The invention relates to novel crosslinkable copolymers which are obtainable by (a) copolymerizing at least two different hydrophilic monomers selected from the group consisting of N,N-dimethyl acrylamide (DMA), 2-hydroxyethyl acrylate (HEA), glycidyl methacrylate (GMA), N-vinylpyrrolidone (NVP), acrylic acid (AA) and a C 1 -C 4 -alkoxy polyethylene glycol(meth)acrylate having a weight average molecular weight of from 200 to 1500, and at least one crosslinker comprising two or more ethylenically unsaturated double bonds in the presence of a chain transfer agent having a functional group; and (b) reacting one or more functional groups of the resulting copolymer with an organic compound having an ethylenically unsaturated group.
1. A process for manufacturing an actinically crosslinkable prepolymer, comprising:
(1) obtaining a reaction mixture comprising a first hydrophilic monomer, at least one polysiloxane-containing crosslinker, a second hydrophilic monomer, and a chain transfer agent having a first functional group and present in an amount to have a desired initial concentration, wherein the second hydrophilic monomer has a free radical chain reaction slower than that of the first hydrophilic monomer, wherein the first hydrophilic monomer is (C1-C4-alkyl)acrylamide, N,N-di-(C1-C4-alkyl)acrylamide, or mixture thereof;
(2) adjusting the temperature of the reaction mixture in order to start the polymerization reaction;
(3) dosing the chain transfer agent to the reaction mixture at a rate sufficient to have a concentration comparable to the desired initial concentration until a desired total amount of the chain transfer agent is added;
(4) following the completion of the chain transfer agent dosing maintaining the reaction mixture at the reaction temperature in order to complete the reaction so as to obtain a copolymerization product with first functional groups; and
(5) reacting an organic compound with the copolymerization product to form the crosslinkable prepolymer having ethylenically unsaturated groups, wherein the organic compound comprises an ethylenically unsaturated group and a second functional group,
wherein the second functional group of the organic compound reacts with one of the first functional groups of the copolymerization product, wherein said crosslinkable prepolymer can be crosslinked to form a silicone hydrogel material, wherein the silicone hydrogel material having about 10% or less of non-volatile extractables.
2. A process according to claim 1 , wherein the portion of chain transfer agent being present in the initial reaction mixture according to (1) is from 10 to 40% by weight of the total weight of chain transfer agent, and the remaining 60 to 90% by weight are dosed in step (3), wherein the second hydrophilic monomer selected from the group consisting of 2-hydroxyethyl acrylate (HEA), glycidyl methacrylate (GMA), N-vinylpyrrolidone (NVP), acrylic acid (AA), and a C 1 -C 4 -alkoxy polyethylene glycol(meth)acrylate having a weight average molecular weight of from 200 to 1500.
3. A process according to claim 2 , wherein the temperature of the reaction mixture is adjusted to a temperature between 35 to 80° C. in step (2) and is maintained in steps (3) and (4).
4. A process for the manufacture of an actinically crosslinkable or polymerizable prepolymer, comprising:
(a) copolymerizing a polymerizable mixture to obtain a copolymerization product with first functional groups, wherein the polymerizable mixture comprises a first hydrophilic monomer, at least one polysiloxane-containing crosslinker, a chain transfer agent having a first functional group, a second hydrophilic monomer selected from the group consisting of 2-hydroxyethyl acrylate (HEA), glycidyl methacrylate (GMA), N-vinylpyrrolidone (NVP), acrylic acid (AA), and a C 1 -C 4 -alkoxy polyethylene glycol(meth)acrylate having a weight average molecular weight of from 200 to 1500, wherein the second hydrophilic monomer has a free radical chain reaction slower than that of the first hydrophilic monomer, wherein the first hydrophilic monomer is (C1-C4-alkyl)acrylamide, N,N-di-(C1-C4-alkyl)acrylamide, or mixture thereof; and
(b) reacting an organic compound with the copolymerization product to form the crosslinkable prepolymer having ethylenically unsaturated groups, wherein the organic compound comprises an ethylenically unsaturated group and a second functional group, wherein the second functional group of the organic compound reacts with one of the first functional groups of the copolymerization product, wherein the second hydrophilic monomer is present in an amount sufficient to produce the resultant prepolymer which, after purification, can be crosslinked actinically or thermally to form a silicone hydrogel material, wherein the silicone hydrogel material having about 10% or less of non-volatile extractables.