Comparative Properties of Ethyl, n -Butyl, and n -Octyl Cyanoacrylate Bioadhesives Intended for Wound Closure - Biologically Responsive Biomaterials for Tissue Engineering - page 97

Table 5.4 Assignment of the
most characteristic signals in
the 13 C NMR spectrum of the
n -butyl

C d (ppm)

C 1 129.38

C 2 103.25

cyanoacrylate

C 3 100.83

monomer

C 4 146.93

C 5 63.46

C 6 53.11

C 7 16.93

C 8 5.39

a b

3

100

Ethyl Cyanoa crylate

80

Butyl Cyanoa crylate

Octyl Cyanoa crylate

2

60

Butyl Cyanoa crylate

Octyl Cyanoa crylate

40

Ethyl Cyanoa crylate

1

20

0

-20

0

0 50 100 150 200 250 300 350 400

0 50 100 150 200 250 300 350 400

Temperature (°C) Temperature (°C)

Fig. 5.8 ( a ) TGA thermograms of the cyanoacrylate monomers. ( b ) Derivative curves of the TGA
thermograms of the cyanoacrylate monomers

the assignment of the carbons of BCN monomer. The signals corresponding to the
carbons corresponding to C=C, C=O, and C≡N groups displace to higher values by
increasing the length of the alkyl hydrocarbon chain in the cyanoacrylate monomer.
The 13 C NMR spectrum of the OCN shows a more noticeable content of aliphatic
carbons with respect to the signals of the other cyanoacrylate monomers.
In this study TGA was found useful and sensitive to analyze the structure of the
cyanoacrylate monomers. Figure 5.8a shows the TGA thermograms of the three
cyanoacrylate monomers and the corresponding derivative curves are given in
Fig. 5.8b ; the derivative curves are useful for showing more precisely the thermal
decompositions in the cyanoacrylate monomers.
The TGA curves of the three cyanoacrylate monomers show the first decomposi-
tion at about 120 °C (Table 5.5 ), likely due to formaldehyde evolution. This first
decomposition becomes less marked by increasing the length of the alkyl chain of
the cyanoacrylate monomer, i.e., the weight loss at this temperature decreases from
ethyl to n -octyl cyanoacrylate monomer. On the other hand, the thermal stability of
the cyanoacrylate monomer increases by increasing the length of the alkyl hydro-
carbon chain, likely due to the increase in its molecular weight.
The presence of more than one decomposition step in the cyanoacrylate mono-
mers is an indication of the presence of oligomers in their structure. Whereas the
ECN is mainly composed of monomer (98.7 wt% is lost at 117 °C), the BCN