Polybutene is a synthetic polymer that belongs to the polyolefin family. It is a hydrocarbon polymer derived from petroleum feedstocks from the C4 fraction. As a class of materials, polybutene is highly valued in manufacturing for its unique combination of properties, including flexibility, low moisture permeability, and thermal stability. This versatility allows it to be used as both a pure thermoplastic and a modifying additive across numerous industrial and consumer products.
Fundamental Chemistry and Structure
Polybutene is created through the polymerization of the monomer butene. The two main commercial forms are Polybutene-1 (PB-1) and Polyisobutylene (PIB). Polybutene-1 is formed from 1-butene, which creates a highly ordered, isotactic polymer chain. This structure results in PB-1 being a semi-crystalline thermoplastic, meaning it possesses both amorphous and organized crystalline regions.
The crystalline structure of PB-1 provides it with high heat resistance and exceptional pressure tolerance, making it resistant to creep. In contrast, Polyisobutylene (PIB) is produced from the isomer isobutylene, yielding a polymer with an amorphous, non-crystalline structure. This molecular arrangement makes PIB highly flexible, viscous, and rubbery, even at room temperature.
The resulting properties of PIB include low gas and moisture permeability, making it an effective barrier material, and high tackiness. Since PIB lacks the organized crystalline structure of PB-1, it is typically used in non-crystallizing forms, often exhibiting a liquid or highly viscous consistency. The inherent difference in molecular structure between the two forms dictates their suitability for various end-use applications.
Clarifying the Confusion: Polybutene Versus Polybutylene
The nomenclature surrounding these materials can be confusing, as the terms Polybutene, Polybutylene, and PB-1 are often used interchangeably. Historically, the term “Polybutylene” (often abbreviated as PB) became notorious in North America for plumbing failures that occurred in residential homes between the late 1970s and mid-1990s. This older piping material was subject to widespread class-action lawsuits.
The primary failure mechanism for the older Polybutylene pipes stemmed from their susceptibility to degradation by chlorine. Exposure to these chemicals caused the plastic to break down and become brittle, leading to premature cracking and subsequent leaks. Production of this specific type of piping for residential use ceased in 1995 due to its high failure rate.
However, modern Polybutene-1 (PB-1) is distinct from the problematic historical material. PB-1 exhibits superior chemical resistance and dimensional stability under stress, which is why it has been utilized successfully for over fifty years in pressurized hot and cold water systems across Europe and Asia. The modern PB-1 material is not associated with the historical failures, but the similar names continue to cause confusion for consumers researching the topic.
Primary Industrial and Consumer Applications
The highly viscous and non-drying nature of Polyisobutylene (PIB) makes it a preferred component in sealants and caulks, where it provides excellent adhesion and a long-lasting, flexible barrier. Higher molecular weight grades of PIB are widely used as the base material in chewing gum, providing the necessary elasticity and chew characteristics. It also functions as a viscosity modifier and dispersant in lubricants and motor oils, helping to maintain oil thickness across a range of operating temperatures.
Polybutene-1 (PB-1) is leveraged in applications demanding high performance and durability, directly benefiting from its semi-crystalline structure and creep resistance. Its primary use is in flexible piping systems for hot and cold water, as it can withstand continuous pressure and temperatures up to 100°C better than many other polyolefins. PB-1 is also used as a film modifier to improve the puncture and tear resistance of polyethylene films used in packaging. Furthermore, its stability and adhesive properties make it a component in certain formulations of hot melt adhesives.