A New Approach Utilizing Aza-Michael Addition for Hydrolysis-Resistance Non-Ionic Waterborne Polyester

This work first synthesized a series of linear polyesters by step-growth polycondensation, then an amino-terminated hydrophilic polyether was grafted to the polyester as side-chains through aza-Michael addition to prepare a self-dispersible, non-ionic waterborne comb-like polyester (NWCPE). In contrast to traditional functionalization methods that usually require harsh reaction conditions and complex catalysts, the aza-Michael addition proceeds efficiently at room temperature without a catalyst. In this facile and mild way, the NWCPE samples with number-average molecular weight (Mn) of about 8000 g mol−1 were obtained. All dispersions showed excellent storage stability, reflected by no delamination observed after 6 months of storage. The NWCPE dispersion displayed better hydrolysis resistance than an ionic waterborne polyester, as was indicated by a more slight change in pH value and Mn after a period of storage. In addition, the film obtained after the NWCPE dispersion was cross-linked with the curing agent, it exhibited good water resistance, adhesion, and mechanical properties.

Synthesis of Bio-Based Poly(Butylene Adipate-co-Butylene Itaconate) Copolyesters with Pentaerythritol: A Thermal, Mechanical, Rheological, and Molecular Dynamics Simulation Study

Bio-based unsaturated poly(butylene adipate-co-butylene itaconate) (PBABI) aliphatic copolyesters were synthesized with pentaerythritol (PE) as a modifier, observing the melting point, crystallization, and glass transition temperatures were decreased from 59.5 to 19.5 °C and 28.2 to -9.1 °C as an increase of itaconate concentration, and T_g ranged from -54.6 to -48.1 °C. PBABI copolyesters tend to the amorphous state by the existence of the BI unit above 40 mol%. The yield strength, elongation, and Young's modulus at different BA/BI ratios were valued in a range of 13.2-13.8 MPa, 575.2-838.5%, and 65.1-83.8 MPa, respectively. Shear-thinning behavior was obtained in all BA/BI ratios of PBABI copolyesters around an angular frequency range of 20-30 rad s^-1. Furthermore, the thermal and mechanical properties of PBABI copolyesters can be well regulated via controlling the itaconic acid contents and adding the modifier. PBABI copolyesters can be coated on a 3D air mesh polyester fabric to reinforce the mechanical property for replacing traditional plaster applications.

Effect of 1,2,4,5-Benzenetetracarboxylic Acid on Unsaturated Poly(butylene adipate-co-butylene itaconate) Copolyesters: Synthesis, Non-Isothermal Crystallization Kinetics, Thermal and Mechanical Properties

Unsaturated poly (butylene adipate-co-butylene itaconate) (PBABI) copolyesters were synthesized through melt polymerization composed of 1,4-butanediol (BDO), adipic acid (AA), itaconic acid (IA) and 1,2,4,5-benzenetetracarboxylic acid (BTCA) as a cross-linking modifier. The melting point, crystallization and glass transition temperature of the PBABI copolyesters were detected around 29.8–49 °C, 7.2–29 °C and −51.1 and −58.1 °C, respectively. Young’s modulus can be modified via partial cross-linking by BTCA in the presence of IA, ranging between 32.19–168.45 MPa. Non-isothermal crystallization kinetics were carried out to explore the crystallization behavior, revealing the highest crystallization rate was placed in the BA/BI = 90/10 at a given molecular weight. Furthermore, the thermal, mechanical properties, and crystallization rate of PBABI copolyesters can be tuned through the adjustment of BTCA and IA concentrations.

Specialty Tough Hydrogels and Their Biomedical Applications

Hydrogels have long been explored as attractive materials for biomedical applications given their outstanding biocompatibility, high water content, and versatile fabrication platforms into materials with different physiochemical properties and geometries. Nonetheless, conventional hydrogels suffer from weak mechanical properties, restricting their use in persistent load-bearing applications often required of materials used in medical settings. Thus, the fabrication of mechanically robust hydrogels that can prolong the lifetime of clinically suitable materials under uncompromising in vivo conditions is of great interest. This review focuses on design considerations and strategies to construct such tough hydrogels. Several promising advances in the proposed use of specialty tough hydrogels for soft actuators, drug delivery vehicles, adhesives, coatings, and in tissue engineering settings are highlighted. While challenges remain before these specialty tough hydrogels will be deemed translationally acceptable for clinical applications, promising preliminary results undoubtedly spur great hope in the potential impact this embryonic research field can have on the biomedical community.

Catalyst-free, aza-Michael polymerization of hydrazides: polymerizability, kinetics, and mechanistic origin of an α-effect

Despite the powerful nature of the aza-Michael reaction for generating C-N linkages and bioactive moieties, the bis-Michael addition of 1° amines remains ineffective for the synthesis of functional, step-growth polymers due to the drastic reduction in reactivity of the resulting 2° amine mono-addition adduct. In this study, a wide range of commercial hydrazides are shown to effectively undergo the bis-Michael reaction with divinyl sulfone (DVS) and 1,6-hexanediol diacrylate (HDA) under catalyst-free, thermal conditions to afford moderate to high molecular weight polymers with M n = 3.8-34.5 kg mol-1. The hydrazide-Michael reactions exhibit two distinctive, conversion-dependent kinetic regimes that are 2nd-order overall, in contrast to the 3rd-order nature of amines previously reported. The mono-addition rate constant was found to be 37-fold greater than that of the bis-addition at 80 °C for the reaction between benzhydrazide and DVS. A significant majority (12 of 15) of the hydrazide derivatives used here show excellent bis-Michael reactivity and achieve >97% conversions after 5 days. This behavior is consistent with calculations that show minimal variance of electron density on the N-nucleophile among the derivatives studied. Reactivity differences between hydrazides and hexylamine are also explored. Overall, the difference in reactivity between hydrazides and amines is attributed to the adjacent nitrogen atom in hydrazides that acts as an efficient hydrogen-bond donor that facilitates intramolecular proton-transfer following the formation of the zwitterion intermediate. This effect not only activates the Michael acceptor but also coordinates with additional Michael acceptors to form an intermolecular reactant complex.

Effect of Ethylenediaminetetraacetic Acid on Unsaturated Poly(Butylene Adipate-Co-Butylene Itaconate) Copolyester with Low-Melting Point and Controllable Hardness

A series of copolyesters, poly(butylene adipate-co-butylene itaconate) (PBABI), was synthesized using melt polycondensation from adipic acid (AA), itaconic acid (IA), 1,4-butanediol (1,4-BDO), and ethylenediaminetetraacetic acid (EDTA). ¹H-NMR, FT-IR, GPC, DSC, TGA, DMA, XRD, Shore D, and tensile test were used to systematically characterize the structural and composition/physical properties of the copolyesters. It was found that the melting point (T_m) and crystallization temperature (T_c) of the copolyesters were, respectively, between 21.1 to 57.5 °C and −6.7 to 29.5 °C. The glass transition (T_g) and the initial thermal decomposition (T_d-5%) temperatures of the PBABI copolyesters were observed to be between −53.6 to −55.8 °C and 313.6 and 342.1 °C at varying ratios of butylene adipate (BA) and butylene itaconate (IA), respectively. The XRD feature peak was identified at the 2θ values of 21.61°, 22.31°, and 23.96° for the crystal lattice of (110), (020), and (021), respectively. Interestingly, Shore D at various IA ratios had high values (between 51.3 to 62), which indicated that the PBABI had soft plastic properties. The Young’s modulus and elongation at break, at different IA concentrations, were measured to be at 0.77–128.65 MPa and 71.04–531.76%, respectively, which could be attributed to a close and compact three-dimensional network structure formed by EDTA as a crosslinking agent. There was a significant bell-shaped trend in a BA/BI ratio of 8/2, at different EDTA concentrations—the ∆H_m increased while the EDTA concentration increased from 0.001 to 0.05 mole% and then decreased at an EDTA ratio of 0.2 mole%. Since the PBABI copolymers have applications in the textile industry, these polymers have been adopted to reinforce 3D air-permeable polyester-based smart textile. This kind of composite not only possesses the advantage of lower weight and breathable properties for textiles, but also offers customizable, strong levels of hardness, after UV curing of the PBABI copolyesters, making its potential in vitro orthopedic support as the “plaster of the future”.

Mechanoresponsive self-growing hydrogels inspired by muscle training

Living tissues, such as muscle, autonomously grow and remodel themselves to adapt to their surrounding mechanical environment through metabolic processes. By contrast, typical synthetic materials cannot grow and reconstruct their structures once formed. We propose a strategy for developing “self-growing” polymeric materials that respond to repetitive mechanical stress through an effective mechanochemical transduction. Robust double-network hydrogels provided with a sustained monomer supply undergo self-growth, and the materials are substantially strengthened under repetitive loading through a structural destruction-reconstruction process. This strategy also endows the hydrogels with tailored functions at desired positions by mechanical stamping. This work may pave the way for the development of self-growing gel materials for applications such as soft robots and intelligent devices.

Facile preparation of stereochemistry-controllable biobased poly(butylene maleate-co-butylene fumarate) unsaturated copolyesters: a chemoselective polymer platform for versatile functionalization via aza-Michael addition

Biobased stereochemistry-controllable poly(butylene maleate-co-butylene fumarate) unsaturated copolyesters were facilely prepared as a chemoselective polymer platform for versatile functionalization via aza-Michael addition.

Engineering DN hydrogels from regenerated silk fibroin and poly(N-vinylcaprolactam)

The development of novel hydrogels that possess adequate elasticity and toughness to withstand mechanically active environments, along with being biocompatible, remains a significant challenge in the design of materials for tissue engineering applications. In this study, a family of regenerated silk fibroin (RSF) based double network (DN) hydrogels were fabricated for the first time using a rapid one-pot method. The DN hydrogels combine the rigid covalently crosslinked RSF with the softer poly(N-vinylcaprolactam) (PVCL) through strong physical interactions. The formation of these DN hydrogels resulted in an improvement of the water uptake capacity, elasticity and toughness compared to the individual RSF hydrogel. The elasticity of the RSF/PVCL DN hydrogels was closer to that of native cartilage, which makes them promising materials for cartilage regeneration applications. An in vitro study on adhesion, proliferation and differentiation of a mouse pre-chondrocyte cell line (ATDC5) conducted using microscopic analysis, a cell proliferation assay and RT-PCR confirmed the cells cultured on the less stiff hydrogels demonstrated the most favourable chondrogenic response. Thus, this study demonstrates the potential of RSF-based hybrid hydrogels for cartilage tissue engineering applications.

Post-polymerisation modification of bio-derived unsaturated polyester resins via Michael additions of 1,3-dicarbonyls

A rapid (5 min), solventless and heterogeneously catalysed methodology is demonstrated for the first time for the Michael addition of 1,3-dicarbonyls to biomass derived unsaturated polyesters.

One-Pot Three-Step Polymerization System Using Double Click Michael Addition and Radical Photopolymerization

A click chemistry synthetic strategy based on aza-Michael addition and radical photopolymerization is proposed to generate a polymeric network via three time-controlled steps. The selection of primary diamines and diacrylates allows two consecutive aza-Michael reactions to occur. This reaction sequence affords the unique opportunity to interpose a radical photopolymerization reaction, enhancing the cross-link density. Consequently, the second aza-Michael addition appears as a valuable postconsolidation step of the polymer network.

Synthesis of Unsaturated Polyester Resins from Various Bio-Derived Platform Molecules

Utilisation of bio-derived platform molecules in polymer synthesis has advantages which are, broadly, twofold; to digress from crude oil dependence of the polymer industry and secondly to reduce the environmental impact of the polymer synthesis through the inherent functionality of the bio-derived platform molecules. Bulk polymerisation of bio-derived unsaturated di-acids has been employed to produce unsaturated polyester (UPEs) which have been analysed by GPC, TGA, DSC and NMR spectroscopy, advancing on the analysis previously reported. UPEs from the diesters of itaconic, succinic, and fumaric acids were successfully synthesised with various diols and polyols to afford resins of M_N 480–477,000 and T_g of −30.1 to −16.6 °C with solubilities differing based on starting monomers. This range of properties allows for many applications and importantly due to the surviving Michael acceptor moieties, solubility and cross-linking can be specifically tailored, post polymerisation, to the desired function. An improved synthesis of itaconate and succinate co-polymers, via the initial formation of an itaconate bis-diol, is also demonstrated for the first time, resulting in significantly improved itaconate incorporation.

Fundamentals of double network hydrogels

Double network (DN) hydrogels as promising soft-and-tough materials intrinsically possess extraordinary mechanical strength and toughness due to their unique contrasting network structures, strong interpenetrating network entanglement, and efficient energy dissipation.