Preparation And Study Of Thermoreversible Multiple Hydrogen-Bonding Supramolecular Polymers

In this thesis, new thermorebersible multiple hydrogen-bonding supramolecualr polymers are designed and synthesized from the concept that multiple hydrogen-bonding supramolecular elastomers with physical network structure are assembled from small molecules or oligomers associated by hydrogen bonds. Hydrogen-bonding supramolecular polymers are successfully prepared by one-pot synthesis from a series of amide and end-capped amide oligomer assembled by multiple hydrogen bonds between chains. Molecular structure, molecular weight and distribution, as well as mechanical, crystallization and melting, thermal decomposition, thermoreversible and processing, rubber-like, dynamical rheological properties are well characterized. The mode for phase transition, chain dynamics, hydrogen-bonding thermodynamics and assembling mechanism of multiple hydrogen-bonding supramolecular polymers are proposed and discussed in this thesis.Amide oligomer BX-1-EAH and end-capped amide oligomers BX-1-EAH-PTSI and BX-4-EAH-PTSI are synthesized from the condensation polymerization of dimer fatty acid (DFA) and anhydrous ethylene diamine (EAH) and then end-capped reaction by adding to p-toluenesulfonyl isocyanate (PTSI) with variable kinds of dimer fatty acid (BX-1 and BX-4) and contents of isocyanate. At cooling of products, oligomer chains assemble to physical network hydrogen-bonding supramolecular polymer by multiple hydrogen-bonding connections between chains.1H-NMR and FT-IR analyses conform that amidation reaction and isocyanate end-capped reaction are successful and multiple hydrogen bonds of CO……NH, S=O……NH between amide and sulfonyl urea groups exist in the hydrogen-bonding supramolecular assembly which indicates the hydrogen-bonding physical network structure of supramolecular polymer. GPC and ESI-TOF-MS characterization show that amide oligomers have low molecular weight and wide molecular weight distribution and polymerization degree of the three oligomers is below 10.Highest ensile strength 13.2 MPa and ball indentation hardness 20.3 N/mm2 indicate that hydrogen-bonding supramolecular polymers have excellent mechanical properties. When molar ratio of EAH and DFA is 1.2:1, tensile strength and elongation reach the highest value. Hydrogen-bonding supramolecular polymer with BX-4 as starting materials has 3.2% indissoluble gel and more chemical crosslinking micro-region from branching, and has higher tensile strength modulus and hardness. Physical network and chemical crosslinking micro-region coexist in hydrogen- bonding supramolecular polymers. DMA results indicate that at low temperature (<-30℃) hydrogen-bonding supramolecular polymers behave like hard plastic at glass state and the glass transition is at around 10℃. Products show high-elastic properties between Tg and room temperature and rubber-like behavior at room temperature.DSC and WXRD results indicate the low melt temperature (88-100℃) and degree of crystalline (△Hm= 8.5-12.5J/g); TGA show the excellent thermal stability of supramolecular polymer and the 10% decomposition temperature (Td10) is> 340℃. The materials have good thermoreversible behavior, hence the moulding process can be operated on general melting mouldling processing equipments. Force-free tensile test indicates that the hydrogen-bonding supramolecular polymers behave like soft rubber with delayed recovery and show rubber-like elasticity between Tg and Tm.Rotational rheological characterization indicates that the melt of hydrogen- bonding supramolecuar polymer behaves like non-linear Bingham flow with very high yield stress. Hydrogen-bonding supramolecular assembly has multi phases including dynamic lamellar ordered phase and 3D network disordered phase with heterogeneous chemical crosslinking micro-regions. Rubber-like solid-liquid transition is at Tc1≈90℃, and liquid-liquid transition of micro-phase separation is at Tc2. Associate-disassociate mechanism of physical interaction and reptation mechanism have cooperatively effect on the relaxation of hydrogen-bonding supramolecular polymer. The mean time of relaxation decreases and the zero shear viscosity with the increase of temperature.At high temperature, the density of hydrogen bonds between oligomer chains is very low, and the system behaves like liquid with low viscosity; at cooling, the hydrogen-bonding density increases, molecular chains assemble by multiple hydrogen-bonding and the order degree of chains increases; viscosity and storage modulus of the system suddenly increases at around 90℃, and the supramolecular polymer has liquid-solid transition; below 90℃, a few dynamic ordered lamellar structures form in the 3D hydrogen-bonding networks, and until room temperature, hydrogen-bonding supramolecular polymer behaves like viscoelastic solid with low crystalline and good mechanical properties. At the heating and cooling cycles, physical cross-linking networks are destroyed and reformed, therefore, the assembling process from hydrogen-bonding is reversible.