Search

Using a micelle-like star polymer as both stabilizer and reductant, a one-pot procedure to ultrastable, narrow-sized and pH-responsive Au nanocomposites in aqueous solution was described. The water-soluble copolymer was composed of a hydrophobic alanine-based hyperbranched poly(ester amide) (HBPEA) core containing thioether moieties, and numerous hydrophilic poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The process was proposed that the Au ions were firstly coordinated and reduced by the amino groups in PDMAEMA arms, and then transferred to thioether ligands in the HBP core, driven by higher affinity of sulfur atom to Au than amine ligand. Growth of the sequentially reduced Au atoms from these nucleis contributes to formation of narrow-sized and ultrastable AuNPs. The size of the prepared AuNPs shifted in response to PDMAEMA arm length, especially pH, indicating that the star-shaped polymers acted as not only a size-tunable nanoreactor but also a pH-sensitive matrix. The nanocomposites were employed in situ as the catalysts for the reduction of p-nitrophenol, exhibiting excellent catalytic activities under mild conditions due to efficient encapsulation of the substrate to the large void spaces near the AuNP surfaces by the HBP core. The thermo-responsible property of the nanocomposites was favorable of catalyst recycle and other applications. (C) 2012 Elsevier Ltd. All rights reserved.

A series of novel hydroxyl- or methyl ester- terminated hyperbranched poly(ester-amide)s (HBPEAs) based on acidic (L-glumatic acid and L-aspartic acid) and basic amino acids (L-lysine) have been synthesized via the "AD + CBB'" couple-monomer approach. The ABB' intermediates were stoichiometrically formed through thio-ene reaction benefited from reactivity differences between functional groups. Without any purification, in situ self-polycondensations of the intermediates at elevated temperature in the presence of Ti(OBu)(4), as a catalyst, afforded HBPEAs with high molecular weights. More rapid polymerization rate and much higher molecular weight as well as broader polydispersity were observed for the polymerization process of intermediates based on acidic amino acids than basic amino acids which is related to the catalytic mechanism and structure difference of intermediates. Moreover, polymerization of intermediate derived from L-aspartic acid was carried out faster by comparison with that from L-glumatic acid. The DB values were approximately estimated to be 47%-49% for the polymers derived from L-aspartic acid and L-glutamic acid. The resultant HBPEAs possessed glass transition temperature (T-g) in the range of 3 to 11 degrees C, among which those derived from L-lysine shows the highest Tg, and decomposition temperatures at 10% weight loss under air and nitrogen are in close regions of 261-271 degrees C and 264-268 degrees C, respectively. (C) 2011 Elsevier Ltd. All rights reserved.

The series of ligands 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinolines was synthesized and used to prepare new iron(II) and cobalt(II) dichloride complexes. X-ray diffraction studies revealed that the coordination geometry around the metal center can best be described as distorted square-based pyramidal. Upon activation with methylaluminoxane (MAO), both families (Fe and Co) of complexes showed good activities in ethylene polymerization, affording highly linear polyethylenes. Enhanced activities were observed on increasing the reaction temperature to 100 degrees C. The optimization of the reaction parameters and the influence of the substituents on the imino-bound aryl group of the chelate ligands were investigated. (C) 2011 Elsevier Ltd. All rights reserved.

In the presence of [Ph(3)C][B(C(6)F(5))(4)] and Triisobutylaluminium, dimethyl pyridylamidohafnium complex exhibited remarkable catalytic activity in the copolymerization of propylene with 1,5-hexadiene, affording high molecular weight copolymers with unimodal molecular weight distributions. More noticeably, the resultant copolymers contain absolutely cyclo-group in the polymer chains without pendent vinyl groups and crosslinking. The solid state structures and properties of the homogeneous copolymers were studied by examining melting behavior, wide-angle X-ray scattering, and tensile deformation. Chain microstructures were analyzed by (13)C NMR spectra, and further confirmed by the measurement of reactivity ratios of the two monomers. These copolymers display a random distribution of the comonomer, and crystallinity decreases with increasing comonomer content. The copolymers contain variable amounts of comonomeric units, showing desired physical properties ranging from thermoplastic to elastoplastomeric to elastomeric. (C) 2011 Elsevier Ltd. All rights reserved.

Several non-metallocene-type titanium(IV) complexes containing phenoxy-phosphine or thiophenoxy-phosphine ligands of type, (2-R-1-4-R-2-6-PPh2-C6H2X)(2)TiCl2 (2a: X O, R-1 = R-2 = t-Bu; 2b X = O, R-1 = R-2 = cumyl, 2c X = S, R-1 = SiMe3, R-2 - H) have been synthesized by treating TiCl4 with the corresponding ligands 2-R-1-4-R-2-6-PPh2-C6H2XH in the presence of n-BuLi The complexes 2a-c were investigated as the catalysts for ethylene with 1-hexene and/or polar alkenes copolymerizations The catalytic activity and the comonomer incorporation were highly dependent upon catalyst and reaction conditions employed Among these complexes, 2a can not only promote ethylene/1-hexene living copolymerization at room temperature, but also can utilize ethylene with methyl 10-undecenoate copolymerization (C) 2010 Elsevier Ltd All rights reserved

Novel terpolymers containing ethylene, 1-hexene and dicyclopentadiene (DCPD) were synthesized using bis(beta-enaminoketonato)titanium catalysts [PhN=C(R-2)CHC(R-1)O](2)TiCl2 (1a: R-1 = Ph, R-2 = CF3; 1b: R-1 = CF3, R-2 = CH3). In the presence of modified methylaluminoxane, these catalysts afforded terpolymers with a broad range of monomer compositions and unimodal molecular weight distributions. C-13 NMR spectra reveal the exclusive insertion manner of DCPD maintained under various reaction conditions. DSC results show the melting temperature and the glass transition temperature are very sensitive to the terpolymer composition and the morphology can be easily tuned from semicrystalline state to amorphous state. With ethylene/1-hexene/DCPD molar ratio about 67/28/5, the terpolymer exhibits low glass transition temperature (T-g = -50 degrees C) and has a great potential to serve as polyolefin elastomer. Additionally, the terpolymer containing 4.3 mol% 1-hexene and 1.6 mol% DCPD was served as the "reactive intermediate polyolefin" for PCL graft reaction. The composition of graft copolymer was well controllable and high graft efficiency was observed. The microscopy studies in conjunction with the tensile tests revealed that PCL graft copolymer is the effective compatibilizer for polyethylene/polar polymer blends by improving the interfacial adhesion between separated phases. (C) 2010 Elsevier Ltd. All rights reserved.

A facile self-condensing vinyl polymerization (SCVP) system, the combination of glycidyl methacrylate, Cp2TiCl2 and Zn, has been firstly used to prepare novel hyperbranched polymers, consisting of vinyl polymers as the backbone, and cyclic ester polymers (poly(c-caprolactone) or poly(L-lactide)) as the side chains. The polymerizations are initiated by the epoxide radical ring-opening catalyzed by Cp2Ti(III)Cl which is generated in situ via the reaction of Cp2TiCl2 with Zn. The key to success is that the polymerizations can proceed concurrently via two dissimilar chemistries possessing the opposite active initiating species, including ring-opening polymerization (ROP) and controlled/living radical polymerization (CRP). We have demonstrated that this facile one-step polymerization technique can be applied successfully to prepare highly branched polymers with a multiplicity of end reactive functionalities including Ti alkoxide, hydroxyl and vinyl functional groups. (C) 2010 Elsevier Ltd. All rights reserved.

A series of novel half-metallocene-type titanium complexes CpTiCl2[PhN=C(R-2)CHC(R-1)O] (2a, R-1 = Cy, R-2 = CF3; 2b, R-1 = Bu-t, R-2 = CF3; 2c, R-1 = Ph, R-2 = CF3; 2d, R-1 = Ph, R-2 = CH3) have been synthesized by treating CpTiCl3 with the corresponding bidentate beta-enaminoketonato ligands PhN=C(R-2)CHC(R-1)OH in the presence of triethylamine. Single crystal X-ray diffraction revealed that complex 2b adopts distorted square-pyramid geometry around the titanium center. The complexes 2a-d were investigated as the catalysts for ethylene polymerization and the copolymerization of ethylene with norbornene. All the complexes were active towards ethylene (co)polymerization in the presence of modified methyl-aluminoxane, and produced high molecular weight (co)polymers. The catalytic activity and the norbornene incorporation were highly dependent upon catalyst and reaction conditions employed. Among four complexes, 2c exhibited both high catalytic activity and efficient norbornene incorporation under the same conditions, affording high molecular weight copolymers with unimodal molecular weight distributions. (C) 2010 Elsevier Ltd. All rights reserved.

Hyperbranched polymers were produced using glycidyl methacrylate (GMA)/CP2TiCl2/Zn as self-condensing vinyl polymerization (SCVP) system. The polymerization is firstly initiated by the epoxide radical ring opening catalyzed by Cp2Ti(III)Cl generated in situ via the reaction of Cp2TiCl2 with Zn. By optimizing the molar ratio of the SCVP inimer (GMA) to the mediator (Cp2Ti(III)Cl), the active propagation chains are reversibly transformed to the dormant species and the cross-linking does not occur until a higher level of monomer conversion (ca. 80%). We detail this facile one-step polymerization technique to prepare highly branched polymers with a multiplicity of particular end reactive functionalities including Ti alkoxide, hydroxyl and vinyl functional groups, which differs from most previously reported SCVP systems. (C) 2010 Elsevier Ltd. All rights reserved.

The copolymerizations of ethylene with polar hydroxyl monomers such as 10-undecen-1-ol, 5-hexen-1-ol and 3-buten-1-ol were investigated by the vanadium(III) catalysts bearing bidentate [N,O] ligands (1, [PhN C(CH3)CHC(Ph)O]VCl2(THF)2; 2, [PhN CHC6H4O]VCl2(THF)2; 3, [PhN CHC(Ph)CHO]VCl2(THF)2). The polar monomers were pretreated by alkylaluminum before the polymerization. High catalytic activities and efficient comonomer incorporations can be easily obtained by changing monomer masking reagents and polymerization conditions in the presence of diethylaluminium chloride as a cocatalyst. The longer the spacer group, the higher the incorporation of the monomer. Under the mild conditions, the incorporation level of 10-undecen-1-ol reached 13.9 mol% in the resultant copolymers was obtained. The reactivity ratios of copolymerization (r1 = 41.4, r2 = 0.02, r1r2 = 0.83) were evaluated by Fineman–Ross method. According to 13C NMR spectra, polar units were located both on the main chain and at the chain end. The end-hydroxylated polymers were probably obtained due to the formation of dormant species after the insertion of the comonomer followed by the chain transfer to alkylaluminum. In addition, the signals derived from polar monomer inverse insertion were detected for the first time.

The strong polar group, carboxylic acid, has triumphantly been introduced into ethylene and allylbenzene copolymers without obvious degradation or crosslinking via Friedel-Crafts (F-C) acylation reaction with glutaric anhydride (GA), succinic anhydride (SA) and phthalic anhydride (PA) in the presence of anhydrous aluminum chloride in carbon disulfide. Some important reaction parameters were examined in order to optimize the acylation process. In the optimum reaction conditions, almost all of the phenyls can be acylated with any anhydride. The microstructure of acylated copolymer was characterized by Fr-IR, H-1 NMR and H-1-H-1 COSY. All the peaks of acylated copolymers can be accurately attributed, which indicates that all the acylation reactions occur only at the para-positions of the substituent of the aromatic rings. The thermal behavior was studied by differential scanning calorimetry (DSC), showing that the melting temperatures (T(m)s) of acylated copolymers with GA firstly decrease slowly and then increase significantly with the increase of the amount of carboxyl acid groups.

The branched copolymers prepared from ethylene and alpha-olefins using rac-Et(Ind)(2)ZrCl2/MMAO catalyst system were studied. Both the absolute molecular weight ((M) over bar (W)) and the molecular size (radius of glyration, R-g) of the polymers eluting from gel permeation chromatography (GPC) columns were obtained simultaneously via a high temperature GPC coupled with a two-angle laser light scattering (TALLS) detector. The branched structures and performances of the copolymers display approximate molecular weight and molecular sizes were investigated. Wide angle X-ray diffraction analyses indicate that 16-carbon side branch could co-crystallize effectively with backbone chain at low alpha-olefin incorporation. The melt behaviors of the copolymers were studied by dynamic rheological measurements. Both branch length and comonomer content affect considerably the loss modulus, storage modulus and complex viscosity of the copolymers. The relationship between the dynamic-mechanical behavior and the comonomer content of the copolymers was also examined by dynamic-mechanical experiments.

Fe(II) pyridinebisimine complexes activated with trialkylaluminium or modified methylaluminoxane (MMAO) as catalysts were employed for the polymerization of methyl methacrylate. Polymer yields, activities and polymer molecular weights as well as molecular weight distributions can be controlled over a wide range by the variation of the structures of the Fe(II) pyridinebisimine complexes and the reaction parameters such as Al/Fe molar ratio, monomer/catalyst molar ratio, monomer concentration, reaction temperature and time applied to the polymerization of methyl methacrylate. Under optimum condition, the catalytic activity of Fe(II) complex is of up to 74.5 kg(polym)/mol(Fe)h.

The four AB2 monomers, N-[3- or 4-bis(4-hydroxyphenyl)toluoyl]-4-chlorophthalimide and N-{3- or 4-[1,1-bis(4-hydroxyphenyl)]ethylphenyl}-4-chlorophthalimides, were prepared and used for synthesis of hyperbranched poly(ether imide)s bearing hydroxyl end groups. These hyperbranched poly(ether imide)s had moderate molecular weights with broad distributions and showed glass-transition temperatures (Tgs) between 177 and 230 °C. The thermogravimetric analytic measurement revealed the decomposition temperature at 5% weight-loss temperatures (Td5%) ranging from 240 to 281 °C. Analysis using 1H NMR spectroscopy revealed the four types of hyperbranched poly(ether imide)s to have similar degrees of branching (ca. 60%). These polymers were modified by acylation or nucleophilic substitution reaction at the hydroxyl end groups. The conversion effectiveness depended on the type of modification reaction, modifier, and reaction conditions. The thermal stability and solubility of hyperbranched poly(ether imide)s were impro...

Para-para linked aromatic poly(amic ester) precursors of rodlike polyimide (PI) BPDA-PDA and polyetherimide (PEI) HQDPA-ODA were synthesized. The para-para linked poly(amic ester)s were employed in this work to obtain, in theory, full-imidized polyimides. The two precursors were mixed by dissolving them in N, N'-dimethyl acetamide and subsequently coagulating in methanol. After thermal imidization, the miscibility behaviour of the resulting composites has been studied by means of dynamic mechanical analysis (d.m.a.) and differential scanning calorimetry (d.s.c.). The composites show a single glass transition temperature (T-g) at both d.m.a. and d.s.c. in which the T-g increases with increasing PI content. These Tg values are reproducible in repeated heating cycles, suggesting the true miscibility of the blends. (C) 1997 Elsevier Science Ltd.