Silicon-based polycarbonates

1. A polyurethane elastomeric composition which includes a silicon-based polycarbonate segment of the formula (Ib):

wherein

R 1 , R 2 , R 3 and R 4 , are the same or different and are hydrogen or an optionally substituted straight chain, branched or cyclic, saturated or unsaturated hydrocarbon radical;

R 5 , R 6 , R 8 and R 9 are the same or different and are a straight chain, branched or cyclic, saturated or unsaturated hydrocarbon radical;

R 7 is a divalent linking group or an optionally substituted straight chain, branched or cyclic, saturated or unsaturated, hydrocarbon radical;

n, y and z are integers of 0 or more; and

x is an integer of 0 or more; provided that z is an integer of 1 or more.

2. A polyurethane elastomeric composition comprising a reaction product of:

wherein

R 1 , R 2 , R 3 and R 4 , are the same or different and are hydrogen or an optionally substituted straight chain, branched or cyclic, saturated or unsaturated hydrocarbon radical;

R 5 , R 6 , R 8 and R 9 are the same or different and are a straight chain, branched or cyclic, saturated or unsaturated hydrocarbon radical;

R 7 is a divalent linking group O, S, NR wherein R is hydrogen or an optionally substituted straight chain, branched or cyclic, saturated or unsaturated, hydrocarbon radical, or an optionally substituted straight chain, branched or cyclic, saturated or unsaturated hydrocarbon radical;

A is an endcapping group;

n, y and z are integers of 0 or more; and

x is an integer of 0 or more; provided that z is an integer of 1 or more;

(ii) a diisocyanate; and

(iii) a chain extender.

3. The polyurethane elastomeric composition as claimed in claim 2 wherein the diisocyanate is selected from 4,4′-methylenediphenyl diisocyanate (MDI), methylene bis (cyclohexyl) diisocyanate (H12MDI), p-phenylene diisocyanate (p-PDI), trans-cyclohexane-1,4-diisocyanate (CHDI) or a mixture of the cis and trans isomers, 1,6-hexamethylene diisocyanate (DICH), 2,4-toluene diisocyanate (2,4-TDI) or its isomers or mixtures thereof; p-tetramethylxylene diisocyanate (p-TMXDI) and m-tetramethylxylene diisocyanate (m-TMXDI).

4. The polyurethane elastomeric composition as claimed in claim 2 wherein the chain extender is selected from 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol 1,4-cyclohexane dimethanol, p-xyleneglycol, 1,4-bis (2-hydroxyethoxy) benzene and 1,12-dodecanediol.

5. A polyurethane elastomeric composition comprising a reaction product of:

(i) a silicon based polycarbonate of the formula (Ia):

wherein R 1 R 2 , R 3 and R 4 are methyl; R 8 is ethyl; R 9 is hexyl; R 5 and R 6 are propyl or butyl; R 7 is O or —CH 2 —CH 2 —; and

n, x and y are integers of 0 or more;

provided z is an integer of 1 or more;

(ii) 4,4′-methylenediphenyl diisocyanate; and

(iii) 1,4-butanediol.

6. A material having improved mechanical properties, clarity, processability and/or degradation resistance comprising a polyurethane elastomeric composition which includes a polycarbonate segment of the formula (Ib) as defined in claim 1 .

7. Medical devices, articles or implants which are composed wholly or partly of the polyurethane elastomeric composition defined in claim 1 .

8. Medical devices, articles or implants of claim 7 wherein said medical devices, articles or implants are cardiac pacemakers, defibrillators, catheters, heart valves, cardiac assist devices, vascular grafts or implantable prostheses.

9. A material having improved mechanical properties; clarity, processability and/or degradation resistance comprising a polyurethane elastomeric composition as defined in claim 1 .

10. Medical devices, articles, or implants of claim 7 wherein said medical devices, articles, or implants are cannulas, extra-corporeal devices, artificial organs, pacemaker leads, defibrillator leads, blood pumps, balloon pumps, A-V shunts, biosensors, membranes for cell encapsulation, drug delivery devices, wound dressings, artificial joints, orthopaedic implants, or soft tissue replacements.

11. A device or article which is composed wholly or partly of the polyurethane elastomeric composition as defined in claim 1 .

12. A device or article according to claim 11 which is selected from artificial leather, shoe soles, cable sheathing, varnishes, coatings, structural components for pumps or vehicles, mining ore screens, conveyor belts, laminating compounds, textiles, separation membranes, sealants, and adhesive components.