Cross-linkable polymer composition
The invention pertains to a polymer obtainable from the steps: polymerizing a mixture, that is substantially free or organic solvents, of ethylenically unsaturated monomers which consist for at least 70% of methacrylates, and which comprises specific chain transfer agents, α-methylstyrene dimer being preferred, to form a first polymer, aqueous emulsion polymerizing a mixture comprising ethylenically unsaturated monomers in the presence of the first polymer to form a dispersion of a water-insoluble second polymer, wherein these steps are preferably performed in the absence or the substantial absence of a surfactant.
1. A polymerization process which includes the steps of:
(a) polymerizing a mixture of ethylenically unsaturated monomers, at least 70% of all ethylenically unsaturated bonds of the monomers being of a methacrylic nature, in the presence of one or more chain transfer agents of the formula,
wherein R 1 and, if present, each R 2 are, independently, the same or different and selected from conventional radical stabilizing groups, n is, on average, 0-10, said chain transfer angents being substantially free of cobalt chelate complexes, to form a first polymer with unsaturated carbon-carbon end groups, said first polymer being essentially free of organic solvents and said monomers being selected such that the first polymer is water-soluble or water-dispersible; and
(b) aqueous emulsion polymerizing a mixture comprising ethylenically unsaturated monomers in the presence of the first polymer and in the substantial absence of surfactant to form a dispersion of a water-insoluble second polymer.
2. The process of claim 1 wherein at least one chain transfer agent is an α-methylstyrene dimer.
3. The process of claim 1 wherein step (a) and step (b) are each performed in the absence or substantial absence of surfactants.
4. The process of claim 1 wherein one or more of the monomers of steps (a) and/or (b) comprise cross-linkable groups.
5. The process of claim 4 wherein the cross-linkable groups are selected from the group consisting of acid groups or hydroxy groups.
6. The process of claim 4 wherein the monomer comprising cross-linkable groups is present in step (a).
7. The process of claim 6 wherein the monomer is selected from the group consisting of methacrylic acid or acrylic acid.
8. The process of claim 1 wherein the weight of the first polymer is between about 5%-60% of the weight of the water-insoluble second polymer.
9. The process of claim 1 comprising a third step (c) wherein a cross-linking compound is added to the dispersion of step (b).