Photopolymerized Triazole‐Based Glassy Polymer Networks with Superior Tensile Toughness

Han, Songjun; Baranek, Austin; Worrell, Brady T.; Bowman, Christopher N.; Cook, Wayne D.

doi:10.1002/adfm.201801095

Cited by 31 publications

(40 citation statements)

References 61 publications

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“…[ 10–14 ] Thiol‐ene‐based polymers are one class of materials that have drawn significant attention owing to their controllable, tunable mechanical properties. [ 15–17 ] This is generally attributed to more uniform molecular networks in thiol‐ene materials, resulting from the step‐growth mechanism of the polymerization reaction. [ 18,19 ] Thiol‐ene materials have already shown promise for applications including use in adhesives, electronics, and as biomaterials.…”

Section: Figurementioning

confidence: 99%

Highly Tunable Thiol‐Ene Photoresins for Volumetric Additive Manufacturing

et al. 2020

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Volumetric additive manufacturing (VAM) is an emerging approach to photo polymerbased 3D printing that produces complex 3D structures in a single step, rather than from layer-by-layer assembly. [1] This paradigm holds promise because it overcomes many of the drawbacks of layerbased fabrication, such as long build times and rough surfaces. VAM also augurs a broadening of the materials available for photopolymer 3D printing, having fewer constraints on viscosity and reactivity compared to layerwise printing. Indeed, though VAM has been demonstrated with extremely soft hydrogels, [2,3] it has relied until now almost exclusively on acrylate-based chemistry. [4] This is natural, because the oxygen inhibition of acrylate polymerization provides the threshold behavior required for VAM. However, acrylate chemistry is in general limiting due to the brittle and glassy properties of the resulting materials. Accordingly, extensive efforts have been made to identify and target specific soft, elastic acrylate formulations. [5-9] Introducing alternative crosslinking chemistries to the VAM realm, as well as AM more broadly, is highly desirable as an alternative method to gain access to a wider range of mechanical, thermal, and optical performance. [10-14] Thiol-ene-based polymers are one class of materials that have drawn significant attention owing to their controllable, tunable mechanical properties. [15-17] This is generally attributed to more uniform molecular networks in thiol-ene materials, resulting from the step-growth mechanism of the polymerization reaction. [18,19] Thiol-ene materials have already shown promise for applications including use in adhesives, electronics, and as biomaterials. [20,21] This work expands the versatility of volumetric AM by introducing a new class of VAM-compatible thiol-ene resins. We demonstrate the formulation of thiol-ene resins with the nonlinear threshold-type kinetics required for VAM and show bulk-equivalent performance in the resulting 3D printed parts, confirming the advantage of the layerless whole-part process. In our volumetric AM system, a 3D distribution of light energy is delivered to the resin vat by superimposing exposures from multiple angles, a method termed computed axial litho graphy (CAL) (Figure 1a). [2] The exposures are a sequence of projections calculated from 3D CAD models using algorithms from computed 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-tetrameth...

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Section: Figurementioning

confidence: 99%

Highly Tunable Thiol‐Ene Photoresins for Volumetric Additive Manufacturing

et al. 2020

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“…[ 26–28 ] Recent work demonstrated that glassy networks with high T g are obtained due to the formation of rigid, thermally and chemically stable triazole moieties present at high concentrations within the network ( Scheme A). [ 29–31 ] Although glassy polymers are stiff with limited mobility, localized segmental motion still occurs and requires little free volume to persist at temperatures well below T g . [ 32–34 ] As was previously proven, such local mobility at the bond level is adequate to change the bond distance and cause bond reconfiguration in glassy systems as has been demonstrated, for example, repeatedly in azobenzene‐containing polymers.…”

Section: Methodsmentioning

confidence: 99%

Light‐Activated Stress Relaxation, Toughness Improvement, and Photoinduced Reversal of Physical Aging in Glassy Polymer Networks

et al. 2020

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A covalent adaptable network (CAN) with high glass transition temperature (Tg), superior mechanical properties including toughness and ductility, and unprecedented spatio‐temporally controlled dynamic behavior is prepared by introducing dynamic moieties capable of reversible addition fragmentation chain transfer (RAFT) into photoinitiated copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC)‐based networks. While the CuAAC polymerization yields glassy polymers composed of rigid triazole linkages with enhanced toughness, the RAFT moieties undergo bond exchange leading to stress relaxation upon light exposure. This unprecedented level of stress relaxation in the glassy state leads to numerous desirable attributes including glassy state photoinduced plasticity, toughness improvement during large deformation, and even photoinduced reversal of the effects of physical aging resulting in the rejuvenation of mechanical and thermodynamic properties in physically aged RAFT‐CuAAC networks that undergo bond exchange in the glassy state. Surprisingly, when an allyl‐sulfide‐containing azide monomer (AS‐N3) is used to form the network, the network exhibits up to 80% stress relaxation in the glassy state (Tg − 45 °C) under fixed displacement. In situ activation of RAFT during mechanical loading results in a 50% improvement in elongation to break and 40% improvement in the toughness when compared to the same network without light‐activation of RAFT during the tensile testing.

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“…The CuAAC reaction has also been applied to the formation of step-growth bulk photopolymer networks, where the photopolymerization generates triazole adducts that are thermally, chemically, and mechanically stable [146]. Triazole structures, especially in a densely cross-linked network, substantially enhance the mechanical stiffness and strength of these materials during the polymerization.…”

Section: Preparation Of Thermosets By Azide-yne Polymerizationmentioning

confidence: 99%

The Use of Click-Type Reactions in the Preparation of Thermosets

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Click chemistry has emerged as an effective polymerization method to obtain thermosets with enhanced properties for advanced applications. In this article, commonly used click reactions have been reviewed, highlighting their advantages in obtaining homogeneous polymer networks. The basic concepts necessary to understand network formation via click reactions, together with their main characteristics, are explained comprehensively. Some of the advanced applications of thermosets obtained by this methodology are also reviewed.

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Photopolymerized Triazole‐Based Glassy Polymer Networks with Superior Tensile Toughness

Cited by 31 publications

References 61 publications

Highly Tunable Thiol‐Ene Photoresins for Volumetric Additive Manufacturing

Highly Tunable Thiol‐Ene Photoresins for Volumetric Additive Manufacturing

Light‐Activated Stress Relaxation, Toughness Improvement, and Photoinduced Reversal of Physical Aging in Glassy Polymer Networks

The Use of Click-Type Reactions in the Preparation of Thermosets

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