Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
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1.6.1 Radical Polymers for Organic Electronic Devices<br />
1.6.1.1 Organic Radical Batteries<br />
- 41 -<br />
Polymerization <strong>and</strong> Applications <strong>of</strong> <strong>Biodegradable</strong> Polyesters<br />
Rechargeable secondary batteries are widely used in portable equipments. Li-ion battery<br />
represents the currently most popular usage. However, the application <strong>of</strong> metal-based<br />
electrodes has come up against some inherent disadvantages, such as limited raw-material<br />
resource <strong>and</strong> tedious waste process. Therefore, organic-based electrode-active materials have<br />
received more <strong>and</strong> more attentions. Over the past few years, we have focused on the<br />
development <strong>of</strong> polymer bearing densely populated unpaired electrons, such as nitroxides,<br />
phenoxyl <strong>and</strong> galvinoxyl, in the pendant per repeating unit <strong>and</strong> utility <strong>of</strong> them as<br />
electro-active or charge-storage material in a rechargeable device. 178, 183-190 The organic<br />
178, 183, 188<br />
radical battery composed <strong>of</strong> the radical polymer electrodes has several advantages:<br />
(1) a high charging <strong>and</strong> -discharging capacity (>100 mAh/g), ascribed to the stoichiometric<br />
redox <strong>of</strong> the radical moieties, (2) a high-charging <strong>and</strong> -discharging rate performance resulting<br />
from the rapid electron-transfer process <strong>of</strong> the radical species <strong>and</strong> from the amorphous state <strong>of</strong><br />
the radical polymers, <strong>and</strong> (3) a long cycle life, <strong>of</strong>ten exceeding 1000 cycles, derived from the<br />
chemical stability <strong>of</strong> the radicals <strong>and</strong> from the amorphous electrode structure.<br />
A variety <strong>of</strong> polymer backbones have been employed by our group to bear the pendant<br />
radicals, such as poly(meth)arylates, polystyrene derivatives, polymer(vinyl ether)s,<br />
polyethers <strong>and</strong> poly(norbornene)s, <strong>and</strong> were depicted in Figure 1.6.2 <strong>and</strong> Figure 1.6.3. Radical<br />
polymers, most <strong>of</strong> time, were synthesized by conventional radical polymerizations, <strong>and</strong> an<br />
additional oxidation processes must be needed in this case. The unpaired electron density <strong>of</strong><br />
the polymers was then measured by SQUID, revealing the presence <strong>of</strong> the radicals in each<br />
repeating unit. The versatile <strong>of</strong> the polymers backbones also have another advantage, i.e. the<br />
polymers allow to be conveniently placed on the surface <strong>of</strong> a current collector by a<br />
solution-based wet process such spin-coating method. When the polymer is placed on the<br />
surface <strong>of</strong> the current collector <strong>and</strong> equilibrated in electrolyte solution, charge propagation<br />
within the polymer layer is sufficiently accomplished, leading to high-density charge storage<br />
because the redox sites are so populated that electron self-exchange reactions are completed<br />
within a finite distance <strong>of</strong> the polymer layer. 189