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ROP
Selected AbstractsOphthalmological problems of the premature infantDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 4 2002Michael X. Repka Abstract Preterm infants are more likely than term infants to have significant abnormalities of all parts of the visual system leading to reduced vision. The most common problem is retinopathy of prematurity (ROP). The frequency and severity of this disorder is inversely related to gestational age. Damage ranges from minor to catastrophic. Preterm infants also have higher rates of amblyopia, strabismus, refractive error, and cortical visual impairment. The later problem is largely associated with neonatal brain injury. Years later, these children may develop glaucoma and retinal detachments. MRDD Research Reviews 2002;8:249,257. © 2002 Wiley-Liss, Inc. [source] Influence of Decreasing Solvent Polarity (1,4-Dioxane/Water Mixtures) on the Acid,Base and Copper(II)-Binding Properties of Guanosine 5,-Diphosphate,HELVETICA CHIMICA ACTA, Issue 3 2005Emanuela The acidity constants of twofold protonated guanosine 5,-diphosphate, H2(GDP),, and the stability constants of the [Cu(H;GDP)] and [Cu(GDP)], complexes were determined in H2O as well as in 30 or 50% (v/v) 1,4-dioxane/H2O by potentiometric pH titrations (25°; I=0.1M, NaNO3). The results showed that in H2O one of the two protons of H2(GDP), is located mainly at the N(7) site and the other one at the terminal , -phosphate group. In contrast, for 50% 1,4-dioxane/H2O solutions, a micro acidity-constant evaluation evidenced that ca. 75% of the H2(GDP), species have both protons phosphate-bound, because the basicity of pyridine-type N sites decreases with decreasing solvent polarity whereas the one of phosphate groups increases. In the [Cu(H;GDP)] complex, the proton and the metal ion are in all three solvents overwhelmingly phosphate-bound, and the release of this proton is inhibited by decreasing polarity of the solvent. Based on previously determined straight-line plots of log,Kvs. pK (where R represents a non-interacting residue in simple diphosphate monoesters ROP(O,)(O)OP(O)(O,)2, RDP3,), which were now extended to mixed solvents (based on analogies), it is concluded that, in all three solvents, the [Cu(GDP)], complex is more stable than expected based on the basicity of the diphosphate residue. This increased stability is attributed to macrochelate formation of the phosphate-coordinated Cu2+ with N(7) of the guanine residue. The formation degree of this macrochelate amounts in aqueous solution to ca. 75% (being thus higher than that of the Cu2+ complex of adenosine 5,-diphosphate) and in 50% (v/v) 1,4-dioxane/H2O to ca. 60%, i.e., the formation degree of the macrochelate is only relatively little affected by the change in solvent, though it needs to be emphasized that the overall stability of the [Cu(GDP)], complex increases with decreasing solvent polarity. By including previously studied systems in the considerations, the biological implications are shortly discussed, and it is concluded that Nature has here a tool to alter the structure of complexes by shifting them on a protein surface from a polar to an apolar region and vice versa. [source] Poly(trimethylene carbonate) from Biometals-Based Initiators/Catalysts: Highly Efficient Immortal Ring-Opening Polymerization ProcessesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Marion Helou Abstract The ring-opening polymerization (ROP) of trimethylene carbonate (TMC) was evaluated in bulk at 60,110,°C using various catalyst systems based on bio-friendly metals, including the metal bis(trimethylsilylamides) Mg[N(SiMe3)2]2, Ca[N(SiMe3)2]2(THF)2, Y[N(SiMe3)2]3, (BDI)Fe[N(SiMe3)2] [BDI=CH(CMeNC6H3 -2,6- i- Pr2)2], Fe[N(SiMe3)2]2, Fe[N(SiMe3)2]3, Zn[N(SiMe3)2]2, (BDI)Zn[N(SiMe3)2] and ZnEt2, associated with an alcohol such as isopropyl or benzyl alcohol. The actual metal alkoxide initiating species has been formed in situ prior to the addition of TMC. Introduction of the alcohol component in excess leads to the "immortal" ring-opening polymerization (ROP) of TMC. According to such an "immortal" ROP process of TMC, whichever the metal species, as many as 200 polycarbonate chains could be successfully grown from a unique metal center in a well controlled ROP process. The best performances were obtained using the discrete (BDI)Zn[N(SiMe3)2] precursor. Under optimized conditions, as many as 50,000 equivalents of TMC could be fully converted from as little as 20,ppm of this metallic precursor, allowing the preparation of a polytrimethylene carbonate (PTMC) with a molar mass as high as 185,200,g,mol,1 with a relatively narrow molar mass distribution (Mw/Mn=1.68). A double monomer feed experiment carried out with the (BDI)Zn[N(SiMe3)2]/BnOH initiating system proved the "living" character of the polymerization. Characterization of the PTMCs by NMR and size exclusion chromatography (SEC) showed well-defined ,-hydroxy-,-alkoxycarbonate telechelic polymers, highlighting the controlled character of this "living and immortal" ROP process. Using the (BDI)Zn[N(SiMe3)2] precursor, varying the alcohol (ROH) to 2-butanol, 3-buten-2-ol or 4-(trifluoromethyl)benzyl alcohol, revealed the versatility of this approach, allowing the preparation of accordingly end-functionalized HO-PTMC-OR polymers. The very low initial loading of metal catalyst considerably limits the potential toxicity and thus allows such polycarbonates to be used in the biomedical field. [source] Surface modification of starch nanocrystals through ring-opening polymerization of ,-caprolactone and investigation of their microstructuresJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Hassan Namazi Abstract Bionanoparticles of starch obtained by submitting native potato starch granules to acid hydrolysis conditions. The resulted starch nanoparticles were used as core or macro initiator for polymerization of ,-caprolactone (CL). Starch nanoparticle- g -polycaprolactone was synthesized through ring-opening polymerization (ROP) of CL in the presence of Sn(Oct)2 as initiator. The detailed microstructure of the resulted copolymer was characterized with NMR spectroscopy. Thermal characteristic of the copolymer was investigated using DSC and TGA. By introducing PCL, the range of melting temperature for starch was increased and degradation of copolymer occurred in a broader region. X-ray diffraction and TEM micrographs confirmed that there was no alteration of starch crystalline structure and morphology of nanoparticles, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Ring opening polymerization of aliphatic cyclic carbonates in the presence of natural amino acidsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Jiyan Liu Abstract Poly(dimethyl trimethylene carbonate) (PDTC) and poly(trimethylene carbonate) (PTMC) were synthesized by ring-opening polymerization (ROP) of dimethly trimethylene carbonate (DTC) and trimethylene carbonate (TMC) in the presence of five kinds of natural amino acids (L -alanine, L -valine, L -leucine, L -proline, and L -phenylalanine). PDTCs with number-average molecular weight (Mn) from 6700 to 18,900 g/mol and PTMCs with Mn from 7200 to 17,800 g/mol were obtained at a feed ratio of [monomer]/[L -phenylalanine] ranging from 50 to 200. The results of 1H nuclear magnetic resonance and titration proved amino acid connecting onto the polymer backbone. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Kinetic Parameter Estimation of Time-temperature Integrators Intended for Use with Packaged Fresh SeafoodJOURNAL OF FOOD SCIENCE, Issue 3 2004T. F. M ENDOZA ABSTRACT: The United States Food and Drug Administration (USFDA) considers any hermetically sealed package containing fresh seafood as a reduced oxygen package (ROP) if the oxygen transmission rate of the package is less than 10000 cm3/m2/d. USFDA's recent Import Alert nr 16-125 effectively bans the use of ROP for fresh seafood in the United States unless adequate temperature control and thermal history monitoring is used. Time-temperature integrators (TTI) were proposed as one potential method to satisfy this thermal monitoring requirement. Evaluation and selection of appropriate TTIs remains a difficult process for seafood manufacturers. Three commercially available TTIs (Vitsab M2-10, C2-10, and Fresh-Check TJ2) and 5 prototype TTIs (Avery Dennison) were evaluated for performance against the Skinner and Larkin (1998) botulinum toxin lag-time relationship. Isothermal treatments at 0°C, 5°C, 10°C, and 15°C were used to determine Arrhenius kinetic parameters of TTIs. Computer models were used to predict and compare actual TTI performance under dynamic thermal conditions. Results suggest that Vitsab M2-10 and Avery Dennison T126(2) and T126(4) TTIs may be used to predict safety of fresh seafood in ROP. [source] Titanium-mediated [CpTiCl2(OEt)] ring-opening polymerization of lactides: A novel route to well-defined polylactide-based complex macromolecular architecturesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2010Nikolaos Petzetakis Abstract Among three cyclopentadienyl titanium complexes studied, CpTiCl2(OEt), containing a 5% excess CpTiCl3, has proven to be a very efficient catalyst for the ring-opening polymerization (ROP) of L -lactide (LLA) in toluene at 130 °C. Kinetic studies revealed that the polymerization yield (up to 100%) and the molecular weight increase linearly with time, leading to well-defined PLLA with narrow molecular weight distributions (Mw/Mn , 1.1). Based on the above results, PS- b -PLLA, PI- b -PLLA, PEO- b -PLLA block copolymers, and a PS- b -PI- b -PLLA triblock terpolymer were synthesized. The synthetic strategy involved: (a) the preparation of OH-end-functionalized homopolymers or diblock copolymers by anionic polymerization, (b) the reaction of the OH-functionalized polymers with CpTiCl3 to give the corresponding Ti-macrocatalyst, and (c) the ROP of LLA to afford the final block copolymers. PMMA- g -PLLA [PMMA: poly(methyl methacrylate)] was also synthesized by: (a) the reaction of CpTiCl3 with 2-hydroxy ethyl methacrylate, HEMA, to give the Ti-HEMA-catalyst, (b) the ROP of LLA to afford a PLLA methacrylic-macromonomer, and (c) the copolymerization (conventional and ATRP) of the macromonomer with MMA to afford the final graft copolymer. Intermediate and final products were characterized by NMR spectroscopy and size exclusion chromatography, equipped with refractive index and two-angle laser light scattering detectors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1092,1103, 2010 [source] One-pot synthesis of ABC miktoarm star terpolymers by coupling ATRP, ROP, and click chemistry techniquesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2009Yanfeng Zhang Abstract We report on the one-pot synthesis of well-defined ABC miktoarm star terpolymers consisting of poly(2-(dimethylamino)ethyl methacrylate), poly(,-caprolactone), and polystyrene or poly(ethylene oxide) arms, PS(- b -PCL)- b -PDMA and PEO (- b -PCL)- b -PDMA, taking advantage of the compatibility and mutual tolerability of reaction conditions (catalysts and monomers) employed for atom transfer radical polymerization (ATRP), ring-opening polymerization (ROP), and click reactions. At first, a novel trifunctional core molecule bearing alkynyl, hydroxyl group, and bromine moieties, alkynyl(OH)Br, was synthesized via the esterification reaction of 5-ethyl-5-hydroxymethyl-2,2-dimethyl-1,3-dioxane with 4-oxo-4-(prop-2-ynyloxy)butanoic acid, followed by deprotection and monoesterification of alkynyl(OH)2 with 2-bromoisobutyryl bromide. In the presence of trifunctional core molecule, alkynyl(OH)Br, and CuBr/PMDETA/Sn(Oct)2 catalytic mixtures, target ABC miktoarm star terpolymers, PS(- b -PCL)- b -PDMA and PEO(- b -PCL)- b -PDMA, were successfully synthesized in a one-pot manner by simultaneously conducting the ATRP of 2-(dimethylamino)ethyl methacrylate (DMA), ROP of ,-caprolactone (,-CL), and the click reaction with azido-terminated PS (PS- N3) or azido-terminated PEO (PEO- N3). Considering the excellent tolerability of ATRP to a variety of monomers and the fast expansion of click chemistry in the design and synthesis of polymeric and biorelated materials, it is quite anticipated that the one-pot concept can be applied to the preparation of well-defined polymeric materials with more complex chain architectures. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3066,3077, 2009 [source] An efficient synthetic route to well-defined theta-shaped copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2009Gang-Yin Shi Abstract A series of well-defined ,-shaped copolymers composed of polystyrene (PS) and poly(,-caprolactone) (PCL) with controlled molecular weight and narrow molecular weight distribution have been successfully synthesized without any purification procedure by the combination of atom transfer radical polymerization (ATRP), ring-opening polymerization (ROP), and the "click" chemistry. The synthetic process involves two steps: (1) synthesis of AB2 miktoarm star copolymers, which contain one PCL chain terminated with two acetylene groups and two PS chains with two azido groups at their one end, (,,,,-diacetylene-PCL) (,-azido-PS)2, by ROP, ATRP, and the terminal group transformation; (2) intramolecular cyclization of AB2 miktoarm star copolymers to produce well-defined pure ,-shaped copolymers using "click" chemistry under high dilution. The 1H NMR, FTIR, and gel permeation chromatography techniques were applied to characterize the chemical structures of the resultant intermediates and the target polymers. Their thermal behavior was investigated by DSC. The mobility decrease of PCL chain across PS ring in the theta-shaped copolymers restricts the crystallization ability of PCL segment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2620,2630, 2009 [source] Degradable star polymers with high "click" functionalityJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2009James T. Wiltshire Abstract Degradable polyester-based star polymers with a high level of functionality in the arms were synthesized via the "arms first" approach using an acetylene-functional block copolymer macroinitiator. This was achieved by using 2-hydroxyethyl 2,-methyl-2,-bromopropionate to initiate the ring-opening polymerization (ROP) of caprolactone monomer followed by an atom transfer radical polymerization (ATRP) of a protected acetylene monomer, (trimethylsilyl)propargyl methacrylate. The hydroxyl end-group of the resulting block copolymer macroinitiator was subsequently crosslinked under ROP conditions using a bislactone monomer, 4,4,-bioxepanyl-7,7,-dione, to generate a degradable core crosslinked star (CCS) polymer with protected acetylene groups in the corona. The trimethylsilyl-protecting groups were removed to generate a CCS polymer with an average of 1850 pendent acetylene groups located in the outer block segment of the arms. The increased functionality of this CCS polymer was demonstrated by attaching azide-functionalized linear polystyrene via a copper (I)-catalyzed cycloaddition reaction between the azide and acetylene groups. This resulted in a CCS polymer with "brush-like" arm structures, the grafted segment of which could be liberated via hydrolysis of the polyester star structure to generate molecular brushes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1485,1498, 2009 [source] Synthesis and rheology of biodegradable poly(glycolic acid) prepared by melt ring-opening polymerization of glycolideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2009Estelle Gautier Abstract Ring-opening polymerization (ROP) of glycolide was studied in melt conditions and in the presence of two different initiators: 1-dodecanol and 1,4-butanediol and tin(II) 2-ethylhexanoate as catalyst. Its subsequent polymerization provided poly(glycolic acid) with controlled molar masses ranging from 2000 to 42,000 g/mol with well-defined structures characterized by NMR. Their thermal properties were evaluated by DSC analysis, and a glass transition temperature at infinite molar mass (Tg,) of 44.8 °C was thus calculated. From rheological data, the critical molar mass for entanglement, Mc, was estimated to be near 11,000 g/mol. Furthermore, in situ polymerizations were also performed between the plates of the rheometer within a same temperature range from 210 to 235 °C. The variation of the storage and loss moduli during the polymerization step have been monitored by time sweep oscillatory experiments under an angular frequency , = 10 rad/s. Finally, the development of an inverse rheological method allowed to calculate the bulk polymerization kinetics in the temperature range 200,230 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1440,1449, 2009 [source] Preparation of H-shaped ABCAB terpolymers by atom transfer radical couplingJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2009Xiaolan Luo Abstract H-shaped ABCAB terpolymers composed of polystyrene (PS) (A), poly(ethylene oxide) (PEO) (B), and poly(tert -butyl acrylate) (PtBA) (C) were prepared by atom transfer radical coupling reaction using ABC star terpolymers as precursors, CuBr and N,N,N,,N,,N,-pentamethyldiethylenetriamine (PMDETA) as catalysts, and nanosize copper as the reducing agent. The synthesis of 3-miktoarm star terpolymer PS-PEO-(PtBA-Br) involved following steps: (1) the preparation of PS with an active and an ethoxyethyl-ptotected hydroxyl group at the same end; (2) the preparation of diblock copolymer PS- b -PEO with ethoxyethyl-protected group at the junction point through the ring-opening polymerization (ROP) of EO; (3) after de-protection of ethoxyethyl group and further modification of hydroxyl group, tBA was polymerized by atom transfer radical polymerization using PS- b -PEO with 2-bromoisobutyryl functional group as macroinitiator. The H-shaped terpolymer could be successfully formed by atom transfer radical coupling reaction in the presence of small quantity of styrene, CuBr/PMDETA, and Cu at 90 °C. The copolymers were characterized by SEC, 1H NMR, and FTIR in detail. The optimized coupling temperature is 90 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 59,68, 2009 [source] Dendrimer-like miktoarm star terpolymers: A3 -(B-C)3 via click reaction strategyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2008Ozcan Altintas Abstract Two samples of dendrimer-like miktoarm star terpolymers: (poly(tert -butyl acrylate))3 -(polystyrene-poly(,-caprolactone))3 (PtBA)3 -(PS-PCL)3, and (PS)3 -(PtBA-poly(ethylene glycol)3 were prepared using efficient Cu catalyzed Huisgen cycloaddition (click reaction). As a first step, azido-terminated 3-arm star polymers PtBA and PS as core (A) were synthesized by atom transfer radical polymerization (ATRP) of tBA and St, respectively, followed by the conversion of bromide end group to azide. Secondly, PS-PCL and PtBA-PEG block copolymers with alkyne group at the junction as peripheral arms (B-C) were obtained via multiple living polymerization mechanisms such as nitroxide mediated radical polymerization (NMP) of St, ring opening polymerization (ROP) of ,-CL, ATRP of tBA. Thus obtained core and peripheral arms were linked via click reaction to give target (A)3 -(B-C)3 dendrimer-like miktoarm star terpolymers. (PtBA)3 -(PS-PCL)3 and (PS)3 -(PEG-PtBA)3 have been characterized by GPC, DSC, AFM, and SAXS measurements. (PtBA)3 -(PS-PCL)3 did not show any self-organization with annealing due to the miscibility of the peripheral arm segments. In contrast, the micro-phase separation of the peripheral arm segments in (PS)3 -(PtBA-PEG)3 resulted in self-organized phase-separated morphology with a long period of , 13 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5916,5928, 2008 [source] Microwave-assisted ring-opening polymerization of p -dioxanoneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2008Yu-Yan Chen Abstract The ring-opening polymerization (ROP) of p -dioxanone (PDO) under microwave irradiation with triethylaluminum (AlEt3) or tin powder as catalyst was investigated. When the ROP of PDO was catalyzed by AlEt3, the viscosity-average molecular weight (Mv) of poly(p -dioxanone) (PPDO) reached 317,000 g mol,1 only in 30 min, and the yield of PPDO achieved 96.0% at 80 °C. Tin powder was successfully used as catalyst for synthesizing PPDO by microwave heating, and PPDO with Mv of 106,000 g mol,1 was obtained at 100 °C in 210 min. Microwave heating accelerated the ROP of PDO catalyzed by AlEt3 or tin powder, compared with the conventional heating method. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3207,3213, 2008 [source] Simultaneous reversible addition fragmentation chain transfer and ring-opening polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2008Maude Le Hellaye Abstract The simultaneous ring-opening polymerization (ROP) of ,-caprolactone (,-CL) and 2-hydroxyethyl methacrylate (HEMA) polymerization via reversible addition fragmentation chain transfer (RAFT) chemistry and the possible access to graft copolymers with degradable and nondegradable segments is investigated. HEMA and ,-CL are reacted in the presence of cyanoisopropyl dithiobenzoate (CPDB) and tin(II) 2-ethylhexanoate (Sn(Oct)2) under typical ROP conditions (T > 100 °C) using toluene as the solvent in order to lead to the graft copolymer PHEMA- g -PCL. Graft copolymer formation is evidenced by a combination of size-exclusion chromatography (SEC) and NMR analyses as well as confirmed by the hydrolysis of the PCL segments of the copolymer. With targeted copolymers containing at least 10% weight of PHEMA and relatively small PHEMA backbones (ca. 5,000,10,000 g mol,1) the copolymer grafting density is higher than 90%. The ratio of free HEMA-PCL homopolymer produced during the "one-step" process was found to depend on the HEMA concentration, as well as the half-life time of the radical initiator used. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3058,3067, 2008 [source] Comparison of micelles formed by amphiphilic star block copolymers prepared in the presence of a nonmetallic monomer activatorJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2008Hoon Hyun Abstract In this article, we describe the synthesis of PEG- b -polyester star block copolymers via ring-opening polymerization (ROP) of ester monomers initiated at the hydroxyl end group of the core poly(ethylene glycol) (PEG) using HCl Et2O as a monomer activator. The ROP of ,-caprolactone (CL), trimethylene carbonate (TMC), or 1,4-dioxan-2-one (DO) was performed to synthesize PEG- b -polyester star block copolymers with one, two, four, and eight arms. The PEG- b -polyester star block copolymers were obtained in quantitative yield, had molecular weights close to the theoretical values calculated from the molar ratio of ester monomers to PEG, and exhibited monomodal GPC curves. The crystallinity of the PEG- b -polyester star block copolymers was determined by differential scanning calorimetry and X-ray diffraction. Copolymers with a higher arm number had a higher tendency toward crystallization. The crystallinity of the PEG- b -polyester star block copolymers also depended on the nature of the polyester block. The CMCs of the PEG- b -PCL star block copolymers, determined from fluorescence measurements, increased with increasing arm number. The CMCs of the four-arm star block copolymers with different polyester segments increased in the order 4a-PEG- b -PCL < 4a-PEG- b -PDO < 4a-PEG- b -PLGA < 4a-PEG- b -PTMC, suggesting a relationship between CMC and star block copolymer crystallinity. The partition equilibrium constant, Kv, which is an indicator of the hydrophobicity of the micelles of the PEG-polyester star block copolymers in aqueous media, increased with decreasing arm number and increasing crystallinity. A key aspect of the present work is that we successfully prepared PEG- b -polyester star block copolymers by a metal-free method. Thus, unlike copolymers synthesized by ROP using a metal as the monomer activator, our copolymers do not contain traces of metals and hence are more suitable for biomedical applications. Moreover, we confirmed that the PEG- b -polyester star block copolymers form micelles and hence may be potential hydrophobic drug delivery vehicles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2084,2096, 2008 [source] Synthesis and characterization of amphiphilic block copolymers with allyl side-groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007Xiuli Hu Abstract The synthesis of a new cyclic carbonate monomer containing an allyl group was reported and its biodegradable amphiphilic block copolymer, poly(ethylene glycol)- block -poly(L -lactide- co -5-methyl-5-allyloxycarbonyl-propylene carbonate) [PEG- b -P(LA- co -MAC)] was synthesized by ring-opening polymerization (ROP) of L -lactide (LA) and 5-methyl-5-allyloxycarbonyl-1,3-dioxan-2-one (MAC) in the presence of poly (ethylene glycol) as a macroinitiator, with diethyl zinc as a catalyst. 13C NMR and 1H NMR were used for microstructure identification of the copolymers. The copolymer could form micelles in aqueous solution. The core of the micelles is built of the hydrophobic P(LA- co -MAC) chains, whereas the shell is set up by the hydrophilic PEG blocks. The micelles exhibited a homogeneous spherical morphology and unimodal size distribution. By using the cyclic carbonate monomer containing allyl side-groups, crosslinking of the PEG- b -P(LA- co -MAC) inner core was possible. The adhesion and spreading of ECV-304 cells on the copolymer were better than that on PLA films. Therefore, this biodegradable amphiphilic block copolymer is expected to be used as a biomaterial for drug delivery and tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5518,5528, 2007 [source] One-pot preparation of 3-miktoarm star terpolymers via click [3 + 2] reactionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2007Ozcan Altintas Abstract The preparation of 3-miktoarm star terpolymers using nitroxide mediated radical polymerization (NMP), ring opening polymerization (ROP), and click reaction [3 + 2] are carried out by applying two types of one-pot technique. In the first one-pot technique, NMP of styrene (St), ROP of ,-caprolactone (,-CL), and [3 + 2] click reaction (between azide end-functionalized poly(ethylene glycol) (PEG-N3)/or azide end-functionalized poly(methyl methacrylate) (PMMA-N3) and alkyne) are carried out in the presence of 2-(hydroxymethyl)-2-methyl-3-oxo-3-(2-phenyl-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)ethoxy) propyl pent-4-ynoate, 2, as an initiator for 48 h at 125 °C (one-pot/one-step). As a second technique, NMP of St and ROP of ,-CL were conducted using 2 as an initiator for 20 h at 125 °C, and subsequently PEG-N3 or azide end-functionalized poly(tert -butyl acrylate (PtBA-N3) was added to the polymerization mixture, followed by a click reaction [3 + 2] for 24 h at room temperature (one-pot/two-step). The 3-miktoarm star terpolymers, PEG-poly(,-caprolactone)(PCL)-PS, PtBA-PCL-PS and PMMA-PCL-PS, were recovered by a simple precipitation in methanol without further purification. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3588,3598, 2007 [source] Ring-opening polymerization of substituted ,-caprolactones with a chiral (salen) AlOiPr complexJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2007Mark R. Ten Breteler Abstract The ring-opening polymerization (ROP) of ,-caprolactone (,-CL), 4-methyl-,-caprolactone (4-MeCL), and 6-methyl-,-caprolactone (6-MeCL) with a single-site chiral initiator, R,R,-(salen) aluminum isopropoxide (R,R,-[1]), was investigated. The kinetic data for the ROP of the three monomers at 90° in toluene corresponded to first-order reactions in the monomer and propagation rate constants of k,-CL > k4-MeCL , k6-MeCL. A notable stereoselectivity with a preference for the R -enantiomer was observed in the ROP of 6-MeCL with R,R,-[1], whereas for 4-MeCL, no stereoselectivity was found. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 429,436, 2007. [source] Synthesis and MALDI-TOF analysis of dendritic-linear block copolymers of lactides: Influence of architecture on stereocomplexationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2006Alexandre Richez Abstract Formation of a stereocomplex from polylactide copolymers can be tuned by changing the size and the chain topology of the second block in the copolymer. In particular, the use of a dendritic instead of linear architecture is expected to destabilize the cocrystallisation of polylactide blocks. With this idea in mind, dendritic-linear block copolymers were synthesized by ring-opening polymerization (ROP) of lactides using benzyl alcohol dendrons of generation 1,3 as macroinitiators and stannous octoate as catalyst. Polymers with controlled and narrow molar mass distribution were obtained. The MALDI-TOF mass spectra of these dendritic-linear block copolymers show well-resolved signals. Remarkably, 10% or less of odd-membered polymers are present, indicating that ester-exchange reactions which occur classically parallel to the polymerization process, were in these conditions, very limited. Thermal analysis of polyenantiomers of generation 1,3 and the corresponding blends were examined. The blend of a pair of enantiomeric dendritic-linear block copolymers exhibit a higher melting temperature than each copolymer, characteristic for the formation of a stereocomplex. Melting temperatures are strongly dependent on the dendron generation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6782,6789, 2006 [source] Synthesis and characterizations of well-defined branched polymers with AB2 branches by combination of RAFT polymerization and ROP as well as ATRPJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2006Bin Luan Abstract A well-defined branched copolymer with PLLA- b -PS2 branches was prepared by combination of reversible addition-fragmentation transfer (RAFT) polymerization, ring-opening polymerization (ROP), and atom transfer radical polymerization (ATRP). The RAFT copolymerization of methyl acrylate (MA) and hydroxyethyl acrylate (HEA) yielded poly(MA- co -HEA), which was used as macro initiator in the successive ROP polymerization of LLA. After divergent reaction of poly(MA- co -HEA)- g -PLLAOH with divergent agent, the macro initiator, poly(MA- co -HEA)- g -PLLABr2 was formed in high conversion. The following ATRP of styrene (St) produced the target polymer, poly(MA- co -HEA)- g -(PLLA- b -PS2). The structures, molecular weight, and molecular weight distribution of the intermediates and the target polymers obtained from every step were confirmed by their 1H NMR and GPC measurements. DSC results show one T = 3 °C for the poly(MA- co -HEA), T = ,5 °C, T= 122 °C, and T = 157 °C for the branched copolymers (poly(MA- co -HEA)- g -PLLA), and T = 51 °C, T = 116 °C, and T = 162 °C for poly(MA- co -HEA)- g -(PLLA- b -PS2). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 549,560, 2006 [source] Synthesis and characterization of poly[styrene- b -methyl(3,3,3-trifluoropropyl)siloxane] diblock copolymers via anionic polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2005Lingmin Yi Abstract A series of narrow molecular weight distribution (MWD) polystyrene- b -poly[methyl(3,3,3-trifluoropropyl)siloxane] (PS- b -PMTFPS) diblock copolymers were synthesized by the sequential anionic polymerization of styrene and trans -1,3,5-trimethyl-1,3,5-tris(3,,3,,3,-trifluoropropyl)cyclotrisiloxane in tetrahydrofuran (THF) with n -butyllithium as the initiator. The diblock copolymers had narrow MWDs ranging from 1.06 to 1.20 and number-average molecular weights ranging from 8.2 × 103 to 37.1 × 103. To investigate the properties of the copolymers, diblock copolymers with different weight fractions of poly[methyl(3,3,3-trifluoropropyl)siloxane] (15.4,78.8 wt %) were prepared. The compositions of the diblock copolymers were calculated from the characteristic proton integrals of 1H NMR spectra. For the anionic ring-opening polymerization (ROP) of 1,3,5-trimethyl-1,3,5-tris(3,,3,,3,-trifluoropropyl)cyclotrisiloxane (F3) initiated by polystyryllithium, high monomer concentrations could give high polymer yields and good control of MWDs when THF was used as the polymerization solvent. It was speculated that good control of the block copolymerization under the condition of high monomer concentrations was due to the slowdown of the anionic ROP rate of F3 and the steric hindrance of the polystyrene precursors. There was enough time to terminate the ROP of F3 when the polymer yield was high, and good control of block copolymerization could be achieved thereafter. The thermal properties (differential scanning calorimetry and thermogravimetric analysis) were also investigated for the PS- b -PMTFPS diblock copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4431,4438, 2005 [source] Stereoselective polymerization of rac -lactide with a bulky aluminum/Schiff base complexJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Zhaohui Tang Abstract An aluminum/Schiff base complex {[2,2-dimethyl-1,3-propylenebis(3,5-di- tert -butylsalicylideneiminato)](isopropanolato)aluminum(III) (2)} based on a bulky ligand and aluminum isopropoxide was prepared and employed for the stereoselective ring-opening polymerization (ROP) of rac -lactide (rac -LA). The initiator was characterized with nuclear magnetic resonance (NMR), crystal structure measurements, and elemental analysis. It contained a five-coordinate aluminum atom that was trigonal bipyramidal in the solid state according to the crystal structure measurements. The two conformational stereoisomers of 2 exchanged quickly on the NMR scale. Compound 2 polymerized rac -LA into a crystalline polymer that was characterized with 1H NMR, wide-angle X-ray diffraction, electrospray ionization mass spectrometry, and gel permeation chromatography. The kinetics of the polymerization were first-order in both the monomer and initiator, and there was a linear relationship between the rac -LA conversion and the number-average molecular weight of poly(rac -LA) with a narrow molecular distribution (1.04,1.08). These features showed that the polymerization was well controlled. The high melting temperature (196,201 °C) and isotacticity of poly(rac -LA) indicated that complex 2 was a highly stereoselective initiator for the ROP of rac -LA. The stereoselectivity was as high as 90%, and the stereoblocks of poly(rac -LA) by complex 2 contained an average of 20 units (average block length = 20) of enantiomerically pure lactic acid. The activation energy (23.6 kJ mol,1) was obtained according to an Arrhenius equation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5974,5982, 2004 [source] Stannous(II) trifluoromethane sulfonate: a versatile catalyst for the controlled ring-opening polymerization of lactides: Formation of stereoregular surfaces from polylactide "brushes"JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2001Michael Möller Abstract A general method for the controlled synthesis of polylactide in solution and from solid supports is presented. The evaluation of stannous(II) trifluoromethane sulfonate [Sn(OTf)2] and scandium(III) trifluoromethane sulfonate [Sc(OTf)3] as catalysts for the ring-opening polymerization (ROP) of L -, D -, and L,D -lactide is described as a route to polylactide using mild and highly selective conditions. These triflate catalysts must be used in conjunction with a nucleophilic compound such as an alcohol that is the actual initiating species via the active metal alkoxide species. Consistent with this process, 1H NMR analysis revealed that the ,-chain-end bears the ester from the initiating alcohol, and upon hydrolysis of the active metal alkoxide chain end, a ,-hydroxyl chain end was clearly detected. Polymers of predictable molecular weights and narrow polydispersities were obtained in high yields in accordance with a controlled polymerization process. The addition of base either as a solvent or additive significantly enhanced the polymerization rate with minimal loss to the polymerization control. The ROP of lactide isomers from an initiator, HO(CH2CH2O)3(CH2)11SH, self-assembled onto a gold surface using Sn(OTf)2 produced polylactide brushes under living conditions and provides the opportunity to prepare stereoregular or chiral surfaces by polymerization of enantiomerically pure monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3529,3538, 2001 [source] Synthesis of PLLA-MPEG Diblock Copolymers by Microwave-Assisted Copolymerization of L -Lactide and Methoxy Poly(ethylene glycol)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2007Chao Zhang Abstract PLLA-MPEG diblock copolymers with a controlled number-average molar mass ranging from 7,330 to 117,610 g,·,mol,1 and an L -lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100,°C by MPEG-initiated ROP of L -lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA-MPEG diblock copolymers with longer PLLA segments. [source] Structure, Morphology and Properties of a Novel Molecular Composite by In-Situ Blending of Anionic Polyamide 6 with a Polyamide Copolymer Containing Rigid SegmentsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2007Xiaochun Wang Abstract Molten caprolactam, in which a polyamide copolymer (HPN) containing rigid segments was dissolved, was polymerized by means of anionic ROP to in produce polyamide (PA, nylon) 6 blends with HPN in situ. A novel molecular composite was achieved in which toughness and strength were simultaneously improved, as well as modulus, compared to virgin PA6. In view of the interchange reaction between PA6 and PA1212 (and PA66) in blends fabricated in the same way, it was deduced that a similar reaction between PA6 and HPN took place during the blending and led to copolymerization between the two components. The formation of copolymers was verified by their single glass transition and single melting peak, measured through DMA and DSC, respectively. DSC analysis also showed that the occurrence of the interchange reaction inhibited the crystallization and suppressed the melting point of PA6. Analysis by FT-IR spectroscopy indicated that the difference in the distance between the amide groups for PA6 and HPN induced a decrease in the amount and strength of hydrogen bonding. Moreover, characterization by POM and XRD revealed that the spherulite size of the PA6 crystals decreased dramatically and the amount of , crystal increased slightly with the majority of crystallites being , crystals. Furthermore, it was found through the observation of the morphology by SEM that no phase separation existed in the composites. On the basis of detailed analysis and a comparison between the in situ PA6/PA66 and PA6/HPN blends, it is believed that the combination of markedly decreasing spherulite size and similar segmental mobility resulted in the simultaneous improvement of mechanical properties for the in situ PA6/HPN blends. [source] Preparation of Poly(, -caprolactone)/Clay Nanocomposites by Microwave-Assisted In Situ Ring-Opening PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2007Liqiong Liao Abstract PCL/clay nanocomposites were prepared by microwave-assisted in situ ROP of , -caprolactone in the presence of either unmodified clay (Cloisite® Na+) or clay modified by quaternary ammonium cations containing hydroxyl groups (Cloisite 30B). This PCL showed significantly improved monomer conversion and molecular weight compared with that produced by conventional heating. An intercalated structure was observed for the PCL/Cloisite Na+ nanocomposites, while a predominantly exfoliated structure was observed for the PCL/Cloisite 30B nanocomposites. Microwave irradiation proved to be an effective and efficient method for the preparation of PCL/clay nanocomposites. [source] Microwave-Assisted Synthesis of PLLA-PEG-PLLA Triblock CopolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2007Chao Zhang Abstract Poly(L -lactide)- block -poly(ethylene glycol)- block -poly(L -lactide) (PLLA-PEG-PLLA) triblock copolymers were synthesized effectively by poly(ethylene glycol) initiated ring-opening polymerization (ROP) of L -lactide under microwave irradiation. The products were characterized by 1H NMR, GPC, and DSC. The experimental results have demonstrated that PLLA-PEG-PLLA triblock copolymer with a number-average molar mass of 28,230 g,·,mol,1 and an L -lactide conversion of 92.4% could be synthesized after the L -lactide/PEG2000 reaction mixture was irradiated for 3 min at 100,°C. The L -lactide/PEG feed ratio had a strong influence on the microwave-assisted ring-opening polymerization, in which higher L -lactide/PEG feed ratios led to copolymers with higher molar masses and lower L -lactide conversions. Prolonged microwave irradiation at 100,°C did not change the molar mass of the copolymers significantly. The DSC study indicated that higher glass transition and melting temperatures were obtained for PLLA-PEG-PLLA triblock copolymers with longer PLLA segment length. The synthesis of the triblock copolymers via microwave heating was much faster than via conventional heating. [source] Retinopathy of prematurity: Mutations in the Norrie disease gene and the risk of progression to advanced stagesPEDIATRICS INTERNATIONAL, Issue 2 2001Mohammad Z Haider AbstractBackground: Retinopathy of prematurity (ROP) is a retinal vascular disease that occurs in infants with short gestational age and low birth weight and may lead to retinal detachment and blindness. Missense mutations in the Norrie disease (ND) gene have been associated with the risk of progression to advanced stages in cases of ROP from the US and also in clinically similar ND and familial exudative vitreoretinopathy. Methods: We have screened two ND gene mutations, namely A105T and Val60Glu, by polymerase chain reaction,restriction fragment length polymorphism (PCR-RFLP) and allele-specific PCR methods, respectively, in 210 Kuwaiti premature newborns to replicate these findings in a different ethnic group. Results: In the Kuwaiti premature newborn cohort, 115 of 210 babies had no eye problems and served as controls, while 95 were cases of ROP. In 71 of 95 ROP cases, the disease regressed spontaneously on or before stage 3, while in 24 of 95 ROP cases the disease progressed to advanced stages 4 and 5. In case of missense mutation (A105T), the AA genotype was detected in 96% of controls compared with 87% of ROP cases (NS); similarly no significant difference was found between spontaneously regressed ROP cases and those who progressed to advanced stages. For the Val60Glu mutation, no significant association was detected between the genotype and progression of ROP to advanced stages. Conclusions: Unlike data from the US, our findings from a Kuwaiti cohort of ROP cases and controls suggest a lack of association between the two ND gene mutations (A105T and Val60Glu) and ROP and the risk of progression of the disease to advanced stages. [source] Synthesis and characterization of amine-functionalized amphiphilic block copolymers based on poly(ethylene glycol) and poly(caprolactone)POLYMER INTERNATIONAL, Issue 4 2007Remant Bahadur KC Abstract A series of amine-functionalized block copolymers, poly(caprolactone)- block -poly(ethylene glycol) (PCL-b-PEG), were synthesized by ring-opening bulk polymerization (ROP) of ,-caprolactone (,-CL) initiated through the hydroxyl end of the amino poly(ethylene glycol) (PEG) used as a macroinitiator in the presence of stannous 2-ethylhexonoate [Sn(Oct)2]. The polymerization and end functionality of the polymer were studied by different physicochemical techniques (1H NMR, Fourier transform infrared and X-ray photoelectron spectroscopy, gel permeation chromatography and thermogravimetric analysis). Thermal, crystalline and mechanical properties of the polymer were thoroughly analyzed using differential scanning calorimetry, wide-angle X-ray diffractometry and tensile testing, respectively. The results showed a linear improvement in crystallinity and mechanical properties of the polymer with the content of PEG. Thus the synthesized functional polymers can be used as excellent biomaterials for the delivery of polyanions, as well as macroinitiators for the synthesis of A,B,C-type block copolymers. Copyright © 2006 Society of Chemical Industry [source] | ||||||||||||||||