Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Chapter 5<br />
5.1 Introduction<br />
Radical polymers bearing pendant 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO) groups<br />
have attracted increasing interest due to their unique characteristics associated with the<br />
unpaired electrons present in free radicals. Up to now, radical polymers have been found<br />
numerous potential applications such as catalyst for redox reaction, 1 one-dimensional<br />
throw-bond organic ferromagnets, 2 probe for in vivo electron paramagnetic resonance (EPR) 3<br />
<strong>and</strong> cathode material for bendable batteries. 4 In Chapter 4 we synthesized graft copolymers<br />
composed <strong>of</strong> poly(2,2,6,6-tetramethylpiperidine-1-oxyl-4-yl acrylamide) (PTAm) <strong>and</strong><br />
polylactide (PLA) <strong>and</strong> preliminarily investigated their application in biomedical field.<br />
However, the graft copolymers did not possessed definite structure due to the r<strong>and</strong>om<br />
location <strong>of</strong> PLA on the PTAm backbone. Therefore, it is necessary to design block<br />
copolymers <strong>of</strong> PLA <strong>and</strong> PTAm with well-defined structure <strong>and</strong> controlled molecular weight.<br />
The block copolymer <strong>of</strong> PTAm <strong>and</strong> PLA should combine the electroactive property <strong>of</strong> radical<br />
polymers <strong>and</strong> biodegradable property <strong>of</strong> PLA together.<br />
In this chapter, well-defined triblock copolymers composed <strong>of</strong> a radical polymer, PTAm,<br />
<strong>and</strong> PLA were synthesized by combination <strong>of</strong> ring-opening polymerization (ROP) <strong>and</strong><br />
reversible addition-fragmentation chain transfer (RAFT) polymerization methods. Compared<br />
to another controlled radical polymerization method, atom transfer radical polymerization<br />
(ATRP), RAFT appears more practical in terms <strong>of</strong> monomer selection <strong>and</strong> reaction<br />
conditions. 5-7 Moreover, RAFT technique requires fewer purification steps after the<br />
polymerization.<br />
The resulted copolymers were then electrospun into mats with varied morphology.<br />
Electro-spinning technique was originally developed to produce ultra-fine polymer fibers, <strong>and</strong><br />
has recently re-emerged as a novel tool for generating micro- or nano-scale biopolymer<br />
scaffolds for tissue engineering. 8-10 The scaffolds fabricated by electro-spinning have highly<br />
porous microstructure with interconnected pores <strong>and</strong> an extremely large specific surface-area,<br />
which allow accommodation <strong>of</strong> a large number <strong>of</strong> cells <strong>and</strong> facilitate uniform distribution <strong>of</strong><br />
cells <strong>and</strong> diffusion <strong>of</strong> oxygen <strong>and</strong> nutrients. We envisioned that this material could exhibit<br />
improved biocompatibility, biodegradability, solubility <strong>and</strong> processability. More importantly,<br />
it may have promising application as electroactive biomedical materials.<br />
‐ 102 ‐