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[Science Sticker] Polypropylene - the difference between copolymerization and homopolymerization

Update:23-08-2019
Summary:

Polypropylene (PP) is classified into homopolypropylene […]

Polypropylene (PP) is classified into homopolypropylene (PP-H), block (impact resistant) copolymer polypropylene (PP-B) and random (optional) copolymerized polypropylene (PP-R).

1. Homopolypropylene (PP-H)v

PP-H is a homopolypropylene, which is what we call type I polypropylene. We know that it is polymerized from a single polypropylene monomer and does not contain ethylene monomer in the molecular chain. The PP-H molecular chain has a high degree of uniformity, so the material has high crystallinity and poor impact resistance.

Main performance: high molecular chain regularity, good high temperature resistance, poor resistance to low temperature impact, and poor light aging resistance.

Application: Generally used in chemical pipelines or other engineering applications.

2. Block (impact resistant) copolymerized polypropylene (PP-B)

PP-B is a block copolymer polypropylene, which is what we call type II polypropylene. It has a high ethylene content, generally 7-15%. In the molecular sequence, the probability of two ethylene monomers and three monomers being linked together is very high, indicating that the ethylene monomer is only present in the block phase. The ethylene segment in the form of a block greatly improves the impact strength of the material, but the crystallinity, melting point and heat resistance of the material cannot be fundamentally improved because the isotacticity of the PP-H molecular chain cannot be lowered. .

Main performance: good low temperature impact resistance, low temperature embrittlement point is -5 °C, poor temperature resistance, suitable temperature range is 0-60 °C.

Application: Generally suitable for cold water systems or low pressure water systems with temperatures below 60 degrees.

3. Random (optional) copolymerized polypropylene (PP-R)

PP-R is a random copolymer polypropylene, which is what we call type III polypropylene. It is obtained by copolymerization of propylene monomer and a small amount of ethylene monomer under heat, pressure and catalyst. The ethylene monomers are randomly distributed into the long chain of propylene, wherein the ethylene monomer is generally controlled between 3-5%. The random addition of ethylene monomer reduces the crystallinity, melting point of the polymer, and improves impact properties and heat resistance.

Main performance: low temperature impact resistance, good creep resistance at high temperature, suitable temperature range of 0-80 °C.

Application: Widely used in building hot and cold water systems.