The “B” in many polymers
In many polyesters you will see the letter B; what is this ingredient and why is it so popular amongst users. This B refers to the building block 1,4-butanediol (CAS 110-63-4), a linear diol with four carbons. By letting the alcohol group react with a dicarboxylic acid, such as adipic acid, succinic acid or terephthalic acid you will obtain a variety of polyesters that you will find in everyday life. Commonly these esterification reactions are done in the presence of a catalyst, such as titanium alkoxides or dibutyltin oxide.
Examples of polymers containing 1,4-butanediol
PBT (poly-Butylene-terephthalate) is one of the most important engineering plastics worldwide. It’s a close analogue of PET (in which the butylene group is ethylene of 2 carbons), which is widely known for its use in clothing and food packaging. Using PBT over PET has certain advantages such as improved flexibility and the material having a higher impact strength. Furthermore, its melting temperature is slightly lower, make processing easier. You will find PBT used in a variety of automotive applications (from plug connectors to the carpet), machinery for food production and the insulation of cables.
PBAT (poly-Butylene-adipate-terephthalate) shows many similarities to PBT, however, the addition of the adipic acid modifies several properties. The most important properties are that the material becomes biodegradable/compostable. As such, it can be used in a variety of applications related to food packaging as well as agricultural applications.
PBS (poly-Butylene-succinate) is a promising polyester for its similar properties to some polyolefins such as polyethylene and polypropylene. Even more interesting is the fact that this material is biodegradable and can potentially be sourced from bio-based raw materials. While bio-based succinic acid (CAS: 110-15-6) can be purchased from several suppliers such as Will & Co B.V., the 1,4-butanediol is not commercially available yet. It is however produced on a kiloton scale by Novamont, who uses this material in their biopolymers.
Production of 1,4-butanediol
While some 1,4-butanediol can be produced via fermentation as mentioned above, the vast majority is still produced from petrochemical sources. Several production methods are used for this.
- Reppe chemistry: starting with acetylene gas and reacting this with 2 equivalents of formaldehyde.
- Davy process: sequence starting from maleic anhydride, which is transformed to dimethyl maleate and subsequently hydrogenated towards 1,4-butanediol.
- From butadiene: oxidation of butadiene leads to the corresponding di-epoxide which can be hydrogenated towards 1,4-BDO
- From propylene oxide: a process developed by Kuraray, first involves isomerization to the allyl alcohol, subsequent hydroformylation and then hydrogenation to the butanediol
- From succinic acid: the reduction of succinic acid towards 1,4-butanediol requires extensive heat and pressure in addition to a strong catalyst. Usually, this process is not cost-efficient. It was proposed to be of interest in reducing bio-based succinic acid towards bio-based 1,4-BDO, but with the introduction of a fermentation process, this seems no longer viable.
1,4-butanediol, a key ingredient
Many industries are depending on 1,4-butanediol as a raw material as a key ingredient for their polyesters, polyester polyols and their polyurethanes. It is used in coating resins, as a cross-linker in elastomers and for example in the production of THT (tetrahydrothiophene). Will & Co is delivering this material to customers throughout Europe and thus enabling them to make their products for a variety of industries.