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US-20260125506-A1 - LOW FREE POLYURETHANE PREPOLYMER COMPOSITION

US20260125506A1US 20260125506 A1US20260125506 A1US 20260125506A1US-20260125506-A1

Abstract

A polyurethane prepolymer composition may include: (a) a polyurethane prepolymer comprising, as a reaction product, (a1) an excess of diisocyanate and (a2) a polyol; and (b) free diisocyanate monomer in a range of from more than 0 to less than 1.0 wt. %, based on total polyurethane prepolymer weight. The NCO content of the polyurethane prepolymer may be in a range of from 0.2 to 15 wt. %. The polyurethane prepolymer may include less than 75 wt. % of a 2:1 stoichiometric adduct of the diisocyanate and the polyol, based on the total polyurethane prepolymer weight. The polyol (a2) may include two polypropylene glycols with different molecular weights.

Inventors

  • Ronald M. Emanuel
  • Polina Ware
  • Gerald King

Assignees

  • URETHANE SYSTEMS USA LLC

Dates

Publication Date
20260507
Application Date
20251215

Claims (19)

  1. 1 . A polyurethane prepolymer composition, comprising: (a) a polyurethane prepolymer comprising, as a reaction product, (a1) an excess of diisocyanate and (a2) a polyol; and (b) free diisocyanate monomer in a range of from more than 0 to less than 1.0 wt. %, based on total polyurethane prepolymer weight, wherein the polyurethane prepolymer (a) has an NCO content in a range of from 0.2 to 15 wt. %, wherein the polyurethane prepolymer (a) comprises less than 75 wt. % of a 2:1 stoichiometric adduct of the diisocyanate (a1) and the polyol (a2), based on the total polyurethane prepolymer weight, wherein the polyol (a2) comprises (a2a) a first polypropylene glycol and (a2b) a second polypropylene glycol, wherein the first polypropylene glycol (a2a) has a different molecular weight from the second polypropylene glycol (a2b).
  2. 2 . The polyurethane prepolymer composition of claim 1 , wherein the first polypropylene glycol (a2a) has a weight average molecular weight Mw in a range of from 200 to 800 g/mol, and wherein the second polypropylene glycol (a2a) has a weight average molecular weight Mw of 800 to 2,000 g/mol.
  3. 3 . The polyurethane prepolymer composition of claim 1 , wherein the diisocyanate (a1) comprises methylene diphenyl diisocyanate, para-phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, cyclohexyl diisocyanate, isophorone diisocyanate, toluene diisocyanate.
  4. 4 . The polyurethane prepolymer composition of claim 1 , wherein the diisocyanate (a1) comprises 4,4′-methylene diphenyl diisocyanate.
  5. 5 . The polyurethane prepolymer composition of claim 1 , wherein the first polypropylene glycol (a2a) has a weight average molecular weight Mw in a range of from 200 to 600 g/mol.
  6. 6 . The polyurethane prepolymer composition of claim 1 , wherein the polyurethane prepolymer (a) comprises the 2:1 stoichiometric adduct in a range of from more than 30 to less than 75 wt. %.
  7. 7 . The polyurethane prepolymer composition of claim 1 , comprising the free diisocyanate monomer (b) in a range of from more than 0 to less than 0.1 wt. %, based on the total polyurethane prepolymer weight.
  8. 8 . A curable polyurethane prepolymer composition, comprising: the polyurethane prepolymer composition of claim 1 ; and a curative, wherein the curative is a diamine, a polyol, or a blend thereof.
  9. 9 . A method for adhesively joining or sealing two substrates, the method comprising: (1) applying onto a substrate the curable polyurethane prepolymer composition of claim 5 ; and (2) contacting the curable polyurethane prepolymer composition applied on the substrate to a second substrate such that a bond is formed.
  10. 10 . An adhesive, comprising: the curable polyurethane prepolymer composition of claim 8 .
  11. 11 . The polyurethane prepolymer composition of claim 1 , comprising the free diisocyanate monomer (b) in a range of from more than 0 to less than 0.5 wt. %.
  12. 12 . The polyurethane prepolymer composition of claim 1 , wherein the NCO content of the polyurethane prepolymer (a) is in a range of from 0.2 to 8 wt. %.
  13. 13 . The polyurethane prepolymer composition of claim 1 , wherein the polyol (a2) has a weight average molecular weight (Mw), determined with gel permeation chromatography (GPC), in a range of from 250 to 4,000 g/mol.
  14. 14 . The polyurethane prepolymer composition according to claim 1 , wherein the weight average molecular weight Mw of the first polypropylene glycol (a2a) is in a range of from 400 to 600 g/mol.
  15. 15 . A curable polyurethane prepolymer composition, comprising: the polyurethane prepolymer composition of claim 1 ; and 1,4-butanediol and/or hydroquinone bis(2-hydroxyethyl) ether.
  16. 16 . The polyurethane prepolymer composition of claim 1 , wherein the polyurethane prepolymer (a) comprises the 2:1 stoichiometric adduct in a range of from more than 30 to 70 wt. %, based on total prepolymer composition weight.
  17. 17 . The polyurethane prepolymer composition of claim 1 , wherein the polyurethane prepolymer (a) comprises the 2:1 stoichiometric adduct in a range of from 35 to 65 wt. %, based on total prepolymer composition weight.
  18. 18 . The polyurethane prepolymer composition of claim 1 , wherein the first polypropylene glycol (a2a) comprises PPG-500.
  19. 19 . The polyurethane prepolymer composition of claim 1 , wherein the first polypropylene glycol (a2a) comprises PPG-500, and wherein the second polypropylene glycol (a2b) comprises PPG-1100.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a continuation of U.S. application Ser. No. 17/642,733, filed Mar. 14, 2022, and published as US 2022/0325028 A1, which was the national stage of international application PCT/US2020/050622, filed on Sep. 14, 2020, claiming the benefit of the filing date of U.S. Prov. Appl. No. 62/899,476, filed on Sep. 12, 2019. The content of each of these applications is incorporated by reference. The present invention relates to a polyurethane prepolymer composition comprising more than 0 wt. % and less than 1.0 wt. % free diisocyanate monomer wherein the polyurethane prepolymer comprise less than 80 wt. % perfect prepolymers, curable compositions comprising these polyurethane prepolymer compositions and the use of these polyurethane prepolymer compositions as adhesives. BACKGROUND OF THE INVENTION Isocyanate terminated polyurethane prepolymers are commonly used to produce polyurethane products like elastomers, foams, coatings, adhesives, sealants, and binders. However, the polyurethane prepolymer manufacturing process typically results in high residual concentrations of the polyisocyanate monomer used in the prepolymer synthesis. The residual polyisocyanate can lead to potential health and safety issues, and may also be detrimental to the performance and attributes of the end use product. For example, residual polyisocyanate can lead to undesired losses in open time, product instability, increased moisture sensitivity and decreased adhesion due to migration of these molecules to the interface. Polyurethane prepolymers that contain low levels of residual diisocyanate of less than 1.0 wt. %, preferably less than 0.1 wt. % based on the total amount of the prepolymer, can reduce health and safety risks and improve end product performance. Since residual polyisocyanate can pose significant health and safety risks as well as reductions in product performance, a number of products and processes have been introduced that offer reduced residual polyisocyanate levels. JP 08-176252 discloses reacting MDI with straight chain molecule with MW 250-4,000 and two active hydrogens at an equivalent ratio (NCO:OH) of 2.5-10:1. Free MDI is vacuum distilled to 1 wt. % or less. The examples show polytetramethylene glycol (PTMEG) and ethylene glycol adipate. U.S. Pat. No. 4,786,703 discloses a process for producing a reaction product comprising a TDI prepolymer, wherein at least about 90% of such prepolymer consists of a prepolymer of two moles TDI per mol long chain diol and the level of unreacted TDI is less than about 0.15%. This document teaches the benefits of high amount of prefect prepolymers of more than 90 wt. %. U.S. Pat. No. 4,888,442 discloses a process for reducing the free monomer content of a polyisocyanate adduct by treating the adduct with 2-30 wt. % inert solvent in an agitated thin-layer evaporator under conditions sufficient to reduce the free monomer content of the polyisocyanate adduct mixture below that level which is obtainable in the absence of a solvent. There are no examples showing the use of MDI as a suitable diisocyanate to prepare the polyisocyanate adduct. U.S. Pat. No. 4,892,920 discloses a process for producing cyclohexanediisocyanate (CHDI) based prepolymers free of unreacted CHDI and essentially free of oligomeric CHDI by-products. U.S. Pat. No. 5,202,001 discloses preparing polyurethane prepolymers having low levels of residual organic diisocyanate. The examples shows prepolymers made from toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and methylene-bis[(4-cyclohexyl)-diisocyanate] (CHDI). U.S. Pat. No. 5,703,193 discloses a process for reducing the amount of residual organic diisocyanate monomer in a polyurethane prepolymer reaction product by distilling in the presence of an inert solvent blend, one with boiling point above the monomer and one with boiling point below. Comparative examples show the removal of MDI monomer from a PTMEG 1000/MDI prepolymer reaction product. U.S. Pat. No. 6,133,415 discloses countercurrent extraction method for making polyurethane prepolymers. The examples show MDI/PTMEG prepolymers processed to give low free MDI. U.S. Pat. No. 6,174,984 discloses a prepolymer of at least one diisocyanate and at least one polyether polyol selected from the group consisting of a homopolymer of ethylene oxide, a homopolymer of propylene oxide, and a copolymer of ethylene oxide and propylene oxide, wherein free diisocyanate has been reduced to a level of less than 1% of the prepolymer. EP 0 827 995 A discloses hot melt adhesives comprising a polyisocyanate prepolymer prepared by reacting a polyisocyanate with a functionality of at least 2 with a polyol with a functionality of at least 2, the reaction product comprising at least 90 wt. % “perfect” prepolymer and less than 2 wt. % unreacted isocyanate monomer and the prepolymer having a free NCO functionality ranging from 0.2 to 8 wt. %. This document teaches the bene