PES C-1 PES C-2 PES C-3 Formation: Adipic acid [% by wt.] 52.45 55.14 56.57 Diethylene glycol [% by wt.] 47.55 44.86 43.43 Analysis: Hydroxyl number [mg KOH/g] 112.2 56.7 26.6 Acid number [mg KOH/g] 0.42 0.37 0.67 Viscosity [mPas, 75 C.] 170 540 2930

D) Preparation of the Polyether Carbonate Polyols, PEC-D

Preparation of Polyether Carbonate Polyol 1 (PEC D-1)

[0111] A nitrogen-purged 60 L pressure reactor with a gas metering unit (gas inlet tube) was initially charged with a suspension of 15.14 g of DMC catalyst (prepared as per example 6 of WO 01/80994 A1) and 4700 g of cyclic propylene carbonate (cPC). The reactor was heated to about 100 C. and inertized with N.sub.2 at a pressure g.sub.abs=100 mbar for 1 h. The reactor was then adjusted to a pressure of 74 bar with CO.sub.2. 500 g of propylene oxide (PO) were metered into the reactor at 110 C. while stirring (316 rpm) within 2 min. The onset of the reaction was signaled by a temperature spike (hotspot) and a pressure drop. On completion of activation, 34.43 kg of propylene oxide at 8.2 kg/h and 3.25 kg of monopropylene glycol at 0.79 kg/h were metered simultaneously into the reactor. In the course of this, the reaction temperature was lowered to 105 C. and the pressure was kept constant by metering in further CO.sub.2. After the metered addition had ended, stirring was continued for 30 min. The cyclic propylene carbonate was separated from the polyether carbonate polyol in a thin-film evaporator (T=140 C., p.sub.abs<3 mbar, 400 rpm).

[0112] Table 2 below states the analytical data for the resulting polyether carbonate polyol (content of incorporated CO.sub.2, hydroxyl number (OHN) and viscosity).

Preparation of Polyether Carbonate Polyol 2 (PEC D-2)

[0113] A nitrogen-purged 60 L pressure reactor with a gas metering unit (gas inlet tube) was initially charged with a suspension of 9.97 g of DMC catalyst (prepared as per example 6 of WO 01/80994 A1) and 4700 g of PET 1004. The reactor was heated to about 100 C. and inertized with N.sub.2 at a pressure g.sub.abs =100 mbar for 1 h. 963 g of propylene oxide (PO) were metered into the reactor at 125 C. while stirring (316 rpm) within 2 min. The onset of the reaction was signaled by a temperature spike (hotspot) and a pressure drop. This operation was then repeated under 54 bar of CO.sub.2, in the course of which 585 g of propylene oxide were metered in. After the activations, 33.62 kg of propylene oxide were metered in at 7.0 kg/h. In the course of this, the reaction temperature was lowered to 105 C. and the pressure was kept constant by metering in further CO.sub.2. After the metered addition had ended, stirring was continued for 30 min. The cyclic propylene carbonate was separated from the polyether carbonate polyol in a thin-film evaporator (T =140 C., p.sub.abs<3 mbar, 400 rpm).

[0114] Table 2 below states the analytical data for the resulting polyether carbonate polyol (content of incorporated CO.sub.2, hydroxyl number (OHN) and viscosity).

Preparation of Polyether Carbonate Polyol 3 (PEC D-3)

[0115] A nitrogen-purged 60 L pressure reactor with a gas metering unit (gas inlet tube) was initially charged with a suspension of 14.25 g of DMC catalyst (prepared as per example 6 of WO 01/80994 A1) and 4700 g of cyclic propylene carbonate (cPC). The reactor was heated to about 100 C. and inertized with N.sub.2 at a pressure p.sub.abs=100 mbar for 1 h. The reactor was then adjusted to a pressure of 74 bar with CO.sub.2. 500 g of propylene oxide (PO) were metered into the reactor at 110 C. while stirring (316 rpm) within 2 min. The onset of the reaction was signaled by a temperature spike (hotspot) and a pressure drop. On completion of activation, 31.898 kg of propylene oxide at 7.6 kg/h and 1.5 kg of monopropylene glycol at 0.4 kg/h were metered simultaneously into the reactor. In the course of this, the reaction temperature was lowered to 107 C. and the pressure was kept constant by metering in further CO.sub.2. After the metered addition had ended, stirring was continued for 30 min. The cyclic propylene carbonate was separated from the polyether carbonate polyol in a thin-film evaporator (T=140 C., p.sub.abs<3 mbar, 400 rpm).

[0116] Table 2 below states the analytical data for the resulting polyether carbonate polyol (content of incorporated CO.sub.2, hydroxyl number (OHN) and viscosity).

TABLE-US-00002 TABLE 2 Overview of polyether carbonate polyols, PEC D-1 to PEC D-3 CO.sub.2 content Hydroxyl number Example [% by wt.] [mg KOH/g] PEC D-1 15.2 118.4 PEC D-2 19.6 27.7 PEC D-3 18.22 55.5
E.) Production of Slabs with the Aid of a Speedmixer:

[0117] The polyol component was initially charged at room temperature (23-27 C.) in a closable 500 mL PE beaker, and the specified amount of isocyanate component was added, the isocyanate component having been equilibrated to room temperature in the examples adduced in table 1 and in example 5-V, and having been preheated to 50 C. in the other examples. After closure of the vessel, the vessel was inserted into the dedicated holder in the Speedmixer, and the two components were mixed vigorously for 30 seconds. The mixture was transferred into an aluminum mold of size 20200.38 cm with a lid, which had been preheated to 80 C. and treated with Indrosil 2000 separating agent.

[0118] The slabs from the examples adduced in table 3 and in the case of example 5-V were demolded after 1 minute, the others after 2 minutes. The density of the moldings for all slabs was 1.1+/0.1 g/cm.sup.3.

F.) Preparation of the Storage Samples:

[0119] One day after the production, pieces of size 55 cm were sawn out of the slabs. Ethanol and a paper tissue were used to remove any residues of separating agent from the test samples. The dry specimens were weighed accurately, then immersed completely in tap water and then removed from the water and weighed again according to the storage cycles specified. The difference in weight was reported in percent in each case.

[0120] The analyses were conducted as follows:

[0121] Water absorption was determined by gravimetric means. For this purpose, the slabs were weighed at room temperature, then stored in water for 7 days and then, after dabbing off residual water, weighed again. The values for water absorption were reported as a percentage based on the starting value.

TABLE-US-00003 TABLE 3 Formulations and properties of inventive and noninventive polyurethanes compared to an aromatic standard system, comparative example 1-V. Example: 1-V* 2 3-V* 4-V* Desmophen L2830 [pts. by wt.] 6.00 PET 5168T [pts. by wt.] 12.00 Polyether V2725 [pts. by wt.] 55.70 55.70 55.70 55.70 PES C-2 [pts. by wt.] 18.00 PES C-3 [pts. by wt.] 18.00 PEC D-3 [pts. by wt.] 18.00 Ethylene glycol [pts. by wt.] 15.00 15.00 15.00 15.00 Desmophen 4050E [pts. by wt.] 3.00 3.00 3.00 3.00 Isopur [pts. by wt.] 6.20 6.20 6.20 6.20 Schwarzpaste N Tinuvin B75 [pts. by wt.] 1.50 1.50 1.50 1.50 Fomrez UL28 [pts. by wt.] 0.30 0.30 0.30 0.30 Dabco 33LV [pts. by wt.] 0.30 0.30 0.30 0.30 Sum total of polyol side [pts. by wt.] 100.0 100.0 100.0 100.0 Polyisocyanate side: Desmodur PA09 [pts. by wt.] 96.13 97.67 96.05 97.70 Index 100.0 100.0 100.0 100.0 Water absorption after 1.63 1.28 1.53 1.7 7 days [% by wt.] *V = comparison

[0122] Comparative example 1-V is an aromatic system. The water absorption here is 1.63% by weight. In inventive example 2, the bifunctional long-chain polyether polyols Desmophen L 2830 and PET 5168T were exchanged for the polyether carbonate polyol PEC D-3. This change in formulation significantly reduced the water absorption value.

[0123] An analogous exchange of the bifunctional long-chain polyether polyols Desmophen L 2830 and PET 5168T for the polyester polyols PES C-2 and PES C-3, by contrast, gives only a small improvement (comparative example 3-V) and, in comparative example 4-V, actually a slight deterioration in the water absorption values.

TABLE-US-00004 TABLE 4 Formulations and properties of inventive and noninventive polyurethanes compared to an aliphatic standard system, comparative example 5-V. Example: 5-V* 6 7 8-V* 9-V* PET 5168T [pts. 65.00 by wt.] PES C-2 [pts. 65.00 by wt.] PES C-3 [pts. 65.00 by wt.] PEC D-2 [pts. 65.00 by wt.] PEC D-3 [pts. 65.00 by wt.] Butane-1,4-diol [pts. 5.00 5.00 5.00 5.00 5.00 by wt.] Polyether L800 [pts. 10.00 10.00 10.00 10.00 10.00 by wt.] Desmophen [pts. 15.00 15.00 15.00 15.00 15.00 4011T by wt.] Isopur [pts. 5.00 5.00 5.00 5.00 5.00 Schwarzpaste N by wt.] Tinuvin B75 [pts. 0.75 0.75 0.75 0.75 0.75 by wt.] Fomrez UL28 [pts. 1.00 1.00 1.00 1.00 1.00 by wt.] Sum total of polyol [pts. 101.75 101.75 101.75 101.75 101.75 side by wt.] Polyisocyanate side: Desmodur [pts. 79.64 79.64 86.35 79.31 86.52 48IF44 by wt.] Index 100.0 100.0 100.0 100.0 100.0 Water absorption 2.61 1.8 0.9 2.35 2.17 after 7 days [% by wt.] *V = comparison

[0124] Comparative example 5-V is an aliphatic system having a water absorption value of 2.61% by weight.

[0125] In the case of inventive examples 6 and 7, the bifunctional long-chain polyether polyol PET 5168T was exchanged for the polyether carbonate polyols PEC D-2 and PEC D-3 respectively. As a result, there was a significant decrease in water absorption from 2.61% by weight (comparative example 5-Vstandard) to 1.8% by weight (inventive example 6) or 0.9% by weight (inventive example 7).

[0126] An analogous exchange for the polyester polyols PES C-2 and PES C-3, by contrast, gives only a small improvement in water absorption (comparative examples 8-V and 9-V).

TABLE-US-00005 TABLE 5 Formulations and properties of inventive and noninventive polyurethanes compared to an aliphatic, polycarbonatediol-containing standard system, comparative example 10-V. Example: 10-V* 11 12-V* PET 3973Y [pts. by wt.] 59.52 59.52 59.52 PES C-1 [pts. by wt.] 17.67 PEC D-1 [pts. by wt.] 17.67 Butane-1,4-diol [pts. by wt.] 8.84 8.84 8.84 Desmophen C XP 2716 [pts. by wt.] 17.67 Desmophen 4011T [pts. by wt.] 8.84 8.84 8.84 IPDA [pts. by wt.] 2.94 2.94 2.94 Isopur Schwarzpaste N [pts. by wt.] 5.00 5.00 5.00 Tinuvin B75 [pts. by wt.] 0.75 0.75 0.75 Irganox 1135 [pts. by wt.] 1.00 1.00 1.00 Fomrez UL28 [pts. by wt.] 0.44 0.44 0.44 Dabco 33LV [pts. by wt.] Sum total of polyol side [pts. by wt.] 105.0 105.0 105.0 Polyisocyanate side: Desmodur XP2489 [pts. by wt.] 52.74 50.24 50.25 Desmodur E 305 [pts. by wt.] 52.74 50.24 50.25 Index 105.0 105.0 105.0 Water absorption after 7 days 3.87 3.39 3.77 [% by wt.] *V = comparison

[0127] Noninventive example 10-V is an aliphatic, polycarbonatediol-containing (Desmophen C XP 2716) system.

[0128] In inventive example 11, the bifunctional aliphatic polycarbonatediol Desmophen C XP 2716 was exchanged for the polyether carbonate polyol PEC D-1. As a result, there was a significant decrease in the water absorption value from 3.87% by weight to 3.39% by weight.

[0129] In noninventive example 12-V, the bifunctional aliphatic polycarbonatediol Desmophen C XP 2716 was exchanged for the polyester polyol PES C-1. The water absorption value decreased only slightly from 3.87% by weight to 3.77% by weight.

[0130] The results from tables 3 to 5 show unambiguously that optimal results in terms of minimum water absorption values are achieved when PEC polyols are used in place of polyether polyols, polyester polyols or polycarbonate polyols.

[0131] A high PEC content (inventive examples 6 and 7) tends to bring about a more significant reduction in water absorption than a low content (inventive example 2).