Isosorbide
is a stiff bicyclic diol derived from glycose-based
polysaccharides, and is thus an attractive building block for novel
rigid bioplastics. In the present work, a highly regioselective biocatalytic
approach for the synthesis of isosorbide 5-methacrylate was developed.
The Lipozyme RM IM (Rhizomucor miehei lipase)-catalyzed process is straightforward, easily scalable, and
chromatography-free; a simple extractive workup afforded the monomer
at >99% purity and in 87% yield. The developed strategy was applied
for the synthesis of a series of monomethacrylated isosorbide derivatives.
Radical polymerization of the monomers produced rigid polymethacrylates
with a certain side group in either endo or exo configuration, exclusively, which generated materials
with great diversity of properties. For example, the two regioisomeric
polymers carrying hydroxyl groups reached a glass transition temperature
at T
g = 167 °C. The polymer tethered
with dodecanoate chains in exo position showed crystallinity
with an unexpectedly high melting point at T
m = 83 °C. In contrast, the corresponding sample with
dodecanoate chains in endo positions was fully amorphous
with T
g = 54 °C. Efficient biocatalytic
synthesis combined with attractive polymer properties opens possibilities
for production of these biobased polymers on an industrial scale.
Conversion of biobased platform chemicals
to enantiopure compounds
has become topical. We report a straightforward synthesis of 4-(acyloxy)-pentanoic
acids from γ-valerolactone (GVL). An alkaline hydrolysis of
GVL is followed by a stereoselective lipase-catalyzed acylation of
the sodium salt. Acidic hydrolysis of the acylation product affords
(R)-4-(acyloxy)pentanoic acid and relactonized (S)-GVL. (R)-4-(Propionyloxy)pentanoic acid
and (R)-GVL are obtained with e.r. > 99/1. An additional enzymatic step following a slightly modified
process affords (S)-4-(acetyloxy)pentanoic acid with e.r. > 99/1. Simple access to enantiopure 4-(acyloxy)pentanoic
acids will stimulate the development of their novel applications,
including biobased isotactic polymers.
We
have prepared a series of 12
d
-isosorbide-2-alkanoate-5-methacrylate
monomers as single regioisomers with different pendant linear C2–C20
alkanoyl chains using biocatalytic and chemical acylations. By conventional
radical polymerization, these monomers provided high-molecular-weight
biobased poly(alkanoyl isosorbide methacrylate)s (PAIMAs). Samples
with C2–C12 alkanoyl chains were amorphous with glass transition
temperatures from 107 to 54 °C, while C14–C20 chains provided
semicrystalline materials with melting points up to 59 °C. Moreover,
PAIMAs with C13–C20 chains formed liquid crystalline mesophases
with transition temperatures up to 93 °C. The mesophases were
studied using polarized optical microscopy, and rheology showed stepwise
changes of the viscosity at the transition temperature. Unexpectedly,
a PAIMA prepared from a regioisomeric monomer (C18) showed semicrystallinity
but not liquid crystallinity. Consequently, the properties of the
PAIMAs were readily tunable by controlling the phase structure and
transitions through the alkanoyl chain length and the regiochemistry
to form fully amorphous, semicrystalline, or semi/liquid crystalline
materials.
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