Strategies to Reduce Oxygen Inhibition in Photoinduced Polymerization

Ligon, Samuel Clark; Husár, Branislav; Wutzel, Harald; Holman, R. J.; Liska, Robert

doi:10.1021/cr3005197

Cited by 569 publications

(529 citation statements)

References 245 publications

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“…When radical-driven curing of PEGDA polymers is performed in the presence of atmospheric oxygen, the oxygen can form radicals that interfere with crosslinking in the polymer network [4]. Several methods can be employed to circumvent this, including curing in an anaerobic environment (requiring engineering controls) or adding a scavenger molecule (PPh3 in our samples) that mitigates the deleterious effects of oxygen [4,5].…”

Section: Resultsmentioning

confidence: 99%

“…One aspect of these reactions must frequently be addressed: atmospheric oxygen can interfere with radical-driven crosslinking reactions at the coating surface. In our experiments, oxygen reacts rapidly with radicals produced during photoinitiation to produce peroxyl radicals that are slow to react with double bonds in monomers, thus retarding the rate of polymerization [4]. Sometimes curing can be performed in an oxygen-free atmosphere, minimizing this interference.…”

Section: Introductionmentioning

confidence: 97%

“…Alternatively, when atmospheric regulation is impractical, antioxidant scavengers can be added to the coating mixture to mitigate the effects of (atmospheric) oxygen radicals, allowing the main crosslinking reaction to proceed [5]. One efficient scavenger is triphenylphosphine (PPh 3 ) which, in our experiments, reacts with a peroxyl radical to form triphenylphosphine oxide and a reactive radical monomer than can participate in chain propagation [4]. Details of these curing processes are described elsewhere [6].…”

Section: Introductionmentioning

confidence: 99%

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Spatially Resolved Measurements of Crosslinking in UV-Curable Coatings Using Single-Sided NMR

2018

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Abstract:The UV-driven photocuring of coatings results in a crosslinked polymeric network. The degree of crosslinking in these coatings is typically assessed via optical spectroscopy; unfortunately, optical methods are typically limited in their maximum depth access. Alternatively, single-sided nuclear magnetic resonance (NMR) can be used to probe the crosslinking of UV-curable coatings in a spatially sensitive manner. Relaxation measurements, which correlate with crosslinking, can be done with a spatial resolution on the order of microns throughout the depth dimension of the coating, regardless of optical transparency of the material. These results can be visualized via a relaxation cross-section that shows the depth at which a particular relaxation value is observed. These measurements are used to probe the effect of a scavenger molecule that is added to the coating mixture, allowing for efficient crosslinking despite the presence of atmospheric oxygen. This method may find purchase in evaluating systems whose crosslinking properties are intentionally varied throughout its thickness; using NMR, these systems, up to approximately one hundred microns thick, can be measured without repositioning or rastering.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Spatially Resolved Measurements of Crosslinking in UV-Curable Coatings Using Single-Sided NMR

2018

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“…Photopolymerization also allows temporal and spatial control over the curing process, since polymerization can be stopped by simply turning off the light source. [34] These and other benefits have fuelled a growing interest in the photochemical behaviour of polymerizable ILs. [35][36][37][38][39][40][41] In this paper, we present the synthesis and photochemical characterization of ILs consisting of an imidazole ring attached to a methacrylate group through a spacer with variable length (C 2 -C 6 ).…”

Section: Introductionmentioning

confidence: 99%

Imidazole-based ionic liquids for free radical photopolymerization

Dworak

Tiefenthaller

Lagref

et al. 2015

Designed Monomers and Polymers

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Ionic liquid (IL) monomers are receiving increased attention due to their versatile range of application, especially in the electrochemical and electromechanical fields. Within this study, imidazole-based ILs containing a polymerizable methacrylate (MA) group were synthesized to examine their influence on the viscosity and reactivity of typical (meth)acrylates. The IL-MAs were prepared from 1-butylimidazole and bromo methacrylates with different spacer lengths (C 2 -C 6 ). The best results with respect to physicochemical properties and double bond conversions could be obtained for ILs with C 3 and C 6 spacers. Bulk polymerizations exhibited unusually high reactivity and double-bond conversion compared with typical mono-methacrylates. Addition of 10 wt% IL-MA to reactive diluents like hexane-1,6-diol diacrylate caused only minor reduction in reaction rate but increased final double bond conversion compared with the pure diacrylate.

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“…S1-S5) (30)(31)(32)(33)(34). Therefore, performing SL on an oxygen-permeable build window results in the formation of a dead zone, or a region of uncured liquid resin (29).…”

mentioning

confidence: 99%

Layerless fabrication with continuous liquid interface production

Janusziewicz

Tumbleston

Quintanilla

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

255

139

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Despite the increasing popularity of 3D printing, also known as additive manufacturing (AM), the technique has not developed beyond the realm of rapid prototyping. This confinement of the field can be attributed to the inherent flaws of layer-by-layer printing and, in particular, anisotropic mechanical properties that depend on print direction, visible by the staircasing surface finish effect. Continuous liquid interface production (CLIP) is an alternative approach to AM that capitalizes on the fundamental principle of oxygen-inhibited photopolymerization to generate a continual liquid interface of uncured resin between the growing part and the exposure window. This interface eliminates the necessity of an iterative layer-by-layer process, allowing for continuous production. Herein we report the advantages of continuous production, specifically the fabrication of layerless parts. These advantages enable the fabrication of large overhangs without the use of supports, reduction of the staircasing effect without compromising fabrication time, and isotropic mechanical properties. Combined, these advantages result in multiple indicators of layerless and monolithic fabrication using CLIP technology.stereolithogaphy | continuous liquid interface production | 3D printing | additive manufacturing | isotropic properties Additive manufacturing (AM), or 3D printing, is a growing field that employs the selective layering of material to build a part, which has distinct advantages compared with subtractive manufacturing (1). The benefits of additive over subtractive manufacturing are numerous and include unlimited design space, freedom of complex geometries, and reduction of waste by-products (2). Significant advancements were made to AM in the 1980s with the development of the stereolithography (SL) apparatus, a platform that uses the exposure of a rastering UV laser to selectively solidify a resin through a photopolymerization process in a top-down manner (3). The method has since been modified to solidify in a bottom-up process through the use of a digital light projection (DLP) chip that eliminates the rastering laser. The process of bottomup SL begins with a computer-aided design (CAD) file that is then converted into a series of 2D renderings using a method called "slicing" (Fig. 1A). The original object is then reconstructed in a layer-by-layer manner by reproducing these 2D renderings, one slice at a time. This process is done iteratively whereby a photoactive resin is selectively exposed to UV light through a transparent substrate, allowing for selective photopolymerization corresponding to a specific slice shape (4). Once the slice has been exposed, a series of mechanical steps of separation, recoating, and repositioning follow (Fig. 1B) to allow for subsequent exposure.The polymeric materials used in the SL process are known to have intrinsic properties that are a function of the chemical structure, molecular weight, and topology (3). Printed part properties differ from intrinsic polymeric properties because they a...

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Strategies to Reduce Oxygen Inhibition in Photoinduced Polymerization

Cited by 569 publications

References 245 publications

Spatially Resolved Measurements of Crosslinking in UV-Curable Coatings Using Single-Sided NMR

Spatially Resolved Measurements of Crosslinking in UV-Curable Coatings Using Single-Sided NMR

Imidazole-based ionic liquids for free radical photopolymerization

Layerless fabrication with continuous liquid interface production

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