Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1994-01-27
1995-05-23
Welsh, Maurice J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521174, 528 60, 528 66, C08G 1810
Patent
active
054182590
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for preparing a polyurethane elastomer from a "soft-segment" isocyanate-terminated prepolymer.
Elastomeric polyurethane polymer for applications such as, for example, shoe soles desirably exhibits good physical properties including especially abrasion resistance, flexibility and durability. Typically such polymer may be obtained by reaction of a polyester polyol with an isocyanate terminated polyester polyol-based prepolymer in the presence of water or alternatively by reaction of a polyether polyol with a "hard segment" isocyanate terminated polyether polyol-based prepolymer in the presence of a blowing agent consisting predominantly of a physical blowing agent such as, for example, trichlorofluoromethane. The preparation of polyurethane polymer by such procedures is described, for example, in patent publications E.P. 235,888; E.P. 175,733; U.S. Pat. No. 3,591,532; U.S. Pat. No. 3,901,959; U.S. Pat. No. 4,647,596 and U.S. Pat. No. 4,757,095.
Isocyanate-terminated prepolymers obtained from low molecular weight polyols or diols are frequently identified as a "hard-segment" prepolymers in contrast to "soft-segment" prepolymers generally obtained from high molecular weight polyols or diols. The terminology, "hard-" and "soft-segment", derives from the morphology of elastomeric polymers which can contain distinct phase separated regions. Such regions can be detected by thermoanalysis techniques and distinguished by, for example, glass transition temperatures. Generally, soft-segments of the polymer can be considered as having glass transition temperatures below room temperature whilst hard-segments can be considered as having glass transition temperatures above room temperature or even melting points if a crystallite. It is the current opinion and hence their classification that "soft-segment" prepolymers are associated with the formation of the soft-segment phase of the elastomer and conversely hard-segment prepolymers with the hard-segment phase of the elastomer. Structure-property relationships of hard- and soft-segment phases are described for example by Redman in "Developments in Polyurethanes-I" J. M. Buist Ed., Elsevier, London--published 1978. The distinction of the prepolymer type on basis of molecular weight of the polyol used in the preparation of the prepolymer is arbitrary but general such prepolymers obtained from diols or triols having an equivalent weight of about 150 or less are considered to be "hard-segment" prepolymers.
The use of "hard-segment" prepolymers when preparing polyether polyol-based polyurethane polymer, restricts and makes it difficult to substitute or eventually replace all of the physical blowing agent with, for example, water. If water is used as the principal blowing means, the physical properties of the resulting polymer and especially flexibility, abrasion resistance and hardness deteriorate. Additionally, processing becomes noticeably inferior with, for example, increased demold times of molded articles. Due to current environmental concern relating to the earths atmosphere and ozone levels it is highly desirable to substitute certain physical blowing agents with alternative blowing agents. Particularly, it is desirable to contemplate the use of water as an alternative blowing means. It is therefore desirable to develop a new process for the preparation of polyurethane polymers, particularly microcellular elastomeric polyurethane polymers, which allows for the use of water as principal blowing agent. To this purpose we have investigated the use of "soft-segment" prepolymers in the preparation of polyether polyol-based polyurethane polymers.
Use of "soft-segment" prepolymers in the preparation of polyurethane foam is known from patent publications such as, for example, E.P. 22,617 and E.P. 398,304; whilst use of "soft-segment" prepolymers in the preparation of elastomeric polyurethane polymers is disclosed in, for example, the patent publications U.S. Pat. No. 4,190,711; U.S. Pat. No. 4,532,316, U.S. Pat. No. 4,559,366 and U.S. Pat. No.
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Broos Rene
Maccari Bruno
Paap Frans
Dow Italia S.p.A.
The Dow Chemical Company
Welsh Maurice J.
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