Polysiloxane block copolymer rubber and process for making same

Claim 1

A PROCESS FOR PREPARING A SILOXANE BLOCK COPOLYMER WHICH COMPRISES (A) MIXING AND HEATING IN AN INERT ORGANIC SOLVENT TO PRODUCE A HEAT-CURABLE SILOXANE BLOCK COPOLYMER (1) 100 PARTS BY WEIGHT OF AN ORGANOPOLYSILOXANE WHICH HAS AN AVERAGE OF AT LEAST 200 SILICON ATOMS PER MOLECULE, SAID SILOXANE CONSISTING ESSENTIALLY OF UNITS OF THE FORMULA RNSIO1-N/2, WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF METHYL, PHENYL AND VINYL RADICALS, N HAS AN AVERAGE VALUE OF FROM 1.98 TO 2.00 INCLUSIVE, THERE BEING AN AVERAGE OF AT LEAST 0.75 METHYL RADICALS PER SILICON ATOM AND AN AVERAGE OF NO MORE THAN 0.15 VINYL RADICAL PER SILICON ATOM IN SAID SILOXANE, NO MORE THAN 50 MOL PERCENT OF SAID SILOXANE BEING (C6H5)2SIO UNITS, SAID SILOXAND HAVING AN AVERAGE OF AT LEAST 2 SILICONBONDED HYDROXYL RADICALS PER MOLECULE, (2) FROM 8 TO 220 PARTS BY WEIGHT OF AN ORGANOSILICON COMPOUND SELECTED FROM THE GROUP CONSISTING OF (A) A SILOXANE REPRESENTED BY THE UNIT FORMULA (C6H5)XR''YSIO4-X-Y/2, WHEREIN R'' IS A MONOVALENT HYDROCARBON RADICAL, X HAS AN AVERAGE VALUE OF FROM 0.65 TO 1.3 INCLUSIVE, Y HAS AN AVERAGE VALUE OF LESS THAN 0.4 AND THE SUM OF X+Y IS FROM 0.95 TO 1.3 INCLUSIVE WITH AT LEAST 60 MOL PERCENT OF SAID SILOXANE BEING (C6H5)SIO1.5 UNITS, SAID SILOXANE CONTAINING AN AVERAGE OF AT LEAST TWO RADICALS PER MOLECULE WHICH ARE SELECTED FROM THE GROUP CONSISTING OF HYDROXYL AND -OM RADICALS WHEREIN M IS SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL ATOMS AND QUATERNARY AMMONIUM RADICALS, (B) A SILANOL OF THE GENERAL FORMULA (C6H5)AR''BSI(OH)4-A-B WHEREIN R'' IS A MONOVALENT HYDROCARBON RADICAL, A HAS AN AVERAGE VALUE OF FROM 0.65 TO 1.3, B HAS AN AVERAGE VALUE OF LESS THAN 0.4, AND THE SUM OF A+B IS FROM 1 TO 1.3 INCLUSIVE, AT LEAST 60 MOL PERCENT OF SAID SILANOL BEING OF THE FORMULA (C6H5)SI(OH)3, (3) A CATALYTIC AMOUNT OF A CATALYST FOR THE CONDENSATION OF SILICON-BONDED HYDROXYL RADICALS, THE CONCENTRATION OF SOLIDS IN THE SOLVENT BEING LESS THAN 50 PERCENT BY WEIGHT BASED ON THE TOTAL WEIGHT OF THE MIXTURE SUCH THAT NO APPRECIAB LE GELATION OCCURS DURING THE HEATING STEP, (B) AND REMOVING THE SOLVENT FROM THE REACTION PRODUCT OBTAINED IN STEP (A), THERE BEING SUFFICIENT AGITATION DURING THIS STEP TO KEEP THE PRODUCT SUBSTANTIALLY HOMOGENEOUS.