Thiol-ene Resin Research Articles

A low-shrinkage-stress and anti-bacterial adherent dental resin composite: physicochemical properties and biocompatibility.

Polymerisation shrinkage and biofilm accumulation are the two main problems associated with dental resin composites (DRCs) that induce secondary caries, which can cause restoration failure. Polymerisation shrinkage can lead to microleakage gaps between the tooth and the DRCs, causing the aggregation of bacteria and development of secondary caries. Reducing the shrinkage stress (SS) and improving the resistance to bacterial adhesion have always been the focus of this field in modifying DRCs. A thiol-ene resin system can effectively reduce the polymerisation SS via its step-growth mechanism for delaying the gel point. Fluorinated compounds can reduce the surface free energies, thereby reducing bacterial adhesion. Thus, in this study, a range of mass fractions (0, 10, 20, 30, and 40 wt%) of a fluorinated thiol-ene resin system were added to a fluorinated dimethacrylate resin system/tricyclo decanedimethanol diacrylate to create a fluorinated methacrylate-thiol-ene ternary resin matrix. DRCs were prepared using the obtained ternary resin matrix, and their physical and chemical properties, effect on bacterial adhesion, and biocompatibility were investigated. The results demonstrated that the volumetric shrinkage and SS of the DRCs were reduced with no reduction in conversion degree even after the thiol-ene resin system was added. All DRC-based fluorinated resin systems exhibited an excellent anti-bacterial adhesion effect, as evidenced by the colony-forming unit counts, live/dead bacterial staining, and crystal violet staining tests against Streptococcus mutans (S. mutans). The genetic expressions associated with the bacterial adhesion of S. mutans were substantially affected after being cultured with fluorinated DRCs. All fluorinated DRCs demonstrated good biocompatibility through the in vitro cytotoxicity test and live/dead staining images of the L-929 cells. The above results illustrate that the DRCs based on the fluorinated methacrylate-thiol-ene resin matrix can be potentially applied in clinical practice due to their low SS and anti-bacterial adhesion effect.

UV-curable thiol-ene system for broadband infrared transparent objects

Conventional infrared transparent materials, including inorganic ceramic, glass, and sulfur-rich organic materials, are usually processed through thermal or mechanical progress. Here, we report a photo-curable liquid material based on a specially designed thiol-ene strategy, where the multithiols and divinyl oligomers were designed to contain only C, H, and S atoms. This approach ensures transparency in a wide range spectrum from visible light to mid-wave infrared (MWIR), and to long-wave infrared (LWIR). The refractive index, thermal properties, and mechanical properties of samples prepared by this thiol-ene resin were characterized. Objects transparent to LWIR and MWIR were fabricated by molding and two-photon 3D printing techniques. We demonstrated the potential of our material in a range of applications, including the fabrication of IR optics with high imaging resolution and the construction of micro-reactors for temperature monitoring. This UV-curable thiol-ene system provides a fast and convenient alternative for the fabrication of thin IR transparent objects.

Model of UV-curing thickness for new thiol-ene resin for additive manufacturing of energetic materials

A new type of photocurable resin, which can be used for additive manufacturing of energetic materials, was prepared by modified polyether and multifunctional mercaptan. For the curing progress of this resin in a single layer of digital light processing (DLP), we incorporate micro-dynamical mechanism of free-radical photopolymerizations into the thickness-time equation to show how the curing thickness varies with initiator concentration ([I]) and incident light intensity ( I 0 ). We show that the temporal variation of curing thickness depends on two key parameters: the characteristic penetration depth h a = 1/(ε 1 [I]+α 0 ), where ε 1 is the molar extinction coefficients of initiator and α 0 is the absorption coefficient of oligomer, and critical time T c = -ln(1-Φ c )/( kI 0 0.5 [I] 0.5 ), where Φ c is the gel point of monomer and k is rate constant. Here, we consider the effects of [I] and I 0 to the characteristic penetration depth h a and the critical time T c in the early stage of radical polymerization, which means that the concentration of initiator and monomer could be deemed as constants. As predicted by the model, T c is a linear function of 1/ I 0 0.5 and 1/[I] 0.5 . Validation experiments show that the curing thickness predicted by the model is in good agreement with the experimental data. These results can be used for the accurate prediction of parameter setting of 3D printing and the component proportion of resin.

Additive Manufacture of Dynamic Thiol-ene Networks Incorporating Anhydride-Derived Reversible Thioester Links.

A photoprintable dynamic thiol-ene resin was developed based on commercially available anhydride, thiol, and ene monomers. The dynamic chemistry chosen for this study relied on the thermal reversibility of the in situ generated thioester-anhydride links. The resin's rheological and curing properties were optimized to enable 3D printing using the masked stereolithography (MSLA) technique. To achieve a desirable depth of cure of 200 μm, a combination of radical photoinitiator (BAPO) and inhibitor (pyrogallol) were used at a weight ratio of 0.5 to 0.05, resulting in more than 90% thiol-ene conversion within 12 s curing time. In a series of stress relaxation and creep experiments, the dynamic reversible exchange was characterized and yielded rapid exchange rates ranging from minutes to seconds at temperatures of 80-140 °C. Little to no exchange was observed at temperatures below 60 °C. Various 3D geometries were 3D printed, and the printed objects were shown to be reconfigurable above 80 °C and depolymerizable at or above 120 °C. By deactivation of the exchange catalyst (DMAP), the stimuli responsiveness was demonstrated to be erasable, allowing for a significant shift in the actuation threshold. These highly enabling features of the dynamic chemistry open up new possibilities in the field of shape memory and 4D printable functional materials.

Highly Tunable Thiol-Ene Photoresins for Volumetric Additive Manufacturing.

Volumetric additive manufacturing (VAM) forms complete 3D objects in a single photocuring operation without layering defects, enabling 3D printed polymer parts with mechanical properties similar to their bulk material counterparts. This study presents the first report of VAM-printed thiol-ene resins. With well-ordered molecular networks, thiol-ene chemistry accesses polymer materials with a wide range of mechanical properties, moving VAM beyond the limitations of commonly used acrylate formulations. Since free-radical thiol-ene polymerization is not inhibited by oxygen, the nonlinear threshold response required in VAM is introduced by incorporating 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a radical scavenger. Tuning of the reaction kinetics is accomplished by balancing inhibitor and initiator content. Coupling this with quantitative measurements of the absorbed volumetric optical dose allows control of polymer conversion and gelation during printing. Importantly, this work thereby establishes the first comprehensive framework for spatial-temporal control over volumetric energy distribution, demonstrating structures 3D printed in thiol-ene resin by means of tomographic volumetric VAM. Mechanical characterization of this thiol-ene system, with varied ratios of isocyanurate and triethylene glycol monomers, reveals highly tunable mechanical response far more versatile than identical acrylate-based resins. This broadens the range of materials and properties available for VAM, taking another step toward high-performance printed polymers.

Biomass derived carbon aerogel as an ultrastable skeleton of form-stable phase change materials for efficient thermal energy storage

Direct conversion of biomass to carbon aerogel provides a promising approach to developing supporting material for phase change materials (PCMs). In present work, carrot and pumpkin derived carbon aerogels (CCA and PCA) were fabricated via a hydrothermal and post-sintering process. N2 adsorption-desorption isotherms were used to evaluate the specific surface area and pore distribution of the carbon aerogels. It showed that the carrot carbon aerogel sintered at 800 °C (CCA800) possessed a specific surface area of 33.80 m2·g−1, which is separately 168%, 165%, and 287% higher than that of carrot carbon aerogel sintered at 1000 °C (CCA1000, 12.59 m2·g−1), pumpkin carbon aerogel sintered at 800 °C (PCA800, 12.77 m2·g−1), and pumpkin carbon aerogel sintered at 1000 °C (PCA1000, 8.74 m2·g−1). Owing to its porosity, the carbon aerogels with a high loading content of palmitic acid (PA)/thiol-ene resin (TE) composite as a PCM without leakage. A thermal conductivity enhancement of 60.5% was achieved by 50PA/TE@PCA1000 compared with 50PA/TE, and DSC result showed its latent heat of 88.26 J/g. The excellent properties of PCMs composites lead to a promising application foreground.

Evaluation of mechanical properties and shrinkage stress of thiol-ene-methacrylate dental composites with synthesized fluorinated allyl ether

It has already been reported that incorporation of thiol-ene into methacrylate resin could reduce shrinkage stress significantly. However, the mass fraction of thiol-ene in thiol-ene-methacrylate resin system should be limited because of deterioration of mechanical properties. In order to increase mass fraction of thiol-ene in thiol-ene-methacrylate ternary resin system, a new fluorinated ally ether (FUAE) was synthesized and mixed with pentaerythritol tetra (3-mercaptopropionate) (PETMA) at molar ratio of 1:1 to form new thiol-ene resin system, and then the thiol-ene resin was incorporated into Bis-GMA/TEGDMA resin to prepare thiol-ene-methacrylate resin system. The results of neat resin system showed that incorporation of new thiol-ene resin into methacrylate resin could increase degree conversion of methacrylate functional group and decrease volumetric shrinkage. In order to achieve the similar mechanical properties as methacrylate resin, mass fraction of thiol-ene in ternary resin system should not exceed 30 wt%. Thiol-ene-methacrylate resin systems with 10 wt% to 30 wt% were chosen to prepare dental resin composites, and physiochemical properties such as degree of conversion, volumetric shrinkage, shrinkage stress, flexural properties, and water sorption and solubility of these composites were investigated. The results showed that, compared with methacrylate resin-based dental composite, ternary resin-based dental composites had several advantages, such as higher DC% of methacrylate functional group, lower volumetric shrinkage, lower shrinkage stress, lower water sorption and solubility. The flexural properties of ternary resin-based dental composites were comparable or even better than those of methacrylate resin-based dental composite.

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin-Silica Nanoparticles Interface.

The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin-filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC-active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol-ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m-3) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin-based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin-filler interface.

A novel fabrication technique to minimize poly(dimethylsiloxane)‐microchannels deformation under high‐pressure operation

PDMS is one of the most common materials used for the flow delivery in the microfluidics chips, since it is clear, inert, nontoxic, and nonflammable. Its inexpensiveness, straightforward fabrication, and biological compatibility have made it a favorite material in the exploratory stages of the bio-microfluidic devices. If small footprint assays want to be performed while keeping the throughput, high pressure-rated channels should be used, but PDMS flexibility causes an important issue since it can generate a large variation of microchannel geometry. In this work, a novel fabrication technique based on the prevention of PDMS deformation is developed. A photo-sensible thiolene resin (Norland Optical Adhesive 63, NOA 63) is used to create a rigid coating layer over the stiff PDMS micropillar array, which significantly reduces the pressure-induced shape changes. This method uses the exact same soft lithography manufacturing equipment. The verification of the presented technique was investigated experimentally and numerically and the manufactured samples showed a deformation 70% lower than PDMS conventional samples.

Thiolene-based microfluidic flow cells for surface plasmon resonance imaging

Thiolene-based microfluidic devices have been coupled with surface plasmon resonance imaging (SPRI) to provide an integrated platform to study interfacial interactions in both aqueous and organic solutions. In this work, we develop a photolithographic method that interfaces commercially available thiolene resin to gold and glass substrates to generate microfluidic channels with excellent adhesion that leave the underlying sensor surface free from contamination and readily available for surface modification through self-assembly. These devices can sustain high flow rates and have excellent solvent compatibility even with several organic solvents. To demonstrate the versatility of these devices, we have conducted nanomolar detection of streptavidin-biotin interactions using in situ SPRI.

Soft-lithography fabrication of microfluidic features using thiol-ene formulations

In this work, a novel thiol-ene based photopolymerizable resin formulation was shown to exhibit highly desirable characteristics, such as low cure time and the ability to overcome oxygen inhibition, for the photolithographic fabrication of microfluidic devices. The feature fidelity, as well as various aspects of the feature shape and quality, were assessed as functions of various resin attributes, particularly the exposure conditions, initiator concentration and inhibitor to initiator ratio. An optical technique was utilized to evaluate the feature fidelity as well as the feature shape and quality. These results were used to optimize the thiol-ene resin formulation to produce high fidelity, high aspect ratio features without significant reductions in feature quality. For structures with aspect ratios below 2, little difference (<3%) in feature quality was observed between thiol-ene and acrylate based formulations. However, at higher aspect ratios, the thiol-ene resin exhibited significantly improved feature quality. At an aspect ratio of 8, raised feature quality for the thiol-ene resin was dramatically better than that achieved by using the acrylate resin. The use of the thiol-ene based resin enabled fabrication of a pinched-flow microfluidic device that has complex channel geometry, small (50 μm) channel dimensions, and high aspect ratio (14) features.

광경화성 아크릴 수지의 경화특성에 관한 연구

광경화성 수지인 아크릴레이트의 경화 특성과 메카니즘에 대하여 Photo-DSC와 FTIR, Raman spectrometer를 이용하여 조사하였다. 아크릴레이트 종류, 관능기 수, 광 세기 등에 따른 경화 속도에 관한 정보는 시간에 따른 Photo-DSC curve에서 계산하였고, FTIR과 Raman을 이용하여 경화 반응의 전환율과 반응 메카니즘을 조사하였다. 광경화 반응에서 산소의 영향을 알아보기 위하여 아크릴레으트 수지와 thiol-ene 수지의 경화과정을 비교하였는데, 공기 중 산소가 아크릴레이트의 라디칼 반응에서 금지제로 작용하여 아크릴레이트 수치는 80% 이하의 전환율을 보인 반면 thiol-ene 수지는 산소가 반응에 영향을 미치지 않는 것을 알 수 있었다.

Thiol−Yne Photopolymerizations: Novel Mechanism, Kinetics, and Step-Growth Formation of Highly Cross-Linked Networks

Radical-mediated thiol−yne step-growth photopolymerizations are utilized to form highly cross-linked polymer networks. This reaction mechanism is shown to be analogous to the thiol−ene photopolymerization; however, each alkyne functional group is capable of consecutive reaction with two thiol functional groups. The thiol−yne reaction involves the sequential propagation of a thiyl radical with either an alkyne or a vinyl functional group followed by chain transfer of the radical to another thiol. The rate of thiyl radical addition to the alkyne was determined to be approximately one-third of that to the vinyl. Chain-growth polymerization of alkyne and vinyl functionalities was only observed for reactions in which the alkyne was originally in excess. Analysis of initial polymerization rates demonstrated a near first-order dependence on thiol concentration, indicating that chain transfer is the rate-determining step. Further analysis revealed that the polymerization rate scaled with the initiation rate to an exponent of 0.65, deviating from classical square root dependence predicted for termination occurring exclusively by bimolecular reactions. A tetrafunctional thiol was photopolymerized with a difunctional alkyne, forming an inherently higher cross-link density than an analogous thiol−ene resin, displaying a higher glass transition temperature (48.9 vs −22.3 °C) and rubbery modulus (80 vs 13 MPa). Additionally, the versatile nature of this chemistry facilitates postpolymerization modification of residual reactive groups to produce materials with unique physical and chemical properties.

Laser-initiated polymerization of a thiol-ene system

Polymerization exotherms of a photopolymerizable thiol-ene system were generated by a pulsed laser source and recorded on a differential scanning calorimeter (DSC) and a specially designed thin-foil heat-flow meter. The laser was operated in both a multiple-pulse and a single-pulse mode. The rate and extent of polymerization increased significantly with the laser average power density, while the rate of polymerization was essentially independent of the energy density per pulse. Using a relatively low-intensity nitrogen laser in the single-pulse mode, a unique method for detecting and characterizing oxygen inhibition of polymerizable monomers was used to generate a curve for diffusion of oxygen (air) into the thiol-ene resin system. A single pulse from a high-intensity xenon fluoride laser readily overcame the oxygen inhibition.