USE OF POLYDIENE DIOLS IN RESILIENT POLYURETHANE FOAMS

Abstract: Polyurethane foams having high resilience and significantly improved humid ageing are formed from a polydiene diol, preferably a hydrogenated polybutadiene diol, having a hydroxyl functionality from 1.6 to 2.0 and from an aromatic polyisocyanate having an isocyanate functionality of from 2.5 to 3.0. The polydiene diol is preferably blended with foaming agents prior to addition of the highly reactive polyisocyanate.

Description: USE OF POLYDIENE DIOLS IN RESILIENT POLYURETHANE FOAMS This invention relates to flexible polyurethane foams containing a polyol, especially polyurethane foams having high resilience. Polyurethane foams having high resilience are typically produced from polyether triols having a number average molecular weight from 4,500 to 6,000 and an isocyanate which provides a narrow range of crosslink density. The polyether triols typically have an average functionality of from 2.4 to 2.7 hydroxyl groups per molecule as a result of unsaturated endgroups that form during manufacture of the triol. Toluene diisocyanate (TDI) , methylene diisocyanate (MDI), TDI/MDI mixtures, and modified TDI or MDI versions are used to produce foams with broad processing latitude. Isocyanate functionality is typically 2.0, and in most cases not higher than 2.3 isocyanate groups per molecule. The polyether triols form resilient foams when combined with the isocyanates having from 2.0 to 2.3 isocyanate groups per molecule under conditions which promote foaming. Making foams from diols and the typically used isocyanates will not provide a crosslink density that corresponds to a stable, high loadbearing and high resilient foam. United States Patent No. 4,939,184 described the production of polyurethane foams from polyisobutylene triols and diols (Example 3) which were prepared cationically. The polyisobutylenes are premixed with an isocyanate, namely MONDUR TD-80 isocyanate which is a mixture of meta and para isomers of toluene diisocyanate having a functionality of 2.0. Then water was added as a blowing agent to form the polyurethane foam. Foams obtained were of low resilience and were useful in energy absorbing applications. The present invention is a high resilient polyurethane foam produced from a polydiene diol, preferably a hydrogenated polybutadiene diol, having a number average molecular weight from 1,000 to 20,000, more preferably from 1,000 to 10,000, most preferably from 3,000 to 6,000, and a functionality of from 1.6 to 2, more preferably from 1.8 to 2 hydroxyl groups per molecule. The resiliency of the foam is achieved by the use of the polydiene diol, which is a highly resilient rubber, and by selecting an appropriate amount of a aromatic polyisocyanate having a functionality of from 2.5 to 3.0 isocyanate groups per molecule to assure adequate crosslinking. The polydiene diol foams show superior humid aging properties in comparison to conventional polyurethane foams. The present invention is a resilient polyurethane foam comprising a polydiene diol having a number average molecular weight from 1,000 to 20,000, more preferably from 1,000 to 10,000, most preferably from 3,000 to 6,000, and a functionality of from 1.6 to 2, more preferably from 1.8 to 2, hydroxyl groups per molecule, from 70 to 130, more preferably 90 to 110, index amount of an aromatic polyisocyanate having a functionality of from 2.5 to 3.0 isocyanate groups per molecule, and a blowing agent. The foam shows superior humid aging characteristics in comparison to conventional polyurethane foams. The polydiene diols used in this invention are prepared anionically such as described in United States Patents Nos. 5,376,745, 5,391,663, 5,393,843, 5,405,911, and 5,416,168 which are incorporated by reference herein. The polydiene diols provide stable, resilient foams when the polydiene diol is hydrogenated although unsaturated polydiene diols will also result in polyurethane foams having high resilience. The polydiene diols have from 1.6 to 2, more preferably from 1.8 to 2 terminal hydroxyl groups per molecule and a number average molecular weight between 1,000 and 20,000, more preferably from 1,000 to 10,000, most preferably from 3,000 to 6,000. Hydrogenated polybutadiene diols are preferred and have 1,4-addition between 30% and 70S. Polymerization of the polydiene diols commences - with a monolithium or dilithium initiator which polymerizes a conjugated diene monomer at each lithium site. The conjugated diene is typically 1, 3-butadiene or isoprene since other conjugated dienes cost more and do not provide advantages that justify the expense. The anionic polymerization is done in solution in an organic solvent, typically a hydrocarbon like hexane, cyclohexane or benzene, although polar solvents such as tetrahydrofuran can also be used. When the conjugated diene is 1, 3-butadiene and when the resulting polymer will be hydrogenated, the anionic polymerization of butadiene in a hydrocarbon solvent like cyclohexane is typically controlled with structure modifiers such as diethylether or glyme (1,2-diethoxyethane) to obtain the desired amount of 1, -addition. The optimum balance between low viscosity and high solubility in a hydrogenated polybutadiene polymer occurs at a 60/40 ratio of 1,4-butadiene/l,2-butadiene. This butadiene microstructure is achieved during polymerization at 50°C in cyclohexane containing about 6% by volume of diethylether or about 1000 ppm of glyme. For polyisoprene diols, high resiliency is achieved with more than 80% 1,4-addition of isoprene. Anionic polymerization is terminated by addition of a functionalizing agent like those in United States Patents 5,391,637, 5,393,843, and 5,418,296 which are also incorporated by reference, but preferably ethylene oxide, prior to termination. The preferred di-lithium initiator is formed by reaction of two moles of sec-butyllithium with one mole of diisopropylbenzene. This diinitiator is used to polymerize the conjugated diene monomer, preferably butadiene, in a solvent composed of 90%w cyclohexane and 10%w diethylether. The molar ratio of diinitiator to monomer determines the molecular weight of the polymer. The living polymer is then capped with two moles of ethylene oxide and terminated with two moles of methanol to yield the desired polydiene diol. The polydiene diol can also be made using a mono- lithium initiator which contains a hydroxyl group which has been blocked as the silyl ether (as in United States Patents 5,376,745 and 5,416,168 which are also incorporated by reference) . A suitable initiator is hydroxypropyllithium in which the hydroxyl group is blocked as the trimethylsilyl ether. This mono-lithium initiator is used to polymerize the conjugated diene in hydrocarbon or polar solvent. The molar ratio of initiator to monomer determines the molecular weight of the polymer. The living polymer is then capped with one mole of ethylene oxide and terminated with one mole of methanol to yield the mono-hydroxy polydiene polymer. The silyl ether is then removed by acid catalyzed cleavage in the presence of water yielding the desired polydiene diol. The polydiene diols are hydrogenated to improve stability such that at least 90%, preferably at least 95%, of the carbon to carbon double bonds in the diols are saturated. Hydrogenation of these polymers and copolymers may be carried out by a variety of well established processes including hydrogenation in the presence of such catalysts as Raney Nickel, nobel metals such as platinum and the like, soluble transition metal catalysts and titanium catalysts as in U.S. Patent 5,039,755 which is also incorporated by reference. A particularly preferred catalyst is a mixture of nickel 2-ethylhexanoate and triethyl- aluminum. The polybutadiene diols have no less than about 40% 1,2-butadiene addition because, after hydrogenation, the polymer will be a waxy solid at room temperature if it contained less than about 40% 1,2-butadiene addition. To minimize viscosity of the diol, the 1,2- butadiene content should be between about 40 and 60%. The isoprene polymers have no less than 80% 1,4- isoprene addition in order to reduce Tg and viscosity. The diene microstructures are typically determined by C-*- 3 nuclear magnetic resonance (NMR) in chloroform. The polydiene diols have hydroxyl equivalent weights between about 500 and about 10,000, more preferably between 500 and 5,000, most preferably between 1,500 and 3,000. Thus, for the polydiene diols, suitable number average molecular weights will be between 1,000 and 20,000, more preferably between 1,000 and 10,000, most preferably between 3,000 and 6,000. The number average molecular weights referred to here are number average molecular weights measured by gel permeation chromatography (GPC) calibrated with polybutadiene standards having known number average molecular weights. The solvent for the GPC analyses is tetrahydrofuran. The isocyanates used in this invention are aromatic polyisocyanates since they have the desired fast reactivity to make foam. As the saturated polydiene diol has a functionality of about 2 hydroxyl groups per molecule, it has been discovered that a polyisocyanate having a functionality of from 2.5 to 3.0 is needed to achieve a crosslink density that results in a stable, high loadbearing and high resilient foam. Using isocyanates of lower functionality results in less stable foams having lower loadbearing capacity and having reduced resiliency. Higher isocyanate functionality will result in foam having a too high closed cell content which will negatively influence the physical properties. An example of a suitable aromatic polyisocyanate which is commercially available is MONDUR MR, from Bayer, a polymeric diphenylmethane polyisocyanate which typically has an isocyanate functionality of 2.7. The polyurethane foams are produced from the polydiene diol, the aromatic polyisocyanate, from 0.5 to 3.5 parts of water, an amine and tin catalyst, and a silicone surfactant. Other ingredients like fire retardants, fillers, etc. may be added by those skilled in the arts of foaming. A variety of amines, tin catalysts, and silicone surfactants for making polyurethane foams are commercially available from Air Products under the tradename DABCO. An example of such a combination useful in making polyurethane foams from polydiene diols is DABCO 33LV amine catalyst, DABCO DC-1 tin catalyst, and DABCO DC-5160 silicone surfactant as described below. The polyurethane foams are preferably prepared by blending all of the components except the isocyanate. The polydiene diol is preferably preheated to reduce viscosity prior to blending. After blending, the aromatic polyisocyanate is quickly added and briefly stirred before pouring the mixture into a mold to hold the expanding foam. The polyurethane foams of the present invention are useful for making articles like seat cushions, carpet backings, gaskets, and air filters. The preferred embodiment of the present invention is a resilient polyurethane foam comprising 100 parts by weight of a hydrogenated polydiene diol having a number average molecular weight from 3,000 to 6,000 and a functionality of from 1.8 to 2.0 hydroxyl groups per molecule, from 0.5 to 3.5 parts by weight of water, from 90 to 110 index amount of an aromatic polyisocyanate having a functionality of from 2.5 to 3.0, preferably 2.7, isocyanate groups per molecule, from 0.1 to 2.0 parts by weight of an amine, from 0.05 to 1.0 parts by weight of a tin catalyst, and from 0 to 2.0 parts by weight of a silicon surfactant. The foam shows superior resiliency and humid aging characteristics in comparison to conventional polyurethane foams. The following examples show that polyurethane foams having high resiliency and significantly improved humid aging are produced in accordance with the present invention. The examples are not intended to limit the present invention to specific embodiments although each example may support a separate claim which is asserted to be a patentable invention. Example 1 A linear, hydrogenated butadiene diol polymer having 1.95 terminal hydroxyl groups per molecule, a number average molecular weight of 3650, and a 1,2- addition of 43%, was obtained from Shell Chemical labelled HPVM 2201. This polymer is a viscous liquid at 25°C but flows readily at slightly elevated temperatures (20 poise viscosity at 60°C) . The hydrogenated polybutadiene diol was heated to 80°C, and 100 parts by weight of the diol were blended with 1 part by weight of water, 0.27 parts by weight of DABCO 33LV amine catalyst, 0.2 parts by weight of DABCO DC-1 tin catalyst, and 0.03 parts by weight of DABCO DC-5160 silicone surfactant. The components were blended for 20 seconds at 2500 rpm. A 100 index amount (22 parts by weight) of MONDUR MR polyisocyanate having a functionality of 2.7 was quickly added and stirring continued for another 15 seconds. A creamy mixture was formed and then poured into a mold sized to hold the resulting polyurethane foam. The polyurethane foam was of good stability, had a regular cellular structure and did not show shrinkage. The density, hardness, rebound resilience, hysteresis, and humid aging hardness loss of the foam was measured according to conventional methods, and also ageing the foam at 90°C and 100% relative humidity for 10 days. The foam properties are reported in Table 1. These data show the excellent ball rebound resilience, the high hardness and the outstanding humid ageing resistance. Comparison Example A The procedure of Example 1 was used to form a comparison Example by replacing the hydrogenated butadiene diol with a polyether triol having a number average molecular weight of 4,600 and an 80% primary hydroxyl content. The polyurethane foam was stable, had a regular cellular structure and did not shrink during cure. The density, hardness, rebound resilience, hysteresis, and humid aging hardness loss of the foam are reported in Table 1. Compared with Example 1, the foam has for about the same density only half the hardness, a lower ball rebound resilience and loses more than 20% of its original hardness after being humid aged. Comparison Example B The procedure of Example 2 was used to form a comparison Example by repeating all steps except that the polyether polyol was preheated to only 22°C. The polyurethane foam was stable, had a regular cellular structure and did not shrink. The density, hardness, rebound resilience, hysteresis, and humid aging hardness loss of the foam are reported in Table 1. Foaming at a lower temperature increases the density and hardness of the foam. Also in this example the ball rebound resilience is lower than for Example 1, and the hardness loss after humid ageing is substantially higher. TABLE 1 Example _1 B Density, g/l 96 94 149 Hardness at 40% indentation, N 25 12 40 Ball rebound resilience, % 68 62 60 Hysteresis, % 11 11 13 Humid Ageing Hardness Loss, % 11 21 25 Example 2 The hydrogenated butadiene diol of Example 1 was heated to 80°C and 100 parts by weight of the diol were blended with 2 parts by weight of water, 0.4 parts by weight of DABCO 33LV amine catalyst, 0.3 parts by weight of DABCO DC-1 tin catalyst, and 0.02 parts by weight of DABCO DC-5160 silicone surfactant. The components were blended for 20 seconds at 2500 rpm. A 100 index amount (37 parts by weight) of MONDUR MR polyisocyanate having a functionality of 2.7 was quickly added and stirring continued for another 15 seconds. A creamy mixture was formed and then poured into a mold sized to hold the resulting polyurethane foam. The polyurethane foam was stable, had a regular cellular structure and did not shrink. The density, hardness, rebound resilience, hysteresis, and humid aging hardness loss of the foam was measured according to conventional methods, and also ageing the foam at 90°C and 100% relative humidity for 10 days. The foam properties are reported in Table 2. Comparison Example C The procedure of Example 2 was used to form a comparison Example by replacing the hydrogenated butadiene diol with a polyether triol having a number average molecular weight of 4,600 and an 80% primary hydroxyl content. The only other variation was that the triol was used at 22°C. The polyurethane foam had a regular cellular structure. The density, hardness, rebound resilience, hysteresis, and humid aging hardness loss of the foam are reported in Table 2. Compared with Example 2, the ball rebound resilience is lower and the humid aged hardness loss is much greater. TABLE 2 Example 2_ C Density, g/l 50 67 Hardness at 40% indentation, N 9 11 Ball rebound resilience, % 73 60 Hysteresis, % 10 16 Humid Ageing Hardness Loss, % 6 21

Claims: C L A I M S 1. A polyurethane foam, produced by a process comprising the steps of: combining a polydiene diol having a number average molecular weight from 1,000 to 20,000 and a functionality of from 1.6 to 2 hydroxyl groups per molecule with an aromatic polyisocyanate having a functionality of from 2.5 to 3.0 isocyanate groups per molecule; and foaming the combined polydiene diol and aromatic polyisocyanate to form a resilient polyurethane foam. 2. The polyurethane foam of claim 1, wherein the polydiene diol has a number average molecular weight of 3,000 to 6,000 and a functionality of from 1.8 to 2 hydroxyl groups per molecule. 3. The polyurethane foam of claim 1, wherein the polydiene diol is hydrogenated. 4. The polyurethane foam of claim 1, wherein the polydiene diol is a polybutadiene diol. 5. The polyurethane foam of claim 1, wherein the polydiene diol is a hydrogenated polybutadiene diol having from 40% to 60% 1,2-addition of butadiene. 6. The polyurethane foam of claim 1, wherein the aromatic polyisocyanate has a functionality of 2.7. 7. The polyurethane foam of claim 1, wherein foaming agents are combined with the polydiene diol prior to combination of the polydiene diol and the aromatic polyisocyanate. 8. The polyurethane foam of claim 7, wherein the foaming agents comprise water, an amine, a tin catalyst, and a silicon surfactant. 9. A polyurethane foam, produced by a process comprising the steps of: mixing 100 parts by weight of a polydiene diol having a number average molecular weight from 1,000 to 10,000 and a functionality of from 1.8 to 2.0 hydroxyl groups per molecule with from 0.5 to 3.5 parts by weight of water, from 0.1 to 2.0 parts by weight of an amine, from 0.05 to 1.0 parts by weight of a tin catalyst, and from 0.0 to 2.0 parts by weight of a silicon surfactant; and adding to the polydiene diol from 90 to 110 index amount of a polymeric isocyanate having a functionality of from 2.5 to 3.0 isocyanate groups per molecule. 10. The polyurethane foam of claim 9, wherein the polydiene diol is a hydrogenated polybutadiene diol having from 40% to 60% 1,2-addition of butadiene. 11. The polyurethane foam of claim 91, wherein the aromatic polyisocyanate has a functionality of 2.7. 12. A polyurethane foam, produced by a process comprising the steps of: mixing 100 parts by weight of a hydrogenated polybutadiene diol having a number average molecular weight from 3,000 to 6,000, from 40% to 60% 1,2- addition of butadiene, and a functionality of from 1.8 to 2.0 hydroxyl groups per molecule with from 0.5 to 3.5 parts by weight of water, from 0.1 to 2.0 parts by weight of an amine, from 0.05 to 1.0 parts by weight of tin catalyst, and from 0.0 to 2.0 parts by weight of a silicon surfactant; and adding to the hydrogenated polybutadiene diol from 90 to 110 index amount of a polymeric isocyanate having a functionality of from 2.5 to 3.0 isocyanate groups per molecule. 13. The polyurethane foam of claim 12, wherein the aromatic polyisocyanate has a functionality of 2.7.

Inventors: CENENS JOZEF LUCYEN RUDOLF, CENENS, JOZEF, LUCYEN, RUDOLF
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1996
Main classification: C08G18
IPC codes: C08G18