Chemistry Reference
In-Depth Information
O
CHO
1.
O
+
O
HO
CHO
O
+
O
2.
OH
O
Products from reactions of rubber with glyoxal have a strong tendency to become spontaneously
insoluble. This is probably due to a presence of residual aldehyde groups, because a treatment of the
product with 2,4-dinitrophenyl-hydrazine eliminates spontaneous gelation.
Chloral adds to polyisoprene similarly. The reaction is catalyzed by Lewis acids [
70
]. Both AlCl
3
and BF
3
are efficient catalysts. Less cross-linking is encountered with aluminum chloride. Infra-red
spectra of the products shows presence of hydroxyl groups, chlorine atoms, and vinylidene
unsaturation [
70
].
9.2.5 Polar Additions
A number of polar additions to unsaturated polymers are known. These include Michael addition,
hydroboration, 1,3-dipolar additions, ene reaction, the Ritter reaction, Diels-Alder additions, and others.
9.2.5.1 Michael Addition
Among polar additions to unsaturated polymers are reactions of amines and ammonia with unsaturated
polyesters in a form of a Michael condensation. Thus, for instance, additions to poly(1,6-hexanediol
maleate) and poly(1,6-hexanediol fumarate) [
71
] show a difference in the reactivity of the two isomers.
The maleate polyester reacts with ammonia to yield a cross-linked product at room temperature, when
stoichiometric quantities or excess ammonia in alcohol is used. At the same reaction conditions, the
fumarate isomer only adds a few percent of ammonia [
71
]. In a 1:1 mixture of chloroform and ethanol,
however, approximately half of the fumarate double bonds react. Also, the maleate polyester reacts
differently with piperidine or cyclohexylamine. In butyl alcohol at 60
C, the polymer initially
isomerizes and precipitates. After the isomerization is complete and the temperature is raised to
80
C, the polymer redissolves. An exothermic reaction follows and Michael type adducts form [
71
].
