Thermoplastic Polyurethane Elastomers with Reversible Hydrogen Bonding
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Solution Overview
Problem
Traditional synthetic methods for replicating the mechanical properties of elastomers, such as high elasticity and tensile strength, face challenges including limited end-of-life options, reduced optical clarity upon deformation, and a tradeoff between strength and extensibility, which are difficult to mimic using chemically crosslinked networks or increased crystalline domains.
Innovation Solution
The synthesis of thermoplastic polyurethane (TPU) elastomers using renewably sourced 1,4:3,6-dianhydrohexitols stereoisomers, which exhibit exceptional strength and elongation due to dynamic transitions between intra- and inter-molecular hydrogen bonding, facilitating stereoisomer-dependent crosslinking and maintaining high optical clarity throughout deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If chemically crosslinked networks are used to achieve high tensile strength and elasticity, then mechanical properties are improved, but end-of-life options are limited and reprocessing becomes difficult
Solution Approach 1:
The patent employs dynamic, reversible hydrogen bonding interactions instead of permanent chemical crosslinks. The urethane groups form reversible H-bonds that provide mechanical strength during use but can be broken and reformed during reprocessing, enabling both high tensile strength and recyclability. This dynamic bonding mechanism allows the material to transition between structured and unstructured states for processing.
Solution Approach 2:
The patent changes the bonding mechanism from permanent covalent crosslinks to reversible hydrogen bonds with specific bond energies. By controlling the density and strength of H-bonding interfaces through stereochemical configuration, the material achieves adequate mechanical properties while maintaining processability. The H-bond strength parameter is optimized to be sufficient for mechanical integrity but weak enough to allow reprocessing.
2Strength
If crystalline domains are increased to improve mechanical strength, then tensile strength is improved, but optical clarity is reduced upon deformation
Solution Approach 1:
The patent creates localized hydrogen bonding interfaces at specific molecular positions (urethane groups adjacent to rigid ring structures) rather than extensive crystalline domains. These localized H-bonding regions provide strength while the overall material remains amorphous and optically clear. The stereochemical configuration ensures H-bonds form at specific locations without causing bulk crystallization.
Solution Approach 2:
The patent combines rigid ring structures with urethane groups to create a composite molecular architecture where the rigid units provide structural integrity and the urethane groups provide reversible H-bonding. This molecular-level composite structure achieves strength without the optical degradation associated with macroscopic crystalline domains.
3Stability of the object's composition
If chemical crosslinking is used to achieve high elasticity, then elastic recovery is improved, but the material loses extensibility and becomes brittle
Solution Approach 1:
The patent uses dynamic hydrogen bonding that can reversibly form and break. During deformation, H-bonds break to allow chain extension; during recovery, H-bonds reform to restore the original shape. This dynamic bonding provides both extensibility and elastic recovery, unlike static chemical crosslinks that restrict movement and cause brittleness.
Solution Approach 2:
The patent exploits the reversible nature of hydrogen bonding as a phase transition mechanism. The H-bonds transition between bound and unbound states during deformation and recovery cycles, enabling the material to switch between a structured state (providing elasticity) and a more flexible state (providing extensibility).
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
These TPU elastomers demonstrate superior mechanical properties, including strain rate-dependent behavior and significant strain hardening, while allowing for facile reprocessing with minimal loss of mechanical performance, making them suitable sustainable alternatives to commodity elastomers.
Implementation Method 1
the ring structure of the dianhydrohexitole and the urethane groups facilitate stereoisomer dependent dynamic crosslinking of the materials via hydrogen bonding
Implementation Method 2
reacting: (a) an acrylate-terminated monomer comprising, consisting of, or consisting essentially of: (i) at least one dianhydrohexitole and (ii) at least one urethane group; (b) a thiol selected from the group consisting of a linear dithiol, a branched tri-thiol, and a branched tetra-thiol; and (c) a catalytic quantity of an alkylphosphine in a base-mediated thiol-ene addition polymerization process
Implementation Method 3
These phenomena are attributed to dynamic transitions between intra- and inter-molecular hydrogen bonding in the transient crosslinking network
Data Source
AI summary
The present disclosure describes, in part, a polymer, for example a thermoplastic polyurethane elastomer, comprising one or more subunits comprising (i) at least one dianhydrohexitole moiety (ii) at least one urethane moiety and (ill) a thiol moiety having two or more sulphur atoms. The thermoplastic polyurethane elastomers may be biodegradable and possess excellent thermoplastic properties, including outstanding toughness, resulting from its semi-crystallinity and low glass transition temperature, that surpasses many leading plastics such as nylon 6 and high-density polyethylene (HOPE) and methods of making same.