The molecular weight of a polymer plays a significant role in determining its printability and mechanical properties when used as a material for 3D printing. Molecular weight refers to the mass of a molecule, and in the case of polymers, it is the mass of the repeating units monomers that make up the polymer chain. The molecular weight of a polymer can be categorized into three main groups: low molecular weight, medium molecular weight, and high molecular weight.1. Printability:Printability refers to the ease with which a polymer can be processed and printed using a 3D printer. The molecular weight of a polymer affects its printability in the following ways:a Viscosity: As the molecular weight of a polymer increases, its viscosity also increases. High molecular weight polymers have higher viscosities, making them more difficult to extrude through the nozzle of a 3D printer. On the other hand, low molecular weight polymers have lower viscosities, making them easier to print but may result in poor layer adhesion and weak printed parts.b Melt flow rate: The melt flow rate MFR of a polymer is a measure of its ability to flow when heated. Polymers with high molecular weights have lower MFRs, making them more challenging to print, while those with low molecular weights have higher MFRs, improving their printability. However, a balance must be struck to ensure that the printed parts have adequate mechanical properties.c Thermal stability: High molecular weight polymers generally have better thermal stability, which is crucial for 3D printing processes that involve high temperatures. Low molecular weight polymers may degrade or decompose at high temperatures, affecting the print quality and the properties of the printed parts.2. Mechanical properties:The mechanical properties of a 3D printed part, such as tensile strength, impact resistance, and flexibility, are significantly influenced by the molecular weight of the polymer used. a Tensile strength: Polymers with high molecular weights have stronger intermolecular forces and entanglements, resulting in higher tensile strength. In contrast, low molecular weight polymers have weaker intermolecular forces, leading to lower tensile strength in the printed parts.b Impact resistance: High molecular weight polymers typically have better impact resistance due to their more extensive molecular entanglements, which can absorb and distribute impact energy more effectively. Low molecular weight polymers have less entanglement and may result in more brittle printed parts with lower impact resistance.c Flexibility: Polymers with high molecular weights tend to have better flexibility and elongation at break due to the increased chain entanglements and intermolecular forces. Low molecular weight polymers may result in more rigid and brittle printed parts.In conclusion, the molecular weight of a polymer significantly affects its printability and mechanical properties when used as a material for 3D printing. High molecular weight polymers generally offer better mechanical properties but may be more challenging to print, while low molecular weight polymers may be easier to print but may result in weaker printed parts. Therefore, it is essential to select a polymer with an appropriate molecular weight that balances printability and mechanical properties for the specific application.