Initiating System (initiating + system)

Distribution by Scientific Domains

Selected Abstracts

Poly(trimethylene carbonate) from Biometals-Based Initiators/Catalysts: Highly Efficient Immortal Ring-Opening Polymerization Processes

Marion 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]

Photografting of acrylic acid and methacrylic acid onto polyolefines initiated by formaldehyde in aqueous solutions

Jianmei Han
Abstract Formaldehyde aqueous solution can act as an effective photoinitiating system for water-borne photografting. The photografting of acrylic acid (AA) and methacrylic acid (MAA) onto high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polypropylene (PP) initiated by formaldehyde aqueous solutions has been reported. The effects of formaldehyde content and monomer concentration on grafting varied with the polymeric substrates and monomers used. For the grafting of AA onto HDPE, the extent of grafting increased with increasing formaldehyde content in the solution, monomer concentration had a little effect on grafting. Whereas for the grafting of MAA onto HDPE, the grafting performed in 8% formaldehyde aqueous solution lead to the highest extent of grafting, the extent of grafting increased with monomer concentration till 2.5 mol/L. MAA was easier to be grafted onto the polyolefins than AA. The easiness of grafting occurring on the polyolefins was in a decreasing order of LDPE > HDPE > PP. Qualitative and semi-quantitative Fourier transform infrared (FTIR) characterizations of the grafted samples were performed. For both grafted LDPE and PP samples, at the same irradiation time, the carbonyl index of the samples grafted with MAA was higher than that grafted with AA. The FTIR results are in accord with the results obtained by gravimetric method. The water absorbency of the grafted samples increased almost linearly with the extent of grafting. The PE films grafted with AA adsorbed more water than those grafted with MAA. This study had broadened the water-borne initiating system for photografting. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Photoinitiating polymerization to prepare biocompatible chitosan hydrogels

Xiaohong Hu
Abstract Chitosan hydrogels were prepared from water soluble chitosan derivatives (chitosan-MA-LA, CML) by photoinitiating polymerization under the existence of Irgacure2959 and the irradiation of UV light. The CML was obtained by amidation of the amine groups of chitosan with lactic acid and methacrylic acid. Gelation time of the hydrogel could be adjusted within a range of 5,50 min, and controlled by factors such as the degree of MA substitution, initiator concentration, existence of oxygen, and salt. The dry hydrogel adsorbed tens to hundred times of water, forming a highly hydrated gel. The swelling ratio was smaller at the higher degree of MA substitution, higher pH, and higher salt concentration. Rheological test showed that the hydrogel is elastomeric in the measuring frequency range, with a storage modulus and loss modulus of 0.8,7 kPa and 10,100 Pa, respectively. In vitro culture of chondrocytes demonstrated that the cells could normally proliferate in the extractant of the hydrogels, showing no cytotoxicity at lower initiator concentration. By contrast, the extractant of the hydrogel made by the redox initiating system, i.e., ammonium persulfate (APS) and N,N,N,,N,-tetramethylethylenediamine (TEMED), showed apparent cytotoxicity. Thus, the chitosan hydrogels initiated by the Irgacure2959 have better comprehensive properties, in particular better biocompatibility, and are more suitable for biomedical applications. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Restraining the associations of anthracene fluorophore by chemically linking to poly(methyl methacrylate)

Fu-Kun Su
Abstract Associations (dimer or aggregate) of anthracene (An) fluorophores tend to interrupt the monomer emission and reduce the quantum yield (,PL); therefore, poly(methyl methacrylate) (PMMA) chain was used in this study to chemically link to anthracene and to block the mutual associations among the anthracene fluorophores. With this aim, the target polymers were prepared by anionic polymerizations with 9,10-dibromoanthracene/s -butyllithium as initiating system to proceed polymerizations of methyl methacrylate (MMA) directly or in the presence of 1,1-diphenylethylene (DPE). Use of DPE before addition of MMA produces stable initiating anionic species and avoids potential side reactions during polymerization; however, it also introduces four ,-phenylene rings around the central anthracene ring, which interfere with the corresponding emission pattern and reduce the ,PL (32%) value due to potential interactions between phenylene rings and anthracene. On the contrast, polymerization without participation of DPE results in polymer with central anthracene ring directly connected to two PMMA chains, which gives clean vibronic emission pattern with limited association emissions and enhanced ,PL (52%) value. Physical blending of anthracene by PMMA is less efficient to restrain the associations and results in a film of lower ,PL (20%). 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Surface modification of nylon-6 fibers for medical applications

S. E. Shalaby
Abstract Hydroxyethylmethacrylate (HEMA) is considered to be one of the important vinyl monomers. The ability of polyhydroxyethyl-methacylate (PHEMA) graft sites to consecutive chemical modification makes the use of nylon-6 fibers grafted with PHEMA a feasible bed for immobilization of a wide range of biologically active reagents, specially enzymes, drugs, cells, and immunadsorbents. Stemming from the above discussions, in this article, the graft copolymerization of HEMA onto modified nylon-6 fibers containing Polydiallyldimethylammonium chloride (PDADMAC) in the presence of Cu2+,K2S2O8 as a redox initiating system was carried out, with very high rate and almost without homopolymer formation. The factors affecting the grafting reaction (monomer, K2S2O8 and cupric ion concentrations, the amount of PDADMAC as well as the reaction temperature) were studied. Kinetic investigation revealed that the rate of grafting (Rp) of HEMA onto modified nylon-6 fibers is proportional to [HEMA]1, [CuSO4.5H2O] 0.7, [PDADMAC]0.4, and [K2S2O8]1.4. The overall activation energy was calculated (71 KJ/mol). The fine structure, surface topography, thermal and electrical properties of parent and grafted nylon-6 fibers were investigated. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3788,3796, 2007 [source]

Cationic polymerization of L,L -lactide

gorzata Ba
Abstract Cationic bulk polymerization of L,L- lactide (LA) initiated by trifluromethanesulfonic acid [triflic acid (TfA)] has been studied. At temperatures 120,160 C, polymerization proceeded to high conversion (>90% within ,8 h) giving polymers with Mn , 2 104 and relatively high dispersity. Thermogravimetric analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)2 initiating system. Also hydrolytic stability of cationically prepared PLA was significantly higher than hydrolytic stability of linear PLA. Because thermal or hydrolytic degradation of PLA starting from end-groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer. High thermal and hydrolytic stability, in spite of moderate molecular weight of cationically prepared PLA, indicate that the fraction of end-groups is considerably lower than in linear PLA of comparable molecular weight. According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal OH and C(O)OSO2CF3 end-groups. The presence of those groups allows efficient end-to-end cyclization. Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2650,2658, 2010 [source]

Preparation of monodisperse nanoparticles containing poly(propylene imine)(NH2)32 -polystyrene

Hu Liu
Abstract Polypropylenimine dendrimer (DAB-Am-32, generation 4.0) was converted into a macroinitiator DAB-Am-32-Cl via reaction with 2-chloropropionyl chloride. Monodisperse nanoparticles containing poly(propylene imine)(NH2)32 -polystyrene were prepared by emulsion atom transfer radical polymerization (ATRP) of styrene (St), using the DAB-Am-32-Cl/CuCl/bpy as initiating system. The structure of macroinitiator was characterized by FTIR spectrum, 1H NMR, and 13C NMR. The structure of poly(propylene imine)(NH2)32 -polystyrene was characterized by FT-IR spectrum and 1H NMR; the molecular weight and molecular weight distribution of poly(propylene imine)(NH2)32 -polystyrene were characterized by gel permeation chromatograph (GPC). The morphology, size and size distribution of the nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The effects of monomer/macroinitiator ratio and surfactant concentration on the size and size distribution of the nanoparticles were investigated. It was found that the diameters of the nanoparticles were smaller than 100 nm (30,80 nm) and monodisperse; moreover, the particle size could be controlled by monomer/macroinitiator ratios and surfactant concentration. With the increasing of the ratio of St/DAB-Am-32-Cl, the number-average diameter (Dn), weight-average diameter (Dw) were both increased gradually. With enhancing the surfactant concentration, the measured Dh of the nanoparticles decreased, while the polydispersity increased. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2892,2904, 2009 [source]

Living cationic polymerization of amide-functional vinyl ethers: Specific properties of SnCl4 -based initiating system

Motomasa Yonezumi
Abstract Living cationic copolymerization of amide-functional vinyl ethers with isobutyl vinyl ether (IBVE) was achieved using SnCl4 in the presence of ethyl acetate at 0 C: the number,average molecular weight of the obtained polymers increased in direct proportion to the monomer conversion with relatively low polydispersity, and the amide-functional monomer units were introduced almost quantitatively. To optimize the reaction conditions, cationic polymerization of IBVE in the presence of amide compounds, as a model reaction, was also examined using various Lewis acids in dichloromethane. The combination of SnCl4 and ethyl acetate induced living cationic polymerization of IBVE at 0 C when an amide compound, whose nitrogen is adjacent to a phenyl group, was used. The versatile performance of SnCl4 especially for achieving living cationic polymerization of various polar functional monomers was demonstrated in this study as well as in our previous studies. Thus, the specific properties of the SnCl4 initiating system are discussed by comparing with the EtxAlCl3,x systems from viewpoints of hard and soft acids and bases principle and computational chemistry. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6129,6141, 2008 [source]

Controlled cationic polymerization of cyclopentadiene with B(C6F5)3 as a coinitiator in the presence of water

Sergei V. Kostjuk
Abstract The controlled cationic polymerization of cyclopentadiene (CPD) at 20 C using 1-(4-methoxyphenyl)ethanol (1)/B(C6F5)3 initiating system in the presence of fairly large amount of water is reported. The number,average molecular weights of the obtained polymers increased in direct proportion to monomer conversion in agreement with calculated values and were inversely proportional to initiator concentration, while the molecular weight distribution slightly broadened during the polymerization (Mw/Mn , 1.15,1.60). 1H NMR analyses confirmed that the polymerization proceeds via reversible activation of the COH bond derived from the initiator to generate the growing cationic species, although some loss of hydroxyl functionality happened in the course of the polymerization. It was also shown that the enchainment in cationic polymerization of CPD was affected by the nature of the solvent(s): for instance, polymers with high regioselectivity ([1,4] up to 70%) were obtained in acetonitrile, whereas lower values (around 60%) were found in CH2Cl2/CH3CN mixtures. Aqueous suspension polymerization of CPD using the same initiating system was successfully performed and allowed to synthesize primarily hydroxyl-terminated oligomers (Fn = 0.8,0.9) with Mn , 1000 g mol,1 and broad MWD (Mw/Mn , 2.2). 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4734,4747, 2008 [source]

Living cationic polymerization of 2-adamantyl vinyl ether

Tamotsu Hashimoto
Abstract Living cationic polymerization of 2-adamantyl vinyl ether (2-vinyloxytricyclo[]3,7decane; 2-AdVE) was achieved with the CH3CH(OiBu)OCOCH3/ethylaluminum sesquichloride/ethyl acetate [CH3CH(OiBu)OCOCH3/Et1.5AlCl1.5/CH3COOEt] initiating system in toluene at 0 C. The number-average molecular weights (Mn's) of the obtained poly(2-AdVE)s increased in direct proportion to monomer conversion and produced the polymers with narrow molecular weight distributions (MWDs) (Mw/Mn = ,1.1). When a second monomer feed was added to the almost polymerized reaction mixture, the added monomer was completely consumed and the Mn's of the polymers showed a direct increase against conversion of the added monomer. Block and statistical copolymerization of 2-AdVE with n -butyl vinyl ether (CH2CHOCH2 CH2CH2CH3; NBVE) were possible via living process based on the same initiating system to give the corresponding copolymers with narrow MWDs. Grass transition temperature (Tg) and thermal decomposition temperature (Td) of the poly(2-AdVE) (e.g., Mn = 22,000, Mw/Mn = 1.17) were 178 and 323 C, respectively. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1629,1637, 2008 [source]

Anionic polymerization of methyl methacrylate initiated with late transition-metal halides/organolithium/triisobutylaluminum systems

Eiji Ihara
Abstract Anionic polymerization of methyl methacrylate (MMA) initiated with late transition-metal halides [manganese chloride (MnCl2), iron dichloride (FeCl2), iron trichloride (FeCl3), cobalt chloride (CoCl2), or nickel bromide (NiBr2)]/organolithium [nButyllithium (nBuLi) or phenyllithium (PhLi)]/triisobutylaluminum (iBu3Al) systems is described. Except for the system with NiBr2, the polymerizations of MMA afforded narrow molecular weight distribution poly(methyl methacrylate)s (PMMAs) with high molecular weights in quantitative yields at 0 C in toluene. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analyses of the PMMAs obtained by the systems with FeCl2, FeCl3, and CoCl2 revealed that the polymers had hydrogen (H) at both chain ends. Accordingly, the reaction of the transition-metal halides with the organolithium in the presence of iBu3Al should result in the formation of transition-metal hydride [M-H], species, which was nucleophilic enough to initiate the MMA polymerization. Because the presence of a six-membered cyclic structure resulting from backbiting was confirmed from the MALDI-TOF MS analyses of the PMMA obtained with the metal halide (FeCl2, FeCl3, or CoCl2)/organolithium systems in the absence of iBu3Al, the introduction of H at the ,-chain end indicated that iBu3Al should prevent the backbiting. However, the MnCl2/nBuLi/iBu3Al initiating system gave PMMAs bearing H at the , chain end and six-membered cyclic structure at the , chain end. 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1962,1977, 2003 [source]

Controlled radical polymerization of 2-hydroxyethyl methacrylate with a hydrophilic ruthenium complex and the synthesis of amphiphilic random and block copolymers with methyl methacrylate,

Yusuke Fuji
Abstract A hydrophilic ruthenium complex with ionic phosphine ligands {1: RuCl2[P(3-C6H4SO3Na)(C6H5)2]2} induced controlled radical polymerization of 2-hydroxyethyl methacrylate (HEMA) in methanol under homogeneous conditions; the initiator was a chloride (R-Cl) such as CHCl2COPh. The number-average molecular weights of poly(HEMA) increased in direct proportion to monomer conversion, and the molecular weight distributions were relatively narrow (Mw/Mn = 1.4,1.7). A similar living radical polymerization was possible with (MMA)2 -Cl [(CH3)2C(CO2CH3)CH2C(CH3)(CO2CH3)Cl] as an initiator coupled with amine additives such as n -Bu3N. In a similar homogeneous system in methanol, methyl methacrylate (MMA) could also be polymerized in living fashion with the R-Cl/1 initiating system. Especially for such hydrophobic polymers, the water-soluble ruthenium catalyst was readily removed from the polymers by simple washing with an aqueous dilute acid. This system can be applied to the direct synthesis of amphiphilic random and block copolymers of HEMA and MMA. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2055,2065, 2002 [source]

Synthesis of poly(cyclohexene oxide)- block -polystyrene by combination of radical-promoted cationic polymerization, atom transfer radical polymerization and click chemistry

Mustafa Degirmenci
Abstract The combination of radical-promoted cationic polymerization, atom transfer radical polymerization (ATRP) and click chemistry was employed for the efficient preparation of poly(cyclohexene oxide)- block -polystyrene (PCHO- b -PSt). Alkyne end-functionalized poly(cyclohexene oxide) (PCHO-alkyne) was prepared by radical-promoted cationic polymerization of cyclohexene oxide monomer in the presence of 1,2-diphenyl-2-(2-propynyloxy)-1-ethanone (B-alkyne) and an onium salt, namely 1-ethoxy-2-methylpyridinium hexafluorophosphate, as the initiating system. The B-alkyne compound was synthesized using benzoin photoinitiator and propargyl bromide. Well-defined bromine-terminated polystyrene (PSt-Br) was prepared by ATRP using 2-oxo-1,2-diphenylethyl-2-bromopropanoate as initiator. Subsequently, the bromine chain end of PSt-Br was converted to an azide group to obtain PSt-N3 by a simple nucleophilic substitution reaction. Then the coupling reaction between the azide end group in PSt-N3 and PCHO-alkyne was performed with Cu(I) catalysis in order to obtain the PCHO- b -PSt block copolymer. The structures of all polymers were determined. Copyright 2010 Society of Chemical Industry [source]

Pyrromethene dye sensitized photopolymer,photochemical behavior in polymer matrix and application to photoresist for printed circuit board

Shota Suzuki
Abstract The photochemical behavior of the visible light initiating system that consists of a sensitizing dye, 2,6-diethyl-8-phenyl-1,3,5,7-tetramethylpyrromethene BF2 complex (EPP), and a photoacid generator, N -trifluoromethylsulfonyloxy-1,8-naphthalimide (NIOTf), was studied mainly by means of absorption and fluorescence spectrometry not in solution but in a polymer matrix which is a closer medium to the one currently employed in the field of photoresists. Excited singlet electron transfer from EPP to NIOTf was considered as the main reaction pathway in this system. The EPP/NIOTf system was applied to a photoresist for printed circuit board with an appropriate binder polymer which contains an acetal protection group. A pattern profile of the photoresist was exceedingly affected by the amount of photogenerated acids, their diffusion, and amine in the atmosphere. Finally, by controlling exposure energy and the post-exposure bake (PEB) process, a photoresist with a high resolution (8,m line and space) was obtained under argon ion laser irradiation. Copyright 2006 John Wiley & Sons, Ltd. [source]

Hybrid Polymerization of Vinyl and Hetero-Ring Groups of Glycidyl Methacrylate Resulting in Thermoresponsive Hyperbranched Polymers Displaying a Wide Range of Lower Critical Solution Temperatures

Zhifeng Jia Dr.
Abstract Hybrid polymerization of glycidyl methacrylate (GMA) with potassium hydride (KH) and various oligo(ethylene glycol)s as the initiating system, in which both vinyl polymerization and ring-opening polymerization occur simultaneously, generates hyperbranched poly(ether-ester)s. The reaction process has been followed by an in situ nuclear magnetic resonance technique. The experimental results indicate that both the vinyl and epoxy groups of GMA undergo polymerization, with the reactivity of the latter being much higher than that of the former. Interestingly, the resulting hyperbranched polymers exhibit a sharp phase transition in water at the lower critical solution temperature (LCST). Significantly, the LCST values can be accurately controlled from 0 to 100,C by changing the hydrophilic/hydrophobic balance of GMA and various oligo(ethylene glycol)s or by modification of the precursor polymer through acetylation. This novel stimuli-responsive hyperbranched polymer is a promising candidate for a new generation of commercially viable thermoresponsive polymers following on from the widely used poly(N- isopropylacrylamide) (PNIPAM). [source]

Living polymerization of substituted acetylenes

Martin G. Mayershofer
Abstract For many years, considerable research efforts have been dedicated to ,-conjugated polymers because of their extraordinary electronic, optical, and structural properties. The employed transition-metal-based initiating systems comprise not only simple transition-metal salts but also rather sophisticated mixtures of two, three, or four compounds and even highly defined single-component systems such as transition-metal alkylidene complexes. Extensive fine-tuning of the electronic and steric properties of initiator,monomer systems eventually allowed the tailor-made synthesis of conjugated materials via living polymerization techniques. This article focuses on recent developments in the field of the living polymerization of substituted acetylene derivatives. Ill-defined group 5 and 6 transition metal halide-based initiators, well-defined transition-metal alkylidene complexes, and rhodium(I)-based systems that induce the living polymerization of numerous substituted acetylenes are reviewed. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5723,5747, 2005 [source]