Biomedical Engineering Reference
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aggregate formation by the intramolecular interaction between neighboring
hydrophobic side chains in the same backbone, whereas polymers with stiff
backbones may be associated with secondary aggregation by the intermolecular
interaction of surfaces between the polymers. The critical concentration to form
self-aggregates is generally called “critical aggregation concentration (cac)”. The
shape and character of the self-aggregates by amphiphilic polyaspartamides is
mainly affected by molecular weight and the T
g
of the graft copolymers, length
and degree of substitution (DS) of the hydrophobic or hydrophilic moiety, and
their crystallinity. Various amphiphlic polyaspartamides, which can form nano-
aggregates in aqueous solution, have been developed by aminolysis reaction of
PSI with various hydrophobic molecules [20-26] and some of them are shown in
Figure 5.
Self-aggregates of amphiphilic alkyl chain-grafted polyaspartic acids and
polycaprolactone-grafted polyasparagines were prepared by Kim and
coworkers.[20, 21] As shown in Figure 6, CAC decreased with increasing length
or DS of the alkyl chains and PCL. Nano-aggregates of PCL-g-PASNs were
formed by a precipitation and dialysis method. Their size decreased from 160 to
60 nm with more stable aggregates forming upon increase of the DS of PCL
Fig. 6. CAC of polyaminoacids grafted with hydrophobic moieties determined by emission
fluorescence of pyrene. (Jeong, J. H., et al., “Polymer Micelle-like Aggregates of Novel
Amphiphilic Biodegradable Poly(asparagines) Grafted with Poly(caprolactone)”,
Polymer,
Vol. 44,
2003, pp. 583-591. With permission).
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