Monomers 1a Research Articles

Reduction-cleavable hyperbranched polymers with limited intramolecular cyclization via click chemistry

In this contribution, we present new reduction-cleavable hyperbranched disulfide bonds-containing poly(ester triazole)s with limited intramolecular cyclization, which can be synthesized by the Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of A2 monomer of dipropargyl 3,3′-dithiobispropionate and B3 monomer of tris(hydroxymethyl)ethane tri(4-azidobutanoate). The hyperbranched poly(ester triazole)s possess numerous terminal groups and weight-average molecular weight up to 20,400 g mol−1 with a polydispersity index in the range 1.57–2.17. The CuAAC introduces rigid triazole units into the backbones of hyperbranched poly(ester triazole)s and reduces intramolecular cyclization, which is proved by topological analysis and 1H NMR spectroscopy. The disulfide bonds on backbones endow the reduction-cleavable feature to the hyperbranched poly(ester triazole)s at the presence of dithiothreitol. It gives a novel and convenient methodology for the synthesis of reduction-responsive functional polymer with controlled topologies, and the reduction-cleavable hyperbranched poly(ester triazole)s with limited intramolecular cyclization are expected to possess potential in the application of stimuli-responsive anticancer drug nanocarriers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2374–2380

Synthesis and Properties of Novel Optically Active Poly(thiophenyleneethynylene-phenyleneethynylene)s

Abstract The Sonogashira–Hagihara coupling polymerization of l-alanine-derived 2,5-dibromothiophene monomers 1a–1d with p- and m-diethynylbenzenes 2p and 2m gave novel optically active poly(thiophenyleneethynylene-phenyleneethynylene)s poly(1a-2p)–poly(1d-2m). p-Phenylene-linked poly(1b-2p)–poly(1d-2p) bearing amide-amide side chains exhibited CD signals based on chiral aggregates, while the m-phenylene-linked counterparts poly(1b-2m)–poly(1d-2m) exhibited no evidence of the formation of secondary structures. Poly(1a-2p) and poly(1a-2m) bearing amide-ester side chains exhibited no CD signal as well.

Synthesis and characterization of hyperbranched poly(aryl ether ketone) terminated with phthalonitrile group

A series of novel cross-linkable hyperbranched poly(aryl ether ketone) (HPAEK) polymers (CN-HPAEK n) were synthesized using 2,4′,6-trifluoro-benzophenone as a BB′2 monomer, hydroquinone as an A2 monomer, and 4-nitrophthalonitrile as an endcapping reagent and characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. The average molecular weights of the prepared polymers were determined by gel permeation chromatographic analysis. Thermal cross-linking of CN-HPAEK n, catalyzed by p-bis[4-(4-aminophenoxy)phenyl]sulfone, was then performed via heating their films up to 350°C. The uncured synthesized polymers had good solubility, while the cured samples became insoluble in common organic solvents. Spectra measurement demonstrated trimerization reaction of terminal cyano groups to form triazine rings. The resulting cured samples had high glass transition temperatures and excellent thermal stability with high char yield. Gel content measurements demonstrated that the cured polymers had high cross-linking density, with significantly high gel content of over 95.0%. Thermal mechanical analysis indicated that the cured phthalonitrile resins possessed good thermal mechanical properties at elevated temperatures. These kinds of phthalonitrile resins may be used as a candidate for high-performance polymeric film materials.

Synthesis of maltopentaose-conjugated surface-active styrenic monomers and their micellar homopolymerization in water

Maltopentaose (Mal5)-conjugated surface-active styrenic monomers 1a, 1b, and 1c are described, which contain hydrophobic spacers, such as C1, C5, and C7 alkylene chains, respectively. The glycomonomers 1a-c were synthesized by the direct β-N-glycosyl reaction of styrene derivatives with aminoalkyl groups 4a-c onto Mal5 in dry methanol, followed by the N-acetylation with acetic anhydride. The self-assembling properties for the aqueous solutions of 1a-c were characterized by surface tension measurements and light scattering experiments, providing the physicochemical parameters for the formed 1a-c micelles including the critical micelle concentration, apparent hydrodynamic radius (Rh,app), and weight average aggregation number (Nagg). The transmission electron microscope observations revealed the most important result in this study that 1a produced loose spherical micelles with the number average diameter (dn) of 26 nm, while both 1b and 1c formed worm-like micelles with the polymerizable core and the Mal5 shell, whose number average contour lengths (lns) were 130 nm and 68 nm, respectively. The radical homopolymerizations of 1a-c in water provided a substantial result in this study that 1b and 1c, that is, the glycomonomers forming the worm-like micelles, showed a very high homopolymerizability in water. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1671–1679

Soluble and meltable hyperbranched polyborosilazanes toward high-temperature stable SiBCN ceramics.

High-temperature stable siliconborocarbonitride (SiBCN) ceramics produced from single-source preceramic polymers have received increased attention in the last two decades. In this contribution, soluble and meltable polyborosilazanes with hyperbranched topology (hb-PBSZ) were synthesized via a convenient solvent-free, catalyst-free and one-pot A2 + B6 strategy, an aminolysis reaction of the A2 monomer of dichloromethylsilane and the B6 monomer of tris(dichloromethylsilylethyl)borane in the presence of hexamethyldisilazane. The amine transition reaction between the intermediates of dichlorotetramethyldisilazane and tri(trimethylsilylmethylchlorosilylethyl)borane led to the formation of dendritic units of aminedialkylborons rather than trialkylborons. The cross-linked hb-PBSZ precursors exhibited a ceramic yield higher 80%. The resultant SiBCN ceramics with a boron atomic composition of 6.0-8.5% and a representative formula of Si1B(0.19)C(1.21)N(0.39)O(0.08) showed high-temperature stability and retained their amorphous structure up to 1600 °C. These hyperbranched polyborosilazanes with soluble and meltable characteristics provide a new perspective for the design of preceramic polymers possessing advantages for high-temperature stable polymer-derived ceramics with complex structures/shapes.

Synthesis of a A2B3-type Hyperbranched Copolymers Based on a 3-Armed Unimolecular 4-N-Methylbenzamide Pentamer and Poly(propylene oxide)

Abstract A novel hyperbranched copolymer (HBCP), with a number-average molecular weight from 11000 to 25000, was successfully prepared by the direct condensation polymerization of a unimolecular 3-armed 4-N-methylbenzamide pentamer (TMA-3MAB5) as a hard segment (B3 monomer), with amine-functionalized poly(propylene oxide) (PPOx) (x: degree of polymerization, 32 or 64) (A2 monomer) at both ends as a soft segment, and investigated its possibility as a thermoplastic elastomer. The highly pure B3 molecule, TMA-3MAB5, was quantitatively obtained by the step-growth reaction of 4-(N-methylamino)benzoic acid (MAB) using thionyl chloride as the condensation reagent and trimesic acid (TMA) as the core molecule in N-methylpyrrolidone (NMP) at 20 °C for 0.5 h for each step. The HBCP showed two glass transitions corresponding to imperfectly segregated PPO-rich and polybenzamide hard segment-rich domains, and the film showed good mechanical properties (Young’s Modulus TM 0.25–4.0 MPa, elongation at break EB 133–1470%), which were controlled by the fraction of the hard segment.

Anionic polymerisation of phosphaalkenes bearing polyaromatic chromophores: phosphine polymers showing “turn-on” emission selectively with peroxide

Three new phosphaalkenes bearing C-aryl chromophores, MesPCPh(Ar) (1a: Ar = 1-naphthyl, 1b: 9-phenanthryl, 1c: 5-dibenzosuberenyl; Mes = 2,4,6-trimethylphenyl), are reported. Each phosphaalkene was characterised by multinuclear NMR spectroscopy (1H, 13C, 31P), X-ray crystallography, mass spectrometry, UV/Visible spectroscopy and elemental microanalysis (1b and 1c). Monomers 1a and 1b were successfully polymerised using anionic methods of initiation (n-BuLi: 5 and 1.5 mol%, respectively) to afford poly(methylenephosphine)s (PMPs: 2a: Mn = 15 100 Da, PDI = 1.14; 2b: Mn = 17 500 Da; PDI = 1.39). Detailed NMR spectroscopic analysis of polymer 2a revealed that its microstructure is primarily composed of [P(CHPhNaph)–(4,6-Me2C6H2)–2-CH2]n units rather than the expected [P(Mes)–CPh2]n. Functional polymer 2a was oxidised to the phosphine oxide 2a·O or phosphine sulfide 2a·S, and coordinated to borane to afford 2a·BH3 or gold(I) to afford 2a·AuCl. Significantly, 2a shows “turn-on” emission properties selectively as its oxide 2a·O (λex = 286 nm; λem = 342 nm) which is prepared by treatment with hydrogen peroxide.

High refractive index hyperbranched polymers with different naphthalene contents prepared through thiol-yne click reaction using di-substituted asymmetric bulky alkynes

In the present study, different aromatic moieties, naphthalene and benzene, were introduced into alkynes to constitute 1,3,5-tris(naphthylethynyl)benzene as B3 monomer. This monomer could be reacted with different ratios of hexane-1,6-dithiol (A2 monomer) via mono-selective Thiol-Yne reaction (TYR) to form hyperbranched polymers PI. TYR yielded in both, model reactions and polymerizations, mono-adducts with high regioselectivity and proved the absence of any bis-adducts. Polymers of very high molecular weights of up to 625,000 g/mol could be achieved without any sign of gel formation. All the polymers exhibit high transparency in the visible wavelength range and also show high refractive indices of up to 1.745 at 589.7 nm due to the high incorporation of naphthalene and phenyl groups. Besides, all polymers prove excellent solubility and processability together with excellent thermal properties.

Optically active helical poly(α,β-unsaturated ketone) from anionic polymerization of (S)-3-acrylyl-2,2′- bis(methoxymethoxy)-1,1′-binaphthyl

(S)-3-acrylyl-2,2′-bis(methoxymethoxy)-1,1′-binaphthyl (3a) was synthesized and anionically polymerized using n-BuLi as an initiator. The polymer derived from 3a had a tremendous specific optical rotation [Formula: see text] = −304.2, while that of the monomer 3a is −68.7. Poly-3a was confirmed to exist in the form of a one-handed helical structure in solution by means of comparing the specific optical rotation, the circular dichroism, and UV-vis spectra with that of 3a and the model compounds such as (S)-3-propionyl-2,2′-bis(methoxymethoxy)-1,1′-binaphthyl (3b) and (S)-3-heptanoyl-2,2′-bis(methoxymethoxy)-1,1′-binaphthyl (3c). This conclusion was also confirmed by the fact that the g value of poly-3a is about 15 times of that of the monomer 3a.

TDDFT study on the excited‐state hydrogen bonding of N‐(2‐hydroxyethyl)‐1,8‐naphthalimide and N‐(3‐hydroxyethyl)‐1,8‐naphthalimide in methanol solution

The time‐dependent density functional theory method was performed to investigate the excited‐state hydrogen‐bonding dynamics of N‐(2‐hydroxyethyl)‐1,8‐naphthalimide (2a) and N‐(3‐hydroxyethyl)‐1,8‐naphthalimide (3a) in methanol (meoh) solution. The ground and excited‐state geometry optimizations, electronic excitation energies, and corresponding oscillation strengths of the low‐lying electronically excited states for the complexes 2a + 2meoh and 3a + 2meoh as well as their monomers 2a and 3a were calculated by density functional theory and time‐dependent density functional theory methods, respectively. We demonstrated that the three intermolecular hydrogen bonds of 2a + 2meoh and 3a + 2meoh are strengthened after excitation to the S1 state, and thus induce electronic spectral redshift. Moreover, the electronic excitation energies of the hydrogen‐bonded complexes in S1 state are correspondingly decreased compared with those of their corresponding monomer 2a and 3a. In addition, the intramolecular charge transfer of the S1 state for complexes 2a + 2meoh and 3a + 2meoh were theoretically investigated by analysis of molecular orbital. Copyright © 2014 John Wiley & Sons, Ltd.

Synthesis, photopolymerization, and adhesive properties of hydrolytically stable phosphonic acid-containing (meth)acrylamides

Three novel dental monomers containing phosphonic acid groups (1a and 2a, based on diethyl amino(phenyl)methylphosphonate and 3a based on diethyl 1-aminoheptylphosphonate) were synthesized in two steps: the reaction of α-aminophosphonates with acryloyl chloride (for monomers 1a and 3a) or methacryloyl chloride (for 2a) to give monomers with phosphonate groups, and the hydrolysis of phosphonate groups by using trimethyl silylbromide. Their (and the intermediates') structures were confirmed by FTIR, 1H, 13C, and 31P NMR spectroscopy. All the monomers dissolve well in water (1<pH<2) and are hydrolytically stable. Their homo- and copolymerizations with 2-hydroxyethyl methacrylate (HEMA) and HEMA/glycerol dimethacrylate were investigated with photo-DSC. Thermal polymerization of the new monomers in water or in ethanol/water solution was investigated, giving polymers in good yields. X-ray diffraction results showed only dicalcium phosphate dehydrate formation upon interaction of 1a-3a with hydroxyapatite indicating its strong decalcification and that monomer-Ca salts are highly soluble. Some results were also compared to those with a bisphosphonic acid-containing methacrylamide (4a) previously reported; and the influence of monomer structure on polymerization/adhesive properties is discussed. These properties, especially hydrolytic stability and good rates of polymerization, make these new monomers suitable candidates as components of dental adhesive mixtures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 511–522

Alternating Asymmetric Self‐Induction in Functionalized Pyrrolidine Oligomers

Artificial structurally well-defined polymers have excited interest as functional mimetics of natural biomacromolecules, exhibiting additional properties not occurring in the living world. Specific conformational organization of natural and synthetic polymeric objects leading to unique folding accounts for the molecular recognition, which is one of the driving principles in important natural processes. Some nonnatural oligomeric species adopt specific and well-defined conformations dictated by the structure of monomeric units and intramolecular interactions and are defined as foldamers. One of the most studied unnatural foldamer types are bpeptides that adopt stable folded helical, sheet, and turn-like conformations. b-Peptides are stable towards natural enzymes, and appropriate design leads to discovery of bpeptide ligands for complicated pharmaceutical targets, such as protein–protein interactions. The application of pyrrolidine-3-carboxylic acid (Pca) for the construction of bpolypeptide chain rigidifies the molecular backbone and provides additional stabilization of the secondary structure of the oligomer in solution. The typical synthesis of a b-peptide backbone is based on the arsenal of peptide chemistry methods, including routine sequences of amino group protection–deprotection steps and multiple activations of carboxylic functionality for amide bond construction. Herein we disclose a fundamentally novel synthetic method towards well-defined highly functionalized short b-peptides that avoids protection, deprotection, and activation procedures and allows to generate efficiently stereoregular oligomeric pyrrolidine-based molecules. The developed method, called cycloadditive oligomerization, has been used for the synthesis of a set of racemic and enantiopure oligomers containing a Pca backbone. The realized approach determines highly diverse structural characteristics of b-peptide oligomers, which are characterized by various physicochemical methods, including X-ray analysis. The oligomerization utilized azomethine ylide 1,3-dipolar cycloaddition as a chain-growth approach (Scheme 1). 5Arylpyrrolidine-2,4-dicarboxylate units serve both as linked elements and as auxiliaries to determine stereoand enantioselectivities of the cycloaddition process. The starting 5arylpyrrolidine-2,4-dicarboxylic acid diesters 3a (X=H, Br) for oligomer synthesis were obtained from iminoesters 1 and tert-butyl acrylate in racemic and enantiopure forms by 1,3-dipolar cycloaddition using Lewis acids for the azomethine ylide generation step (Scheme 1, Table 1). Asymmetric synthesis of the monomer ( )-3a-H was effectively conducted with the enantiopure ligand 4 on a gram scale, and single recrystallization provided the target compound with more than 99% ee. Subsequent N-acryloylation of monomers 3a with acryloyl chloride transformed them into dipolarophiles 2b with a sterically hindered amide residue connected to the ethylene fragment. We supposed that these unique dipolarophiles would induce good diastereoand enantioselectivities under iterative cycloaddition steps with iminoesters 1 (Scheme 1). Indeed, dimers 3b were effectively synthesized by cycloaddition of acrylamides 2b with Schiff bases 1 (X=H, Br) in presence of AgOAc as a Lewis acid agent for azomethine ylide generation (Table 1, entries 4–6). Comparison of H NMR spectra of the cycloaddition reaction mixtures and

Synthesis and characterization of A2 + B3 type hyperbranched aromatic-aliphatic polyester with carboxyl end groups

New types of carboxyl-terminated hyperbranched polyesters (HBPEs) with aromatic-aliphatic structure were synthesized by single step-melt polycondensation of adipic acid (as A2 monomer) and phloroglucinol (as B3 monomer) as a core via A2 + B3 approach, at three different monomer mole ratios (A2/B3 = 1: 1, 1.5: 1, 2: 1, respectively). FTIR spectroscopy indicated that the polymers contained hydroxyl groups, ester bonds, benzene ring, methyl and methylene groups, which were in agreement with the expected HBPEs. The HBPEs have inherent viscosities about 0.24 to 0.27 dL/g. The degree of branching of the HBPEs was estimated to be 0.45–0.49% by 1H-NMR and 13C-NMR measurements. The melting temperature of HBPE-1, HBPE-2 and HBPE-3 were 154, 155 and 160°C respectively measured by differential scanning calorimetry (DSC). The synthesized polymers were thermally stable; the thermogravimetric analysis (TGA) measurement revealed that HBPEs had 10% weight loss at 310°C in nitrogen.

Synthesis and characterization of highly branched sulfonated poly(aryl ether ketone) copolymers as proton exchange membranes

Highly branched sulfonated poly(aryl ether ketone) copolymers (Br-SPAEKs) were synthesized based on 4,4′-(hexafluoroisopropylidene) diphenol (A2 monomer), 4,4′-difluorobenzophenone (unsulfonated B2 monomer), 3,3′-disodiumsulfonyl-4,4′-difluorobenzophenone (sulfonated B2 monomer), and 3,4′,5-trifluoro-benzophenone (branched BB2′ monomer). Structures of Br-SPAEKs were confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Compared to the linear SPAEK (L-SPAEK) copolymer membrane with similar ion exchange capacity, the Br-SPAEK-30 (branched monomer of 20 mol% and sulfonated monomer of 30 mol%) membrane showed higher proton conductivity and lower methanol permeability. This synergistic effect on proton conductivity and methanol permeability was mainly due to the characteristics of large free volume and similar cross-linking architecture arising due to the introduction of the branched monomers. Moreover, the selectivity of the Br-SPAEK-30 membrane is almost three times higher than that of the L-SPAEK membrane. Proton conductivities of Br-SPAEK membranes are higher than 10−2 S cm−1 and increase gradually with increasing temperature. At 80°C, the proton conductivity of the Br-SPAEK-50 (branched monomer of 20 mol% and sulfonated monomer of 50 mol%) membrane reaches 0.127 S cm−1, comparable to that of Nafion-117 (0.139 S cm−1). Additionally, the methanol permeability of Br-SPAEK-50 is one order magnitude lower than that of Nafion-117.

Synthesis of branched sulfonated poly(aryl ether ketone) copolymers and their proton exchange membrane properties

Branched sulfonated poly(aryl ether ketone) copolymers (Br-SPAEKs) were synthesized based on 4,4′-(hexafluoroisopropylidene) diphenol (6F-BPA, A2 monomer), 4,4′-difluorobenzophenone (DFBP, unsulfonated B2 monomer), 3,3′-disodiumsulfonyl-4,4′-difluorobenzophenone (SDFBP, sulfonated B2 monomer) and 2,4′,6-trifluoro-benzophenone (TFBP, branched BB′2 monomer). Structures of Br-SPAEKs were confirmed by FT-IR and NMR. Compared to linear sulfonated poly(aryl ether ketone) copolymer (L-SPAEK) membrane with similar ion exchange capacity (IEC), these Br-SPAEK membranes showed a higher proton conductivity and a lower methanol permeability. This synergistic effect on proton conductivity and methanol permeability was mainly due to the characteristics of large free volume and similar to cross-linking architecture arising from the introduction of the branched monomers. Moreover, the Br-SPAEK membrane containing 20mol% branched monomer possesses the best selectivity, and the value of selectivity is almost 3 times higher than that of L-SPAEK. Proton conductivities of Br-SPAEK membranes are higher than 10−2S/cm and increase gradually with increasing temperature. At 80°C, the proton conductivity of Br-20-SPAEK-40 (branched monomer of 20mol% and sulfonated monomer of 40mol%) membrane reaches 0.121Scm−1, compare to that of Nafion 117 (0.139Scm−1). Additionally, the methanol permeability of Br-20-SPAEK-40 is one order magnitude lower than that of Nafion 117.

Synthesis of well-defined aromatic polyamide-graft-poly(tetrahydrofuran) by chain-growth condensation polymerization of macromonomer

Well-defined aromatic polyamide grafted with poly(tetrahydrofuran) [poly(THF)] is obtained by the chain-growth condensation polymerization of 4-aminobenzoic acid ester macromonomers 1 bearing poly(THF) on the amino group. The macromonomers are easily prepared by the reaction of living poly(THF) with 4-aminobenzoic acid ester. Polymerization of phenyl ester monomer 1a at −10 °C is accompanied by self-polycondensation, whereas that of methyl ester monomer 1b at 10 °C proceeds exclusively in a chain-growth polymerization manner.

Polyarylidene containing saturated silicon spacers in the polymers main chain

A new series of photoactive polymers were synthesized by condensing polymerization of different diarylidine monomers 1a,b –3a,b with 1,2-bis(chloromethylsilyl)ethane in Tetrahydrofuran and in the presence of butyllithium. These polymers were characterized by elemental and spectral analyses. The optical properties of these polymers were comparable to those of parent monomer units, by using ultraviolet–visible absorption and emission in solution, and they possessed the physical characteristics of macromolecules. In addition, the thermal properties of these polymers were evaluated by thermogravimetric analysis and DSC measurements. These polymers are thermally stable up to 207 °C except for polymer P3a up to 180 °C and underwent degradation thereafter. The polymers exhibit glass transition temperatures lower than 0 °C except for polymer P3a where its T g was at 35 °C. The molar masses of all polymers were determined by gel permeation chromatography (GPC), and all polymers have high molar masses. The starting monomers 1a, 2a, and 3b were crystallized and their structures in the crystal were determined by X-ray diffraction. The polymerizable points were found not to be in proper spatial relation to allow for solid-state polymerization.

THEORETICAL STUDY OF THE STRUCTURES AND PROPERTIES OF (Cl2AlN3)n(n = 2–4) CLUSTERS

Density functional theory has been employed to study the molecular geometries, energies, infrared vibrational spectra, and thermodynamic properties of the clusters ( Cl2AlN3 )n(n = 1–4) at the B3LYP/6-311+G* level. The optimized clusters ( Cl2AlN3 )n(n = 2–4) all possess cyclic structures formed by Al atoms bridged by the α-nitrogen of the azide groups, and azido in azides has linear structure. The relationships between geometrical parameters and oligomerization degree n are discussed. The gas-phase structures of the trimers prefer to exist in boat-twisting conformation. As for the tetramer, the S4 symmetry structure is the most stable. The infrared spectra are obtained and assigned by vibrational analysis. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms clusters (2A, 3A and 3B) can occur spontaneously in the gas phase at temperatures up to 800 K. However, monomer 1A forms tetramers can occur spontaneously at temperatures below 600 K.

Synthesis and properties of novel hyperbranched polyimides end-capped with metallophthalocyanines

A fluorinated hyperbranched polyimide (HBPI) is synthesized by using a triamine monomer, 1,3,5-tris(2-trifluoromethyl-4-aminophenoxy)benzene (TFAPOB) (B3), as a “core” molecule, 4,4′-oxydiphthalic anhydride (ODPA) as a A2 monomer, and 4-aminophthalonitrile as an end-capping reagent. After that, a series of novel fluorinated hyperbranched polyimides end-capped with metallophthalocyanines were prepared by the reactions of dicyanophenyl end-capped hyperbranched polyimide with excessive amounts of 1,2-dicyanobenzene and the corresponding metal salt in quinoline. The resulting polyimides containing metallophthalocyanine unites shows optical absorption in the visible region. The absorption bands of the polymers in chloroform solution are in the range of 665–701 nm. These polyimides show glass transition temperatures between 216 and 225°C, and the 5 wt % weight loss temperature of the polymers varied from 440 to 543°C under nitrogen. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Bluish-violet light-emitting liquid crystalline hyperbranched polymers using three trisalcohol B3 monomers: Preparation, characterisation and structure–property relationship

Bluish-violet light-emitting liquid crystalline (LC) A2+B3 type hyperbranched (HB) polymers composed of an internal 2,5-diphenyl-1,3,4-thiadiazole (DTD) as a mesogen were prepared by melt polycondensation of a dimethyl ester A2 monomer with three trisalcohol B3 monomers, and the effect of the B3 monomer structures on LC and optical properties in the A2+B3 type HB polymers was evaluated. All the HB polymers 4a and 4b, having short aliphatic spacers between the central site of the B3 monomers and the DTD unit, formed thermotropic smectic phases independent of feed mole ratios of A2/B3, and the phase transition temperatures and LC temperature ranges depended on the molecular weights of their HB polymers. However, in the HB polymers 4c, having long aliphatic spacers and a benzene ring between the central site of B3 monomers and the DTD unit, only the HB polymer 4c1 prepared in the highest feed mole ratio of A2/B3 = 3/1 showed the LC property, probably due to steric hindrance of the B3 monomer 3c. The HB polymers 4a and 4c displayed UV-vis absorption and photoluminescence spectra with bluish-violet light emission on the basis of the DTD unit, at almost the same wavelengths in chloroform solutions independent of the feed mole ratios of A2/B3 and the B3 monomer structures, but the spectra of 4a and 4c in film displayed peak maxima at wavelengths depending on the feed mole ratios of A2/B3 and the B3 monomer structures because of intermolecular interactions or aggregations.