Rapid Modular Synthesis and Processing of Thiol–Ene Functionalized Styrene–Butadiene Block Copolymers

Quantifying the effects of cooperative hydrogen bonds between vicinal diols on polymer dynamics

Transient cross-links such as hydrogen bonds (H-bonds) are a central concept for creating polymers with mechanical functionalities, including toughness and self-healing properties. While conventional strong H-bonding groups are based on rigid and planar molecular motifs with multidentate intermolecular interactions, we recently discovered that a structurally simple and flexible vicinal diol (VDO) could serve as a robust yet dynamic cross-link with multiple intermolecular H-bonds between hydroxy groups. In this work, we investigated the effects of cooperativity of H-bonds in VDOs on polymer dynamics. We synthesized model polybutadienes with either VDO or monool (MO) side groups by a radical-mediated thiol-ene click reaction. The oscillatory shear rheology data were analyzed by using the sticky Rouse model. The characteristic time of a single modified segment (δτ₀) was significantly longer for the VDO-modified polymers than for the MO-modified polymers, even when they had the same number density of hydroxy groups. The increase in δτ₀ with increasing degree of modification was much more drastic for the VDO-modified polymers than for the MO-modified polymers. Moreover, the characteristic time of an unmodified Rouse segment (τ₀) was found to increase upon increasing the number of VDOs in the chain, while it was unchanged against the number of MOs. These observations highlight the cooperative effects of placing two hydroxy groups in a close vicinal arrangement. The multiplicity of H-bonds and the structural flexibility of VDOs led to efficient retardation of the chain dynamics.

Synthesis and Properties of Side-Chain Functionalized Polytetrahydrofuran Derivatives via the Blue-Light Photocatalytic Thiol-Ene Reaction

A series of side-chain functionalized polytetrahydrofuran (PTHF) derivatives were synthesized via the blue-light photocatalytic thiol-ene "click" reaction. Firstly, unsaturated polytetrahydrofuran (UPTHF) as a new unsaturated polyether was synthesized via condensation polymerization of cis-2-butene-1,4-diol and trans-1,4-dibromo-2-butene using potassium hydroxide (KOH) as a catalyst. Then, double bonds in the backbone of UPTHF were modified into different pendant functionality side groups by blue-light photocatalytic thiol-ene "click" reaction using Ru(bpy)₃Cl₂ as a photoredox catalyst, obtaining different side-chain functionalized PTHF derivatives. The structure and the morphology of the side-chain functionalized PTHF derivatives was characterized via Fourier-transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS), and differential scanning calorimeter (DSC). The results showed that the blue-light photocatalytic thiol-ene reaction exhibited high efficiency, and all the unsaturated bonds were modified. Different branch units bestowed different performance of PTHF derivatives; we systematically investigated the thermal properties, pH-triggered and temperature-triggered, self-assembly behaviors of different PTHF derivatives.

TUNING PROPERTIES AND MORPHOLOGY IN HIGH VINYL CONTENT SBS BLOCK COPOLYMER, A THERMOPLASTIC ELASTOMER VIA THIOL-ENE MODIFICATION

Thiol-ene modification of high vinyl content thermoplastic elastomeric styrene butadiene styrene (SBS) block copolymer (BCP) was carried out using different thiolating agents in toluene at 70 °C. 1H NMR analysis confirmed the participation of vinyl double bond in the thiol-ene modification reaction of SBS. Surface morphology of the block copolymers evaluated by atomic force microscopy analysis showed higher roughness after the thiol-ene reaction. The thiol-modified SBS block copolymer showed better adhesion strength and oil resistance properties than the pristine SBS.

Orthogonally Spin-Coated Bilayer Films for Photochemical Immobilization and Patterning of Sub-10-Nanometer Polymer Monolayers

Versatile and spatiotemporally controlled methods for decorating surfaces with monolayers of attached polymers are broadly impactful to many technological applications. However, current materials are usually designed for very specific polymer/surface chemistries and, as a consequence, are not very broadly applicable and/or do not rapidly respond to high-resolution stimuli such as light. We describe here the use of a polymeric adhesion layer, poly(styrene sulfonyl azide-alt-maleic anhydride) (PSSMA), which is capable of immobilizing a 1-7 nm thick monolayer of preformed, inert polymers via photochemical grafting reactions. Solubility of PSSMA in very polar solvents enables processing alongside hydrophobic polymers or solutions and by extension orthogonal spin-coating deposition strategies. Therefore, these materials and processes are fully compatible with photolithographic tools and can take advantage of the immense manufacturing scalability they afford. For example, the thicknesses of covalently grafted poly(styrene) obtained after seconds of exposure are quantitatively equivalent to those obtained by physical adsorption after hours of thermal equilibration. Sequential polymer grafting steps using photomasks were used to pattern different regions of surface energy on the same substrate. These patterns spatially controlled the self-assembled domain orientation of a block copolymer possessing 21 nm half-periodicity, demonstrating hierarchical synergy with leading-edge nanopatterning approaches.

INSIGHTS INTO THE PREPARATION OF VINYL POLYBUTADIENE VIA COBALT-BASED CATALYST: TUNING ITS PROPERTIES BY THIOL-ENE MODIFICATION OF VINYL GROUP

Elastomers with pendant alkenyl functionality can be easily modified using different types of postpolymerization reactions that lead to improved properties. This investigation reports the preparation of polybutadiene (PB) with control vinyl content by Co-based catalyst followed by modification of vinyl functionality via thiol-ene reaction. In this case, the polymerization of butadiene was carried out in cyclohexane using cobalt octanoate (Co[oct]2) in combination with diethylaluminium chloride (DEAC) and triethylaluminium (TEAL) as cocatalysts. The effects of different parameters, such as the concentration of catalyst and cocatalyst, monomer concentration, and reaction temperature on polymerization of butadiene (BD), were evaluated and optimized to obtain the desired vinyl content in the polymer. The microstructures in PB were investigated by 1H nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy analyses. Molecular weights and dispersity (Ð) of the polymers were determined by gel permeation chromatography analysis. The viscosity average molecular weight was calculated from the intrinsic viscosity [η] using the Mark-Houwink equation. Synthesized vinyl-PB was modified by the thiol-ene reaction using benzyl mercaptan as thiolating agent and 2,2′-azobis(isobutyronitrile) as an initiator. Thiol-ene modification was confirmed by 1H NMR analysis. Surface characteristics of thiol-modified PB were characterized by goniometer. Thiol-ene–modified PB showed greatly improved adhesive strength in metal–rubber bonding, as determined by lap shear test.

Largely improved electromechanical properties of thermoplastic dielectric elastomers by grafting carboxyl onto SBS through thiol–ene click chemistry

Modified SBS with largely improved electromechanical properties is prepared by grafting carboxyl groups onto the polybutadiene domains using a simple, effective and controllable photochemical thiol-ene click reaction.

Thiol–ene “click” reactions and recent applications in polymer and materials synthesis: a first update

This contribution serves as an update to a previous review (Polym. Chem.2010,1, 17–36) and highlights recent applications of thiol–ene ‘click’ chemistry as an efficient tool for both polymer/materials synthesis as well as modification.