Browsing by Author "Hillmyer research group UMN Chemistry"

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    Entropically-driven macrolide polymerizations for the synthesis of aliphatic polyester copolymers using titanium isopropoxide
    (2019-03-11) Amador, Adrian G; Watts, Annabelle; Neitzel, Angelika, E; Hillmyer, Marc A; hillmyer@umn.edu; Hillmyer, Marc A; Hillmyer research group UMN Chemistry
    Thermal and mechanical properties of sustainable aliphatic polyesters can be tuned through the synthesis of copolymers. The synthesis of two 14-membered macrolides are reported: a cyclic tetraester with alternating lactic acid (LA) and 3-hydroxypropionic acid (3HP) units and a cyclic diester with alternating glycolic acid (GA) and 2-methyl-1,3-propanediol (2MD) units. Ring-opening transesterification polymerization (ROTEP) of these macrolides to yield poly(LA-stat-3HP) and poly(GA-alt-2MD), respectively, were found to be modestly endothermic (ΔHp° = 2.0 kJ mol-1 and 0.5 kJ mol-1, respectively) and endoentropic (ΔSp° = 27 J mol-1 K-1 and 23 J mol-1 K-1, respectively). Inexpensive and non-toxic titanium isopropoxide Ti(Oi-Pr)4 functions as an active catalyst for these entropically-driven ROTEPs, achieving high conversions (> 90%) in under 1 h. The polymerizations exhibit control over molar mass with dispersity values < 1.7. P(GA-alt-2MD) is an amorphous polymer with a low glass transition temperature near −30 °C. P(LA-co-3HP) exhibits a glass transition temperature up to 13 °C and depending on the regioregularity, exhibits a melting temperature up to 96 °C.