Boron-functionalized
polymers are used in opto-electronics,
biology,
and medicine. Methods to produce boron-functionalized and degradable
polyesters remain exceedingly rare but relevant where (bio)dissipation
is required, for example, in self-assembled nanostructures, dynamic
polymer networks, and bio-imaging. Here, a boronic ester-phthalic
anhydride and various epoxides (cyclohexene oxide, vinyl-cyclohexene
oxide, propene oxide, allyl glycidyl ether) undergo controlled ring-opening
copolymerization (ROCOP), catalyzed by organometallic complexes [Zn(II)Mg(II)
or Al(III)K(I)] or a phosphazene organobase. The polymerizations are
well controlled allowing for the modulation of the polyester structures
(e.g., by epoxide selection, AB, or ABA blocks), molar masses (9.4
<Mn< 40 kg/mol), and uptake of
boron functionalities (esters, acids, “ates”, boroxines,
and fluorescent groups) in the polymer. The boronic ester-functionalized
polymers are amorphous, with high glass transition temperatures (81
<Tg< 224 °C) and good thermal
stability (285 <Td< 322 °C).
The boronic ester-polyesters are deprotected to yield boronic acid-
and borate-polyesters; the ionic polymers are water soluble and degradable
under alkaline conditions. Using a hydrophilic macro-initiator in
alternating epoxide/anhydride ROCOP, and lactone ring opening polymerization,
produces amphiphilic AB and ABC copolyesters. Alternatively, the boron-functionalities
are subjected to Pd(II)-catalyzed cross-couplings to install fluorescent
groups (BODIPY). The utility of this new monomer as a platform to
construct specialized polyesters materials is exemplified here in
the synthesis of fluorescent spherical nanoparticles that self-assemble
in water (Dh= 40 nm). The selective copolymerization,
variable structural composition, and adjustable boron loading represent
a versatile technology for future explorations of degradable, well-defined,
and functional polymers.