Hydroxyl-terminated polybutadiene

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Abbreviation: HTPB, Butadiene hydroxyl rubber

Alias: Hydroxyl-terminated polybutadiene liquid rubber

HTPB is a polyol with a polybutadiene main chain. Its CAS number is 69102-90-5.

The typical structural formula of hydroxyl-terminated polybutadiene is as follows：

The functionality of HTPB is generally in the range of 2 to 2.6. Products with 1,4-cis/1,4-trans/1,2-vinyl mass ratios other than 20/60/20 are also available internationally.

Physical and Chemical Properties

HTPB is a colorless or light yellow transparent liquid at room temperature, with a density of 0.89–0.92 g/cm³ at room temperature. It is insoluble in water, soluble in toluene, chloroform, mineral spirits, methyl ethyl ketone, ethyl acetate, and 100# aromatic solvent, and slightly soluble in acetone, hexane, and isopropanol.

Characteristics and Uses

HTPB reacts with chain extenders and polyisocyanate crosslinkers at room temperature or high temperature to form a three-dimensional network structure. The polybutadiene main chain gives the polymer properties similar to natural rubber and butyl rubber, exhibiting strong hydrophobicity. The cured product has excellent mechanical properties, good transparency, and particularly excellent hydrolysis resistance, electrical insulation, acid and alkali resistance, excellent low-temperature flexibility, aging resistance, good adhesion to non-polar and low-polar materials, excellent airtightness, and very low moisture permeability. It is generally used in the manufacture of binders for solid propellants, etc. In recent years, it has been increasingly used in the production of civil castable polyurethane elastomers, RIM polyurethane products, and CASE polyurethane elastic materials. Specific application areas include rubber products for automobile and aircraft tire structures, building materials, shoe materials, special foamed plastics, coatings, adhesives, potting materials, electrical insulation encapsulation materials, waterproof and anticorrosive materials, underwater sealing materials, sports tracks, wear-resistant conveyor belts, and for the modification of other rubbers and epoxy resins, among many other uses. HTPB is used in electrical potting compounds and adhesives, possessing excellent low-temperature resistance and flexibility.

Generally, small molecule diol chain extenders have poor compatibility with HTPB. Suitable chain extenders for the HTPB/MDI system include: N,N-diisopropanol aniline (DIPA, Dow Chemical’s Voranol 220-530), 2-ethyl-1,3-hexanediol (EHD), 2-butyl-2-ethyl-1,3-propanediol (BEPG), and 2,2,4-trimethyl-1,3-pentanediol (TMPD).