Aqueous solution of polymer having upper critical solution temperature, aqueous dispersion of particle modified with the polymer and method of storing the same
It is intended to provide an aqueous solution of a thermoresponsive polymer and an aqueous dispersion of a thermoresponsive particle, which show an upper critical solution temperature (UCST) and are capable of maintaining a dissolved state and a dispersed state, respectively, even if they are stored for a long period of time at a temperature at which a ligand such as an antibody or an antigen is not inactivated. A UCST lowering agent is incorporated in a predetermined amount in an aqueous solution of a thermoresponsive polymer which shows a UCST in a state of containing water or an aqueous dispersion of a thermoresponsive particle containing the polymer, thereby lowering the UCST of the aqueous solution or aqueous dispersion to less than the storage temperature, and the resulting aqueous solution or aqueous dispersion is stored.
1. A method of storing a thermoresponsive particle in a state of an aqueous dispersion, wherein the aqueous dispersion of the thermoresponsive particle containing a thermoresponsive particle, having a carrier particle and a thermoresponsive polymer carried on the carrier particle, is stored at a storage temperature, said storage temperature is less than an upper critical solution temperature, and the thermoresponsive particle has said upper critical solution temperature due to the thermoresponsive polymer according to a composition of the aqueous dispersion,
the method comprises the step of adding to the aqueous dispersion an upper critical solution temperature lowering agent, which lowers the upper critical solution temperature, in an amount so that the upper critical solution temperature is lowered to less than the storage temperature, to lower the upper critical solution temperature to less than the storage temperature.
2. The storage method according to claim 1 , wherein the carrier particle is a magnetic particle.
3. The storage method according to claim 2 , wherein the particle size of the thermoresponsive particle is from 50 to 200 nm.
4. The storage method according to claim 2 , wherein the thermoresponsive particle further has a ligand carried on the thermoresponsive polymer.
5. The storage method according to claim 1 , wherein the thermoresponsive polymer is a polymer obtained by polymerization or copolymerization of a monomer containing one or both of N-acryloylglycinamide and N-acryloylasparaginamide as a principal component.
6. The storage method according to claim 5 , wherein the thermoresponsive polymer is a polymer obtained by polymerization or copolymerization of a monomer containing 90% by mole or more in total of one or both of N-acryloylglycinamide and N-acryloylasparaginamide.
7. The storage method according to claim 1 , wherein the storage temperature is from 2 to 6° C.
8. The storage method according to claim 7 , wherein the upper critical solution temperature lowering agent is sodium chloride, sodium nitrate, magnesium sulfate, lithium chloride or dimethyl sulfoxide.
9. The storage method according to claim 8 , wherein the upper critical solution temperature lowering agent is sodium chloride, sodium nitrate, magnesium sulfate or lithium chloride, and is added to the aqueous solution or aqueous dispersion at a concentration of 1,000 mM or more.
10. The storage method according to claim 8 , wherein the upper critical solution temperature lowering agent is sodium chloride, sodium nitrate or magnesium sulfate, and is added to the aqueous solution or aqueous dispersion at a concentration of 450 mM or more.
11. The storage method according to claim 8 , wherein the upper critical solution temperature lowering agent is dimethyl sulfoxide, and is added to the aqueous solution or aqueous dispersion at a concentration of 60% by volume or more.