1,3-Butadiene, homopolymer, hydroxy-terminated
[CAS 69102-90-5]

Identification

• Classification: Catalysts and additives >> Polymer
• Name: 1,3-Butadiene, homopolymer, hydroxy-terminated
• CAS Registry Number: 69102-90-5
• EC Number: 614-926-3

Safety Data

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Reproductive toxicity	Repr.	2	H361fd

chemBlink Chemical Story

Hydroxyl-terminated polybutadiene, or HTPB, is a polymer designed so that the middle of the chain and the ends do different jobs. The backbone is largely polybutadiene, giving a low glass-transition temperature and rubber-like flexibility. The chain ends carry hydroxyl groups, which provide defined reactive sites for converting the liquid polymer into a crosslinked polyurethane network. This telechelic architecture explains why HTPB became an important binder in demanding elastomeric systems.

HTPB is not one perfectly uniform molecule. Commercial material contains a distribution of chain lengths and microstructures, including cis-1,4, trans-1,4, and vinyl units, and its functionality is described statistically through hydroxyl value and average molecular weight. The liquid can be mixed with fillers or other ingredients before curing. When reacted with multifunctional isocyanates, terminal OH groups form urethane bonds and connect chains into an elastic network.

One of the best-known applications is as binder and liner material in composite solid propellants. In that role HTPB is the continuous polymer phase that holds solid particles together and transfers mechanical stress. Its low-temperature flexibility and processable liquid precursor are critical because a large composite grain must survive casting, curing, storage, temperature cycling, vibration, and mechanical loading without cracking or debonding. The polymer's job is therefore as much mechanical as chemical.

Research continues to modify HTPB because the balance is difficult. Increasing crosslink density can strengthen a material but reduce elongation. Changing microstructure or adding functional groups may alter glass transition, viscosity, aging, or compatibility. Modern studies examine functionalized HTPB, nanoparticle reinforcement, low-temperature variants, and alternative energetic binders, yet conventional HTPB remains widely studied because its combination of processing and mechanical properties is hard to replace.

The word "binder" can understate how much of the composite's integrity depends on the polymer. A particulate composite may contain far more solid than polymer by mass, yet cracks usually propagate through or along the continuous binder and interfaces. HTPB must wet particles during processing and later accommodate thermal expansion mismatch between ingredients. Its cure chemistry, molecular-weight distribution, and adhesion therefore influence not only stiffness but damage tolerance and aging. A small fraction of polymer can control whether a much larger composite remains mechanically coherent.

HTPB matters because it shows the power of end-group chemistry. Most of a polymer chain can be optimized for flexibility while only a few terminal groups are reserved for network formation. Those few hydroxyl groups determine how thousands of backbone atoms become connected into a macroscopic solid. A seemingly minor detail at the chain ends therefore controls the transition from pourable polymer to structural elastomer.

References:

1. Quagliano Amado JC et al. Propellants, Explosives, Pyrotechnics. 2022;47:e202100283. DOI: 10.1002/prep.202100283.

2. da Silva G, Rufino SC, Iha K. Journal of Aerospace Technology and Management. 2013;5. DOI: 10.5028/jatm.v5i3.242.

3. Lee F et al. European Polymer Journal. 2025;238:114209. DOI: 10.1016/j.eurpolymj.2025.114209.

4. Polymer literature on HTPB polyurethane network formation and microstructure.

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