No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Vat photopolymerization of unsaturated polyesters utilizing a polymerizable ionic liquid as a non-volatile reactive diluent
Abstract
Unsaturated polyester resins (UPRs) enjoy numerous applications as structural adhesives in glass fiber laminates, concrete flooring, and masonry repair. Typically, UPRs consist of unsaturated polyester (UPE) oligomers with up to 50 wt.% of a reactive diluent such as styrene. The ability of these resins to cure rapidly upon UV irradiation, in conjunction with a photoinitiator, enables vat photopolymerization (VP) 3D printing. However, the volatility and toxicity of styrene limits the use of traditional UPRs for VP. This report describes a nonvolatile ionic liquid reactive diluent for UPRs, which, in combination with the unreactive diluent dimethoxyethane, produce resins suitable for VP. Photorheological experiments help guide resin design for VP based on a series of synthesized UPEs and PIL concentrations. Photocured networks exhibit increasing degradation temperatures with increasing PIL incorporation from 215 to 279 °C. VP of a selected UPR composition demonstrated the ability to form self-supporting, geometrically complex 3D printed structures, suggesting the opportunity to utilize a common industrial feedstock as a component of a novel VP resin system. Dried and unextracted 3D printed test specimens exhibit ionic conductivities spanning from 10⁻⁸ to 10⁻⁵ S cm⁻¹ between 60 and 150 °C, which indicate a potential additional attribute for 3D printed UPE parts.
... [7,8] This improves the printability of the resin and results in a more homogeneous thermoset matrix in the final printed part. While styrene is the most industrially ubiquitous reactive diluent, other reactive compounds such as poly(ethylene glycol) diacrylate, [9,10] polymerizable ionic liquids, [11,12] diethyl fumarate, [13][14][15] and thiols [16] serve as alternatives. For these free-radical processes, the fumarate isomer exhibits higher reactivity compared to the maleate isomer. ...
... For example, there has been increasing interest in unsaturated polyesters (UPEs) as a sustainable feedstock for lithographic additive manufacturing. While previous investigations demonstrated the ability to 3D print unsaturated polyesters in the presence of a reactive diluent, [11,14,16,23,25] these studies were performed in the presence of an unreactive solvent, a custom printer with a heated vat, or a resin formulation consisting of a higher weight fraction of reactive diluent to UPE. Our research presents the development of a solvent-free UPE-based resin for vat photopolymerization at ambient temperatures with diethylene glycol as a diol. ...
... The synthesis of unsaturated polyester oligomers was conducted in a step-wise melt polycondensation reaction adapted and modified from previous works. [11] In a typical synthesis, a 500 mL, 3-neck round bottomed flask equipped with a magnetic stir bar, N 2 adapter, septum, and a Dean-Stark trap with a reflux condenser was loaded with MA (30 g, 306 mmol), PA (45.3 g, 306 mmol), SA (30.6 g, 306 mmol), and DEG (97.41 g, 918 mmol). The SA and PA content was varied to enable synthesis across a compositional range. ...
Additive manufacturing with vat photopolymerization (VP) as an emerging manufacturing method addresses various goals for enhanced sustainability including waste reduction, dematerialization, and the customization of intricate and complex 3D parts. Unsaturated polyesters (UPEs) recently gained attention as a sustainable material source for lithographic additive manufacturing. While previous methods demonstrated the printability of UPE-based resins, these studies lack the solvent-free approach demonstrated herein. Furthermore, the effective depolymerization of polyester thermosets has remained relatively unexplored. This report demonstrates structure–property relationships and subsequent solvent-free VP of UPEs with PEGDA-575 as a reactive diluent with effective depolymerization of polyester thermosets through base-catalyzed methanolysis.
Graphical abstract
... As photocuring occurs, the storage modulus increases until it exceeds the loss modulus; this point is known as the curing time. [35] Calculation Method: All the calculations were performed within the framework of the density functional theory (DFT) as implemented in the Vienna Ab initio Software Package (VASP 5.4.4) code within the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation and the projected augmented wave (PAW) method. [36] The cutoff energy for the planewave basis set was set to 450 eV. ...
Photo‐triggered shape morphing structures can be found in myriads of areas. Utilizing light as a switch can effectively control and regulate the precise deformation of structures. However, the integration of photo‐switching functions in shape‐morphing structures with complex geometries remains a challenge. Here, photoswitchable digital light processing based 4D printing high‐resolution and highly complex geometries, based on UV curable WO2.9 nanoparticle doped shape memory polymer nanocomposites is reported, which are highly deformable (stretchability up to ≈1000% at rubbery state) and fatigue resistant (repeatedly loaded >1200 times at ambient temperature). The presence of just trace WO2.9 nanoparticles (<0.20 wt.‰) contributes to the controlled photothermal property of nanocomposite via selective absorption of light, which enables reversibly photoswitchable (>50 times), spatial and remote control of 4D printing shape morphing structures. These findings offer a promising approach to expanding the applications of photo‐triggered shape‐morphing structures.
... This involves the UV light illumination during oscillatory measurements within the linear viscoelastic region (1 rad s −1 of angular frequency and 0.1% of strain) at the 300th second and taking the cross-over of G′ and G′′ as the gelation time ( Fig. S5a-e). This method is widely adopted for evaluating the curing behavior of photo-reactive materials in 3D printing [26,[62][63][64][65][66]. We examined the impact of various factors such as UV intensity, photo-curable monomer content, and cross-linker:monomer ratio (Bis:AAm) on the photo-polymerization kinetics and the gelation time of the chiral inks ( Fig. S5a-e). ...
Helical hierarchy found in biomolecules like cellulose, chitin, and collagen underpins the remarkable mechanical strength and vibrant colors observed in living organisms. This study advances the integration of helical/chiral assembly and 3D printing technology, providing precise spatial control over chiral nano/microstructures of rod-shaped colloidal nanoparticles in intricate geometries. We designed reactive chiral inks based on cellulose nanocrystal (CNC) suspensions and acrylamide monomers, enabling the chiral assembly at nano/microscale, beyond the resolution seen in printed materials. We employed a range of complementary techniques including Orthogonal Superposition rheometry and in situ rheo-optic measurements under steady shear rate conditions. These techniques help us to understand the nature of the nonlinear flow behavior of the chiral inks, and directly probe the flow-induced microstructural dynamics and phase transitions at constant shear rates, as well as their post-flow relaxation. Furthermore, we analyzed the photo-curing process to identify key parameters affecting gelation kinetics and structural integrity of the printed object within the supporting bath. These insights into the interplay between the chiral inks self-assembly dynamics, 3D printing flow kinematics and photo-polymerization kinetics provide a roadmap to direct the out-of-equilibrium arrangement of CNC particles in the 3D printed filaments, ranging from uniform nematic to 3D concentric chiral structures with controlled pitch length, as well as random orientation of chiral domains. Our biomimetic approach can pave the way for the creation of materials with superior mechanical properties or programable photonic responses that arise from 3D nano/microstructure and can be translated into larger scale 3D printed designs.
Supplementary Information
The online version contains supplementary material available at 10.1007/s40820-023-01286-0.
... White et al. reported a nonvolatile and "green" ionic liquid 4-vinylbenzyl trioctyl phosphonium bis(trifluoromethanesulfonyl)imide (VBTOP Tf 2 N) as a reactive diluent for UPE oligomers containing internal double bonds from maleic acid anhydride. 6 In combination with dimethoxyethane as an unreactive diluent, they produced resins suitable for stereolithography, where 3D printed networks reached an ionic conductivity of 1 Â 10 À5 S cm À1 at 150 C. Another grafting using maleate esters with an internal double bond was done by Esen et al. 7 First, epoxidized soybean oil was reacted with monomethyl maleate. Afterward, monomethyl maleate was treated with maleic anhydride, yielding a high unsaturation of 4.9 maleates per triglyceride. ...
Unsaturated furan‐based ester (UES) was prepared by green electrosynthesis using a single‐cell setup and inexpensive graphite electrodes. The UES was validated as a reactive diluent for a bio‐based acrylated rapeseed oil (ARO). UV‐light photopolymerization of the bio‐based resin was initiated using a diphenyl (2,4,6‐trimethylbenzoyl)phosphine oxide (TPO) radical photoinitiator. The addition of 20 wt% UES to ARO dropped the resin viscosity by 1.6‐fold. Incorporating 5 wt% UES into the ARO resin increased crosslinking density ν e from 1.07 to 1.65 mol/m ³ . Fourier‐transform infrared spectroscopy (FT‐IR) spectra revealed that ARO has been grafted with UES. The UES functional moieties promote the formation of soft mobile dangling chain end segments in the developed macromolecular network. UV‐cured thermoset polymer reveals distinct morphologies in SEM micrographs, indicating notable structural changes with the addition of UES. A total of 5 wt% UES increased tensile strength from 0.49 to 0.55 MPa and storage modulus from 7.9 to 12.0 MPa at room temperature (22 ± 1 °C). The biodegradability in composting conditions was investigated, and up to 28% of the initial mass was lost after 60 days. UES was shown as to be efficient reactive diluent that can successfully replace fossil‐based acrylate monomers in vegetable oil‐based thermoset polymer synthesis.
... Printable IL materials are opening new opportunities in material design, as well as broadening applications for 3D printing technologies. For example, Long and co-workers prepared a PIL-based 3D printable resin that was much more conductive, stable, and environmentally friendly than using styrene, a common neutral polymer [78]. In a short period, these materials have had a significant impact across various areas of AM (e.g., photoactive, antimicrobial, catalyst, electronic, robotic, and bio applications) [24,41,66,[79][80][81]. ...
Innovation in materials specially formulated for additive manufacturing is of great interest and can generate new opportunities for designing cost-effective smart materials for next-generation devices and engineering applications. Nevertheless, advanced molecular and nanostructured systems are frequently not possible to integrate into 3D printable materials, thus limiting their technological transferability. In some cases, this challenge can be overcome using polymeric macromolecules of ionic nature, such as polymeric ionic liquids (PILs). Due to their tuneability, wide variety in molecular composition, and macromolecular architecture, they show a remarkable ability to stabilize molecular and nanostructured materials. The technology resulting from 3D-printable PIL-based formulations represents an untapped array of potential applications, including optoelectronic, antimicrobial, catalysis, photoactive, conductive, and redox applications.
... The polymer matrix plays the role of wave transmission, interfacial bond, and load transfer in wave-transparent composites [32]. Polymer matrices commonly used in wave-transparent composites, such as epoxy resin [33,34], unsaturated polyester resin [35,36], polyimide resin [37,38], and bismaleimide resin [39], etc., generally have disadvantages of high ε value, poor mechanical properties and/or complex molding process, which cannot meet high performance requirements [40,41]. Cyanate ester resins have good mechanical and dielectric properties, and excellent heat resistance, which are the best candidate for preparing polymer-based wave-transparent composites [42,43]. ...
Polydopamine hybrid zeolitic imidazolate framework-8 (PDA*ZIF-8) membrane, synthesized by zinc nitrate hexahydrate (ZnNO3•6H2O), 2-methylimidazole (2-MI), and dopamine (DA), uniformly grows on the surface of poly(p-phenylene-2, 6-benzobisoxazole) (PBO) fibers by heterogeneous nucleation method to obtain [email protected]*ZIF-8 fibers. [email protected]*ZIF-8 fibers are then applied as the reinforcement, bisphenol A dicyanate ester (BADCy) as the matrix, and [email protected]*ZIF-8 fibers/BADCy wave-transparent laminated composites are prepared by high-temperature molding. Results indicate that PDA*ZIF-8 membrane increases the surface roughness and chemical activity of PBO fibers. The interlaminar shear strength (ILSS) and flexural strength of [email protected]*ZIF-8 fibers/BADCy laminated composites are 45.3 and 656.3 MPa, respectively, which are increased by 23.4% and 11.7% compared with those of PBO fibers/BADCy composites (587.4 and 36.7 MPa). The dielectric constant and dielectric loss values at 1 MHz are 2.76 and 0.0046, respectively, lower than PBO fibers/BADCy (3.06 and 0.006). At 0.3–40 GHz, [email protected]*ZIF-8 fibers/BADCy laminated composites have excellent wave-transparent performance (The simulated wave-transparent rate is greater than 87%, d = 1.5–3.5 mm). Meanwhile, the corresponding volume resistivity and breakdown strength are 3.7 × 1015 Ω•cm and 23.61 kV/mm, higher than PBO fibers/BADCy composites (2.2 × 1015 Ω•cm and 17.69 kV/mm), respectively.
Network engineering strategies offer a promising pathway toward tunable thermomechanical properties of bio-derivable, aromatic (meth)acrylate thermosets to expand their application library. In this work, a series of acrylate thermosets, synthesized from lignin-derivable vanillyl alcohol/bisguaiacol F diacrylates (VDA/BGFDA) and a bio-based n-butyl acrylate (BA), were designed as a sustainable platform to explore structure-architecture-property relationships. Using this approach, we examined a series of processable, fully bio-derivable acrylates. Increasing the diacrylate content across all networks improved storage moduli at 25 °C (E′25) by up to 2 GPa (1.1 GPa for VDA/BA-25/75 vs. 3.1 GPa for VDA/BA-75/25, and 1.5 GPa for BGFDA/BA-25/75 vs. 1.7 GPa for BGFDA/BA-50/50), and led to a more inhomogeneous network as evidenced by lower acrylate group conversion and a broader tan δ peak, indicating heterogeneous relaxation modes. Modifying the aromatic content of the starting diacrylate impacted the final inhomogeneity of the network, with increasing inhomogeneity observed for the bis-aromatic BGFDA relative to the mono-aromatic VDA. Similarly, combining the mono- and bis-aromatic diacrylates generated a network with a biphasic-like thermal relaxation mode. By correlating network architecture and material performance, the increasing architectural complexity suggested a more convoluted thermal relaxation mode while the enhancement of thermomechanical properties could still be achieved for potential application as damping materials. Overall, we presented a design strategy utilizing bio-derivable acrylates to expand the suite of renewable material platforms from a network engineering perspective.
Driven by environmental considerations, the scientific community has directed great effort towards the synthesis of new materials derived from renewable resources. However, for photocurable resins, most commercially available building blocks still rely on petroleum-based precursors. Herein, we present a simple synthesis route for bio-based acrylate-modified polyester resins, whose viscosity is sufficiently low for processing them with vat photopolymerization 3D printing. The established synthesis route enables the gradual substitution of fossil-based raw materials with bio-based alternatives. The acid number, color and viscosity of the bio-based acrylic resins are characterized and photocurable formulations are prepared by adding a radical photoinitiator. The photopolymerization kinetics, and thermomechanical and mechanical properties of the photopolymers are investigated as a function of the resin structure and benchmarked against a commercially available petroleum-based counterpart. Finally, the processability of the new bio-based resins via digital light processing 3D printing is demonstrated and test specimens are successfully 3D printed with a resolution in the millimeter range.
Photo-triggered shape morphing structures can be found in myriads of areas. Utilizing light as a switch can effectively control and regulate the precise deformation of structures. However, the integration of photo switching functions in shape morphing structures with complex geometries remains a challenge. Here, we report photo switchable digital light processing based 4D printing high-resolution and highly complex geometries, based on UV curable WO 2.9 nanoparticle doped shape memory polymer nanocomposites, which are highly deformable (stretchability up to ~1000% at rubbery state) and fatigue resistant (repeatedly loaded > 1200 times at ambient temperature). The presence of just trace WO 2.9 nanoparticles (< 0.20 wt.‰) contributes to the controlled photothermal property of nanocomposite via selective absorption of light, which enables reversibly photo switchable (＞50 times), spatial and remote control of 4D printing shape morphing structures. These findings offer a promising approach to expanding the applications of photo-triggered shape morphing structures.
Photo-curing 3D printing technology has promoted the advanced manufacturing in various fields, but has exacerbated the environmental crisis by the demand for the chemically cross-linked thermosetting photopolymers. Here, we report a generic strategy to develop catalyst-free dynamic thermosetting photopolymers, based on photopolymerization and transesterification, that can enable users to realize repeatable 3D printing, providing a practical solution to the environmental challenges. We demonstrate that the β-carbonyl group adjacent to the ester group greatly accelerates the rate of transesterification. The generated resins from the immobilization of the catalyst-free reversible bonds into the photopolymers leads to a dynamic covalently crosslinked network structure upon UV based 3D printing, which exhibit controllable mechanical properties with elastomeric behaviors to thermadapt shape memory polymers. Furthermore, the resulting network can be reverted into an acrylate-functioned photopolymer that is suitable for 3D printing again, presenting an on-demand, repeatedly recyclable thermosetting photopolymer platform for sustainable 3D printing. This article is protected by copyright. All rights reserved.
Vat photopolymerization (VP) is an advanced additive manufacturing (AM) platform that enables production of intricate three‐dimensional (3D) monoliths that are unattainable with conventional manufacturing methods. In this work, modification of amorphous poly(arylene ether sulfone)s (PSU) allowed for VP printing. Post‐polymerization telechelic functionalization with acrylate functionality yielded photo‐crosslinkable PSUs across a molecular weight range. 1H NMR spectroscopy confirmed chemical composition and quantitative acrylate functionalization. Addition of diphenyl‐(2,4,6‐trimethylbenzoyl)phosphine oxide (TPO) photo‐initiator to 30 wt. % PSU solutions in NMP provided a photo‐curable composition. However, subsequent photo‐rheological studies elucidated rapid photo‐degradation of the polysulfone main chain, which was especially apparent in high Mn (15 kg·mol−1) PSU formulations. UV‐light intensity and wavelength range were altered to reduce degradation while allowing for efficient crosslinking. The addition of 0.5 wt. % of avobenzone photo‐blocker produced an ill‐defined structure with 6 kg·mol−1 PSU. For higher molecular weights (>12 kg·mol−1), solutions with a low molar mass reactive diluent, i.e., trimethylolpropane triacrylate, enabled the printing of an organogel with a storage modulus (>105 Pa) sufficient for vat photopolymerization. Employing multicomponent solutions provided well‐defined parts with complex geometries through vat photopolymerization. This article is protected by copyright. All rights reserved
Ageing population and new diseases are requiring the development of novel therapeutical strategies. 3D bioprinting an novel application domain of additive manufacturing emerged as a potential transformative strategy for tissue engineering and regenerative medicine. This paper introduces the concept of 3D bioprinting, discussing in detail key requirements of bio-inks and main materials used to encapsulate cells. Recent advances related to the use of smart materials and the concept of 4D printing is also discussed. Main 3D bioprinting techniques are described in detail and key limitations highlighted. Successful cases, demonstrating the relevance of 3D bioprinting are also presented. Finally, the paper addresses the main research challenges and future perspectives in the field of 3D bioprinting.
Herein, the successful design of a highly bio‐based family of unsaturated polyester resins (UPRs) is presented, comprising of an isosorbide (ISO) incorporated unsaturated polyester prepolymer (UP) and a reactive diluent of 4‐vinylguaiacol acetyl ester (ACVG). A series of UPs are prepared by copolymerizing ISO with other green monomers, i.e., itaconic acid, ethylene glycol and oxalic acid, in a variation of ISO fraction. The UP/ACVG mixtures exhibit very low viscosity ranging from 2.8 to 3.7 Pa s. After curing at 135 °C to form a network, the resulting thermosets exhibit remarkable improvements in terms of glass transition (Tg, about 131 °C), storage modulus (2564–3342 MPa), and tensile strength (around 76.6 MPa), which are significantly better than the UP thermosets reported in previous works, The incorporation of ISO units into the UPs reveals a favorable effect on thermal stability of the thermosets as well. The best Td5% is measured to be 320.4 °C, and the volatile molecular information collected using a TGA‐GC/MS set suggests that the decomposition mechanism of the cross‐linked resins becomes heat‐resistant due to the ISO incorporation. Moreover, after being reinforced by cotton fabrics, an outstanding compatibility between the ISO containing UPRs and cotton fibers is found to be suitable for composite fabrication. The prepared ISO‐based UPs exhibit excellent miscibility with green diluent of ACVG and the combination of ISO‐based UPs and ACVG results in a high Tg.After reinforcement with cotton fabrics, an outstanding compatibility between the resins and cotton fabrics is found to be suitable for composite fabrication.
Ion-conductive unsaturated polyesters were synthesised from poly(ethylene oxide) and maleic anhydride for use in the development of improved methods for the structural health monitoring of infrastructural buildings. The unsaturated polyesters (UPs) were cross-linked with styrene using a redox initiator in the presence of LiClO4. Electrochemical impedance spectroscopy was used to study the effects of initiator and styrene concentration as well as the EO:Li+ ratio. Increasing the initiator or styrene content results in an increased resistivity of the final materials. Cross-linking with styrene does not appear to cause microphase separation into pure UP and polystyrene phases, since the resulting resistivities are significantly lower than predicted by the rule of mixtures. For all temperatures under investigation (0 to 60 °C), the lowest resistivities were found for a EO:Li+ ratio of 50 (400 Ω m at 22 °C), which is in accordance with previous findings. The electrical properties of the present materials are determined by diffusion-controlled process in such a way polarisation prevails at high temperatures. In a proof of principle experiment, one selected UP formulation was injected into drill holes in concrete and cured at different temperatures and moisture conditions. This system reliably monitors the resistivity against an embedded reference electrode.
A ring opening polymerization method for synthesizing oligomeric poly(propylene fumarate) (PPF) provides a rapid, and scalable method of synthesizing PPF with well-defined molecular mass, molecular mass distribution (Ðm), and viscosity properties suitable for 3D printing. These properties will also reduce the amount of solvent necessary to insure sufficient flow of material during 3D printing. MALDI mass spectrometry shows precisely the end group fidelity and size exclusion chromatography (SEC) demonstrates narrow mass distributions (<1.6) of a series of low molecular mass oligomers (700-3000 Da). The corresponding intrinsic viscosities range from 0.0288±0.0009 dL/g to 0.0780±0.0022 dL/g. The oligomers were printed into scaffolds via established photochemical methods and standardized ISO 10993-5 testing shows that the 3D printed materials are non-toxic to both L929 mouse fibroblasts and human mesenchymal stem cells.
New micro three-dimensional (3D) scaffolds using biobased unsaturated polyesters (UPs) were prepared by microstereo-thermal-lithography (μSTLG). This advanced processing technique offers indubitable advantages over traditional printing methods. The accuracy and roughness of the 3D structures were evaluated by scanning electron microscopy and infinite focus microscopy, revealing a suitable roughness for cell attachment. UPs were synthesized by bulk polycondensation between biobased aliphatic diacids (succinic, adipic and sebacic acid) and two different glycols (propylene glycol and diethylene glycol) using fumaric acid as the source of double bonds. The chemical structures of the new oligomers were confirmed by proton nuclear magnetic resonance spectra, attenuated total reflectance Fourier transform infrared spectroscopy and matrix assisted laser desorption/ionization-time of flight mass spectrometry. The thermal and mechanical properties of the UPs were evaluated to determine the influence of the diacid/glycol ratio and the type of diacid in the polyester's properties. In addition an extensive thermal characterization of the polyesters is reported. The data presented in this work opens the possibility for the use of biobased polyesters in additive manufacturing technologies as a route to prepare biodegradable tailor made scaffolds that have potential applications in a tissue engineering area.
Results of investigations on novel formulations, structure-property relationships, curing, and
compositions with fillers and reinforcing fibers (1997--2004) are reviewed with about 200 references
to articles and several references to patents. The following topics are considered in particular:
novel dibasic acids, glycols, crosslinking monomers, and curing systems, “vinyl ester”
resins, fire retardant materials, IPNs and other systems comprising built-in thermoplastic polymers
and oligomers with terminal functional groups. Information on unsaturated polyesters manufactured
using PET scrap is given. Analytical (mainly spectrometric) methods for studying the chemical structure
of crosslinked unsaturated polyester resins are presented. Approaches to the decrease in styrene
emission on processing of unsaturated polyester resins are also discussed.
Unsaturatedpolyesterresins–Reinforcedpolyesters–Poly(ethyleneterephthalate)–Vinylesterresins–Curing
We demonstrate high-resolution photocross-linking of biodegradable poly(propylene fumarate) (PPF) and diethyl fumarate (DEF) using UV excimer laser photocuring at 308 nm. The curing depth can be tuned in a micrometre range by adjusting the total energy dose (total fluence). Young's moduli of the scaffolds are found to be a few gigapascal, high enough to support bone formation. The results presented here demonstrate that the proposed technique is an excellent tool for the fabrication of stiff and biocompatible structures on a micrometre scale with defined patterns of high resolution in all three spatial dimensions. Using UV laser photocuring at 308 nm will significantly improve the speed of rapid prototyping of biocompatible and biodegradable polymer scaffolds and enables its production in a few seconds, providing high lateral and horizontal resolution. This short timescale is indeed a tremendous asset that will enable a more efficient translation of technology to clinical applications. Preliminary cell tests proved that PPF : DEF scaffolds produced by excimer laser photocuring are biocompatible and, therefore, are promising candidates to be applied in tissue engineering and regenerative medicine.
This work describes the first example of a hydrogenated polybutadiene elastomer photopolymer that addresses the process constraints of vat photopolymerization (VP) additive manufacturing. A synthetic method, which involves simultaneous thiol-ene step growth chain extension and acrylate crosslinking, addresses traditional challenges associated with this leading 3D printing platform. This facile, one-pot strategy combines the processing advantages of low molecular weight oligomers with the tunable thermomechanical and mechanical performance of higher molecular weight polymeric networks directly during printing, without requiring a post-processing step. The addition of photo-initiator to mixtures of liquid polybutadiene oligomer and miscible dithiols enabled selective photocuring under UV exposure to form high-strain, elastic parts in comparison to neat diacrylate systems. Photolithographic printing of these photopolymers enabled the fabrication of three-dimensional, hydrocarbon elastomer objects. Photorheology elucidated curing behavior as a function of composition and UV intensity, while optical imaging and SEM revealed quality and resolution.
Ionic liquids (ILs) and poly(ionic liquid)s (PILs) are attracting significant research interest as safe and efficient electrolytes. Most research efforts focus on nitrogen based ILs and PILs (ammonium, imidazolium, pyridinium, etc.), while phosphorus based ILs and PILs have received relatively less attention despite exhibiting comparable ion conductivity over their nitrogen-based counterparts. In this review, we provide an overview of the structural elements in phosphorus based ILs and PILs that influence ion conductivity, such as ion size, ion polarizability, counterion selection, and backbone flexibility. We also highlight dominant physical parameters dictating ion conductivity including viscosity and glass transition temperature. A fundamental understanding of this structure-ion conductivity relationship will benefit the future rational design of phosphorus based ILs and PILs as electrolytes.
A novel, poly(dimethyl siloxane)-based photopolymer that exhibits simultaneous linear chain extension and crosslinking was suitable for vat photopolymerization additive manufacturing. Photopolymer compositions consisted of dithiol and diacrylate functional poly(dimethyl siloxane) oligomers, where simultaneous thiol-ene coupling and free radical polymerization provided for linear chain extension and crosslinking, respectively. Compositions possessed low viscosity before printing and the modulus and tensile strain at break of a photocured, higher molecular weight precursor after printing. Photorheology and soxhlet extraction demonstrated highly efficient photocuring, revealing a calculated molecular weight between crosslinks of 12,600 g/mol and gel fractions in excess of 90% while employing significantly lower molecular weight precursors (i.e. < 5300 g/mol). These photocured objects demonstrated a 2× increase in tensile strain at break as compared to a photocured 5300 g/mol PDMS diacrylamide alone. These results are broadly applicable to the advanced manufacturing of objects requiring high elongation at break.
The success of Tissue Engineering (TE) based approaches is strongly dependent on the development of novel biomaterials for the design of 3D matrices with tailored biomechanical properties to promote the regeneration of human tissues and organs.
This review covers the critical aspects related with the preparation of new unsaturated polyester (UP) resin formulations with suitable biological, chemical, thermal and morphological properties for the additive manufacturing (AM) of TE constructs. In this context, the basic principles of available AM technologies, with a special focus on novel stereolithography processes such as microstereolithography (micro-SLA), stereo-thermal-lithography (STLA), two-photon polymerization (TPP) and nanostereolithography (nano-SLA), are also presented and discussed. Ultimately, the present review will provide a better insight into the limitations and potential of combining UP and AM towards the rationale design/fabrication of complex artificial tissue substitutes.
This chapter describes the development of unsaturated polyester and related resins. The morphology of these cured resins is discussed with respect to their cure chemistry and mechanical properties. The curing systems are considered with respect to the choice of manufacturing process. The need for reinforcement with glass fibers is also considered. The form of glass fibers, continuous or discontinuous, and their textile configuration are discussed with regard to the achievable properties of the reinforced plastics or composites. The selection of glass fiber sizing and coupling agents and the formation of interfaces and interphases in the composites are described. The manufacturing techniques for composite materials from these resins are reviewed with regard to the choice of direct or indirect impregnation. The competition between mechanical performance, complexity of shape, and the rate of production are also considered.
Photopolymerization coupled with mask projection microstereolithography successfully generated various 3D printed phosphonium polymerized ionic liquids (PILs) with low UV light intensity requirements and high digital resolution. Varying phosphonium monomer concentration, diacrylate cross-linking comonomer, and display images enabled precise 3D design and polymeric properties. The resulting cross-linked phosphonium PIL objects exhibited a synergy of high thermal stability, tunable glass transition temperature, optical clarity, and ion conductivity, which are collectively well-suited for emerging electro-active membrane technologies. Ion conductivity measurements on printed objects revealed a systematic progression in conductivity with ionic liquid monomer content, and thermal properties and solvent extraction demonstrated the formation of a polymerized ionic liquid network, with gel fractions exceeding 95%.
Unsaturated polyester (UP)/montmorillonite (MMT) nanocomposite was prepared by using hydroxypropylacrylate (HPA) as a reactive diluent instead of conventional styrene monomer and the effect of polarity of reactive diluent on properties of nanocomposite was investigated. X-ray and mechanical test data indicated that mixing for an extended period of time is essential to enhance the physical properties of nanocomposites in the UP/Cloisite 6A system. This was attributed to the high polarity of HPA that may disturb the preintercalation of UP resin into the galleries of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 238–242, 2004
Unsaturated polyester resin has been synthesized using different proportions of phthalic anhydride and maleic anhydride for the esterification with propylene glycol. Initially, maleic anhydride was allowed to react with propylene glycol for some time before the addition of phthalic anhydride. The condensate obtained was mixed with styrene monomer to obtain at an unsaturated polyester resin formulation. Mechanical properties such as tensile strength, elongation-at-break, tensile modulus, impact strength, water absorption, toughness, and surface hardness were tested after curing the resin in appropriate molds. The results show that most of the properties are maximum at 60-70% of maleic anhydride.
Imidazolium-based ionic liquids and ionic liquid monomers are becoming increasingly popular in a variety of areas including biphasic reaction catalysis, electromechanical actuator membranes and diluents, separation science membranes, and water purification agents. Ionic liquids first incorporated the imidazole ring in 1984 and this heterocyclic ring has emerged as the focal point of the ionic liquid field. Imidazole was targeted for its ability to form cationic compounds, which are molten salts at low molar mass. Ionic liquids offer several beneficial attributes including fixed charge, potential as green solvents, and relatively high thermal stability. Due to an ionic liquid's ability to facilitate electron or ion motion, they are now enabling electroactive devices. Commercially available conductive membranes are swollen with ionic liquids to enhance their conductivity; alternatively, conductive membranes are synthesized from novel ionic liquid monomers, also termed polymerizable ionic liquids. The imidazole ring has gained much attention for its ability to tune the properties of the resulting ionic liquid. Careful selection of substituents on any of the positions in the ring and exchange of the counteranion influences many physical properties such as the melting point, the boiling point, and the viscosity. Finally, imidazolium ionic liquids utilize two of their unique properties in biphasic catalysis, i.e. their ability to coordinate transition metals and their hydrophilic ionic nature. Several imidazolium-based ionic liquid molecules have displayed the ability to catalyze atom transfer radical polymerization and facilitate the synthesis of polymers with narrow molecular weight distributions. This manuscript reviews some of the more recent advances that are associated with these unusual liquids.
Unsaturated polyester (UP) resins are linear polycondensation products based on unsaturated and saturated acids/anhydrides and diols or oxides. Depending on the chemical composition and molecular weight, these oligomers may be viscous liquids or brittle solids. Because of their versatility and low cost, they are widely used throughout the world and considerable work has been made on the synthesis, characterization, curing behavior and properties of these materials. The current status unsaturated polyester resins is reviewed.
Research on the volatility of aprotic ionic liquids is reviewed. This topic is limited to aprotic liquids since measurements have led to a generalization that this class of substances possesses extremely low vapor pressures. For research related to this topic, the period covered is 2003 to 2008. The review begins with a discussion of the earliest successful study of thermal vaporization of aprotic ionic liquids, the earliest indirect measurements of their vapor pressure, the first proof of conventional distillation of ionic liquids, and competition of vaporization with thermal decomposition seen at moderately high temperatures of (200 to 300) °C. The review then briefly discusses the nature of the vapor phase and proceeds to analyze the various approaches used to measure or predict the vapor-liquid equilibrium properties of ionic liquids, including their normal boiling point, vapor pressure, and enthalpy of vaporization. It is proposed that the most reliable thermodynamic data exist solely for the enthalpy of vaporization, and thus this property would be the best target for predictive approaches. Predictive approaches to calculate the enthalpy of vaporization are discussed in light of their ability to predict the experimentally observed trends with molar mass. The review concludes with a forward look at the following: expected effect of gas-phase ion clusters; anticipated trade-off between the energetic gain and the entropic penalty for cluster formation; and the possibility of a Trouton rule for the vaporization of ionic liquids.
The utility of nuclear magnetic resonance (NMR) spectroscopy to follow the extent of maleate (cis) to fumarate (trans) isomerization during preparation of standard unsaturated polyesters was demonstrated. NMR analysis indicated that most of the cis-trans isomerization occurred during the early stages of the cook. High cis-trans conversions (95%) were effected in cooks containing sterically hindered or low-reactivity glycols - e.g., propylene glycol. Lower conversions (50%) were obtained with less sterically hindered glycols of greater reactivity such as diethylene glycol. The presence of aromatic dibasic acids increased the cis-trans isomerization. In general, this study confirms earlier work cited in the literature in which the cis-trans conversions were determined by other analytical techniques.
The present study presents the synthesis of unsaturated polyester resins using only one glycol i.e., ethylene glycol. Polyesters of inorganic solubility in styrene were prepared. Properties of the resins in the noncrosslinked state in the process of crosslinking and after curing were studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3143–3150, 2006
In this study, a fatty acid-based comonomer is employed as a styrene replacement for the production of triglyceride-based thermosetting resins. Styrene is a hazardous pollutant and a volatile organic compound. Given their low volatility, fatty acid monomers, such as methacrylated lauric acid (MLA), are attractive alternatives in reducing or eliminating styrene usage. Different triglyceride-derived cross-linkers resins were produced for this purpose: acrylated epoxidized soybean oil (AESO), maleinated AESO (MAESO), maleinated soybean oil monoglyceride (SOMG/MA) and maleinated castor oil monoglyceride (COMG/MA). The mechanical properties of the bio-based polymers and the viscosities of bio-based resins were analyzed. The viscosities of the resins using MLA were higher than that of resins with styrene. Decreasing the content of MLA increased the glass transition temperature (Tg). In fact, the Tg of bio-based resin/MLA polymers were on the order of 60°C, which was significantly lower than the bio-based resin/styrene polymers. Ternary blends of SOMG/MA and COMG/MA with MLA and styrene improved the mechanical properties and reduced the resin viscosity to acceptable values. Lastly, butyrated kraft lignin was incorporated into the bio-based resins, ultimately leading to improved mechanical properties of this thermoset but with unacceptable increases in viscosity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
The NMR (nuclear magnetic resonance) and GPC (gel permeation chromatography) studies of the polymerization of maleic anhydride and 1,2-propylen glycol are reported. Assignment of individual groups was made and their concentration dependence on reaction time was established. The first step of the reaction is the formation of monoesters, which, immediately after the temperature increased, reacted to diesters. The reactivity ratio between the primary and the secondary hydroxyl group of 1,2-propylene glycol was 2.6:1. The concentration of water formed was followed as a function of reaction time by the Karl–Fischer method.
Ionic liquids (ILs) are continuing as important media in which to effect various kinds of polymerizations, and it is particularly noteworthy that ionic polymerizations are being developed in IL solvents and that atom transfer radical polymerization (ATRP) catalysts are being attached to ILs to make them more easily recoverable in living polymerizations. In addition, the number of polymerizable ILs is steadily increasing, and ionic liquid polymers of polymerizable ionic liquid monomers have been produced as exotic polyelectrolytes. ILs are being used as plasticizers of various kinds of polymers and as key components in new classes of polymer gels. Polymers and inorganic substrates are being used to support ILs through covalent binding of the ILs, in which case the properties of the IL are modified to some extent, and polymer membranes and porous materials absorb ILs with concomitant changes in ionic conductivity and mobility. New applications of ILs include creating new classes of advanced materials, such as a new class of solvogels that are stimuli responsive and reversibly porate via pinned spinodal decomposition and the development of ILs derived from inorganic nanoparticle cores for use as new resin components for diverse materials and coatings applications.
Bony defects have been three-dimensionally (3D) created in many clinical circumstances; however, many defects cannot be reconstructed because most of the current bony substitutes cannot provide the necessary exact 3D structure. Therefore, to overcome this limitation, a 3D scaffold with embedded growth factor-delivering microspheres was developed by solid free-form fabrication (SFF) technology using computer-aided design/manufacturing (CAD/CAM). In this study, BMP-2-loaded poly(DL-lactic-co-glycolic acid) (PLGA) microspheres were incorporated into a 3D scaffold that was fabricated using a microstereolithography (MSTL) system with a suspension of microspheres and a poly(propylene fumarate) (PPF)/diethyl fumarate (DEF) photopolymer. By measuring release profiles in vitro, we verified that the fabricated microsphere-containing 3D scaffold could gradually release growth factor. The effects of BMP-2 were also assessed in vitro by observing cell differentiation using MC3T3-E1 pre-osteoblasts. Finally, we confirmed that SFF scaffolds created by MSTL were superior to traditional scaffolds produced using a particulate leaching/gas foaming method. In addition, based on in vivo tests, the scaffolds that released BMP-2 promoted bone formation. Based on these results, we concluded that our 3D scaffold might be a useful tool for enhancing reconstruction quality in many complex bony defects that should be reconstructed using a customized 3D scaffold.
Modeling of unsaturated polyester prepolymer structures. I. Chain branches and overall chain end numbers
- Yang
Modern Polyesters: Chemistry and Technology of Polyesters and Copolyesters
- J Scheirs
- T E Long
Additive Manufacturing Technologies 3D Printing, Rapid Prototyping, and Direct Digital Manufacturing
- I G Ian Gibson