H12MDI

In certain niche applications, aliphatic isocyanates, such as isophorone diisocyanate (IPDI), hexamethylene diisoeyanate (HDI), methylene 4,4 -biscyclo-hexylisocyanate (H12MDI), and polymeric versions of these diisocyanates, are used, e.g., in instances where light stability or reduced reactivity is needed. These isocyanates usually cost more than the aromatic diisocyanates. Thus, they are used in adhesive areas that can Justify the higher costs. 

Polyurethane dispersions (PUD s) are usually high-performance adhesives based on crystalline, hydrophobic polyester polyols, such as hexamethylene adipate, and aliphatic diisocyanates, such as methylene bis(cyclohexyl isocyanate) (H12MDI) or isophorone diisocyanate (IPDI). These PUD s are at the more expensive end of the waterborne adhesive market but provide excellent performance. 

Where color and light stability of the adhesive are important, and cure speed or cost is less important, aliphatic isocyanates are frequently used. Adhesives derived from isophorone diisocyanate (IPDI), hexamethyl-ene diisocyanate (HDI), or 4,4 -dicyclo-hexylmethane diisocyanate (H12MDI) are available. 

Triohdiisocyanate 1 1 NCO OH, 70% solution in dioxane 70 °C, 1,6-hexamethylene diisocyanate (HDD, 5-isocyanato-1-(isocyanato-methyl)-1,3,3-trimethyl-cyclohexane (IPDI), 1,1 -methylenebis[4-isocyanato-cyclohexane (H12MDI), 1,1 -methylenebis [isocyanato-benzene (MDI) and 1,3-diisocyanatomethyl-benzene (TDI). Me % = percent metal based on polymer solids... 

Figure 3.39 Alicyclic isocyanates, (a) Isophorone diisocyanate (or 3-isocyanato-methyl-3,5,5—trimethylcyclohexyl isocyanate), Huels IPDI (b) l,4-bis(isocyanatometh-yl)cyclohexane, Mobay s p-Desmodur (c) l,3-bis(isocyanatomethyl)cyclohexane, Takeda s Hr,XDI (S3.50) (d) Methylene bis(4—cyclohexylisocyanate), Mobay s Desmodur W ( 3.00). also known as H12MDI, RMDI (reduced MD1), and PACM [bis-/ -aminocyclohcxyl methane].

Although p-phenylene diisocyanate (PPDI) has been synthesized as early as 1913 (18). the Akzo Corp. has developed more recently a modified Hofmann process for the preparation of PPDI (19). A comparison of the reactivity of PPDI in comparison with MDI and NDI (1,5-naphthalene diisocyanate) as well as with aliphatic diisocyanates (H12MDI, IPDI, and CHDI—see Aliphatic Isocyanates) was reported by Wong and Frisch (20). 

A number of other aliphatic diisocyanates that impart excellent color stability to urethane coatings have been introduced into the U.S. market. Foremost among these are 4,4 -methylene bis(cyclohexyl isocyanate) (H12MDI) and Isophorone diisocyanate (25. 26). An isocyanurate ring containing isocyanate produced by trimerization of IPDI is also commercially available (T-1890). 

H12MDI exists in three isomeric forms, the trans-trans, trans-cis, and cis-cis forms. Due to the fact the cis isomer is more sterically hindered, the trans isomer reacts considerably faster with a hydroxyl group than the cis isomer (27). As with other aliphatic isocyanates, catalysis (generally organotln catalysts) is usually used for both the prepolymer preparation and the cure reaction (cross-linking). 

H12MDI) n. A diisocyanate used in making urethane elastomers and foams. 

When the properties of H12MDI elastomers are compared with those of the analogous MDI series it is found that elastomers based on the aliphatic isocyanate generally had superior mechanical properties. This pattern of behaviour applies to both polyester, polyether, polycaprolactone and polybutadiene polyol-based urethane elastomers. 

Aliphatic isocyanates, as well as possessing superior light stability have also been seen to show increased phase separation behaviour over aromatic isocyanates. The T s of systems based upon HDI, H12MDI and IPDI are lower than that of TDI and MDI systems. This is attributed to stronger hydrogen bonding being obtained in the hard block domains. 

CHDI > PPDI > MDI > TDI > H12MDI Decreasing thermal stability - ... 

Aliphatic diisocyanates can have strong, adverse skin irritation effects and two are well known for this problem, namely dicyclohexylmethane diisocyanate (H12MDI) (Desmodur W by Bayer) and hexamethylene diisocyanate (HDI). Usually care in handling and good hygiene prevents undue problems. Occasionally a more serious effect has been observed in one instance a chemical worker exposed her face to the hot vapour of dicyclohexylmethane diisocyanate and within 24 h her head had swollen to 20% of its original size and characteristic red spots with a white centre were present over the exposed area. Recovery took place slowly over a period of 3 weeks with cortisone-type ointment treatments. Her central nervous system was also affected and took some months to become normal. This was a very unusual and unique incident and is recorded to show that occasionally the unexpected human response can occur with diisocyanates. 

H12MDI 4,4 -Methylen bis(cyclohexyl isocyanate) Allied Chem. Co. 

More recently, Frisch and Frisch reported on the toluene vapor transmission through an SIN film based on poly(l,4-oxybutylene) glycol, MW 1000, and 4,4 -methylene bis(cyclohexyl isocyanate) (H12MDI), and epoxy resin. The coefficient of diffusion decreased, as did the permeability, as the epoxy content was increased. 

The principal aliphatic isocyanates used are 1,6-hexamethylene diisocyanate (HDD (1,6-isocyanatohexane) [822-06-0], bis(4-isocyanatocyclohexyl)methane (H12MDI) [5124-30-1], and isophorone diisocyanate (IPDI) (3-isocyanato-l-iso-cyanatomethyl)-l,3,3-trimethylcyclohexane [4098-71-9]. Tetramethyl-m-xylidene diisocyanate (TMXDI) [2778-42-9] and m-isopropenyl-a,a-dimethylbenzyl-isocyanate (TMI) (l-(l-isocyanato-l-methylethyl)-3-(l-methylethenyl)benzene [2094-99-7] are specialty products used on a much smaller scale. Diisocyanates are only used as higher molecular weight derivatives in coatings to increase functionality and reduce toxic hazard. 

H12MDI is less volatile than HDI and is sometimes used as afree diisocyanate in coatings to be applied by roll coating, but not by spray coating. It is a mixture of stereoisomers since both isocyanate groups are secondary, reactivity is lower than HDI or IPDI. Combined allophanate-isocyanurate derivatives are available with low free monomer content. Reference 7 covers the chemistry and uses of H12MDI. 

Speckhard T, et al. Properties of polyisobutylene polyurethane block copolymers 3. Hard segments based on 4, 4 -dicyclohexylmethane diisocyanate (H12MDI) and butane diol. Polymer 1985 26(l) 70-8. 

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