Chemical structures aromatic isocyanates

Lights stability of polyurethanes depends to a large extent on their chemical structure, and both components (Le., isocyanate and polyol) have an influence. Polyurethanes based on aliphatic isocyanates and polyester diols show the best light stability if yellowing is considered, whereas polyurethanes based on aromatic isocyanates and polyether diols are worst in this respect. 

RIM polyurethanes made with aromatic isocyanates (such as pure or polymeric MDI) have a tendency to darken as a result of the effect of UV light on the chemical ring structure of the MDI component. Soft white limestone or line carbon black is often used as filler to mask the effect of this color change. 

The above groups contain plasticizers which have several representatives of similar chemical structure. There still are plasticizers in common use or that were invented for specific purposes. These can be grouped as follows biphenyl derivatives,calcium stearate,carbon dioxide, difurans, " fluorine-containing plasticizers, " hydroxyben-zoic acid esters, " isocyanate adducts, " " malonates, " multi-ring aromatic... 

Due to the necessity for aromatic structure in the commodity isocyanates, and the intensive chemical conversions required to derive the isocyanate reactant, no high-carbon frameworks derived principally from plant sources have been developed into isocyanates. The majority of the derivation of raw materials from high carbon conjugates has been focused on the development of polyols, for which the structural demands are a better fit for available renewable feedstocks. Although there are some notable exceptions [1], as a general rule modification of the... 

Most of the commercially used isocyanates are diisocyanates and R is an aromatic ring. MIC is an exception its structure is H3C-N=C=0. The physicochemical properties of MIC differ from those of other isocyanates (Lowe, 1970 Tse and Pesce, 1978 Westcott, 1985 Worthy, 1985). Because of high chemical reactivity of MIC with alcohols, it serves as an intermediate in the production of the pesticide carbaryl. Diisocyanates are primarily used for the manufacture of polyurethanes. 

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