Method for preparing nylon microspheres and nylon microspheres prepared thereby

1. A method for preparing nylon microspheres, wherein the method includes steps (1), (2) and (3) or steps (1′), (2) and (3) as follows:

(1) dispersing a radically polymerizable monomer in a molten lactam monomer, and adding a free radical initiator, so that radical polymerization of the radically polymerizable monomer is carried out, to give a mixture of a free radical polymer and the lactam monomer; or

(1′) providing a mixture of a free radical polymer and a molten lactam monomer; and

(2) adding an initiator and an activator, used for anionic ring-opening polymerization of the lactam monomer, to the mixture obtained in step (1) wherein the remaining radically polymerizable monomer and water are removed, or to the mixture obtained in step (1′), so that the anionic ring-opening polymerization of the lactam is carried out to give a polymer alloy of the free radical polymer/polyamide; and

(3) removing the free radical polymer in the polymer alloy obtained in step (2) by dissolution, giving nylon microspheres.

2. A method as described in claim 1 , wherein the free radical polymer can be dissolved in the lactam monomer; and the radically polymerizable monomer is one or more of those selected from the monomers from which the free radical polymer can be formed and be soluble in the lactam monomer.

3. A method as described in claim 1 , wherein in step (1), the amount of the radically polymerizable monomer used is 5-80 weight % based on the total weight of the radically polymerizable monomer and the lactam monomer; and in step (1′), the amount of the free radical polymer used is 5-80 weight % based on the total weight of the free radical polymer and the lactam monomer.

4. A method as described in claim 1 , wherein the lactam monomer is one or more of those selected from C 4 -C 12 lactam, in which case when the lactam is of one type, the polyamide is a homopolymer thereof, and when the lactam is of two or more types, the polyamide is a co-polymer thereof.

5. A method as described in claim 1 , wherein the free radical polymerization in step (1) is carried out at 60-150° C.; and/or

the anionic ring-opening polymerization in step (2) is carried out at 120-250° C.; and/or

the anionic ring-opening polymerization process of the lactam monomer is selected from static casting process or reactive extrusion process.

6. A method as described in claim 1 , wherein in step (1), the free radical initiator is one or more of those selected from the group consisting of azo initiators, organic peroxides initiators and oil soluble redox initiation systems, wherein the content of the free radical initiator is 0.05-5 weight % based on the total weight of the radically polymerizable monomer and the lactam monomer; and/or

in step (2), the initiator is one or more of those selected from the group consisting of lactam metal compounds, alkali metals, alkali metal hydrides, alkali metal hydroxides, alkali alkoxides and alkaline carbonates; and the activator is one or more of those selected from the group consisting of substituted or unsubstituted isocyanates, acetyl caprolactam, acyl chlorides and anhydrides.

7. A method as described in claim 1 , wherein the particle size of the nylon microspheres is controlled by tailoring the ratio of the free radical polymer to the lactam monomer.

8. A method as described in claim 1 , wherein the free radical polymer removed by way of dissolution in step (3) is recycled and combined with the molten lactam monomer, providing a mixture of the free radical polymer and the lactam monomer as defined in step (1′), so that microspheres can be prepared by sequentially carrying out steps (2) and (3).