Janus Hybramers: Self-Adapting Amphiphilic Hyperbranched Polymers

Ultrafine Network-Like Monolayer Structures of Amphiphilic Hyperbranched Copolymers Revealed by the Relative Aggregation Number Method

The aggregation behavior of two amphiphilic hyperbranched copolymers of poly[oligo(ethylene glycol) methacrylate-co-lauryl methacrylate] (H-[P(OEGMA-co-LMA)]) at the air/water interface was investigated by using the Langmuir film balance technique and atomic force microscopy (AFM). At the air/water interface, H-[P(OEGMA-co-LMA)] copolymers spontaneously form the ultrafine network-like monolayer structures of micelles; each micelle consists of a tiny hydrophobic core of one or two carbon backbones and lauryl side groups and a short hydrophilic shell of oligo(ethylene glycol) (OEG) side groups, and the micellar cores are connected by the branching agent ethylene glycol dimethacrylate (EGDMA). These ultrafine micellar structures are successfully revealed by our relative aggregation number method presented in this work, which is based on our previous relative mass method and methylene number method. The surface pressure-molecular area isotherms of POEGMA29%-PLMA71% (weight percent) and POEGMA69%-PLMA31% are condensed and expanded, respectively, because the density/number of OEG side groups in the former shells is smaller than that in the latter case. Upon monolayer compression, the isotherms of the former are classified into regions I-IV, whereas those of the latter are classified into regions II and III based on their different variation trends of surface pressure. Subphase pH has little influence on the isotherms of the two copolymers because the stretching degrees of hydrophilic OEG side groups in the shells are probably limited by the connected cores, which is different from the large effects in our previous block copolymers containing POEGMA or poly[oligo(ethylene glycol) acrylate] blocks. Under neutral and alkaline conditions, in region III, the mean molecular area (mmA) values of the isotherms of the two copolymers at 20 °C are smaller than those at 10 °C due to the collapse of the OEG side groups above 15 °C. Furthermore, the isotherms of POEGMA69%-PLMA31% move to larger mmA values at 30 °C due to the increased thermal mobility and stretching degrees of more OEG side groups.

Hyperbranched polymers: growing richer in flavours with time

Hyperbranched polymers (HBPs) have been studied for over three decades now; yet several interesting aspects continue to draw the attention of researchers worldwide. This is because of the simplicity of synthesis, their unique globular structure, and the numerous peripherally located functional groups that can be utilised to impart a variety of attributes, such as core-shell amphiphilicity, Janus amphiphilicity, clickable polymeric scaffolds, multifunctional crosslinkers, etc. Several reviews have been written on HBPs with a focus on synthetic strategies, structural diversity, and their potential applications; in this short feature article, we have taken an alternate approach to highlight some of the unique structural features of HBPs and their influence on the properties of HBPs. We also discuss their versatility and adaptability for the generation of several interesting functional polymeric systems. In the latter half, we focus on the utilisation of HBPs as multifunctional scaffolds, that rely on the numerous peripheral terminal groups. We conclude by drawing a structuro-functional analogy between the range of peripherally functionalised HBPs and other analogous, but more complex, polymeric systems. We believe that this review will serve as a visual sounding board that would encourage the development of several other applications for this class of unique polymers.

Synthesis of Fluorescent, Dumbbell-Shaped Polyurethane Homo- and Heterodendrimers and Their Photophysical Properties

Fluorescent dendrimers have wide applications in biomedical and materials science. Here, we report the synthesis of fluorescent polyurethane homodendrimers and Janus dendrimers, which often pose challenges due to the inherent reactivity of isocyanates. Polyurethane dendrons (G1-G3) were synthesized via a convergent method using a one-pot multicomponent Curtius reaction as a crucial step to establish urethane linkages. The alkyne periphery of the G1-G3 dendrons was modified by a copper catalyzed azide-alkyne click reaction (CuAAC) to form fluorescent dendrons. In the reaction of the surfaces functionalized two different dendrons with a difunctional core, a mixture of three dendrimers consisting of two homodendrimers and a Janus dendrimer were obtained. The Janus dendrimer accounted for a higher proportion in the products' distribution, being as high as 93% for G3. The photophysical properties of Janus dendrimers showed the fluorescence resonance energy transfer (FRET) from one to the other fluorophore of the dendrimer. The FRET observation accompanied by a large Stokes shift make these dendrimers potential candidates for the detection and tracking of interactions between the biomolecules, as well as potential candidates for fluorescence imaging.

Janus Micelles by Crystallization-Driven Self-Assembly of an Amphiphilic, Double-Crystalline Triblock Terpolymer

Surface-compartmentalized micellar nanostructures (Janus and patchy micelles) have gained increasing interest due to their unique properties opening highly relevant applications, e.g., as efficient particulate surfactants, compatibilizers in polymer blends, or templates for catalytically active nanoparticles. We present a facile method for the production of worm-like Janus micelles based on crystallization-driven self-assembly of a double-crystalline triblock terpolymer with a crystallizable polyethylene middle block and two highly incompatible corona blocks, polystyrene and poly(ethylene oxide). This approach enables the production of amphiphilic Janus micelles with excellent interfacial activity by a comparably simple heating and cooling protocol directly in solution.

Remarkable untangled dynamics behavior of multicyclic branched polystyrenes

A typical multicyclic branched-topology polystyrene (c-BPS) with high molecular weight (30 K ≤ Mw MALLS ≤ 300 K g mol-1) and narrow dispersity (1.2 ≤ Đ ≤ 1.3) was efficiently synthesized by combining atom transfer radical polymerization (ATRP) and atom transfer radical coupling (ATRC) techniques. The topological constraints imposed by the presence of cyclic units and branch points had a marked influence on the entanglement behaviors of the polymer chains in solution. Therefore, c-BPS possesses the lowest loss modulus (G'') and viscosity (η), the highest diffusion coefficient (D0), the largest mesh size (ξ) and the fastest terminal relaxation (TR), compared with branched and linear precursors.

Amphiphilic hyperbranched polymers: synthesis, characterization and self-assembly performance

Abstract

A series of amphiphilic hyperbranched polymers (AHP-s, the “s” refers to the algebra of AHP) were synthesized by the reaction between hydroxyl-terminated hyperbranched polymers (HBP-s, the “s” refers to the algebra of HBP) and palmitoyl chloride. FTIR, NMR and GPC were used to determine the structure of AHP-s, the results showed that AHP-s exhibits core-shell structure. The thermal properties of polymers were investigated by DSC and TGA. It was found that AHP-2, AHP-3 and AHP-4 display higher thermal stability than AHP-1 (AHP-1, AHP-2, AHP-3 and AHP-4 represent the first, second, third and fourth generation AHP, respectively). Furthermore, the self-assembly performance of AHP-s in THF solvent was investigated by TEM and SEM. Finally, the encapsulation capacity of the AHP-s for methyl orange (MO) was explored at different concentrations of AHP-s and pH conditions. It was found that AHP-s is capable of accommodating hydrophilic guest MO. Moreover, the higher generation of AHP-s, the stronger encapsulation capacity obtained. And the encapsulation capacity closely associated with the pH of encapsulation system.

Graphical abstract

Direct estimation of polymer crystallinity with Raman spectroscopy using ratio of scattering cross-sections estimated from variable temperature measurements

Physical properties of polymers (e.g. crystallinity, lamella thickness, thermodynamic properties etc.) can in principle be reliably estimated from their Raman spectral intensities by converting intensities to corresponding concentrations of conformers. However, such conversions are not straightforward due to the unknown scattering cross-sections. The study demonstrates that for several practical applications of Raman spectroscopy, a ratio of cross-sections can be used instead of the absolute values. A straight forwards method for accurately estimating ratio of scattering cross-section from variable temperature measurements is described here. In order to demonstrate its applicability, percent crystallinity (PC) of polyethylene has been directly estimated from Raman intensities without external calibration with other techniques. This general method can be applied to any polymer when there is a continuous change in composition of conformers over a range of temperatures.

Orthogonally clickable hyperbranched polymers: effect of reactant size and polarity on core-functionalization of peripherally jacketed HBPs

Using an orthogonally clickable strategy, the accessibility of internal allyl groups in jacketed HBPs, bearing either PEG or docosyl peripheral segments, was shown to depend both on the size and relative polarity of the reactant thiol.

Hybrasurfs-A New Class of Hyperbranched Surfactants

A hyperbranched (HB) polyester carrying peripheral allyl groups was prepared by melt-condensation of a suitably designed AB₂ monomer bearing two allyl ester groups and one hydroxyl group. The periphery of the hyperbranched polymer was co-clicked with two different organic thiols, namely, hexadecane thiol and 3-mercaptopropionic acid, using the thiol-ene reaction. Three different samples with varying mole fractions of the hydrophilic carboxylic acid groups were prepared; the conformational adaptability of the hyperbranched polymer backbone permitted these amphiphilic systems to form Janus structures that exhibit surfactant-like properties and, therefore, we have termed them hybrasurfs. These polymers behave like clusters of surfactants that have been stitched at the waist by the HB polymer backbone; the Langmuir isotherms revealed the formation of a monolayer, and in two of the samples having higher mole fractions of hexadecyl segments a weak inflection in the isotherm is seen. This suggests a densification, typically implying the crystallization of the alkyl segment at the air-water interface. The monolayers were transferred onto a substrate, and their heights were estimated using atomic force microscopy; the values thus obtained were in reasonable agreement with the expected value. The water contact angles of the substrates bearing the transferred monolayers of the three different samples (transferred at two different points along the isotherm) were measured; it was seen that the sample carrying the highest mole fraction of hexadecyl chains exhibited a significantly larger contact angle when compared to that of the other two samples. Interestingly, these hybrasurfs also formed vesicles in water and were shown to encapsulate water-soluble dyes, such as Eosin Y. Thus, this class of readily accessible amphiphilic HB polymers that behave as a cluster of surfactants opens some interesting possibilities for further exploration.

Hyperbranched Aliphatic Polyester via Cross-Metathesis Polymerization: Synthesis and Postpolymerization Modification

A novel postpolymerization modification methodology is demonstrated to achieve selective functionalization of hyperbranched polymer (HBP). Terminal and internal acrylates of HBP derived from cross-metathesis polymerization (CMP) are functionalized in a chemoselective fashion using the thiol-Michael chemistries. Model reactions between different thiols (benzyl mercaptan and methyl thioglycolate) and acrylates (n-hexyl acrylate and ethyl trans-2-decenoate) by using dimethylphenylphosphine or amylamine as the catalyst are investigated to optimize the modification protocol for HBP. High-molecular-weight HBP P0 is generated through CMP of AB₂ monomer 2, a compound containing one α-olefin and two acrylate metathetically polymerizable groups. CMP kinetics is monitored by NMR and gel permeation chromatography (GPC). Accordingly, microstructural analysis is conducted in detail, and CMP procedure is optimized. Postpolymerization modification of HBP P0 is performed via two distinguished strategies, namely one-step complete modification and sequential modification, to generate terminally and/or internally functionalized HBPs P1-P3 in a chemoselective fashion by using phosphine-initiated and/or base-catalyzed thiol-Michael chemistries. Finally, thermal stability and glass transition behaviors of HBPs P0-P3 are studied by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively.

Long-subchain Janus-dendritic copolymers from locally confined click reaction and generation-dependent micro-phase separation

Long-subchain Janus-dendritic copolymers composed of PSt and PtBA half-dendrons, up to the third generation, were prepared under alternating chemical and local confinement. All the Janus-dendritic copolymers exhibited generation-dependent microphase separation.

Hyperbranched polysiloxane with highly constrained rings and the effect of the attached arms on the assembly behavior

Attachment of incompatible arms to a designed hyperbranched polymer with highly constrained rings and the toroidal assembly.

Amphiphilic nanosheet self-assembly at the water/oil interface: computer simulations

The self-assembly of amphiphilic Janus triangular-plates at the water/oil interface is simulated for the first time.

Janus long-chain hyperbranched copolymers of PSt and POEGMA from a self-assembly mediated click reaction

A Janus hyperbranched POEGMA/PSt copolymer with long sub-chains was prepared through a self-assembly mediated click reaction in selective solvents.

Hierarchical self-assembly of protoporphyrin IX-bridged Janus particles into photoresponsive vesicles

Photoresponsive vesicles formed by PPIX-bridged Janus particles exhibited excellent photostability against intense infrared radiation and good singlet oxygen producing ability.

Soft amphiphilic polyesters obtained from PEGs and silicon fatty compounds: structural characterizations and self-assembly studies

Transesterification polymerizations between a silicon fatty ester derived from methyl 10-undecenoate and polyethylene glycol (PEG) monomers generate amphiphilic biopolyesters ​showing abilities to form micelle and fiber structures.

Mesoscopic simulation of the self-assembly of the weak polyelectrolyte poly(ethylene oxide)-block-poly(methyl methacrylate) diblock copolymers

We designed twelve types of weak polyelectrolytes (i.e., PEO-b-PMMA copolymers (BCP) in multi-arm structures, where six include EO blocks as joint points and the other six have MMA blocks as joint points). All of the BCPs with EO as the joint points form disordered phases with the exception of long-chained and four-armed BCP. The main mesophases of all of the BCPs with MMA as joint points are micelle-like and bicontinuous phases. In particular, the short-chained BCP with four-arms and EO segments outside form a new phase type (i.e., crossed lamellar phase). Using MesoDyn, we provide a comprehensive representation of the micelle and crossed lamellar phase formation mechanisms based on both thermodynamic and dynamic analyses. A shear force on a micelle-like phase could promote a hexagonal columnar phase, which is a good technique for generating an ordered arrangement of nanotube arrays. Blending homopolymers with the same constituents could promote uniformity of the micelle size and decrease the polydispersity, especially for blends with a high BCP concentration, which may provide a new approach for regulating the properties of materials.

One-pot synthesis of indolizine functionalized nanohyperbranched polyesters with different nano morphologies and their fluorescent response to anthracene

Two nanohyperbranched polyesters of HBPE–CIDA₁ (nanospheres) and HBPE–CIDA₄ (nanospindles) were synthesized. The HBPE–CIDA₄ was established to be a fluorescent sensor for anthracene.

Effects of hydroxy substituents on Cu(ii) coordination polymers based on 5-hydroxyisophthalate derivatives and 1,4-bis(2-methylimidazol-1-yl)benzene

Hydroxyl substituents of 5-hydroxyisophthalate derivatives have imposed important effects on the structures and properties of Cu(ii) coordination polymers.

Hyperbranched polymers: advances from synthesis to applications

This review summarizes the advances in hyperbranched polymers from the viewpoint of structure, click synthesis and functionalization towards their applications in the last decade.

Self-assembly of amido-ended hyperbranched polyester films with a highly ordered dendritic structure

Self-assemblies fabricated from dendrimers and amphiphilic polymers have demonstrated remarkable performances and a wide range of applications. Direct self-assembly of hyperbranched polymers into highly ordered macrostructures with heat-resistance remains a big challenge due to the weak amphiphilicity of the polymers. Here, we report the self-assembly of amphiphilic amido-ended hyperbranched polyester (HTDA-2) into millimeter-size dendritic films using combined hydrogen bond interaction and solvent induction. The self-assembly process and mechanism have been studied. Hydrogen bond interaction between amido-ended groups assists the aggregation of inner and outer chains of the HTDA-2, resulting in phase separation and micelle formation. Some micelles attach to and grow on the glass substrate like seedlings. Other micelles move to the seedlings and connect with their branches via solvent induction and hydrogen bond interaction, leading to the fabrication of highly ordered crystalline dendritic films that show high heat-resistance. HTDA-2 can further self-assemble into sheet crystals on the dendritic films.

Understanding Self-Segregation of Immiscible Peripheral Segments in Pseudodendritic Hyperbranched Polydithioacetals: Formation of Improved Janus Structures

Peripherally heterofunctionalized hyperbranched polymers (HBPs) undergo immiscibility-driven self-segregation of the outer segments to form Janus molecular entities (Macromolecules 2012, 45, 2348). In HBPs prepared via AB₂ type self-condensation, single-step peripheral heterofunctionalization would lead to random distribution of the two types of terminal units, namely, homofunctionalized (homo-T) and heterofunctionalized (hetero-T) termini. Here, we examine the role of such hetero-T units on the self-segregation of heterofunctionalized pseudodendritic hyperbranched polydithioacetals. Three different heterofunctionalized HB dithioacetals bearing roughly 50 mol % each of docsyl (C-22) and MPEG-350 chains at the periphery were prepared: one of them carried a statistical distribution of homo-T and hetero-T units, and the other carried only two types of homo-T (-TR₁R₁ and -TR₂R₂) termini, whereas the third carried largely hetero-T (-TR₁R₂) termini. Careful examination of DSC and SAXS data reveals that the self-segregation is most effective in HBPs devoid of hetero-T units; interestingly, however, it also showed that randomly heterofunctionalized HBPs self-segregated nearly as effectively.

Self-adapting peripherally heterofunctionalized hyperbranched polymers: formation of Janus and tripodal structures

A peripherally clickable hyperbranched polyester carrying numerous propargyl terminal groups was prepared by a simple melt transesterification polycondensation of a suitably designed AB(2) monomer; this clickable hyperscaffold was then transformed into a variety of different derivatives by using the Cu-catalyzed azide-yne click reaction. Functionalization of the periphery with equimolar quantities of mutually immiscible segments, such as hydrocarbon, fluorocarbon, and PEG, yielded frustrated molecular systems that readapt and form structures wherein the immiscible segments appear to self-segregate to generate either Janus structures (when two immiscible segments are present) or tripodal structures (when three immiscible segments are present). Evidence for such self-segregation was obtained from a variety of studies, such as differential scanning calorimetry, Langmuir isotherms, AFM imaging, and small-angle X-ray scattering measurements. Crystallization of one or more of the peripheral segments reinforced this self-segregation; the weight-fraction-normalized enthalpies of melting associated with the different domains revealed a competition between the segments to optimize their crystalline organization. When one or more of the segments are amorphous, the remaining segments crystallize more effectively and consequently exhibit a higher melting enthalpy. AFM images of monolayers, transferred from the Langmuir trough, revealed that the thickness matches the expected values; furthermore, contact angle measurements clearly demonstrated that the monolayer films are fairly hydrophobic, and in the case of the tripodal hybramers, the presence of domains of hydrocarbon and fluorocarbon appears to impart nanoscale chemical heterogeneity that is reflected in the strong hysteresis in the advancing and receding contact angles.

Defect-Free Hyperbranched Polydithioacetal via Melt Polymerization

Degree of branching (DB) describes the level of structural perfection of a hyperbranched polymer when compared to its defect-free analogue, namely the dendrimer. The strategy most commonly used to achieve high DB values, specifically while using AB₂ type self-condensations, is to design an AB₂ monomer wherein the reaction of the first B-group leads to an enhancement of the reactivity of the second one. In the present study, we show that an AB₂ monomer carrying a dimethylacetal unit and a thiol group undergoes a rapid self-condensation in the melt under acid-catalysis to yield a hyperbranched polydithioacetal with no linear defects. NMR studies using model systems reveal that the intermediate monothioacetal is relatively unstable under the polymerization conditions and transforms rapidly to the dithioacetal; because this second step occurs irreversibly during polymer formation, it leads to a defect-free hyperbranched polydithioacetal. TGA studies of the polymerization process provided some valuable insights into the kinetics of polymerization. An additional virtue of this approach is that the numerous terminal dimethylacetal groups are very labile and can be quantitatively transformed by treatment with a variety of functional thiols; the terminal dimethylacetals were, thus, reacted with various thiols, such as dodecanethiol, benzyl mercaptan, ethylmercaptopropionate, and so on, to demonstrate the versatility of these systems as sulfur-rich hyperscaffolds to anchor different kinds of functionality on their periphery.