Chemistry Reference
In-Depth Information
the polymer using the thiol-ene reaction (see Scheme 4.25). All five thiols
modified the double bonds to sulfide with conversions above 99%, as
determined by
1
H-NMR. The grafted polymers showed higher T
g
values than
the starting material.
4.4.3.2 Synthesis of Thiol-ene Polymers using Synthetically
Introduced Thiol Groups
Goethals et al.
60
synthesized 10-undecenoylthiolactonamide from 10-
undecenoic acid. Upon reaction with amine, the thiolactone structure
generated a thiol capable of reaction with the double bonds (Scheme 4.26).
A series of polymers was synthesized utilizing different amines. The poly-
mers started degrading in air above 250 1C and the C-S bond was reported
to be the most prone to oxidation. The T
g
values ranged between 5 and
50 1C, and the elongation at break approached 1000%. Oxidation of
the sulfide groups to sulfoxide and sulfone increased the elastic
modulus, but decreased the elongation at break. Cross-linked polymers,
with a soluble fraction of 5 to 23%, were prepared using diamines as cross-
linkers.
van den Berg et al.
61
made polymers containing only bio-based
carbons and hydrogens, achieved by a lengthy conversion of carboxylic
groups into -CH
2
SH groups (Scheme 4.27). The physical properties of the
prepared polymer resemble those of low-density polyethylene (LDPE), with
an elastic modulus of about 300 MPa and a melting temperature of 90 1C.
Oxidation of the polythioether with hydrogen peroxide resulted in an
intermediate sulfoxide-functionalized polymer, which was still soluble in
common polar solvents. Further oxidation yielded a sulfone-functionalized
polymer that was insoluble in any solvent tested. The elastic modulus of
the polymer increased almost 1.5 times upon oxidation. The melting
temperature increased to 175 1C, accompanied by the occurrence of mul-
tiple melting peaks. The onset of thermal decomposition was found to be
around 350 1C.
The radical thiol-ene addition is well known to be anti-Markovnikov, e.g.,
the sulfur atom is expected to attach to the 11
th
atom of the 10-undecenoic
group. The authors report that some of the sulfur atoms attached to the 10
th
atom. This report suggests that similar partial Markovnikov attachment
could occur undetected in similar
reactions carried out with 10-
undecenoic acid.
Firdaus et al.
55
used an indirect approach to introduce thiol groups to
bio-based compounds with two olefinic bonds (undecenylic ether (UE) and
D-limonene) per molecule (Schemes 4.10 and 4.28). They reacted the
synthesized dithiols (di(11-thiol undecyl)ether (DTUE) and 5-((R)-1
0
-mercap-
topropan-20-yl)-2-methylcyclohexanethiol (DTL)) with one of the starting
olefinic materials (UE). The polymer formed from DTUE was insoluble in
