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...
Reexamination Certificate
1999-06-08
2001-04-03
Gorr, Rachel (Department: 1711)
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...
C528S075000, C525S123000, C525S130000, C525S131000
Reexamination Certificate
active
06211324
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydrophobic polyurethane elastomer prepared by combining a polybutadiene diol and a diisocyanate to form an isocyanate terminated prepolymer and chain extending the prepolymer with an asymmetric diol.
BACKGROUND OF THE INVENTION
It is well known to prepare isocyanate terminated polyurethane prepolymers from polyether and or polyester polyols and aromatic diisocyanates. Furthermore, it is also well known to prepare polyurethane elastomers by chain extending these prepolymers with low molecular weight diols. The resulting polyurethanes have excellent mechanical properties, but are rather hydrophilic, which can limit their utility in certain moisture sensitive applications.
Hydroxyl terminated polyols with very non-polar backbones (e.g., hydroxyl functional polybutadiene) can be used to introduce hydrophobicity into polyurethane elastomers. However, the mechanical properties of the resulting polyurethane elastomers are generally rather poor when they are prepared using the conventional diisocyanates and diol chain extenders. In particular, they suffer from poor tear strengths and low elongation at break. In addition, the elastomers are opaque. This combination of properties limits their utility in applications requiring optical clarity or good resistance to tearing.
The modest mechanical properties of the polybutadiene containing polyurethane elastomers are probably at least partially due to the high functionality of the commercially available polybutadiene polyols (2.2 to 2.8 functional). In contrast, the polyether or polyester polyols used to make polyurethane elastomers with excellent mechanical properties generally have functionalities very near 2.0.
Hydroxy-terminated polybutadienes having a functionality of 2.0 are disclosed in Chung, et al. (U.S. Pat. No. 5,247,023), Grubbs, et al. (U.S. Pat. No. 5,750,815) and Nubel, et al. (U.S. Pat. Nos. 5,512,635, 5,559,190, 5,519,101 and 5,403,904). These diols, when formulated into polyurethane systems, may offer the opportunity to produce hydrophobic polyurethane elastomers with improved mechanical properties over the current state of the art.
SUMMARY OF THE INVENTION
The present invention relates to a hydrophobic polyurethane elastomer comprising:
A) An isocyanate terminated prepolymer comprising:
i) from about 30 to 90 percent by weight of an OH terminated homopolymer of butadiene having a molecular weight ranging from 1000 to 4000 and an OH functionality of from 1.9 to 2.1;
ii) from about 10 to 70 percent by weight of an isocyanate.
B) An asymmetric diol chain extender having a molecular weight ranging from 75 to 200.
Surprisingly, it was determined that with the hydroxy terminated polybutadiene described above, an asymmetric diol chain extender (e.g., 2,2,4-trimethylpentane-1,3-diol) was necessary to produce elastomeric materials. In addition, these elastomers were optically clear and showed dramatic improvement in tear strength and elongation at break over conventional polybutadiene based elastomers.
REFERENCES:
patent: 5247023 (1993-09-01), Chung et al.
patent: 5403904 (1995-04-01), Nubel et al.
patent: 5512635 (1996-04-01), Nubel et al.
patent: 5519101 (1996-05-01), Nubel et al.
patent: 5559190 (1996-09-01), Nubel et al.
patent: 5750815 (1998-05-01), Grubbs et al.
patent: 5925724 (1999-07-01), Cenens et al.
Saunders & Frisch; Polyurethanes; Part I; p. 311, 1962.
Chan Jack C.
Franz Uli W.
Haider Karl W.
Jonsson E. Haakan
Bayer Corporation
Brown N. Denise
Cheung Noland J.
Gil Joseph C.
Gorr Rachel
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