David F. Iwig

A biodegradable thermoset polymer made by esterification of citric acid and glycerol.

A new biomaterial, a degradable thermoset polymer, was made from simple, economical, biocompatable monomers without the need for a catalyst. Glycerol and citric acid, nontoxic and renewable reagents, were crosslinked by a melt polymerization reaction at temperatures from 90 to 150°C. Consistent with a condensation reaction, water was determined to be the primary byproduct. The amount of crosslinking was controlled by the reaction conditions, including temperature, reaction time, and ratio between glycerol and citric acid. Also, the amount of crosslinking was inversely proportional to the rate of degradation. As a proof-of-principle for drug delivery applications, gentamicin, an antibiotic, was incorporated into the polymer with preliminary evaluations of antimicrobial activity. The polymers incorporating gentamicin had significantly better bacteria clearing of Staphylococcus aureus compared to non-gentamicin gels for up to 9 days.

Synthesis and Polymerization of Renewable 1,3‐Cyclohexadiene Using Metathesis, Isomerization, and Cascade Reactions with Late‐metal Catalysts

Synthesis and subsequent polymerization of renewable 1,3-cyclohexadiene (1,3-CHD) from plant oils is reported via metathesis and isomerization reactions. The metathesis reaction required no plant oil purification, minimal catalyst loading, no organic solvents, and simple product recovery by distillation. After treating soybean oil with a ruthenium metathesis catalyst, the resulting 1,4-cyclohexadiene (1,4-CHD) was isomerized with RuHCl(CO)(PPh3)3. The isomerization reaction was conducted for 1 h in neat 1,4-CHD with [1,4-CHD]/[RuHCl(CO)(PPh3)3] ratios as high as 5000. The isomerization and subsequent polymerization of the renewable 1,3-CHD was examined as a two-step sequence and as a one-step cascade reaction. The polymerization was catalyzed with nickel(II)acetylacetonate/methaluminoxane in neat monomer, hydrogenated d-limonene, and toluene. The resulting polymers were characterized by FTIR, DSC, and TGA.

Diglycerol‐Based Polyesters: Melt Polymerization with Hydrophobic Anhydrides

The melt polymerization of diglycerol with bicyclic anhydride monomers derived from a naturally occurring monoterpene provides an avenue for polyesters with a high degree of sustainability. The hydrophobic anhydrides are synthesized at ambient temperature via a solvent-free Diels-Alder reaction of α-phellandrene with maleic anhydride. Subsequent melt polymerizations with tetra-functional diglycerol are effective under a range of [diglycerol]/[anhydride] ratios. The hydrophobicity of α-phellandrene directly impacts the swelling behavior of the resulting polyesters. The low E factors (<2), large amount of bio-based content (>75%), ambient temperature monomer synthesis, and polymer degradability represent key factors in the design of these sustainable polyesters.

Streamlining the conversion of biomass to polyesters: bicyclic monomers with continuous flow

A three-step transformation of 1,4-cyclohexadiene (1,4-CHD) using continuous flow produced an aliphatic bicyclic monomer for polyester synthesis. The monomer synthesis involved catalytic alkene isomerization of 1,4-CHD to 1,3-CHD using a heterogeneous Na2O/Na/Al2O3 catalyst, a Diels Alder reaction with maleic anhydride, and hydrogenation of the bicyclic monomer. A partially continuous strategy was compared with a fully continuous method. The continuous flow process streamlined the transformation of waste by-product biomass by minimizing workup procedures and reducing the synthesis time from ∼1 day for batch processes to ∼2.5 h. The monomer synthesis was easily scalable and allowed recycling of the catalysts for alkene isomerization and hydrogenation. The resulting bicyclic monomers were polymerized with glycerol and 1,4-butanediol (BDO) to obtain renewable polyesters with high thermal stability and tunable glass transition temperatures.