Provided is a polyamide composition including a linear and high molecular weight polyamide and having a low residual monomer content. The composition includes a polyamide having a site formed of repeating structural units having at least one alkylene group and at least one amide bond, each of the at least one alkylene group having a carbon number of 1 to 3, the polyamide having a linear structure with a weight average molecular weight of 200000 or greater, and the content of the included raw material monomer, which is a raw material of the structural units, being less than 1000 ppm.

Provided is a polyamide composition including a linear and high molecular weight polyamide and having a low residual monomer content. The composition includes a polyamide having a site formed of repeating structural units having at least one alkylene group and at least one amide bond, each of the at least one alkylene group having a carbon number of 1 to 3, the polyamide having a linear structure with a weight average molecular weight of 200000 or greater, and the content of the included raw material monomer, which is a raw material of the structural units, being less than 1000 ppm.

A method for producing a polyamide-4 particle that includes polymerizing 2-pyrrolidone in an aprotic solvent incompatible with 2-pyrrolidone in the presence of a polymerization initiator and a 2-pyrrolidone lithium salt or polymerizing 2-pyrrolidone in an aprotic solvent incompatible with 2-pyrrolidone in the presence of a polymerization initiator, a 2-pyrrolidone lithium salt and a 2-pyrrolidone sodium salt. A volume average particle size of the resulting polyamide-4 particle is 1 m to 100 m, and a molecular weight distribution (Mw/Mn) of the polyamide-4 particle is 1.0 to 5.0.

A method for producing a polyamide-4 particle that includes polymerizing 2-pyrrolidone in an aprotic solvent incompatible with 2-pyrrolidone in the presence of a polymerization initiator and a 2-pyrrolidone lithium salt or polymerizing 2-pyrrolidone in an aprotic solvent incompatible with 2-pyrrolidone in the presence of a polymerization initiator, a 2-pyrrolidone lithium salt and a 2-pyrrolidone sodium salt. A volume average particle size of the resulting polyamide-4 particle is 1 m to 100 m, and a molecular weight distribution (Mw/Mn) of the polyamide-4 particle is 1.0 to 5.0.

The present invention is to provide a spherical polyamide fine particle having smooth sliding properties and causing a low degree of environmental pollution. The polyamide fine particle according to the present invention includes: a polyamide including a repetition of a structural unit having at least one alkylene group and at least one amide bond, each of the at least one alkylene group having from 1 to 5 carbon atoms, wherein the polyamide fine particle has a sphericity of 80 or greater.

The present invention is to provide a spherical polyamide fine particle having smooth sliding properties and causing a low degree of environmental pollution. The polyamide fine particle according to the present invention includes: a polyamide including a repetition of a structural unit having at least one alkylene group and at least one amide bond, each of the at least one alkylene group having from 1 to 5 carbon atoms, wherein the polyamide fine particle has a sphericity of 80 or greater.

Polyamide fine particles include a polymer or a copolymer including a repeating structure unit represented by Formula (1) as a main component, wherein a ratio (r/A.sub.BET) of a porosity r occupying a particle surface and a BET specific surface area A.sub.BET that is a specific surface area of the particle surface measured by a BET method is 6.0 or more and 100.0 or less:

##STR00001##

wherein x is an integer of 2 or more and 3 or less.

Polyamide fine particles include a polymer or a copolymer including a repeating structure unit represented by Formula (1) as a main component, wherein a ratio (r/A.sub.BET) of a porosity r occupying a particle surface and a BET specific surface area A.sub.BET that is a specific surface area of the particle surface measured by a BET method is 6.0 or more and 100.0 or less:

##STR00001##

wherein x is an integer of 2 or more and 3 or less.

Provided are non-spherical polyamide particles having small variations in particle shape. The polyamide particles include a polyamide including repeating structural units having at least one alkylene group and at least one amide bond, wherein each of the at least one alkylene group has 1 to 3 carbon atoms. The main shape of the particles is a non-spherical shape with a circularity of less than 0.98, and a coefficient of variation (CV) of the circularity distribution is 30% or less.

[Chemical Formula 1]
Formula (1)
[Chemical Formula 2]
Formula (2)
(Equation 1)

Sphericity=[((short diameter/long diameter))/n]100(4)

Provided are non-spherical polyamide particles having small variations in particle shape. The polyamide particles include a polyamide including repeating structural units having at least one alkylene group and at least one amide bond, wherein each of the at least one alkylene group has 1 to 3 carbon atoms. The main shape of the particles is a non-spherical shape with a circularity of less than 0.98, and a coefficient of variation (CV) of the circularity distribution is 30% or less.

[Chemical Formula 1]
Formula (1)
[Chemical Formula 2]
Formula (2)
(Equation 1)

Sphericity=[((short diameter/long diameter))/n]100(4)