The key physical and chemical properties of polymers that make them suitable for 3D printing include:1. Thermoplasticity: Polymers used for 3D printing should be thermoplastic, meaning they can be melted and solidified multiple times without significant degradation of their properties. This allows them to be extruded or deposited in layers to build up a 3D object.2. Melt viscosity: Polymers should have an appropriate melt viscosity, which determines how easily they flow when heated. A suitable melt viscosity allows the polymer to be extruded smoothly and accurately through the 3D printer nozzle.3. Glass transition temperature Tg and melting temperature Tm : The Tg and Tm of a polymer influence its processing temperature and the final properties of the printed object. Polymers with a lower Tg and Tm are generally easier to print, as they require less energy to melt and solidify. However, a higher Tg and Tm can result in better mechanical properties and heat resistance in the final product.4. Adhesion: Polymers should have good adhesion properties, allowing them to bond well with adjacent layers during the printing process. This ensures the structural integrity of the final 3D printed object.5. Mechanical properties: Polymers should have suitable mechanical properties, such as tensile strength, elongation at break, and impact resistance, to meet the requirements of the intended application.6. Chemical resistance and stability: Polymers used for 3D printing should be resistant to various chemicals and have good stability to ensure the durability and longevity of the printed objects.Some specific polymers with the best properties for 3D printing include:1. Polylactic acid PLA : PLA is a biodegradable thermoplastic derived from renewable resources such as corn starch. It has a low Tg and Tm, making it easy to print. PLA is widely used for 3D printing due to its ease of use, low odor, and environmentally friendly nature.2. Acrylonitrile butadiene styrene ABS : ABS is a petroleum-based thermoplastic with a higher Tg and Tm than PLA, resulting in better mechanical properties and heat resistance. It is commonly used for 3D printing due to its strength, durability, and flexibility.3. Polyethylene terephthalate glycol PETG : PETG is a thermoplastic with excellent mechanical properties, chemical resistance, and durability. It combines the ease of printing of PLA with the strength and heat resistance of ABS, making it a popular choice for various applications.4. Thermoplastic polyurethane TPU : TPU is a flexible, rubber-like thermoplastic with excellent mechanical properties, including high elasticity and abrasion resistance. It is used for 3D printing flexible and durable parts, such as gaskets, seals, and protective cases.5. Polycarbonate PC : PC is a high-performance thermoplastic with excellent mechanical properties, high heat resistance, and good transparency. It is used for 3D printing parts that require high strength, toughness, and heat resistance, such as automotive components and protective gear.Each of these polymers has its advantages and disadvantages, and the choice of the best polymer for 3D printing depends on the specific requirements of the application.