Degree of branching of the hyperbranched polymers resulted from ab<Subscript>2</Subscript> polycondensation with substitution effect

The analytical expressions of the various structural units and the average degree of branching for the hyperbranched polymers resulted from AB₂ polycondensation with substitution effect were derived by the kinetic mechanism.The reactivity difference between the B group in linear unit and that in terminal group has great effect on the molecular parameters of the products obtained.The concentration of terminal units has a maximum with the increase of the conversion of A groups（x）.The higher the reactivity ratio（r） of linear B group to branched one is,the later the maximum appears and the larger it is.The degree of branching of the hyperbranched polymers obtained is controllable by adjusting the parameters of r and x,which increases with increasing both x and r.     

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.     

Synthesis of hyperbranched polymers with precise conjugation length

A set of AB₂ type monodisperse conjugated oligomers carrying two bromo functional groups and one boronic ester functional group were prepared by iterative deprotection and Sonogashira cross‐coupling reactions. Suzuki polycondensation of these AB₂ type monodisperse oligomers afforded hyperbranched polymers. The hyperbranched conjugated polymers we prepared possess not only precisely controlled conjugation length like monodisperse conjugated oligomers but also the structural feature of hyperbranched polymers. Optical property investigation demonstrated that the maximum absorption and emission wavelength red‐shifted along with the increasing of the conjugation length between the two branching points and the hyperbranched structure could effectively reduce the aggregation of the conjugated polymer chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1084–1092, 2007     

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     

Polysiloxanes polymers with hyperbranched structure and multivinyl functionality

Hyperbranched polysiloxane polymers with multivinyl functionality were designed and synthesized through a “one‐step and one‐pot” deactivation enhanced atom transfer polymerization (DE‐ATRP) approach from the copolymerization of polydimethylsiloxane (PDMS) macromonomers and divinylbenzene (DVB). Various feed ratios of siloxane‐based monomer and divinyl monomers were investigated. We showed that even at DVB concentrations as high as 80 mol % in the feed, 65% yield of hyperbranched polymer could be obtained without gelation because the DE‐ATRP suppressed the rapid formation of macronetwork structures. The molecular weight, polydispersity, macromolecular structure of hyperbranched poly(DVB‐co‐PDMS) as well as its viscosity in silicone oil were characterized by GPC‐MALLS, ¹H NMR and rheometer. By tracking the relationship between the radius of gyration, elution volume and molecular weight from MALLS analysis, solid evidences of the highly branched and condensed structure of the polymers were obtained. Furthermore, the oil thickening experiments demonstrate that this hyperbranched polymer can act as a well‐controlled viscosity‐modifier for Silicone oils, which potentially will have important application in coating, cosmetic and pharmaceutical products. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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.     

Synthesis of aromatic hyperbranched PAMAM polymers

Our preliminary results towards the synthesis of hyperbranched polyamidoamine (PAMAM) polymers as ‘dendrimer equivalents’ is described. An aromatic AB₂ bis-amino acid monomer was polymerised at 165 °C (under vacuum) and the crude mixture purified by dialysis. Analysis by GPC and MALDI-TOF mass spectroscopy showed that the purified hyperbranched polymers possessed an M_n of 2000 and a PD of 3.2.     

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.     

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     

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.     

Calculation of the effect of substitution on the yield and topological parameters of hyperbranched polymers synthesized by the cyclotrimerization of mono- and bifunctional monomers

A kinetic model allowing for the effect of substitution has been developed for the synthesis of hyperbranched polymers through the cocyclotrimerization of mono- and bifunctional monomers. The calculation has been performed by means of a mathematical apparatus for generating functions. New theoretical relationships have been obtained that enable one to predict critical conversion and variations in the structural and molecular-mass parameters of hyperbranched polymers during reaction in relation to the initial monomer ratio, relative reactivities of functional groups, and variations in the reactivities during the process.     

Morphology of reactive PP/PS blends with hyperbranched polymers

To study the efficiency of different mechanism for reactive compatibilization of polypropylene/polystyrene (PP/PS) blends main chain or terminal functionalized PP and terminal functionalized PS have been synthesized by different methods. While the in-situ block and graft copolymer formation results in finer phase morphologies compared to the corresponding non-reactive blends, the morphology development in the ternary blend system PP/PS + HBP (hyperbranched polymer) is a very complex process. HBP with carboxylic acid endgroups reacts preferably with the reactive sites of the oxazoline functionalized PS (PS-Ox) and locates mainly within the dispersed PS-Ox phase. A bimodal size distribution of the PS-Ox particles within the oxazoline modified PP (PP-Ox) matrix phase is observed with big PS-Ox particles (containing the HBP as dispersed phase) and small PS-Ox particles similar in size like the unimodal distributed particles in the non-reactive PP-Ox/PS-Ox blends. Factors influencing the morphology are discussed.     

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.     

Statistics of substitution polymers

Equations are developed for predicting the distributions of degree of substitution and block length in substitution copolymers which result when homopolymers are subjected to substitution reactions. Several different cases are treated differing in complexity from entirely random substitution to substitution affected by substituents already present on the same and on the neighboring repeat units. The equations are then applied to chlorinated polyethylene as an example of their use.     

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.