Isocyanates equivalent, defined

The isocyanate equivalent is defined as the weight of sample which will combine with 1 g equivalent weight of phenyl isocyanate. The sample is generally a polyol, amine or other compound that possesses groups capable of reacting with an isocyanate. 

Hydroxyl Number. The molecular weight of polyether polyols for urethanes is usually expressed as its hydroxyl number or percent hydroxyl. When KOH (56,100 meg/mol) is the base, the hydroxyl number is defined as 56,100/equivalent weight (eq wt). Writing the equation as eq wt = 56,100/OH No. allows one to calculate the equivalents of polyol used in a urethane formulation, and then the amount of isocyanate required. The molecular weight can be calculated from these equations if the fiinctionahty, is known mol wt = / eq wt. 

Over the last 12 years direct formation of a four-membered /8-lactam ring via [2 + 2 jcyclo addition of ketenes to imines and of isocyanates to olefins dominated over other methods. Because of the well-defined transition states, both cycloadditions usually offer an excellent stereoselectivity. In the case of cycloaddition of ketenes or their equivalents to imines, the cycloadducts were used not only for the synthesis of /8-lactam antibiotics, but also as intermediates for the preparation of other biologically active compounds. 

---