Photo-differential Scanning Calorimetry Research Articles

Sustainable Light‐Assisted 3D Printing of Bio‐Based Microwave‐Functionalized Gallic Acid

AbstractThe development of 3D printing technologies and the requirement for more sustainable 3D printing materials is constantly growing. However, ensuring both sustainability and performance of the new materials is crucial to replace current fossil‐based polymers. Here, a bio‐based UV‐curable resin is produced in high yield from gallic acid (GA), a natural polyphenolic compound, by means of rapid and efficient microwave‐assisted methacrylation (5 min heating time and 10 min at 130 °C). The successful microwave‐assisted methacrylation with a high degree of substitution is confirmed by Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance spectroscopy. The radical UV‐photopolymerization of the methacrylated gallic acid (MGA) is further investigated by real‐time FTIR and differential scanning photo calorimetry (photo‐DSC) analyses, clearly demonstrating the high photo‐reactivity of MGA. Moreover, the %gel assessment demonstrates the formation of highly insoluble fractions after the UV‐curing, with 98% gel content. The photo‐rheology and rheology support the suitability of MGA for light‐assisted 3D printing. Indeed, a honeycomb and a hollow cube are 3D printed by means of the digital light processing 3D printing technique with high accuracy in a small scale. Finally, the cured‐MGA illustrates high Tg and thermal stability.

Influence of reactive diluent composition on properties and bio-based content of itaconic acid-based additive manufacturing materials

Among the additive manufacturing techniques, UV-curing processes are of special interest, as they allow for the fabrication of thermosetting materials with high resolutions and optical clarity. Traditionally, these processes require the use of formulations, consisting of polyester or polyurethane oligomers, combined with photoinitiators and reactive diluents. The latter are usually vinyl monomers such as acrylates or acrylamides, used to reduce the viscosity of the formulation and render it processable by additive manufacturing machines. In this work, we investigate whether a combination of diluents can be used to tune the thermomechanical properties of the printed materials, and if it can be exploited to increase their overall bio-based content without compromising their performance. To do so, a series of itaconic acid-based polyesters with different chemical structures (aliphatic–aromatic) were synthesized and formulated with reactive diluents acryloyl morpholine (ACMO) and isobornyl acrylate (IBOA). The physicochemical properties of the prepared formulations, together with their reactivity towards UV-light were assessed via photo differential scanning calorimetry (photo-DSC) and photo-rheology measurements. The same formulations were then used to fabricate test specimen via digital light processing (DLP) 3D printing, which were characterized on their thermomechanical properties by means of dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) measurements. The glass transition temperature of the printed samples reached a maximum of 98 °C, while the diluent ratio could be used to manipulate the Tg in a linear trend. All materials of this study exhibited Td,5% above 250 °C, suggesting good thermal stability. These results show that materials with a very high bio-based content (up to 85%) and very promising thermomechanical properties could be obtained by employing a diluent mixture during the formulation phase.

Preparation and photocuring performance of itaconic acid-derived hyperbranched macromers with internal and terminal C[dbnd]C bonds catalyzed by tetramethylguanidine

A series of hyperbranched polymers derived from biomass itaconic acid was prepared via aliphatic nucleophilic substitution polycondensation reaction under mild conditions by using bis(2-bromoethyl) itaconate and trimeric acid as A2 and B3 monomers, respectively, and tetramethylguanidine as catalyst. On this basis, the hyperbranched macromers that contained C = C double bonds in the internal skeleton and the periphery were obtained by further adding A1 monomer (2-bromoethyl acrylate) directly into the reaction system. The successful synthesis of these macromers were confirmed via proton nuclear magnetic resonance, Fourier transform infrared and gel permeation chromatography. The results of photo-differential scanning calorimetry and rheological experiments showed that these macromers exerted a positive effect on the ultraviolet (UV) curing of commercial resin. The properties of cured splines and coatings, such as mechanical properties, pencil hardness, and thermal stability, were considerably improved with the addition of hyperbranched macromers. They were significantly better than those of linear macromers and macromers that contained polymerizable groups only in the inner framework or their terminal units. The results show that both the inner and terminal C = C double bonds of hyperbranched macromers can participate in UV cross-linking. Thus, such macromers may be used as potential additives for high-performance UV curable coatings.

Coumarin based glyoxylate photoinitiators for free radical and cationic Photopolymerizations with UV-Visible LED irradiation

High-performance photoinitiators (PIs) play a crucial role in ultraviolet–visible (UV–Vis) photopolymerization. In this study, three coumarin-3-oxoacetic acid methyl esters (COAEs) which demonstrate significant UV–Vis absorption within the 300–500 nm range were synthesized and studied. Real-time fourier transform infrared (RT-FTIR) and photo-differential scanning calorimetry (photo-DSC) experiments demonstrated that these PIs can function as Type I and Type II PIs for initiating free radical polymerization (FRP) of acrylate monomers. Additionally, they can serve as photosensitizers for iodonium salts and sulfonium salts, enabling cationic photopolymerization (CP) of epoxy and oxetane monomers. Remarkably, even at low concentrations of 0.01 wt%, they can effectively initiate the deep curing of Tri-(propylene glycol) diacrylate (TPGDA) to a depth of approximately 9 cm after 5 min of irradiation with a 415 nm or 450 nm LED light source. Furthermore, the COAEs exhibit satisfactory photobleaching properties, making them suitable for colorless applications in photopolymerization. The photochemical and photophysical properties of the COAEs were thoroughly investigated using absorption spectroscopy, electron spin resonance, cyclic voltammetry experiments, and photoinduced decarboxylation experiments to elucidate the photoinitiation mechanism. Cytotoxicity experiments revealed that COAE-N exhibited good cytocompatibility. Therefore, the exceptional polymerization properties of COAEs offer promising prospects for FRP and CP applications. Additionally, their efficient photobleaching characteristics make them highly suitable for deep photopolymerization applications. Moreover, the low cytotoxicity of COAEs suggests significant potential for biomedical applications such as dental restoration.

Vat photopolymerization additive manufacturing process modeling: a thermal-chemical coupling approach informed by in-situ and ex-situ characterization data

Vat photopolymerization (VPP) is one of the most widely used additive manufacturing methods. The VPP process temperature and material curing reaction interplay with each other to critically determine the final product quality. Insights about the time-varying process temperature and degree of conversion (DoC) is desired for VPP process control but difficult to attain due to lacking effective operando characterization technologies. This work reports a new method to create a thermal-chemical model of the VPP process by solving an inverse heat conduction problem (IHCP) based on in-situ observable temperature measurement to estimate the chemistry reaction-induced heat source that is a function of DoC. Ex-situ photo differential scanning calorimetry (Photo-DSC) characterization is used to initialize the chemistry reaction model parameters so that DoC can be calculated. Specifically, vat substrate temperature is measured using an in-situ infrared thermal camera and used as input to solve an IHCP for estimating exothermic heat generation rate for the internal heat generation component at the curing part. Overall, the newly developed VPP modeling framework combines an IHCP that is optimized by in-situ thermal monitoring with a chemical reaction heat generation and conduction model that is educated by Photo-DSC characterization. The model predictions of temperature and DoC are experimentally validated by comparing against in-situ temperature measurement and ex-situ spectroscopy measurement of prints at different exposure times.

Characteristics of novel cycloaliphatic epoxides based on UV-induced cationic ring-opening polymerization for plastic coatings

Cationic ring-opening polymerization (CROP)-capable cycloaliphatic epoxide monomers bearing a benzyl ether group (CE-BEs) were developed as glass-replacement plastic coatings for lightweight automobiles. Three different monomers of bis(((7-oxabicyclo[4,1,0]heptan-3-yl)methoxy)methyl)benzene isomers were synthesized to provide the cycloaliphatic epoxide functional groups. 1H and 13C nuclear magnetic resonance and Fourier transform infrared (FT-IR) spectroscopic analyses confirmed that the monomers were successfully synthesized. The shear viscosity and real-time crosslinking behavior of the CROP coatings were investigated using a rheometer. In particular, the release of thermal energy via CROP under UV irradiation was monitored using differential scanning photocalorimetry. The reaction conversion of cycloaliphatic epoxides by CROP before and after UV irradiation was verified using FT-IR spectroscopy. The transparency of the CROP coating films cured on a polycarbonate substrate was measured using an ultraviolet–visible spectrophotometer, and their adhesion was confirmed using cross-cut tests. For characterization of the surface mechanical properties, a nanoindentation tester and a nanoscratch tester were used in conjunction with an atomic force microscope to evaluate the surface hardness and scratch resistance, respectively. In addition, the thermomechanical properties of the cured CROP coating films were investigated using a rigid-body pendulum tester operated in dynamic physical mode. The ternary coating systems with CE-BEs were found to exhibit high photoreactivity, a dense crosslinking density, a transparent appearance, and enhanced adhesion and mechanical properties, making it suitable for glass-replacement plastic coatings.

A Practical Primer: Raman Spectroscopy for Monitoring of Photopolymerization Systems.

Photopolymerization systems provide compelling advantages for industrial applications due to their fast reaction kinetics, wide selection of monomers for physical property development, and energy-efficient initiation via illumination. These same advantages can present challenges when attempting to monitor these reactions or characterize their resulting polymers; however, Raman spectroscopy can provide the flexibility and resolution needed. In this overview, Raman spectroscopy is compared to common characterization techniques, such as photo-differential scanning calorimetry and infrared spectroscopy, highlighting advantages of Raman spectroscopy. Examples are provided of how Raman spectroscopy has been used to monitor photopolymerizations and to provide insight on the impact of monomer chemistry and processing conditions, as well as paired with other techniques to elucidate physical properties. Finally, practical tips are provided for applying Raman spectroscopy and microscopy in photopolymerization systems.

UV-Curing Additive Manufacturing of Bio-Based Thermosets: Effect of Diluent Concentration on Printing and Material Properties of Itaconic Acid-Based Materials.

In the quest toward sustainable thermosets, research has been conducted on various polymer classes like epoxy, benzoxazines, acryl-/methacrylates, etc. One particular group that can also be utilized as sustainable inks for additive manufacturing is itaconic acid-based unsaturated polyester resins. However, due to increased viscosity of the resins, the use of reactive diluents is required to increase their processability. While research has focused on creating different polymeric structures to expand the possible applications, the required amount of diluent has not received equal attention. In this work, a group of itaconic acid-based polyesters was synthesized to create a series of formulations with different reactive diluent contents. The physicochemical properties of the prepared formulations, along with their reactivity toward UV light, were assessed via photo-differential scanning calorimetry (photo-DSC), real-time attenuated total reflectance (RT-ATR), and photorheology measurements. The same formulations were then used to fabricate test specimens via digital light processing (DLP) three-dimensional (3D) printing, which were examined as to their thermomechanical properties by means of dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) measurements.

Radical-Mediated Ring-Opening Photopolymerization for Semicrystalline Thermoplastic Additive Manufacturing

Conventional approaches to stereolithographic additive manufacturing (SLA) employ liquid resin formulations based on multifunctional (meth)acrylates and epoxides that afford cross-linked polymeric networks upon polymerization. Nevertheless, the utilization of resins that yield semicrystalline thermoplastics provides facile access to physical and mechanical properties that are otherwise difficult to attain, such as high toughness and resistance to solvent swelling as well as additional postfabrication processing options that can be used to extend the life cycle of three-dimensional printed polymers. Here, we report the SLA-based additive manufacturing of semicrystalline thermoplastics utilizing the radical-mediated ring-opening photopolymerization of seven- and eight-membered cyclic allylic sulfides. Photopolymerization of resin formulations incorporating seven- and eight-membered cyclic allylic sulfides and crystallization of the resultant (co)polymers were examined using Fourier transform infrared spectroscopy, photorheology, and isothermal photo-differential scanning calorimetry. The formulated resins were found to polymerize and subsequently crystallize rapidly upon irradiation under ambient conditions. The mechanical properties of stereolithographically printed copolymers approached the bulk copolymer mechanical properties, demonstrating unusually strong interlayer adhesion atypical of layerwise, stereolithographic printing of semicrystalline polymers. Finally, high-quality, recyclable, semicrystalline thermoplastic parts were printed and melted down, demonstrating the potential for these semicrystalline materials to provide a path for improved sustainability of polymeric parts produced via SLA.

From soft hyperbranched polymers to hard crosslinkers: UV curable macromers that contained oxetane on and around hyperbranched frameworks

On the basis of aliphatic nucleophilic substitution polycondensation reactions, a series of hyperbranched macromers that contained cationic polymerizable groups, e.g., oxetane, internally and peripherally, was prepared using 3,3-dibromomethyl-1-oxetane and 3,5-dihydroxybenzoic acid as A2 and CB2 monomers, respectively. The structures of these macromers were confirmed via proton nuclear magnetic resonance, Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography analyses. The effect of the hyperbranched macromers on the ultraviolet (UV) curing of commercial resin was investigated via photo-differential scanning calorimetry and rheological experiments. The addition of hyperbranched macromers substantially improves the performance of the coating, such as its mechanical properties, pencil hardness, adhesive force, and thermogravimetric stability. It is superior to the addition of small molecule monomers, linear macromers, and hyperbranched macromers with oxetane only at the periphery under the same conditions. The best overall performance of the coating is achieved when the molar ratio of A2 to CB2 is 1.4. Results show that because hyperbranched internal units can also participate in crosslinking during the curing process, such macromers may be good candidates for high-performance UV curing coatings.

Design and synthesis of photocrosslinker and light blocker based on l-Amino acid polyester and their application in solvent-free resin formulation for DLP/SLA 3D printing

Customising material design for new technological applications like additive manufacturing (AM) is a challenging yet promising approach to create a palette of materials suitable for developing eco-friendly products. l-Glutamic acid and l-aspartic acid based aliphatic, photocurable polyester crosslinkers were designed and developed and incorporated into a solvent-free photocurable resin formulation with hydroxyl (ethyl)methacrylate (HEMA). Proof-of-concept 3D printing of clear and transparent objects was demonstrated using digital light processing (DLP) and Stereolithography (SLA) techniques. Resolution of the 3D printed objects could be improved by incorporating a Dansyl labelled l-glutamic acid polyester, which not only aided in modulating the viscosity of the resin formulation but could also function as a light blocker, thereby avoiding polymerization of unwanted areas while 3D printing. The curing kinetics of the photocurable formulation was analyzed using photo differential Scanning Calorimetry. Enzymatic degradability studies of 3D printed films were undertaken in PBS buffer containing esterase enzyme and compared with 3D printed samples using HEMA and a commercial crosslinker (Trimethylolpropane triacrylate (TMPTA)). Scanning electron microscopy (SEM) was used to evaluate the morphology of the 3D printed films before and after enzymatic degradation in the PBS buffer for 60 days. The 3D printed amino acid crosslinked films of HEMA presented high degree of degradation in contrast to the near total absence of any degradation in the 3D printed film crosslinked using TMPTA. The availability of new photocurable formulations that are enzymatically degradable are highly sought after for 3D printing applications.

Influence of Methacrylate and Vinyl Monomers on Radical Bulk Photopolymerization Process and Properties of Epoxy-Acrylate Structural Adhesives

In this paper, epoxy-acrylate structural adhesives tapes (SATs) were obtained from Bisphenol A-based liquid epoxy resin and epoxy acrylic resins (EARs). A new method of EARs preparation, i.e., the free radical bulk photopolymerization process (FRBP), was studied in detail. The influence of methacrylic monomers (methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, (2-acetoacetoxy)ethyl methacrylate) and vinyl monomers (N-vinylpyrrolidone and styrene) on the FRBP process of base monomers (i.e., butyl acrylate, glycidyl methacrylate and 2-hydroxyethyl acrylate) was investigated. The kinetics of photopolymerization process was monitored by photo-differential scanning calorimetry method. The properties of the obtained EARs (viscosity and average molecular weights), as well as monomers conversion using 1H NMR, were determined. It was revealed that styrene significantly decreases the photopolymerization rate and increases the final monomers conversion (+27%). However, the resulting tetrapolymers BA-co-GMA-co-HEA-co-STY have low molecular weights and low polydispersity (2.2). Methacrylate monomers with shorter aliphatic chains (<C4) also decrease the rate of photopolymerization due to the length of the aliphatic chain increasing. Surprisingly, the best results of adhesion to steel and shear strength were obtained for SAT based on epoxy acrylate resin with styrene (11 N/25 mm and 20.8 MPa, respectively). However, the thermomechanical properties of SAT with styrene were weaker than those with methacrylates.

Synthesis of photoactive nanocomposite hydrogels via in-situ photoinitiated thiol-ene click polymerization of acrylates containing norbornene-POSS and norbornene-POSS/Ag NPs

Radical-mediated thiol-ene photopolymerization is a method that has been studied intensively since the beginning of the century due to the nature of click chemistry which can be carried out in a fast, controllable, and easy way under mild environment conditions with no or minimal formation of by-products. In order to improve the properties of the polymeric nanocomposite materials which have been obtained by photopolymerization method and to prepare them for a particular purpose, various nano-sized photo-reactive groups or cross-linking agents have been added to the formulations. The advantage of this study for the preparation of thin-film and hydrogel nanocomposites is based on one-pot thiol-ene photo-click polymerization. The main contribution made by one-component Type II photoinitiator, 2-Mercaptothioxanthone (TX-SH) carries both thiol functionality and chromophoric group on it. Polyhedral oligomeric silsesquioxane (POSS) functionalized with 1 or 3 norbornene units was used as alkene and played a good role in the preparation of nanocomposite hydrogels with/without in-situ formed silver nanoparticles (Ag NPs) with various acrylate content by thiol-ene photo-click polymerization. Especially the good contribution of norbornenylethyl disilanol isobutyl polyhedral oligomeric silsesquioxane (1NBPOSS) or tris-norbornenyl isobutyl polyhedral oligomeric silsesquioxane (3NBPOSS) was seen in terms of conversion percentage of acrylates which was determined by photo differential scanning calorimetry (photo-DSC) and swelling ratios of hydrogels in phosphate buffer solution (PBS) buffer solution. Besides them, obtained nanocomposites displayed good thermal stability values according to the Thermogravimetric analysis (TGA) measurements and scanning electron microscopy (SEM) images confirmed rather small-sized and uniform in-situ formed Ag NPs.

Self-Crosslinkable Pressure-Sensitive Adhesives from Silicone-(Meth)acrylate Telomer Syrups.

In this study, a novel and environmentally friendly method for the preparation of photoreactive pressure-sensitive adhesives (PSAs) was demonstrated. Adhesive binders based on n-butyl acrylate, methyl methacrylate, acrylic acid, and 4-acryloyloxy benzophenone were prepared with a UV-induced telomerization process in the presence of triethylsilane (TES) as a telogen and acylphosphine oxide (APO) as a radical photoinitiator. The influence of TES (0-10 wt. parts) and APO (0.05-0.1 wt. parts/100 wt. parts of monomer mixtures) concentrations on the UV telomerization process kinetics was investigated using a photodifferential scanning calorimetry method and selected physicochemical features of the obtained silicone-(met)acrylate telomeric syrups (K-value, solid content, glass-transition temperature, and dynamic viscosity), as well as properties of the obtained PSAs (Tg, adhesion, tack, and cohesion), were studied. An increase in TES content caused a significant decrease in the Tg values (approx. 10 °C) and K-value (up to approximately 25 a.u.) of the dry telomers, as well as the dynamic viscosity of the telomeric syrups. PSAs were obtained through UV irradiation of thin polymer films consisting only of silicone-(meth)acrylate telomer solutions (without the use of additional chemical modifiers or of a protective gas atmosphere and protective layers). PSAs were characterized by very good adhesion (12.4 N/25 mm), cohesion at 20 °C (&gt;72 h) and 70 °C (&gt;72 h), and low glass-transition temperature (-25 °C).

A polymerizable difunctional photoinitiator featuring a bio-based group and its photoinitiating properties

A polymerizable difunctional photoinitiator 2-methylene-succinic acid bis-{2-[4-(2-hydroxy-2-methylpropionyl)phenoxy]ethyl} ester (IAHHMP) based on the commercial photoinitiator 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methylpropanone (HHMP) and a biorenewable itaconic acid is synthesized by esterification. The structure is confirmed by ultraviolet spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (1H NMR, 13C NMR) and thermogravimetric analysis. The photopolymerization behaviour of the photoinitiator is investigated using photo-differential scanning calorimetry and compared with that of two commercial photoinitiators, HHMP (or photoinitiator 2959) and 1-hydroxycyclohexyl phenyl ketone (or photoinitiator 184). The results show that IAHHMP has a strong UV absorption capacity at 245~300 nm and can initiate polymerization of monomers containing a double bond. The relative migration of IAHHMP is less than that of the systems containing an HHMP or 1-hydroxycyclohexyl phenyl ketone photoinitiator. Therefore, IAHHMP is expected to have potential applications in more environmentally friendly materials, such as in food and medical packaging.

Biodegradable, Solvent‐Free Photocrosslinkable PLLA Resin Formulations for Additive Manufacturing

AbstractAcrylate end‐functionalized linear and star poly l‐lactide (PLLA) based aliphatic, photocurable oligomeric crosslinkers are developed, which are formulated with hydroxyl (ethyl)methacrylate (HEMA) as a biodegradable reactive diluent to demonstrate successful application for solvent‐less 3D printing using digital light processing (DLP) technique as well as a custom‐designed direct ink writing 3D printer. The resin formulation for 3D printing is optimized using spot curing, photodifferential scanning calorimetry and cure depth analysis. The 3D printed parts exhibit promising mechanical property along with improved hydrophilicity and biodegradability. The development of new photocurable resin formulations are expected to meet the growing demand for raw materials that can be applied for developing custom designed bio implantable objects.

Visible Light Induced High Resolution and Swift 3D Printing System by Halogen Atom Transfer.

3Dprinting technology offers solutions for numerous needs in industry and the daily life of individuals. In recent years, most research efforts have focused on this technology as the market share has grown and requirements have become specified in their related fields. In this work, a novel visible light induced 3D printing system with high resolution and short printing time using dimanganese decacarbonyl (Mn2 (CO)10 ) in combination with organic halides is reported. The radicals formed through halogen abstraction by photochemically generated manganese pentacarbonyl from organic halides with high quantum efficiency initiate the polymerization of acrylic resins. The kinetics of the process using various halide-containing molecules in the photoinitiaiting system are investigated with real-time fourrier transform infrared spectroscopy and photo-differential scanning calorimetry analyses, and the characteristics of 3D printouts are presented and compared with that of the commercial photoinitiator, 2,4,6-trimethylbenzoyl)phosphine oxide without Mn2 (CO)10 . The results obtained confirm that the combination of Mn2 (CO)10 and structurally diverse organic halides is a class of promising 3D system for various applications.

Photo-Curing Kinetics of 3D-Printing Photo-Inks Based on Urethane-Acrylates.

In this study, photo-curing kinetics for urethane-acrylate-based photo-inks for 3D printing were evaluated using a photo-differential scanning calorimetry analysis. Initially, the photopolymerization kinetics of di- and monofunctional monomers were separately studied at different temperatures (5–85 °C). Later, the photo-curing kinetics and mechanical properties of photo-inks based on different monomer mixtures (40/60–20/80) were evaluated. The results showed that urethane-dimethacrylate (UrDMA) and urethane-acrylate (UrA) had no light absorption in the region of 280–700 nm, making them a proper crosslinker and a reactive diluent, respectively, for the formulation of 3D-printing photo-inks. The kinetics investigations showed a temperature dependency for the photo-curing of UrDMA, where a higher photopolymerization rate (Rp,max: from 5.25 × 10−2 to 8.42 × 10−2 1/s) and double-bound conversion (DBCtotal: from 63.8% to 92.2%) were observed at elevated temperatures (5–85 °C), while the photo-curing of UrA was independent of the temperature (25–85 °C). Enhancing the UrA content from 60% to 80% in the UrDMA/UrA mixtures initially increased and later decreased the photopolymerization rate and conversion, where the mixtures of 30/70 and 25/75 presented the highest values. Meanwhile, increasing the UrA content led to lower glass transition temperatures (Tg) and mechanical strength for the photo-cured samples, where the mixture of 30/70 presented the highest maximum elongation (εmax: 73%).

Gel Polymer Electrolytes with Mixture of Triazolium Ionic Liquids and Propylene Carbonate.

This study is focused on the structural influence of 1,2,4-triazolium ionic liquid (IL), that is, the effect of the length of the substituent and the type of substitution (1-methyl-4-alkyl or 1-alkyl-4-methyl) used in the mixture with propylene carbonate (PC) on the properties of thiol–ene polymer ionogels and on the preparation of an ionogel with satisfactory mechanical and conductive properties. PC allows for higher conductivity but also causes electrolyte leakage from the gel. When using triazolium IL (instead of the imidazolium one), because of the stronger interactions between components of the system, the ionogels do not leak. In this study, 1,4-dialkyl-1,2,4-triazolium ILs were successfully synthesized by the alkylation of 1,2,4-triazole. Subsequently, gel polymer electrolytes were obtained by one-pot thiol–ene photopolymerization reactions of tetrafunctional thiols with different chemical structures: pentaerythritol tetra(3-mercaptopropionate) (PETMP) or pentaerythritol tetra(3-mercaptobutyrate) (PETMB) and trifunctional ene (TATT) in the presence of a mixture of 1,4-dialkyl-1,2,4-triazolium IL with PC. Measurements made by electrochemical impedance spectroscopy showed that all ionogels with TATT+PETMB as a polymer matrix presented smaller relative ionic conductivity compared to ionogels containing TATT+PETMP. The puncture resistance and elongation at puncture, measured by the puncture resistance method, were higher for ionogels with poly(TATT+PETMB) than for those with poly(TATT+PETMP). Moreover, ILs containing a methyl group in position N1 of the 1,2,4-triazole ring presented lower puncture resistance than ionogels with ILs containing a methyl group in position N4, especially for shorter alkyl chains. Additionally, the photo-differential scanning calorimetry method was employed to characterize the course of photopolymerization. The compositions and their constituents were characterized by UV and IR spectroscopy.

Synthesis of Epoxy Methacrylate Resin and Coatings Preparation by Cationic and Radical Photocrosslinking.

This work involves the synthesis of hybrid oligomers based on the epoxy methacrylate resin. The EA resin was obtained by the modification of industrial-grade bisphenol A-based epoxy resin and methacrylic acid has been synthesized in order to develop multifunctional resins comprising both epoxide group and reactive, terminal unsaturation. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Monitoring of EA synthesis reactions over time using PAVs, MAAC and NV parameters, and the FT-IR method reveals that esterification reactions proceed faster at the start, exhibiting over 40% of conversion within the initial 60 min, which can be associated with a relatively high concentration of reactive sites and low viscosity of the reaction mixture at the initial reaction stage. With the further increase in the reaction time, the reaction rate tends to decrease. The control of the EA synthesis process can guide how to adjust reactions to obtain EAs with desired characteristics. Based on obtained values, one can state that the optimum synthesis time of about 4–5 h should be adopted to prepare EAs having both epoxy groups and unsaturated double bonds. The structure of the obtained EA was confirmed by FT-IR and NMR methods, as well as the determination of partial acid value and epoxy equivalent. Samples at various stages of synthesis were cured with UV radiation in order to study the kinetics of the process according to cationic and radical polymerization determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) and then the properties of the cured coatings were tested. It turned out that the cationic polymerization was slower with a lower conversion of the photoreactive groups, as compared to the radical polymerization. All the obtained EA coatings were characterized by good properties of cured coatings and can be successfully used in the coating-forming sector.