3902.20 - Polyisobutylene:

This category, HTS code 3902.20, encompasses polyisobutylene, which is a synthetic polymer derived from isobutylene. Polyisobutylene is characterized by its unique properties, including excellent impermeability to gases, good resistance to aging and ozone, and a tacky, rubber-like nature when produced in certain molecular weights. These characteristics make it suitable for a range of industrial applications.

Within the broader chapter on polymers of propylene or other olefins, this subcategory is distinct from its siblings. Polypropylene (3902.10) is a homopolymer of propylene, while propylene copolymers (3902.30) incorporate other olefins alongside propylene. "Other" (3902.90) covers polymers of olefins that are not specifically classified elsewhere under this heading. Therefore, 3902.20 specifically isolates polymers where isobutylene is the primary or sole monomer.

Polyisobutylene itself is further divided into two subcategories to refine classification based on specific properties and uses. HTS code 3902.20.10.00 covers "Elastomeric" polyisobutylene, typically referring to forms with higher molecular weights that exhibit rubber-like elasticity and are often used in applications requiring flexibility and resilience. The remaining polyisobutylene falls under 3902.20.50.00, designated as "Other," which would include polyisobutylene with different molecular weights or formulations not specifically defined as elastomeric, such as those used in adhesives, sealants, or as tackifiers.