Journal of Polymer Science Part A: Polymer Chemistry

Cover image for Vol. 44 Issue 5

1 March 2006

Volume 44, Issue 5

Pages 1569–1783

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      Self-immolative dendrimers as novel drug delivery platforms (pages 1569–1578)

      Doron Shabat

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21258

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      Self-immolative dendrimers were recently developed and introduced as a potential platform for a single-triggered multi-prodrug. These unique structural dendrimers can release all of their tail units through domino-like chain fragmentation, which is initiated by a single cleavage at the dendrimer core. The incorporation of drug molecules as the tail units and an enzyme substrate as the trigger generates a multi-prodrug unit that is activated with a single enzymatic cleavage. We have demonstrated several examples of self-immolative dendritic prodrug systems and have shown significant advantages with respect to the appropriate monomeric prodrug. We anticipate that single-triggered, dendritic prodrugs will be exploited to further improve selective chemotherapeutic approaches in cancer therapy.

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    1. Synthesis and characterization of model diblock copolymers of poly(dimethylsiloxane) with poly(1,4-butadiene) or poly(ethylene) (pages 1579–1590)

      Andrés Ciolino, Giorgos Sakellariou, Dimitris Pantazis, Marcelo A. Villar, Enrique Vallés and Nikos Hadjichristidis

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21252

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      Model diblock copolymers of poly(1,4-butadiene) (PB) and poly(dimethylsiloxane) (PDMS), PB-b-PDMS, were synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene and hexamethylciclotrisiloxane (D3) in the presence of sec-BuLi. By homogeneous hydrogenation of PB-b-PDMS, the corresponding poly(ethylene) and poly(dimethylsiloxane) block copolymers, PE-b-PDMS, were obtained. The synthesized block copolymers were characterized by nuclear magnetic resonance (1H and 13C NMR), size-exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and rheology, to establish the accurate structure–property relationships.

    2. Divinylsiloxane-bisbenzocyclobutene-based polymer modified with polystyrene–polybutadiene–polystyrene triblock copolymers (pages 1591–1599)

      Ying-Hung So, Pamela Foster, Jang-Hi Im, Philip Garrou, Jack Hetzner, Edmund Stark and Kayla Baranek

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21262

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      Polystyrene–polybutadiene–polystyrene triblock copolymer was incorporated into divinlysiloxane-bisbenzocyclobutene (DVS-bisBCB)-based polymer matrix to enhance its toughness. The cured thermoset matrix showed different morphology when the elastomer was added to the B-staged prepolymer or when the elastomer was B-staged with the DVS-bisBCB monomer. The elastomer increased the fracture toughness of DVS-bisBCB polymer. The modified material maintains excellent electrical properties, high Tg, and good thermal stability, but shows higher coefficient of thermal expansion values.

    3. Thermal and mechanical analysis of metallocene-catalyzed ethene–α-olefin copolymers: The influence of the length and number of the crystallizing side chains (pages 1600–1612)

      C. Piel, P. Starck, J. V. Seppälä and W. Kaminsky

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21265

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      Copolymers of ethene and α-olefins with branch lengths of 6–26 carbon atoms were synthesized, and the influence of the length and number of the side chains on the mechanical properties of the materials was investigated. Thermal fractionation of the polymers was performed with a differential scanning calorimetry/successive self-nucleation and annealing technique; by dynamic mechanical analysis, the mechanical behavior of the materials was studied, and the results were related to the measurements of the density and tensile strength. The 24-carbon-long side chains of the ethene–hexacosene copolymers crystallized separately, depending on the comonomer concentration. This led to new copolymers with remarkable material properties.

    4. Novel amorphous perfluorocopolymeric system: Copolymers of perfluoro-2-methylene-1,3-dioxolane derivatives (pages 1613–1618)

      Yu Yang, František Mikeš, Liang Yang, Weihong Liu, Yasuhiro Koike and Yoshiyuki Okamoto

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21278

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      The copolymerization between two perfluoro-2-methylene-dioxole derivatives yields nearly ideal random, thermally stable, and amorphous copolymers with low refractive indices and high optical transparency from UV to near-infrared. Their films are flexible and tough. These properties make the copolymers ideal candidates as optical and electrical materials.

    5. Poly(ortho-phenylene ethynylene)s: Synthetic accessibility and optical properties (pages 1619–1627)

      Anzar Khan and Stefan Hecht

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21238

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      Poly(ortho-phenylene ethynylene)s carrying nonpolar side chains have been synthesized from AB′ monomers via an in situ activation/coupling polycondensation protocol involving microwave acceleration. The prepared polymers display a solvent-induced conformational transition between extended transoid and helical cisoid conformations, as indicated by optical spectroscopy.

    6. Reverse atom transfer radical polymerization of butyl methacrylate in a miniemulsion stabilized with a cationic surfactant (pages 1628–1634)

      Ryan W. Simms and Michael F. Cunningham

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21270

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      The miniemulsion reverse atom transfer radical polymerization of butyl methacrylate was successfully conducted with the cationic surfactant cetyltrimethylammonium bromide (CTAB). A minimal amount of CTAB (1 wt % with respect to the monomer) was sufficient to prevent coagulation of the latex at temperatures as high as 90 °C, while still allowing for effective control over the polymerization.

    7. Active center determinations on MgCl2-supported fourth- and fifth-generation Ziegler–Natta catalysts for propylene polymerization (pages 1635–1647)

      Andrew K. Yaluma, Peter J. T. Tait and John C. Chadwick

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21277

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      Active center determinations on state-of-the art Ziegler–Natta polypropylene catalysts, comprising MgCl2, TiCl4, and either a diether or a phthalate ester as internal donor, have been carried out by quenching propylene polymerization with tritiated ethanol. A strong correlation between catalyst activity and active center content was found, indicating that the high activity of the diether-containing catalysts is due to an increased proportion of active centers, rather than to differences in propagation rate coefficients.

    8. Polypyrrole/poly(N-isopropylacrylamide-co-acrylic acid) thermosensitive and electrically conductive composite microgels (pages 1648–1659)

      Chia-Lung Lin and Wen-Yen Chiu

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21281

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      A novel composite microgel containing both thermosensitive and electrically conducting properties was prepared. The electrically conductive PPy/DBSA/poly(NIPAAm-co-AA) composite microgels were synthesized by a chemical oxidation of pyrrole directly inside the poly(NIPAAm-co-AA) microgels. The composite microgels thus formed showed electrically conducting behavior dependent on humidity and temperature. At temperatures lower than LCST, the conductivity decreased with increasing the humidity and a small hysteresis phenomenon was observed. The hysteresis became indistinct when temperature was near volume phase transition temperature. However, after the treatment of high temperature and high humidity, the conductivity increased surprisingly due to the structure reorganization inside the composite microgels.

    9. Improvement of α-tocopherols long-term efficiency by modeling its heterogeneous natural environment in polyethylene (pages 1660–1666)

      Clara Strandberg and Ann-Christine Albertsson

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21286

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      α-Tocopherol is located in the lipid phase of the cell and it has been shown that it is more efficient in a polar substrate. PE is more hydrophobic and homogenous than the heterogeneous and hydrophilic lipid phase in the cell. Three different additive systems were investigated to model α-tocopherols heterogeneous natural environment in PE. Two of these had carboxylic acid groups, EAA and polyTRIM/PAA core-shell particles (Core), and the third, oat starch, had no carboxylic acid groups. The chemiluminescence and FTIR results revealed that the systems with EAA or Core improved the antioxidant properties of α-tocopherol in PE, and the Core system had the best performance. Starch has been shown to have stabilizing properties in PE, but it had no effect on the efficiency of α-tocopherol.

    10. Preparation of block copolymers via Diels Alder reaction of maleimide- and anthracene-end functionalized polymers (pages 1667–1675)

      Hakan Durmaz, Bige Colakoglu, Umit Tunca and Gurkan Hizal

      Version of Record online: 26 JAN 2006 | DOI: 10.1002/pola.21275

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      A number of diblock copolymers, PMMA-b-PS, PEG-b-PS, PtBA-b-PS, and PMMA-b-PEG, were successfully prepared by Diels-Alder reaction between maleimide- and anthracene-end functionalized poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(tert-butyl acrylate) (PtBA), and poly(ethylene glycol) (PEG) in toluene at 110 °C. Thus-obtained block copolymers were characterized by 1H NMR, UV, and GPC.

    11. Curing studies of epoxy resins with phosphorus-containing amines (pages 1676–1685)

      L. A. Mercado, G. Ribera, M. Galià and V. Cádiz

      Version of Record online: 17 JAN 2006 | DOI: 10.1002/pola.21268

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      The curing system of diglycidyl ether of bisphenol A with two phosphorus-containing amine compounds—bis(3-aminophenyl)methyl phosphine oxide and bis(4-aminophenyl)-bis(9,10-dihydro-9-oxa-10-oxide-10-phosphaphenanthrene-10-yl)methane—was studied by the isoconversional method to evaluate the dependence of the effective activation energy on the extent of conversion. Modulated differential scanning calorimetry and dynamic mechanical thermal analysis were used to study the phenomena of vitrification and gelation. The thermal and flame-retardant properties were evaluated.

    12. Photoinitiators with functional groups. IX. Hydrophilic bisacylphosphine oxides for acidic aqueous formulations (pages 1686–1700)

      G. Ullrich, B. Ganster, U. Salz, N. Moszner and R. Liska

      Version of Record online: 17 JAN 2006 | DOI: 10.1002/pola.21276

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      Due to the promising results on photoreactivity of a commercially available bisacylphosphine oxide in aqueous acidic formolations but the lack of sufficient solubility new oligo(ethylene glycole) substituted bisacylphosphine oxides were prepared and investigated. Beside good solubility and significantly increased reactivity in these formulations, sufficient storage stability was found.

    13. Novel flame-retardant thermosets: Diglycidyl ether of bisphenol A as a curing agent of boron-containing phenolic resins (pages 1701–1710)

      C. Martín, J. C. Ronda and V. Cádiz

      Version of Record online: 20 JAN 2006 | DOI: 10.1002/pola.21274

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      Boron-containing novolac resins were crosslinked with diglycidyl ether of bisphenol A (DGEBA), and their thermal, thermodynamomechanical, and flame-retardant properties were evaluated. The boron-containing novolac resins were less thermally stable than the unmodified novolac resin. Their modification degree and DGEBA content were related to the crosslinking density of the materials. The boron-containing novolac resins generated boric acid at high temperatures and gave an intumescent char that slowed down the degradation and prevented it from being total. They also showed good flame-retardant properties.

    14. Cationic copolymerization of diglycidyl ether of bisphenol A with phthalide or 3,3′-diphtalide catalyzed by lanthanide triflates (pages 1711–1721)

      Cristina Mas, Xavier Ramis, Josep Maria Salla, Ana Mantecón and Angels Serra

      Version of Record online: 27 JAN 2006 | DOI: 10.1002/pola.21285

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      DGEBA was copolymerized with different proportions of phthalide or diphthalide in the presence of ytterbium and lanthanum triflates to obtain networks with ester groups in their chemical structure. By FTIR/ATR, different processes were detected and by DSC the kinetics of the curing were studied. The mechanical and thermal characteristics of the materials and also the changes in the density were evaluated.

    15. Influence of the side group shape on the arrangement of liquid-crystalline polyethers obtained by ring opening polymerization of oxiranes (pages 1722–1733)

      Marta Giamberini, José Antonio Reina and Joan Carles Ronda

      Version of Record online: 27 JAN 2006 | DOI: 10.1002/pola.21280

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      A family of mono-, di-, and trisubstituted benzylglycidylether derivatives with 4-dodecyloxybenzyloxy groups at the 4-, 3,5-, and 3,4,5- position of the aromatic ring was synthesized and characterized. These monomers were subsequently polymerized with an aluminium-based ionic-coordinative initiator, [(CH3)2CHO]2Al[BOND]O[BOND]Zn[BOND]O[BOND]Al[OCH(CH3)2]2 (the Teyssie' catalyst) or an anionic initiator, potassium t-butoxide. The resulting polymers exhibited liquid crystalline phases, which were smectic for the calamitic monomer and columnar for the tapered monomers. The results of mesophase characterization suggested that higher molecular weights and stereoregularity increase the stability of the mesophase and give rise to more compact structures.

    16. Double-hydrophilic block copolymer for encapsulation and two-way pH change-induced release of metalloporphyrins (pages 1734–1744)

      Qi Bo and Yue Zhao

      Version of Record online: 27 JAN 2006 | DOI: 10.1002/pola.21287

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      A pH-sensitive double hydrophilic block copolymer of poly (acrylic acid) (PAA) and poly(4-vinyl pyridine) (P4VP) was synthesized. This polymer forms water-soluble micelles with PAA core and P4VP corona at low (acidic) pH, and micelles with P4VP core and PAA corona at high (basic) pH. Due to a pH change-induced destruction-reorganization process of the micelles, zinc tetraphenylporphyrin (ZnTPP) loaded in the micelles with PAA core can be released on pH increase, while ZnTPP loaded in the micelles with P4VP core can be released on pH decrease.

    17. Atom transfer radical polymerization of N-vinyl carbazole: Optimization to characterization (pages 1745–1757)

      A. S. Brar and Sukhdeep Kaur

      Version of Record online: 24 JAN 2006 | DOI: 10.1002/pola.21296

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      Atom Transfer Radical Polymerization (ATRP) of N-vinylcarbazole (VCz) using Cu(I)/Cu(II)/bpy as the catalyst system at 90 °C in toluene was carried out with N-2-bromoethyl carbazole (NBC) as initiator. The optimized ratio of Cu(I)/Cu(II) was found to be 1/0.3. Linearity in molecular weight distribution as well as semi-logarithmic plot was observed. Initiator efficiency, effect of addition of CuBr2, variation of catalyst concentration and initiator concentration, and effect of CuX (X = Br, Cl) on kinetics was carried out. With Cu(0)/CuBr2/bpy as catalyst, faster polymerization was observed. For chain extension experiment, PVK (Mn = 1900; PDI = 1.24) was used as macroinitiator for ATRP of methyl methacrylate, resulting in formation of block copolymer.

    18. Growth of poly(methyl methacrylate) brushes on silicon surfaces by atom transfer radical polymerization (pages 1758–1769)

      A. Ramakrishnan, R. Dhamodharan and J. Rühe

      Version of Record online: 24 JAN 2006 | DOI: 10.1002/pola.21266

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      The growth of poly(methylmethacrylate) brushes on silicon surfaces through surface-initiated atom transfer radical polymerization (ATRP) is studied. The brushes are grown under mild conditions at room temperature or even well below. The evolution of layer thickness, molecular weight and the polydispersity of the surface-attached chains is investigated as a function of the duration of the polymerization reaction. Mild growth conditions are a prerequisite if temperature sensitive substrates and/or thermally unstable compounds are employed. The presence of active ends in the polymers is used for chain extension experiments and for the growth of block copolymers.

    19. Effect of the molecular weight and architecture on the size and glass transition of arborescent polyisobutylenes (pages 1770–1776)

      Judit E. Puskas, Yaohong Chen, Kevin Kulbaba, Gabor Kaszas and Ali Soleymannezhad

      Version of Record online: 27 JAN 2006 | DOI: 10.1002/pola.21273

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      This article discusses the effect of architecture on the size and thermal transition of branched (arborescent of tree-like) polyisobutylenes arb-PIBs. The radius of gyration measured from the angle dependence of light scattering of high molecular weight arb-PIBs was larger than the hydrodynamic radius (Rh) from SEC/viscometry, and Rh values were smaller than Rh of linear PIBs. The Tg of arb-PIBs having branch molecular weight higher than the critical entanglement molecular weight was dependent on both the total Mn and BR up to BR ∼ 15. A modified Fox–Flory equation is proposed to describe the effect of architecture on thermal transition.

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      Comparison of the molecular weight and size measurement of polyisobutylenes by size exclusion chromatography/multi-angle laser light scattering and viscometry (pages 1777–1783)

      Judit E. Puskas, Yaohong Chen, Kevin Kulbaba and Gabor Kaszas

      Version of Record online: 27 JAN 2006 | DOI: 10.1002/pola.21272

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      This note reviews hyphenated size exclusion chromatography (SEC) techniques and compares polyisobutylene SEC analyses by multi-angle laser light scattering and viscometry. The weight-average molecular weight and number-average molecular weight were found to be independent of the molecular weight measurement technique used. The reproducibility was found to be better when a known refractive-index increment was used. Significantly, large differences were found in z-average molecular weight data measured by the different techniques. The low shear (Mooney) viscosity correlated well with the weight-average molecular weight and z-average molecular weight only in the case of good SEC separation.