Chemistry Reference
In-Depth Information
and has been extensively reviewed in the literature [244-247]. Some recent data on
new urethane polymeric materials are presented below.
Substituted 4,4
0
-methylenebis(3-chloro-2-alkylphenyl isocyanate)s, prepared with
phosgene, form isocyanate prepolymers useful for producing polyurea-polyur-
ethanes with high chemical resistance and good thermal stability, and for conver-
sion to polyether-polyurea-polyurethane elastomers [248].
Methylenediphenyldicarbamate-based aromatic polycarbamate mixtures, useful for
preparing polyurethanes, are prepared by nitration of diphenylmethane and re-
action of the resulting dinitrodiphenylmethane-based mixtures with hydroxyl-
containing organic compounds and carbon monoxide in presence of a catalyst
[249].
Aromatic urethanes, useful as starting materials for polymethylene polyphenyl
polyisocyanates, are prepared by treating aromatic nitro compounds with hydroxyl-
containing organic compounds and CO in the presence of platinum group cata-
lysts and promoters comprising Lewis acids and
0.5 mol (per 1 g-ion of anion
of the Lewis acids) of N-containing heteroaromatic bidentate ligands [250]. Ure-
thanes, useful for the preparation of polyurethanes, are prepared by the reaction
of alcohols and CO with organic nitro compounds in the presence of a Cu cat-
alyst. For example, pressurizing a mixture of nitrobenzene, CuCl
2
<
2H
2
O, EtOH,
and pyridine (promoter) with CO to 1000 psig at room temperature and stirring at
180
C for 4 h gave a 76% conversion of nitrobenzene to ethyl phenylcarbamate
(90% selectivity) [251]. A method for manufacturing aromatic urethanes involving
a process for producing N,N-disubstituted ureas using carbon monoxide in the
presence of a catalyst and a solvent is described in a European patent [252].
Polyurethane leather substitute and nylon-6 melt-coated vinyl fabrics were
treated with elastomeric polycarbonates, such as polytetramethylene glycol-
bisphenol A-phosgene polymer, poly(ethylene adipate)-4,4
0
-dihydroxydiphenyl-
methane-phosgene polymer, or ethylene bis( p-hydroxybenzoate)-polytetra-
methylene glycol-phosgene polymer to give products with improved abrasion
resistance and flexural strength [253].
Nematic polyurethanes derived from 4,4
0
-dihydroxybiphenyl and 4,4
0
-bipiperidine,
ethylene-4,4
0
-bipiperidine, or trimethylene-4,4
0
-bipiperidine have been reported
[254]. 4,4
0
-Bipiperidine, 1,2-bis(4-piperidinyl)ethane, and 1,3-bis(4-piperidinyl)pro-
pane were condensed with the dichloroformates of p-phenylene, 2-methyl-1,4-
phenylene, or 2,5-biphenylylene. Furthermore, two copolyurethanes were prepared
either by mixing 4,4
0
-bipiperidine and 1,2-bis(4-piperidinyl)ethane or by mixing the
dichloroformates of p-phenylene and 2,5-biphenylene. The polyurethanes derived
from hydroquinone or methylhydroquinone were semicrystalline polymers with a
short-term thermostability up to 310
C. The polyurethanes derived from phenyl-
hydroquinone were amorphous with a thermostability up to 360
C. The homo-
and co-polyurethanes containing 4,4
0
-biphenylylene units formed a smectic layer
structure in the solid state and a nematic melt above the melting point [254].
A new method for the synthesis of linear, film- and fibre-forming polyur-
ethanes free of allophanate branches and cross-links, by reacting activated diol
bis(carbonate)s with diamines, has also been reported [255].
