Porphyrin cored hyperbranched polymers as heme protein models

The single step synthesis of an Fe(II) porphyrin cored hyperbranched polymer, possessing similar size and topology to the natural heme containing proteins, is reported: UV spectroscopy successfully demonstrated the ability of this polymer to reversibly bind oxygen.     

New developments in hyperbranched polymers

In the last 12 years the field of hyperbranched polymers has been well established with a large variety of synthetic approaches and fundamental studies on structure and properties of these unique materials. However, new developments involving hyperbranched materials appeared recently, for example, different synthetic strategies, new reaction mechanisms, formation of more complex architectures, a deeper understanding of the branched structure and their kinetic development, and intensive studies on the material properties and possible applications. This demonstrates the high versatility and the possibilities that are still involved in hyperbranched polymers and render it one of the most active fields in polymer science with a very promising future. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2505–2525, 2000     

New polynitrogen hyperbranched polymers

A method for the preparation of new representatives of polynitrogen hyperbranched polymers of heterocyclic series was developed involving polymerization of monomeric 2,4-diazido-6-propynyloxy-1,3,5-triazine by 1,3-dipolar cycloaddition. Kinetics of polymerization of diazidoacetylene monomer was compared with the kinetic data of polymerization of its closest analog, 2-azido-4,6-bis(propynyloxy)-1,3,5-triazine monomer. Properties of hyperbranched poly(1,2,3-triazole-1,3,5-triazine)s with terminal azide groups and terminal triple bonds were compared, as well.     

Dendrimers and hyperbranched polymers as high-loading supports for organic synthesis

Polymeric supports have become a big necessity for automated synthesis and combinatorial chemistry, yet, the loading capacities of most polystyrene resins are very limited (typically < 1.5 mmol x g(-1)). Dendrimers and hyperbranched polymers have been discussed for this application and now became readily available. These soluble polymers can either be used directly as high-loading supports for substrates, reagents, and catalysts or alternatively in hybrid polymers linked to conventional polystyrene resins.     

Aminated styrene polymers as dehydrohalogenating agents

Copolymers of styrene and methyl methacrylate, cross-linked with divinylbenzene, can be chloromethylated and then aminated to almost the theoretical extent. The aminated polymers can utilise approx 50% of the amine residues to dehydrobrominate n-bromoalkanes.     

Theoretical models of hyperbranched polymers

We have investigated linear, starbranched and hyperbranched X_nH_m polymers and determined the number of atoms, rotors, internal coordinates, valence and HOMO molecular orbitals as well as molecular mass for each generation and valency. We use the semi-empirical MNDO model to obtain full geometry optimization for increasingly larger clusters for each generation in order to obtain total relative energies. We then generate analytical functions, which correlate the total relative energies with the generation, for each valency, for the hyperbranched polymers. We have also generated analytic functions, which correlate total relative energies, experimental van der Waals coefficients and standard enthalpy of combustion with the number of carbon atoms in each chain of the linear alkanes. These results are used to predict the enthalpy of combustion for higher generations of alkanes in good agreement with experiment. Due to the exponential increase in size with generation of the hyperbranched polymers alternative analytical models may be of interest to theoretical chemists working in this line of research.     

Amphiphilic branched polymers as antimicrobial agents

Cationic amphiphilic polymers were prepared from PEI and functional ethylene carbonates bearing cationic, hydrophobic or amphiphilic groups. The polymers are designed to exhibit antimicrobial properties. In a one-step addition, different functional ethylene carbonates were added to react with the primary amine groups of PEI. The water soluble polymers were studied regarding their ability to form soluble aggregates. Their hydrodynamic radii, their inhibition potential against proliferation of E. coli and their hemolytic potential were determined. A structure-property relationship was established by analyzing the antimicrobial activity as a function of the ratio of alkyl to cationic groups, length of the alkyl chains, and molecular weight of the PEI.     

Trapping in dendrimers and regular hyperbranched polymers

Dendrimers and regular hyperbranched polymers are two classic families of macromolecules, which can be modeled by Cayley trees and Vicsek fractals, respectively. In this paper, we study the trapping problem in Cayley trees and Vicsek fractals with different underlying geometries, focusing on a particular case with a perfect trap located at the central node. For both networks, we derive the exact analytic formulas in terms of the network size for the average trapping time (ATT)-the average of node-to-trap mean first-passage time over the whole networks. The obtained closed-form solutions show that for both Cayley trees and Vicsek fractals, the ATT display quite different scalings with various system sizes, which implies that the underlying structure plays a key role on the efficiency of trapping in polymer networks. Moreover, the dissimilar scalings of ATT may allow to differentiate readily between dendrimers and hyperbranched polymers.     

pH-responsive self-assembly of carboxyl-terminated hyperbranched polymers

This work has presented a typical example to reveal the great influence of the terminal groups on the self-assembly of hyperbranched polymers. The hyperbranched polymers with hydroxyl terminal groups (HBPO-OH) were hydrophobic and precipitated in water, however, they displayed a pH-responsive self-assembly behavior when the terminal groups were replaced by carboxyl groups. The obtained carboxyl-terminated hyperbranched polymers (HBPO-COOH) existed as unimolecular micelles at high pH (12.21) due to the ionization of carboxyl groups, while the polymers aggregated into multimolecular micelles from 10 to 500 nm with the decrease of pH as a result of the partial protonation of the carboxyl groups. The size of the obtained micelles depended strongly on the solution pH - the lower the pH, the bigger the micelles. TEM, DLS, ATR-FT-IR, (1)H NMR and AFM measurements substantiated that the multimolecular micelles were formed by the secondary aggregation of unimolecular micelles driven by the hydrogen bonding interaction depending on the solution pH.     

Synthesis and applications of hyperbranched polymers

The development of hyperbranched polymers is a rapidly expanding field in the area of macromolecular science. This short review highlights some of the notable examples in the synthesis of hyperbranched polymers and some of the key advances that have been made in the application of these hyperbranched materials in the areas of material property modifications and in high value technologies.     

Diffusion-limited hyperbranched polymers with substitution effect

Highly branched structure has the essential influence on macromolecular property and functionality in physics and chemistry. In this work, we proposed a diffusion-limited reaction model with the consideration of macromolecular unit relaxations and substitution effect of monomers to study the structure of hyperbranched polymers prepared by slow monomer addition to a core molecule. The exponential relationship (R(g) ～ N(λ)) between the radius of gyration R(g) and the degree of polymerization N, was systematically analyzed at various branching degrees. It is shown that the effective exponent λ(eff) decreases at lower N and but increases toward that of diffusion-limited aggregation (DLA) clusters (λ(DLA) = 0.4) with the degree of polymerization increasing. The substitution effect of monomers in reaction strongly influences the evolution pathway of λ(eff). With the static light scattering technique, the fractal property of internal chains was further calculated. A general law about the radial distribution of the units of diffusion-limited hyperbranched polymers was found that, at smaller reactivity ratio k(12), the radial density of all monomer units D(A) declines from the center region to the peripheral layer revealing the dense core structure; however, at larger k(12), the density distribution shows a loose-dense-loose structure. These structural characteristics are helpful to deeply understand the property of hyperbranched polymers.     

A structural characteristic of hyperbranched polymers

The structural characterization of hyperbranched polymers is discussed. Current approaches describing the structure of these polymers in terms of such parameters as the degree of branching and the average number of branches are shown to be inadequate. We propose characterizing the structure of polymers using the distribution over the degree of branching and the $ \bar D_w /\bar D_n $ ratio as the quantitative measure of distribution width. Using the example of AB₂ type monomer polycondensation, it is shown how this value varies in the course of the process along with other structural parameters.     

Membrane preparation from hyperbranched perfluorinated polymers

In this research, membrane formation with hyperbranched perfluorinated polymers (HBFP) was investigated. To create a tough membrane, HBFP was blended and crosslinked with a tougher linear polymer. Blending only or crosslinking only was not sufficient to create a tough membrane, but combining blending with crosslinking was successful. Miscibility, phase separation, and thermal and mechanical properties were evaluated for a variety of systems. By using a toughening linear polymer with lower polarity, reduced phase separation and improved mechanical properties were seen. Overall, imidazole‐containing HBFPs produced the clearest and toughest blends. These new hyperbranched ionomers and copolymers are strong candidates for future use in anhydrous proton exchange membranes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 961–972     

Curing kinetics of epoxy resins with hyperbranched polyesters as toughening agents

The effects of hyperbranched polyesters on the cure kinetics of diglycidyl ether of bisphenol A (DGEBA) in the presence of m‐phenylene diamine were investigated with nonisothermal differential scanning calorimetry. The results showed that the addition of hyperbranched polyesters enhanced the cure reaction of DGEBA with m‐phenylene diamine, and this resulted in a reduction of the peak temperature of the curing curve and the activation energy because of the low viscosity and large number of terminal hydroxyl groups. However, when linear poly(ethylene glycol) was added, the activation energy of the blends also slightly decreased, whereas the peak temperature of the curing curve increased. The curing kinetics of the blends were calculated by the isoconversional method of Málek. The two‐parameter autocatalytic model (i.e., the ?esták–Berggren equation) was found to be the most adequate for describing the cure kinetics of the studied systems. The obtained nonisothermal differential scanning calorimetry curves showed results in agreement with those theoretically calculated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2649–2656, 2004     

Doubly hydrophilic multiarm hyperbranched polymers with acylhydrazone linkages as acid-sensitive drug carriers

A novel type of drug carrier capable of controlled drug release is proposed. It consists of an acid-sensitive doubly hydrophilic multiarm hyperbranched copolymer with a hyperbranched polyamidoamine core and many linear poly(ethylene glycol) arms. Using pH-sensitive acylhydrazone linkages, the polymer forms unimolecular micelles that can encapsulate hydrophobic drugs. Due to their amphiphilicity, the drug-loaded unimolecular micelles can self-assemble into multimolecular micelles that show acid-triggered intracellular delivery of the hydrophobic drugs.     

Spacers' role in the dynamics of hyperbranched polymers

We investigate hyperbranched polymers (HBPs) and highlight the relation between their architecture and their viscoelastic behavior, while paying special attention to the role of the chainlike spacer segments between branching points. For this we study the dynamics of HBP in solution, based on the generalized Gaussian structure formalism, an extension of the Rouse model, which disregards hydrodynamical and excluded volume effects. For HBP the dynamical effects display, beside the obvious contributions of localized modes on the spacers, also remarkable features, as we highlight based on the exact renormalization procedure recently developed by us in J. Chem. Phys. 123, 034907 (2005). We exemplify these features by analyzing the dynamics of randomly linked star polymers and study the impact both of the length and of the spacers' mobility on the normal modes' spectra. We compute these modes both by numerical diagonalization and also by employing our renormalization procedure; the excellent agreement between these methods allows us to extend the range of investigations to very large HBP.     

Novel hyperbranched polymers as host materials for green thermally activated delayed fluorescence OLEDs

A series of novel hyperbranched polymers(HBPs) consisting of a 2,7-subsituted 9-(heptadecan-9-yl)-9H-carbazole unit(A_2+A_2') and a tetra-substituted green thermally activated delayed fluorescence(TADF) dye of 2,3,5,6-tetra(9Hcarbazol-9-yl)-4-pyridinecarbonitrile(4CzCNPy, B4) have been synthesized via Suzuki cross-coupling reaction following an "A2+A2'+B_4" method. The polymers are named according to the polymerization ratio of 4CzCNPy monomer(5 mol%, 10 mol% and 15 mol% for HBPs of P2-P4 respectively, and 0 mol% for the control linear polymer P1). Their thermal, optoelectronic and electrochemical properties have been characterized by a combination of techniques. All the polymers exhibit high thermal stability with the decomposition temperatures(Td) above 400 ℃ and glass transition temperatures(Tg) up to 98 ℃. Unfortunately, the incorporation of TADF moiety into these HBP materials induced non-TADF characteristics. However, when the HBPs functionalized as the host for our previously developed 4CzCNPy TADF dopant in solution processed devices, maximum external quantum efficiency of 5.7% and current efficiency of 17.9 cd/A have been achieved in P3-based device, which is significantly higher than those of 1.5% and 4.2 cd/A for the linear polymer P1.     

Branched polymeric labels used as drag-tags in free-solution electrophoresis of ssDNA

In the framework of the classical blob theory of end-labeled free-solution electrophoresis of ssDNA, and based on recent experimental data with linear and branched polymeric labels (or drag-tags), the present study puts forward design principles for the optimal type of branching that would give, for a given total number of monomers, the highest effective frictional drag for ssDNA sequencing purposes. The hydrodynamic radii of the linear and branched labels are calculated using standard models like the freely jointed chain model and the Kratky-Porod worm-like chain model. Based on comparisons of the theory with the experimental data, we propose that the design of new branched labels should use either side chains whose length is comparable to the distance between the branching points or two long branches located near the ends of the molecule's backbone.     

Synthesis of fluorinated hyperbranched polymers capable as highly hydrophobic and oleophobic coating materials

A series of coating materials were prepared from two classes of hyperbranched polymers containing short fluorocarbon chains (HPEFs/HPUFs). The obtained hyperbranched polymers were characterized by FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, GPC and TG analyses. HPEFs/HPUFs exhibited very low surface free energies (13.67-24.49 mJ/m²) which almost are independent of their internal backbone but dependent on the terminal fluorocarbon chains. Highly hydrophobic and/or oleophobic surfaces of cotton woven fabric can be achieved from these polymers by solution-immersion coating method. The static and dynamic wettabilities of the HPEFs/HPUFs treated fabrics have been investigated. The static contact angles reached to 146°, 122° and 102° for water, hexadecane and decane, respectively. The lowest contact angle hysteresis reached to 5.9°.     

Porous membranes modified by hyperbranched polymers: I. Preparation and characterization of PVDF membrane using hyperbranched polyglycerol as additive

Porous membranes were prepared via phase inversion process from casting solution composed of poly(vinylidene fluoride) (PVDF), N,N-dimethylacetamide (DMAc), and hyperbranched polyglycerol (HPG). The membranes were characterized in terms of surface and bulk chemical compositions, morphology, water contact angle, porosity, and water flux. The effects of HPG content on membrane structures and properties were investigated. The effect of HPG addition on the hydrophilicity was discussed as well when the compositions of coagulation bath were changed. To better understand the special effects of HPG on the structures and properties of the membranes, PVDF membranes prepared using HPG as the additive were compared with those prepared using polyethylene glycol (PEG) as the additive.