Polypropylene (English name: polypropylene, abbreviated as: PP, commonly known as: 100 times glue) is the representative of poly-α-olefin, which is a thermoplastic resin polymerized from propylene, and its monomer is propylene CH2 = CH-CH3. According to different initiators and polymerization processes, polypropylene can be divided into three configurations: isotactic polypropylene, atactic polypropylene and syndiotactic polypropylene. Isotactic polypropylene is easy to form crystalline state, the crystallinity is above 95%, and the molecular weight is between 80- 1.5 million, which gives it good heat resistance and solvent resistance. Random polypropylene is an amorphous and slightly sticky ash at room temperature, with a low molecular weight of 3000- 10000, irregular structure and lack of cohesion, so it is rarely used.
The English name of polyethylene: polyethylene, abbreviated as PE, is a thermoplastic resin polymerized from ethylene. In industry, it also includes copolymers of ethylene and a small amount of α-olefins. Polyethylene is odorless and nontoxic, feels like wax, and has excellent low temperature resistance (the lowest service temperature can reach -70 ~- 100℃), good chemical stability, resistance to most acids and alkalis (oxidation-resistant acids), insolubility in general solvents at room temperature, low water absorption and excellent electrical insulation.
Polyvinyl chloride (PVC) is a polymer material, which uses chlorine atoms to replace hydrogen atoms in polyethylene. PVC is a white powder with amorphous structure and low branching degree. The molecular weight of industrial PVC is generally between 500 ~ 65438+200 thousand, which has great polydispersity and the molecular weight increases with the decrease of polymerization temperature. Without a fixed melting point, it begins to soften at 80~85℃, becomes viscoelastic at 130℃, and becomes viscous at 160~ 180℃. Its tensile strength is about 60MPa, and its impact strength is 5 ~ 10kJ/m2. Has excellent dielectric properties. Poor stability to light and heat. Exposure to sunlight above 100℃ or for a long time will decompose to produce hydrogen chloride, which will automatically catalyze decomposition and cause discoloration. In practical application, stabilizers must be added to improve the stability to heat and light. PVC is very hard and can only be dissolved in a few solvents such as cyclohexanone, dichloroethane and tetrahydrofuran. It is stable to organic and inorganic acids, bases and salts, and its chemical stability decreases with the increase of service temperature.
The chemical formula of polyethylene terephthalate is -OCH2-CH2OCOC6H4CO- English name: polyethylene, abbreviated as PET, which is a high polymer obtained by dehydration and condensation of polyethylene terephthalate. Ethylene terephthalate is obtained by esterification of terephthalic acid and ethylene glycol. PET is a kind of high crystalline polymer with milky white or light yellow, and its surface is smooth and shiny. It has excellent physical and mechanical properties in a wide temperature range, the long-term use temperature can reach 65438 0 20℃, and the electrical insulation performance is excellent. Even at high temperature and high frequency, its electrical properties are still good, but its corona resistance is poor, and its creep resistance, fatigue resistance, friction resistance and dimensional stability are good.