Ring Opening Copolymerization of Boron-Containing Anhydride with Epoxides as a Controlled Platform to Functional Polyesters

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

Automated summary

Boron-functionalized polymers have wide applications in opto-electronics, biology, and medicine. However, methods to produce boron-functionalized and degradable polyesters are rare. This study presents a controlled ring-opening copolymerization method to produce boron-functionalized polyesters. The resulting polymers have adjustable structures, molecular weights, and boron functionalities. The boronic ester-functionalized polymers are amorphous and have high glass transition temperatures and good thermal stability. The utility of this method is demonstrated by synthesizing fluorescent spherical nanoparticles. This versatile technology provides a platform for future explorations of degradable and functional polymers.