Method of making vinyl-silicone copolymers using mercapto functional silicone chain-transfer agents and release coatings made therewith

Claim 1

A stack of superimposed sheets of coated sheet material wherein the coated sheet material comprises: (a) a flexible sheet; and (b) a release coating covering at least a portion of one major surface of one side of said flexible sheet wherein said release coating comprises a vinyl-silicone copolymer formed according to the method of: (a) mixing (1) free radically polymerizable monomer mixed, if needed, with sufficient solvent to produce a charge which possesses a net dielectric constant greater than about 2.5, (2) a mercapto functional silicone compound represented by the formula ##STR20## wherein R 1 are monovalent moieties which can independently be the same or different and are selected from the group consisting of alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl, hydrogen, and fluoroalkyl; R 2 can independently be the same or different and are divalent linking groups; R 3 are monovalent moieties which can independently be the same or different and are selected from the group consisting of alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl, hydrogen, and fluoroalkyl; R 4 can independently be the same or different and are divalent lining groups; R 5 are monovalent moieties which can independently be the same or different and are selected from the group consisting of alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl, hydrogen, fluoroalkyl and -ZSH, wherein Z is a divalent linking group; R 6 are monovalent moieties which can independently be the same or different and are selected from the group consisting of alkyl, aryl, alkaryl, alkoxy, alkylamino, ahydroxyl, fluoroalkyl, hydrogen, and -ZSH wherein Z is a divalent linking group; wherein x is an integer of 0 to 3; y is an integer of 10 or greater; q is an integer of 0 to 3; R 5 comprises 0 to y -ZSH moieties; R 6 comprises 0 to y -ZSH moieties; and wherein at least one of the following is true: q is an integer of at least 1: x is an integer of at least 1; R 5 comprises at least one -ZSH moiety; R 6 comprises at least one -ZSH moiety; and (3) an initiator capable of forming free radicals upon being subjected to a means of initiation wherein said free radicals are capable of abstracting the -ZSH hydrogen atoms of the mercapto functional silicone compound to form mercapto functional silicone free radicals, wherein said mercapto functional silicone free radicals are capable of initiating free radical polymerization of said free radically polymerizable monomer to form a graft copolymer or block copolymer represented by the formula ##STR21## wherein G 5 are monovalent moieties which can independently be the same of different selected from the group consisting of alkyl, aryl, alkaryl, alkoxy, alkylamino, fluoroalkyl, hydrogen, and -ZSA; A is a vinyl polymeric segment or block consisting essentially of polymerized free radically polymerized monomer; G 6 are monovalent moieties which can independently be the same or different selected from the group consisting of alkyl, aryl, alkaryl, alkoxy, alkylamino, fluoroalkyl, hydrogen, and -ZSA; G 2 comprises A; G 4 comprises A; and R 1 , R 2 , R 3 , R 4 , x, q, y, and Z are as previously defined; (b) initiating free-radical polymerization; and (c) sustaining said free-radical polymerization until said vinyl-silicone copolymer is produced, wherein A comprises at least about 40 weight percent of copolymer and possesses a Tg or Tm above about -20° C., and wherein a silicone segment of the copolymer has a number average molecular weight above about 1000 and wherein the silicone segment is present at a weight percent great enough to provide said copolymer with a surface release value not greater than about 50 Newtons/dm, wherein the release agent is on one side of the sheet and a pressure sensitive adhesive is on the other side, the pressure-sensitive adhesive on each sheet being in contact with the release agent on an immediately adjacent sheet, and wherein the pressure sensitive adhesive is a normally tacky pressure-sensitive adhesive.