Chemistry Reference
In-Depth Information
bearing hydroxyl groups. Such compounds may be glycols, dihydroxy-terminated polyethers or
polyesters, and others. Difunctional reactants will produce linear polyurethanes:
HH
R
+
ON
NO
ON
R'
NO
HO
OH
R
R'
n
O
O
A special method for the preparation of polyurethane polymers was reported [
245
]. In this new
procedure, use is made of “latent” aminimide monomers that are stable and not reactive under normal
storage conditions. An example is a monomer, an aminimide, like 1,1,1-trimethylamine 2-(4-
hydroxymethylbenzoyl)-imide that undergoes self-polyaddition above 150
C to yield the polyure-
thane [
245
]:
Δ
NCO
HO
N
N
HO
+
N
O
O
O
N
n
H
The above monomer can be prepared by reacting methyl
para
-hydroxymethyl-benzoate with I,l,l-
-toluene sulfonate, catalyzed by sodium methoxide. At 170
C, 90% of this
monomer converts to polymer in 5 h [
245
].
trimethylhydrazinium
p
7.10.1 Preparations of Polyfunctional Isocyanates
Polyfunctional isocyanates can be formed in many ways [
122
]. Commercially, the most important
one is through reactions of phosgene with amines or amine salts. Other reactions, however, like that of
carbon monoxide with nitro compounds are also utilized. Additions of isocyanic acid to olefins are
also gaining prominence.
7.10.2 Commercial Polyisocyanates
Two types of diisocyanates are employed in polymer preparations, aromatic and aliphatic ones. Themost
commonly used aromatic diisocyanates are toluene diisocyanate and 4,4
0
-diphenylmethane diiso-
cyanate. Commercial toluene diisocyanate often comes as a mixture of 2,4 and 2,6 isomers in ratios of
80/20 or 65/35. When the reaction takes place at room temperature, the four position is 8-10 times more
reactive than two. At elevated temperatures, however, this difference in reactivity decreases, and at
100
C the reactivity of the isocyanate groups in both positions is approximately equal.
