Softening non-swelling polyurethane

DETAILED DESCRIPTION While this invention is satisfied by embodiments in many different forms, there will herein be described in detail preferred embodiments of the invention, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to limit the invention to the embodiments described.
The scope of the invention will be measured by the appended claims and their equivalents.
In accordance with the present invention, a radiation stable, melt processable polyurethane having a desirable ratio of stiffness when dry and softness without swelling when wet is achieved in a catalyst free process using a mixture of nonhydrophilic soft segment polyols and a mixture of chain extenders.
The polyurethanes are useful for medical device components such as catheters, adapters, intravenous tubing, needle hubs, lancets and the like.
Polyisocyanates useful in the present invention are aliphatic or alicyclic isocyanates.
Representative of suitable isocyanates are aliphatiac diisocyanates such as 1,6-hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMDI) and 1,10d-ecamethylene diisocyanate.
Preferred isocyanates are alicyclic diisocyanates such as isophorone diisocyanate.
The most preferred isocyanate is HMDI.
Stiffness, softness and swelling may be controlled by the choice of the soft segment material and the ratio of soft segment to hard segment.
The soft segment preferably is substantially non-hydrophilic since any appreciable water absorption causes swelling.
In the present disclosure, the term non-hydrophilic means 30% or less, preferably 15% or less by weight water absorption.
Suitable soft segments of the polyurethanes of the instant invention may be a non-hydrophilic polycarbonate, polyester, polyether or silicone glycol having a molecular weight of 500 to 8000.
Preferred polyglycols are substantially non-hydrophilic polyether glycols.
The preferred polyetherglycol for the soft segment is PTMEG having a molecular weight of 500 to 3000