Journal of Polymer Science Part A: Polymer Chemistry

Cover image for Vol. 44 Issue 11

1 June 2006

Volume 44, Issue 11

Pages 3411–3728

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      Dendrimers based on [1,3,5]-triazines (pages 3411–3433)

      Mackay B. Steffensen, Emily Hollink, Frank Kuschel, Monika Bauer and Eric E. Simanek

      Version of Record online: 6 APR 2006 | DOI: 10.1002/pola.21333

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      A comprehensive and chronological account of dendrimers based on [1,3,5]-triazines is provided. Synthetic strategies to install the triazine through cycloaddition, cyclotrimerization, and nucleophilic aromatic substitution of cyanuric chloride are discussed. Motivations and applications of these architectures are surveyed, including the preparation of supramolecular assemblies in the solution and solid states and their use in medicines, advanced materials, and separations when anchored to solid supports.

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    1. Atom transfer radical polymerization directly from poly(vinylidene fluoride): Surface and antifouling properties (pages 3434–3443)

      Yiwang Chen, Dongmei Liu, Qilan Deng, Xiaohui He and Xiaofeng Wang

      Version of Record online: 6 APR 2006 | DOI: 10.1002/pola.21456

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      Hydrophilic polymer brushes were prepared from the secondary fluorinated site of a poly(vinylidene fluoride) (PVDF) surface with direct surface-initiated atom transfer radical polymerization. Diblock copolymer brushes were synthesized with the living chain ends as macroinitiators. Protein adsorption experiments revealed a substantial antifouling property of polymer-grafted PVDF surfaces.

    2. Synthesis, characterization, and proton-conducting properties of organic–inorganic hybrid membranes based on polysiloxane zwitterionomer (pages 3444–3453)

      Wuu-Jyh Liang, Chien-Pang Wu, Chang-Yu Hsu and Ping-Lin Kuo

      Version of Record online: 6 APR 2006 | DOI: 10.1002/pola.21455

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      The synthesis and characterization of a series of zwitterionic hybrid membranes based on polysiloxane zwitterionomer are described. Flexible, transparent, optically homogeneous films were prepared. The proton conductivity enhanced by the addition of the plasticizing component of PEG to the hybrid matrix; this was ascribed to the increased water uptake and free volume of the hybrid matrix and the dissociation of sulfonic acid groups. The proton conductivity of these hybrid membranes could be increased up to 3.5 × 10−2S/cm by the temperature and relative humidity being increased to 85 °C and 95%, respectively.

    3. Synthesis and properties of flame-retardant benzoxazines by three approaches (pages 3454–3468)

      Ching Hsuan Lin, Sheng Xiong Cai, Tsu Shang Leu, Ting Yu Hwang and Hao Hsin Lee

      Version of Record online: 7 APR 2006 | DOI: 10.1002/pola.21454

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      A novel benzoxazine (dopot-m) from a phosphorus-containing triphenol (dopotriol), formaldehyde, and methyl amine has been synthesized. Dopot-m has been copolymerized with a commercial benzoxazine [6′,6-bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazineyl)methane (F-a)] or diglycidyl ether of bisphenol A (DGEBA). The thermal properties and flame retardancy of the F-a/dopot-m copolymers increase with the content of dopot-m. As for the dopot-m/DGEBA curing system, the glass-transition temperature of the dopot-m/DGEBA copolymer is 252 °C, which is higher than that of poly(dopot-m). The 5% decomposition temperature of the dopot-m/DGEBA copolymer increases from 323 to 351 °C because of the higher crosslinking density caused by the reaction of phenolic OH and epoxy.

    4. Phenylene vinylene-based electroluminescent polymers with electron transport block in the main chain (pages 3469–3478)

      Honghao Sun, Chongyu Mei, Quanguo Zhou, Ze Liu, Dongge Ma, Lixiang Wang, Xiabin Jing and Fosong Wang

      Version of Record online: 11 APR 2006 | DOI: 10.1002/pola.21437

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      Novel PPV based electroluminescent polymers with electron transport block (OXD and TZ) in the main chain were synthesized. By properly adjusting the OXD and/or TZ content through copolymerization, we can achieve an enhanced balance of hole- and electron injections, such that the single layer devices efficiency using these polymers as emitting layer is significantly improved. At the optimal ratio (OXD/MEH-PV = 100/100 mol), the electroluminescent efficiency of P4 is 0.325 cd/A and the maximum brightness is 1300 cd/m2, 10 times brighter than that of polymer P1 without OXD. This approach provides an opportunity to achieve high efficient single-layer polymer LEDs.

    5. Design, synthesis, and characterization of main-chain, aromatic polyesters based on 3,4-ethylenedioxythiophene (pages 3479–3486)

      Uma P. Ojha and Anil Kumar

      Version of Record online: 13 APR 2006 | DOI: 10.1002/pola.21414

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      A series of new thermoplastic polyesters based on 3,4-ethylenedioxythiophene (EDOT) with flexible aliphatic spacers have been synthesized and characterized for the first time. The thermal properties of these polyesters based on EDOT are comparable to those of conventional polyesters based on the 1,4-phenyl unit, indicating that EDOT is a viable replacement for the phenyl units. Theoretical calculations have revealed that the core angle for EDOT (149°) is comparable to that of unsubstituted thiophene (150°) and hence is compatible with the formation of the mesophase. This has been confirmed experimentally by the synthesis of a main-chain, thermotropic, liquid-crystalline polyester based on EDOT that exhibits fluid birefringence.

    6. Synthesis, characterization, and properties of novel epoxy resins and cyanate esters (pages 3487–3502)

      Ching Hsuan Lin, Kai Zhi Yang, Tsu Shang Leu, Chun Hung Lin and Jhao Wei Sie

      Version of Record online: 11 APR 2006 | DOI: 10.1002/pola.21453

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      We synthesized a novel epoxy (dopotep) and cyanate ester (dopotcy) based on a phosphorus-containing triphenol (dopotriol). The synthesized dopotep or dopotcy was copolymerized with diglycidyl ether of bisphenol A (DGEBA), 6′,6-bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazineyl)methane (F-a), or dicyanate ester of bisphenol A (BADCY). Thus, copolymers based on DGEBA/dopotep/diphenylmethane, F-a/dopotep, BADCY/dopotcy, and DGEBA/dopotcy were developed. The thermal properties, microstructure, curing kinetics, dielectric properties, and flame retardancy of these copolymers were investigated.

    7. Development of novel flame-retardant thermosets based on boron-modified phenol–formaldehyde resins (pages 3503–3512)

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

      Version of Record online: 11 APR 2006 | DOI: 10.1002/pola.21458

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      New boron-containing novolac resins were prepared through the modification of a commercial novolac resin with bis (benzo-1,3,2-dioxaborolanyl)oxide. Then, they were crosslinked with hexamethylenetetramine, and their thermal, thermodynamomechanical, and flame-retardant properties were evaluated. A thermal degradation study showed the presence of boric acid at high temperatures leading to an intumescent char that slowed the degradation and prevented it from being complete. Thus, the benefit of boron for the flame retardancy of novolac resins was demonstrated.

    8. Sonochemical synthesis of novel blue-emissive, water-soluble, cationic polysilanes as fluorescent sensors (pages 3513–3525)

      Wei-Zhi Wang, Qu-Li Fan, Fan Cheng, Ping Zhao and Wei Huang

      Version of Record online: 11 APR 2006 | DOI: 10.1002/pola.21457

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      Novel blue-emissive, water-soluble, cationic polysilanes were obtained by three synthesis steps: (1) the Wurtz-type reductive coupling of dihalodiorganosilanes to prepare polysilanes 1, 2, and 3; (2) the reaction of these polysilanes with 2-(dimethylamino)ethyl methacrylate through hydrosilylation to produce polysilanes 4, 5, and 6, respectively; and (3) the conversion of the neutral polymers to the corresponding water-soluble, cationic polymers via stirring with iodomethane in tetrahydrofuran/CH3OH (4/1) at 40 °C for 3 days.

    9. Dehydrogenation of poly(1,3-cyclohexadiene)–polystyrene binary block copolymers (pages 3526–3537)

      Itaru Natori and Hisaya Sato

      Version of Record online: 14 APR 2006 | DOI: 10.1002/pola.21461

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      The dehydrogenation of poly(1,3-cyclohexadiene)-polystyrene binary block copolymers was investigated. The dehydrogenation of the poly(1,3-cyclohexadiene) block, which was composed of 1,2-cyclohexadiene (1,2-CHD) and 1,4-cyclohexadiene (CHD) units, was strongly affected by the polymer chain structure. The 1,2-CHD units prevented the dehydrogenation. The rate of dehydrogenation was fast on a long sequence of 1,4-CHD units, whereas it was relatively slow for 1,2-CHD/1,4-CHD (≈1/1) unit sequences. The bonding of the polystyrene block to the polymer chain effectively improved the rate of dehydrogenation. The dehydrogenation of a poly(1,3-cyclohexadiene) block containing a small amount of 1,2-CHD units progressed via step-by-step reactions.

    10. Synthesis of liquid crystalline poly(1-pentyne)s and fabrication of polyacetylene–perovskite hybrids (pages 3538–3550)

      Jianli Hua, Jacky Wing Yip Lam, Zhen Li, Anjun Qin, Jingzhi Sun, Yongqiang Dong, Yuping Dong and Ben Zhong Tang

      Version of Record online: 14 APR 2006 | DOI: 10.1002/pola.21448

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      Nematic poly(1-pentyne)s bearing biphenyl and phthalimido pendants are synthesized by WCl6-Ph4Sn catalyst. Upon hydrolysis and acidification, the resulting polymers can complex with lead bromide to furnish polyacetylene–perovskite hybrids in high yields. The organic polymer contributes good solubility to the hybrids, while the perovskite framework induces the polyacetylene chains to align between the inorganic layers.

    11. Comparison of the C1-symmetric diastereoisomers of a zirconocene-based catalyst in ethylene polymerization: A benzyl substituent as a regulator in branch formation (pages 3551–3555)

      Lorella Izzo, Arto J. Puranen, Timo Repo and Leone Oliva

      Version of Record online: 14 APR 2006 | DOI: 10.1002/pola.21467

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      Some C1-symmetric zirconocene-based catalysts are able to produce branched polyethylene with only ethyl branches in the backbone by homopolymerization. The mechanism of β-hydrogen transfer to the monomer seems strictly dependent on the encumbrance of the two diastereoisomeric catalytic sites. The presence of a benzyl substituent in only one of the two indenyl moieties regulates the number of branches in the polymer chain by controlling the β-hydrogen transfer to the monomer.

    12. Synthesis and optical properties of a poly(p-phenylenevinylene) derivative and polyfluorenes with bipolar groups along the main chain (pages 3556–3566)

      Vasilis P. Barberis and John A. Mikroyannidis

      Version of Record online: 14 APR 2006 | DOI: 10.1002/pola.21459

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      A poly(p-phenylenevinylene) derivative (PPV–TPA)] and a series of statistical copolyfluorenes (PF–TPA)] containing oxadiazole and triphenylamine segments along the main chain were synthesized. PPV–TPA and the PF–TPA copolyfluorenes with relatively low contents of oxadiazole and triphenylamine units dissolved readily in common organic solvents. Thin films of the polymers emitted blue-green light with a photoluminescence maximum at 414–522 nm and optical band gaps of 2.76–2.98 eV. The copolyfluorene PF–TPA thin films with high contents of oxadiazole and triphenylamine moieties emitted pure blue light that remained stable even after annealing at 150 °C for 4 h in air.

    13. Heterogeneous surface saponification of suspension-polymerized monodisperse poly(vinyl acetate) microspheres using various ions (pages 3567–3576)

      Se Geun Lee, Jae Pil Kim, Ick Chan Kwon, Ki Hong Park, Seok Kyun Noh, Sung Soo Han and Won Seok Lyoo

      Version of Record online: 17 APR 2006 | DOI: 10.1002/pola.21406

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      The ion-specificities to the heterogeneous saponification of monodisperse poly(vinyl acetate) (PVAc) were investigated using SOmath image, Cl, NOmath image, Br, and I for anions and Li+, Na+, and K+ for cations, respectively. The ions affected significantly on the degree of saponification (DS). DSs had different values between by weight loss (DSw) and by 1H NMR (DSNMR) measurements. The order of DSws was SOmath image < Cl < NO3 < Br < I for anions and K+ < Na+ < Li+ for cations, and for DSNMRs, the order was reverse. The differences between DSws and DSNMRs were caused by the dissolution of PVA skin.

    14. Direct measurements of the addition and recombination of acrylate radicals: Access to propagation and termination rate constants? (pages 3577–3587)

      J. Lalevée, X. Allonas and J. P. Fouassier

      Version of Record online: 17 APR 2006 | DOI: 10.1002/pola.21463

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      In this article, the direct observation of acrylate radicals is reported. In this way, new and convenient access to their reactivity is proposed. It is principally possible (1) to characterize their corresponding absorption in the visible part of the spectrum, (2) to monitor the kinetics of the subsequent addition to another monomer unit, and (3) to follow the recombination of two acrylate radicals. These two latter points can mimic the propagation and termination reactions of polymerization-propagating acrylate radicals. The obtained results are in good agreement with the propagation rate constants determined by the well-established pulsed laser polymerization techniques.

    15. Acyclic N-halamine-based fibrous materials: Preparation, characterization, and biocidal functions (pages 3588–3600)

      Jie Luo and Yuyu Sun

      Version of Record online: 14 APR 2006 | DOI: 10.1002/pola.21465

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      Methacrylamide (MAA) was grafted onto cotton cellulose. The influence of the reaction conditions on the grafting was studied in detail. Upon a chlorine bleach treatment, some of the amide groups in the grafted MAA side chains were transformed into stable acyclic N-halamines; Hoffman-type degradation was not observed. The resultant cotton celluloses provided a total kill of 108–109 CFU/mL for Escherichia coli (Gram-negative bacteria), Staphylococcus aureus (Gram-positive bacteria), and Candida tropicalis (fungi) in 3 min, 106–107 PFU/mL for the MS2 virus in 5 min, and 106–107 spores/mL for Bacillus subtilis in 4 h. The antibacterial, antifungal, antiviral, and antispore activities were both durable and rechargeable.

    16. Isothermal frontal polymerization: Confirmation of the isothermal nature of the process and the effect of oxygen and polymer seed molecular weight on front propagation (pages 3601–3608)

      Svetlana I. Evstratova, Daniel Antrim, Chip Fillingane and John A. Pojman

      Version of Record online: 17 APR 2006 | DOI: 10.1002/pola.21447

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      Temporal temperature profiles for the system PMMA–MMA with 2 × 10−2 M azoisbutyronitrile were measured at three different locations during front propagation: thermocouple 1 was placed in the monomer solution 7 mm above the seed; thermocouple 2 was placed on the seed surface; thermocouple 3 recorded the temperature of the air in the thermostated box.

    17. Simultaneous control of the stereospecificity and molecular weight in the ruthenium-catalyzed living radical polymerization of methyl and 2-hydroxyethyl methacrylates and sequential synthesis of stereoblock polymers (pages 3609–3615)

      Takuya Shibata, Kotaro Satoh, Masami Kamigaito and Yoshio Okamoto

      Version of Record online: 25 APR 2006 | DOI: 10.1002/pola.21469

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      The simultaneous control of the stereospecificity and molecular weight was achieved with a combination of ruthenium-catalyzed living radical and solvent-mediated stereospecific radical polymerizations of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA). A ruthenium complex [RuCp*Cl(PPh3)2] gave syndiotactic polymers (r = 88%) with controlled molecular weights (weight-average molecular weight/number-average molecular weight ∼ 1.1) of MMA and HEMA in (CF3)2C(Ph)OH and N,N-dimethylformamide, respectively, whereas HEMA was polymerized in (CF3)2C(Ph)OH to give more or less atactic polymers (mm/mr/rr = 7.2/40.9/51.9%). A successive living radical polymerization of HEMA in two solvents, first N,N-dimethylacetamide followed by (CF3)2C(Ph)OH, resulted in stereoblock poly(2-hydroxyethyl methacrylate) with syndiotactic–atactic segments.

    18. Copolycarbonates of isosorbide and various diols (pages 3616–3628)

      Saber Chatti, Hans R. Kricheldorf and Gert Schwarz

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21444

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      Copolycondensations of isosorbide with various diols and diphosgenes yielded random copolycarbonates, which mainly consisted of cycles under optimized reaction conditions. A different approach yielded alternating polycarbonates that surprisingly showed higher glass-transition temperatures.

    19. Polydiphenylsiloxane–polydimethylsiloxane–polydiphenylsiloxane triblock copolymers (pages 3629–3639)

      Thomas M. Gädda and William P. Weber

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21468

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      Triblock copolymers were prepared by the sequential addition of monomers and by a convergent approach. The formation of distinct blocks with regular microstructures in these materials was confirmed by NMR spectroscopy and differential scanning calorimetry. The molecular weights were determined by gel permeation chromatography, and the thermal stabilities were evaluated by thermogravimetric analysis. Dynamic mechanical analysis was used to evaluate the mechanical properties of the materials and to confirm the thermal transitions obtained by differential scanning calorimetry.

    20. Syntheses and properties of hyperbranched polybenzoxazole by thermal cyclodehydration of hyperbranched poly[o-(t-butoxycarbonyl)amide] via A2 + B3 approach (pages 3640–3649)

      Hiroto Kudo, Ken Maruyama, Syoko Shindo, Tadatomi Nishikubo and Isao Nishimura

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21449

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      Syntheses and properties of A2 + B3 type hyperbranched poly(o-hydroxyamide), poly[o-(t-butoxycarbonyl)amide], and polybenzoxazole were examined. Poly(o-hydroxyamide) was obtained from the polycondensation reaction of 3,3-dihydroxy-4,4′-diaminobiphenyl as A2-monomer and 1,3,5-benzenetricarboxylchloride as B3-monomer with 2-amino-4-t-butylphenol. The reaction of poly(o-hydroxyamide) and di-t-buthylcarbonate was performed to obtain the corresponding poly[o-(t-butoxycarbonyl)amide] with pendant t-BOC groups. The thermal cyclodehydration of poly[o-(t-butoxycarbonyl)amide] was carried out in the film sate at 400 °C, affording the polybenzoxazole in quantitative yield. Furthermore, the solubility and thermal properties of these polymers were examined.

    21. Synthesis and application as polymer electrolyte of hyperbranched polyether made by cationic ring-opening polymerization of 3-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxymethyl}-3′-methyl-oxetane (pages 3650–3665)

      Ye Lin, Feng Zeng-Guo, Zhao Yu-Mei, Wu Feng, Chen Shi and Wang Guo-Qing

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21450

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      A novel hyperbranched polyether was synthesized through CROP of 3-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxymethyl}-3′-methyloxetane using BF3·Et2O as initiator. The ionic conductivity was measured to reach 5.6 ×·10−5 S/cm at room temperature and 6.3 × 10−4 S/cm at 80 °C after doping with LiTFSI at a ratio of Li:O = 0.05.

    22. Copolymers containing a spiro orthoester moiety that undergo no shrinkage during cationic crosslinking (pages 3666–3673)

      Makoto Kume, Atsunori Hirano, Bungo Ochiai and Takeshi Endo

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21462

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      A spiro orthoester with an exomethylene group was radically copolymerized with acrylonitrile or vinyl acetate at several feed ratios to obtain the corresponding copolymers having spiro orthoester moieties in the side chain. The obtained copolymers could be crosslinked via the cationic double ring-opening polymerization of the spiro orthoester structure without shrinkage.

    23. Solution properties of dendronized poly(hydroxy ethyl methacrylate) polymers (pages 3674–3683)

      Sami Hietala, Andreas Nyström, Heikki Tenhu and Anders Hult

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21471

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      Four generations of dendronized polymers with a methacrylate backbone and hydroxy-functionalized aliphatic polyester dendrons were studied in solutions. Aggregation upon heating of the first-generation polymer in an aqueous solution was observed, reflecting the effect of the hydrophobic polymer backbone, whereas the higher generation polymers did not show aggregation upon heating. The dimensions of the polymers increased with increasing generation, although all the polymers exhibited low viscosities and Newtonian flow behavior in both aqueous and dimethyl sulfoxide solutions.

    24. Preparation of novel poly(ethylene oxide-co-glycidol)-graft-poly(ε-caprolactone) copolymers and inclusion complexation of the grafted chains with α-cyclodextrin (pages 3684–3691)

      Juan Huang, Zhongyu Li, Xuewei Xu, Yong Ren and Junlian Huang

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21480

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      A series of grafted poly(ethylene oxide-co-glycidol)-graft-poly(ε-caprolactone) [poly(EO-co-Gly)-g-PCL] copolymers were synthesized by the combination of anionic polymerization and ring-opening polymerization. The crystalline inclusion complexes (ICs) that were formed from the grafted copolymers and α-cyclodextrin (α-CD) were characterized with 1H NMR, differential scanning calorimetry, X-ray diffraction, thermogravimetric analysis, and 13C cross-polarization/magic-angle spinning NMR in detail. X-ray diffraction indicated that all the ICs with α-CD had a channel-type crystalline structure. The stoichiometry of the ε-caprolactone unit to the α-CD ring for the ICs given by 1H NMR spectra indicated that the PCL branches were not completely covered by α-CDs. This could be explained as follows: the steric hindrance between the backbone and side chains prevented α-CDs from being fully covered.

    25. Living free-radical polymerization of sterically hindered monomers: Improving the understanding of 1,1-disubstituted monomer systems (pages 3692–3710)

      Zachary Szablan, Andrew Ah Toy, Alexandre Terrenoire, Thomas P. Davis, Martina H. Stenzel, Axel H. E. Müller and Christopher Barner-Kowollik

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21470

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      Itaconates (dimethyl, dibutyl, and dicyclohexyl) were successfully polymerized with both reversible addition–fragmentation chain transfer (RAFT) and atom transfer radical polymerization (ATRP) techniques. The resulting molecular weight distributions were broad for the RAFT-mediated systems. The molecular weight distributions generated via the ATRP of dicyclohexyl itaconate were narrower. Chain-transfer-to-monomer constants for the itaconate monomers were determined at 60 °C and were relatively large in comparison with similar 1,1-disubstituted systems, suggesting that the transfer-to-monomer reaction is significant. PREDICI simulations confirmed that a significant chain-transfer-to-monomer step resulted in broad molecular weight distributions. The viscosity of the polymerizing system was also shown to be an important factor for the resulting width of the molecular weight distributions.

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    1. Immobilization of Ti(OiPr)4 onto silicon oxide surfaces and surface-initiated polymerization of ϵ-caprolactone (pages 3711–3716)

      Sungjin Park, Young Shik Chi and Insung S. Choi

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21424

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      Titanium-catalyst-immobilized surfaces were generated from the reaction of [BOND]OH-terminated self-assembled monolayers and Ti(OiPr)4 on a Si/SiO2 substrate. The immobilized Ti species catalyzed surface-initiated ring-opening polymerization of ϵ-caprolactone, resulting in thin films of poly(ϵ-caprolactone), with benzyl alcohol as an external initiator.

    2. Thermally responsive polyrotaxanes synthesized through the telomerization of N-isopropylacrylamide with polypseudorotaxanes made from α-cyclodextrin threaded onto thiolated poly(ethylene glycol) (pages 3717–3723)

      Huaiqing Yu, Zeng-Guo Feng and Ai-Ying Zhang

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21475

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      A novel kind of thermally responsive polyrotaxanes were prepared via the photoinitiated telomerization of N-isopropylacrylamide with polypseudorotaxanes made from α-cyclodextrins threaded onto thiolated poly(ethylene glycol). The poly(N-isopropylacrylamide) blocks were bulky enough to impede the dethreading of the α-cyclodextrins from the thiolated poly(ethylene glycol) backbones. Furthermore, both transmittance and differential scanning calorimetry analyses showed that these polyrotaxanes possessed a lower critical solution temperature around 38 °C, close to the temperature of the human body.

    3. Origin of the formation of the 4-butenyl end group in zirconocene-catalyzed propylene polymerization (pages 3724–3728)

      Bernabe Quevedo-Sanchez, Michael A. Henson and E. Bryan Coughlin

      Version of Record online: 24 APR 2006 | DOI: 10.1002/pola.21460

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      It has been proposed that the 4-butenyl end group in polypropylene is formed by isomerization of the 2-butenyl end group. Prior experimental evidence has shown that the isomerization is not produced thermally or upon an acidic treatment during the workup or analysis of the polymer. We postulate that the production of the 4-butenyl end group by isomerization might be catalyzed by a zirconocene hydride complex that forms during the β-hydride elimination reaction. The isomerization of a preformed olefinic-end-group isotactic polypropylene with a well-known transition-metal hydride shows the disappearance of the 2-butenyl end group concomitant with the appearance of the 4-butenyl end group.

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