On distance dependent entropy measures of poly propylene imine and zinc porphyrin dendrimers

A key paradigm in contemporary research is the use of graphs to represent physical systems, molecular structures, or particularly metal frameworks. Graphs are increasingly widely used in a variety of fields, including the study of quantum and molecular systems, macromolecules and their interactions, socioeconomic and ecological systems, and technical and infra-structural systems. Understanding how these systems function, are robust, and are stable begins with structural characterization. The use of entropies and entropy-like measurements of graphs/structures of molecules/networks is crucial from both a mathematical and physical standpoint. Several entropy measures of graphs have been defined and studied extensively during the last few decades. The current paper is devoted to investigation of distance dependent entropy measures of Poly Propylene Imine (PPI) dendrimers and Zinc Porphyrin dendrimers. The analytical formulae of distance dependent entropy measures have been developed and their patterns have been presented through graphical tools.     

Quaternary ammonium ion dendrimers from methylation of poly(propylene imine)s

The poly(propylene imine) dendrimers DAB‐dendr‐(NH₂)₈, DAB‐dendr‐(NH₂)₃₂, and DAB‐dendr‐(NH₂)₆₄ were fully converted with iodomethane to quaternary ammonium ions at both chain ends and branch points and, with less iodomethane, were partially converted to quaternary ammonium ions mainly at end groups. Amidation of the primary amine ends followed by treatment with iodomethane gave the first dendrimers with quaternary ammonium ions only at branch points. After an exchange of iodide counterions for chloride, all of the quaternary ammonium ion dendrimers slightly increased the rate of decarboxylation of 6‐nitrobenzisoxazole‐3‐carboxylate ion in an aqueous solution. Similar quaternary ammonium ion dendrimers with more hydrophobic interiors or more hydrophobic chains on the ends were much more active catalysts for the decarboxylation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 821–832, 2001     

Poly(propylene imine) dendrimers as hydrogen donor in Type II photoinitiated free radical polymerization

Three generations of poly(propylene imine) dendrimers, namely (PPI-16, PPI-32 and PPI-64; 16, 32 and 64 for generations 3, 4 and 5, respectively) were used as hydrogen donors in photoinitiated free radical polymerization of methyl methacrylate by using one of the following photosensitizers; benzophenone and thioxanthone. The effect of generation number of the dendrimer on photoinitiation efficiency and molecular weight of the resulting polymers was investigated. Glass transition temperatures and particle size measurements of the resulting polymers indicated the presence of nearly stretched polymer chains around the dendrimers. The location of hydrogen donating sites was evaluated by photolysis studies in the absence of monomer by using a stable radical namely, 2,2,6,6-tetramethylpiperidine-N-oxyl free radical (TEMPO) and showed that hydrogen abstraction occurs from the inner tertiary amino groups. The TEMPO attached dendrimers were further used in the nitroxide mediated radical polymerization (NMP) of styrene to yield star polymers.     

Poly(propylene imine) dendrimer complexes as catalysts for oxidation of alkenes

Complexes of poly(propylene imine) dendrimers D8[DAB-dendr-(NH₂)₈] and D32 [DAB-dendr-(NH₂)₃₂] were prepared by interaction of the dendrimers with transition metal salts such as FeCl₃.6H₂O; CoCl₂.6H₂O; CuCl₂.2H₂O; VOSO₄.5H₂O; Na₂MoO₄.2H₂O and Na₂WO₄.2H₂O at room temperature in aqueous solutions. The content of metal ions in the complexes was found to be from 8.2 to 69.6 mg metal ion/g polymer carrier. The complexes were characterized by using IR, UV-VIS, Moessbauer spectroscopy and EPR. The anticipated co-ordination structure of the compounds was suggested. It was found that the order of the catalytic activity of the complexes of poly(propylene imine) dendrimers D8 and D32 in the reaction of epoxidation of cyclohexene with organic hydroperoxides such as tert-butyl hydroperoxide (t-BHP), ethylbenzene hydroperoxide (EBHP) and cumene hydroperoxide (CHP) was as follows: D32-MoО₂²⁺>D32-VО²⁺>D32-WО₂²⁺ > D32-Co²⁺ > D32-Cu²⁺>D32-Fe³⁺. The order of reactivity of organic hydroperoxides in the reaction studied was: t-BHP > EBHP > CHP.     

Morphology-dependent luminescence properties of poly(benzyl ether) dendrimers

Poly(benzyl ether) dendrimers with o-, m-, and p-isomers of dialkoxybenzene at their focal points [o-, m-, and p-(Gn)₂Ar], having generation numbers (n) of 0–3, were synthesized. ¹H NMR pulse relaxation times (T₁) of the exterior MeO groups of o- and m-(Gn)₂Ar (n = 0–3) all remained in the range of 0.92–1.43 s. In sharp contrast, an exceptionally short T₁ value (0.23 s) was observed for p-(G3)₂Ar. Although their absorption spectral profiles were slightly different from one another, an essential difference was observed for their fluorescence properties. When the generation number was increased, the fluorescence efficiency of o-(Gn)₂Ar increased, but that of p-(Gn)₂Ar decreased, whereas m-(Gn)₂Ar exhibited a relatively small change in the fluorescence efficiency. Fluorescence depolarization studies showed a highly efficient intramolecular energy migration in p-(G3)₂Ar as compared with o-(G3)₂Ar and m-(G3)₂Ar. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3524–3530, 2003     

Synthesis of on resin poly(propylene imine) dendrimer and its use as organocatalyst

Solid phase synthesis of poly(propylene imine) dendrimer is described. An iterative synthesis including double Michael addition of acrylonitrile to the primary amino groups on crosslinked polystyrene support followed by reduction of nitrile groups to amino groups give poly(propylene imine) dendrimers up to third generation attached to the polystyrene support. The supported dendrimer is used as an organocatalyst to Knoevenagel condensations. The supported catalyst showed good selectivity and the product was obtained in excellent yield under green reaction conditions. Densely packed amino groups enhance catalysis by a co-operative effect. The catalyst is recoverable and reusable.     

Multiarm star nanocarriers containing a poly(ethylene imine) core and polylactide arms

Star polymers (SPs) containing a hyperbranched poly(ethylene imine) (PEI; number‐average molecular weight = 10,000) core and polylactide arms were synthesized via the ring‐opening polymerization of lactide. PEI was used as a multifunctional macroinitiator for the ring‐opening polymerization of lactide. Different lactide monomer/amino‐functional group (LA/NH_n; n = 1 or 2) ratios were used for preparing SPs with different molecular weights. SPs were able to encapsulate small guest molecules such as Rose Bengal; they also transported small, hydrophilic molecules from water to the organic phase. The transport capacity of all the nanocarriers depended on the LA/NH_n ratio used for synthesizing the SPs. Nanocarriers with a higher LA/NH_n ratio had higher transport capacities. The size of all the nanocarriers depended on the type of solvent. In chloroform, these nanoparticles had several sizes that were related to the self‐assembly of these nanocarriers, but in acetone, they were monodisperse, and their size was smaller than that in chloroform. Also, the transport of polar dyes from water to the chloroform phase was possible. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5740–5749, 2006     

Synthesis of poly(propylene imine) dendrimers via homogeneous reduction process using lithium aluminium hydride: Bioconjugation with folic acid and doxorubicin release kinetics

The heterogeneous reduction process for synthesis of poly(propylene imine) (PPI) dendrimer has been replaced by a novel and homogeneous process. Accordingly, to prepare half generations, acrylonitrile was added to amine groups via Michael addition reaction. Then, nitrile groups were reduced via homogeneous hydrogenation using lithium aluminium hydride to synthesize fifth‐generation PPI dendrimers with ethylenediamine core. Also, peripheral primary amine groups were conjugated with folic acid (FA). Fourier transform infrared and ¹³C NMR spectroscopies and gel permeation chromatograph y were used to prove the synthesis of the various structures. Finally fifth‐generation and FA‐conjugated fifth‐generation PPI dendrimers were loaded with doxorubicin and exposed to environments with different pH values to examine the release properties of the structures. Also, drug release kinetics was investigated by fitting experimental data with various release models. The synthesized dendritic structures showed Higuchi model release behaviour due to better solubility of drug in release media with respect to dendrimer cavities.     

Transition metal compatibilization of poly(vinylamine) and poly(ethylene imine)

Poly(vinylamine), PVA, complexes with cobalt chloride hexahydrate exhibit a 45 °C enhancement in the glass‐transition temperature per mol % of the d‐block metal cation. Poly(ethylene imine), PEI, complexes with CoCl₂(H₂O)₆ exhibit a 20 °C enhancement in T_g per mol % Co²⁺. Since the basicities of primary and secondary amines are comparable (i.e., pK_b,PVA ≈ 3.34 vs. pK_b,PEI ≈ 3.27) and the rates at which each polymeric ligand displaces waters of hydration in the coordination sphere of Co²⁺ are similar, transition metal compatibilization is operative in blends of both polymers with CoCl₂(H₂O)₆. These two polymers are immiscible in the absence of the inorganic component. Infrared spectroscopy suggests that nitrogen lone pairs in PVA and PEI coordinate to Co²⁺. The stress–strain response of a 75/25 blend of PVA and PEI with 2 mol % Co²⁺ reveals a decrease in elastic modulus from 4.4 × 10⁹ N/m² to 5.7 × 10⁷ N/m², a decrease in fracture stress from 3.7 × 10⁷ N/m² to 2.0 × 10⁶ N/m², and an increase in ultimate strain from 1.3 to 12% relative to the 75/25 immiscible polymer–polymer blend. A plausible explanation for this effect is based on the fact that cobalt chloride hexahydrate compatibilizes both polymers by forming a coordination bridge between nitrogen lone pairs in dissimilar chains. Hence, poly(ethylene imine), which is very weak with a T_g near −40 °C, is integrated into a homogeneous structure with poly(vinylamine) and the mechanical properties of the individual polymers are averaged in the compatibilized ternary complex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 552–561, 2000     

The degree of crystallinity of monoclinic isotactic poly(propylene)

The degree of crystallinity of a set of monoclinic (alpha) isotactic poly(propylenes), prepared by a metallocene‐type catalyst, were determined at room temperature. Three different methods were used: density, enthalpy of fusion, and wide‐angle X‐ray scattering, and the results compared. The relation between the heat of fusion and the specific volume of these poly(propylenes) was found to be nonlinear, thus precluding any linear extrapolation to obtain the heat of fusion of the pure crystal (ΔH_u). The value of ΔH_u obtained from depression of the melting temperature by diluents is used. Based on the unit cell density of monoclinic crystals formed from a low defected fraction, the density obtained crystallinity levels were found to be between 0.l5–0.25 higher than those calculated from the heat of fusion. This relatively large difference holds for the isothermally crystallized and quenched isotactic poly(propylenes), and reflects the contribution of the interphase to the density determined crystallinity, which does not contribute to the heat of fusion. Paralleling results found in other systems, the crystallinity levels obtained from wide‐angle X‐ray scattering agree with those obtained from density, indicating a significant contribution of the partially ordered phase to the total diffraction. Emphasis is given on the need to account for the large differences in the crystallinities of poly(propylene) measured by different techniques when evaluating the dependence of properties on this quantity. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 323–334, 1999     

聚碳酸丙烯酯中碳酸丙烯酯含量的测定

建立了气相色谱分析聚碳酸丙烯酯中碳酸丙烯酯含量的方法,该方法操作简单,准确度高,可满足工业检测需求.     

The influence of stereoregularity on the miscibility of poly(propylene)s

The melt miscibility of atactic poly(propylene) (a-PP) with isotactic (i-PP) and syndiotactic poly(propylene) (s-PP), respectively, is investigated by diffusion experiments of i-PP/a-PP/i-PP or s-PP/a-PP/s-PP sandwich specimens using polarized light microscopy. It is shown that the system a-PP/i-PP is miscible in the melt, whereas for the system a-PP/s-PP no evidence for melt mixing is found. Pressure-volume-temperature (PVT) measurements of the three poly(propylene)s are carried out in order to determine the characteristic parameters of the Flory-Orwoll-Vrij equation-of-state theory. Theoretical predictions using the solubility parameter concept are in agreement with the observed miscibility behavior of the blends. Differences in the cohesive energy densities of a-PP and i-PP on the one side, and s-PP on the other side, are found to be responsible for the phase behavior of the mixtures of poly(propylene)s with different stereoregularity. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1135–1144, 1997     

Toughening of poly(propylene carbonate) by carbon dioxide copolymer poly(urethane-amine) via hydrogen bonding interaction

A carbon dioxide copolymer poly(urethane-amine)(PUA) was blended with poly(propylene carbonate)(PPC) in order to improve the toughness and flexibility of PPC without sacrificing other mechanical properties. Compared with pure PPC, the PPC/PUA blend with 5 wt% PUA loading showed a 400% increase in elongation at break, whilst the corresponding yielding strength remained as high as 33.5 MPa and Young's modulus showed slightly decrease. The intermolecular hydrogen bonding interaction in PPC/PUA blends was comfirmed by FTIR, 2D IR and XPS spectra analysis, and finely dispersed particulate structure of PUA in PPC was observed in the SEM images, which provided good evidence for the toughening mechanism of PPC.     

Self‐assembly of a new class of amphiphilic poly(amidoamine) dendrimers and their electrochemical properties

Amphiphilic poly(amidoamine) (PAMAM) dendrimers consisting of a hydrophilic dendrimer core and hydrophobic aromatic dansyl or 1‐(naphthalenyl)‐2‐phenyldiazene (NPD) shells have been synthesized. These amphiphilic dendrimers from the zero generation to the third generation self‐assemble into vesicular aggregates in water. The self‐assembly behavior of these dendrimers strongly depends on their generations. The generation dependence has been further investigated by an exploration of their electrochemical properties. For the PAMAM–NPD aggregates, the photoisomerization process leads to a change in the aggregate size. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5512–5519, 2005     

共混方法对聚氯乙烯/聚丙撑碳酸酯相容性影响

本文分别用溶液法和熔融法制得聚氯乙烯（PVC）与聚丙撑碳酸酯（PPC）共混试样，用DSC证明PVC／PPC共混物不相容，但它们不相容的程度受分子量、共混比例等因素的影响，并根据玻璃化转变温度（Tg）计算出溶液共混试样PPC富相中PVC的重量百分含量。NBR／PPC弹性体作偶联剂对PVC／PPC共混体系具有较好的增容作用，共混物中PPC的用量及分子量对共混体系性能有一定的影响。     

Neopenthyl glycol containing poly(propylene terephthalate)s: structure–properties relationships

Poly(propylene/neopenthyl terephthalate) random copolymers (PPT‐PNT) and poly(neopenthyl terephthalate) (PNT) were synthesized and subjected to molecular characterization. Afterwards, the polyesters were examined by TGA, DSC, andX‐ray. The copolymers, which displayed a good thermal stability, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PPT. XRD measurements allowed the identification of the PPT crystalline structure in all cases. Amorphous samples were obtained after melt quenching, with the exception of PPT‐PNT5, and an increment of T_g as the content of NT units is increased was observed due to the effect of the side methylene groups in the polymeric chain. The Wood equation described well T_g‐composition data. Lastly, the presence of a rigid‐amorphous phase was evidenced in the copolymers, whose amount depended on composition and on thermal treatment. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 170–181, 2008     

The conformational effect of form I helical poly(L-proline) and form II helical poly(L-proline) to the complex formation with helical poly(L-glutamic acid) through hydrogen bonding

The complex formation between helical poly-L-glutamic acid (PLGA) and helical poly-L-proline (PLP) was studied in a methanol-water (2 : 1) cosolvent and a propanol-water cosolvent (9 : 1). Reduced viscosity, circular dichroism, pH, and molar absorptivity were measured. The experimental results exhibit that the interpolymer complex was formed between helical PLGA and helical PLP through hydrogen bonding. When the complex was formed the unit mole ratio of PLGA : PLP(II) is 2 : 1 and PLGA : PLP(I) is 1.5 : 1, the ability of complex formation of PLP (II) with PLGA is better than that of PLP(I). On complexation the conformations of PLGA and PLP change and this change is more enhanced in the PLGA-PLP(II) than the PLGA-PLP(I) complex; its cause is studied. © 1993 John Wiley & Sons, Inc.     

Isothermal and nonisothermal crystallization kinetics of poly(propylene terephthalate)

The kinetics of crystallization of poly(propylene terephthalate) (PPT) samples of different molecular weights were studied under both isothermal and nonisothermal conditions. The Avrami and Lauritzen–Hoffmann treatments were applied to evaluate kinetic parameters of PPT isothermal crystallization. It was found that crystallization is faster for low‐molecular‐weight samples. The modified Avrami equation, and the combined Avrami–Ozawa method were found to successfully describe the nonisothermal crystallization process. Also, the analysis of Lauritzen–Hoffmmann was tested and it resulted in values close to those obtained with isothermal crystallization data. The nonisothermal kinetic data were corrected for the effect of the temperature lag and shifted alone with the isothermal kinetic data to obtain a single master curve, according to the method of Chan and Isayev, testifying to the consistency between the isothermal and corrected nonisothermal data. A new method for ranking of polymers, referring to the crystallization rates, was also introduced. This involved a new index that combines the maximum crystallization rate observed during cooling with the average crystallization rates over the temperature range of the crystallization peak. Furthermore, the effective energy barrier of the dynamic process was evaluated with the isoconversional methods of Flynn and Friedmann. It was found that the energy barrier is lower for the low‐molecular‐weight PPT. The effect of the catalyst remnants on the crystallization kinetics was also investigated and it was found that this is significant only for low‐molecular‐weight samples. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3775–3796, 2004     

Positive dendritic effects on the electron-donating potencies of poly(propylene imine) dendrimers

[structure: see text] Two series of poly(propylene imine), PPI, dendrimers terminated with a redox-active donor, 4-dimethylaminobenzyl (4-DMAB), including their respective nondendronized model compounds, are reported. In these two series, a positive dendritic effect was observed for the formation of charge-transfer (CT) complexes between the dendrimers and 7,7,8,8-tetracyanoquinodimethane (TCNQ). However, the nondendronized compounds did not form CT complexes with TCNQ, even though their redox potentials are similar to those of the 4-DMAB units attached to the dendrimers.