Process for preparing copolymers by anionic solvent-free polymerization
The invention concerns a process for preparing a block or comb copolymer comprising at least one hydrophilic portion and at least two hydrophobic portions, by anionic solvent-free polymerization of a prepolymer selected from a polyethylene glycol and a polyvinyl alcohol, and of a lactone or dilactone monomer. The process is carried out in the presence of an alkaline-earth metal hydride, in an inert atmosphere, and the polymerization step is not carried out under vacuum. The invention also concerns copolymers obtained by this process.
1. A process for preparing a block or comb copolymer comprising at least one hydrophilic portion and at least two hydrophobic portions, said process comprising:
polymerizing a prepolymer selected from the group consisting of a polyethylene glycol and a polyvinyl alcohol, and a lactone monomer or a dilactone monomer by anionic solvent-free polymerization,
wherein said anionic solvent-free polymerization is carried out in the presence of an alkaline-earth metal hydride and in an inert atmosphere, with the proviso that the polymerization step is not carried out under vacuum.
2. The process according to claim 1 , wherein said alkaline-earth metal hydride is selected from the group consisting of calcium hydride CaH 2 and magnesium hydride MgH 2 .
3. The process according to claim 1 , wherein said lactone monomer or dilactone monomer is selected from the group consisting of L-lactide, glycolide, β-butyrolactone, δ-valerolactone and ε-caprolactone.
4. The process according to claim 1 , wherein said inert atmosphere is an argon atmosphere or is a nitrogen atmosphere.
5. The process according to claim 1 , wherein the prepolymer is polyethylene glycol, and the polymerization is carried out at a temperature of 115° C. to 125° C. for a period of 14 to 16 hours.
6. The process according to claim 1 , wherein the prepolymer is polyvinyl alcohol, and the polymerization is carried out at a temperature of 140° C. to 150° C. for a period of 36 to 54 hours.