Chemo-enzymatic synthesis of comb polymers

The paper describes the synthesis and characterization of comb polymers by a two-step chemo-enzymatic process. In the first step macromonomers bearing unsaturation at the chain end were prepared by lipase catalyzed ring-opening polymerization (ROP) of ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO). The ROP was carried out in bulk at 60 °C under anhydrous conditions using 2-hydroxyethyl methacrylate (HEMA) as the initiator. The DP of the macromonomers was controlled by regulating the monomer: HEMA molar feed concentration. The macromonomers were then homo- or co-polymerized in the second step with alkyl methacrylate monomers (methyl methacrylate or HEMA) using AIBN initiated free radical polymerization. Characterization of the polymers was done by ¹H NMR, SEC and DSC techniques.     

Supramolecular pseudorotaxane polymers from complementary pairs of homoditopic molecules

Self-assembly of supramolecular pseudorotaxane polymers from complementary homoditopic building blocks comprised of bis(dibenzo-24-crown-8) esters derived from the hydroxymethyl crown ether and aliphatic diacid chlorides (CxC, x = number of methylene units in the diacid segment) and 1,10-bis[p-(benzylammoniomethyl)phenoxy]alkane bis(hexafluorophosphate)s (AyA, y = number of methylene units in the linker) has been studied. (1)H NMR spectroscopic studies of bis[(2-dibenzo-24-crown-8)methyl] sebacate (C8C) with dibenzylammonium hexafluorophosphate (6) showed that the two binding sites of the ditopic host are equivalent and independent (no positive or negative cooperativity). Likewise the binding sites in 1,10-bis[p-(benzylammoniomethyl)phenoxy]decane bis(hexafluorophosphate) (A10A) were shown to behave independently with dibenzo-24-crown-8 (1a). Then using (1)H NMR spectroscopy on dilute equimolar solutions (<1 mM) of CxC and AyA association constants were estimated for the formation of the linear (lin-CxC*AyA) and cyclic (cyc-CxC*AyA) dimers, thus enabling effective molarities to be estimated for the various systems. Finally (1)H NMR spectroscopy was used to semiquantitatively or qualitatively demonstrate the formation of linear supramolecular polymers lin-[CxC*AyA](n) in more concentrated solutions (up to 2.0 M) of the complementary pairs of CxC and AyA. The sizes of the assemblies (n values) are not as great as the dilute solution studies predict; this is attributed to the deleterious effect of ionic strength and exo complexation at high concentrations. However, as expected from the dilute solution results, linear extension is indeed favored with the longer building blocks, meaning that "monomer" end-to-end distance is a key factor in reducing the amount of cyclic species that form. Viscosity experiments clearly demonstrate the formation of large noncovalent polymers lin-[CxC*AyA](n) in concentrated solutions. Cohesive film and fiber formation also indicate that supramolecular polymers of sufficient size to enable entanglement self-assemble in these solutions.     

Supramolecular polymers: from scientific curiosity to technological reality

Supramolecular polymers^[1] are introduced as a new approach to come to materials in which the repeating units are not connected by covalent bonds but by specific secondary interactions. Self-complementary quadruple hydrogen bonded structures with high association constants are presented as easy to synthesize fragments in supramolecular polymers. Some of the many possibilities of equilibrium polymers are discussed, while it is shown that these supramolecular polymers can obtain materials properties normally only obtained with macromolecules.     

Supramolecular polymers having chiral interactions

Poly(L-glutamate) having amphiphilic side chains was designed as membrane materials for optical resolution of α-amino acids. Solvent-cast films of the poly(glutamate) (PLG) had a self-ordered structure containing α-helix of the poly(L-glutamate). Optical resolutions of various amino acids were carried out through the thin membranes of the amphiphilic poly(L-glutamate). Racemic mixtures of Tryptophan were completely separated through the membrane. Mechanism of the optical resolutions was investigated in terms of molecular recognitions of racemic Tryptophan by the ordered structure of the membrane. Polymers having pendant PLG and α-amino acids were synthesized and their permeation behaviors were investigated.     

Size exclusion chromatography of branched polymers: Star and comb polymers

Monte Carlo simulations were conducted to estimate the elution curve of size exclusion chromatography (SEC). The present simulation can be applied to various types of branched polymers, as long as the kinetic mechanism of nonlinear polymer formation is given. We considered two types of detector systems, (1) a detector that measures the polymer concentration in the elution volume to determine the calibrated molecular weights, such as by using the differential refractive index detector (RI), and (2) a detector that determines the weight‐average molecular weight of polymers within the elution volume directly, such as a light scattering photometer (LS). For polydisperse star polymers, both detector systems tend to give a reasonable estimate of the true molecular weight distribution (MWD). On the other hand, for comb‐branched polymers, the RI detector underestimates the molecular weight of branched polymers significantly. The LS detector system improves the measured MWD, but still is not exact. The present simulation technique promises to establish various types of complicated reaction mechanisms for nonlinear polymer formation by using the SEC data quantitatively. In addition, the present technique could be used to reinvestigate a large amount of SEC data obtained up to the present to estimate the true MWD.     

Supramolecular polymers based on dative boron-nitrogen bonds

Heteroditopic monomers containing an arylboronate ester and a dialkyl-4-aminopyridine group aggregate via dative boron-nitrogen bonds to give main chain supramolecular polymers. The degree of polymerization can be tuned by changing the electronic and steric properties of the boronate ester.     

Synthesis and liquid-crystalline behaviour of liposaccharide based comb polymers

In order to investigate the relationship between the liquid-crystalline state and the biological properties of polymers, we synthesized and studied liquid-crystalline comb polymers with a polyacrylamide main chain and three types of lipo-saccharidic side chains. These comb polymers were synthesized in four steps: first the polymerizable group was linked to the amino end of an α,ω-aliphatic amino acid; in the second step the ω-carboxylic acid function was activated in the form of an N-hydroxysuccinimidylester; in the third step the active ester was aminolysed by the amine function of the saccharide (N-methyl-D-glucamine, 2-amino-2-deoxy-β-D-glucose or 1-amino-1-deoxy-β-D-galactose) and a polymerizable liposaccharide was obtained; finally the liposaccharides were transformed into comb polymers by free-radical polymerization. Comb polymers exhibit mesophases in concentrated aqueous, ethanol or dimethylsulphoxide solution, and their mesomorphic character remains after the slow evaporation of the solvent. X-ray diffraction studies have shown that the mesophases have smectic or nematic ordering, depending upon the nature of the saccharidic residues of the liposaccharidic side chains.     

Supramolecular nanoribbons and nanoropes generated from hydrogen-bonded supramolecular polymers containing perylene bisimide chromophores

A perylene bisimide anchored with melamine hydrogen-bonding units has been prepared, and its supramolecular polymerization upon binding with N-dodecylcyanurate (CA) was examined. The resulting flexible supramolecular polymers self-organized via a pi-pi stacking interaction between perylene chromophores, affording ribbonlike aggregates in cyclic alkanes and ropelike aggregates in acyclic alkanes to form gels. [structure: see text]     

Supramolecular recognition of estrogens via molecularly imprinted polymers

The isolation and preconcentration of estrogens from new types of biological samples (acellular and protein-free simulated body fluid) by molecularly imprinted solid-phase extraction has been described. In this technique, supramolecular receptors, namely molecularly imprinted polymers (MIPs) are used as a sorbent material. The recognition sites of MIPs were prepared by non-covalent multiple interactions and formed with the target 17β-estradiol as a template molecule. High-performance liquid chromatography with spectroscopic UV, selective, and a sensitive electrochemical CoulArray detector was used for the determination of 17β-estradiol, estrone, and estriol in simulated body fluid which mimicked human plasma.     

Surface-initiated polymerization of conjugated polymers

In this feature article, we highlight the recent developments in the chain growth polymerization mechanism of conjugated polymers. With a particular emphasis on Kumada catalyst-transfer polycondensation, this article focuses on the surface-initiated polymerization of conjugated polymers, along with the opportunities and challenges associated with this technique.     

Supramolecular polymers constructed by crown ether-based molecular recognition

Supramolecular polymers, polymeric systems beyond the molecule, have attracted more and more attention from scientists due to their applications in various fields, including stimuli-responsive materials, healable materials, and drug delivery. Due to their good selectivity and convenient enviro-responsiveness, crown ether-based molecular recognition motifs have been actively employed to fabricate supramolecular polymers with interesting properties and novel applications in recent years. In this tutorial review, we classify supramolecular polymers based on their differences in topology and cover recent advances in the marriage between crown ether-based molecular recognition and polymer science.     

Supramolecular polymers as dynamic multicomponent cellular uptake carriers

Supramolecular synthesis represents a flexible approach to the generation of dynamic multicomponent materials with tunable properties. Here, cellular uptake systems based on dynamic supramolecular copolymers have been developed using a combination of differently functionalized discotic molecules. Discotics featuring peripheral amine functionalities that endow the supramolecular polymer with cellular uptake capabilities were readily synthesized. This enabled the uptake of otherwise cell-impermeable discotics via cotransport as a function of supramolecular coassembly. Dynamic multicomponent and multifunctional supramolecular polymers represent a novel and unique platform for modular cellular uptake systems.     

Supramolecular polymerization of oligopyrenotides--control by single, natural nucleotides

Amphiphilic heptapyrenotides (Py(7)) assemble into supramolecular polymers. Here we present a comprehensive spectroscopic study of aggregates and co-aggregates of the non-chiral Py(7) and its mono- or di-substituted nucleotide analogs (Py(7)-N and N-Py(7)-N'). The data show that the formation of supramolecular polymers from oligopyrenotides is highly sensitive to the nature of the attached, chiral auxiliary. A single natural nucleotide may be sufficient for the fine tuning of the aggregates' properties by changing the mechanism of aggregation from an isodesmic to a nucleation-elongation process, which results in a high degree of amplification of chirality in the formed supramolecular polymers. Watson-Crick complementarity does not play a significant role, since co-aggregates of oligomers modified with complementary nucleotides show no signs of supramolecular polymerization. Depending on the nucleotide, the helical sense of the polymers is shifted to an M-helix or a P-helix. The findings demonstrate the value of oligopyrenotides as oligomeric building blocks for the generation of optically active supramolecular polymers.     

From comb polymers to polysoaps: a Monte Carlo attempt

The pivot algorithm is used on a cubic lattice to study comb polymers large enough to have side-chains obeying scaling behaviour. The connectivity of the chain induces the formation of side-chain clusters whose size distribution is investigated as a function of side-chain length n and spacer length m. When an attractive interaction is set between the side-chains, the comb polymer displays the behaviour of an associating polymer below the critical aggregation concentration, as observed experimentally.     

Supramolecular liquid crystallinity as a mechanism of supramolecular polymerization

Two types of supramolecular self-assembling polymers should be distinguished: the open type characterized by units with binding sites exposed to the surface and thus capable of extended growth (e.g. some synthetic and natural supramolecular polymers), and the closed type with binding sites internally compensated yielding well defined oligomeric complexes (e.g. DNA, collagen,haemoglobin). The growth of the open assemblies may be defined as a supramolecular polymerization. Both types form corresponding supramolecular liquid crystalline (SLC) phases, but the behaviour of the closed-type SLC is generally indistinguishable from that of liquid crystals formed by molecularly dispersed units. Quite different is the case of the open-type SLC when the anisotropic forces stabilizing the nematic phase interact with the contact forces that promote the growth of theassembly. In this case a cooperative enhancement of growth occurs simultaneously with the formation of the ordered phase. The theoretical basis for the growth coupled to orientation mechanism, laid down to explain the formation of linear micelle aggregates, may apply to most types of supramolecular polymerization. Outstanding resulting expectations are a large degree of supramolecular polymerization, orientation, superimposition of other growth mechanisms, dampened polydispersity and termination steps.     

Controlled synthesis of thermoresponsive polymers derived from L-proline via RAFT polymerization

Well-defined polymers derived from L-proline are synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization and the amino acid-based polymers exhibit thermosensitive phase separation at lower critical solution temperatures (LCST = 15-45 degrees C) in aqueous medium.     

Supramolecular main chain liquid crystalline polymers utilizing azopyridine derivatives

A series of main chain liquid crystalline polymers were formed through intermolecular hydrogen bonding between a functionalized bisazopyridine phenol and aromatic bisacids. The behaviour of these complexes was studied through differential scanning calorimetry and thermal polarizing optical microscopy. The presence of the hydrogen bonds was confirmed through infrared spectroscopy. These complexes formed thermotropic mesophases. The phases were determined to be nematic in nature from the schlieren textures of the optical micrographs. As the length of flexible spacer groups separating the mesogenic portions increased, the clearing temperatures of the mesophases decreased. As the length of the rigid component increased, the clearing temperature increased. A new bisacid species based on 2-hydroxy-6-naphthoic acid was used to increase clearing temperatures while remaining within an acceptable temperature window.