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1. Parameters controlling the strength of stochastic fibrous materials

   https://doi.org/doi.org/10.1016/j.ijsolstr.2019.03.033  

   S. Deogekar, M.R. Islam (March 2019, International journal of solids and structures)

   Many materials of everyday use are fibrous and their strength is important in most applications. In this work we study the dependence of the strength of random fiber networks on structural parameters such as the network density, cross-link density, fiber tortuosity, and the strength of the inter-fiber cross-links. Athermal networks of cellular and fibrous type are considered. We conclude that the network strength scales linearly with the cross-link number density and with the cross-link strength for a broad range of network parameters, and for both types of networks considered. Network strength is independent of fiber material properties and of fiber tortuosity. This information can be used to design fiber networks for specified strength and, generally, to understand the mechanical behavior of fibrous materials. 

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2. Systematic Investigation of Liquid Crystalline Elastomers Prepared by Thiol–Ene Photopolymerization

   https://doi.org/10.1021/acs.macromol.4c02423  

   Lewis, Kristin L; Phillips, Alexis T; Aye, Sarah S; Chen, Judy C; Hoang, Jonathan D; White, Timothy J (January 2025, Macromolecules)

   Liquid crystalline elastomers (LCEs) prepared via thiol−ene photopolymerization result in homogeneous distribution of molecular weight between cross-links. Numerous prior reports emphasize that LCEs are material actuators that undergo a thermomechanical response associated with an order−disorder transition. However, modern and widely utilized approaches to create LCEs result in heterogeneous networks. Theoretical examination suggests that network heterogeneity and high degrees of cross-linking cause a continuous association of strain with temperature, rather than a first-order, stepwise association. Alternatively, thiol−ene photopolymerization historically yields homogeneous polymers with tailorable cross-link densities. This report extends these prior studies to formulations, which are conducive to LCE preparation. Specifically, this examination copolymerizes a liquid crystalline dialkene mesogen with a tetrathiol cross-linker and dithiol chain extender via a purely thiol−ene polymerization. Notably, this composition is amenable to surface-enforced alignment. This contribution exploits the tunability of thiol−ene photopolymerization to emphasize the influence of cross-linking on the coupling of strain and temperature. 

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3. Surface-Aligned Cholesteric Liquid Crystalline Elastomers with Tunable Mechanical Properties via Thiol–Ene Chemistry

   https://doi.org/10.1021/acs.macromol.5c00861  

   Phillips, Alexis T; Chen, Judy C; Kennedy, David T; White, Timothy J (June 2025, Macromolecules)

   Cholesteric liquid crystals (CLCs) exhibit Bragg reflection due to their spontaneous self-assembly into a one-dimensional photonic structure. Retaining this cholesteric order in a polymer network requires functionalizing liquid crystals with reactive end groups. However, conventional chemistries for synthesizing cholesteric liquid crystalline polymers often result in poor surface alignment and reduced optical quality. In this work, we investigate a thiol−ene step-growth polymerization approach to fabricate cholesteric liquid crystalline elastomers (CLCEs) with tunable mechanical properties and improved optical quality. By varying the cross-link density, we systematically study the effects on haze, cross-linking degree, and mechanical response. Compared to existing cholesteric liquid crystalline polymers, the thiol−ene-based CLCEs exhibit enhanced surface alignment, reduced haze, and greater mechanical tunability. These materials are further benchmarked against CLCEs synthesized via thiol−acrylate chain transfer polymerization, highlighting the advantages of the thiol−ene reaction for achieving precisely controlled properties in cholesteric polymer networks. 

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4. Sequencing of Side-Chain Liquid Crystalline Copolymers by Matrix-Assisted Laser Desorption/Ionization Tandem Mass Spectrometry

   https://doi.org/10.3390/polym11071118  

   Snyder, Savannah R.; Wei, Wei; Xiong, Huiming; Wesdemiotis, Chrys (July 2019, Polymers)

   Polyether based side-chain liquid crystalline (SCLC) copolymers with distinct microstructures were prepared using living anionic polymerization techniques. The composition, end groups, purity, and sequence of the resulting copolymers were elucidated by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and tandem mass spectrometry (MS/MS). MALDI-MS analysis confirmed the presence of (CH3)3CO– and –H end groups at the initiating (α) and terminating (ω) chain end, respectively, and allowed determination of the molecular weight distribution and comonomer content of the copolymers. The comonomer positions along the polymer chain were identified by MS/MS, from the fragments formed via C–O and C–C bond cleavages in the polyether backbone. Random and block architectures could readily be distinguished by the contiguous fragment series formed in these reactions. Notably, backbone C–C bond scission was promoted by a radical formed via initial C–O bond cleavage in the mesogenic side chain. This result documents the ability of a properly substituted side chain to induce sequence indicative bond cleavages in the polyether backbone. 

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5. UV- and thermally-active small bi-functional gelator for creating gradient polymer network coatings

   https://doi.org/10.1116/6.0002268  

   Chinnayan Kannan, Pandiyarajan; Genzer, Jan (January 2023, Biointerphases)

   We present a versatile one-pot synthesis method for creating surface-anchored orthogonal gradient networks using a small bi-functional gelator, 4-azidosulfonylphenethyltrimethoxysilane (4-ASPTMS). The sulfonyl azide (SAz) group of 4-ASPTMS is UV (≤254 nm) and thermally active (≥100 °C) and, thus, enables us to vary the cross-link density in orthogonal directions by controlling the activation of SAz groups via UV and temperature means. We deposit a thin layer (∼200 nm) of a mixture comprising ∼90% precursor polymer and ∼10% 4-ASPTMS in a silicon wafer. Upon UV irradiation or annealing the layers, SAz releases nitrogen by forming singlet and triplet nitrenes that concurrently react with any C–H bond in the vicinity leading to sulfonamide cross-links. Condensation among trimethoxy groups in the bulk connects 4-ASPTMS units and completes the cross-linking. Simultaneously, 4-ASPTMS near the substrate reacts with surface-bound –OH motifs that anchor the cross-linked polymer chains to the substrate. We demonstrate the generation of orthogonal gradient network coatings exhibiting cross-link density (or stiffness) gradients in orthogonal directions using such a simple process. 

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