Three-dimensional printing

A method of 3D printing comprising:

• iteratively applying individual build material layers of polymer particles to a powder bed, the polymeric particles including a polyalkylene backbone with both ethylene and propylene polymerized monomeric units, wherein from 2 mol % to 15 mol % of the polymerized monomeric units include a grafted side chain having an epoxide moiety;
• based on a 3D object model, selectively jetting a fusing agent onto the individual build material layers, wherein the fusing agent comprises water and a radiation absorber that absorbs electromagnetic energy and converts the electromagnetic energy to heat;
• based on the 3D object model, selectively jetting a hardener onto the individual build material layers to cause epoxide moieties to open and become crosslinked, wherein the hardener is present in the fusing agent or separately jetted onto the individual build material layers as part of a separate hardening agent;
• and
• exposing the powder bed to electromagnetic energy to selectively fuse the polymer particles in contact with the radiation absorber at individual build material layers to form a 3D printed article.

A 3D printing system comprising:

• a powder bed material comprising from about 80 wt % to 100 wt % polymer particles, the polymeric particles including a polyalkylene backbone with both ethylene and propylene polymerized monomeric units, wherein from 2 mol % to 15 mol % of the polymerized monomeric units include a grafted side chain having an epoxide moiety;
• a fusing agent to selectively apply to the powder bed material, wherein the fusing agent comprises water and a radiation absorber that absorbs electromagnetic energy and converts the electromagnetic energy to heat;
• a hardener to selectively apply to the powder bed material, wherein the hardener is present in the fusing agent or is included in a hardening agent that is separate from the fusing agent;
• and
• a radiant energy source positioned to expose a layer of powder bed material to the electromagnetic energy to selectively fuse the polymer particles in contact with the radiation absorber and thereby form a 3D printed article that thermally fused and chemically crosslinked.