Hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s: Synthesis,characterization, end‐group modification,and optical properties

Novel AB₂‐type monomers such as 3,5‐bis(4‐methylolphenoxy)benzoic acid ( monomer 1 ), methyl 3,5‐bis(4‐methylolphenoxy) benzoate ( monomer 2 ), and 3,5‐bis(4‐methylolphenoxy)benzoyl chloride ( monomer 3 ) were synthesized. Solution polymerization and melt self‐polycondensation of these monomers yielded hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s. The structure of these polymers was established using FTIR and ¹H NMR spectroscopy. The molecular weights (M_w) of the polymers were found to vary from 2.0 × 10³ to 1.49 × 10⁴ depending on the polymerization techniques and the experimental conditions used. Suitable model compounds that mimic exactly the dendritic, linear, and terminal units present in the hyperbranched polymer were synthesized for the calculation of degree of branching (DB) and the values ranged from 52 to 93%. The thermal stability of the polymers was evaluated by thermogravimetric analysis, which showed no virtual weight loss up to 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.010 to 0.120 dL/g. End‐group modification of the hyperbranched polymer was carried out with phenyl isocyanate, 4‐(decyloxy)benzoic acid and methyl red dye. The end‐capping groups were found to change the thermal properties of the polymers such as T_g. The optical properties of hyperbranched polymer and the dye‐capped hyperbranched polymer were investigated using ultraviolet‐absorption and fluorescence spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5414–5430, 2008     

Preparation and properties of novel thermotropic liquid crystalline hyperbranched polyesters composed of five‐membered heterocyclic mesogen by A2 + B3 approach

New thermotropic liquid crystalline (LC) hyperbranched (HB) polyesters containing 2,5‐diphenyl‐1,3,4‐thiadiazole (DTD) unit as mesogen in the interiors were prepared at various mole ratios (A₂/B₃) by melt and solution polycondensations of a dioxydiundecanol of DTD (A₂) and 1,2,3‐propanetricarboxylic acid (B₃) via the A₂ + B₃ approach and their LC and optical properties were investigated. FTIR and ¹H‐NMR spectroscopies indicated that all the expected HB polyesters, which show good solubilities in organic solvents, are produced without gelation during the polymerization. Among them, the HB polymer prepared in the mole ratio of A₂/B₃ = 3/2 by the solution polycondensation had the highest inherent viscositiy. DSC measurents, polarizing microscope observations of optical textures, and X‐ray analyses suggested that the LC properties of HB polymers depend on the polymerization methods and the feed mole ratios. In the HB polymers prepared using the melt polycondensation, only the polymer prepared in the mole ratio of A₂/B₃ = 3/1 formed a highly‐ordered, tilted, crystal‐like smectic phase, but all the polymers prepared by the solution polycondensation formed highly‐ordered, tilted, smectic phases. Solution and solid‐state UV‐vis and photoluminescent (PL) spectra indicated that the HB polymers show maximum absorbances and blue‐light emission on the basis of the DTD unit, where the Stokes‐shifts were observed, probably because of intermolecular aggregation effects © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2998–3008, 2007     

Blue light‐emitting hyperbranched polymers using fluorene‐co‐dibenzothiophene‐S,S‐dioxide as branches

A series of blue light‐emitting hyperbranched polymers comprising poly(fluorene‐co‐dibenzothiophene‐S,S‐dioxide) as the branch and benzene, triphenylamine, or triphenyltriazine as the core were synthesized by an “A₂ + A₂' + B₃” approach of Suzuki polymerization, respectively. All resulted copolymers exhibited quite comparable thermal properties with the glass transition temperatures in the range of 59–68 °C and relatively high decomposition temperatures over 420 °C. Photoluminescent spectra exhibited slight variation with the molar ratio of the dibenzothiophene‐S,S‐dioxide unit and the size of the core units. Polymer light‐emitting devices demonstrated blue emission with excellent stability of electroluminescence. Copolymers based on smaller core units of benzene and triphenylamine exhibited enhanced device performances regarding to that of triphenyltriazine. With the device configuration of ITO/PEDOT:PSS/polymer/CsF/Al, a maximum luminous efficiency of 4.5 cd A^?1 was obtained with Commission Internationale de L'.Eclairage (CIE) coordinates of (0.16, 0.19) for the copolymer PFSO15B. These results indicated that hyperbranched structure can be a promising strategy to attain spectrally stable blue‐light‐emitting polymers with high efficiency. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1043–1051     

Linear and A2+B3‐type hyperbranched polyesters comprising phenylbenzothiazole unit: Preparation,liquid crystalline,and optical properties

Novel liquid crystalline (LC) hyperbranched (HB) polyesters comprising phenylbenzothiazole (PBT) unit as mesogen in the interiors were prepared at various feed mole ratios (A₂/B₃) by solution polycondensation of a dioxydiundecanol derivative of PBT (A₂ monomer) with trimesic acid trimethyl ester (B₃ monomer) via A₂+B₃ approach and their LC and optical properties were investigated. Analogous linear polyesters containing the PBT unit in the main chains were also prepared by the solution polycondensation of A₂ monomer with aromatic or aliphatic dimethyl esters. FTIR and ¹H‐NMR spectroscopies indicated that the HB polyesters are produced without gelation during the polycondensation and have degree of branching (DB) of 7–46%. The structures of HB polymers changed depending on the feed mole ratios and the polymer prepared in the mole ratio of A₂/B₃ = 3/2 had the highest inherent viscosity and DB. Acetylation of terminal OH group‐having HB polyesters prepared in excess mole ratios of A₂/B₃ afforded ones bearing acetoxy groups in the terminals. DSC measurements, polarizing microscope observations of textures, and X‐ray analyses suggested that only the terminal OH group‐having HB polymer prepared in the mole ratio of A₂/B₃ = 3/1 form smectic C phase. In the linear polymers, the polymers derived by using the aromatic dimethyl esters had no LC melt, but those from the aliphatic dimethyl esters formed LC smectic C phase. The acetoxy group‐bearing HB polymers showed more stable smectic A or C phase than those with the OH terminals. Solution UV‐vis and photoluminescent (PL) spectra indicated that the linear and the HB polymers have analogous optical properties and display maximum absorbances and blue‐light emission on the basis of the PBT unit, where the Stokes shifts were observed because of intermolecular aggregation effects, but there is a large difference between the optical behaviors of the linear and the HB polymers in film, whose E_g values of the linear polymers decreased and those of the HB polymers vice versa. Quantum efficiencies (Φ) had a tendency of increase in the linear polymers and the HB polymers forming LC phases. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6688–6702, 2008     

Synthesis and properties of new orange red light‐emitting hyperbranched and linear polymers derived from 3,5‐dicyano‐2,4,6‐tristyrylpyridine

Two new orange red light‐emitting hyperbranched and linear polymers, poly(pyridine phenylene)s P1 and P2, were prepared by the Heck coupling reaction. In particular, an A₂ + B₃ approach was developed to synthesize conjugated hyperbranched polymer P2 via one‐pot polycondensation. The polymers were characterized by NMR, Fourier transform infrared, ultraviolet–visible, and elemental analysis. They showed excellent solubility in common solvents such as tetrahydrofuran, CH₂Cl₂, CHCl₃, and N,N‐dimethylformamide and had high molecular weights (up to 6.1 × 10⁵ and 5.8 × 10⁵). Cyclic voltammetry studies revealed that P2 had a low‐lying lowest unoccupied molecular orbital energy level of ?3.22 eV and a highest occupied molecular orbital energy level of ?5.43 eV. The thin film of P2 emitted strong orange‐red photoluminescence at 595 nm. A double‐layer light‐emitting diode fabricated with the configuration of indium tin oxide/P2/tris(8‐hydroxy‐quinoline)aluminum/Al emitted orange‐red light at 599 nm, with a brightness of 662 cd/m² at 7 V and a turn‐on voltage of 4.0 V; its external quantum efficiency was calculated to be 0.19% at 130.61 mA/cm². This indicated that this new electroluminescent polymer (P2) based on 3,5‐dicyano‐2,4,6‐tristyrylpyridine could possibly be used as an orange‐red emitter in polymer light‐emitting displays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 493–504, 2005     

Michael addition polymerizations of difunctional amines (AA′) and triacrylamides (B3)

Novel hyperbranched poly(amido amine)s containing tertiary amines on the backbones and acryl or secondary amines as the surface groups were successfully synthesized via the Michael addition polymerizations of a triacrylamide [1,3,5‐triacryloylhexahydro‐1,3,5‐triazine (TT)] and a difunctional amine [n‐butylamine (BA)] NMR techniques were used to clarify the structures of hyperbranched polymers and polymerization mechanism. The reactivity of the secondary amine formed in situ was much lower than that of the primary amines in BA. When the feed molar ratio was 1:1 TT/BA, the secondary amine formed in situ was almost kept out of the reaction before the BA (AA′) and TT (B₃) monomers were consumed, and this led to the formation of A′B₂ intermediates containing one secondary amine group and two acryl groups. The self‐polymerization of the A′B₂ intermediates produced hyperbranched polymers bearing acryl as surface groups. For the polymerization with the feed molar ratio of 1:2 TT/BA, A′₂B intermediates containing one acryl group and two secondary amine groups were accumulated until self‐polymerization started; the self‐polymerization of the intermediates formed hyperbranched polymers with secondary amines as their surface groups. Modifications of surface functional groups were studied to form new hyperbranched polymers. The hyperbranched poly(amido amine)s were amorphous. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6226–6242, 2006     

Acid chloride‐functionalized hyperbranched polyester for facile and quantitative chain‐end modification: One‐pot synthesis and structure characterization

Carboxylic acid chloride end‐functionalized all‐aromatic hyperbranched polyesters were prepared from the bulk polycondensation of the AB₂ monomer 5‐(trimethylsiloxy)isophthaloyl dichloride. The acid chloride end functionality of the hyperbranched polyester was modified in situ with methanol and yielded methyl ester ends in a one‐pot process. Chain‐end functionalization and esterification were quantitative according to both potentiometric titration and ¹H NMR analysis. The signals of ¹H and ¹³C NMR spectra of the esterified hyperbranched polyester were fully assigned from model compounds of the focal, linear, dendritic, and terminal units. The degree of branching and molecular weight averages measured by ¹H and ¹³C NMR spectroscopy and multidetector size exclusion chromatography increased systematically with increasing polymerization temperatures between 80 and 200 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2855–2867, 2002     

Novel Functional Conjugative Hyperbranched Polymers with Aggregation‐Induced Emission: Synthesis Through One‐Pot “A2+B4” Polymerization and Application as Explosive Chemsensors and PLEDs

With the aim to develop new tetraphenylethylene (TPE)‐based conjugated hyperbranched polymer, TPE units, one famous aggregation‐induced emission (AIE) active group, are utilized to construct hyperbranched polymers with three other aromatic blocks, through an “A₂+B₄” approach by using one‐pot Suzuki polycondensation reaction. These three hyperbranched polymers exhibit interesting AIEE behavior and act as explosive chemsensors with high sensitivity both in the nanoparticles and solid states. This is the first report of the AIE activity of the TPE‐based conjugated hyperbranched polymers. Their corresponding PLED devices also demonstrate good performance.     

Thermoreversible nonlinear diels‐alder polymerization of furan/plant oil monomers

Novel trifunctional monomers based on renewable resources were prepared and subsequently polymerized via the Diels‐Alder (DA) polycondensation between furan and maleimide complementary moieties. Three basic approaches were considered for these nonlinear DA polycondensations, namely the use of (i) a bisfuran monomer in combination with a trismaleimide (A₂ + B₃ system) and (ii) a trisfuran monomer in conjunction with a bismaleimide (A₃ + B₂ system) leading to branched or crosslinked materials, and (iii) the use of monomers incorporating both furan and maleimide end groups (A₂B or AB₂ systems), which lead to hyperbranched structures. The application of the retro‐DA reaction to the ensuing polymers confirmed their thermoreversible character. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

One‐pot synthesis and characterization of hyperbranched poly(ester‐amide)s from commercially available dicarboxylic acids and multihydroxyl secondary amines

A convenient and cost‐effective strategy for synthesis of hyperbranched poly(ester‐amide)s from commercially available dicarboxylic acids (A₂) and multihydroxyl secondary amine (CB₂) has been developed. By optimizing the conditions of model reactions, the AB₂‐type intermediates were formed dominantly during the initial reaction stage. Without any purification, the AB₂ intermediate was subjected to thermal polycondensation in the absence of any catalyst to prepare the aliphatic and semiaromatic hyperbranched poly(ester‐amide)s bearing multi‐hydroxyl end‐groups. The FTIR and ¹H NMR spectra indicated that the polymerization proceeded in the proposed way. The DBs of the resulting polymers were confirmed by a combination of inverse‐gated decoupling ¹³C NMR, and DEPT‐135 NMR techniques. The DBs of the hyperbranched poly(ester‐amide)s were in the range of 0.44–0.73, depending on the structure of the monomers used. The hyperbranched polymers exhibited moderate molecular weights with relatively broad distributions determined by SEC. All the polymers displayed low inherent viscosity (0.11–0.25 dL/g) due to the branched nature. Structural and end‐group effects on the thermal properties of the hyperbranched polymers were investigated using DSC. The thermogravimetric analysis revealed that the resulting polymers exhibit reasonable thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5077–5092, 2008     

The preparation of hyperbranched aromatic and aliphatic polyether epoxies by chloride‐catalyzed proton transfer polymerization from ABn and A2 + B3 monomers

Hyperbranched polymers consisting of aromatic or aliphatic polyether cores and epoxide chain‐end peripheries were prepared by proton transfer polymerization. AB₂ diepoxyphenol monomer 1 proved to be well suited for the preparation of hyperbranched aromatic polymer 2 by this proton transfer polymerization. The use of chloride‐ion catalysis, rather than conventional base catalysis, for the preparation of polymers from diepoxyphenol 1 offered a unique method to control the ultimate molecular weight of the polymer product through variations of the initial concentration of monomer 1 in tetrahydrofuran. An alternative route to hyperbranched polyether epoxies made use of commercially available or easily prepared aliphatic monomers of the types AB₂, AB₃, and A₂ + B₃. Although these aliphatic polymerizations can be initiated with a base, chloride‐ion catalysis proved most effective for controlling the polymerization. The hyperbranched epoxies were characterized by NMR spectroscopy, gel permeation chromatography, and multi‐angle laser light scattering. Chemical modification of the polymers after polymerization was carried out via nucleophilic addition on the epoxide groups or derivatization of the hydroxy substituents within the hyperbranched polymer structure. Spectroscopic measurements suggested that some such ring‐opened materials may adopt reverse unimolecular micellar structures in appropriate solution environments. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4850–4869, 2000     

Self‐controlled synthesis of hyperbranched poly(ether‐ketone)s from A2 + B3 approach in poly(phosphoric acid)

Self‐controlled synthesis of hyperbranched poly(ether‐ketone)s (HPEKs) were prepared from “A₂ + B₃” approach by using different monomer solubility in reaction medium. 1,3,5‐Triphenoxybenzene as a hydrophobic B₃ monomer was reacted with commercially available terephthalic acid or 4,4′‐oxybis(benzoic acid) as a hydrophilic A₂ monomer in a hydrophilic reaction medium, polyphosphoric acid (PPA)/phosphorous pentoxide (P₂O₅). The resultant HPEKs were soluble in various common organic solvents and had the weight‐average molecular weight in the range of 3900–13,400 g/mol. The results implied that HPEKs were branched structures instead of crosslinked polymers. The molecular sizes and shapes of HPEKs were further assured by morphological investigation with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Hence, the applied polymerization condition was indeed strong enough to efficiently facilitate polycondensation via “direct” Friedel‐Crafts reaction without gelation. It could be concluded that the polymer forming reaction was kinetically controlled by automatic and slow feeding of the hydrophobic B₃ monomer into the hydrophilic reaction mixture containing hydrophilic comonomer. As a result, hyperbranched structures were formed instead of crosslinked polymers even at full conversion (equifunctional monomer feed ratio). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3326–3336, 2009     

Unimolecular micelles and reverse micelles based on hyperbranched polyethers—Comparative study of AB2 + A‐R and A2 + B3 + A‐R type strategies

Core‐shell type hyperbranched polymers that are capable of forming unimolecular micelles and reverse micelles in aqueous and hydrocarbon medium, respectively, were synthesized via two approaches, namely AB₂ + A‐R and A₂ + B₃ + A‐R type copolymerizations. In case of micelle‐forming polymers, an AB₂ monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A‐R type comonomer. One the other hand, for the preparation of reverse micelle‐forming polymers, an AB₂ monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A‐R type comonomer. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein about 65–70% of the terminal B groups were capped by the A‐R comonomer. Dye‐uptake measurements revealed that the polymers prepared via the AB₂ + A‐R approach exhibited a significantly larger uptake compared with those prepared via the A₂ + B₃ + A‐R approach. This suggests that the AB₂ + A‐R approach generates hyperbranched polymers with better defined core‐shell topology when compared with polymers prepared via the A₂ + B₃ + A‐R approach, which is in accordance with previous studies that suggest that A₂ + B₃ approach yields polymers with significantly lower branching levels and consequently less compact structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 80–91, 2009     

Photoactive,liquid‐crystalline,hyperbranched benzylidene polyesters: Synthesis and characterization

A novel photoactive, liquid‐crystalline, hyperbranched benzylidene polyester (PAHBP) was synthesized from a dilute solution of an A₂ photoactive monomer [bis(4‐hydroxybenzylidene)‐4‐phenyl cyclohexanone] and a B₃ monomer (1,3,5‐benzene tricarboxylic acid chloride) by the solution polycondensation method in the presence of pyridine as a condensing agent. PAHBP was thoroughly characterized by Fourier transform infrared, ¹H and ¹³C NMR, ultraviolet–visible spectrometry, and gel permeation chromatography. The inherent viscosity of the polymer was 0.35 dL/g in tetrahydrofuran. The degree of branching was 0.53, which confirmed the branched architecture of the polymer. Furthermore, thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy were used to examine the thermal stability and thermotropic liquid‐crystalline properties of the hyperbranched polyester. The polymer exhibited a nematic mesophase over a wide range of temperatures. The photoreactivity of PAHBP was studied by photolysis under ultraviolet light. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 53–61, 2006     

Cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures: Synthesis and gradient stimuli‐responsive properties

We report the synthesis and gradient stimuli‐responsive properties of cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures. A ionic hyperbranched poly(β‐cyclodextrin) (β‐CD) core was firstly synthesized via a convenient “A₂+B₃” approach. Double‐layered shell architectures, composed of poly(N‐isopropyl acrylamide) (PNIPAm) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) miktoarms as the outermost shell linked to poly(N,N‐diethylaminoethyl methacrylate) (PDEAEMA) homoarms which form the inner shell, were obtained by a sequential atom transfer radical polymerization (ATRP) and parallel click chemistry from the modified hyperbranched poly(β‐CD) macroinitiator. The combined characterization by ¹H NMR, ¹³C NMR, ¹H‐²⁹Si heteronuclear multiple‐bond correlation (HMBC), FTIR and size exclusion chromatography/multiangle laser light scattering (SEC/MALLS) confirms the remarkable hyperbranched poly(β‐CD) core and double‐shell miktoarm architectures. The gradient triple‐stimuli‐responsive properties of hyperbranched core‐double‐shell miktoarm architectures and the corresponding mechanisms were investigated by UV–vis spectrophotometer and dynamic light scattering (DLS). Results show that this polymer possesses three‐stage phase transition behaviors. The first‐stage phase transition comes from the deprotonation of PDEAEMA segments at pH 9–10 aqueous solution under room temperature. The confined coil‐globule conformation transition of PNIPAm and PDMAEMA arms gives rise to the second‐stage hysteretic cophase transition between 38 and 44 °C at pH 10. The third‐stage phase transition occurs above 44 °C at pH = 10 attributed to the confined secondary conformation transition of partial PDMAEMA segments. This cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures are expected to solve the problems of inadequate functionalities from core layer and lacking multiresponsiveness for shell layers existing in the dendritic core‐multishell architectures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Kinetics of nonideal hyperbranched A2 + B3 polycondensation: Simulation and comparison with experiments

To overcome the deficiency of mean field method in introducing the intramolecular cyclization and the steric effects, the reactive bond fluctuation model was applied to study nonideal hyperbranched A₂ + B₃ polycondensation, which has high sensitivity of gelation to the concentration of monomers, the feed ratio and the reactivity of functional groups. Simulation demonstrated that the mean field theory overestimated hyperbranched polymerization especially at high reaction conversion in the system with low monomer concentration where the intramolecular cyclization and the steric hindrance play crucial influences on molecular weight, molecular weight distribution and gel point (GP). The dependences of GP on the monomer concentration, feed ratio, and the reactivity of groups are clearly shown. We further simulated a specific polycondensation system with aromatic terephthaloyl chloride (TCl, A₂) and 1,1,1‐tris(4‐trimethylsiloxyphenyl)ethane (TMS‐THPE, B₃) (Macromolecules 2007, 40, 6846) using fitting technology, and estimated molecular weight, molecular weight distribution, GPs, and the conformation of hyperbanched polymer. It provides a feasible way to quantitatively understand hyperbranched polymerization with the reaction specificity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

New hyperbranched second‐order nonlinear optical poly(arylene‐ethynylene)s containing pentafluoroaromatic rings as isolation group: Facile synthesis and enhanced optical nonlinearity through Ar‐ArF self‐assembly effect

In this article, a facile route was designed to prepare four new hyperbranched poly(arylene‐ethynylene)s containing azo‐chromophore moieties through one‐pot “A₂+B₃” approach via simple Sonogashira coupling reaction. The polymers were all soluble in organic solvents and demonstrated good nonlinear optical (NLO) properties, because of the three‐dimensional spatial isolation effect of these hyperbranched polymers. Due to the different B₃‐type comonomer, the self‐assembly effect of pentafluoroaromatic in the interior of these polymers were different, leading to the different trends of the NLO activities. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Rotaxane‐type hyperbranched polymers from a crown ether host and paraquat guests containing blocking groups

Rotaxane‐type hyperbranched polymers are synthesized for the first time from A₂B type semi‐rotaxane monomers formed in situ via complexation of bis(m‐phenylene)‐32‐crown‐10 dimethanol ( 1 ) and two paraquat ω‐n‐alkylenecarboxylic acid derivatives with tris(p‐t‐butylphenyl)methylphenylalkylene stoppers ( 8 and 9) . Rotaxane and taco complexes exist in solutions of the hyperbranched polyesters in CD₃CN/CDCl₃ as confirmed by NMR spectroscopy, but the taco complexes, which derive from non‐rotaxanated paraquat units, disappear in DMSO‐d₆. NMR spectroscopy indicates the portion of rotaxanes strongly interlocked by the environment (inner rotaxanes) is larger in HP1?9 , which has longer alkylene spacers, perhaps indicating a higher degree of polymerization. The molecular size increases upon formation of the hyperbranched polymers are confirmed by dynamic light scattering and by viscometry. As with covalent hyperbranched polymers a number of potential applications exist; the unique mechanically linked character and the presence of uncomplexed host and guest moieties foreshadow the use of such systems for their responses to external stimuli with the added benefit of providing molecular recognition sites useful as delivery vehicles. Use of other host‐guest motifs to form the semirotaxane A₂B monomers is possible and complementary systems with higher binding constants will enable efficient syntheses of high molecular weight, mechanically linked hyperbranched polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1647–1658     

Synthese und Kristallstruktur von 2‐Azido‐4,6‐dichloro‐s‐triazin

Synthesis and Crystal Structure of 2‐Azido‐4,6‐dichloro‐s‐triazine Single crystals of 2‐azido‐4,6‐dichloro‐s‐triazine were obtained from a reaction between cyanuric chloride and sodium azide. The structure of this compound was determined by single crystal X‐ray diffraction. 2‐Azido‐4,6‐dichloro‐s‐triazine crystallizes in the orthorhombic space group Pbca (no. 61), Z = 8, a = 746.48(8) pm, b = 952.6(1) pm, c = 2001.6(2) pm. The crystal structure contains (C₃N₃)(N₃)Cl₂ molecules being arranged in a tape‐like fashion, with tapes running along a‐axis direction. The tapes are combined with each other by interlocking azide‐ligands including an angle of approximately 90°. This arrangement leads to the formation of corrugated layers in the crystal structure.     

Photoactive liquid crystalline polymers: A comprehensive study of linear and hyperbranched polymers synthesized by A2B2, A2B3, A3B2, and A3B3 approaches

A series of linear and hyperbranched polyester epoxies, with varied structural parameters such as kinked structure and different dendritic architectures, were synthesized by A₂ + B₂, A₂ + B₃, A₃ + B₂, and A₃ + B₃ approaches. The structures of synthesized monomers and polymers were confirmed by Fourier transform infrared, ¹H NMR, and ¹³C NMR spectroscopic techniques. The effect of varied structural parameters on phase behavior and photoresponsive properties was investigated by using differential scanning calorimeter, thermal optical polarized microscope, UV–visible spectroscopy, photoviscosity, and refractive index studies. The transition temperatures of hyperbranched polymers were higher than that of the corresponding linear analogues. All the polymers showed nematic phase (nematic droplets) over a broad temperature range. The effect of kinked structural unit on photoresponsive property is less in both linear and hyperbranched architectures. Although the effect of architectural nature is highly considerable within the hyperbranched architectures, the polymer (HPE–33) synthesized by A₃ + B₃ approach showed highest rate of photocrosslinking, followed by HPE–I 32; HPE–T 32, and HPE–23, which were synthesized by A₃ + B₂ and A₂ + B₃ approaches, respectively. The findings in photoresponsive properties were further supported by molecular modeling studies. Substantial variation of refractive index (0.015–0.024) indicates that these polymers could be used for optical recording. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011