Polymerization
Induced Self-Assembly of Alginate Based
Amphiphilic Graft Copolymers Synthesized by Single Electron Transfer
Living Radical Polymerization
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Abstract
Alginate-based
amphiphilic graft copolymers were synthesized by
single electron transfer living radical polymerization (SET-LRP),
forming stable micelles during polymerization induced self-assembly
(PISA). First, alginate macroinitiator was prepared by partial depolymerization
of native alginate, solubility modification and attachment of initiator.
Depolymerized low molecular weight alginate (∼12 000
g/mol) was modified with tetrabutylammonium, enabling miscibility
in anhydrous organic solvents, followed by initiator attachment via
esterification yielding a macroinitiator with a degree of substitution
of 0.02, or 1–2 initiator groups per alginate chain. Then,
methyl methacrylate was polymerized from the alginate macroinitiator
in mixtures of water and methanol, forming poly(methyl methacrylate)
grafts, prior to self-assembly, of ∼75 000 g/mol and
polydispersity of 1.2. PISA of the amphiphilic graft-copolymer resulted
in the formation of micelles with diameters of 50–300 nm characterized
by light scattering and electron microscopy. As the first reported
case of LRP from alginate, this work introduces a synthetic route
to a preparation of alginate-based hybrid polymers with a precise
macromolecular architecture and desired functionalities. The intended
application is the preparation of micelles for drug delivery; however,
LRP from alginate can also be applied in the field of biomaterials
to the improvement of alginate-based hydrogel systems such as nano-
and microhydrogel particles, islet encapsulation materials, hydrogel
implants, and topical applications. Such modified alginates can also
improve the function and application of native alginates in food and
agricultural applications