A straightforward strategy for the efficient synthesis of acrylate and phosphine oxide‐containing vegetable oils and their crosslinked materials

Phosphorus‐containing triglycerides were prepared from a new route that involves the singlet oxygen photo‐oxygenation of high oleic sunflower oil and further reduction of the resulting hydroperoxide derivatives to a mixture of secondary allylic alcohols. These allylic alcohols in presence of chlorodiphenylphosphine give allylic phosphinites capable to undergo a [2,3]‐sigmatropic rearrangement leading to tertiary phosphine oxides directly linked to triglyceride in a one‐pot two‐step reaction. The obtained phosphorus‐containing triglycerides with different hydroxyl content were activated to polymerization by acrylation and these acrylate triglycerides were radically crosslinked in presence of different amounts of pentaerythritol tetra‐acrylate. The thermal, dynamic‐mechanical, and flame retardancy properties of the final materials were evaluated. Thermal and thermo‐oxidative degradation was studied by gas chromatography/mass spectrometry, ³¹P HR‐MAS NMR spectroscopy, and scanning electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4051–4063, 2009     

Modification of polysaccharides via thiol‐ene chemistry: A versatile route to functional biomaterials

We present herein a mild and rapid method for the modular functionalization of polysaccharides. Several ene‐functional charged and neutral polysaccharides, that is, hyaluronic acid and dextran, were prepared by esterification of the hydroxyl groups with pentenoic anhydride. The modified polysaccharides were then reacted with six model mercaptans under UV light, leading to linear polymers modified with hydrophobic groups, peptides, or oligosaccharides as well as chemical hydrogels. The thiol‐ene coupling reactions were found to proceed with high efficiency in short reaction times and with nearly no degradation of the polysaccharide backbone. Moreover, they were carried out in aqueous media, without the use of any metal catalysts, enhancing the attractive nature of this process. Notably, we investigated whether it is feasible to prepare cell‐responsive hydrogels by sequential bioconjugation and cross‐linking of the polysaccharide backbone with a bioactive peptide and poly(ethylene glycol)‐dithiol, respectively. All together, these results highlight the potential of this coupling strategy for the modular functionalization of polysaccharides under click chemistry‐like conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of polybenzoxazine precursors using thiols: Simultaneous thiol–ene and ring‐opening reactions

A new class of polybenzoxazine precursors of combined molecular structure of benzoxazine in the open and ring form has been developed. Thermally curable benzoxazine networks were obtained by simultaneous photoinduced thiol‐ene and Catalytic Opening of the Lateral Benzoxazine Rings by Thiols (COLBERT). The thiol‐ene reactions were initiated by photolysis of a free radical photoinitiator, 2, 2‐dimethoxy‐2‐phenyl acetophenone (DMPA), and the competing COLBERT reaction was triggered by thiol compound, 1,2‐ethanedithiol, present in the reaction mixture. The extent of reactions was evaluated by conducting experiments both under UV irradiation and in dark using model benzoxazines. The precursor soft films (pre‐P(B‐ala‐DTE)) were prepared by irradiating solutions of diallyl functional benzoxazine (B‐ala), 1,2‐ethanedithiol and DMPA. The obtained pre‐P(B‐ala‐DTE) films were then cured through thermally activated ring opening reaction of remaining benzoxazine groups yielding a more rigid and tough film. Thermal and mechanical properties of the films were investigated by DSC, DMA and TGA and compared with a typical polybenzoxazine, P(B‐ala). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A versatile approach to the synthesis of polyphosphazene derivatives via the thiol–ene reaction

The thiol–ene radical addition reaction has been successfully used to synthesize polyphosphazene derivatives. Poly[bis(allylamino)phosphazene] with pendant allyl groups was reacted with different thiol reagents under UV irradiation. These thiol reagents include 1‐pentanethiol, 3‐mercaptopropionic acid, 3‐mercapto‐1,2‐propane‐diol, and 2,3,4,6‐tetra‐O‐acetyl‐1‐thio‐β‐D ‐glucopyranose. ¹H NMR analyses confirm that the allyl polyphosphazene can be quantitatively modified by the mercaptans. In total, 100% conversion of the allyl groups was reached in <60 min toward the first three mercaptans, whereas about 80% conversion of the allyl groups was reached after 120‐min reaction toward the thioglucose. This method is a facile route for the synthesis of functional polyphosphazenes without the needs for protection/deprotection procedures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A new route to acrylate oils: Crosslinking and properties of acrylate triglycerides from high oleic sunflower oil

Triglycerides with acrylate functionality were prepared from a new route that involves the singlet oxygen photooxygenation of high oleic sunflower oil and further reduction of the resulting hydroperoxide derivatives to a mixture of secondary allylic alcohols. These unsaturated alcohols can be further reduced to saturated alcohols. These two new hydroxyl‐containing triglycerides were functionalized as acrylate esters and radically crosslinked in presence of different amounts of pentaerythritol tetraacrylate. The crosslinking reactions were followed by FTIR spectroscopy and the thermal properties of the final materials were evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1159–1167, 2009     

Novel suberin‐based biopolyesters: From synthesis to properties

This article reports the successful synthesis and characterization of two types of completely biobased polymers prepared by the polycondensation or polytransesterification of suberin fragments, isolated by different procedures and from two different vegetable sources. These polymerizations were conducted with different experimental conditions in terms of the type of catalyst, the reaction medium and temperature, as well as the molar ratio between the reactive moieties. The ensuing linear or partly crosslinked polyesters were characterized by conventional spectroscopic techniques, SEC, DSC, XRD, DMA, and TGA. These hydrophobic materials represent an original contribution to the growing field of polymers from renewable resources. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Novel,environmentally friendly crosslinking system of an epoxy using an amino acid: Tryptophan‐cured diglycidyl ether of bisphenol A epoxy

Tryptophan, an amino acid, has been used as a novel, environmentally friendly curing agent instead of toxic curing agents to crosslink the diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The curing reaction of tryptophan/DGEBA mixtures of different ratios and the effect of the imidazole catalyst on the reaction have been evaluated. The optimum reaction ratio of DGEBA to tryptophan has been determined to be 3:1 with 1 wt % catalyst, and the curing mechanism of the novel reaction system has been studied and elucidated. In situ Fourier transform infrared spectra indicate that with the extraction of a hydrogen from NH₃⁺ in zwitterions from tryptophan, the formed nucleophilic primary amine and carboxylate anions of the tryptophan can readily participate in the ring‐opening reaction with epoxy. The secondary amine, formed from the primary amine, can further participate in the ring‐opening reaction with epoxy and form the crosslinked network. The crosslinked structure exhibits a reasonably high glass‐transition temperature and thermal stability. A catalyst‐initiated chain reaction mechanism is proposed for the curing reaction of the epoxy with zwitterion amino acid hardeners. The replacement of toxic curing agents with this novel, environmentally friendly curing agent is an important step toward a next‐generation green electronics industry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 181–190, 2007     

Controlled synthesis of thermoresponsive polymers derived from l‐Lysine,a biorenewable resource

Renewable lysine was cyclized to its corresponding α‐amino‐ε‐caprolactam and then underwent the reaction with acryloyl chloride to harvest a 2‐acrylamido‐caprolactam (ACL) monomer. Subsequent reversible addition–fragmentation chain transfer copolymerization of the obtained monomer with oligo(ethylene glycol)acrylate (OEGA) gave well‐defined P(ACL‐co‐OEGA) with low distribution. Nuclear magnetic resonance , size exclusion chromatography, and matrix‐assisted laser desorption ionization–time‐of‐flight–mass spectrometry measurements indicated the controlled feature of the polymerization. Moreover, the resultant copolymers demonstrated thermoresponsiveness, and the cloud points (T_cp) can be adjusted from 34 to 79 °C, by changing pH values, and the fraction of cyclic lysine. These results suggested that these lysine‐based thermoresponsive polymers might be used as new materials in biomedical fields. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 862–868     

Preparation of polymer nanoparticles from renewable biobased furfuryl alcohol and maleic anhydride by stabilizer‐free dispersion polymerization

The spherical polymer nanoparticles of biobased renewable monomers, furfuryl alcohol (FA) and maleic anhydride (MAn), with diameters (D_n) in the range of 120 to 500 nm have been prepared by stabilizer‐free dispersion copolymerization. In acetate or its mixture, the conversion of the monomers greatly depended on the concentration of AIBN. When the molar ratio of AIBN/monomers was 3.6% (wt), the monomer conversion could be as high as 80%. The aggregations of the solvated polymer chains formed the nuclei of the polymer particles. After the nucleation stage, both the monomer conversions and particle sizes increased steadily, while the coefficient of variation of the particle size decreased. The almost linear relationship between the D_n³ and the weight of polymer suggested that there is no significant secondary nucleation. The copolymer of FA and MAn could not dissolve in common organic solvents. Elemental analyses, FTIR and ¹³CP‐MAS spectra showed that the copolymer was close to the alternative copolymer of FA and MAn irrespective to the molar ratios of FA/MAn in monomer feed. Furthermore, the two 2,5‐ and 3,4‐dihydrofuran ring configurations exist in the copolymer and the later is the major one. The reaction of copolymer particles with triethylenetetramine confirmed the reactivity of the succinic anhydride groups at the surface of copolymer particles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of amphiphilic A4B4 star‐shaped copolymers by mechanisms transformation combining with thiol‐ene reaction

Using core‐first strategy, the amphiphilic A₄B₄ star‐shaped copolymers [poly(ethylene oxide)]₄[poly(ε‐caprolactone)]₄ [(PEO)₄(PCL)₄], [poly(ethylene oxide)]₄[poly(styrene)]₄ [(PEO)₄(PS)₄], and [poly(ethylene oxide)]₄[poly(tert‐butyl acrylate)]₄ [(PEO)₄(PtBA)₄] were synthesized by mechanisms transformation combining with thiol‐ene reaction. First, using a designed multifunctional mikto‐initiator with four active hydroxyl groups and four allyl groups, the four‐armed star‐shaped polymers (PEO‐Ph)₄/(OH)₄ with four active hydroxyl groups at core position were obtained by sequential ring‐opening polymerization (ROP) of ethylene oxide monomers, capping reaction of living oxyanion with benzyl chloride, and transformation of allyl groups into hydroxyl groups by thiol‐ene reaction. Then, the A₄B₄ star‐shaped copolymers (PEO)₄(PS)₄ or (PEO)₄(PtBA)₄ were obtained by atom transfer radical polymerization (ATRP) of styrene or tert‐butyl acrylate (tBA) monomers from macroinitiator of (PEO‐Ph)₄/(Br)₄, which was obtained by esterification of (PEO‐Ph)₄/(OH)₄ with 2‐bromoisobutyryl bromide. The A₄B₄ star‐shaped copolymers (PEO)₄(PCL)₄ were also obtained by ROP of ε‐caprolactopne monomers from macroinitiator of (PEO‐Ph)₄/(OH)₄. The target copolymers and intermediates were characterized by size‐exclusion chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy, and nuclear magnetic resonance in detail. This synthetic route might be a versatile one to various A_nB_n (n ≥ 3) star‐shaped copolymers with defined structure and compositions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4572–4583     

Photoinduced thiol–ene crosslinking of globalide/ε‐caprolactone copolymers: Curing performance and resulting thermoset properties

The increasing demand for bioderived polymers led us to investigate the potential use of the macrolactone globalide in thermoset synthesis via the photoinduced thiol–ene reaction. A series of six lipase‐catalyzed poly(globalide‐caprolactone) copolyesters bearing internal main‐chain unsaturations ranging from 10 to 50 and 100 mol % were successfully crosslinked in the melt with equal amounts of thiol groups from trimethylolpropane‐trimercapto propionate affording fully transparent amorphous elastomeric materials with different thermal and viscoelastic properties. Three major conclusions can be drawn from this study: (i) high thiol–ene conversions (>80%) were easily attained for all cases, while maintaining the cure behavior, and irrespective of functionality at reasonable reaction rates; (ii) parallel chain‐growth homopropagation of the ene monomer is insignificant when compared with the main thiol–ene coupling route; and (iii) high ene‐density copolymers result in much lower extracted sol fractions and high T_g values as a result of a more dense and homogeneous crosslinked network. The thiol–ene system evaluated in this contribution serve as model example for the sustainable use of naturally occurring 1,2‐disubstituted alkenes in making semisynthetic polymeric materials in high conversions with a range of properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

A facile method to synthesize high‐molecular‐weight biobased polyesters from 2,5‐furandicarboxylic acid and long‐chain diols

In this study, biobased furan dicarboxylate polyesters have been prepared using 2,5‐furandicarboxylic acid (FDCA) and diols with high number of methylene groups (long‐chain diols), namely, 8, 9, 10, and 12. Because of the high boiling points of these diols, a modified procedure of the well‐known melt polycondensation was applied in this work. According to this, the dimethyl ester of FDCA (DMFD) reacted in the first transesterification stage with the corresponding diols forming bis‐hydroxy‐alkylene furan dicarboxylates (BHFD). In the second stage, the BHFD reacted with DMFD again at temperatures of 150–170 °C (for 4–5 h), and in the final stage, the temperature was raised to 210–230 °C (vacuum was applied for 2–3 h). The molecular weight of the polyesters and the content of oligomers, as was verified by gel permeation chromatography analysis, depend on the polycondensation time and temperature. The chemical structure of the polyesters was verified from ¹H NMR spectroscopy. All the polymers were found to be semicrystalline, with melting temperatures from 69 to 140 °C depending on the diol used. In addition, the mechanical properties also varied with the type of diol. The higher values were observed for poly(octylene 2,5‐furanoate), whereas the lowest values were observed for poly(dodecylene 2,5‐furanoate) with the higher number of methylene groups in its repeating unit. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2617–2632     

Computational synthesis,structure, and glass transition of (1,4) Cis‐polyisoprene‐based nanocomposite by multiscale modeling

The main goal of the present study was to produce insights from the atomistic modeling into the structural changes in elastomer‐based polymer nanocomposites caused by the surface modifications of the filler particles, and by the crosslinking of the participating polymer matrix. The fully atomistic molecular‐dynamics computer simulations of crosslinked (1,4) cis‐polyisoprene (PI) films capped by amorphous silica substrates was set‐up, in the presence of realistic coupling and covering agents. The PI film stratified structure has been studied in the proximity of the corresponding glass transition, by varying the degree of crosslinking and the PI film thickness. Some monomer ordering induced by the pristine (bare) silica disappeared almost completely in films with modified surfaces. The average monomer density increased with degree of crosslinking. As compared with PI bulk, the glass‐transition temperature was slightly larger for highly crosslinked PI films with bare silica and surfaces with coupling agents, and increased with increasing confinement. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 473–485     

One‐pot preparation of mercaptotetrazole‐silica hybrid monoliths by the thiol‐ene click reaction for mixed‐mode capillary liquid chromatography

A novel mercaptotetrazole‐silica hybrid monolithic column was prepared for capillary liquid chromatography, in which the thiol‐end mercaptotetrazole was mixed with hydrolyzed γ‐methacryloxypropyltrimethoxysilane and tetramethyloxysilane for the co‐polycondensation and thiol‐ene click reaction in a one‐pot process. The effects of the molar ratio of silanes, the amount of mercaptotetrazole, and the volume of porogen on the morphology, permeability and pore properties of the as‐prepared mercaptotetrazole‐silica hybrid monoliths were investigated in detail. A series of test compounds including alkylbenzenes, amides and anilines were employed for evaluating the retention behaviors of the mercaptotetrazole‐silica hybrid monolithic columns. The results demonstrated that the mercaptotetrazole‐silica hybrid monoliths exhibited hydrophobic, hydrophilic as well as ion‐exchange interaction. The run‐to‐run, column‐to‐column and batch‐to‐batch reproducibilities of the mercaptotetrazole‐silica hybrid monoliths were satisfactory with the relative standard deviations less than 1.4 (n  = 5), 3.9 (n  = 3) and 4.0% (n  = 5), respectively. In addition, the mercaptotetrazole‐silica hybrid monolith was further applied to the separation of sulfonamides, nucleobases and protein tryptic digests. These successful applications confirmed the promising potential of the mercaptotetrazole‐silica hybrid monolith in the separation of complex samples.     

A new enone‐containing triglyceride derivative as precursor of thermosets from renewable resources

A novel triglyceride containing α,β‐unsaturated ketone was prepared through photoperoxidation from high oleic sunflower oil by two steps one pot environmentally friendly procedure. This new enone‐containing triglyceride was crosslinked with diaminodiphenylmethane (DDM) via aza‐Michael addition. A kinetic study of the reaction of p‐toluidine with either enone‐containing methyl oleate or epoxidized methyl oleate, as model compounds, allowed us to establish the higher reactivity of the former, thus confirming this curing system as an alternative to amine‐cured epoxidized vegetable oils. The thermal properties of thermosets from enone‐ and epoxy‐containing triglycerides with DDM have been evaluated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6843–6850, 2008     

Structural and phenomenological study on the cationic curing of mixtures of epoxy resin and 5,5‐dimethyl‐1,3‐dioxane‐2‐one

Ytterbium and lanthanum triflates were used as initiators to cure a mixture of diglycidylether of bisphenol A (DGEBA) and 5,5‐dimethyl‐1,3‐dioxane‐2‐one (DMTMC). The evolution of the curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing process. We observed the formation of a five‐membered cyclic carbonate, which remains unreacted at the chain ends because of an equilibrium process between the spiroortho carbonates that had formed as intermediate species and also the loss of CO₂, which was quantified by thermogravimetry. The kinetics were studied by DSC and analyzed by isoconversional procedures. Thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) experiments were used to evaluate the properties of the thermosets obtained. The phenomenological changes that take place during curing were studied and represented in a time‐temperature‐transformation (TTT) diagram. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4546–4558, 2006     

Liquid‐crystalline thermosets from liquid‐crystalline epoxy resins containing bisazomethinebiphenylene mesogens in the central core: Copolymerization with a nonmesomorphic epoxy resin

A new series of liquid‐crystalline epoxy resins was synthesized, and their mesomorphic behavior was investigated with differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray scattering. These glycidylic compounds had central aromatic imine mesogens derived from benzidine and aliphatic spacers of up to 10 methylene units that linked the mesogens to the glycidylic groups. Crosslinking these monomers with primary aromatic diamines led to nematic networks, some of which contained crystal inclusions. However, through curing with tertiary amines as catalytic agents or through copolymerization with different proportions of the nonmesomorphic epoxy monomer and primary amines as crosslinking agents, smectic C organized thermosets were prepared when the spacers had at least four methylene carbons. When they had fewer than four, the networks were nematic. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3631–3643, 2004     

Calorimetric studies on an anhydride‐cured epoxy resin from diglycidyl ether of bisphenol‐A and diglycidyl ether of poly(propylene glycol). I. Onset of diffusion control during isothermal polymerization

Calorimetric studies on a series of anhydride‐cured epoxy resins, in which the epoxy oligomer is a mixture of diglycidyl ether of bisphenol‐A (DGEBA) and diglycidyl ether of poly(propylene glycol) (DGEPPG) in different mole ratios, were carried out. DGEPPG is a flexible epoxy oligomer that was used to tune glass transition temperature for the fully reacted epoxy resin. Conversion versus time curves for the systems with different DGEBA/DGEPPG mole ratios (not including the neat DGEPPG system) were found to overlap with each other in mass‐controlled reaction regime, indicating similar reactivities of epoxy groups in both epoxy oligomers. Onset of diffusion‐controlled reaction regime for different systems was estimated by fitting the conversion versus time data using a phenomenological kinetic equation, as well as from direct comparison of the conversion versus time curves. For the systems (i.e., 0, 10, and 30% DGEPPG) that vitrify during reaction, the crossover from mass‐controlled to diffusion‐controlled reaction occurs close to the onset of the vitrification, where T_g is about 25–30 K below the reaction temperature. For the system (i.e., 50% DGEPPG system) that does not vitrify during the reaction, such crossover still occurs when the T_g of the mixture reaches a value about 25 K below the reaction temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2155–2165, 2008     

Modification of RAFT‐polymers via thiol‐ene reactions: A general route to functional polymers and new architectures

An investigation into the aminolysis of ω‐end groups of RAFT‐polymers and simultaneous thiol‐ene reactions with ene‐bearing compounds is described. Three different polymers, P(MMA), P(HPMA), and P(NIPAAm), with low PDIs were synthesized using dithiobenzoate and trithiocarbonate RAFT agents. P(NIPAAm) synthesized with trithiocarbonate RAFT agent and P(HPMA) synthesized with dithiobenzoate RAFT agent were both functionalized with a methacrylate‐modified mannose and a maleimide‐modified biotin via one‐pot simultaneous aminolysis and thiol‐ene reactions with product yields above 85%. The presence of ene‐compounds during aminolysis was shown to prevent the formation of disulfide interchain crosslinking. Using the same approach, P(MMA), P(HPMA), and P(NIPAAm) were converted to (meth)acrylate macromonomers with high yields (>80%). In the case of P(MMA), the simultaneous aminolysis and thiol‐ene addition prevented any intrachain side reactions, i.e., thiolactone formation. New architectures such as graft and block copolymers were successfully generated from the macromonomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3773–3794, 2009     

Optimization of the surface modification process of cross‐linked polythiol‐coated chiral stationary phases synthesized by a two‐step thiol‐ene click reaction

A new platform technology for the preparation of stable chiral stationary phases was successfully optimized. The chiral selector tert‐butylcarbamoylquinine was firstly covalently connected to the polymer poly(3‐mercaptopropyl)methylsiloxane by thiol‐ene click reaction. Secondly, the quinine carbamate functionalized polysiloxane conjugate was coated onto the surface of vinyl modified silica particles and cross‐linked via thiol‐ene click reaction. The amount of polysiloxane, chiral selector, radical initiator, reaction solvent (chloroform and methanol), reaction time, and pore size of the supporting silica particles were varied and systematically optimized in terms of achievable plate numbers while maintaining simultaneously enantioselectivity. The optimization was based on elemental analysis data, chromatographic results, and H/u‐curves (Van Deemter) of the resultant chiral stationary phases. The results suggest that better chromatographic efficiency (higher plate numbers) at equal enantioselectivity can be achieved with methanol (a poor solvent for the polysiloxane that is dispersed rather than dissolved) and a lower film thickness of quinine carbamate functionalized polysiloxane. In this study, chiral stationary phases based on 100 Å silica slightly outperformed 200 Å silica particles (each 5 μm). The optimized two step material exhibited significantly reduced mass transfer resistance compared to the one step material and equal performance as a brush‐type chiral stationary phase.