Multifunctional Thiol Monomers Research Articles

Fast synthesis of crosslinked self-blowing poly(β-hydroxythioether) foams by decarboxylative-alkylation of thiols at room temperature

A novel strategy was developed to prepare a self-blowing poly(β-hydroxythioether) foam at room temperature by S-alkylation of 5-membered bis-cyclic carbonate using multifunctional thiol monomers. Two different thiol compounds, trimethylolpropane tris(3-mercaptopropionate) and pentaerythritol tetrakis(3-mercaptopropanoic acid) were used for the decarboxylative s-alkylation reaction. The thiol compounds simultaneously act as crosslinking agents and generate carbon dioxide during the decarboxylative s-alkylation reaction. This enables foam preparation without an external blowing agent. The use of tetrathiol monomer improves thermal stability, provides flexibility to the foams, and induces an increase in the glass transition temperature (Tg) due to a higher degree of cross-linking. The apparent density of the foams decreases with the increase of the tetrathiol ratio. This novel solvent-free approach paves the way to design sustainable foams with modular properties using accessible components and additives, as well as provides an alternative to non-isocyanate polyurethane foams.

Joint-Linker Type Ionic Gels Using Polymerizable Ionic Liquid as a Crosslinker via Thiol-Ene Click Reactions.

In this work, we report the synthesis of ion-conductive gels, or ionic gels, via thiol-ene click reactions. The novel gel systems consist of the multifunctional thiol monomers tris[(3-mercaptopropionyloxy)-ethyl]-isocyanurate (TEMPIC), pentaerythritol tetrakis(3-mercaptopropionate) (PEMP), and dipentaerythritol hexakis(3-mercaptopionate) (DPMP) as joint molecules and bifunctional allyl ionic liquid (IL) as a crosslinker. The thiol-ene reaction was carried out in lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) in a propylene carbonate (PC) (1 M) solvent system via a photopolymerization process. The chemical structure and mechanical, thermal, and conductive properties of the gels were investigated using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), compression tests, and impedance spectroscopy, respectively. The mechanical and conductive properties of the ionic gels were found to be largely dependent on the monomer content and functionalities of the joint molecules. TGA revealed good thermal stability of the gels up to 100 °C. An ionic conductivity of 4.89 mS cm−1 was realized at room temperature (298 K) for low-functional thiol monomers, and a further increase in ionic conductivity was observed with an increase in Li+ ion content and temperature.

(Invited) Development of Ionic Porous Polymer for Sensing Applications

Porous polymers with macr/micro- sized pores have potential applications in separation, batteries, fuel cells and sensors [1, 2]. Thiol-ene "click" is a widespread method for monolith preparation owing to its exceptional versatility, simplicity and facile tunability. In our previous work, we reported on the fabrication of extremely soft type thiol-ionic gels (T-IGs) incorporating ionic liquid (IL) (70–85 wt%) in the thiol–ene network of thiol-based end-crosslinker and acrylate monomers [3, 4]. The T-IGs exhibited tunable mechanical and conductive properties and conductivity as high as 5.40 mS cm−1 is attained for longer acrylate group containing gels at room temperature. In this work we developed a series of porous polymers through polymerization induced phase separation by utilizing thiol-ene reaction between multi-functional thiol monomers and diacrylate crosslinkers in ionic Liquid solvent medium. The matrix of the polymers constructed of interconnected micro-globules forming a three-dimensional network. These microporous polymers exhibited tunable mechanical prosperities and morphology. In contrary to the ionic gels, the porous structure with entrapped ILs exhibited high ionic conductivity possibly due to relatively unperturbed transport of ions within the interconnected polymer particles compared to the bulk polymeric network. Physical properties of these porous ionic polymers have been investigated to optimize suitable condition for best performance in piezoresistive sensors (enabling sensing of both pressure and strain). This work is expected to add potential functionality in the applied field of the polymer materials.References Sakakibara, K., Kagata, H., Ishizuka, N., Sato, T., Tsujii, Y. Fabrication of surface skinless membranes of epoxy resin-based mesoporous monoliths toward advanced separators for lithium ion batteries. J. Mater. Chem. A, 5, 6866–6873 (2017).Liu, Z., Ou, J., Zou, H., Click polymerization for preparation of monolithic columns for liquid chromatography. Trends Anal. Chem., 82, 89–99 (2016).Ahmed, K., Naga, N., Kawakami, M. & Furukawa, H. Development of ionic gels using thiol-based monomers in ionic liquid. 9800,980005 (2016).Ahmed K, Naga N., Kawakami M. and Furukawa H., Extremely Soft, Conductive and Transparent Ionic Gels by 3D Optical Printing, Macromol. Chem. Phys., 1800216 (2018).

(Invited) Structural Analysis of Multifunctional Ionic Gels

Ionic liquied mediated gels commonly known as ion gels or ionic gels have received remarkable attention for their advanced application in electrochemical and electromechanical devices, such as actuators, lithium batteries, electric double-layer capacitors, dye-sensitized solar cells and fuel cells [1, 2]. Investigation of the internal structure of ionic gels have been previously reported by our research group to understand their network homogeneity in association with mechanical characterization[3]. In this work we focused to determine structural analysis of ionic gels combining multifunctional thiol monomers and IL 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide (BMImFSI). Therefore, we developed thiol monomer-based ionic gels via thiol-ene click reaction with theoretically homogeneous uniform network and investigated their mechanical properties using both conventional destructive method i.e. compression test and a unique nondestructive method using mesh size by scanning microscopic light scattering (SMILS) techniques [4]. The mesh size of the IGs was found to be highly dependent on the functionality of the monomer both in IL and conventional solvent media. Also long chain crosslinkers have been found to form dangling chain within the network hindering their homogeneous network formation. Thus our systems can offer to combine internal structures with the mechanical properties for characterization of soft materials in smart nondestructive ways.

Incorporating allylated lignin-derivatives in thiol-ene gel-polymer electrolytes

Growing environmental and economic concerns as well as the uncertainty that accompanies finite petrochemical resources contributes to the increase in research and development of bio-based, renewable polymers. Concurrently, industrial and consumer demand for smaller, safer, and more flexible technologies motivates a global research effort to improve electrolytic polymer separators in lithium-ion batteries. To incorporate the aromatic structural advantages of lignin, a highly abundant and renewable resource, into gel-polymer electrolytes, lignin-derived molecules, vanillyl alcohol and gastrodigenin are functionalized and UV-polymerized with multi-functional thiol monomers. The resulting thin, flexible, polymer films possess glass transition temperatures ranging from −42.1°C to 0.3°C and storage moduli at 25°C ranging from 1.90MPa to 10.08MPa. The crosslinked polymer films swollen with electrolyte solution impart conductivities in the range of 7.04×10−7 to 102.73×10−7Scm−1. Thiol molecular weight has the most impact on the thermo-mechanical properties of the resulting films while polymer crosslink density has the largest effect on conductivity. The conducting abilities of the bio-based gel-polymer electrolytes in this study prove the viability of lignin-derived feedstock for use in lithium-ion battery applications and reveal structurally and thermally desirable traits for future work.

High performance thiol-ene thermosets based on fully bio-based poly(limonene carbonate)s

High glass transition temperature (Tg) thiol-ene networks (TENs) based on poly(limonene carbonate)s (PLCs), derived from orange oils and of potential degradability are described here. PLCs with moderate molecular weight were prepared by copolymerization of limonene oxide with CO2 and subsequent breakdown reactions. These PLCs were cured with multifunctional thiol monomers in the presence of thermal initiators via thiol-ene chemistry to generate poly(thioether-co-carbonate) networks. The thermal curing experiments were optimized by a kinetic study using real-time ATR-FTIR, in which a delayed gelation was observed. For the first time, an interesting “cage” effect was observed during the network formation initiated by DCP, in which the addition reactions of pendant isopropenyls on high molecular weight PLC chains were significantly enhanced by thiol-ene crosslinking at 160°C. The resulting homogeneous TENs with high Tgs (>100°C) and a wide range of thermomechanical properties, including rubbery moduli from 2.9 to 28.2MPa, were obtained. The TENs also showed promising properties such as high transparency, good acetone resistance and high hardness, suggesting their potential application in coatings.

Investigating Photocurable Thiol‐Yne Resins for Biomedical Materials

This study deals with the investigation of photocurable thiol‐yne resins covering several important aspects for the production of medical devices by UV‐based manufacturing processes. In this context, the performance of different low‐toxic photoinitiators (PIs) and stabilizers are evaluated in thiol‐yne formulations based on di(but‐1‐yn‐4‐yl) carbonate and various multifunctional thiol monomers. Photodifferential scanning calorimetry measurements reveal that the conversion of all resin formulations is mostly independent on the type and concentration of the applied photoinitiator; however, significant differences in their curing speed are observed. It turns out that the migration of an alkyne derivatized photoinitiator is significantly reduced while providing almost similar photoactivity as its nonfunctionalized reference. Moreover, it is found that lauryl gallate and butylated hydroxytoluene lead to significant stabilization without affecting the overall photoreactivity. Notably, the thermomechanical properties of the investigated photopolymers are only slightly affected by water absorption. Using ester free thiols, water absorption can be reduced and hydrolytically stable polymers are realized. These results highlight the versatility of the present thiol‐yne system for the production of medical materials by photopolymerization. image

Photo-cross-linked poly(thioether-co-carbonate) networks derived from the natural product quinic acid.

Polycarbonate networks derived from the natural product quinic acid that can potentially return to their natural building blocks upon hydrolytic degradation are described herein. Solvent-free thiol-ene chemistry was utilized in the copolymerization of tris(alloc)quinic acid and a variety of multifunctional thiol monomers to obtain poly(thioether-co-carbonate) networks with a wide range of achievable thermomechanical properties including glass transition temperatures from -18 to +65 °C and rubbery moduli from 3.8 to 20 MPa. The network containing 1,2-ethanedithiol expressed an average toughness at 25 and 63 °C of 1.08 and 2.35 MJ/m(3), respectively, and an order-of-magnitude increase in the average toughness at 37 °C of 15.56 MJ/m(3).

Triple Shape Memory Materials Incorporating Two Distinct Polymer Networks Formed by Selective Thiol–Michael Addition Reactions

We present a composite material composed of dual polymer networks uniquely formed from a single reaction type and catalyst but involving monomers with dramatically different reactivities. This powerful new approach to creating polymer networks produces two narrow glass transition, homogeneous networks sequentially from a single reaction but with all monomers present and uniformly mixed prior to any polymerization. These materials exhibit a triple shape memory effect based on the dual polymer networks, which were both formed using the thiol–Michael addition reaction. Two multifunctional thiol monomers (i.e., mercaptoacetate (MA) and mercaptopropionate (MP)) and two multifunctional vinyls (i.e., vinyl sulfone (V) and acrylate (A)) were polymerized in situ using a nucleophilic initiator. The MA-V polymer network (Tg = 55 °C) was generated first associated with the higher functional group reactivities followed by the formation of the MP-A network (Tg = 10 °C) which was confirmed by FT-IR, SEM, DMA, and a sepa...

New structural lithium battery electrolytes using thiol–ene chemistry

A series of solid poly(ethylene oxide)-methacrylate lithium ion electrolytes containing thio-ether segments have successfully been produced and evaluated with respect to mechanical and electrical performance. The series have been varied in crosslink density and thio-ether content. The study presents thiol–ene compounds as yet another tool to design multifunctional electrolytes, and that they are compatible with and usable for polymer electrolyte systems. The electrolytes, produced in a solvent free process where the oligomers are active diluents of the lithium salt, express a broad range of both mechanical as well as ion conducting properties. Conductivity values presented ranges up to about 8×10−7S/cm, and a wide spectrum of values of the storage modulus is presented in a range from 2MPa to 2GPa at 20°C. The influence of the crosslink density of the poly(ethylene oxide)-methacrylates with and without thio-ether segments is discussed. In order to present correlations between crosslink density and how the lithium ion transport is affected by incorporating multifunctional thiol monomers, density measurements have been undertaken to calculate the average molar mass between the crosslinks.