ARTICLE
Figure 13 gives the plot of shear loss modulus versus tem-
perature, the peak value of which is generally a good indica-
tion of the glass transition temperature. The Tg obtained
and the effect of catalyst concentration, were investigated
with DSC dynamic scans. For both the BE-diyne/BA-bisazide
and TeEG-diyne/BA-bisazide system, the polymer Tg
increases with increasing catalyst concentration and decreas-
ing heating rates. Since oligoethylene glycol groups are more
flexible than rigid phenyl groups, the Tg of poly (T/B) is
much lower than poly (B/B). The effect of catalyst concentra-
tion on the reaction kinetics is complicated. Overall, the acti-
vation energy decreases with increasing catalyst concentra-
tion for both systems. The kinetic model developed suggests
that the bulk ‘‘click’’ polymerization follows nth order reac-
tion kinetics with a reaction order of about 1.2 for all sam-
ples except B/B-3, which follows autocatalytic reaction
kinetics and has a total reaction order (n þ m) of 1.9. The
resulting polymers were confirmed by 1H NMR and eval-
uated by rheological experiments. In the thermogravimetry
analysis, the catalyst concentration and heating rate do not
show significant effects on the thermal stability of the result-
ing polymers. Both systems have a decomposition tempera-
ꢂ
from the peaks are 97.1 and 41.7 C, for poly (B/B) and poly
(T/B), respectively. After these torsional dynamic mechanical
analysis experiments, DSC samples were prepared from the
resulting polymers and evaluated in dynamic scan DSC
ꢂ
experiments at 10 C/min. There is no exothermic peak pres-
ent in the resulting DSC curve, which indicates that the bulk
polymerization was complete. The glass transition tempera-
tures measured by DSC are about 20 ꢂC lower than the val-
ues measured by DMA.
The thermal stability of the resulting ‘‘click’’ polymers was
evaluated by using thermogꢂravimetry (TG). The samples
were heated to 800 ꢂC at 20 C/min with an air purge (Fig.
14). The temperature at the 5% mass loss is taken as the
decomposition temperature, Td. It was found that Td is not
significantly affected by such polymerization conditions as
heating rate or catalyst coꢂncentration. The Td of poly(TeEG-
diyne/BA-bisazide) is 320 C and slightly higher than that of
poly(BE-diyne/BA-bisazide), 318 ꢂC. Since the poly (T/B)
contains the less stable tetraethylene glycol groups in the
backbone of the polymer chains, they are less stable and
decompose faster than the poly (B/B) as shown as a steeper
drop on the TG curve in the temperature range between 300
and 450 ꢂC. Above 700 ꢂC, both polymers are completely
degraded, with no residual char.
ꢂ
ture of about 320 C in air. Furthermore, the TeEG-diyne has
a very low viscosity, making the TeEG-diyne/BA-bisazide sys-
tem attractive for self-healing applications.
Financial support from the US Army Corps of Engineers,
Engineer Research and Development Center Construction En-
gineering Research Laboratory is gratefully acknowledged.
The work was conducted under contract number W9132T-
09-C-0003. The COTR was Jonathan Trovillion.
For self-healing materials, the viscosity of the healing mono-
mer must be low to achieve successful self-healing. A low
viscosity healing monomer can flow freely into a damage
region and easily diffuse to the tips of the growing micro-
cracks. Viscosity tests were performed on a rheometer with
a cone/plate geometry. Five samples were tested: the three
monomers and the two mixtures of alkyne and azide (1:1
mole ratio). A continuous flow test was conducted for each
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AZIDE/ALKYNE ‘‘CLICK’’ POLYMERIZATION, SHENG, MAULDIN, AND KESSLER
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