CH2CHCH3n

CH2CHCH3n is a shorthand notation used in polymer chemistry to denote the repeating unit of polypropylene, also known as poly(propene). In this representation the repeating unit is -(CH2-CH(CH3))- and n indicates the number of such units in the polymer chain. Each repeating unit corresponds to the propene monomer (C3H6); thus the polymer population can be described by (C3H6)n.

Polypropylene exists in several tacticities, which describe the arrangement of the methyl groups relative to the chain. Isotactic polypropylene has all methyl groups on the same side and tends to be semi-crystalline with a high melting point, typically around 160 to 170°C. Syndiotactic polypropylene also crystallizes but with a different packing arrangement. Atactic polypropylene is largely amorphous and has no well-defined melting point. The material’s density is about 0.9 g/cm³, and crystallinity—and therefore mechanical properties—depend strongly on tacticity and processing conditions.

Production and processing typically involve polymerization of propene using catalysts such as Ziegler–Natta or metallocene systems. The resulting polymer can be fabricated into films, fibers, and molded parts. polypropylene is valued for its toughness, chemical resistance, relatively high heat resistance, and low density, making it a common choice for packaging, automotive components, consumer goods, and textiles. It can be stabilized against UV light and heat with suitable additives.

Safety and recycling considerations: polypropylene is generally regarded as inert and safe for many consumer applications. It is recyclable under coding system code 5 (PP) in many facilities, though recycling rates vary by region.