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Cure Reactions of Polymer Coatings
Published in Sanjay Mavinkere Rangappa, Jyotishkumar Parameswaranpillai, Suchart Siengchin, Polymer Coatings, 2020
The thiol-ene reaction is included in the click chemistry reaction groups, and its advantages are as follows: mild operating conditions and at the same high rate, very high reagent conversion and yield of the reaction, stereoselectivity, lack of by-products and, therefore, high purity of the main product. Two possible mechanisms of the thiol–ene reaction are considered: a free radical addition (initiated by light, heat or radical initiators) and a catalysed (a base or a nucleophilic catalyst) Michael addition. The thiol–ene reaction is a very convenient method of introducing branching into the linear molecule as well as joining the molecules together (as can be seen in Figure 8.20). This reaction is very willingly used in the synthesis of hyperbranched polymers and dendrimers, but it can also be useful for cross-linking polymers with unsaturated bonds located along the chain.
Thiol-ene reaction based polymer dispersed liquid crystal composite films with low driving voltage and high contrast ratio
Published in Liquid Crystals, 2020
Tingjun Zhong, Richard J. Mandle, John W. Goodby, Cuihong Zhang, Lanying Zhang
The thiol-ene reaction forms an alkyl sulphide from a thiol and an alkene and has been widely employed in the preparation of both linear and cross-linked polymer networks [27,28]. The simple chemistry and highly accessible starting materials render the thiol-ene reaction a useful stratagem for preparing PDLC films. The nucleophile-initiated thiol-ene click reaction demonstrated in PDLC system has been investigated by Shi et al, whom have illustrated that with the increase of thiol functionality, the threshold voltage and saturation voltage of the thiol-ene based PDLC films increases and the off-state transmittance decreases [29,30]. Except for changing the conditions of polymerization, Shi et al. have reported a dye-doped thiol-ene based PDLC system with a low threshold voltage [31]. Without UV irradiation, they have also added nitrogen-centred catalysts such as 4-dimethylaminopyridine for fabricating thiol-ene based PDLCs [32]. Zhang et al. achieved a thiol-ene based PDLC film with superior properties of a low-driving voltage (37.2 V), a high contrast ratio (148.2), and ashort response time (14.9 ms) via the investigation of the effects of crosslinking agent/diluents/thiol on the electro-optic properties [33]. Sun et al. found a thiol-acrylate PDLC system where the polymer network and electro-optic properties were easily tunable by the introduction of thiol monomers [34] Moreover, when adding a poly-mercaptan curing agent with an appropriate concentration into a polymer dispersed cholesteric liquid crystal system, lower voltages and high contrast ratios were achieved [35,36].
Effects of the chain length of crosslinking agent and dye-doped amount on the electro-optical properties of polymer-dispersed liquid crystal films prepared by nucleophile-initiated thiol-ene click reaction
Published in Liquid Crystals, 2020
Li Zhang, Zhiqing Shi, Taoyu He, Yawen Liu, Yinghan Wang
The concept of ‘click chemistry’ has drawn a great deal of attention since Sharpless and his colleagues introduced it in 2001, because of its exceptional utility in organic synthesis, polymer functionalisation and network synthesis/modification [19–21]. The click chemistry reactions could form carbon heteroatomic bonds (C-X-C) under mild conditions. The reactions are simple, fast, practical and easy to handle [22,23]. As a kind of ‘click chemistry’, thiol-ene reaction has been extensively studied in recent years due to its wide applicability. Hoyle et al. [21] divided thiol-ene click reaction into two categories. One is the radical-mediated anti-Markovnikov addition, the other is the base – or nucleophile-catalysed thiol-Michael addition [23–26]. Recent literatures clearly demonstrate the versatility, high efficiency and ease of implementation of the nucleophile-initiated thiol-Michael reactions [20,27–31].
Fabrication of dye-doped polymer-dispersed liquid crystals with low driving voltage based on nucleophile-initiated thiol-ene click reaction
Published in Liquid Crystals, 2018
Zhiqing Shi, Leishan Shao, Fei Wang, Feifei Deng, Yawei Liu, Yinghan Wang
Thiol-ene polymerisations are reactions between multifunctional thiol and alkene monomers which proceed via a step-growth addition mechanism widely used in organic synthesis, polymer functionalisation and network synthesis/modification [1]. It has features of easy implementation, rapid reaction kinetics and high yields [2]. The thiol-ene reaction typically proceeds via two pathways: (1) radical-mediated anti-Markovnikov addition, commonly referred to as the thiol-ene reaction; (2) base- or nucleophile-catalysed thiol-Michael addition [3–7]. From a practical standpoint, nucleophile-initiated thiol-Michael reactions have the same general features as a typical radical-mediated thiol-ene click reaction, facilitating the rapid, modular and orthogonal addition of thiols to electron-deficient enes in a quantitative manner with minimal amounts of simple, cheap and commercially available catalysts, under nondemanding conditions (no heat or light needed) [1].