Catalytic Synthesis and Characterization of Biodegradable ...

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