Hydrogenated polyisobuten (HPBI) is a saturated branched-chain hydrocarbon polymer derived from polyisobuten. HPBI has a chemical formula of (C4H8)n and is typically a pale yellow, viscous liquid. The process of hydrogenation converts the double bonds in polyisobuten to saturated single bonds, resulting in increased stability. Let's take a closer look at the properties and applications of this industrial hydrocarbon polymer.
What is Polyisobuten?
Hydrogenated Polyisobutene also known as poly(isobutylene) or PIB, is a synthetic rubber produced through cationic polymerization of isobutylene. It has the chemical formula (C4H8)n and is a clear, colorless, and odorless liquid at room temperature. Due to the presence of double bonds along the polymer chain, polyisobuten exhibits properties akin to natural rubber. However, polyisobuten is not as resistant to chemical and thermal decomposition as saturated polymers. This limitation spurred the development of hydrogenated polyisobuten with improved stability characteristics.
The Hydrogenation Process
To produce HPBI, polyisobuten is exposed to hydrogen gas in the presence of a catalyst at high pressure and elevated temperature. This process, known as selective hydrogenation, breaks the carbon-carbon double bonds in the polymer but leaves the tertiary carbon-hydrogen single bonds intact. As a result, the double bonds are converted to single bonds without forming any branching along the polymer backbone. Complete hydrogenation yields HPBI that contains a fully saturated linear hydrocarbon structure with uniform methyl branching.
Properties and Characteristics of HPBI
The hydrogenation of polyisobuten imparts distinctive properties and performance benefits. Compared to the precursor PIB, HPBI has lower gas permeability, greater resistance to oxidation and ozone cracking. Since it is saturated, HPBI is colorless and odorless with low volatility at room temperature. It also displays higher flexibility at lower temperatures, improved UV stability, and increased resistance to chemical degradation. Some key properties of liquid HPBI include:
- Density: 0.86–0.88 g/cm3
- Refractive Index: 1.45–1.47
- Viscosity: 10–1,000 cSt (depending on molecular weight)
- Softening Point: Below room temperature
- Flash Point: >230°C
- Soluble in non-polar organic solvents
Due to its saturated and inert nature, HPBI demonstrates superior performance characteristics versus unsaturated polymers under demanding environmental conditions and applications. The combination of low gas permeability, flexibility, and chemical resistance make it suitable for varied industrial uses.
Adhesive Formulations
One of the primary uses of HPBI is as a base resin in pressure-sensitive adhesives (PSAs) and hot melt adhesives. Its saturated structure provides strong and durable bonds resistant to heat, oxidation and plasticizer migration. Adhesive tapes made from HPBI-based PSAs maintain high tack even at elevated temperatures. Hot melt formulations with HPBI also spray or string easily while solidifying into tough, yet flexible bonds. Common products that use HPBI adhesives include automotive and appliance trim pieces, carpet backing, bookbinding, and tapes.
Coatings and Sealants
The oxidation resistance, moisture barrier properties, and flexibility of HPBI make it adaptable for coating and sealant applications. It can be blended into moisture curing hot melt polyurethane formulations. Such sealants display long-term weatherability and find application as roof coatings, caulks, gaskets and encapsulants. HPBI is also compatible with asphalt, bitumen and other polymers to produce high-performance coatings for protection of infrastructure, containment linings and vapour barriers.
Cosmetics and Pharmaceuticals
In the cosmetic industry, hydrogenated polyisobutenes (HPIBs) find usage as emollients, viscosity control agents and stabilizers in personal care formulations. Grades compatible with skin and hypoallergenic are utilized in moisturizers, makeup, baby products and sunscreens. HPIBs help disperse pigments uniformly while lending a powdery, lightweight feel. They also enable controlled release of active ingredients in topical pharmaceutical formulations and transdermal patches. The non-greasy nature, stability and skin-friendliness of HPIBs expand their application potential in these industries.
Lubricants
The exceptional viscosity index and shear stability properties of HPBI have made it a preferred base stock for industrial lubricants. It is utilized as a thickener in greases as well as an additive to improve the performance of engine and hydraulic oils. In greases, HPBI enhances structural stability while maintaining its soft, superplastic character. This prevents oil separation and leakage under boundary lubrication conditions. As an oil additive, HPBI helps reduce friction and wear. It is compatible with petroleum-based fluids and supports the load-carrying ability of formulated lubricants.
Hydrogenated polyisobuten is a unique synthetic polymer with a palette of beneficial attributes stemming from its fully saturated structure. The exceptional stability, flexibility, and non-reactivity have enabled widespread commercial adoption of HPBI in adhesive tapes, sealants, cosmetic formulations, lubricants, and other demanding applications. Going forward, ongoing formulation advances are further broadening the scope of HPBI-based formulations. Its balance of performance and cost-effectiveness is likely to sustain HPBI's importance in diverse industries with stringent product specifications.
Resources – Sustainability and Environmental Impact of Hydrogenated Polyisobutene Production
Recent development in Hydrogenated Polyisobutene Market
Applications of Hydrogenated Polyisobutene in Cosmetics and Personal Care
The Chemical Properties and Benefits of Hydrogenated Polyisobutene in Industrial Applications
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