Thiol-isocyanate Reaction Research Articles

Recyclable dual-curing thiol-isocyanate-epoxy vitrimers with sequential relaxation profiles

Two series of poly(thiourethane)s-poly(thiol-epoxy) hybrids were prepared from dual-curing, stoichiometric thiol:isocyanate:epoxy mixtures. 1-methylimidazole (MI) was used as initiator for the thiol-isocyanate and thiol-epoxy curing reactions. A salt of tetraphenylborate derived from highly basic amine 1,5,7 triazabicyclo [4,4,0]dec-5-ene (TBD) was used as catalyst for the activation of bond exchange reactions. The curing kinetics and the glass transition temperature (Tg) of the samples were studied by differential scanning calorimetry (DSC). Thermal stability was characterized by thermogravimetric analysis (TGA). Stress relaxation dynamics related to the bond exchange reactions were studied by dynamic mechanical analysis (DMA). Recyclability of the fully cured samples according to the DMA results was carried out by hot-pressing at elevated temperatures. The results show that the curing process takes place in a controlled and sequential way: the thiol-isocyanate reaction takes place first, at moderate temperatures, followed by the thiol-epoxy reaction, which is completed at higher temperatures. The analysis of stress relaxation evidences a complex two-step relaxation behavior depending on the contribution of isocyanate and epoxy groups to the mixture. Isocyanate-rich materials show a simple relaxation process corresponding to the trans-thiocarbamoylation exchange reactions. Epoxy-rich materials show, in contrast, a two-step relaxation processes evidencing that trans-thiocarbamoylation alone may not be sufficient to relax the stress completely, due to an apparently permanent network structure. However, complete stress relaxation is possible for epoxy-rich materials through additional bond exchange reactions such as transesterification or dynamic thiol-Michael, but at a slower rate. Depending on the composition and the temperature, full recycling of the material can be achieved at moderate temperatures in a timescale of minutes to hours.

Autocatalyzed interfacial thiol–isocyanate click reactions for microencapsulation of ionic liquids

In recent years, ionic liquids (ILs) have received increasing attention because of low vapor pressure, environment friendliness, good thermal and chemical stability and strong solubility. However, the liquid nature and high viscosity restrict their applications in some fields. Encapsulation of ILs is an attractive way to handle them easily. Herein, we proposed a facile method to prepare IL-loaded microcapsules using IL-in-oil emulsion as template, poly(amide-thioether) as surfactant and interfacial thiol–isocyanate click reaction for shell formation. In this system, core materials ILs were proved to be able to catalyze thiol–isocyanate reaction without side products, which significantly simplified the preparation process of microcapsules. The shell of the microcapsules was composed of polythiourethane and poly(amide-thioether), which provided a strong protection for ILs. In addition, compared with IL-in-water emulsion, the application of IL-in-oil emulsion avoided the side reactions of the highly active isocyanate. The IL content of the resulted microcapsules could reach as high as 70 wt.%. It was also demonstrated that the proposed encapsulation technology was suitable for ILs with different polarities. This work provides an efficient way to encapsulate ILs using emulsion template, which will make ILs find widespread applications across various fields.

Thermoreversible Folding as a Route to the Unique Shape-Memory Character in Ductile Polymer Networks.

Ductile, cross-linked films were folded as a means to program temporary shapes without the need for complex heating cycles or specialized equipment. Certain cross-linked polymer networks, formed here with the thiol-isocyanate reaction, possessed the ability to be pseudoplastically deformed below the glass transition, and the original shape was recovered during heating through the glass transition. To circumvent the large forces required to plastically deform a glassy polymer network, we have utilized folding, which localizes the deformation in small creases, and achieved large dimensional changes with simple programming procedures. In addition to dimension changes, three-dimensional objects such as swans and airplanes were developed to demonstrate applying origami principles to shape memory. We explored the fundamental mechanical properties that are required to fold polymer sheets and observed that a yield point that does not correspond to catastrophic failure is required. Unfolding occurred during heating through the glass transition, indicating the vitrification of the network that maintained the temporary, folded shape. Folding was demonstrated as a powerful tool to simply and effectively program ductile shape-memory polymers without the need for thermal cycling.

Tough thiourethane thermoplastics for fused filament fabrication

ABSTRACTFused filament fabrication (FFF) is the most common form of additive manufacturing. Most FFF materials are variants of commercially available engineering plastics. Their performance when printed can widely vary, thus there is an increasing volume of research on alternative materials with thermal and mechanical performance optimized for FFF. In this work, thiol–isocyanate polymerization is used for the development of a one‐pot synthesis for polythiourethane thermoplastics for tough three‐dimensional (3D) printing applications. The thiol–isocyanate reaction mechanism allows for rapid polymer synthesis with minimal byproduct formation and few limitations on reaction conditions. The resulting elastomer has high toughness and a low melting point, making it favorable for use as a 3D printing filament. The elastomer outperforms commercial filaments in tension when printed. Considering the rapid advancement of additive manufacturing and the limitations of many engineering polymers with the 3D printing process, these results are encouraging for the development of bespoke 3D printing thermoplastics. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45574.

Temperature-modulated DSC study of network formation via Thiol-Isocyanate “click” reaction

The thiol-isocyanate chemistry was used to create crosslinked polymer networks without the use of solvent and catalyst. The preliminary study of a model thiol-isocyanate reaction was performed to confirm the “efficient linking” feature of the reaction, as indicated by online FTIR method. Temperature-modulated differential scanning calorimetry (TMDSC) was used to characterize the occurrence of the networks thiol-isocyanate reaction between multifunctional reactants, the influence of temperature on the reaction rate and the glass transition temperatures of the partially and fully cured networks. The investigation could pave the way for the design and tailoring of new cross-linked polymer materials for on-demand applications.

One-step thiol-isocyanate dispersion polymerization: Preparation of uniform, cross-linked and functional particles

Uniform and highly cross-linked particles with functional groups are very useful but difficult to be achieved in traditional dispersion polymerization. Herein, we develop a one-step dispersion polymerization based on thiol-isocyanate reaction to prepare such particles. This polymerization proceeds energy-efficiently at ambient temperature without additional catalyst/initiator or UV treatment, achieves high monomer conversion and has little side reaction. It is demonstrated that particles with size ranging from 1.8 to 8μm can be fabricated via adjusting the concentration of stabilizer and ratio of monomer/ethanol. The generated thiourethane linkages endow particles with high glass transition temperature (Tg) and uniform networks. In addition, the particles can be intrinsically functionalized and available for further modification due to thiol-isocyanate step-growth mechanism. As an attempt to perform thiol-isocyanate reaction in dispersion polymerization, this method offers feasibility for preparing uniform, functional and highly cross-linked particles in one-step dispersion polymerization.

Interfacial thiol-isocyanate reactions for functional nanocarriers: a facile route towards tunable morphologies and hydrophilic payload encapsulation.

Functional nanocarriers were synthesized using an in situ inverse miniemulsion polymerization employing thiol-isocyanate reactions at the droplet interface to encapsulate hydrophilic payloads. The morphology of the nanocarriers is conveniently tunable by varying the reaction conditions and the dispersions are easily transferable to the aqueous phase.

Water-borne thiol–isocyanate click chemistry in microfluidics: rapid and energy-efficient preparation of uniform particles

A nucleophile-catalyzed thiol–isocyanate reaction has been exploited as an efficient route to fabricate uniform particles in a water-borne system.

One‐pot deprotection and functionalization of polythiol copolymers via six different thiol–X reactions

Thiol chemistry is a versatile and powerful tool for the preparation of functional polymers and materials via post‐polymerization modification. However, polythiols are generally difficult to handle since they are prone to gel formation due to oxidative coupling between pendant thiol groups to form disulfide bridges. One‐pot deprotection and functionalization procedures that avoid polythiol manipulation are therefore attractive. In that regard, a methacrylate monomer carrying a xanthate moiety was used to prepare protected polythiol copolymers via concurrent atom transfer radical polymerization/reversible addition–fragmentation chain transfer. One‐pot deprotection and functionalization were carried out via aminolysis with a primary amine and subsequent functionalization without isolating the intermediate polythiols. Functionalization was exemplified with six different thiol–X reactions. Thiol–ene radical addition was not conclusive since it led to partial gelation. However, one‐pot deprotection and functionalization via thiol–halogen nucleophilic substitution, thiol–epoxy ring opening, thiol–isocyanate reaction, thiol–acrylate Michael addition and thiol–disulfide exchange were quantitative and led to well‐defined polymers. © 2013 Society of Chemical Industry

Temporal Control of Thiol-Click Chemistry

A chemical clock protocol that enables enhanced temporal control over the onset of two base-catalyzed ‘click’ reactions, the thiol-Michael addition reaction, and the thiol-isocyanate reaction, is described and used in polymerization reactions. Initiating protocols with predictable induction times for both click reactions are developed and characterized using a pair consisting of an electron deficient vinylic species and a nucleophile with an acid. The approach was successfully demonstrated such that the reaction onset is effectively and predictably delayed by up to 20 min, with rapid complete reaction following the controllable induction period. By implementing initiation systems with varying relative concentrations of the electron deficient vinyl, nucleophile, and acid, this approach to formulating a comprehensive initiator system affords a previously unavailable degree of temporal control that is extremely useful for designing and processing cross-linked polymers and other thiol-Michael and thiol-isocya...

Nanoparticle Vesicles Through Self Assembly of Cyclodextrin‐ and Adamantyl‐Modified Silica

Stable nanoparticle vesicles were for the first time prepared from adamantyl- and cyclodextrin (CD)-modified silica nanoparticles forming host-guest interactions in aqueous solution. Adamantyl-functionalized nanoparticles were obtained from thiol-isocyanate reaction of thiol-modified nanoparticles with 1-adamantyl isocyanate. The CD modified silica particles were isolated from a reaction of mono-6-para-toluenesulfonyl-β-cyclodextrin with the thiol functionalized silica under microwave conditions in basic media. The obtained particles were characterized in respect of agglomeration and self-assembly behavior in aqueous solution by dynamic light scattering and transmission electron microscopy. The found vesicle structures are exceptionally stable even after evaporation of water. Such inorganic hollow spheres formed through self-assembly processes may be important for chemical storage and transport. The technique of chemically-driven assembly is an attractive option to form useful complex structures by tunable agglomeration.

Thiol‐isocyanate‐acrylate ternary networks by selective thiol‐click chemistry

AbstractThiol‐isocyanate‐acrylate ternary networks were formed by the combination of thiol‐isocyanate coupling, thiol‐acrylate Michael addition, and acrylate homopolymerization. This hybrid polymerization reaction sequence was preferentially controlled by using phosphine catalyst systems in combination with photolysis. The reaction kinetics of the phosphine/acrylate thiol‐isocyanate coupling reactions were systematically investigated by evaluating model, small molecule reactions. The thiol‐isocyanate reaction was completed within 1 min while the thiol‐acrylate Michael addition reaction required ∼10 min. Both thiol‐isocyanate coupling and thiol‐acrylate Michael addition reactions involving two‐step anionic processes were found to be both quantitative and efficient. However, the thiol‐isocyanate coupling reaction was much more rapid than the thiol‐acrylate Michael addition, promoting initial selectivity of the thiol‐isocyanate reaction in a medium containing thiol, isocyanate, and acrylate functional groups. Films were prepared from thiol‐isocyanate‐acrylate ternary mixtures using 2‐acryloyloxyethylisocyanate and di‐, tri‐, and tetra‐functional thiols. The sequential thiol‐isocyanate, thiol‐acrylate, and acrylate homopolymerization reactions were monitored by infrared spectroscopy during film formation, whereas thermal and mechanical properties of the films were evaluated as a function of the chemical composition following polymerization. The results indicate that the network structures and material properties are tunable over a wide range of properties (Tg ∼ 14–100 °C, FWHM ∼ 8–46 °C), while maintaining nearly quantitative reactions, simply by controlling the component compositions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3255–3264, 2010