1,4-butanediol (BDO/1,4-BD) is a versatile liquid diol intermediate with reactive primary hydroxyl functionality and a linear structure that lends itself to formulating polyurethanes with a good balance of hardness and low temperature flexibility; high strength and durability; and thermal stability.
1,4-butanediol is characterized by…
A molecular weight (MW) of 90.12.
An equivalent weight (EW) of 45.06.
And a hydroxyl value of 1245 mg KOH/g.
A melting point of 20.1°C (68.2℉)
A boiling point of 235°C (455℉)
A flash point of 121°C (250℉)
While 1,4-BDO has a number of uses as a polymer intermediate, BDO plays a key role in the creation of polyurethanes, with urethane grade BDO being particularly advantageous because of its low moisture content (< 150 ppm moisture specification) and very high purity (> 99.85 % purity by gc).
In this article, we'll explain 5 key properties that set urethane grade BDO apart, covering everything from its function as a chain extender to its various applications.
1. The Role of 1,4-Butanediol (BDO/1,4-BD) as a Polyurethane Building Block
The properties of a polyurethane greatly depend on the structure of the molecular backbone, and chain extenders play a significant role in enhancing the final mechanical properties of polyurethanes.
In polyurethanes, BDO is used as a urethane chain extender (difunctional reactants like BDO are considered chain extenders while reactants with higher functionality are considered crosslinkers) and an intermediate for polyester polyols.
And, when it comes to MDI systems, the chain extender of choice for most processors is 1,4-BDO. Functioning in this role, BDO reacts with MDI or MDI-based prepolymers and H12 MDI systems to create the "hard segment" domains of polyurethanes. 1,4-butanediol yields crystalline urethane domains that efficiently microphase separate to afford tough elastomeric networks.
In thermoplastic polyurethane (TPU) compositions, uncrosslinked BDO-MDI domains can be melted and will flow at elevated temperatures to allow thermoplastic processing. The associated networks reform when cooled to form tough elastomeric compositions.
For polyurethanes in which butanediol is the chain extender in the hard segment (MDI based), you can find the following structural unit:
-NH-CO-O-CH2CH2CH2CH2-O-CO-NH-C6H4-CH2-C6H4-
1,4-butanediol also serves as an intermediate for polyester polyols. BDO polyester polyols, such as poly (butylene adipate) polyol, help create the "soft segment" domains in polyurethane elastomers.
Using BDO polyester polyol, formulators develop polyurethanes with excellent mechanical properties over a broad temperature range. These polyurethanes exhibit good abrasion resistance; cut and chip resistance; excellent oil, grease, and chemical resistance; and weatherability.