Novel Branched Polyphenylenes based on A2/B3 and AB2/AB Monomers via Diels‐Alder Cycloaddition

Summary: Novel hyperbranched polyphenylenes based on both an A₂ + B₃ and an AB₂ + AB approach were synthesised and characterised. Different monomers were prepared and polymerised using a Diels‐Alder reaction with subsequent decarbonylation. The polymer backbones consist of hexaphenylbenzene units which are linked in different positions and functionalised by cyclopentadienone (A) and/or alkyne groups (B) depending on the monomer ratio. The structure and properties of the resulting polymers were compared to those of hyperbranched polyphenylenes based solely on an AB₂ monomer. All branched products showed high thermal stability and good solubility in common organic solvents such as chloroform or toluene. However, due to steric hindrance, the polyphenylenes produced using the A₂ + B₃ approach exhibited a high percentage of linear units within the polymer structure.

Schematic structure of hyperbranched polyphenylenes from A₂ and B₃ monomers.     

Synthesis of Polymers Bearing Oligo‐Aromatic Esters for Second‐Order Nonlinear Optics

We synthesized methacrylate‐type polymers bearing oligo‐aromatic esters as side chains to create unique second‐order nonlinear optical (NLO) active polymers ( PMA n ‐x , PMA n C‐x , PMA2N‐x , and PBA3N‐x , x = oligo‐aromatic ester contents) for the investigation of the resulting architecture. The polymers were obtained from the polymerization of methacrylated oligo‐aromatic esters and the copolymerization of the esters with methyl methacrylate or tert‐butyl methacrylate using a radical initiator. The cut‐off wavelength (λ_co) of these polymers was shorter than the visible region aimed at, i. e. λ_co = ca. 330–370 nm, which is much shorter than λ_co of the typical second‐order NLO polymers containing groups such as azobenzene chromophores. Second‐harmonic generation (SHG) measurements of these polymer films after treatment by corona poling were carried out using the Maker‐fringe method. These polymer films exhibited good transparency in the visible region and a second‐order nonlinear optical coefficient d₃₃ of 2.2–9.8 pm·V^–1. The d₃₃ values of some derivatives decreased with an increase of the chromophore content, which is due to a strong interaction between the side chains with increasing chromophore content.     

Second Order Nonlinear Optical Performances of Polymers Containing Imidazole and Benzimidazole Chromophores

Summary: Condensation polymers based on two different NLO‐active chromophores, namely 2‐[4‐[(4‐N,N‐dihydroxyethylamino)phenylazo]phenyl]‐5(6)‐nitrobenzimidazole (BZI) and 2‐[4‐(4‐N,N‐dihydroxyethylamino)phenylazo]‐4,5‐dicyanoimidazole (IMI), have been synthesized and their basic properties measured. The second order NLO properties of poled polymers were investigated by SHG procedures at different temperatures (35, 65 and 85 °C) and exposure times. Resonance free d₃₃ coefficients (λ = 1 368 nm) took values in the range 1.8–4.0 pm · V^?1, but the time stability of their SHG signal was fairly acceptable, particularly for the high T_g (e.g. 188 °C) polymer for which a relaxation time (at 25 °C) of 2.8 years has been determined.

BZI and IMI chromophores.     

Preparation of AB2 Monomers and the Corresponding Hyperbranched Polyureas in a One‐Pot Procedure

Novel AB₂ monomers and corresponding hyperbranched polyureas are prepared in a one‐pot process. AB₂ monomers are synthesized by a highly selective reaction of carbonyl biscaprolactam (CBC) with triamines comprising one secondary and two primary amino groups. Only the primary amines react with CBC, yielding blocked isocyanates. On heating, self‐condensation of the obtained monomer solution takes place, yielding polymers with M _n up to 11 000 Da. Mark‐Houwink exponents of 0.3 and branching frequencies of 0.3 demonstrate the hyperbranched topology. Each polymer molecule comprises one secondary amino group in the focal point and numerous active blocked isocyanates located at the end of the polymer branches. The polymers are fully characterized by means of ¹H NMR, ¹³C NMR, MALDI‐TOF, SEC, and DSC.     

High Refractive Index Hyperbranched Polymers Prepared by Two Naphthalene‐Bearing Monomers via Thiol‐Yne Reaction

High refractive index (HRI) materials play an important role in optic‐electronic devices. In this study, two compounds with high content of naphthalene groups, 1,5‐dithiolnaphthalene and 1,3,5‐tris(naphthalyl–ethylnyl) benzene, are selected as “A₂” and “B₃” monomers, respectively to prepare hyperbranched HRI polymers. Metal‐free radical‐initiated “A₂ + B₃” thiol‐yne polyaddition is conducted successfully at different monomer molar ratios even for those sterically demanding molecules being able to adjust the molar mass as well as RI. Polymers with refractive index up to 1.79 at 589.7 nm are obtained, which are among the highest RI values so far reported for pure polymer‐based materials. The high RI, based on the high molar refraction of naphthalene group, metal‐free and easy one‐pot synthesis, high transparency in the visible area, good thermal stability, good solubility, and easy processability into thin films, make these polymers excellent candidates for optic‐electronic applications.

     

Novel Hyperbranched Poly(aryl ether urethane)s Using AB2‐Type Blocked Isocyanate Monomers and Copolymerization with AB‐Type Monomers

A novel AB₂‐type blocked isocyanate monomer was synthesized which was de‐blocked to provide a hyperbranched poly(aryl ether urethane). Copolymerization of this monomer with a functionally similar AB monomer yielded polymers with molecular weights in the range 8.0–310 kDa with a DB of 41–59% that underwent two‐stage decomposition above 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.09 to 1.10 dL · g^?1. End‐group modification of hyperbranched poly(aryl ether urethane)s was carried out with PEG monomethyl ether and 1‐decanol and affected the thermal properties and solubilities of the polymers. T_g of the polymers was reduced significantly from 201 to 71 °C upon incorporation of AB monomer in the copolymerization.

     

Novel Polymers with Inherent Conductivity and Enhanced Second‐Order NLO Activity

A new polythiophene derivative bearing an azobenzene substituent at the end of a ethylenic side‐chain was synthesized and characterized by FT‐IR spectroscopy, ¹H and ¹³C NMR spectroscopy, DSC, TGA, XRD, and UV‐vis spectroscopy. Its electrical conductivity was measured and its second‐order NLO activity was by SHG. Structure‐property relations were elucidated by comparison with a similar polymer only partially substituted by the NLO‐active chromophore. The molecular design of the chromophoric system allows high and stable non‐linear coefficients d₃₃ to be obtained, making these polymers suitable for the construction of second‐harmonic generators with improved efficiency and life‐time.

     

New Carbazole‐Based Hyperbranched Conjugated Polymer with Good Hole‐Transporting Properties

A copper‐catalyzed Ullmann C–N coupling reaction was used for the preparation of a new carbazole‐based HPU in good yield with a high molecular weight through a facile “AB₂ + A₂ + B₂”‐type approach. The HPU exhibited good solubility, high thermal stability with a T_g of 196 °C, as well as a suitable HOMO level for good hole injection and transporting properties. A two‐layer OLED device, using HPU as hole‐transporting layer (HTL) and Alq₃ as the light‐emitting layer, was fabricated to investigate the hole‐transporting properties of HPU. The luminance efficiency reached 1.14 cd · A^?1 at the maximum current density of 1 240 mA · cm^?2, while the maximum luminance efficiency was 1.65 cd · A^?1, indicating the high morphological and thermal stability of HPU.

     

Synthesis of Branched Polymers by Means of Living Anionic Polymerization, 9. Radical Coupling Reaction of 1,1‐Diphenylethylene‐Functionalized Polymers with Potassium Naphthalenide and Its Application to Syntheses of In‐Chain‐Functionalized Polymers and Star‐Branched Polymers

Radical coupling reactions of both 1,1‐diphenylethylene (DPE)‐chain‐end‐ and DPE‐in‐chain‐functionalized polymers with potassium naphthalenide have been studied under the conditions mainly in THF at –78°C. Chain‐end‐functionalized polymers having M̄_n values of less than 10 kg/mol were very efficiently coupled in more than 90% yield to afford the polymeric dianion that were dimeric coupled products with two 1,1‐diphenylalkyl anions in the middle of the chains. However, the dimer yield decreased with increasing the molecular weight. The dimer was obtained in 59% yield with use of the chain‐end‐functionalized polymer having M̄_n of 33.9 kg/mol. Well‐defined in‐chain‐functionalized polymers with two benzyl bromide and DPE moieties each have been successfully synthesized by the reaction of the polymeric dianion thus obtained with 1‐(4‐bromobutyl)‐4‐(tert‐butyldimethylsilyloxymethyl)benzene and 1‐[4‐(4‐bromobutyl)phenyl]‐1‐phenylethylene, respectively. The radical coupling reaction of in‐chain‐functionalized polymers with DPE (M̄_n ca. 20 kg/mol) with potassium naphthalenide also proceeded efficiently to afford the coupled products that were A₂A′₂ and A₂B₂ four‐arm star‐branched polymers with well‐defined structures (M̄_n ca. 40 kg/mol).     

Oxa‐ and Thiazolidine‐Containing Polymers Derived via the Asinger Four‐Component Reaction: the Ring Matters

Novel structural motifs in macromolecular chemistry are introduced by the use of the Asinger multicomponent reaction. The combination of ammonia, acetone, α‐chloroisobutyraldehyde, and either water or sodium hydrosulfide, leads to an oxazoline or thiazoline scaffold, respectively, which is subsequently modified with 10‐undecenol and 10‐undecenoyl chloride to obtain heterocycle‐functionalized α,ω‐dienes. These substrates are used as monomers in an acylic diene metathesis (ADMET) or thiol‐ene step‐growth polymerization. The thus‐obtained polymers are studied in post‐polymerization modifications, like hydrogenation and oxidation. Here, the thiazolidine‐ and oxazolidine‐containing polymers show dramatically different chemical stability due to the heterocyclic moieties.

     

The Synthesis of Poly(ethylene glycol) (PEG) Containing Polymers via Step‐Growth Click Coupling Reaction for CO2 Separation

The synthesis of step‐growth polymers via a step‐growth click coupling reaction of diazides based on poly(ethylene glycol) (PEG) and dialkynes based on aromatics is reported. The polymers are characterized by proton nuclear magnetic resonance spectroscopy (¹H‐NMR), carbon‐13 nuclear magnetic resonance spectroscopy (¹³C‐NMR), Fourier transform infrared spectroscopy (FT‐IR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Gas transport properties of one polymer are measured by the time lag (constant volume, variable pressure) method. Low gas permeabilities are a consequence of the rather high glass transition temperature. The rather high selectivities in separation of CO₂/N₂ and CO₂/CH₄ result from the CO₂‐philic groups such as PEG, triazole, and benzoxazine. According to the gas permeation measurements, the membrane is stable in the temperature range from 30 to 90 °C.

     

Polymethacrylate Copolymers Containing 4,5‐Dicyanoimidazole‐Based Chromophores and their Nonlinear Optical Behavior

Summary: Two series of methacrylate copolymers were prepared, based on two new nonlinear optically (NLO) active chromophores 2‐[4‐(N‐methacryloyloxyethyl‐N‐methylamino)phenylazo]‐4,5‐dicyanoimidazole (chromophore A ) and 1‐ethyl‐2‐[4‐(N‐methacryloyloxyethyl‐N‐methylamino)phenylazo]‐4,5‐dicyanoimidazole (chromophore B ). Second order NLO properties of the two series of copolymers ( A or B as monomer and methyl methacrylate as the comonomer) were investigated by SHG procedures at the fundamental wavelength 1368 nm; d₃₃ values in the range 0.2–3.3 pm · V⁻¹ were obtained, depending on the chromophore and on its molar content. The dependence of d₃₃ on the molar content of chromophore was investigated in the two cases.

     

Atom Transfer Radical Polymerization and Third‐Order Nonlinear Optical Properties of New Azobenzene‐Containing Side‐Chain Polymers

The atom transfer radical polymerization (ATRP) technique has been successfully applied to synthesize a series of nonlinear optically (NLO) active homopolymers, 4‐(4‐nitrophenyl‐diazenyl) phenyl acrylate ( P ‐ NPAPA ) and 4‐(4‐methoxyphenyl‐diazenyl) phenyl acrylate ( P ‐ MPAPA ), containing azobenzene groups on the side chain. The third‐order NLO properties of the polymer films were measured by the degenerated four‐wave mixing (DFWM) technique. A dependence of the χ⁽³⁾ values and response times of polymers on their number‐average molecular weight and the electronic effect of the substituent (nitro‐ or methoxy‐) on the azobenzene group have been evidenced. The increasing χ⁽³⁾ value of the polymer films at the magnitude of about 10^?10 was displayed with increasing molecular weight and the presence of the push‐pull electronic system contributes much in enhancing the third‐order NLO susceptibility of polymers.

     

A New Dithienylbenzotriazole‐Based Poly(2,7‐carbazole) for Efficient Photovoltaics

A new dithienyl benzotriazole‐based conjugated polymer was synthesized by Suzuki coupling reaction. The polymer was found to be soluble in common organic solvents, such as chloroform, tetrahydrofuran and chlorobenzene, with excellent film‐forming properties. The structure of the polymer was confirmed by ¹H NMR, the molecular weights determined by GPC and the thermal properties investigated by TGA and DSC. The polymer films exhibited an absorption band in the wavelength range 300 to 610 nm. Preliminary photovoltaic cells based on the composite structure of indium tin oxide (ITO)/PEDOT:PSS/ PCDTBTz:PC ₆₀ BM (1:2 w/w)/Al showed an open‐circuit voltage of 0.92 V, a power conversion efficiency of 2.2% and a short circuit current of 5.33 mA cm^?2.

     

New Functional Block Copolymers via RAFT Polymerization and Polymer‐Analogous Reaction

The synthesis of block copolymers consisting of nonfunctional and reactive blocks is reported. The precursor polymers are ABA triblock copolymers, consisting of S/VBC or MMA/GMA and prepared via RAFT polymerization. The reactive blocks are converted into blocks with new functionalities that are hard to achieve by direct polymerization. The new polymers are either amphiphilic, with acidic or basic blocks on the outside and a nonfunctional core, or have functionalities that are useful for further reactions like thiol‐ene or alkyne‐azide click reactions. Reaction success and degree of functionalization are determined via FTIR, elemental analysis, and MALDI‐TOF MS. The stability of the RAFT functionalities during the modification reactions is analyzed.     

Nonlinear Optical Properties and Liquid‐Crystalline Behavior of New Polyesters with Dipole Moments Aligned Transverse to the Backbone

Side‐chain azobenzene‐based second‐order nonlinear optical (NLO) polyesters ( PNPAR , PNPAPAR , PPAR‐TC , PPAPAR‐TC ) containing nitro or tricyanovinyl groups as acceptors with their dipole moments aligned transverse to the polymer backbone, were synthesized and characterized, and their thermal properties, liquid‐crystalline (LC) phase behavior, and NLO properties studied. Polymers containing nitro groups as acceptors were found to exhibit LC properties, while those containing tricyanovinyl groups as acceptors did not. The LC polymers were of smectic nature. The polymer PNPAR with a nitro group, when poled at the LC phase‐transition temperature range, was found to exhibit higher NLO activity than that with a tricyanovinyl group ( PPAR‐TC ). When polymer PNPAPAR containing a nitro group, also exhibiting an LC phase, was poled at a temperature different from that of its transition temperature, the NLO activity observed was comparable to, and/or lower than, that of the similar polymer ( PPAPAR‐TC ) having a tricyanobvinyl group in the place of the nitro group. All the polymers were found to possess moderate temporal stability of second harmonic generation activity and were found to have stability over the whole process.     

Investigation on Naphthalene and Its Derivatives‐Based Microporous Organic Hyper‐Cross‐Linked Polymers via Different Methodologies

A series of cost‐effective hyper‐cross‐linked polymers (HCLPs) are synthesized from naphthalene via the external cross‐linker (ECL) knitting method, the solvent knitting method, and the Scholl coupling reaction, respectively. According to multiple characterizations, the resulting polymers are thermally stable and fluorescent with large specific surface areas (SSAs) and narrow pore distributions. In particular the HCLP synthesized using dimethoxymethane as the ECL exhibits SSAs up to 2870 m² g^?1 and shows a great potential in gas adsorption applications. Naphthol and 1‐methylnaphthalene are used as monomers to synthesize HCLPs by the above three methods to investigate whether introducing functional groups to naphthalene would improve properties of the resulting polymers. Moreover, HCLPs feature high SSAs, outstanding thermal and fluorescent performances, and facile synthesis, making them promising candidates for industrial applications.     

Synthesis and Optical Properties of Poly[2‐{N‐Methyl‐N‐(4‐(4‐ethynylphenylazo)phenyl)amino}ethyl butyrate]

Summary: The high‐molecular‐weight functional polyacetylene that contain a para‐aminoazobenzene chromophore, poly[2‐{N‐Methyl‐N‐(4‐(4‐ethynylphenylazo)phenyl)amino}ethyl butyrate] [poly(EAPAB)], was synthesized in moderate yield and characterized by FT‐IR, ¹H NMR, UV‐vis, TGA, and GPC. The nonlinear optical and optical limiting properties were performed with 8 ns pulse width at 532 nm wavelength. The results show that the introduction of the flexible amino group effectively improved the solubility of polymer [poly(EAPAB)] in common organic solvent, such as CHCl₃, THF, and dioxane, while poly(4‐ethynylazobenzene) [poly(4EAB)] without the flexible amino group shows poor solubility in common organic solvent. Simultaneously, poly(EAPAB) still shows good thermal stability, large third‐order nonlinear optical property, and novel optical limiting property owing to the functionalization of the para‐aminoazobenzene chromophore.

Polymerization of EAPAB by Rh(nbd)Cl₂‐Et₃N to poly(EAPAB).     

Amphiphilic Hyperbranched Polymers Containing Two Types of β‐Cyclodextrin Segments: Synthesis and Properties

Amphiphilic hyperbranched polymers carrying two types of β‐cyclodextrin groups including ionic and covalent bonding were synthesized via atom transfer radical polymerization and immobilization reaction. Their inclusion capabilities for single or double‐guest molecules were investigated by UV‐visible spectroscopy. Using Chlorambucil and Lonidamine as the double model drugs, their encapsulation efficiencies indicate that these polymers possess the capabilities of high drug‐loading. Furthermore, the release behaviors of these polymers were studied via UV‐visible spectroscopy. The results indicate that they can slow the release rate of double model drugs. Varying the pH values of environment or regulating their shell layer structures can control the release behaviors of double model drugs.

     

New Insights into Nickel(II), Iron(II), and Cobalt(II) Bis‐Complex‐Based Metallo‐Supramolecular Polymers

One of the most important characterization methods for macromolecules is SEC. The main difficulty for this type of measurements concerning metallo‐supramolecular polymers based on terpyridines is related to the interaction between the charged supramolecular species and the SEC column material. In this paper, we report new studies on the characterization and the stability of supramolecular polymers based on terpyridine metal complexes utilizing SEC. The main aspects concerning the equilibrium between complexed and uncomplexed species are discussed in detail. The present study reveals a strong relationship between the binding strength of the metal ion used and the stability of the terpyridine metal complex during the SEC measurements, which is in agreement with previously published results regarding the stability of small terpyridine metal complexes in solution. These results can lead to improved analytic possibilities and to a better fundamental understanding of the mentioned metallo‐supramolecular polymers. Furthermore, the prepared chain‐extended supramolecular‐polymer was analyzed by depth‐sensing indentation proving an increase in elastic modulus in comparison with the starting material.