Synthesis and helix-sense-selective polymerization of a novel phenylacetylene having a trisiloxanyl group and two hydroxyl groups and enantioselective permeability of the resulting chiral polymeric membrane: Effect of the trisiloxanyl group on the polymerization and enantioselective permeability

To develop a new phenylacetylene monomer suitable for helix-sense-selective polymerization (HSSP) we reported previously and to improve the efficiency of the HSSP and membrane performance of the resulting polymer, a novel phenylacetylene having a trisiloxanyl group (S3BDHPA) was synthesized and polymerized by using a chiral catalytic system and enantioselectivity in permeation of its membrane was examined. S3BDHPA was suitable for the HSSP and the CD absorption of poly(S3BDHPA) was stronger and more stable than that of the corresponding polymer having no siloxanyl groups. In addition, enantioselectivity in permeation of poly(S3BDHPA) was much higher than that of a polymer membrane having no siloxanyl groups. They are thought to be caused by the flexibility and hydrophobicity of the trisiloxane groups.     

A fluorescence sensor based on chiral polymer for highly enantioselective recognition of phenylalaninol

The chiral polymer P-1 incorporating (S)-2,2′-binaphthol (BINOL) and (S)-2,2′-binaphthyldiamine (BINAM) moieties in the main chain of the polymer backbone was synthesized by the polymerization of (S)-6,6′-dibutyl-3,3′-diformyl-2,2′-binaphthol (S-M-1) with (S)-2,2′-binaphthyldiamine (S-M-2) via nucleophilic addition-elimination reaction, and the chiral polymer P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence intensity of the chiral polymer P-1 exhibits gradual enhancement upon addition of (d)- or (l)-phenylalaninol and keeps nearly a linear correlation with the concentration molar ratios of (d)- or (l)-phenylalaninol. The value of enantiomeric fluorescence difference ratio (ef) is 6.85 for the chiral polymer on (d)-phenylalaninol. On the contrary, the chiral polymer P-2 shows no obvious fluorescence response toward either (d)- or (l)-phenylalaninol.     

Stereoelective polymerization of racemic propylene oxide using a diethylzinc-chiral-1,2-diol system as initiator

The polymerization of racemic propylene oxide was performed using a chiral initiator obtained from the reaction of diethylzinc with (?) 3,3-dimethyl-1,2-butanediol. With this initiator R(+) enantiomer is preferentially incorporated into the polymer with a stereoelectivity ratio r equal to 1.8, the r value remaining constant during the polymerization. The polymer was fractionated into a crystalline isotactic part and an amorphous heterotactic part, both optically active. Partial stereoelectivities were determined for both fractions and found to be equal to 2.6 and 1.6 respectively for polymerization at 80°C. Two types of sites, stereospecific and non-stereospecific, formed in the first reaction between monomer and initiator are both active for the stereoelective polymerization. The stereospecificity of the monomer-initiator system increased at low temperatures, but the overall stereoelectivity remained constant and seemed to be an intrinsic property of the system.     

Kinetics of ‘living’ radical polymerizations of multifunctional monomers

The polymerizations of multifunctional monomers with an iniferter, p-xylylene bis-(N,N-diethyldithiocarbamate) (XDT), were studied with differential photocalorimetry. The iniferter was used to simulate a ‘living’ radical polymerization. The normal autoacceleration behavior that is often observed in the polymerization of multifunctional monomers was not evident in the reactions with the iniferter. The reversible reaction between the propagating polymer chain and the sulfur radical from the XDT molecule dominated the reaction and drastically decreased the rate of polymerization. Various parameters of the reaction (length between functional groups in the monomer, iniferter concentration, UV light intensity, and temperature) were investigated to determine the effect on the polymerization. The rate of polymerization and the final conversion of the polymer were increased significantly by increasing the temperature, initiator concentration and UV light intensity, and decreasing the length between functional groups. Mechanical properties of the resulting polymers were also examined. It was concluded that the presence of the iniferter during the polymerization of the multifunctional monomers had no effect on the heterogeneity of the polymer network. This was in agreement with previous modeling results.     

Patterning a π-conjugated polyelectrolyte through sequential polymerization of a bifunctional ionic liquid monomer

An electronically conductive polyelectrolyte is prepared by the sequential polymerization of a bifunctional imidazolium-based ionic liquid (IL) monomer, composed of a thienyl and vinyl containing cation paired with a tetrafluoroborate anion. In the first step, potentiodynamic electropolymerization of the thienyl moiety forms a cationic polyalkylthiophene that is soluble in select organic solvents. Cyclic voltammetry (CV) was used to determine the polymer p-doping potential (0.31 V) and the bipolaronic state (1.49 V). The polymer exhibits electrochromism, converting from red in the neutral state (λ_max = 443 nm) to dark blue in the polaronic state (λ_max = 819 nm). The solution-processable polymer can be cast into a film, masked and patterned by UV-initiated free radical polymerization of the vinyl moiety. Small-angle X-ray scattering (SAXS) revealed that the insoluble crosslinked polyalkylthiophene–polyvinylimidazolium adopts a lamellar structure with a lattice spacing of 3.3 nm. Four-probe d.c. conductivity measurements determined the de-doped electrical conductivity was 1.0 × 10⁻² S/cm. The results underscore the importance of the anion in controlling the polymerization of IL monomers.     

Studies with microgels as matrices for molecular receptor and catalytic sites: stereoselectivity of copolymers of (−)-menthyl acrylate and N-methacryloyl-hydroxylamineversus chiral esters

The reactivity of 4-nitrophenyl esters has been studied against an optically active microgel copolymer containing hydroxamic acid pendant groups. Saturation phenomena are observed in the kinetics consistent with formation of a complex followed by reaction of the ester in the complexed species. The polymer discriminates between R- and S-forms of a chiral substrate in both complexing and catalytic steps. The data are consistent with the existence of chiral spaces in the microgel bead which accept the chiral substrate. The selectivity of the polymer for the chiral substrate (α ～ 2) compares favourably with that shown by conventional chiral chromatographic supports.     

Optically active thermosensitive amphiphilic polymer brushes based on helical polyacetylene: preparation through “click” onto grafting method and self-assembly

Optically active, thermosensitive, and amphiphilic polymer brushes, which consist of helical poly(N-propargylamide) main chains and thermosensitive poly(N-isopropylacrylamide) (PNIPAm) side chains, were prepared via a novel methodology combining catalytic polymerization, atom transfer radical polymerization (ATRP), and click chemistry. Helical poly(N-propargylamide) bearing α-bromoisobutyryl pendent groups was synthesized via catalytic polymerization, followed by substituting the –Br moieties with azido groups. Then, alkynyl terminated PNIPAm formed via ATRP was successfully grafted onto the azido functionalized helical polymer backbones via click chemistry, providing the expected polymer brushes. GPC, FT-IR, and ¹H-NMR measurements indicated the successful synthesis of the novel amphiphilic polymer brushes. UV–vis and CD spectra evidently demonstrated the helical structures of the polymer backbones and the considerable optical activity of the final brushes. The polymer brushes self-assembled in aqueous solution forming core/shell structured nanoparticles, which were comprised of optically active cores (helical polyacetylenes) and thermosensitive shells (PNIPAm).     

Ultrasonic assisted organo-modification of mesoporous SBA-15 with N-trimellitylimido-l-methionine and preparation of the poly(amide–imide)/SBA nanocomposites

Mesoporous SBA-15 materials were functionalized with N-trimellitylimido-l-methionine through ultrasonic irradiation, and the resulting functionalized materials were investigated as reinforcing agent for the preparation of the polymer based nanocomposites (NCs). An optically active and organo-soluble l-methionine containing poly(amide–imide) (PAI) was synthesized by the direct step-growth polymerization reaction of the above chiral diacid and 3,5-diamino-N-(pyridin-3-yl) benzamide in molten tetrabutylammonium bromide as a green solvent. A simple solution blending process was used to efficiently disperse modified-SBA into the chiral PAI to obtain PAI/modified-SBA NCs. The obtained NCs were characterized by Fourier transform-infrared spectroscopy, thermogravimetry analysis (TGA), X-ray diffraction, field emission-scanning electron microscopy, and transmission electron microscopy (TEM) techniques. TGA data indicated an increasing in thermal stability of the NCs when compared to the pure polymer. TEM images show well-ordered hexagonal arrays of mesopores SBA and the average distances between neighboring pores is around 3–5 nm.     

Dye-labelled polymer chains at specific sites: Synthesis by living/controlled polymerization

Dye-labelled polymer chains are extremely useful in many fields, such as optical imaging, signal amplification in biological diagnostics, light-harvesting and photochromic materials as well as in fluorescence studies about intra- and inter-molecular polymer chain associations, conformations and dynamics of polymer chains. However, in many cases, it is particularly useful that the dye is localized at a specific site, such as the chain-end or the junction between blocks. With the development of living/controlled polymerization techniques, end- and junction-functionalized polymers can be prepared with controlled molecular weights from a huge variety of monomers. This review highlights the state of the art in the strategies leading to one and only one precisely localized dye per polymer chain. Such dye can be introduced at three different steps of the polymerization: i) at the very beginning via the initiator or a chain transfer agent, ii) during polymerization via a functional monomer or a quencher, or iii) after polymerization via covalent binding of a dye-derivative.     

Allyl functionalized telechelic linear polymer and star polymer via RAFT polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene using bisallyl trithiocarbonate as a chain transfer agent (CTA) was studied. The polymerization exhibited first-order kinetics and the molecular weight increased linearly with increase of monomer conversion. Well defined allyl-functionalized telechelic polystyrene (PS), poly(tert-butyl acrylate) (PtBA) and corresponding triblock copolymers, polystyrene-b-poly(n-butyl acrylate)-b-polystyrene (PS-b-PnBA-b-PS) and poly(tert-butyl acrylate)-b-polystyrene-b-poly(tert-butyl acrylate) (PtBA-b-PS-b-PtBA) were prepared as characterized with GPC and NMR analysis. The allyl-end groups of the telechelic PS have been switched to 1,2-dibromopropyl groups quantitatively by bromine addition reaction, further substitution of the bromide with azide was also made. Furthermore, star PS with allyl-end-functionalized arms was synthesized by RAFT polymerization of divinyl benzene using allyl-functionalized PS as a macro-CTA via arm-first approach. Star polymer with a thiol-functionalized core was generated by aminolysis reaction of the star polymer and ethylenediamine. As a result, difunctionalized star polymer with allyl and thiol groups was obtained and was used as a stabilizer for the formation of gold nanoparticles.     

A highly selective and sensitive fluorescence chemosensor based on optically active polybinaphthyls for Hg

The chiral polymer was synthesized by the polymerization of 4,7-diethynylbenzo[2,1,3]-thiadiazole (M-1) with (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bis(diethylaminoethoxy)-1,1′-binaphthyl (R-M-1) via Pd-catalyzed Sonogashira reaction. The chiral polymer has orange fluorescence due to the extended π-electronic structure between binaphthyl unit and benzo[2,1,3]thiadiazole (BT) group via ethynyl bridge. The responsive optical properties of the polymer on various metal ions were investigated by fluorescence spectra. The fluorescence of the chiral polymer can produce the pronounced enhancement as high as 1.8-fold upon addition of 1:2 molar ratio of Hg²⁺. Compared with other cations, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Zn²⁺, Mn²⁺ and Fe³⁺, Hg²⁺ can produce the pronounced fluorescence response of the polymer. The result indicates this kind of chiral polybinaphthyls incorporating diethylamino and benzo[2,1,3]thiadiazole (BT) moieties as receptors exhibits highly sensitive and selective behavior for Hg²⁺ detection.     

In situ Cu(II)-containing chiral polymer complex sensor for enantioselective recognition of phenylglycinol

A chiral polymer P1 was synthesized by the polymerization of 2,5-dibutoxy-1,4-di(benzaldehyde)-1,4-diethynylbenzene (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via Schiff's base formation, and the chiral polymer P2 could be obtained by the reduction reaction of P1 with NaBH₄. P2 can serve as a “turn-off” fluorescent sensor toward Cu²⁺ and Ni²⁺. The in situ generated Cu(II)-containing polymer complex of P2 (Cu(II)-P2) can exhibit remarkable “turn-on” fluorescence enhancement response and considerable enantioselectivity toward unmodified phenylglycinol via a ligand displacement mechanism. More importantly, (R,R)-Cu(II)-P2 solution can turn on bright blue fluorescence color change again upon addition of l-phenylglycinol under a commercially available UV lamp, which can be clearly observed by the naked eyes for direct visual discrimination at low concentration. The simple, rapid and sensitive benign process makes this protocol promising for recognition of phenylglycinol enantiomers.     

Effect of nitrobenzene on initiator-fragment incorporation radical polymerization of divinylbenzene with dimethyl 2,2′-azobisisobutyrate

The polymerization of divinylbenzene (DVB) with dimethyl 2,2′-azobisisobutyrate (MAIB) was conducted at 70 and 80 °C in benzene in the presence of nitrobenzene (NB) as a retarder. When the concentrations of DVB, MAIB, and NB were 0.45, 0.50, and 0.50 mol/l, respectively, the polymerization proceeded without any gelation to yield soluble polymers. The polymer yield (up to 65%) and the molecular weight (M_n=1.5-4.2×l0⁴ at 70 °C and 1.3-3.9×l0⁴ at 80 °C) increased with time. The polymer formed in the polymerization at 80 °C for 4 h consisted of the DVB units with (4 mol%) and without double bond (41 mol%), methoxycarbonylpropyl group as MAIB-fragment (48 mol%), and NB unit (7 mol%). Incorporation of such a large number of the initiator-fragments as terminal groups in a polymer molecule indicates that the polymer is of a hyperbranched structure. The polymer showed an upper critical solution temperature (40 °C on cooling) in an acetone-water [14:1 (v/v)] mixture. The results of MALLS and viscometric measurements and TEM observation supported that the polymers formed in the present polymerization have a hyperbranched structure. The polymerization system at 70 °C involved an ESR-observable nitroxide radical formed by the addition of polymer radical to the nitro group of NB. The polymerization was kinetically investigated in dioxane. The initial polymerization rate (R_p) at 70 °C was expressed by R_p=k[MAIB]^0.5[DVB]^0.9[NB]^−0.4. The kinetic results were explained on the basis of the reversible addition of polymer radical to NB and the termination between the polymer radical and the nitroxide radical. The overall activation energy of the polymerization was 27.8 kcal/mol.     

Polymerization kinetics for the preparation of poly(p-divinylbenzene) via a miniemulsion polymerization process

The polymerization kinetics for the preparation of poly(p-divinylbenzene (p-DVB)) via a miniemulsion polymerization process was studied by the gravimetric analysis and the transmission electron microscopy (TEM) analysis. The influence of the variation of both initiator concentration and polymerization temperature on the polymerization rate was investigated and also the activation energy of p-divinylbenzene was estimated. The evolution of polymer particles was observed by the electronmicrographs and the relatively large size of polymer particles without the formation of coagulum was obtained in the miniemulsion polymerization process.     

A facile strategy for preparation of single-chain polymeric nanoparticles by intramolecular photo-crosslinking of azide polymers

A series of well-defined azide polymers, poly(styrene-co-4-vinylbenzyl azide) with different content of azide groups, were synthesized by RAFT polymerization. The single-chain polymeric nanoparticles were then facilely prepared via single polymer chain collapse and intramolecular crosslinking reaction of the azide polymer in a dilute solution at room temperature under UV irradiation within several minutes. The polymeric nanoparticles were characterized with ¹H NMR, GPC, DSC, TEM and DLS measurements, and the mean diameter of the nanoparticles was evaluated to be 5.5 ± 0.8 nm in the dry state. Furthermore, the polymeric nanoparticles containing azide groups were successfully used to prepare the single-chain polymeric fluorescent nanoparticles via click reaction with N-propargyl carbazole.     

Molecular weight effect on polymer dissolution: a steady state fluorescence study

In situ steady state fluorescence (SSF) technique was used to study the dissolution of disc-shaped polymer glasses in various molecular weights, M_W. The glass discs were formed by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the dissolution process in chloroform. Desorption of poly(methyl methacrylate) (PMMA) chains from discs were monitored simultaneously by observing the change of P fluorescence intensity, I. Diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It is observed that desorption coefficient, D decreased by increasing molecular weight, M_W by obeying D≈M⁻¹ law.     

Control of main chain structure and possibility of molecular weight control of polymer on polymerization of vinyl chloride with tert-butyllithium

The controlled polymerization of vinyl chloride (VC) with tert-butyllithium (tert-BuLi) was investigated. The polymerization of VC with tert-BuLi at −30 °C proceeded to give a high molecular weight polymer in good yield. In the polymerization of VC −30 to 0 °C under nearly bulk, the relationship between the M_n of polymers and polymer yields gave a straight line passed through the origin, but the M_w/M_n of PVC was not narrow. When CH₂Cl₂ was used as polymerization solvent, the M_n of PVC increased with the polymer yield, and the M_w/M_n of 1.25 was obtained. Structure analysis of the resulting polymers indicates that the main chain structure could be regulated in the polymerization of VC with tert-BuLi. Accordingly, a control of molecular weight of polymer and main chain structure is possible in the polymerization of VC with tert-BuLi.     

Effects of chemical structure of phenolic antioxidants on Ziegler–Natta catalyst performance during propylene polymerization

Present work studied the synthesis of in-reactor stabilization of polypropylene via introducing antioxidant into polymerization media. Special attention was dedicated to assess the efficiency of antioxidant in catalyst deactivation. Three different types of antioxidants (Irganox 1076, Irganox 1010 and Irganox 1330) which contain ester and/or phenolic OH functional groups were chosen to investigate their impact on Ziegler–Natta catalyst performance during slurry propylene polymerization. Our Results indicated that not only phenolic OH groups but also esteric bond of antioxidants are capable of interacting with active center of catalyst and consequently decreasing the catalyst activity. Our propylene polymerization results showed that determining factors such as antioxidant chemical structures and its steric hindrance effect and the number of functional groups (phenolic and esteric groups) affected on the Ziegler–Natta catalyst performance. Therefore, effects of these three types of antioxidants on polymer characteristics such as particle size distribution, morphology, T _m , T _c , X _c , and isotacticity were evaluated. Morphological analysis using scanning electron microscopy (SEM) showed that introducing antioxidant during propylene polymerization did not destroy the spherical morphology of the polypropylene particles. Conclusively, due to the negative effect of esteric bond of antioxidant on Ziegler–Natta catalyst performance, the use of antioxidant without ester groups (Irganox 1330) is more recommended during propylene polymerization.     

Synthesis of polymers from chiral monomers in chiral liquid crystals

Polymer prepared from a monomer ((S)‐configuration at stereogenic center) in a cholesteric liquid crystal (CLC) medium consisting of chiral molecules in (R)‐configuration, a three‐dimensional (3D) chiral continuum, exhibits intense Cotton effect compared to polymer prepared in the CLC with (S)‐configuration. This result can be explained by intermolecular interaction between the monomer and the CLC medium in the polymerization process. The intramolecular twisted structure along the polymer chain (secondary structure) and the helical aggregation between the polymer chains (intermolecular structure and tertiary structure) induced by the liquid crystal medium as 3D chiral continuum are discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Chiral Polymers and Polymeric Particles for Enantioselective Crystallization

Chiral polymers and chiral polymeric particles have emerged as a new and exciting field of research in recent years mainly due to their possibly applications in chiral chemistry. This paper reviews the present state of the art regarding production techniques for the synthesis and applications of chiral polymeric particles. The main methods for preparing of chiral polymeric particles such as: direct polymerization, emulsion, precipitation, and suspension polymerization of chiral monomers, are reviewed. Moreover, in this article we also present the use of chiral polymers as chiral templates for the synthesis of chiral mesoporous materials. In this review we highlighted the properties and parameters involved in the preparation of these chiral polymeric materials. The present review focuses mainly on the use of chiral polymer and chiral polymeric particles for enantioselective crystallization and enantioseparation. References of the most relevant literature published by various research groups are provided. Anyway, it is clear that chiral polymeric particles are a distinctive type of chiral nanomaterials that can find many new application in other fields like, chiral drug delivery systems, enantioselective catalysis. We hope that this review article will inspired new researchers in this field and will boost the research dealing on chiral polymeric particles especially in their implementation in new areas in chiral chemistry.