Helix-sense-selective Polymerization Research Articles

Facile preparation of optically active helical polycarbenes with salicylate substituents and their postpolymerization modification.

Optically active helical polycarbenes were constructed through the living and controlled helix-sense-selective polymerization (HSSP) of methyl salicylate modified diazoacetate monomer catalysed via π-allylPdCl with chiral phosphine ligands. The obtained helical polycarbenes could undergo postpolymerization modification to afford functional polycarbenes efficiently.

Synthesis of Optically Active Helical Polycarbenes through Helix-Sense-Selective Polymerization Strategy and Their Application in Chiral Separation.

In this work, helical polycarbenes with optical activity were designed and facilely synthesized through the helix-sense-selective polymerization (HSSP) of the diazoacetate monomer with a dimethylbenzyl ester pendant catalyzed by π-allylPdCl with chiral phosphine ligands at room temperature. The polymerization was carried out in a living and controlled style, and a range of helical polycarbenes with the desired number-average molecular weights and narrow molecular weight distributions were obtained. Circular dichroism and UV-vis analyses revealed that these polycarbenes exhibited a stable helical conformation with a preferred handedness, and their helical directions were dependent on the chirality of the chiral phosphine ligands. Further studies showed that the helical conformation of the obtained polycarbenes was from the polymeric backbone rather than the intermolecular aggregation in the solutions. Moreover, the prepared, optically active, helical polycarbenes possessed excellent enantioselective crystallization ability for threonine racemates. The enantiomeric excess (e.e.) of the induced crystals could be up to 83% via utilizing the prepared helical polycarbenes as a chiral separation agent.

Helix-Sense-Selective Polymerization of Achiral Monomers for the Preparation of Chiral Helical Polyacetylenes Showing Intense CPL in Solid Film State.

Polymer-based circularly polarized luminescent (CPL) materials have attracted ever-increasing interest. However, to construct CPL materials from achiral monomers is still a big challenge. Here, a series of chiral helical substituted polyacetylenes are prepared by helix-sense-selective polymerization (HSSP) of achiral acetylenic monomers (achiral monomer + fluorescent monomer). HSSPs are accomplished in a bi-solvent mixture consisting of chloroform and chiral α-pinene (chiral component). Chirality transfers from the chiral component to the helical copolymers during polymerization, thereby endowing the copolymers with helical chirality. The resulting copolymers are then fabricated into blend films which exhibit intense optical activity and CPL. The monomer ratio and the physical state of the copolymers have significant impacts on their chiroptical and CPL properties. The maximum luminescence dissymmetry factor of the blend films can be up to 1.3 × 10-2 . The universality of the established strategy for exploring polymer-based CPL materials is demonstrated by using different achiral fluorescent monomers. The present work opens a novel alternative for developing CPL-active polymeric materials starting from achiral monomers.

Recent Advances in Polyallenes: Preparation, Self-Assembly, and Stimuli-Responsiveness.

Polyallenes, as a typical type of reactive polymers, are of great significance and have aroused widespread interest because they contain double bonds that can be post-modified into other functionalities to afford varieties of functional materials. This Minireview firstly highlights the recent advances in the preparation of polyallenes, including preparation of helical polyallenes through directly polymerization of chiral allene monomers or helix-sense-selective polymerization (HSSP) of achiral allene monomers, synthesis of 1,2-regulated polyallenes and 2,3-regulated polyallenes via selective polymerization of allene monomers, polymerization of allene monomers catalyzed by Ni(II)-terminated poly(3-hexylthiophene) (P3HT), and so on. Then, latest progress on the self-assembly and stimuli-responses of polyallene-based diblock, ABA and ABC triblock copolymers is summarized. We hope this Minireview will inspire more interest in developing polyallenes and encourage further advances in functional materials.

Chiral helical polymer materials derived from achiral monomers and their chiral applications

Helix-sense-selective polymerization (HSSP) of achiral monomers and chiral post-induction of racemic helical polymers provide two alternative approaches for constructing chiral helical polymer materials.

Helix-Sense-Selective Polymerization of 3,5-bis(hydroxymethyl)phenylacetylene Rigidly Bearing Galvinoxyl Residues and Their Chiroptical Properties.

Four kinds of newly synthesized achiral phenylacetylenes bearing a phenylhydrogalvinoxyl residue at 4-position were polymerized by using a chiral rhodium catalyst system, [Rh(nbd)B(C6H5)4] or [Rh(nbd)Cl]2 catalysts in the presence of chiral (R)-(+)- or (S)-(–)-1-phenylethylamine ((R)- or (S)-PEA) cocatalysts. Poly(m-HGDHPA) and poly(m-HGTHPA) in THF showed Cotton signals at the absorption regions of the main chain and hydrogalvinoxyl in the circular dichroism (CD) spectra. It indicated that excess of one-handed helical polyacetylene backbone was induced by helix-sense-selective polymerization (HSSP) under the asymmetric conditions despite the achiral monomer, and the hydrogalvinoxyl moieties were also arranged to form one-handed helical structure. However, there was no Cotton effect for poly(p-HGDHPA) and poly(p-HGTHPA) because the intramolecular hydrogen bonding did not act well to stabilize the helical conformation. The hydrogalvinoxyl units of poly(m-HGDHPA) and poly(m-HGTHPA) were converted to the corresponding galvinoxyl radicals after treatment with PbO2. In the CD spectra of the polyradicals, the Cotton effects decreased depending on their static stability of helical conformation, suggesting that reversal conformation of the polymer chain arose.

Stereocomplexation of Helical Polycarbodiimides Synthesized from Achiral Monomers Bearing Isopropyl Pendants

A high level of the permanent asymmetry was built into the poly(N-methyl-N′-(2-isopropyl-6-methylphenyl)carbodiimide) system by introducing a bulky, substituted phenyl group which revealed a very interesting phenomenological behavior upon heating. This polymer undergoes P/M racemization upon thermal annealing, thus leading to the formation of a stereocomplexed structure. Predominantly P and M helices have been obtained through helix sense selective polymerization by using chiral BINOL-Ti(IV) diisopropoxide initiator with achiral N-methyl-N′-(2-isopropyl-6-methylphenyl)carbodiimide monomer. Upon thermal annealing, the specific optical rotation (SOR) of the single-handed polymer begins to decrease but never reaches zero. The SOR plateaus at a large value (−286° for M helices or +283° for P helices), and shortly thereafter the polymer forms a precipitate. The process that polymer undergoes is attributed to stereocomplexation between two complementary strands via racemization. Inspired by the phenomena analog...

Optically Active Helical Polyacetylene Self-Assembled into Chiral Micelles Used As Nanoreactor for Helix-Sense-Selective Polymerization.

Chiral micelles have been drawing ever-increasing attention because of their potentials in mimicking the unique stereochemical effects of enzymes. This article reports on the first success in preparing chiral micelles through self-assembly of helical polyacetylene bearing cholic acid pendants. The micelles were further used as chiral nanoreactor, in which achiral acetylenic monomer smoothly underwent helix-sense-selective polymerization (HSSP). The HSSPs directly established optically active core/shell nanoparticles whose shell and core both were constructed by helical polymers. The shells (or micelles) provided a protective effect for the preferably induced one-handed helical polymer chains in the cores. The present work provides insights into the self-assembly of chiral helical polymers, and also provides a powerful strategy for constructing novel chiral polymer nanoarchitectures.

Synthesis of One-Handed Helical Block Copoly(substituted acetylene)s Consisting of Dynamic cis-transoidal and Static cis-cisoidal Block: Chiral Teleinduction in Helix-Sense-Selective Polymerization Using a Chiral Living Polymer as an Initiator.

By using a living one-handed helical cis-transoidal poly(chiral substituted phenylacetylene) as a polymer initiator (poly(1n)), helix-sense-selective polymerization (HSSP) of an achiral phenylacetylene 2 having two hydroxy groups successfully afforded a diblock copoly(phenylacetylene) (copoly(1n/2m)) consisting of a dynamic one-handed helical cis-transoidal block and a static one-handed helical cis-cisoidal block. The formation of the diblock structure was confirmed by consumption of the chiral initiator, appearance of characteristic CD indicating the one-handed helical cis-cisoidal block, and occurrence of the selective photocylic aromatization reaction in the cis-cisoidal block. Therefore, HSSP has been achieved by using the chiral alkenyl groups in the initiator as a chiral source for the first time. In addition, since the HSSP was achieved in spite of the long distance between the chiral initiation site and the propagating site, chiral teleinduction through the rigid and static one-handed helical cis-cisoidal block based on domino effects was confirmed.

Novel isolated, L-amino acid-ligated rhodium catalysts that induce highly helix-sense-selective polymerization of an achiral 3,4,5-trisubstituted phenylacetylene

Two novel chiral well-defined rhodium complexes, Rh(cod)(L-Phe) (cod = 1,5-cyclooctadiene, Phe = phenylalanine) and Rh(cod)(L-Val) (Val = valine) were synthesized, isolated by recrystallization, and characterized. The helix-sense-selective polymerization (HSSP) of an achiral 3,4,5-trisubstituted phenylacetylene, p-dodecyloxy-m,m-dihydroxyphenylacetylene (DoDHPA) was examined by using the two Rh complexes as catalysts. These catalysts provided high molecular weight polymers (Mw 28 × 104−45 × 104) in about 40%–85% yields. The resulting polymers exhibited a bisignated CD signal at about 300 nm and a broad signal around 470 nm, indicating that they have preferential one-handed helical structure. The present catalysts achieved larger molar ellipticity up to [θ]310 = 13.0 × 104 deg cm2/dmol than those with binary chiral catalytic systems, [Rh(cod)Cl]2/(L-phenylalaninol), [Rh(cod)Cl]2/(L-valinol), and [Rh(nbd)Cl]2/(R)-PEA. All these results manifest that the present, well-defined Rh complexes serve as excellent catalysts for the HSSP of DoDHPA. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2346–2351

Helix-Sense-Selective Precipitation Polymerization of Achiral Monomer for Preparing Optically Active Helical Polymer Particles

Optically active polymer particles constitute a unique type of polymer particle. However, nearly all the particles of this kind so far reported in the literature were prepared from chiral monomers. On the other hand, helix-sense-selective polymerization (HSSP) techniques were majorly applied in solution polymerization systems for preparing helical polymers adopting predominant one-handed helicity. In the present study, we report the first HSSP in precipitation polymerization systems, by which optically active helical polymer particles were constructed from an achiral monomer. Achiral acetylenic monomer with bulky adamantyl group smoothly underwent helix-sense-selective precipitation polymerization (HSSPP) with (nbd)Rh+B–(C6H5)4 as catalyst in the presence of Boc-l- or Boc-d-alanine as chiral additive. The HSSPPs provided optically active polymer particles consisting of helical polymer forming predominantly one-handed screw sense. SEM images show that the resulting polymer particles were obtained in high y...

Synthesis of a Fluorine-Containing Cis-Cisoidal One-Handed Helical Polyphenylacetylene and Application of Highly Selective Photocyclic Aromatization Product on Oxygen Permselective Membrane.

A novel phenylacetylene monomer having a perfluorinated alkyl group (M-F) was synthesized and polymerized in a chiral catalytic system to yield a one-handed helical polymer. The ability and efficiency of the chiral induction of the fluorine-containing monomer in the helix-sense-selective polymerization (HSSP) was much higher than those of a monomer having the corresponding alkyl group (M-H) we reported before. The resulting polymer showed cis-cisoidal one-handed helical conformation, and was suitable for highly selective photocyclic aromatization (SCAT) to give a 2D surface modifier (). Oxygen permselectivity through a base polymer membrane was highly enhanced from 1.83 to 2.36 by adding a small amount (1-5 wt%) of the 2D surface modifier . The improvement was thought to be caused by improvement of solution selectivity on the membrane surface which the 2D surface modifier effectively covered.

Helix-sense-selective Polymerization of Achiral Phenylacetylenes by Using One-handed Helical Poly(phenylacetylene)s as Chiral Cocatalysts Prepared by Helix-sense-selective Polymerization of Achiral Phenylacetylenes

Abstract We found that the helix-sense-selective polymerization (HSSP) of achiral phenylacetylenes having two hydroxy groups was realized by using one-handed helical poly(phenylacetylene)s as chiral cocatalysts prepared by HSSP of the same or similar achiral phenylacetylenes having two hydroxy groups. In other words, the chirality caused only by the one-handed helical backbone was found to be able to work as a cocatalyst in the chiral catalytic system. In addition, the efficiency of the chiral induction was high and almost the same as that of the HSSP by using enatiomerically pure phenylethylamine as a cocatalyst.

Helix-sense-selective Polymerization of Substituted Acetylenes by Using an Isolated Rh Chiral Initiator with an Amino Acid Ligand

Abstract Helix-sense-selective polymerization (HSSP) of substituted acetylenes by using an isolated chiral Rh initiator with an amino acid ligand has been achieved. The sense of the helix of the main chain of the resulting polymer was controlled by the sign of the chirality of the ligand. The isolated initiator needed less of the chiral ligand and gave polymers having a higher [θ] value than the two component chiral initiator systems we reported previously. The resulting polymers had a higher Mw.

Living-like helix-sense-selective polymerization of an achiral substituted acetylene having bulky substituents

By using a new achiral phenylacetylene having bulky substituents as a monomer, living-like helix-sense-selective polymerization (HSSP) has been achieved. This is the first example of the HSSP of substituted acetylenes where the degree of polymerization was controlled. The resulting one-handed helical living polymer initiated polymerization of a second monomer to successfully yield a block copolymer.

Two modes of asymmetric polymerization of phenylacetylenes having anL-amino alcohol residue and two hydroxy groups

Four novel chiral phenylacetylenes having an L-amino alcohol residue and two hydroxymethyl groups were synthesized and polymerized by an achiral catalyst ((nbd)Rh+[η6-(C6H5)B−(C6H5)3]) or a chiral catalytic system ([Rh(nbd)Cl]2/(S)- or (R)-phenylethylamine ((S)- or (R)-PEA)). The two resulting polymers having an L-valinol or L-phenylalaninol residue showed Cotton effects at wavelengths around 430 nm. This observation indicated that they had an excess of one-handed helical backbones. Positive and negative Cotton effects were observed only for the polymers having an L-valinol residue produced by using (R)- and (S)-PEA as a cocatalyst, respectively, although the monomer had the same chirality. Even when the achiral catalyst was used, the two resulting polymers having an L-valinol or L-phenylalaninol residue showed Cotton effects despite the long distance between the chiral groups and the main chain. We have found the first example of a new type of chiral monomer, that is, a chiral phenylacetylene monomer having an L-amino alcohol residue and two hydroxy groups that was suitable for both modes of asymmetric polymerization, that is, the helix-sense-selective polymerization (HSSP) with the chiral catalytic system and the asymmetric-induced polymerization (AIP) with the achiral catalyst. The other two monomers having L-alaninol and L-tyrosinol were found to be unsuitable to neither HSSP nor AIP because of their polymers' low solubility. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis of stable and soluble one-handed helical poly(substituted acetylene)s without chiral pendant groups via polymer reaction in membrane state

A soluble and stable one-handed helical conjugated polymer without the coexistence of any other chiral moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer having two hydroxyl groups followed by desubstitution of the chiral groups in a solid membrane state. The reason for the success was the polymer reaction was carried out in the membrane state. This is an alternative method to obtain such a unique chiral polymer which was obtained only by the helix-sense-selective polymerization (HSSP) we reported before. In addition the efficiency of the chiral induction was higher than that of the HSSP. It is interesting that the “Membrane state” acted like as if a protecting group.

New Achiral Phenylacetylene Monomers Having an Oligosiloxanyl Group Most Suitable for Helix-Sense-Selective Polymerization and for Obtaining Good Optical Resolution Membrane Materials

To develop new phenylacetylene monomers more suitable for helix-sense-selective polymerization (HSSP) we reported previously and to improve the efficiency of the HSSP and membrane performance of the resulting polymers, novel phenylacetylenes having a flexible oligosiloxanyl group (SnBDHPA) together with the other related three series of monomers were synthesized and polymerized by using a chiral catalytic system and enantioselectivity in permeation of the membranes from the resulting chiral polymers were examined. SnBDHPA was the most suitable for the HSSP and the CD absorptions (G values) of poly(SnBDHPA) were stronger and more stable than those of the corresponding polymers having rigid alkyl groups. The polymers could be fabricated to flexible self-supporting membranes by using solvent-casting method. In addition, enantioselectivity in permeation of one of poly(SnBDHPA) membranes was much higher than that of a poly(phenylacetylene) membrane having alkyl groups. This was because the polymers having oligosiloxane groups had high regularity of structures, i.e., chemical structures of the macromolecules such as one handedness and high order structures such as columnar contents in the membranes, and the membranes were flexible and had almost no defects. These good properties as optical resolution membrane materials were caused by flexibility, hydrophobicity, and bulkiness of the oligosiloxane chains. S3BDHPA having a trisiloxanyl group was found to be the best monomer for the HSSP and for obtaining good optical resolution membrane materials.

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.

Optically active helical structure and magnetic interaction of poly(phenylacetylene)-based polyradicals

We synthesized optically active polyradicals possessing an excess of one-handed helical backbone by helix-sense-selective polymerization (HSSP) of achiral monomers which was promoted by rhodium complex catalyst in the presence of ( R)- or ( S)-1-phenylethylamine. The monomer, which had two hydroxy groups and a hydrogalvinoxyl unit, gave the corresponding polymer with an optically active helical conformation stabilized by intramolecular hydrogen bonding. The chemical oxidation of the polymer yielded the corresponding optically active helical polyradical with high spin concentration. The static magnetic susceptibility of the chiral polyradical was measured using a SQUID magnetometer. We have found that the stronger antiferromagnetic interaction was observed for the polyradical synthesized by HSSP in comparison with the polyradical via polymerization in the presence of racemic phenylethylamine.