Mingtao Chen

Non-isocyanate poly(amide-hydroxyurethane)s from sustainable resources

A two-step synthesis of epoxidation and carbonation afforded a hetero-functional AB monomer with cyclic carbonate and methyl ester (CC-ME) using plant oil-based methyl 9-decenoate and CO2. A unprecedented one-pot synthetic platform of CC-ME with 1,12-diaminododecane and poly(tetramethylene oxide) (PTMO)-based polyether diamine allowed synthesis of both nonsegmented poly(amide-hydroxyurethane) (PA12HU) and segmented PA12HU-PTMOs with varying polyether contents. 1H NMR spectroscopy confirmed complete conversion of cyclic carbonates and methyl esters to hydroxyurethanes and amides, respectively. Thermal analysis revealed distinctive thermal stability and transitions of PA12HU and PA12HU-PTMOs compared to their precursors and model oligomers. PA12HU and PA12HU-PTMOs were melt compression molded into semicrystalline, free-standing films, except for PA12HU-PTMO100 with 100% polyether diamine. PA12HU-PTMO100 was a viscous liquid with a glass transition temperature (Tg) of −64 °C and zero-shear melt viscosity of 449 Pa s. PA12HU formed a semicrystalline, rigid film with Tg of 11 °C. Polyether incorporation afforded creasable PA12HU-PTMO films with broad glass transitions near −50 °C. Thermal and thermomechanical analysis revealed significant phase-mixing of the hard and soft segments from annealed PA12HU-PTMO films. Polyether soft segments mixed with the amorphous hard segments, forming a miscible soft phase; crystallizable hard segments with ordered hydrogen bonding formed a hard phase. Surface morphological analysis of each PA12HU-PTMO film displayed ribbon-like, hard domains with composition-dependent aspect ratios. PA12HU-PTMOs exhibited higher moisture uptake than traditional thermoplastic polyurethane (TPU) due to resultant hydroxyls. Variable temperature FTIR spectroscopy demonstrated that ordered hydrogen bonding in the crystalline domains was disrupted or dissociated as the crystallites melted. Although tensile strength of segmented PA12HU-PTMOs proved lower than traditional polyurethanes due to phase-mixing, these compositions represent the first examples of film-forming, linear isocyanate-free polyurethanes with mechanical integrity and processability.

Ureido cytosine and cytosine-containing acrylic copolymers

Regioselective Michael addition afforded a novel N1-substituted cytosine acrylate monomer for the synthesis of acrylic random copolymers with cytosine pendant groups. Quantitative post-functionalization converted cytosine to ureido-cytosine (UCy) with an increased self-association strength due to quadruple hydrogen bond formation. Thermogravimetric analysis (TGA) revealed a lower onset temperature of weight loss (∼200 °C) for UCy-containing copolymers, however, they proved to be more thermally stable at ≤130 °C than the cytosine-containing precursors during isothermal rheological experiments. The incorporation of UCy into random copolymers resulted in higher Tgs, enhanced mechanical performance, and better microphase-separation than the cytosine-containing precursors. Both dynamic mechanical analysis and rheological analysis revealed a plateau regime for each UCy-containing copolymer as well as a tan delta transition that corresponded to hydrogen bond dissociation. In contrast, the viscoelastic behavior of cytosine-containing random copolymers resembled entangled, non-associating polymers with increasing Tg as the cytosine content increased. A solution-cast UCy-containing copolymer film exhibited a more well-defined surface morphology with nano-fibrillar hard domains compared to the cytosine control. Variable temperature FTIR spectroscopy verified the presence of hydrogen bonding, and thermogravimetric sorption analysis (TGA-SA) compared the water uptake of UCy and cytosine-containing copolymers. UCy-containing random copolymers showed various advantages for applications as adhesives and thermoplastic elastomers compared to the cytosine copolymers, including superior cohesive strength, higher thermal stability, wider service temperature window, and lower moisture uptake. Free radical copolymerization of a quadruple hydrogen bond containing acrylic monomers provides a versatile avenue to supramolecular polymers with a tunable composition and improved scalability compared to earlier telechelic oligomers. This report describes the first synthesis of an acrylic monomer family and complementary evidence for tunable association in random copolymers.

Nanoscale Resolution of Electric-field Induced Motion in Ionic Diblock Copolymer Thin Films

Understanding the responses of ionic block copolymers to applied electric fields is crucial when targeting applications in areas such as energy storage, microelectronics, and transducers. This work shows that the identity of counterions in ionic diblock copolymers substantially affects their responses to electric fields, demonstrating the importance of ionic species for materials design. In situ neutron reflectometry measurements revealed that thin films containing imidazolium based cationic diblock copolymers, tetrafluoroborate counteranions led to film contraction under applied electric fields, while bromide counteranions drove expansion under similar field strengths. Coarse-grained molecular dynamics simulations were used to develop a fundamental understanding of these responses, uncovering a nonmonotonic trend in thickness change as a function of field strength. This behavior was attributed to elastic responses of microphase separated diblock copolymer chains resulting from variations in interfacial tension of polymer-polymer interfaces due to the redistribution of counteranions in the presence of electric fields.