Test solvent for evaluating the compatibility of biologically active substances and graft copolymers

1. A liquid mixture, comprising

(a) at least one compound selected from polyols, polyol ethers wherein at least one hydroxyl group is unetherified, or polyalkylene ethers wherein at least one terminal hydroxyl group is unetherified,

(b) 1,3-bis(caprolactam-1-yl) butane, and

(c) diacetoxybutane,

wherein the liquid mixture is non-aqueous and components (a), (b) and (c) are present in a weight ratio of [a]:[b]:[c] and [a] is 3-23, [b] is 47-67 and [c] is 20-40.

2. The mixture according to claim 1 , wherein component (a) is selected from ethylene glycol, propylene glycol, glycerol, 2-methoxyethanol, 2-ethoxyethanolpoly-(ethylene glycols) having a weight-average molecular mass of from 200 to 400, and poly(ethylene glycol) monoethers having a weight-average molecular mass of from 200 to 400.

3. The mixture according to claim 1 , wherein component (c) is 1,4-diacetoxybutane.

4. The mixture according to claim 1 , wherein components (a), (b) and (c) are present in a weight ratio of [a]:[b]:[c] and [a] is 8-18, [b] is 52-62 and [c] is 25-35.

5. The mixture according to claim 1 , additionally comprising at least one formulation auxiliary.

6. A method for evaluating the compatibility of a biologically active substance with a graft copolymer comprising a poly(ethylene glycol) backbone and a vinyl acetate/N-vinylcaprolactam copolymer grafted onto the backbone; the method comprising

i. bringing the biologically active substance into contact with a non-aqueous liquid mixture according to claim 1 to provide a non-aqueous test system, and

ii. determining the phase behavior of the non-aqueous test system and/or the solubility of the biologically active substance in the non-aqueous mixture.

7. The method according to claim 6 , wherein the graft copolymer comprises a weight proportion XPEG of poly(ethylene glycol) moieties, a weight proportion xVc of N-vinylcaprolactam moieties and a weight proportion XVA of vinyl acetate moieties, and the liquid mixture comprises a weight proportion of XPEG±5% of component (a), a weight proportion of xVc±5% of component (b), and a weight proportion of XVA±5% of component (c).

8. The method according to claim 6 , wherein the phase behavior of the test system is analyzed visually, spectroscopically and/or by thermal analysis.

9. The method according to claim 6 , wherein the test system is heated to a temperature of up to 200° C.

10. The method according to claim 9 , wherein the test system is heated to a temperature of up to 70° C.

11. The method according to claim 6 , wherein the test system comprises 10 to 70 percent by weight of the biologically active substance.

12. The method according to claim 6 , further comprising

i) providing a plurality of non-aqueous test systems with stepwise increasing amounts of the biologically active substance, relative to the amount of the liquid mixture, and

ii) determining the maximum amount of the biologically active substance resulting in a one-phase test system.

13. The method according to claim 6 , further comprising

i) bringing a sufficient amount of the biologically active substance into contact with the liquid mixture such that the biologically active substance dissolves incompletely in the liquid mixture to provide a two-phase test system comprised of a biologically active substance bottom and a supernatant, and

ii) determining the concentration of the biologically active substance in the supernatant.