Post-polymerization Functionalization Research Articles

Glaser-Hay-Coupled Random Copolymers Containing Boron Difluoride Formazanate Dyes.

𝜋-Conjugated polymers, including those based on acetylenic repeating units, are an exciting class of materials that offer narrow optical band gaps and tunable frontier orbital energies that lead to their use in organic electronics. This work expands the knowledge of structure-property relationships of acetylenic polymers through the synthesis and characterization of a series of Glaser-Hay-coupled model compounds and random copolymers comprised of BF2 formazanate, fluorene, and/or bis(alkoxy)benzene units. The model compounds and copolymers synthesized exhibit redox activity associated with the reversible reduction of the BF2 formazanate units and the irreversible reduction of the fluorene and bis(alkoxy)benzene units. The copolymers exhibit absorption profiles characteristic or intermediate of their respective models and homopolymers, leading to broad absorption of UV-vis light. The alkyne linkages of the model compounds and copolymers are reacted with [Co2(CO)8] to convert the alkyne functional groups into cobalt carbonyl clusters. This transformation leads to blue-shifted absorption profiles due to a decrease in π-conjugation, demonstrating the ability to tune the properties of these materials through post-polymerization functionalization. The redox activity and broad absorption bands of the polymers reported make them excellent candidates for use in photovoltaics and other light-harvesting applications.

Silver-Mediated ARGET-ATRP of Reactive Acrylates Using TPMANMe2 Ligand: A Universal Strategy for Controlled Copolymerization.

A controlled polymerization using activated acrylate monomers via ARGET-ATRP is developed with a tris[(4-dimethylamino pyridyl)methyl]amine ligand to address issues with weaker ligands and monomers that can undergo postpolymerization functionalization. This catalyst system enables the polymerization of N-acryloxy succinimide, fluorinated monomers, and isocyanato ethyl acrylate under controlled homogeneous conditions, ensuring linear molecular-weight growth and low polydispersity. Two block copolymerization strategies produce amphiphilic copolymers with narrow molecular-weight distributions and customizable compositions, allowing for various postpolymerization functionalizations.

Mechanochemically Promoted Functionalization of Postconsumer Poly(Methyl Methacrylate) and Poly(α-Methylstyrene) for Bulk Depolymerization.

We describe a methodology of post-polymerization functionalization to enable subsequent bulk depolymerization to monomer by utilizing mechanochemical macro-radical generation. By harnessing ultrasonic chain-scission in the presence of N-hydroxyphthalimide methacrylate (PhthMA), we successfully chain-end functionalize polymers to promote subsequent depolymerization in bulk, achieving up to 81% depolymerization of poly(methyl methacrylate) (PMMA) and poly(α-methylstyrene) (PAMS) within 30 min. This method of depolymerization yields a high-purity monomer that can be repolymerized. Moreover, as compared to the most common methods of depolymerization, this work is most efficient with ultra-high molecular weight (UHMW) polymers, establishing a method with the potential to address highly persistent, non-degradable all-carbon backbone plastic materials. Lastly, we demonstrate the expansion of this depolymerization method to commercial cell cast PMMA, achieving high degrees of depolymerization from post-consumer waste. This work is the first demonstration of applying PhthMA-promoted depolymerization strategies in homopolymer PMMA and PAMS prepared by conventional polymerization methods.

Poly(2-isopropenyl-2-oxazoline) as a Versatile Functional Polymer for Biomedical Applications.

Functional polymers play an important role in various biomedical applications. From many choices, poly(2-isopropenyl-2-oxazoline) (PIPOx) represents a promising reactive polymer with great potential in various biomedical applications. PIPOx, with pendant reactive 2-oxazoline groups, can be readily prepared in a controllable manner via several controlled/living polymerization methods, such as living anionic polymerization, atom transfer radical polymerization (ATRP), reversible addition-fragmentation transfer (RAFT) or rare earth metal-mediated group transfer polymerization. The reactivity of pendant 2-oxazoline allows selective reactions with thiol and carboxylic group-containing compounds without the presence of any catalyst. Moreover, PIPOx has been demonstrated to be a non-cytotoxic polymer with immunomodulative properties. Post-polymerization functionalization of PIPOx has been used for the preparation of thermosensitive or cationic polymers, drug conjugates, hydrogels, brush-like materials, and polymer coatings available for drug and gene delivery, tissue engineering, blood-like materials, antimicrobial materials, and many others. This mini-review covers new achievements in PIPOx synthesis, reactivity, and use in biomedical applications.

Solvent-free thiol-Ene/-Yne click reactions for the synthesis of alkoxysilyl telechelic poly(propylene oxide)s

Thiol-ene/−yne click reactions can be a versatile toolbox for the design and modification of polymers, enhancing functionality and providing opportunities for the development of innovative materials and applications. Here, we report a simple strategy to synthesize alkoxysilyl telechelic poly(propylene oxide)s (PPO)s: a) through a post-polymerization functionalization via Williamson reactions, commercial PPO is modified at the chain-end secondary alcohols with allyl or propargyl units, achieving >99% conversion; b) subsequent click reactions of (3-mercaptopropyl)trimethoxysilane (MPTMS), triggered by thermal and photochemical radical initiators, result in the incorporation of alkoxysilane groups on the polyether chain. Both thermal and photochemical thiol-ene/−yne click pathways are robust methodologies for preparing alkoxysilyl-modified PPOs in excellent yields (> 99%). Optimal conditions were identified as solvent-free, at 65 °C with 2,2′-azobis(2-methylpropionitrile) (AIBN) as the radical source. Detailed NMR analyses confirm the quantitative transformation of vinyl/propargyl functionalities in the resulting alkoxysilyl telechelic PPOs. Preliminary studies on the stability of alkoxysilyl end-groups are reported using 29Si NMR spectroscopy.

Copolymerization of β-Butyrolactones into Functionalized Polyhydroxyalkanoates Using Aluminum Catalysts: Influence of the Initiator in the Ring-Opening Polymerization Mechanism.

Within bioplastics, natural poly(3-hydroxybutyrate) (PHB) stands out as fully biocompatible and biodegradable, even in marine environments; however, its high isotacticity and crystallinity limits its mechanical properties and hence its applications. PHB can also be synthesized with different tacticities via a catalytic ring-opening polymerization (ROP) of rac-β-butyrolactone (BBL), paving the way to PHB with better thermomechanical and processability properties. In this work, the catalyst family is extended based on aluminum phenoxy-imine methyl catalyst [AlMeL2], that reveals efficient in the ROP of BBL, to the halogeno analogous complex [AlClL2]. As well, the impact on the ROP mechanism of different initiators is further explored with a particular focus in dimethylaminopyridine (DMAP), a hardly studied initiator for the ROP of BBL. A thorough mechanistic study is performed that evidences the presence of two concomitant DMAP-mediated mechanisms, that lead to either a DMAP or a crotonate end-capping group. Besides, in order to increase the possibilities of PHB post-polymerization functionalization, the introduction of a side-chain functionality is explored, establishing the copolymerization of BBL with β-allyloxymethylene propiolactone (BPLOAll), resulting in well-defined P(BBL-co-BPLOAll) copolymers.

Development of reversibly photo-crosslinkable water-stable poly(2-ethyl-2-oxazoline) nanofibers via functionalization with cinnamoyl moieties

Poly(2-ethyl-2-oxazoline) (PEtOx) is a potent member of the versatile poly(2-oxazoline) polymer platform with its high hydrophilicity that could be beneficial in numerous biomedical applications, especially in the form of a nanofibrous membrane. However, its water-solubility limits its application in situations where a stable, nanofibrous morphology is required in aqueous environments. The present work offers a straightforward route towards water-stable PEtOx-based nanofibrous membranes, via post-polymerization functionalization with cinnamoyl moieties (PEtOx-Cin) and photo-crosslinking of the electrospun membranes. It is shown that a UVB treatment does not significantly affect the nanofibrous morphology, while successfully inducing the cinnamoyl dimerization process and hence the formation of a polymeric network, as evidenced by spectral analysis. The hereby crosslinked PEtOx-based nanofibers exhibit a prolonged water-stability (at least 45 days), while, interestingly, intermediate irradiation times yield the best results. Full disintegration of the photo-crosslinked nanofibers in aqueous media could be achieved by subsequent UVC exposure. This is not only due to decrosslinking of the cinnamoyl dimers, but was also found to be due to partial degradation of the polymeric backbone. The investigation of UVB/UVC exposure on pure PEtOx nanofibrous membranes confirmed the photo-degradation of the polymeric backbone by a significant decrease in molar mass as observed by size exclusion chromatography and supported by spectral analysis. The hereby proposed, straightforward route for reversible crosslinking of PEtOx-based nanofibrous membranes and their accessible disintegration will contribute to the promotion of these materials in biomedical applications where a water-stable, nanofibrous morphology combined with high hydrophilicity and easy removal is required.

Bioreducible Amphiphilic Hyperbranched Polymer-Drug Conjugate for Intracellular Drug Delivery.

This paper reports synthesis of a bioreducible hyperbranched (HB) polymer by A2+B3 approach from commercially available dithiothreitol (DTT) (A2) and an easily accessible trifunctional monomer (B3) containing three reactive pyridyl-disulfide groups. Highly efficient thiol-activated disulfide exchange reaction leads to the formation of the HB polymer (Mw = 21000; Đ = 2.3) with bioreducible disulfide linkages in the backbone and two different functional groups, namely, hydroxyl and pyridyl-disulfide in the core and periphery, respectively, of the HB-polymer. Postpolymerization functionalization of the hydroxyl-groups with camptothecin (CPT), a topoisomerase inhibitor and known anticancer drug, followed by replacing the terminal pyridyl-disulfide groups with oligo-oxyethylene-thiol resulted in easy access to an amphiphilic HB polydisulfide-CPT conjugate (P1) with a very high drug loading content of ∼40%. P1 aggregated in water (above ∼10 μg/mL) producing drug-loaded nanoparticles (Dh ∼ 135 nm), which showed highly efficient glutathione (GSH)-triggered release of the active CPT. Mass spectrometry analysis of the GSH-treated P1 showed the presence of the active CPT drug as well as a cyclic monothiocarbonate product, which underpins the cascade-degradation mechanism involving GSH-triggered cleavage of the labile disulfide linkage, followed by intramolecular nucleophilic attack by the in situ generated thiol to the neighboring carbonate linkage, resulting in release of the active CPT drug. The P1 nanoparticle showed excellent cellular uptake as tested by confocal fluorescence microscopy in HeLa cells by predominantly endocytosis mechanism, resulting in highly efficient cell killing (IC50 ∼ 0.6 μg/mL) as evident from the results of the MTT assay, as well as the apoptosis assay. Comparative studies with an analogous linear polymer-CPT conjugate showed much superior intracellular drug delivery potency of the hyperbranched polymer.

Synthesis and Deconstruction of Polyethylene-type Materials.

Polyethylene deconstruction to reusable smaller molecules is hindered by the chemical inertness of its hydrocarbon chains. Pyrolysis and related approaches commonly require high temperatures, are energy-intensive, and yield mixtures of multiple classes of compounds. Selective cleavage reactions under mild conditions (<ca. 200 °C) are key to improve the efficacy of chemical recycling and upcycling approaches. These can be enabled by introduction of low densities of predetermined breaking points in the polyethylene chains during the step-growth or chain-growth synthetic construction of designed-for-recycling polyethylene-type materials. Alternatively, they can be accomplished by postpolymerization functionalization of postconsumer polyethylene waste via dehydrogenation and follow-up reactions or through oxidation to long-chain dicarboxylates. Deconstruction of litter under environmental conditions via the aforementioned break points can alleviate plastics' persistency, as a backstop to closed-loop recycling.

Poly(vinylpyridine-co-vinylpyridine N-oxide) Excipients Mediate Rapid Dissolution and Sustained Supersaturation of Posaconazole Amorphous Solid Dispersions.

The chemical structure of excipients molecularly mixed in an amorphous solid dispersion (ASD) has a significant impact on properties of the ASD including dissolution behavior, physical stability, and bioavailability. Polymers used in ASDs require a balance between hydrophobic and hydrophilic functionalities to ensure rapid dissolution of the amorphous dispersion as well as sustained supersaturation of the drug in solution. This work demonstrates the use of postpolymerization functionalization of poly(vinylpyridine) excipients to elucidate the impact of polymer properties on the dissolution behavior of amorphous dispersions containing posaconazole. It was found that N-oxidation of pyridine functionalities increased the solubility of poly(vinylpyridine) derivatives in neutral aqueous conditions and allowed for nanoparticle formation which supplied posaconazole into solution at concentrations exceeding those achieved by more conventional excipients such as hydroxypropyl methylcellulose acetate succinate (HPMCAS) or Eudragit E PO. By leveraging these functional modifications of the parent poly(vinylpyridine) excipient to increase polymer hydrophilicity and minimize the effect of polymer on pH, a new polymeric excipient was optimized for rapid dissolution and supersaturation maintenance for a model compound.

Radical polymerisation and thiol–ene post-polymerisation functionalisation of terpenoid acrylates in conventional and renewably sourced organic solvents

Geranyl acrylate has been synthesized and polymerized by various radical polymerisation techniques.

Post-polymerization functionalization of aliphatic polycarbonates using click chemistry

Presently there is much interest in the synthesis of degradable, more sustainable polymers from resources that minimize the use of petroleum-based feedstocks.

Cationic amino-acid functionalized polymethacrylamide vectors for siRNA transfection based on modification of poly(2-isopropenyl-2-oxazoline)

Poly(2-isopropenyl-2-oxazoline) (PiPOx) is a functional polymer showing great potential for the development of smart biomaterials. The straightforward synthesis and post-polymerization functionalization of PiPOx offers many opportunities for tailoring the properties of the polymer towards biomaterials. In this study we report for the first time PiPOx-based cationic charged polymethacrylamides with amino acid side chains that can complex siRNA and promote transfection in vitro. Therefore, PiPOx was fully modified via ring opening addition reactions with the carboxylic acid groups of a series of N-Boc-L-amino acids and their reaction kinetics were investigated. Based on the determined kinetic constants, another series of PiPOx-based copolymers with balanced hydrophilic/hydrophobic content of N-Boc-L-amino acids were obtained via one-pot modification reaction with two different N-Boc-L-amino acids. The N-Boc protected homopolymers and related copolymers were deprotected to obtain (co)polymers with the targeted side chain cationic charged units. The (co)polymers' structures were fully investigated via FT-IR and 1H NMR spectroscopy, size exclusion chromatography (SEC), and TGA–DSC–MS analysis. The polarimetry measurements revealed that the homopolymers retain their chiroptical properties after post-modification, and a sign inversion is noticed from (L) N-Boc-protected analogues to (D) for the TFA cationic charged homopolymers. Generally, cationically charged homopolymers with hydrophilic amino acids on the side chain showed efficient complexation of siRNA, but poor transfection while cationic copolymers having both tryptophan and valine or proline side chains revealed moderate siRNA binding, high transfection efficiency (> 90% of the cells) and potent gene silencing with IC50 values down to 5.5 nM. Particularly, these cationic copolymers showed higher gene silencing potency as compared to the commercial JetPRIME® reference, without reducing cell viability in the concentration range used for transfection, making this a very interesting system for in vitro siRNA transfection.

Water-Soluble Squaramide-Functionalised Copolymers for Anion Recognition.

A series of ethylene glycol-based squaramide-containing copolymers were synthesised via a post-polymerisation functionalisation strategy. Conversion of polymeric amines to squaramides was found to proceed in good yields, representing a versatile method of incorporating squaramides into polymers for anion recognition. Analysis of the polymers by UV-Vis and fluorescence spectroscopy revealed that anion binding takes place similarly to that of small-molecule squaramides. The presence of a fluorescent sensing group on polymer-bound squaramides allowed for a fluorescent sensing mechanism for anions that followed a similar trend in selectivity in aqueous DMSO solution, with selectivity observed for H2 PO4 - , AcO- and SO4 2- over other common anions tested. The anion response and selectivity towards anions was similar to that of analogous small-molecule squaramides, however polymeric squaramides exhibited a greater resistance to deprotonation by more basic anions, which was attributed to the closer proximity of individual squaramides on a macromolecule. The squaramide containing polymers exhibited good water solubility, overcoming a common problem for anion sensors which are typically not sufficiently soluble in water to function in many required applications. Despite no anion binding being observed in water, this represents a simple and effective method of creating fully water-soluble anion receptors which may be adapted to give improved binding affinity and selectivity depending on the anion binding moiety. This article is protected by copyright. All rights reserved.

Impact of pendant substituents on post-polymerization functionalization and electronic properties in stereoregular non-conjugated pendant electroactive polymers

Recent reports on non-conjugated pendant electroactive polymers (NCPEPs) have demonstrated the significance of altering structural variables specifically the stereoregularity, the nature of the pendant group and the length of the spacer connecting that group to the backbone for tuning of their optoelectronic properties. The only synthetic approach that allows for selectively studying the effects of tuning these variables without additional superimposed effects of varied molecular weights and tacticities is the post-polymerization functionalization methodology in which parent polymers are synthesized first and then functionalized with the respective pendant groups and spacers. However, specifically for tuning of the pendant group itself, the scope of such post-polymerization functionalization methods remains largely underexplored. Here, the compatibility of the established photochemical thiol-ene post-polymerization method with various pendant groups is investigated for functionalization of stereoregular and stereorandom poly(allyl methacrylates) made via anionic polymerization using an organolithium initiator. Carbazole and a family of four 3,6-disubstituted carbazoles with phenyl, methoxy, nitrile and t-butyl substituents were investigated as the respective pendant groups. With the phenyl, methoxy and nitrile substituted pendant groups limitations of the scope of the thiol-ene methodology due to limited solubility and vulnerability to photochemical side reactions could be demonstrated. In contrast, t-butyl substituents did not impede the post-polymerization functionalization. The corresponding functionalized NCPEPs were characterized and effects of substitution of the carbazole pendant group with t-butyl groups on the optoelectronic properties of the polymers are discussed. Overall, this work demonstrates critical limitations of the thiol-ene functionalization method as well as their origin when applied to differently substituted pendant groups.

Poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith with bonded Tris ligands for use in hydrophilic interaction capillary electrochromatography

The facile preparation of a monolithic capillary column with surface bound polar ligands for use in hydrophilic interaction capillary electrochromatography is described. It involved the conversion of poly(carboxyethyl acrylate[CEA]-co-ethylene glycol dimethacrylate[EDMA]) precursor monolith (the so-called carboxy monolith) into a Tris bonded monolith by a post-polymerization functionalization process in the presence of a water soluble carbodiimide, namely N-(3-dimethylaminopropyl)-N´-ethylcarbodiimidehydrochloride. The carbodiimide assisted conversion, allowed the covalent attachment of the carboxyl group of the precursor monolith to the amino group of the Tris ligand via a stable amide linkage. This resulted in the formation of Tris poly(CEA-co-EDMA) monolith, which exhibited the typical retention behavior of hydrophilic interaction stationary phase when analyzing polar and slightly polar neutral or charged compounds. In fact, neutral polar species such as dimethylformamide, formamide and thiourea were retained in the order of increased polarity with acetonitrile rich mobile phase. Also, neutral p-nitrophenyl maltooligosaccharides (PNP-maltooligosaccharides) served as a polar homologous series for gauging the hydrophilicity of the Tris poly(CEA-co-EDMA) monolith, thus forming a versatile testing homologous series for other hydrophilic columns. Other polar anionic species (e.g., hydroxy benzoic acids and nucleotides) and weakly polar anionic compounds (e.g., dansyl amino acids and phenoxy acid herbicides) as well as polar weak bases namely nucleobases and nucleosides were used to probe the hydrophilic characters of the Tris poly(CEA-co-EDMA) monolith. The various polar and weakly polar compounds just mentioned revealed the wide potentiality of the hydrophilic interaction column under investigation.

Modular Synthesis and Patterning of High-Stiffness Networks by Postpolymerization Functionalization with Iron-Catechol Complexes.

Bioinspired iron-catechol cross-links have shown remarkable success in increasing the mechanical properties of polymer networks, in part due to clustering of Fe3+-catechol domains which act as secondary network reinforcing sites. We report a versatile synthetic procedure to prepare modular PEG-acrylate networks with independently tunable covalent bis(acrylate) and supramolecular Fe3+-catechol cross-linking. Initial control of network structure is achieved through radical polymerization and cross-linking, followed by postpolymerization incorporation of catechol units via quantitative active ester chemistry and subsequent complexation with iron salts. By tuning the ratio of each building block, dual cross-linked networks reinforced by clustered iron-catechol domains are prepared and exhibit a wide range of properties (Young's moduli up to ∼245 MPa), well beyond the values achieved through purely covalent cross-linking. This stepwise approach to mixed covalent and metal-ligand cross-linked networks also permits local patterning of PEG-based films through masking techniques forming distinct hard, soft, and gradient regions.

The Rapid Mechanochemical Synthesis of Microporous Covalent Triazine Networks: Elucidating the Role of Chlorinated Linkers by a Solvent‐Free Approach

AbstractThe mechanochemical synthesis of porous covalent triazine networks (CTNs), exhibiting theoretically ideal C/N ratios and high specific surface areas, is presented. Employing this solvent‐free approach allows to minimize the ecological impact of the synthesis by bypassing hazardous wastes, while simultaneously observing the reactions between the individual starting materials separately for the first time. Especially the role of dichloromethane needs to be reconsidered, functioning as a linker between the nitrogen‐containing node cyanuric chloride and the aromatic monomer 1,3,5‐triphenylbenzene, as proven by X‐ray photoelectron spectroscopy and 1H → 13C Cross‐Polarization magic‐angle‐spinning nuclear magnetic resonance spectroscopy. This results in a drastic enhancement of the reaction rate, reducing the synthesis time down to 1 minute. Additionally, this linkage over a C1 bridge enables the incorporation of nitrogen into already synthesized polymers by post polymerization functionalization. The variation of the synthesis building blocks, namely the linker, node, and monomer, results in a variety of nitrogen‐containing polymers with specific surface areas of up to 1500 m2 g−1. Therefore, the presented approach is capable to target the synthesis of various CTNs with a minimal use of chlorinated linker, rendering the concept as a sustainable alternative to the classical solution‐based synthesis.

Tunable control of the performance of aqueous-based electrochemical devices by post-polymerization functionalization.

Functionalized polymeric mixed ionic-electronic conductors (PMIECs) are highly desired for the development of electrochemical applications, yet are hindered by the limited conventional synthesis techniques. Here, we propose a "graft-onto-polymer" synthesis strategy by post-polymerization functionalization (GOP-PPF) to prepare a family of PMIECs sharing the same backbone while functionalized with varying ethylene glycol (EG) compositions (two, four, and six EG repeating units). Unlike the typical procedure, GOP-PPF uses a nucleophilic aromatic substitution reaction for the facile and versatile attachment of functional units to a pre-synthesized conjugated-polymer precursor. Importantly, these redox-active PMIECs are investigated as a platform for energy storage devices and organic electrochemical transistors (OECTs) in aqueous media. The ion diffusivity, charge mobility and charge-storage capacity can be significantly improved by optimizing the EG composition. Specifically, g2T2-gBT6 containing the highest EG density gives the highest charge-storage capacity exceeding 180 F g-1 among the polymer series, resulting from the improved ion diffusivity. Moreover, g2T2-gBT4 with four EG repeating units exhibits a superior performance compared to its two analogues in OECTs, associated with a high μC* up to 359 F V-1 cm-1 s-1, owing to the optimal balance between ionic-electronic coupling and charge mobility. Through the GOP-PPF, PMIECs can be tailored to access desirable performance metrics at the molecular level.

Poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith with bonded (S)-(-)-1-(2-naphthyl) ethylamine ligands for use in chiral and achiral separations by capillary electrochromatography

In this research report, the previously developed poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith (referred to as carboxy monolith) is further exploited in the preparation of a chiral stationary phase for enantiomeric separations. The carboxy monolith precursor was subjected to post polymerization functionalization (PPF) with the chiral selector (S)-(-)-1-(2-naphthyl) ethylamine (NAS) at room temperature in the presence of N, N´-dicyclohexylcarbodiimide (DCC) in chloroform. The DCC, which is an organic soluble carbodiimide, permits the linkage for the amine functionality of the chiral ligand NAS to the carboxy group of the monolithic surface forming a stable amide linkage. The NAS column thus obtained allowed not only enantiomeric separations in the RP mode via its chiral site but also the separation of nonpolar species via its achiral functionality offering both hydrophobic and π-π interactions for aromatic compounds such toluene derivatives and polyaromatic hydrocarbons. The dual interaction sites (e.g., chiral, and achiral) of the NAS present a convenient column for the separations of slightly polar and nonpolar chiral and achiral solutes in the RP mode.