Chemistry Reference
In-Depth Information
Fig. 7.6
Intercrosslinked
biohybrid from amino-starch
and epoxy-amine silicate
colloids
Fig. 7.7
Biohybrid formation
using epoxysilicate colloids
and amine functionalized
starch
functionalizing starch in aqueous solution via a one-pot reaction using epichloro-
hydrin under basic conditions followed by reaction with ammonia to yield propyl
amine groups distributed over the length of the starch backbone. Work by Ayoub
et al. has demonstrated that the reaction performed with glycidyl ammonium ana-
logs in the presence of a moderate excess of NaOH results in degrees of substitution
(DS) in the 0.05 range, or one substitution every 20 saccharide rings approximately.
[
21
,
22
] Reacting an alkaline starch solution with epichlorohydrin in similar condi-
tions, then treating the resulting glycidyl starch product with excess ammonia leads
to a 0.085 DS aminoglyceryl grafted starch. This corresponds to one substitution
every 11 or 12 sugar units as measured by elemental analysis and NMR. The reac-
tion can be followed readily in the solid state by infrared spectroscopy to demon-
strate the appearance of the epoxide CH
2
stretch at 3045 cm
−1
and its subsequent
consumption.
By reacting this amine functionalized starch with the prefabricated epoxy and
amine silicates, we have formed intercrosslinked polymer networks with covalent
interactions between the epoxy-silicate and the amine functionalized starch as well
as between the epoxy and amine silicates as above in the IPN biohybrid. The inter-
crosslinked polymer is shown schematically in Fig.
7.6
.
A different intercrosslinked material can also be obtained by excluding the amine
decorated silicate so that only the epoxy silicate and the amine functionalized starch
are used to produce a solid. This is shown schematically in Fig.
7.7
. This material is
typically much slower to solidify as the concentration of amine groups is relatively
low however the resulting material is much more dense and glassy. This is thought
to be due to the fact that more of the amine groups of the starch are reacted with
the silicate epoxide whereas in the case of the intercrosslinked hybrid using both
amino silicate colloids and amine functionalized starch, the more rapidly reacting
amino silicate colloids are predominantly responsible for crosslinking the material
and more of the amine groups on the starch remain unreacted, allowing for greater
flexibility in the material.
