Novel thermoplastic polyhydroxyurethane elastomers as effective damping materials over broad temperature ranges

Multiple energy dissipation modes in dynamic polymer networks with neutral and ionic junctions

Polymer networks with controlled ratios of neutral and ionic dynamic crosslink points were prepared from ethylene glycol, boric acid, and lithium hydroxide. Both neutral and ionic sites led to the emergence of distinct damping modes separate from the glass transition. This work highlights the potential of polymer networks for multimodal damping spectra through dynamic bond selection.

Nonisocyanate Polyurethane Segmented Copolymers from Bis-Carbonylimidazolides

Bis-carbonylimidazolide (BCI) functionalization enables an efficient synthetic strategy to generate high molecular weight segmented nonisocyanate polyurethanes (NIPUs). Melt phase polymerization of ED-2003 Jeffamine, 4,4'-methylenebis(cyclohexylamine), and a BCI monomer that mimics a 1,4-butanediol chain extender enables polyether NIPUs that contain varying concentrations of hard segments ranging from 40 to 80 wt. %. Dynamic mechanical analysis and differential scanning calorimetry reveal thermal transitions for soft, hard, and mixed phases. Hard segment incorporations between 40 and 60 wt. % display up to three distinct phases pertaining to the poly(ethylene glycol) (PEG) soft segment Tg , melting transition, and hard segment Tg , while higher hard segment concentrations prohibit soft segment crystallization, presumably due to restricted molecular mobility from the hard segment. Atomic force microscopy allows for visualization and size determination of nanophase-separated regimes, revealing a nanoscale rod-like assembly of HS. Small-angle X-ray scattering confirms nanophase separation within the NIPU, characterizing both nanoscale amorphous domains and varying degrees of crystallinity. These NIPUs, which are synthesized with BCI monomers, display expected phase separation that is comparable to isocyanate-derived analogues. This work demonstrates nanophase separation in BCI-derived NIPUs and the feasibility of this nonisocyanate synthetic pathway for the preparation of segmented PU copolymers.

Synthesis of Bis(cyclic carbonates) from Epoxy Resin under Microwave Irradiation: The Structural Analysis and Evaluation of Thermal Properties

This article describes the use of microwave irradiation in the synthesis of bis(cyclo carbonate) compounds (BCCs) in bulk (without solvent) from carbon dioxide capture using an epoxidized compound-a commercial epoxy resin-and compares this process to the conventional method. CO2 cycloaddition to epoxides is an ecological and efficient method for the formation of bis(cyclic carbonates). Moreover, the introduction of gas into the reaction mixture was carried out at atmospheric pressure with a controlled flow rate, which is advantageous from an economic point of view. Progressive structural changes and the presence of characteristic chemical groups were monitored using attenuated total reflectance infrared spectroscopy with Fourier transform. The obtained crude products were purified to obtain three fractions, which were subjected to detailed structural analysis using FT-IR and 13CNMR. The formation of the main product with two cyclic carbonates was confirmed. The presence of monomers, dimers and trimers in individual fractions as well as their thermal stability were determined, and the molecular masses in individual fractions were determined using gel permeation chromatography (GPC).

Polyhydroxyurethane and Poly(ethylene oxide) Multiblock Copolymer Networks: Crosslinking with Polysilsesquioxane, Reprocessing and Solid Polyelectrolyte Properties

This contribution reports the synthesis of polyhydroxyurethane (PHU)-poly(ethylene oxide) (PEO) multiblock copolymer networks crosslinked with polysilsesquioxane (PSSQ). First, the linear PHU-PEO multiblock copolymers were synthesized via the step-growth polymerization of bis(6-membered cyclic carbonate) (B6CC) with α,ω-diamino-terminated PEOs with variable molecular weights. Thereafter, the PHU-PEO copolymers were allowed to react with 3-isocyanatopropyltriethoxysilane (IPTS) to afford the derivatives bearing triethoxysilane moieties, the hydrolysis and condensation of which afforded the PHU-PEO networks crosslinked with PSSQ. It was found that the PHU-PEO networks displayed excellent reprocessing properties in the presence of trifluoromethanesulfonate [Zn(OTf)2]. Compared to the PHU networks crosslinked via the reaction of difunctional cyclic carbonate with multifunctional amines, the organic-inorganic PHU networks displayed the decreased reprocessing temperature. The metathesis of silyl ether bonds is responsible for the improved reprocessing behavior. By adding lithium trifluoromethanesulfonate (LiOTf), the PHU-PEO networks were further transformed into the solid polymer electrolytes. It was found that the crystallization of PEO chains in the crosslinked networks was significantly suppressed. The solid polymer electrolytes had the ionic conductivity as high as 7.64 × 10-5 S × cm-1 at 300 K. More importantly, the solid polymer electrolytes were recyclable; the reprocessing did not affect the ionic conductivity.

Polymer architecture dictates multiple relaxation processes in soft networks with two orthogonal dynamic bonds

Materials with tunable modulus, viscosity, and complex viscoelastic spectra are crucial in applications such as self-healing, additive manufacturing, and energy damping. It is still challenging to predictively design polymer networks with hierarchical relaxation processes, as many competing factors affect dynamics. Here, networks with both pendant and telechelic architecture are synthesized with mixed orthogonal dynamic bonds to understand how the network connectivity and bond exchange mechanisms govern the overall relaxation spectrum. A hydrogen-bonding group and a vitrimeric dynamic crosslinker are combined into the same network, and multimodal relaxation is observed in both pendant and telechelic networks. This is in stark contrast to similar networks where two dynamic bonds share the same exchange mechanism. With the incorporation of orthogonal dynamic bonds, the mixed network also demonstrates excellent damping and improved mechanical properties. In addition, two relaxation processes arise when only hydrogen-bond exchange is present, and both modes are retained in the mixed dynamic networks. This work provides molecular insights for the predictive design of hierarchical dynamics in soft materials.

Structure-Property Relationship and Multiple Processing Studies of Novel Bio-Based Thermoplastic Polyurethane Elastomers

Currently, the growing demand for polymeric materials has led to an increased need to develop effective recycling methods. This study focuses on the multiple processing of bio-based thermoplastic polyurethane elastomers (bio-TPUs) as a sustainable approach for polymeric waste management through mechanical recycling. The main objective is to investigate the influence of two reprocessing cycles on selected properties of bio-TPUs. Two series of bio-based TPUs were synthesized via a solvent-free two-step method with the use of hexamethylene diisocyanate or hexamethylene diisocyanate/partially bio-based diisocyanate mixtures, bio-based poly(triamethylene ether) glycol, and bio-based 1,3 propanediol. Both the raw bio-TPUs and those subjected to two reprocessing cycles were examined with respect to their chemical, physical, thermal, thermomechanical, and mechanical properties. The conducted research revealed that reprocessing led to changes in the phase separation between the hard and soft segments, thereby affecting the bio-TPUs' properties. Both series of materials showed similar chemical structures regardless of reprocessing (slight changes were observed in the range of carbonyl peak). The thermal properties of TPUs exhibited slight differences after each reprocessing cycle, but generally, the non-processed and reprocessed bio-TPUs were thermally stable up to about 300 °C. However, significant differences were observed in their mechanical properties. The tensile strength increased to 34% for the twice-reprocessed bio-TPUs, while the elongation at break increased by ca. 200%. On the other hand, the processing cycles resulted in a decrease in the hardness of both bio-TPU series (ca. 3-4 °ShA). As a result, the prepared bio-TPUs exhibited characteristics that were closer to those of the sustainable materials model, promoting the circular economy of plastics, with environmental benefits arising from their recyclability and their high content of bio-based monomers (78.4-78.8 wt.%).

High-Performance Branched Polymer Elastomer Based on a Topological Network Structure and Dynamic Bonding

High performance has always been the research focus of elastomers. However, there are inherent conflicts among properties of elastomers, such as strength and toughness, strength and damping performance, strength and self-healing ability, etc. Herein, first, we synthesized a unique structure of the dangling chain containing proton donors and receptors. Then, we design and fabricate a kind of high-performance elastomer with a gradient distribution of a dangling chain and a dynamic bond structure. The dangling chains of different lengths intertwine with each other and self-assemble to form a "dense accumulation" structure driven by hydrogen bonds, and the elastomer exhibits special micro/nano scale aggregated states and microphase separation. The "dense accumulation" structure plays a vital role in the increase of mechanical properties. Meanwhile, under the joint action of a dangling chain and a dynamic bond, the damping performance and self-healing performance of the elastomer are greatly enhanced. High strength (27.5 MPa), toughness (121.9 MJ·m-3), 94.8% healing efficiency and outstanding damping performance (tan δ ≥ 0.4, high damping temperature range up to 144 °C) are simultaneously achieved beyond the current state-of-the-art. This topoarchitected polymer with a gradient distribution of dangling chains successfully solves the defects of conventional branched polymers in deteriorating their mechanical properties. This material design provides a new strategy for the development of high-performance structural and functional integrated elastomers.

Bio-Based Polyurethane and Its Composites towards High Damping Properties

The operation of mechanical equipment inevitably generates vibrations and noise, which are harmful to not only the human body but also to the equipment in use. Damping materials, which can convert mechanical energy into thermal energy, possess excellent damping properties in the glass transition region and can alleviate the problems caused by vibration and noise. However, these materials mainly rely on petroleum-based resources, and their glass transition temperatures (T_g) are lower than room temperature. Therefore, bio-based materials with high damping properties at room temperature must be designed for sustainable development. Herein, we demonstrate the fabrication of bio-based millable polyurethane (BMPU)/hindered phenol composites that could overcome the challenges of sustainable development and exhibit high damping properties at room temperature. BMPUs with a high T_g were prepared from modified poly (lactic acid)-based polyols, the unsaturated chain extender trimethylolpropane diallylether, and 4,4'-diphenylmethane diisocyanate, and 3,9-Bis-{1,1-dimethyl-2[β-(3-tert-butyl-4-hydroxy-5-methylphenyl-)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro [5,5]-undecane (AO-80) was added to prepare BMPU/AO-80 composites. Finally, the properties of the BMPUs and BMPU/AO-80 composites were systematically evaluated. After adding 30 phr of AO-80, the Tg and maximum loss factor (tan δ_max) of BMPU/AO-80 composites increased from 7.8 °C to 13.5 °C and from 1.4 to 2.0, respectively. The tan δ_max showed an improvement of 43%. Compared with other polyurethanes, the prepared BMPU/AO-80 composites exhibited higher damping properties at room temperature. This study proposes a new strategy to reduce society's current dependence on fossil resources and design materials featuring high damping properties from sustainable raw materials.

Effect of the content and strength of hard segment on the viscoelasticity of the polyurethane elastomer: insights from molecular dynamics simulation

Due to the wide application, it is very crucial to understand the viscoelasticity of the polyurethane elastomer (PU, denoted by soft-hard block copolymer), which contains the soft segments (SS) and hard segments (HS). Thus, in this work, the effect of the content and strength of HS on the viscoelasticity of PU is explored in detail by adopting a coarse-grained model. First, the phase morphology of PU is characterized where both the single continuous phase and the bicontinuous phase are observed by varying the content of HS. Then, the viscoelasticity of PU is calculated by analyzing the storage modulus, the loss modulus, and the loss factor, which depends on the content and strength of HS. To further elucidate the mechanism for the storage modulus, the normalized interaction energy, the order parameter, and the formation probability of the HS or SS phase are characterized with the shear strain amplitude, which reflects the deformation of the phase structure. Then, the energy dissipation is quantified, which can rationalize the loss modulus well. A parameter is introduced, which considers the relative slippage and the content of HS or SS. It can explain the change in the loss factor with the content and strength of HS. In summary, this work can help to further understand how the content and strength of hard segments affect the viscoelasticity of the soft-hard block PU and structure evolution at the molecular level.

Computational Design for the Damping Characteristics of Poly(ether ether ketone)

To investigate the damping characteristics of poly(ether ether ketone) (PEEK), various potential modifications of the molecular structure, including sulfonate groups, hydroxyl groups, amino groups, carboxyl groups, methyl groups, fluorines, and benzene rings, were considered. It was found that these functional groups can mediate both the storage and loss modulus of PEEK derivatives, and the loss factors of PEEK derivatives are sensitive to the content and type of functional groups, indicating an ideal designability of energy dissipation performance. The reciprocating process of H-bonds and C_π-H bonds breaking and reforming during material deformation and the available free volume in the material are critical to the energy dissipation capacities in polymers.

Reprocessable polyhydroxyurethane networks exhibiting full property recovery and concurrent associative and dissociative dynamic chemistry via transcarbamoylation and reversible cyclic carbonate aminolysis

We developed reprocessable polyhydroxyurethane (PHU) networks with full property recovery and incorporating both associative and dissociative dynamic chemistry.

Reinforced poly(hydroxyurethane) thermosets as high performance adhesives for aluminum substrates

High performance adhesives for bare aluminum are prepared by reinforcing poly(hydroxyurethane) (PHU) thermosets with (functional) nanofillers and poly(dimethylsiloxane).

Non-isocyanate polyurethane/epoxy hybrid materials with different and controlled architectures prepared from a CO2-sourced monomer and epoxy via an environmentally-friendly route

A series of polyurethane/epoxy hybrid materials with different and controlled architectures were prepared by a non-isocyanate route. The properties and architectures of materials were regulated by adjusting the ratio and type of amine.

Organocatalyzed coupling of carbon dioxide with epoxides for the synthesis of cyclic carbonates: catalyst design and mechanistic studies

The coupling of carbon dioxide (CO₂) with epoxides with the formation of cyclic carbonates is a highly attractive 100% atom economic reaction. It represents a greener and safer alternative to the conventional synthesis of cyclic carbonates from diols and toxic phosgene.