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Block Copolymerization (block + copolymerization)
Selected AbstractsOne-Pot Synthesis of Micelles with a Cross-Linked Poly(acrylic acid) CoreMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2006Genhua Zheng Abstract Summary: Stable micelles with polystyrene (PS) as a shell and cross-linked poly[(acrylic acid)- co -(ethylene glycol diacrylate)] as a core have been successfully prepared by reversible addition fragmentation chain transfer (RAFT) copolymerization of acrylic acid and ethylene glycol diacrylate in a selective solvent with PS-SC(S)Ph as a RAFT agent. For the preparation of stable micelles, the RAFT polymerizations are carried out in different solvents: benzene, cyclohexane, and mixtures of tetrahydrofuran and cyclohexane. The monomer/PS-SC(S)Ph molar ratio and molecular weight of the macro-RAFT agent, PS-SC(S)Ph, influence the RAFT polymerization and the formation of micelles. Block copolymerization in selective solvent with the RAFT agent. [source] Synthesis and Characterization of Block Copolymers of , -Caprolactone and DL -Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2003Ming-Hsi Huang Abstract Biodegradable copolymers were prepared by ring-opening polymerization of sequentially added , -caprolactone and DL -lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by 1H NMR, SEC, IR, DSC, TGA, and X-ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA-containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering. Block copolymerization of , -caprolactone and DL -lactide initiated by dihydroxyl PEG. [source] Synthesis and properties of the polythiourethanes obtained by the cationic ring-opening polymerization of cyclic thiourethanesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2006Daisuke Nagai Abstract The cationic ring-opening polymerization of a five-membered thiourethane [3-benzyl-1,3-oxazolidine-2-thione (BOT)] with boron trifluoride etherate afforded the corresponding polythiourethane with a narrow molecular weight distribution in an excellent yield. The molecular weight of the polymers could be controlled by the feed ratio of the monomer to the initiator. A kinetic study of the polymerization revealed that the polymerization rate of BOT (1.3 × 10,2 L mol,1 min,1) was two times larger than that of the six-membered thiourethane [3-benzyltetrahydro-1,3-oxazolidine-2-thione (BTOT); 6.8 × 10,3 L mol,1 min,1], and the monomer conversion obeyed the first-order kinetic equation. These observations, along with the successful results in the two-stage polymerization, supported the idea that this polymerization proceeded in a controlled manner. Block copolymerizations of BOT with BTOT were also carried out to afford the corresponding di- and triblock copolymers with narrow molecular weight distributions. The order of the 5% weight loss temperatures was as follows: poly(3-benzyltetrahydro-1,3-oxazolidine-2-thione) [poly(BTOT)] > poly(BTOT54 - b -BOT46) > poly(3-benzyl-1,3-oxazolidine-2-thione) [poly(BOT)]. This indicated that an increase in the BTOT unit content raised the decomposition temperature. The order of the refractive indices was poly(BOT) > poly(BTOT54 - b -BOT46) > poly(BTOT54 - b -BOT46 - b -BTOT50) > poly(BTOT); this was in accord with the order of the sulfur content in the polymer chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4795,4803, 2006 [source] Block copolymerizations of higher 1-olefins with traditional polar monomers using metallocene-type single component lanthanide initiatorsPOLYMER INTERNATIONAL, Issue 8 2004Hajime Yasuda Abstract Block copolymerizations of 1-pentene or 1-hexene with methyl methacrylate or ,-caprolactone were explored using [Me2Si(2-SiMe3 -4- t -BuMe2SiC5H2)2YH]2 (1) or [Me2Si(2-SiMe3 -4- t -BuC5H2)2SmH]2 (2) as an initiator in toluene or in neat mixtures by the successive additions of monomers in this order. Random copolymerizations of 1-pentene with 1-hexene, and random copolymerization of ethylene with 1-hexene were also performed using 1 as an initiator. Copyright © 2004 Society of Chemical Industry [source] New Iron(II) Complexes for Atom-Transfer Radical Polymerization: The Ligand Design for Triazacyclononane Results in High Reactivity and Catalyst PerformanceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Mitsunobu Kawamura Abstract Mononuclear cordinatively unsaturated iron(II) complexes having a triazacyclononane ligand were developed as highly efficient and environmentally friendly catalysts for the atom-transfer radical polymerization (ATRP). These iron catalysts showed high performance in the well-controlled ATRP of styrene, methacrylates, and acrylates. The high reactivity of these catalysts led to well-controlled polymerization and block copolymerization even with lower catalyst concentrations. [source] Recent advances in controlled/living radical polymerization in emulsion and dispersionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2008Jung Kwon Oh Abstract Effective ways to conduct controlled/living radical polymerization (CRP) in emulsion systems are necessary for commercial latex production without significant modification of current industrial facilities. Conducting CRP in emulsion media is more complicated and more challenging than its application in homogeneous bulk. These challenges come from the intrinsic kinetics of emulsion polymerization. They include mass transport, slow chain growth mechanism, and exit of short radicals from polymeric particles. This review describes the recent developments of CRP in heterogeneous dispersion, including miniemulsion, microemulsion, dispersion, and especially emulsion. Various approaches for conducting emulsion CRP are detailed, including controlled seeded emulsion polymerization, nanoprecipitation, use of short oligomers as macroinitiators for in situ block copolymerization, and RAFT-mediated self-assembly. In addition many remaining challenges of the current methods barring wide spread industrial application of emulsion CRP are also suggested. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6983,7001, 2008 [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] Nitroxide-mediated homo- and block copolymerization of styrene and multifunctional acryl- and methacryl derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005Meizhen Yin Abstract The ability of different alkoxyamines (I1, I2, I3, I4, and I5) to initiate controlled radical polymerization of styrene was evaluated. Among them, 2-hydroxymethyl-2-[(2-methyl-1-phenyl-propyl)-(1-phenyl-ethoxy)-amino]-propane-1,3-diol (I5) gave the highest polymerization rate of styrene, and the best control over the molecular weight and the molecular weight distribution of polystyrene. Kinetic studies confirmed that with initiator I5 the polymerization of styrene proceeded in a controlled way. The controlled radical homopolymerization of multifunctional acryl- and methacryl derivatives using initiator I5 could not be realized as demonstrated by the high polydispersities (PD) obtained. However, it was possible to polymerize multifunctional acryl- and methacryl derivatives using a polystyrene macroinitiator (Pst) and, thus, novel amphiphilic block copolymers with a narrow molecular weight distribution were obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1873,1882, 2005 [source] Ring-opening polymerization and block copolymerization of L -lactide with divalent samarocene complexJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2003Dongmei Cui Abstract Divalent samarocene complex [(C5H9C5H4)2Sm(tetrahydrofuran)2] was prepared and characterized and used to catalyze the ring-opening polymerization of L -lactide (L-LA) and copolymerization of L-LA with caprolactone (CL). Several factors affecting monomer conversion and molecular weight of polymer, such as polymerization time, temperature, monomer/catalyst ratio, and solvent, were examined. The results indicated that polymerization was rapid, with monomer conversions reaching 100% within 1 h, and the conformation of L-LA was retained. The structure of the block copolymer of CL/L-LA was characterized by NMR and differential scanning calorimetry. The morphological changes during crystallization of poly(caprolactone) (PCL)- b -P(L-LA) copolymer were monitored with real-time hot-stage atomic force microscopy (AFM). The effect of temperature on the morphological change and crystallization behavior of PCL- b -P(L-LA) copolymer was demonstrated through AFM observation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2667,2675, 2003 [source] Method of preparing clean poly(4-methylstyrene)- block -polyisobutene by the combination of sequential monomer addition and sequential initiation in the solvent CH3ClJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2003Yuhong Ma A novel method of synthesizing a clean diblock copolymer via cationic polymerization was developed. First, a poly(4-methylstyrene) macroinitiator was prepared, and then a second comonomer (isobutene) and a coinitiator (AlEt2Cl) were added for the initiation of block copolymerization. [source] Atom transfer radical polymerization of n -butyl acrylate catalyzed by CuBr/N -(n -hexyl)-2-pyridylmethanimineJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Huiqi Zhang Abstract The homogeneous atom transfer radical polymerization (ATRP) of n -butyl acrylate with CuBr/N -(n -hexyl)-2-pyridylmethanimine as a catalyst and ethyl 2-bromoisobutyrate as an initiator was investigated. The kinetic plots of ln([M]0/[M]) versus the reaction time for the ATRP systems in different solvents such as toluene, anisole, N,N -dimethylformamide, and 1-butanol were linear throughout the reactions, and the experimental molecular weights increased linearly with increasing monomer conversion and were very close to the theoretical values. These, together with the relatively narrow molecular weight distributions (polydispersity index , 1.40 in most cases with monomer conversion > 50%), indicated that the polymerization was living and controlled. Toluene appeared to be the best solvent for the studied ATRP system in terms of the polymerization rate and molecular weight distribution among the solvents used. The polymerization showed zero order with respect to both the initiator and the catalyst, probably because of the presence of a self-regulation process at the beginning of the reaction. The reaction temperature had a positive effect on the polymerization rate, and the optimum reaction temperature was found to be 100 °C. An apparent enthalpy of activation of 81.2 kJ/mol was determined for the ATRP of n -butyl acrylate, corresponding to an enthalpy of equilibrium of 63.6 kJ/mol. An apparent enthalpy of activation of 52.8 kJ/mol was also obtained for the ATRP of methyl methacrylate under similar reaction conditions. Moreover, the CuBr/N -(n -hexyl)-2-pyridylmethanimine-based system was proven to be applicable to living block copolymerization and living random copolymerization of n -butyl acrylate with methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3549,3561, 2002 [source] Synthesis of comb-shaped poly(methyl methacrylate)- b -poly(polytetrahydrofuran acrylate) under 60Co ,-ray irradiationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Tao He Abstract Comb-shaped graft copolymers with poly(methyl methacrylate) as a handle were synthesized by the macromonomer technique in two steps. First, polytetrahydrofuran acrylate (A-PTHF), prepared by the living cationic ring-opening polymerization of tetrahydrofuran, underwent homopolymerization with 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate as an initiator under 60Co , irradiation at room temperature; Second, the handle of the comb-shaped copolymers was prepared by the block copolymerization of methyl methacrylate with P(A-PTHF) as a macroinitiator under 60Co , irradiation. The two-step polymerizations were proved to be controlled with the following evidence: the straight line of ln[M]0/[M] versus the polymerization time, the linear increase in the number-average molecular weight with the conversion, and the relatively narrow molecular weight distribution. The structures of the P(A-PTHF) and final comb-shaped copolymers were characterized by 1H NMR spectroscopy and gel permeation chromatography. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3367,3378, 2002 [source] Atom transfer radical homo- and block copolymerization of methyl 1-bicyclobutanecarboxylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2002Xiao-Ping Chen Abstract A non-olefinic monomer, methyl 1-bicyclobutanecarboxylate (MBC), was successfully polymerized by the controlled/"living" atom transfer radical polymerization (ATRP) technique, resulting in a well-defined homopolymer, PMBC, with only cyclobutane ring units in the polymer chain. An AB block copolymer poly(methyl 1-bicyclobutanecarboxylate)- b -polystyrene (PMBC- b -PS), having an all-ring unit segment, was also synthesized with narrow polydispersity and designed number-average molecular weight in addition to precise end groups. The 1H NMR spectra, glass-transition temperature, and thermal stability of PMBC, PMBC- b -PS, and PS- b -PMBC were investigated. The experimental results showed that the cyclobutane rings in the two block polymers improved their thermal stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1929,1936, 2002 [source] Rare-earth-metal-initiated polymerizations of (meth)acrylates and block copolymerizations of olefins with polar monomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2001Hajime Yasuda Abstract The organo-rare-earth-metal-initiated living polymerization of methyl methacrylate (MMA) was first discovered in 1992 with (C5Me5)2LnR (where R is H or Me and Ln is Sm, Yb, Y, or La) as an initiator. These polymerizations provided highly syndiotactic (>96%) poly(methyl methacrylate) (PMMA) with a high number-average molecular weight (Mn > 1000 × 103) and a very narrow molecular weight distribution [weight-average molecular weight/number-average molecular weight (Mw/Mn) < 1.04] quantitatively in a short period. Bridged rare-earth-metallocene derivatives were used to perform the block copolymerization of ethylene or 1-hexene with MMA, methyl acrylate, cyclic carbonate, or ,-caprolactone in a voluntary ratio. Highly isotactic (97%), monodisperse, high molecular weight (Mn > 500 × 103, Mw/Mn < 1.1) PMMA was first obtained in 1998 with [(Me3Si)3C]2Yb. Stereocomplexes prepared by the mixing of the resulting syndiotactic and isotactic PMMA revealed improved physical properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 1955,1959, 2001 [source] Synthesis, Sequential Crystallization and Morphological Evolution of Well-Defined Star-Shaped Poly(, -caprolactone)- b -poly(L -lactide) Block Copolymer,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2006Jing-Liang Wang Abstract Summary: Well-defined star-shaped poly(, -caprolactone)- b -poly(L -lactide) copolymers (PCL- b -PLLA) were synthesized via sequential block copolymerization, and their molecular weights and arm length ratio could be accurately controlled. Both differential scanning calorimetry and wide angle X-ray diffraction analysis indicated that the crystallization of both the PLLA and PCL blocks within the star-shaped PCL- b -PLLA copolymer could be adjusted from the arm length of each block, and both blocks mutually influenced each other. The sequential isothermal crystallization process of both the PLLA and PCL blocks within the PCL- b -PLLA copolymers was directly observed with a polarized optical microscope, and the isothermal crystallization of the PCL segments was mainly templated by the existing spherulites of PLLA. Moreover, the PLLA blocks within the star-shaped PCL- b -PLLA copolymer progressively changed from ordinary spherulites to banded spherulites when the arm length ratio of PCL to PLLA was increased while concentric spherulites were observed for the linear analog. Significantly, these novel spherulites with concentric or banded textures and the morphological evolution of the spherulites have been observed for the first time in the PCL- b -PLLA block copolymers. [source] Synthesis of block copolymers by combination of ATRP and photoiniferter processesPOLYMER INTERNATIONAL, Issue 10 2008Yasemin Yuksel Durmaz Abstract BACKGROUND: Block copolymers of monomers polymerizing by different mechanisms can be prepared by the transformation approach. A wide range of combinations of different polymerization modes has been reported in the literature. In this work, the transformation approach was further extended to the preparation of block copolymers by combining atom transfer radical polymerization (ATRP) and photoiniferter processes. RESULTS: Photoactive morpholine-4-dithiocarbamate-terminated polystyrene (MDC-PS-MDC) was prepared by the reaction of dibrominated polystyrene, obtained by ATRP, with morpholine-4-dithiocarbamate sodium salt in dimethylformamide. The structure of MDC-PS-MDC was confirmed by 1H NMR and UV-visible spectral analysis. The ability of MDC-PS-MDC to act as a photoiniferter for the block copolymerization of methyl acrylate was examined. The polymerization shows a ,living' character at up to 25% conversion and produces well-defined polymers with molecular weights close to those predicted from theory and relatively narrow polydispersities (Mw/Mn , 1.40). CONCLUSION: It is demonstrated that the end groups of polymers obtained by ATRP can be converted into morpholino-4-dithiocarbamate groups which act as photoiniferters. In this way, the desired mechanistic transformation between two controlled free radical polymerization methods can be achieved. Copyright © 2008 Society of Chemical Industry [source] Living Radical Polymerization of Acrylates Mediated by 1,3-Bis(2-pyridylimino)isoindolatocobalt(II) Complexes: Monitoring the Chain Growth at the MetalCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2008Björn Abstract A new type of mediator for cobalt(II)-mediated radical polymerization is reported which is based on 1,3-bis(2-pyridylimino)isoindolate (bpi) as ancillary ligand. The modular synthesis of the bis(pyridylimino)isoindoles (bpiH) employed in this work is based on the condensation of 2-aminopyridines with phthalodinitriles. Reaction of the bpiH protio-ligands with a twofold excess of cobalt(II) acetate or cobalt(II) acetylacetonate in methanol gave [Co(bpi)(OAc)], which crystallize as coordination polymers, and a series of [Co(acac)(bpi)(MeOH)], which are mononuclear octahedral complexes. Upon heating the [Co(acac)(bpi)(MeOH)] compounds to 100,°C under high vacuum, the coordinated methanol was removed to give the five-coordinate complexes [Co(acac)(bpi)]. The polymerization of methyl acrylate at 60,°C was investigated by using one molar equivalent of the relatively short-lived radical source 2,2,-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as initiator (monomer/catalyst/V-70: 600:1:1). The low solubility of the acetato complexes inhibits their significant activity as mediators in this reaction, whereas the acetylacetonate complexes control the radical polymerization of methyl acrylate more effectively. The radical polymerizations of the hexacoordinate complexes did not show a linear increase in number-average molecular weight (Mn) with conversion; however, the polydispersities were relatively low (PDI=1.12,1.40). By using the pentacoordinate complexes [Co(acac)(bpi)] as mediators, a linear increase in Mn values with conversion, which were very close to the theoretical values for living systems, and very low polydispersities (PDI<1.13) were obtained. This was also achieved in the block copolymerization of methyl acrylate and n -butyl acrylate. The intermediates with the growing acrylate polymer radical (.PA) were identified by liquid injection field desorption/ionization mass spectrometry as following the general formula [Co(acac)(4-methoxy-bpi)-(MA)n -R] (MA: methyl acrylate; R: C(CH3)(CH2C(CH3)2OCH3)CN), a notion also confirmed by NMR end-group analysis. [source] Rare-earth-metal-initiated polymerizations of (meth)acrylates and block copolymerizations of olefins with polar monomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2001Hajime Yasuda Abstract The organo-rare-earth-metal-initiated living polymerization of methyl methacrylate (MMA) was first discovered in 1992 with (C5Me5)2LnR (where R is H or Me and Ln is Sm, Yb, Y, or La) as an initiator. These polymerizations provided highly syndiotactic (>96%) poly(methyl methacrylate) (PMMA) with a high number-average molecular weight (Mn > 1000 × 103) and a very narrow molecular weight distribution [weight-average molecular weight/number-average molecular weight (Mw/Mn) < 1.04] quantitatively in a short period. Bridged rare-earth-metallocene derivatives were used to perform the block copolymerization of ethylene or 1-hexene with MMA, methyl acrylate, cyclic carbonate, or ,-caprolactone in a voluntary ratio. Highly isotactic (97%), monodisperse, high molecular weight (Mn > 500 × 103, Mw/Mn < 1.1) PMMA was first obtained in 1998 with [(Me3Si)3C]2Yb. Stereocomplexes prepared by the mixing of the resulting syndiotactic and isotactic PMMA revealed improved physical properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 1955,1959, 2001 [source] | |||||||||||||