Copolymers Prepared by Exchange Reactions Enhance the Properties of Miscible Polymer Blends

Abstract

Although many polymers are not miscible or chemically incompatible, some form miscible blends, which feature tunable properties relative to those of their constituent polymers. Here, we introduce an approach to enhance the mechanical properties of miscible blends of a thermoplastic polyurethane and a sustainable polyester, polycaprolactone (PCL), by introducing a copolymer of the two corresponding monomers. Rather than polymerizing the copolymers from new monomers, they were generated by a solvent-free, ester/urethane bond-exchange process conducted during the coextrusion of polyurethane and PCL. Urethane/ester exchange was confirmed by quantitative 13C NMR spectroscopy, along with well-defined size-exclusion chromatography of the copolymers. Extrusion time and temperature affected the extent of exchange, with shorter residence times and lower temperatures giving limited bond exchange and blockier copolymers. In contrast, longer extrusion times and higher temperatures provided more extensive exchange and approximately random copolymers. Mixtures of the polyurethane and polyester homopolymers with 10 wt % copolymer demonstrated improved tensile stress and strain relative to coextruded mixtures of thermoplastic polyurethane and polyethylene because of the enhanced crystallization of the miscible homopolymer blend facilitated by the added copolymer compatibilizer. This approach represents a simple and general strategy for obtaining copolymers from homopolymers rather than using specialized polymerization techniques, allowing for products from mixed polymer waste to be used as compatibilizers or otherwise enhance the properties of the original homopolymer mixtures.

Thermal Activation of Zirconium(IV) Acetylacetonate Catalysts to Enhance Polyurethane Synthesis and Reprocessing

“…Previously, we developed a 13 C NMR spectroscopy method to quantify the exchange between a thermoplastic polyester and TPU by integrating their distinct carbonyl resonances. 31 We applied this method to chemically distinct TPUs to evaluate the catalyst activity of pristine, activated, and self-heated Zr catalysts (Figure 2). Two TPUs were prepared for the crossover experiment: the first was synthesized from toluene-2,6-diisocyanate (TDI) and an aliphatic diol, and the second was synthesized from diphenyl diisocyanate (MDI) and an aromatic diol (Figure 2A).…”

“…Quantitative 13 C NMR spectroscopy was used to monitor carbamate exchange between thermoplastic urethanes (TPUs), and this experiment showed that the rate of carbamate exchange increases after Zr­(acac) 4 is heated in the presence of the polymers (Figure ). Previously, we developed a 13 C NMR spectroscopy method to quantify the exchange between a thermoplastic polyester and TPU by integrating their distinct carbonyl resonances . We applied this method to chemically distinct TPUs to evaluate the catalyst activity of pristine, activated, and self-heated Zr catalysts (Figure ).…”

Preparation of Block Copolymers by a Sequential Transesterification Strategy: A Feasible Route for Upcycling End-of-Life Polyester Plastics to Elastomers

“…Moreover, the random exchange reaction between two different types of polymers (polyurethane and polyester) was achieved to synthesize a copolymer of polyurethane and PCL during the coextrusion of the two homopolymers at 200 °C by Dichtel's team. 24 Besides, the transesterification between poly(glycolic acid) and "nonpolymerizable" γ-butyrolactone (BL) was conducted by Hong and Chen 25 (Scheme 1, Route b). Based on the difference in transesterification ability between the polymer and monomer, they successfully incorporated BL into PGA to obtain copolymer poly(GA-co-BL).…”

“…Poly­(lactic acid- stat -salicylic acid) was successfully prepared through the intermolecular random transesterification of poly­(salicylic methyl glycolide) and PLA at elevated temperatures (Scheme , Route a). Moreover, the random exchange reaction between two different types of polymers (polyurethane and polyester) was achieved to synthesize a copolymer of polyurethane and PCL during the coextrusion of the two homopolymers at 200 °C by Dichtel’s team . Besides, the transesterification between poly­(glycolic acid) and “nonpolymerizable” γ-butyrolactone (BL) was conducted by Hong and Chen (Scheme , Route b).…”