Tetramethylxylylene diisocyanate explained

Tetramethylxylylene diisocyanate (TMXDI) is an organic compound with the formula C₆H₄(CMe₂NCO)₂ (Me = CH₃). Introduced in the 1980s by American Cyanamid, the molecule features two isocyanate groups.^{[1] [2] [3]} TMXDI is generally classified as an aliphatic isocyanate, which are generally more UV stable than their aromatic counterparts.

Production

Many isocyanates are produced by phosgenation of amines, but TMXDI is not. It is produced by the reaction of diisopropenylbenzene with hydrogen chloride followed by isocyanic acid:

C₆H₄(C(Me)=CH₂)₂ + 2 HCl → C₆H₄(CMe₂Cl)₂

C₆H₄(CMe₂Cl)₂ + 2 HNCO → C₆H₄(CMe₂NCO)₂ + 2 HCl

Uses

A key use for TMXDI is in manufacturing polyurethane prepolymers. It is also used to manufacture polyurethane dispersions (PUDs).^{[4] [5] [6] [7] [8]} These materials are then further used to manufacture coatings, adhesives, sealants and elastomers.

TMXDI has been considered as a replacement for Isophorone diisocyanate (IPDI). IPDI has a molecular weight of 222.3 and thus a NCO equivalent weight of 111.15. TMXDI has a molecular weight of 244.3 and thus an equivalent weight of 122.15. Thus per mole, approximately 10% more is required than the equivalent prepolymer based on IPDI. This difference increases cost.When making polyurethanes dispersions (PUDs) TMXDI is advantageous. Being sterically hindered, the NCO groups are slower reacting which is good when dispersing a prepolymer in water to make a PUD. It reduces side reactions and allows more time to allow the dispersion stage before the mix is chain extended. This is done usually with a diamine.^[9] It has even found use in a rocket propellant binder by the US military.^[10]

Safety

Extensive data has become available.^[11]

See also

• Hexamethylene diisocyanate
• Isophorone diisocyanate
• Methylene diphenyl diisocyanate
• Toluene diisocyanate

External links

• Technical Data Sheet TMXDI
• Safety Data Sheet TMXDI
• Incorez website

Notes and References

1. Web site: m-Tetramethylxylene diisocyanate . United States Environmental Protection Agency . iaspub.epa.gov . 2018-11-02 . https://web.archive.org/web/20181106004857/https://iaspub.epa.gov/sor_internet/registry/substreg/searchandretrieve/advancedsearch/externalSearch.do?p_type=CASNO&p_value=2778-42-9 . 2018-11-06 . live .
2. Web site: 1,3-Bis(1-isocyanato-1-methylethyl)benzene . National Center for Biotechnology Information, U.S. National Library of Medicine . pubchem.ncbi.nlm.nih.gov . 2018-10-23 . https://web.archive.org/web/20181106005040/https://pubchem.ncbi.nlm.nih.gov/compound/1_3-bis_1-isocyanato-1-methylethyl_benzene . 2018-11-06 . live .
3. Web site: Tetramethylxylene diisocyanate . National Center for Biotechnology Information, U.S. National Library of Medicine . pubchem.ncbi.nlm.nih.gov . 2018-11-02 . https://web.archive.org/web/20181106004907/https://pubchem.ncbi.nlm.nih.gov/compound/21908508#section=Top#section=Top . 2018-11-06 . live .
4. Web site: Oxazolidines and tetramethylxylenediisocyanate based polyurethanes in legislation-compliant anticorrosion coatings – PDF Free Download. slideheaven.com. en. 2018-10-23.
5. Aqueous polyurethane dispersion and method for making and using same. US. 7342068. Eric Howard Klingenberg. Shafiq Nisarali Fazel. Versum Materials US LLC. 2003-11-18.
6. Web site: Aqueous PUDs. KG. Vincentz Network GmbH & Co.. European Coatings. en-GB. 2018-10-23.
7. Howarth . G A . Manock . H L . July 1997 . Water-borne polyurethane dispersions and their use in functional coatings . Surface Coatings International . en . 80 . 7 . 324–328 . 10.1007/bf02692680 . 137433262 . 1356-0751 .
8. Web site: Water Based Polyurethanes Dispersions(PUDs)-An Overview. www.linkedin.com. en. 2018-10-23.
9. Web site: TMXDI Technical Bulletin.
10. TMXDI, curing agent for hydroxy terminated propellant binders . US. 4913753. Apr. 3, 1990. Marjorie E. Ducote. The United States of America as represented by the Secretary of the Army, Washington, D.C..
11. Web site: 1,3-Bis(1-isocyanato-1-methylethyl)benzene . Pubchem . pubchem.ncbi.nlm.nih.gov . en . 2018-10-23 . https://web.archive.org/web/20181106005040/https://pubchem.ncbi.nlm.nih.gov/compound/1_3-bis_1-isocyanato-1-methylethyl_benzene#section=Top#section=Top . 2018-11-06 . live.