Molecular Engineering of Polycarbonates Derived from Polyhydroxyl Natural Products as Resourceful Materials
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Utilizing renewable resources can address toxicological and environmental issues associated with commodity plastics and engineering materials. In addition, scientists can exploit the various structures and chemistries of naturally occurring feedstocks to create a myriad of polymers with unique functionalities and tunable properties. With this in mind, linear polycarbonates incorporating glucose into the main chain were synthesized by AA’/BB polymerizations of phosgene, diphosgene or triphosgene and one of four different glucose-based regioisomeric diols. Each monomer exhibited unique reactivities and produced polymers with varying thermal properties. Monomers bearing hemiacetal functionalities produced polymers with low molecular weights, (>10,000 Da), whereas the remaining monomers permitted higher molecular weights (>30,000 Da). Polymers with the carbonate linkage connected to the anomeric center of the glucose ring were more thermally sensitive, with onset decomposition temperatures (Tds) ranging from 137 to 230 °C. TGA-MS analysis revealed early degradation was due to loss of carbon dioxide and benzyl protecting groups. In addition, by modifying the monomer synthetic scheme to produce AA’A’A bis-adducts, regioregular polymers possessing high molecular weights (>100,000 Da) and elevated glass transition temperatures were obtained. Functional linear polycarbonates bearing an endocyclic alkene were formed via organocatalyzed ring-opening polymerization of a six-membered carbonate monomer synthesized from ᴅ-glucal. Using 1,5,7-triazabicyclo[4.40]dec-5-ene catalyst (1 mol %) a polymer with a molecular weight of 9900 Da and polydispersity of 1.21 was obtained, whereas a 1,8-diazabicyclo[5.4.0]undec-7-ene and 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexyl-2-thiourea cocatalyst system (2 mol%) afforded a polymer with a molecular weight of 5000 Da and a unimodal polydispersity of 1.20. Both catalyst systems reached full conversions in dichloromethane under argon at 30 °C in fewer than ten minutes, forming amorphous polymers with a Tg at 65 °C and Tds ca. 200 °C. Tunable three-dimensional polycarbonate networks were synthesized from quinic acid, a polyhydroxyl natural product, similarly structured to glucose. Solvent-free thiol−ene chemistry was utilized in the copolymerization of tris(alloc)quinic acid and a variety of multifunctional thiol monomers to obtain poly(thioether-co-carbonate) networks with a wide range of achievable thermomechanical properties including glass transition temperatures from −18 to +65 °C. Addition of diallyl carbonate was explored as a comonomer, which allowed for the lowering of glass transitions (38 to 65°C), without altering rubbery modulus. Control force cyclic testing demonstrated excellent shape memory; high percent recoverable strains were obtained, reaching 100% recovery during fourth and fifth cycles.
Shape Memory Polymer
Lonnecker, Alexander (2017). Molecular Engineering of Polycarbonates Derived from Polyhydroxyl Natural Products as Resourceful Materials. Doctoral dissertation, Texas A & M University. Available electronically from