Urethane prepolymer and polyurethane compositions comprising the

Details Urethane prepolymer and polyurethane compositions comprising the Urethane prepolymer and polyurethane compositions comprising the

1992-04-07

1993-07-13

Welsh, Maurice J.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

528 60, 528 65, C08G 1810

Patent

active

052274519

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a urethane prepolymer used for preparing a paint, coating agent, adhesive, or the like, and also to a polyurethane composition prepared by using such a prepolymer, in particular a paint, a coating agent or an adhesive.
A two-pack urethane paint, coating agent, or adhesive is a two-component system comprising a urethane prepolymer having isocyanate groups, and a polyol. There are known two major classes of urethane prepolymers having isocyanate groups, i.e. (1) adducts obtained by reacting polyhydric alcohols such as trimethylolpropane, or water with di-isocyanates, and (2) isocyanurates obtained by the cyclic trimerization of di-isocyanates by catalysts. These urethane prepolymers generally contain not more than three isocyanate groups in a molecule on average. The urethane prepolymers give polyurethane compositions if mixed with polyols, etc. The polyurethane compositions are hardened by urethane reaction (crosslinking) to exhibit such physical properties as desired. There is a need for polyurethane compositions which can be hardened at a higher rate and exhibit better physical properties when hardened.
Processes including preparing multifunctional urethane prepolymers are known as one of the approaches to the manufacture of polyurethane compositions giving excellent physical properties when hardened. It has, for example, been proposed that pentaerythritol containing four functional groups, dipentaerythritol containing six functional groups, or sucrose containing eight functional groups be used as the polyhydric alcohol feedstock, and be reacted directly with a di-isocyanate to prepare a urethane prepolymer containing four to eight isocyanate groups per molecule. These polyhydric alcohols have, however, been difficult to react uniformly with di-isocyanates, since their compatibility with di-isocyanates is low and their melting points are high. Therefore, attempts have been made to react di-isocyanates with polyols prepared by the addition reaction of polyhydric alcohols with alkylene oxides to improve the compatibility of polyhydric alcohols with di-isocyanates. The polyhydric alcohols have, however, been difficult to react directly with alkylene oxides, since they have high melting points and have low solubility. It has, therefore, been usual practice to use alkylene oxides diluted with glycerol, water, or the like. It has been possible, however, to obtain only an adduct of low purity and it has been difficult to prepare satisfactory urethane prepolymers, since the reaction of di-isocyanates with any such adduct has resulted in the formation of a gel, or a product having too few functional groups.
U.S. Pat. Nos. 2,778,885; and 3,291,865 and Japanese Patent Application Laid-Open No. 51-93995 disclose processes for manufacturing polyols by reacting erythritol with epoxy compounds, such as alkylene oxides. U.S. Pat. No. 2,778,855, however, describes only a process for manufacturing polyols and does not contain any disclosure of the specific use of these polyols. U.S. Pat. No. 3,291,865 does suggest the application of polyols to the manufacture of polyurethanes, etc., but does not describe any specific example of such an application. Japanese Patent Application Laid Open No. 51-93995 describes a process for manufacturing urethane foams from polyols directly in a single step, but does not disclose any process for reacting polyols with di-isocyanates to prepare urethane prepolymers. It does not teach any use of polyols for purposes other than the manufacture of foams, either.
There is known a polyether polyol prepared by adding propylene oxide to ethylenediamine and containing four functional groups. This polyol, however, is likely to form a gel as a result of a side reaction during the synthesis of a prepolymer, since it contains tertiary nitrogen. The polyurethane composition manufactured using this polyol is easily degraded by oxidation, is undesirably colored, and is unstable to heat.
Other possible polyhydric alcohols include condensation polyester polyols having low molecular we

REFERENCES:
patent: 3049513 (1962-08-01), Damusis et al.
patent: 3846347 (1974-11-01), Satterly
Chemical Abstracts, AN 82787W, vol. 114, No. 10, Mar. 1991, p. 17, & JP-A-02206612, Tsushimo, et al., "Manufacture of Isocyanate-Terminated Urethane Prepolymers".
World Patents Index Latest, Derwent Publications, Ltd., AN 90-294054, & JP-A-02 206 612, Aug. 16, 1990, "Urethane Prepolymers Prodn.--By Reacting Propylene Oxide and Ethylene Oxide With Mesoerythritol--And Relating Prod. With Di:Isocyanate".

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