2.2 EO Polymerization Methods
Synthetic approaches to degradable PEGs that do not rely on postpolymerization
reactions of commercial PEGs have evolved very recently and rely on initiation
from a macroinitiator with a cleavable moiety [69, 70], elimination of HCl
from EO/epichlorohydrin copolymers [147] and copolymerization of EO with a
cleavable AROP inimer [68]. In 2011, Gnanou, Taton and coworkers presented an
elegant synthetic route to acid-degradable dendrimer-like PEOs (poly(ethylene oxide)
s, i.e., high molecular weight PEGs) with ketal branching units (Scheme 1) [69]. All
of the degradable dendritic PEOs from the second (G2, M n, NMR ¼ 10,600 g mol
À1
)
to the seventh generation (G7, M n, NMR ¼ 446,000 g mol
À1
) were well-defined, with
PDIs below 1.10. Degradation of these materials was proven under different
conditions. In extremely acidic media, three samples of different generations (G2,
G3, and G7) degraded completely to PEG derivatives with molecular weights of
Scheme 1 Synthesis of acid-degradable dendrimer-like PEO. From [69]. Copyright Wiley-VCH.
Reproduced with permission
From Biocompatible to Biodegradable: Poly(Ethylene Glycol)s with. . .
173
Synthetic approaches to degradable PEGs that do not rely on postpolymerization
reactions of commercial PEGs have evolved very recently and rely on initiation
from a macroinitiator with a cleavable moiety [69, 70], elimination of HCl
from EO/epichlorohydrin copolymers [147] and copolymerization of EO with a
cleavable AROP inimer [68]. In 2011, Gnanou, Taton and coworkers presented an
elegant synthetic route to acid-degradable dendrimer-like PEOs (poly(ethylene oxide)
s, i.e., high molecular weight PEGs) with ketal branching units (Scheme 1) [69]. All
of the degradable dendritic PEOs from the second (G2, M n, NMR ¼ 10,600 g mol
À1
)
to the seventh generation (G7, M n, NMR ¼ 446,000 g mol
À1
) were well-defined, with
PDIs below 1.10. Degradation of these materials was proven under different
conditions. In extremely acidic media, three samples of different generations (G2,
G3, and G7) degraded completely to PEG derivatives with molecular weights of
Scheme 1 Synthesis of acid-degradable dendrimer-like PEO. From [69]. Copyright Wiley-VCH.
Reproduced with permission
From Biocompatible to Biodegradable: Poly(Ethylene Glycol)s with. . .
173