Controlling open‐shell loading in norbornene‐based radical polymers modulates the solid‐state charge transport exponentially

Radical polymers are an emerging class of electronically active macromolecules; however, the fundamental mechanism by which charge is transferred in these polymers has yet to be established in full. To address this issue, well‐defined norbornene‐based nitroxide radical polymers were synthesized using the controlled ring‐opening metathesis polymerization technique. These polymers were blended in solution with a quenched, electrically insulating hydroxylamine derivative to dilute the radical content of the system. Electron paramagnetic resonance spectroscopy data were used to characterize the radical content as well as to reveal that hydrogen atom transfer occurred between the open‐shell and closed‐shell polynorbornene derivatives when they were blended in solution. Using these platform macromolecules, we demonstrate that the systematic manipulation of the radical content in open‐shell macromolecules leads to exponential changes in the macroscopic electrical conductivity. When coupled with the fact that these materials show a clear temperature‐independent charge transport behavior, a picture emerges that charge transfer in radical polymers is dictated by a tunneling mechanism between localized donor and acceptor sites within the redox‐active thin films. These results constitute the first experimental insight into the mechanism of solid‐state electrical conduction in radical polymers, and this provides a design paradigm for open‐shell macromolecular charge transport. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1516–1525     

Synthesis of polymeric 1‐iminopyridinium ylides as photoreactive polymers

Two synthetic routes to polymeric 1‐imino pyridinium ylides as new photoreactive polymeric architectures were investigated. In the first approach, polymerization of newly synthesized 1‐imino pyridinium ylide containing monomers yielding their polymeric analogues was achieved by free radical polymerization. Alternatively, reactive precursor polymers were synthesized and converted into the respective 1‐imino pyridinium ylide polymers by polymer analogous reactions on reactive precursor polymers. Quantitative conversion of the reactive groups was achieved with pentafluorophenyl ester containing polymers and newly synthesized photoreactive amines as well as by the reaction of poly(4‐vinylbenzoyl azide) with a photoreactive alcohol. The polymers obtained by both routes were examined regarding their photoreaction products and kinetics in solution as well as in thin polymer films. Contact angle measurements of water on the polymer films before and after irradiation showed dramatic changes in the hydrophilicity of the polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 832–844, 2010     

RAFT‐based synthesis and the gelation property of telechelic polymers that can immobilize biomacromolecules

Telechelic polymers, macromolecules having two reactive end groups, can serve as building blocks for constructing polymers or polymeric materials that have complex architectures. Among the telechelic polymers, polymers bearing hydroxyl groups at two terminals have been used as components for preparation of functional materials. In the present study, RAFT polymerization of both N‐acryloylmorphorin and N‐succinimidyl acrylate by using a newly synthesized dithiobenzoate‐type chain transfer agent bearing hydroxyl groups at both terminals (HECPHD) was reported. After the acryloylation of the hydroxyl terminals of the obtained polymer, gelation was observed. Furthermore, the polymer could react with a protein via the conjugation of the succinimidyl esters‐containing polymers to the amino groups present on the protein surface. The results show that activated esters‐bearing polymers with hydroxyl groups at both terminals can be used as building blocks for constructing polymeric materials for an immobilization of biomacromolecules. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1356–1365     

Direct synthesis of tetrazine functionalities on polymer backbones

Tetrazine mediated inverse Electron Demand Diels–Alder Reaction (IEDDA) is an important modification technique due to its high selectivity and super‐fast kinetics. Incorporation of tetrazine moieties on polymer chains requires multistep synthetic pathways and a post‐polymerization step leading to functional polymeric materials. Such approaches involve separate syntheses of polymer and the molecule which will be employed in modification. Herein, we introduce a straightforward synthetic approach for direct synthesis of tetrazine groups on polymers as side chains. As model systems, tetrazine functional poly(N‐isopropylacrylamide)‐and poly(ethylene glycol)‐based polymers from corresponding precursor polymers with nitrile moieties as pendant groups are prepared and IEDDA Click Reaction is achieved with trans‐cyclooctene derivatives. The click reaction is monitored by both NMR and UV–vis spectroscopies. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 673–680     

Synthesis of conjugated polymers possessing diketopyrrolopyrrole units bearing phenyl,pyridyl, and thiazolyl groups by direct arylation polycondensation: Effects of aromatic groups in DPP on physical properties

Conjugated polymers containing phenyl‐, pyridyl‐, and thiazolyl‐flanked diketopyrrolopyrrole (DPP) were synthesized by direct arylation polycondensation of 3,4‐ethylenedioxythiophene derivatives and dibrominated DPP‐based monomers, in order to probe the effects of the aromatic groups in the DPP units on the absorption property, energy level, and crystallinity. A polymer possessing thiazolyl‐flanked DPP units was found to display long‐wavelength absorption properties and higher crystallinity than the polymers bearing phenyl‐ and pyridyl‐flanked DPP units. These features of the thiazolyl‐based polymer were afforded by its coplanar structure of the main chain. The synthesized polymers showed semiconducting properties in organic field effect transistors and organic photovoltaics. Direct arylation polycondensation is an efficient synthetic method that affords a series of DPP‐based polymers in a simple fashion and, thus, helping in a comprehensive understanding on the relationship between the aromatic groups in DPP units and their physical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2337–2345     

Hydrodynamic properties and conformation of poly(3‐hexylthiophene) in dilute solutions

Conducting polymers demonstrate low solubility in organic solvents. Introducing aliphatic substituents into polymer chains improves their solubility, but may also lead to changes in conformational characteristics of macromolecules. In the present work, the studies of hydrodynamic properties and conformational characteristics of comb‐shaped poly(3‐hexylthiophene) with aliphatic side substituents were carried out in chloroform solutions. Conformational analysis of the studied macromolecules was performed for the first time using homologous series with a wide range of molecular weights of the polymers in dilute solutions. The hydrodynamic properties of these macromolecules were interpreted using the worm‐like spherocylinder model and the straight spherocylinder model. The projection of the monomer unit in the direction of the main polymer chain λ = 0.37 nm was determined experimentally. The following parameters of poly(3‐hexylthiophene) were characterized and quantified: equilibrium rigidity (Kuhn segment length) А = 6.7 nm and hydrodynamic diameter of a polymer chain d = 0.6 nm. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 875–883     

Preparation and functionalization of linear and reductively degradable highly branched cyanoacrylate‐based polymers

Ethyl cyanoacrylate (ECA) was polymerized radically in the presence of small amounts of trifluoroacetic acid as effective inhibitor of incidental anionic polymerization. Methyl methacrylate and other functional vinyl monomers (e.g., 2‐chloroethyl and 2‐bromoethyl methacrylate) were copolymerized with ECA, yielding linear ECA‐rich copolymers, which could readily undergo further modifications, for instance nucleophilic substitution with azide. In the presence of a disulfide‐containing dimethacrylate crosslinker and a chain transfer agent (CBr₄) during the free radical copolymerizations of ECA with methacrylates, highly branched ECA‐based polymers containing disulfide groups at the branching points were obtained prior to gelation. The polymers degraded upon addition of reducing agents. The prepared polymers, which contained peripheral (chain end) alkyl bromide groups as well as pendant alkyl chloride or bromide groups were then reacted with sodium azide, affording azide‐containing polymers that were reacted with functional alkynes under copper‐catalyzed “click” chemistry conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3683–3693     

Biological–synthetic hybrid block copolymers: Combining the best from two worlds

Although biopolymers and synthetic polymers share many common features, each of these two classes of materials is also characterized by a distinct and very specific set of advantages and disadvantages. Combining biopolymer elements with synthetic polymers into a single macromolecular conjugate is an interesting strategy for synergetically merging the properties of the individual components and overcoming some of their limitations. This article focuses on a special class of biological–synthetic hybrids that are obtained by site‐selective conjugation of a protein or peptide and a synthetic polymer. The first part of the article gives an overview of the different liquid‐phase and solid‐phase techniques that have been developed for the synthesis of well‐defined, that is, site‐selectively conjugated, synthetic polymer–protein hybrids. In the second part, the properties and potential applications of these materials are discussed. The conjugation of biological and synthetic macromolecules allows the modulation of protein binding and recognition properties and is a powerful strategy for mediating the self‐assembly of synthetic polymers. Synthetic polymer–protein hybrids are already used as medicines and show significant promise for bioanalytical applications and bioseparations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1–17, 2005     

A versatile synthetic path to thiol containing polysiloxanes

A synthetic strategy to polydimethylsiloxanes and polymethylsiloxanes containing thiol functions as end‐ or side‐groups, respectively, is presented. Such polymers are important starting materials for elastomeric networks and postpolymerization modifications. The synthesis starts either with vinyl end‐functionalized polydimethylsiloxanes or with polymethylvinylsiloxanes. The vinyl groups are reacted either with thioacetic acid or with a thioacetic acid/butanethiol mixture via a UV‐initiated thiol‐ene reaction to form the respective thioester quantitatively within few minutes. The thioesters are subsequently deprotected to the respective thiols by reduction with LiAlH₄. The resulting thiol containing polysiloxanes can be used for the formation of networks or another functionalization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2940–2948     

Designing Branched Deoxybenzoin Polyesters as Polymeric Flame Retardants

AB₂ monomers present opportunities to conduct one‐pot syntheses of highly branched or “hyperbranched” polymers, which are known for their distinct physical and chemical properties relative to linear polymers. This paper describes the synthesis of a deoxybenzoin‐containing AB₂ monomer and its use in step‐growth polymerization to prepare branched aromatic polyesters. Highly soluble deoxybenzoin polymers were obtained with degrees of branching reaching 0.36 and estimated molecular weights approaching 20 kDa. The phenolic chain ends of the polymer allowed for post‐polymerization modification by silylation and esterification chemistry. TGA and microscale combustion calorimetry revealed these novel aromatic polyesters to possess the critically important characteristics of flame‐retardant polymers, such as high char yield and low heat release. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1765–1770     

Synthesis,characterizations, and electrochromic properties of donor–acceptor type polymers containing 2, 1, 3‐benzothiadiazole and different thiophene donors

Three donor–acceptor type π‐conjugated monomers containing 2, 1, 3‐benzothiadiazole (Tz) as the acceptor unit and different thiophene derivatives (thiophene, 3,4‐ethylenedioxythiophene, and thieno[3,2‐b]thiophene) as the donor units have been synthesized via Stille coupling reaction. The corresponding polymers are electrochemically deposited onto FTO glass by cyclic voltammetry (CV). The maximum absorption wavelength of the neutral polymers varies with the electron‐rich character of incorporated thiophene moieties, giving rise to tunable colors. In addition, the prepared polymer films demonstrate reasonable transmittance modulation, fast switching rate, high color efficiency and good stability, which meet the requirements of smart windows and electrochromic display applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2239–2246     

Optically active core/shell nanoparticles prepared using self‐assembled polymer micelle as reactive nanoreactor

This article reports on optically active core/shell nanoparticles constituted by chiral helical polymers and prepared by a novel approach: using self‐assembled polymer micelles as reactive nanoreactors. Such core/shell nanoparticles were composed of optically active helical‐substituted polyacetylene as the core and thermosensitive poly(N‐isopropylacrylamide) as the shell. The synthetic procedure is divided into three major steps: (1) synthesis of amphiphilic diblock copolymer bearing polymerizable C[tbond]C bonds via atom transfer radical polymerization, followed by (2) self‐assembly of the diblock copolymer to form polymer micelles; and (3) catalytic emulsion polymerization of substituted acetylene monomer conducted using the polymer micelles as reactive nanoreactors leading to the core/shell nanoparticles. The core/shell nanoparticles simultaneously exhibited remarkable optical activity and thermosensitivity. The facile, versatile synthesis methodology opens new approach toward preparing novel multifunctional core/shell nanoparticles.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Multiarm star polymers with a thermally cleavable core: A “grafting‐from” approach paves the way

Thermally cleavable multiarm star polymers containing thermo‐reversible furan–maleimide cycloadduct‐based core were synthesized using dendritic macroinitiators. Peripheries of dendritic macroinitiators were modified with bromine containing free radical initiators to obtain multiarm polymers by utilizing atom transfer radical polymerization (ATRP). Cleavage of thus obtained multiarm polymers was achieved via the retro Diels–Alder cycloreversion reaction of the furan–maleimide core at elevated temperatures. As an alternative approach, combination of multiarm polymers containing a furan and maleimide functional group at their core was attempted to realize that the steric bulk does not allow their formation. Hence the “grafting‐from” route using a thermally fragmentable trigger containing multiarm initiators provides a plausible methodology for fabrication of such thermally cleavable multiarm polymeric materials. Syntheses of dendritic initiators, formation of star polymers as well as their fragmentation were followed by proton nuclear magnetic resonance spectroscopy and size exclusion chromatography. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 885–893     

Well‐defined polymers containing high density of pendant viologen groups

Atom transfer radical polymerization (ATRP) of a viologen‐containing methacrylate, 1‐propyl‐1′‐[2‐(methacryloyloxy)ethyl]‐4,4′‐bipyridinium dihexafluorophosphate, is reported. To achieve good polymerization control, it was essential to use the viologen‐based monomer with a hexafluorophosphate instead of halide counterion, and 2,2′‐bipyridine as the ligand for the Cu‐based ATRP catalyst. The solubility of produced cationic polymers could be tuned by anion metathesis: the polymers with hexafluorophosphate counterions were soluble in organic solvents (e.g., acetone, DMF), and those with chloride counterions were water‐soluble. In aqueous solutions, the polymers (chloride salts) formed large aggregates, the sizes of which ranged from about 200 to about 400 nm (based on dynamic light scattering measurements) depending on the molecular weight. Upon addition of electrolytes (e.g., NaCl), the aggregates underwent dissociation. The apparent diffusion coefficients of the aggregates existing in aqueous solutions and the products of their electrolyte‐induced dissociation were measured by diffusion‐ordered NMR spectroscopy. The association–dissociation processes were also studied by fluorescence spectroscopy: the aqueous polymer solutions, which were originally fluorescent (λ _em = 402 nm at λ _ex = 350 nm), lost their fluorescence in the presence of NaCl. The addition of small amounts of the viologen‐containing polyelectrolytes to solutions of inorganic salts (NaCl) altered the crystal morphology of the salts due to interaction of the multiple charged pendant groups with small ions. In the presence of reducing agents, the pendant viologen groups were converted to viologen radical‐cations, which are prone to dimerize reversibly in aqueous solutions. Indeed, marked dimerization of viologen radical cations (with absorbance maxima at 520 and 870 nm) was observed in relatively dilute aqueous solutions (4 mg mL^?1) upon addition of reducing agents (hydrazine). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55 , 1173–1182     

A new access to polypyrrole‐based functionalized magnetic core‐shell nanoparticles

Magnetic nanoparticles (NP) have found various important applications in nanotechnology and nanomedicine, because they can be manipulated by external magnetic field and can be functionalized on their surface. Although a variety of magnetic core shell NP are known present research focuses on new NP with better properties (reduced toxicity, high colloidal and chemical stability, wide scope of application) and more straightforward and reproducible syntheses. In this work, we report the synthesis of azido‐functionalized polypyrrole (PPy)‐based superparamagnetic core shell NP by surface initiated polymerization wherein miniemulsion technique have been applied in this field for the first time. The new NP are attractive for biomedical applications because the PPy is biocompatible, the shell can easily be functionalized by Cu‐catalyzed click‐reaction as shown by the introduction of biotin and the material exhibits superparamagnetic behavior. The surface initiated polymerization is carried out at new magnetite NP, which are stabilized by pyrrol‐containing fatty acids. Although these starting NP lack a polymer shell, they show a remarkable stability and thus have the potential for further functionalization. The magnetic NP are characterized by various methods such as FTIR, X‐ray photoelectron spectroscopy, magnetic measurements, thermal gravimetric analysis, and dynamic light scattering. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Postpolymerization modification of polynorbornene side chains via tetramethyl guanidine promoted esterification

We demonstrate that polynorbornene containing primary activated bromide moieties is a novel chemically modifiable platform for postpolymerization modification. Polymer P0 was synthesized via ring‐opening metathesis polymerization of monomer 1 with the assistance of Grubbs third generation (G‐III) catalyst. Subsequently, nucleophilic substitution was conducted by mixing P0 with n‐caproic acid, sorbic acid, m‐toluic acid or 4‐nitrobenzoic acid in the presence of 1,1,3,3‐tetramethylguanidine (TMG) under mild and stoichiometric condition to generate functionalized polymers P1–P4 . NMR results approved full conversion of the reactive sites and exemplified the “click” nature of TMG promoted esterification. Thermal stability and glass transition behaviors of all the polymer samples were investigated by thermal gravimetric analysis and differential scanning calorimetry. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3733–3740     

Recent progress on cyclic polymers: Synthesis,bioproperties, and biomedical applications

Polymer topologies exert a significant effect on its properties, and polymer nanostructures with advanced architectures, such as cyclic polymers, star‐shaped polymers, and hyperbranched polymers, are a promising class of materials with advantages over conventional linear counterparts. Cyclic polymers, due to the lack of polymer chain ends, have displayed intriguing physical and chemical properties. Such uniqueness has drawn considerable attention over the past decade. The current review focuses on the recent progress in the design and development of cyclic polymer with an emphasis on its synthesis and bio‐related properties and applications. Two primary synthetic strategies towards cyclic polymers, that is, ring‐expansion polymerization and ring‐closure reaction are summarized. The bioproperties and biomedical applications of cyclic polymers are then highlighted. In the end, the future directions of this rapidly developing research field are discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1447–1458     

Syntheses of pyrimidine‐based polymers containing electron‐withdrawing substituent with high open circuit voltage and applications for polymer solar cells

Polymers using new electron‐deficient units, 2‐pyriminecarbonitrile and 2‐fluoropyrimidine, were synthesized and utilized for the photovoltaics. Donor‐acceptor (D‐A) types of conjugated polymers ( PBDTCN, PBDTTCN, PBDTF, and PBDTTF ) containing 4,8‐bis(2‐octyldodecyloxy)benzo[1,2‐b;3,4‐b′]dithiophene (BDT) or 4,8‐bis(5‐(2‐octyldodecyloxy)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) as electron rich unit and 2‐pyriminecarbonitrile or 2‐fluoropyrimidine as electron deficient unit were synthesized. We designed pyrimidine derivatives in which strong electron‐withdrawing group (C?N or fluorine) was introduced to the C2 position for the generation of strong electron‐deficient property. By the combination with the electron‐rich unit, the pyrimidines will provide low band gap polymers with low highest occupied molecular orbital (HOMO) energy levels for higher open‐circuit voltages (V_OC). For the syntheses of the polymers, the electron‐rich and the electron‐deficient units were combined by Stille coupling reaction with Pd(0)‐catalyst. Absorption spectra of the thin films of PBDTTCN and PBDTTF with BDTT unit show shift to a longer wavelength region than PBDTCN and PBDTF with BDT unit. Four synthesized polymers provided low electrochemical bandgaps of 1.56 to 1.96 eV and deep HOMO energy levels between ?5.67 and ?5.14 eV. © 2015 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 771–784     

Innovative macromolecular syntheses via isocyanide multicomponent reactions

Isocyanide multicomponent reactions assemble more than two reaction components by exploiting the reactivity of the isocyanide carbon atom toward addition of electrophiles and nucleophiles. Reactions such as the Passerini three‐component and Ugi four‐component coupling reactions have a long and successful history in organic synthesis, which has only recently been explored in polymer chemistry. In a short time, this class of multicomponent reactions has been established as a viable method for the synthesis of linear polymers as well as more complex architectures such as miktoarm star polymers and dendrimers. This highlight discusses the recent accomplishments made with regard to innovative syntheses of polymers and dendrimers via the Passerini and Ugi reactions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3985–3991