Catalytic Synthesis and Characterization of Biodegradable ...

Chapter 4
4.4 Thermal Properties
The DSC thermograms of the PTAm homopolymer, PLA-HEMA and PTAm-g-PLA2 were
recorded and shown in Figure 4.6A. PTAm showed no thermal transition at temperatures
above 20 o C. The melting temperature Tm of PLA-HEMA was low, around 133 o C, due to its
low molecular weight. For PTAm-g-PLA copolymer, no Tg or Tm was observed in the tested
temperature ranges, which may be ascribed to the low PLA content in the copolymer. The
TGA curves of the PTAm homopolymer, PLA-HEMA and PTAm-g-PLA also demonstrated
that the copolymers had similar thermal properties with that of PTAm (Figure 4.6B).
Figure 4.6 (A) DSC traces of the PLA-HEMA, PTAm, and PTAm-g-PLA2 in second heating. (B)
TGA curves of PLA-HEMA, PTAm, and PTAm-g-PLA.
4.5 Phase Separation Behavior of PTAm-g-PLA
The phase behavior of the PTAm-g-PLA copolymer is very important to its application.
Therefore, the phase images of blend of PTAm and PLA, blend of PLA and PTAm-g-PLA2,
PTAm-g-PLA2 and PTAm-g-PLA1 films cast from their chloroform solutions were examined
by AFM (Figure 4.7). It was observed in Figure 4.7B and 4.7C that the film of copolymer
exhibited two different phases. One was continuous and another phase was uniformly
dispersed in the film. Considering the low PLA content in PTAm-g-PLA2 and PTAm-g-PLA1,
it can be safely concluded that the continuous phase was PTAm. This unique phase behavior
can probably be attributed to the immiscible nature of PTAm and PLA as shown in Figure
4.7A. It had been demonstrated that the incorporation of two immiscible chains into one
copolymer prevented the macro-phase separation of these incompatible materials, which can
restrict the partition of the components to nanoscopic (1-100 nm) domains. 23 As shown in
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