Synthesis and properties of hyperbranched copolymers based on perfluorinated germanium hydrides

Hyperbranched copolymers of various structures and molecular masses in the range 2.0 × 10⁴?4.4 × 10⁵ are prepared via the activated copolycondensation of tris- and bis(pentafluorophenyl)germane in tetrahydrofuran performed in the presence of triethylamine as an activator. The kinetics of copolycondensation is studied via the method of heat-conduction reaction calorimetry. It is found that tris(pentafluorophenyl)germane shows a higher activity in copolycondensation than bis(pentafluorophenyl)germane. Shear moduli, loss factors, and glass-transition temperatures of the copolymers are determined by dynamic mechanical analysis and differential-scanning calorimetry. The copolymers feature glass-transition temperatures up to 250°C. These values are considerably higher than those of perfluorinated polyphenylenegermane (162°C).     

Calorimetric study of the copolymers on basis perfluorinated germanium hydrides with different structures

The temperature dependences of heat capacity of copolymers on the basis of perfluorinated germanium hydrides have been measured using an adiabatic vacuum calorimeter over the temperature range from 6 K to the final temperature of their stability for the first time. Thus, the physical transformations were detected and their thermodynamic characteristics were estimated. The experimental results were used to calculate the standard thermodynamic functions, namely heat capacity, enthalpy, entropy and Gibbs function over the range from T → 0 to the final temperature stability of copolymers. The standard entropy of formation of the under study copolymers at T = 298.15 K was calculated. The obtained results were compared with corresponding data for hyperbranching perfluor polyphenylenegermaniums with other structures. Some conclusions about dependences of the thermodynamic polymers properties versus their structures were made.     

Synthesis and structural and conformational properties of hybrid polymers of styrene with perfluorinated compounds of germanium

Polymers of various structures, namely, the model PS with pentafluorophenyl groups, the linear-dendrite perfluorinated polyphenylenegermane-polystyrene, and diblock copolymer polystyrene-Ge(C₆F₅)₂-polystyrene, have been prepared by radical polymerization and activated copolycondensation. The polymers have been studied in dilute solutions by GPC, static and dynamic light scattering, and viscometry. The addition of a bis(pentafluorophenyl group) to the ends of a PS chain facilitates the development of supramolecular structures in solutions of hybrid systems. If the fluorinated group is incorporated at the center of the polymer chain, no associative phenomena are observed, because of its screening by the molecular coil.     

Synthesis and drug release properties of novel pH- and temperature-sensitive copolymers based on a hyperbranched polyether core

Multi-arm star amphiphilic hyperbranched copolymers with poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) shell and hyperbranched poly(3-ethyl-3-(hydroxymethyl)oxetane) (HBPO) core were synthesized by reversible addition?Cfragmentation chain transfer method. The hyperbranched copolymers were further modified by succinic anhydride (SUC) to obtain the novel pH- and thermosensitive hyperbranched copolymer HBPO-star-PDMAEMAs-SUC. The composition and morphology of synthesized copolymers were investigated by ¹H NMR, dynamic light scattering, and transmission electron microscopy. These copolymers exhibited phase transitions in response to pH and temperature. The pH-dependent release properties of the drug-loaded micelles were also investigated using indomethacin (IND) as a model drug. The IND-loaded micelles displayed a rapid drug release at an alkaline pH.     

Molecular mass characteristics and hydrodynamic and conformational properties of hyperbranched poly-L-lysines

Hydrodynamic and conformational properties of hyperbranched poly(amino acids) based on lysine have been studied by static and dynamic light scattering, velocity sedimentation, translational diffusion, and viscometry in dilute aqueous-saline solutions (0.2 M NaCl). The effects of synthesis conditions of hyperbranched poly(amino acids), modification of their end groups by histidine fragments, and incorporation of diacylated lysine residues between branching points of oligomers and polymers composed of lysine and glutamic acid on the molecular mass characteristics of the hyperbranched polymers have been ascertained. The hydrodynamic properties of the hyperbranched poly(amino acids) differ appreciably from the behavior of both linear polylysine and lysine dendrimers due to conformational features of their macromolecules.     

Hydrodynamic and conformational properties of a hyperbranched polymethylallylcarbosilane in dilute solutions

The hydrodynamic and conformational properties of a hyperbranched polymethylallylcarbosilane in hexane solutions have been studied by light scattering, sedimentation, translational diffusion, and viscometry. Fractions with M = (1–75) × 10³ have been used in experiments. The solution behavior of the hyperbranched polymer significantly differs from the properties of both spherical particles and linear polymers. The shape of hyperbranched polymethylallylcarbosilane macromolecules differs from spherical—the asymmetry factor is p ≤ 1.5. Polymethylallylcarbosilane macromolecules in solutions are characterized by compact structure—the hydrodynamic radius is not higher than 4 nm at M = 75 × 10³.     

Effect of the length of branches on hydrodynamic and conformational properties of hyperbranched polycarbosilanes

The hydrodynamic and conformational properties of hyperbranched polycarbosilanes with different lengths of branches, namely, poly(methyl(allyl)carbosilane) containing three CH₂ groups between branching centers and poly(methyl(undecenyl)carbosilane) whose branches are composed of 11 CH₂ groups, have been studied in dilute solutions in hexane using the methods of molecular hydrodynamics and optics. Fractions with M < 17.5 × 10⁴ have been used in experiments. The hydrodynamic properties of the above polycarbosilanes differ significantly from those of linear polymers since hyperbranched macromolecules are compact and their shape differs only slightly from spherical. The lengthening of chains between branching centers causes a change in the hydrodynamic characteristics, and the difference between hyperbranched polymers and dendrimers becomes more pronounced. As the length of branches increases, their conformation changes from an extended trans chain to a more or less bent rod.     

Thermal studies and chromium removal efficiency of thermoresponsive hyperbranched copolymers based on PEG-methacrylates

This study deals with the removal of chromium species from aqueous dilute solutions using thermoresponsive linear and hyperbranched copolymers based on PEG-methacrylates. The thermal stability of polymers was studied by thermogravimetric analysis and chemiluminescence emission, which evidenced a slightly enhanced stability for hyperbranched polymers respect to linear structures. Their LCST was successfully determined by TOPEM (temperature-modulated DSC), and similar values to those obtained by UV spectroscopy were obtained. The adsorption capacities for chromium hexavalent of the polymers have been investigated as function of LCST. The results showed highest retention capacity of Cr(VI) for all polymers above LCST. Hyperbranched polymers were more efficient than linear polymers, because of the structure of the polymers. Hyperbranched polymers when precipitate form a network with more nanocavities where the chromium can be adsorbed. The efficiency increased with ratio of OEGMA/DEGMA, reaching a maximum retention capacity value of 40 mg Cr(VI)/g polymer.     

Structural and dynamic properties of the polyanionic hydrides SrAlGeH and BaAlGeH

The quaternary aluminium hydrides SrAlGeH and BaAlGeH were synthesized from either hydrogenating the intermetallic AlB₂-type precursors SrAlGe and BaAlGe or reacting SrH₂ with a mixture of Al and Ge in the presence of pressurized hydrogen. Their structures were characterized by X-ray and neutron powder diffraction of the corresponding deuterides. The compounds crystallize with the trigonal SrAlSiH structure type (space group P3m1, Z = 1, a = 4.2435(2) and 4.3450(2) Å, c = 4.9710(3) and 5.2130(4) Å for SrAlGeH and BaAlGeH, respectively) and feature a two-dimensional polyanion [AlGeH]²⁻ which represents a corrugated hexagon layer built from three-bonded Al and Ge atoms. H is terminally attached to Al. Polyanions [AlGeH]²⁻ are electron precise and, according to electronic structure calculations, the quaternary hydrides display band gaps with sizes between 0.7 and 0.8 eV. Infrared and inelastic neutron scattering spectroscopy show Al–H stretching and bending mode frequencies at around 1250 and 870 cm⁻¹, respectively. SrAlGeH and BaAlGeH are thermally stable up to at least 500 °C. When exposed to air the hydrides decompose rapidly to amorphous, orange colored materials.     

The amphiphilic multiarm copolymers based on hyperbranched polyester and lysine: Synthesis and self-assembly

The amphiphilic multiarm copolymers were synthesized through the modification of commercially available hyperbranched polyesters(Boltorn H40) with N-ε-carbobenzoxy-L-Lysine N-carboxyanhydride(ZLys-NCA).After being condensed with N-Boc-phenylalanine(Boc-~NPhe) and deprotected the Boc-groups in trifluoroacetic acid(TFA),the original terminal hydroxyl groups were transformed into the amino groups and then initiated the ring-opening polymerization of ZLys-NCA.The hydrophilic poly(L-lysine) was grafted to the surface of Boltorn H40 successfully after the protecting benzyl groups were removed by the HBr solution in glacial acetic acid(33 wt%).The resulting multiarm copolymers were characterized by the ~1H-NMR,GPC and FTIR.The arm length calculated by NMR and GPC analysis was about 3 and 13 lysine-units for H40-Phe-PLysl and H40-Phe-PLys2 respectively.Due to the amphiphilic molecular structure,they displayed ability to self-assemble into spherical micelles in aqueous solution with the average diameter in the range from 70 nm to 250 nm.The CMC of H40-Phe-PLysl and H40-Phe-PLys2 was 0.013 mg/mL and 0.028 mg/mL,respectively, indicating that H40-Phe-PLysl with shorter arm length is easier to self-assemble than H40-Phe-PLys2 with longer arm length.     

Hexamethylsilirane; ring cleavage by germanium and tin hydrides

Under the appropriate conditions, organogermanium and organotin hydrides react with hexamethylsilirane to give ring-opening products of type R₃GeSiMe₂(CMe₂CMe₂H and R₃SnSiMe₂(CMe₂CMe₂H), respectively (CMe₂CMe₂H) and R₃SnSiMe₂(CMe₂CMe₂H), respectively.     

Bioreducible unimolecular micelles based on amphiphilic multiarm hyperbranched copolymers for triggered drug release

A novel type of bioreducible amphiphilic multiarm hyperbranched copolymer (H40-star-PLA-SS-PEG) based on Boltorn® H40 core, poly(l-lactide) (PLA) inner-shell, and poly(ethylene glycol) (PEG) outer-shell with disulfide-linkages between the hydrophobic and hydrophilic moieties was developed as unimolecular micelles for controlled drug release triggered by reduction. The obtained H40-star-PLA-SS-PEG was characterized in detail by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and thermal gravimetric analysis (TGA). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analyses suggested that H40-star-PLA-SS-PEG formed stable unimolecular micelles in aqueous solution with an average diameter of 19 nm. Interestingly, these micelles aggregated into large particles rapidly in response to 10 mM dithiothreitol (DTT), most likely due to shedding of the hydrophilic PEG outer-shell through reductive cleavage of the disulfide bonds. As a hydrophobic anticancer model drug, doxorubicin (DOX) was encapsulated into these reductive unimolecular micelles. In vitro release studies revealed that under the reduction-stimulus, the detachment of PEG outer-shell in DOX-loaded micelles resulted in a rapid drug release. Flow cytometry and confocal laser scanning microscopy (CLSM) measurements indicated that these DOX-loaded micelles were easily internalized by living cells. Methyl tetrazolium (MTT) assay demonstrated a markedly enhanced drug efficacy of DOX-loaded H40-star-PLA-SS-PEG micelles as compared to free DOX. All of these results show that these bioreducible unimolecular micelles are promising carriers for the triggered intracellular delivery of hydrophobic anticancer drugs.     

Synthesis and properties of hyperbranched polyurethanes,hyperbranched polyurethane copolymers with and without ether and ester groups using blocked isocyanate monomers

Starting from 3,5‐diamino benzoic acid, 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzyl ether, an AB₂‐type blocked isocyanate monomer with flexible ether group, and 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzoate, an AB₂‐type blocked isocyanate monomer with ester group, were synthesized for the first time. Using the same starting compound, 3,5‐bis{(benzoxycarbonyl)imino}benzylalcohol, an AB₂‐type blocked isocyanate monomer, was synthesized through a highly efficient short‐cut route. Step‐growth polymerization of these monomers at individually optimized experimental conditions results in the formation of hyperbranched polyurethanes with and without ether and ester groups. Copolymerizations of these monomers with functionally similar AB monomers were also carried out. The molecular weights of the polymers were determined using GPC and the values (M_w) were found to vary from 1.5 × 10⁴ to 1.2 × 10⁶. While hyperbranched polyurethanes having no ether or ester group were found to be thermally stable up to 217 °C, hyperbranched poly(ether–urethane)s and poly(ester–urethane)s were found to be thermally stable up to 245 and 300 °C, respectively. Glass transition temperature (T_g) of polyurethane was reduced significantly when introducing ether groups into the polymer chain, whereas T_g was not observed even up to 250 °C in the case of poly(ester–urethane). Hyperbranched polyurethanes derived from all the three different AB₂ monomers were soluble in highly polar solvents and the copolymers showed improved solubility. Polyethylene glycol monomethyl ether of molecular weight 550 and decanol were used as end‐capping groups, which were seen to affect the thermal, solution, and solubility properties of polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3877–3893, 2007     

Alkali metal hydrides: New metallating reagents for germanium and tin

New procedures for the preparation of organogermyl- and stannyl-sodium or -potassium, which undergo coupling reactions with alkyl, allyl, and benzyl halides and α-enones, are reported.     

Structural effects on the thermal properties of PDPS/PDMS copolymers

A series of PDPS/PDMS copolymers were synthesized through living anionic polymerization withn-butyllithium as an initiator. The changes of thermal property as a function of PDPS content were compared with respect to different types of monomer sequence using differential scanning calorimetry and thermogravimtery. The results indicated that the related variations of the thermal propertiesvs. the PDPS content and the monomer sequence provided independent operative control for preparing materials with desired thermal properties. The thermal stability of these copolymers was dramatically improved with introducing PDPS segment. However, the degree of these improvement pedended greatly on the monomer sequence in the copolymers.     

Synthesis and properties of organosoluble polyimides based on novel perfluorinated monomer hexafluoro-2,4-toluenediamine

New highly fluorinated aromatic polyimides based on hexafluoro-2,4-toluenediamine and commercially available dianhydrides (6FDA and ODPA) were synthesized by one-pot high temperature polycondensation in benzoic acid melt. Owing to the CF₃ group and fluorine atoms in the meta-linked phenylenediamine fragment, these polyimides combine good solubility in organic solvents including such a low boiling point solvent as chloroform with high glass transition temperatures (330-345 °C), thermal and thermooxidative stability (T₅ is >500 °C). The highly fluorinated polyimide films (hydrogen content is ≤1%) exhibit good dielectric properties and low water absorption as well as excellent optical transparency in the UV-vis region (cut-off wavelength is 311 nm for 6FDA-based and 357 nm for ODPA-based polyimides), which is very important for optoelectronic materials.     

Synthesis and photovoltaic properties of copolymers based on bithiophene and bithiazole

Three simple structured D‐A copolymers, PBTBTz‐1 , PBTBTz‐2 , and PBTBTz‐3 , containing bithiophene (BT) donor unit and bithiazole (BTz) acceptor unit with different alkyl chain length were synthesized by the Pd‐catalyzed Stille‐coupling method. The copolymers were characterized by thermogravimetric analysis, UV–vis absorption, electrochemical cyclic voltammetry, and photovoltaic measurements. The results indicate that the introduction of BTz unit to the polythiophene main chain effectively decreases highest occupied molecular orbital levels of the copolymers and increases the open circuit voltage (V_oc) of polymer solar cells (PSCs) based on the copolymers as donor, and the alkyl chain length influences the photovoltaic properties of the polymers significantly. The PSCs based on PBTBTz‐2 and PBTBTz‐3 show higher V_oc up to 0.77 and 0.81 V, respectively. The power conversion efficiency of the PSC based on PBTBTz‐2 :PC₇₀BM = 1:1(w/w) reached 2.58% with short circuit current of 8.70 mA/cm², under the illumination of AM1.5, 100 mW/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Electrochemical synthesis and properties of copolymers based on N-alkylpyrroles and thiophene

A series of mixed N-substituted alkylpyrrole/thiophene monomers have been synthesised. Several monomers could be electropolymerised to the corresponding polymers. Redox behaviour, spectroscopic and conductivity measurements are reported. Several electroactive films are stable in the dedoped and doped states with conductivity as high as 10 S cm⁻¹.