Biomedical Engineering Reference
In-Depth Information
CNT growth. This proved to be the case. Uniform bundles of CNTs were
grown by the CVD process at 700
◦
Cwithacetylenegasasthecarbonsource
(Fig. 20). The diameters and lengths of the CNTs were alterable by varia-
tion of the surface activation as well as the growth time [171]. As expected
from a CNT growing temperature below 800
◦
C [172, 173], the formed CNTs
were multiwalled in nature. Their diameters were, however, as small as 15 nm
(Fig. 20E).
4
Concluding Remarks
In this review we have briefly summarized the results on the synthesis of
a variety of functional hyperbranched polymers from acetylene triple-bond
building blocks. Effective polymerization reactions including polycoupling,
polyhydrosilylation, polycycloaddition and polycyclotrimerization of mono-,
di- and triynes catalyzed by metallic and non-metallic species have been
developed, which have enabled the creation of hyperbranched polyynes,
polyenes, polyarylenes and polytriazoles with high molecular weights and
macroscopic processability in high yields. The new polymerization routes
opened and the new structural insights gained offer versatile synthetic tools
and valuable guidelines for further developments in this area of research.
Using the triple-bond building blocks in combination with functional
groups have resulted in the generation of conjugated polymers with func-
tional properties. The carbon-rich polymers exhibited outstanding thermal
stabilities. Incorporation of chromophoric units enabled the modulation of
emission colors and efficiencies of the polymers at the molecular level. The
numerous aromatic rings in the
hb
-PAs conferred high optical limiting power
on the polymers, while the poled films of the azo-functionalized
hb
-PAEs
showed stable NLO performance with high SHG coefficients. Combination of
the slim diyne linker with the polarizable TPA core results in high optical
transparency with exceptionally high photorefractivity. The photosensitive
benzyl, benzophenone and diyne units endowed the polymers with photocur-
ability and hence the potential to be used as photoresists and active matrixes
in optical devices. The assemblies of hexagonal arrays of breath figures and
the micrometer-long polymer nanotubes were obtained from the dynamic
and static templating processes. The complexation with the cobalt carbonyls
yielded spin-coatable hyperbranched organometallic polymers, whose RIs
were readily tuned by UV irradiation. The hyperbranched polymer complexes
also served as precursors to advanced soft ferromagnetic ceramics and as
catalysts for the growth of CNTs.
Their simple syntheses and ready processability, coupled with their unique
structures and useful functionalities, make this group of hyperbranched poly-
mers attractive and promising for an array of high-technology applications.
