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Viscoelastic foams and elastomers based on a reaction system comprising a monomeric polyisocyanate composition, a specified mixture of polyols, and a specified package of additives. The viscoelastic materials offer superior combinations of physical properties, including surprisingly low compression

Viscoelastic foams and elastomers based on a reaction system comprising a monomeric polyisocyanate composition, a specified mixture of polyols, and a specified package of additives. The viscoelastic materials offer superior combinations of physical properties, including surprisingly low compression sets. Very soft viscoelastic foams and microcellular elastomers can be conveniently prepared from the reaction system without the necessity of using plasticizers. The reaction system can be processed into useful polymeric articles using a wide range of conventional polyurethane processing methods.

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What is claimed is: 1. A reaction system for the preparation of a viscoelastic thermoset polyurethane material comprising: (a) an organic monomeric polyisocyanate composition having a number averaged functionality of organically bound isocyanate groups of from 2 to 3 and a total concentration of or

What is claimed is: 1. A reaction system for the preparation of a viscoelastic thermoset polyurethane material comprising: (a) an organic monomeric polyisocyanate composition having a number averaged functionality of organically bound isocyanate groups of from 2 to 3 and a total concentration of organically bound isocyanate groups of from 25 to 50% by weight; (b) an isocyanate reactive component comprising: (i) from 0 to 12% by weight of the isocyanate reactive component of water; (ii) from 30 to 70% by weight of the isocyanate reactive component of a polyoxyethylene based polyol having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 4, a number averaged molecular weight of from 400 to 1500, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from 200 to 750, wherein the polyoxyethylene based polyol is composed of greater than 70% by weight of oxyethylene units and at least 50 mole percent of the aliphatically bound hydroxyl groups are primary hydroxyl groups; (iii) from 30 to 70% by weight of the isocyanate reactive component of a second polyoxyalkylene based polyol having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 4, a number averaged molecular weight of from 400 to 1500, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from 200 to 750, wherein the second polyoxyalkylene based polyol is composed of greater than 70% by weight of oxyalkylene units selected from the group consisting of oxypropylene units, oxytetramethylene units, and combinations of oxypropylene and oxytetramethylene units; (iv) from 0 to 20% by weight of the isocyanate reactive component of a polyoxypropylene or polyoxyethylene-polyoxypropylene polyol different from (b)(ii) and (b)(iii), having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 4, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from greater than 750 to 4000, wherein the polyoxypropylene or polyoxyethylene-polyoxypropylene polyol contains a weight ratio of oxyethylene to oxypropylene units of from 0:100 to 90:10; (v) from 0 to 15% by weight of the isocyanate reactive component of an organic polyol having a combined isocyanate reactive group functionality of 2 to 4 and an equivalent weight of isocyanate reactive groups of from 30 to less than 200, wherein the isocyanate reactive groups are limited to one or more members selected from the group consisting of primary aliphatic alcohol groups, secondary aliphatic alcohol groups, and aliphatic secondary amine groups and at least two of the isocyanate reactive groups are alcohol groups; wherein the weight ratio of (b)(ii) to (b)(iii) is from 70:30 to 30:70, and the combined weight of (b)(ii) and (b)(iii) constitutes at least 53% by weight of the isocyanate reactive component; (c) an optional surfactant; (d) a catalyst; and (e) an optional additive selected from the group consisting of dyes, pigments, internal mold release agents, physical blowing agents, chemical blowing agents, fire retardants, fillers, reinforcements, plasticizers, smoke suppressants, fragrances, antistatic agents, biocides, antioxidants, light stabilizers, adhesion promoters, and combinations of these; wherein the ratio of organically bound isocyanate groups to the total of isocyanate reactive groups in the reaction system varies from greater than 0.50 to 1.10. 2. The reaction system of claim 1, wherein the ratio of organically bound isocyanate groups to the total of isocyanate reactive groups is from greater than 0.70 to less than 1.00. 3. The reaction system of claim 1, wherein the total weight of the optional additive is less than 30% of the total weight of the reaction system. 4. The reaction system of claim 3, wherein the reaction system is essentially free of blowing agents other than water. 5. The reaction system of claim 3, wherein at least one of (b) (ii) and (b)(iii) has a nominal functionality of isocyanate reactive groups of greater than 2. 6. The reaction system of claim 3, wherein at least one of (b) (ii) and (b)(iii) is a nominal triol. 7. The reaction system of claim 3, wherein both (b)(ii) and (b)(iii) are nominal triols. 8. The reaction system of claim 3, wherein the organic monomeric polyisocyanate composition has a number averaged functionality of isocyanate groups of greater than 2. 9. The reaction system of claim 3, wherein the organic monomeric polyisocyanate composition has a number averaged functionality of isocyanate groups of greater than 2.1 and consists predominantly, on a weight basis, of one or more polyisocyanates of the MDI series. 10. The reaction system of claim 3, wherein the oxyalkylene units in the structure of (b)(iii) consist essentially of oxypropylene units. 11. The reaction system of claim 3, wherein the number averaged hydroxyl equivalent weight of each of (b)(ii) and (b)(iii) varies from 350 to 500. 12. The reaction system of claim 3, wherein the reaction system contains 0.1 to 5% by weight of a polysiloxane-polyether surfactant, relative to the total weight of the reaction system. 13. A viscoelastic polyurethane material prepared from the reaction system of claim 1. 14. The viscoelastic polyurethane material of claim 13, wherein the foaming agent consists of water optionally in combination with one or more dissolved or dispersed atmospheric gases. 15. A reaction system for the preparation of cellular viscoelastic polyurethane thermoset materials comprising: (a) an organic monomeric polyisocyanate composition having a number averaged functionality of organically bound isocyanate groups of from 2 to 3 and a total concentration of organically bound isocyanate groups of from 28 to 35% by weight; (b) an isocyanate reactive component comprising: (i) from 0.15 to 10% by weight of the total isocyanate reactive component of water; (ii) from 30 to 70% by weight of the total isocyanate reactive component of a polyoxyethylene based polyol having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 3, a number averaged molecular weight of from 400 to 1500, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from 300 to 550, wherein the polyoxyethylene based polyol is composed of greater than 75% by weight of oxyethylene units and at least 75 mole percent of the aliphatically bound hydroxyl groups are primary hydroxyl groups; (iii) from 30 to 70% by weight of the total isocyanate reactive component of a second polyoxyalkylene based polyol having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 3, a number averaged molecular weight of from 400 to 1500, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from 300 to 550, wherein the second polyoxyalkylene based polyol is composed of greater than 90% by weight of oxyalkylene units selected from the group consisting of oxypropylene units, oxytetramethylene units, and combinations of oxypropylene and oxytetramethylene units; (iv) from 0 to 20% by weight of the isocyanate reactive component of a polyoxypropylene or polyoxyethylene-polyoxypropylene polyol different from (b)(ii) and (b)(iii), having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 4, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from greater than 750 to 4000, wherein the polyoxypropylene or polyoxyethylene-polyoxypropylene polyol contains a weight ratio of oxyethylene to oxypropylene units of from 10:90 to 30:70; (v) from 0.15 to less than 10% by weight of the isocyanate reactive component of an organic polyol having a combined isocyanate reactive group functionality of 2 to 3 and an equivalent weight of isocyanate reactive groups of from 30 to less than 95, wherein the isocyanate reactive groups are limited to one or more members selected from the group consisting of primary aliphatic alcohol groups, secondary aliphatic alcohol groups, and aliphatic secondary amine groups and at least two of the isocyanate reactive groups are alcohol groups; wherein the weight ratio of (b)(ii) to (b)(iii) is from 60:40 to 40:60, and the combined weight of (b)(ii) and (b)(iii) constitutes at least 85% by weight of the isocyanate reactive component; (c) a surfactant; (d) a catalyst; and (e) an optional additive selected from the group consisting of dyes, pigments, internal mold release agents, physical blowing agents, chemical blowing agents, fire retardants, fillers, reinforcements, plasticizers, smoke suppressants, fragrances, antistatic agents, biocides, antioxidants, light stabilizers, adhesion promoters, and combinations of these; wherein the ratio of organically bound isocyanate groups to the total of isocyanate reactive groups in the reaction system varies from greater than 0.8 to less than 0.95. 16. The reaction system of claim 15, wherein the total weight of the optional additive is less than 20% of the total weight of the reaction system. 17. The reaction system of claim 16, wherein the reaction system is essentially free of blowing agents other than water. 18. The reaction system of claim 16, wherein at least one of (b)(ii) and (b)(iii) has a nominal functionality of isocyanate reactive groups of greater than 2. 19. The reaction system of claim 16, wherein at least one of (b)(ii) and (b)(iii) is a nominal triol. 20. The reaction system of claim 16, wherein both (b)(ii) and (b)(iii) are nominal triols. 21. The reaction system of claim 16, wherein the organic monomeric polyisocyanate composition has a number averaged functionality of isocyanate groups of greater than 2.1 and consists predominantly, on a weight basis, of one or more polyisocyanates of the MDI series. 22. The reaction system of claim 16, wherein the oxyalkylene units in the structure of (b)(iii) consist essentially of oxypropylene units. 23. The reaction system of claim 16, wherein the number averaged hydroxyl equivalent weight of (b)(ii) is in the range of from 350 to 500 and the number averaged hydroxyl equivalent weight of(b)(iii) is in the range of from 350 to 500. 24. The reaction system of claim 16, wherein the reaction system contains 0.25 to 2.5% by weight of a polysiloxane-polyether surfactant, relative to the total weight of the reaction system. 25. A viscoelastic polyurethane cellular thermoset material prepared from the reaction system of claim 16. 26. The viscoelastic polyurethane cellular thermoset material of claim 25, wherein the foaming agent consists of water optionally in combination with one or more dissolved or dispersed atmospheric gases. 27. A reaction system for the preparation of cellular viscoelastic polyurethane thermo set materials comprising: (a) an organic monomeric polyisocyanate composition having a number averaged functionality of organically bound isocyanate groups of from 2 to 3 and a total concentration of organically bound isocyanate groups of from 28 to 35% by weight; (b) an isocyanate reactive component comprising: (i) from 2 to 5% by weight of the total isocyanate reactive component of water; (ii) from 30 to 70% by weight of the total isocyanate reactive component of a polyoxyethylene based polyol having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 3, a number averaged molecular weight of from 400 to 1500, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from 300 to 550, wherein the polyoxyethylene based polyol is composed of greater than 90% by weight of oxyethylene units and at least 90 mole percent of the aliphatically bound hydroxyl groups are primary hydroxyl groups; (iii) from 30 to 70% by weight of the total isocyanate reactive component of a second polyoxyalkylene based polyol having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 3, a number averaged molecular weight of from 400 to 1500, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from 300 to 550, wherein the second polyoxyalkylene based polyol is composed of greater than 90% by weight of oxyalkylene units selected from the group consisting of oxypropylene units, oxytetramethylene units, and combinations of oxypropylene and oxytetramethylene units; (iv) from 0 to 20% by weight of the isocyanate reactive component of a polyoxypropylene or polyoxyethylene-polyoxypropylene polyol different from (b)(ii) and (b)(iii), having a combined nominal functionality of primary and secondary aliphatically bound hydroxyl groups of 2 to 3, and a number averaged equivalent weight of the combined primary and secondary aliphatically bound hydroxyl groups of from greater than 750 to 4000, wherein the polyoxypropylene or polyoxyethylene-polyoxypropylene polyol contains a weight ratio of oxyethylene to oxypropylene units of from 10:90 to 30:70; (v) from 0.15 to less than 3% by weight of the isocyanate reactive component of an organic polyol having a combined isocyanate reactive group functionality of 2 to 3 and an equivalent weight of isocyanate reactive groups of from 30 to less than 95, wherein the isocyanate reactive groups are limited to one or more members selected from the group consisting of primary aliphatic alcohol groups, secondary aliphatic alcohol groups, and aliphatic secondary amine groups and at least two of the isocyanate reactive groups are alcohol groups; wherein the weight ratio of (b)(ii) to (b)(iii) is from 60:40 to 40:60, and the combined weight of (b)(ii) and (b)(iii) constitutes at least 85% by weight of the isocyanate reactive component; (c) an optional surfactant; (d) a catalyst; and (e) an optional additive selected from the group consisting of dyes, pigments, internal mold release agents, physical blowing agents, chemical blowing agents, fire retardants, fillers, reinforcements, plasticizers, smoke suppressants, fragrances, antistatic agents, biocides, antioxidants, light stabilizers, adhesion promoters, and combinations of these; wherein the ratio of organically bound isocyanate groups to the total of isocyanate reactive groups in the reaction system varies from greater than 0.8 to 0.95. 28. The reaction system of claim 27, wherein the total weight of the optional additive is less than 15% of the total weight of the reaction system. 29. The reaction system of claim 28, wherein the reaction system is essentially free of blowing agents other than water. 30. The reaction system of claim 28, wherein at least one of (b)(ii) and (b)(iii) has a nominal functionality of isocyanate-reactive groups of greater than 2. 31. The reaction system of claim 28, wherein at least one of (b)(ii) and (b)(iii) is a nominal triol. 32. The reaction system of claim 28, wherein both (b)(ii) and (b)(iii) are nominal triols. 33. The reaction system of claim 28, wherein the organic monomeric polyisocyanate composition has a number averaged functionality of isocyanate groups of greater than 2.1 and consists predominantly, on a weight basis, of one or more polyisocyanates of the MDI series. 34. The reaction system of claim 28, wherein the oxyalkylene units in the structure of (b)(iii) consist essentially of oxypropylene units. 35. The reaction system of claim 28, wherein the number averaged hydroxyl equivalent weight of (b)(ii) is in the range of from 350 to 500, and the number averaged hydroxyl equivalent weight of (b)(iii) is in the range of from 350 to 500. 36. The reaction system of claim 28, wherein the reaction system contains 0.25 to 2.5% by weight a polysiloxane-polyether surfactant, relative to the total weight of the reaction system. 37. A viscoelastic polyurethane cellular thermoset material prepared from the reaction system of claim 28. 38. The viscoelastic polyurethane cellular thermoset material of claim 37, wherein the foaming agent consists of water optionally in combination with one or more dissolved or dispersed atmospheric gases.