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Lido Porri - One of the best experts on this subject based on the ideXlab platform.

Chun B Yang - One of the best experts on this subject based on the ideXlab platform.

  • propene Polymerization with mgcl2 supported ticl4 dioctylphthalate catalyst ii effects of Polymerization conditions on the microstructure of Isotactic Polymer
    Journal of Applied Polymer Science, 1995
    Co-Authors: Chun B Yang
    Abstract:

    Propene was Polymerized over the MgCl2-supported TiCl4/dioctylphthalate catalyst in heptane. Polymer products obtained under different Polymerization conditions were separated into Isotactic and atactic polypropenes by the extraction of boiling n-heptane. The effects of Polymerization time, cocatalyst type, cocatalyst/catalyst ratio, Polymerization temperature, and external base/cocatalyst ratio on the Isotactic triad of the Isotactic portion of polypropene were investigated 2,2,6,6-Tetramethyl piperidine (TMPIP), dimethoxy diphenyl silane (DMDPS), and t-butylmethyl ether (TBME) were employed as the external Lewis base. High concentrations of the first two bases caused a decrease in Isotactic triads in the Isotactic Polymer, while TBME showed no significant effects. The difference can be attributed to the different roles these external bases play in Polymerization. © 1995 John Wiley & Sons, Inc.

  • Propene Polymerization with MgCl2‐supported TiCl4/dioctylphthalate catalyst. II. Effects of Polymerization conditions on the microstructure of Isotactic Polymer
    Journal of Applied Polymer Science, 1995
    Co-Authors: Chun B Yang
    Abstract:

    Propene was Polymerized over the MgCl2-supported TiCl4/dioctylphthalate catalyst in heptane. Polymer products obtained under different Polymerization conditions were separated into Isotactic and atactic polypropenes by the extraction of boiling n-heptane. The effects of Polymerization time, cocatalyst type, cocatalyst/catalyst ratio, Polymerization temperature, and external base/cocatalyst ratio on the Isotactic triad of the Isotactic portion of polypropene were investigated 2,2,6,6-Tetramethyl piperidine (TMPIP), dimethoxy diphenyl silane (DMDPS), and t-butylmethyl ether (TBME) were employed as the external Lewis base. High concentrations of the first two bases caused a decrease in Isotactic triads in the Isotactic Polymer, while TBME showed no significant effects. The difference can be attributed to the different roles these external bases play in Polymerization. © 1995 John Wiley & Sons, Inc.

  • Propene Polymerization with MgCl2‐supported TiCl4/dioctylphthalate catalyst. III. Effects of Polymerization conditions on molecular weights and molecular weight distribution
    Journal of Applied Polymer Science, 1995
    Co-Authors: Chun B Yang
    Abstract:

    In propene Polymerization over the MgCl2-supported TiCl4/dioctylphthalate (DOP) catalyst, the weight- and number-average molecular weights and the molecular weight distribution (MWD) of polypropene products and of the Isotactic and atactic Polymer portions were studied. The average molecular weights and MWD were found to be independent of time. The Isotactic Polymer had higher molecular weight and broader distribution than the atactic portion by almost an order of magnitude. An increase in temperature and cocatalyst/catalyst ratio resulted in lowering molecular weight due to increasing transfer reaction. Alkyl aluminum was used as a cocatalyst, and the molecular weight did not vary significantly with different alkyl groups. Of the three external bases studied, 2,2,6,6-tetramethyl piperidine (TMPIP), dimethoxydiphenyl silane (DMDPS), and t-butylmethyl ether (TBME), the addition of a small amount of one of the first two bases caused a substantial increase in both molecular weight and polydispersity of the Isotactic Polymer. Those increases leveled off quickly with increasing amounts of the external base. On the other hand, both average molecular weights and polydispersity of the atactic Polymer decreased with a net increase in the molecular weight of the whole Polymer. TBME, however, has no significant effect on either molecular weight or MWD. These effects are discussed in the context of the roles of the external base in propene Polymerization. © 1995 John Wiley & Sons, Inc.

Yoshio Okamoto - One of the best experts on this subject based on the ideXlab platform.

  • Study of the effect of Isotacticity on some physical properties of poly(N-isopropylacrylamide)
    Colloid and Polymer Science, 2015
    Co-Authors: Chandra Sekhar Biswas, Kheyanath Mitra, Shikha Singh, Kalyan Ramesh, Nira Misra, Biswajit Maiti, Amiya Kumar Panda, Pralay Maiti, Masami Kamigaito, Yoshio Okamoto
    Abstract:

    Some physical properties of high molecular weight linear poly( N -isopropylacrylamide)s (PNIPAM) having different Isotacticities ( m , meso dyad = 47, 62, 68, 81, and 88 %) have been studied. The solubility of these Polymers in different solvents varied with their Isotacticity. Thermal degradation of higher Isotactic Polymer started slightly earlier. Cloud point of these Polymers in water gradually decreased with increase in m up to 68 %. Surface tension of these Polymers in N , N -dimethylformamide (DMF) was slightly lower than DMF and almost independent of their Isotacticity in the temperature range of 20–60 °C. But it decreased linearly with the increase in temperature. Moreover, for all Polymers, it decreased very slightly with the increase in their concentrations in the range of 0.001–0.01 % ( w / v ). Viscosity of these Polymers in DMF increased with (i) the increase in the concentration range of 1–5 % ( w / v ), (ii) the increase in their m values, and (iii) the decrease in the temperature in the range of 20–60 ^oC.

  • (−)‐Sparteine: The compound that most significantly influenced my research
    Journal of Polymer Science Part A, 2004
    Co-Authors: Yoshio Okamoto
    Abstract:

    A chiral diamine alkaloid, (−)-sparteine (Sp), has been found to be very effective as a ligand for Grignard reagents when used for the enantiomer-selective Polymerization of racemic RS-1-phenylethyl methacrylate. The enantiomeric excess of the initially Polymerized monomer is 93%, and at about a 60% conversion, nearly optically pure R-monomer is recovered. This enantiomer selectivity is today the highest in Polymer chemistry. Triphenylmethyl methacrylate (TrMA) is a unique monomer that gives a highly Isotactic Polymer even during radical Polymerization. When TrMA is Polymerized with the Sp complex with n-butyllithium in toluene at −78 °C, an optically active, Isotactic Polymer [poly(triphenylmethyl methacrylate) (PTrMA)] with a one-handed helical conformation is obtained. The helical structure is maintained even at room temperature in solution. Analogous helical polymethacrylates that show various conformational changes have also been found. One-handed helical PTrMA exhibits high chiral recognition to a variety of racemates as a chiral stationary phase (CSP) for high-performance liquid chromatography. This finding has led to the development of very powerful CSPs based on polysaccharides, such as cellulose and amylose. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4480–4491, 2004

  • Stereospecific Anionic Polymerization of α-(Alkylthiomethyl)acrylates and α-(2-Thienylmethyl)acrylate
    Polymer Journal, 1999
    Co-Authors: Shigeki Habaue, Tomoyuki Shibagaki, Yoshio Okamoto
    Abstract:

    Novel α-substituted acrylates having various functional groups containing a sulfur atom at the α-position, such as benzyl α-(butylthiomethyl)acrylate, benzyl α-( t -butylthiomethyl)acrylate, benzyl α-(benzylthiomethyl)acrylate, benzyl α-(triphenylmethylthiomethyl)acrylate, ethyl α-(2-thienylmethyl)acrylate, benzyl α-(benzylsulfinylmethyl)acrylate, and benzyl α-(benzylsulfonylmethyl)acrylate, were synthesized, and Polymerizability and stereoregularity of the obtained Polymers using lithium reagents were investigated. In the anionic Polymerization of α-(alkylthiomethyl)acrylates and ethyl α-(2-thienylmethyl)acrylate in toluene, highly Isotactic Polymers were obtained in good yields. A bulky α-substituent, triphenylmethylthiomethyl group, prevents Polymerization. The anionic Polymerization of α-(alkylthiomethyl)acrylates in tetrahydrofuran (THF) resulted in low yields and Isotacticities, ethyl α-(2-thienylmethyl)acrylate gave an Isotactic Polymer in a good yield. A side reaction, the elimination of alkylthiolate anion from the propagating end, seems to take place in the Polymerization of α-(alkylthiomethyl)acrylates in THF.

  • Asymmetric Polymerization of Diphenyl-3-pyridylmethyl Methacrylate Leading to Optically Active Polymer with Helical Conformation and Chiral Recognition Ability of the Polymer
    Polymer Journal, 1997
    Co-Authors: Tamaki Nakano, Kyoichi Taniguchi, Yoshio Okamoto
    Abstract:

    Diphenyl-3-pyridylmethyl methacrylate was synthesized and Polymerized using the complexes of N , N ′-diphenylethylenediamine monolithium amide with (+)-1-(2-pyrrolidinylmethyl)pyrrolidine, (+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane, and (−)-sparteine in toluene at −78°C (helix-sense-selective Polymerization). The obtained Polymers were highly Isotactic and exhibited large dextrorotation based on helical conformation with excess single-handed helicity. Free radical Polymerization with (iso-PrOCOO)_2 in toluene at 40°C also gave an Isotactic Polymer ( mm ∼74%). The optically active Polymer exhibited chiral recognition ability toward several racemic compounds including hexahelicene, trans -stilbene oxide, and binaphthyl derivatives when adsorbed on macro porous silica gel and used as a stationary phase for high-performance liquid chromatography (HPLC).

  • Asymmetric Polymerization of Triphenylmethyl Methacrylate Using 9-Alkyl-9-fluorenyllithium–(–)-Sparteine Complexes. Influence of Organolithium Structure on the Propagation Stereochemistry
    Polymer Journal, 1995
    Co-Authors: Tamaki Nakano, Yoshio Okamoto, Koichi Hatada
    Abstract:

    Asymmetric anionic Polymerization and oligomerization of triphenylmethyl methacrylate (TrMA) were carried out with the complexes of (–)-sparteine (Sp) with 9-methyl-9-fluorenyllithium (MeFlLi) and 9-ethyl-9-fluorenyllithium in toluene at −78°C in conjunction with the Polymerization of TrMA with Sp–9-fluorenyllithium (FlLi) complex. As well as Sp–FlLi complex, Sp–MeFlLi complex gave an optically active ([α]_D+360°), highly Isotactic Polymer with one-handed helical conformation; the Polymer had a higher molecular weight than that obtained by Sp–FlLi under the same reaction conditions. The oligomers obtained at the feed ratio of monomer to initiator of two, three, and five were converted to oligo(methyl methacrylate) [oligo(MMA)]; the oligo(MMA)s were first separated in terms of degree of Polymerization and then into diastereomers. The dimer meso ( m ) and racemo ( r ) and the trimer mm and mr were resolved into enantiomers to determine the ratio of isomers for each oligomer. On the basis of the change in isomer content of the dimer with the change in the feed ratio of monomer to initiator, it was concluded that the dimer anion having S absolute configuration is more active toward TrMA monomer than that having R configuration in both the systems with MeFlLi and EtFlLi in contrast to the reaction with Sp–FlLi where the R -dimer anion is more active. The stereochemistry in the propagation of a trimer anion to a tetramer anion and thereafter appeared similar to the reaction system with Sp–FlLi where ---RRR--- isomers predominantly propagate. The predominant propagation of the S -dimer anion results in a larger amount of the isomeric anions which do not propagate to the optically active Polymer.

Koichi Hatada - One of the best experts on this subject based on the ideXlab platform.

  • Asymmetric Polymerization of Triphenylmethyl Methacrylate Using 9-Alkyl-9-fluorenyllithium–(–)-Sparteine Complexes. Influence of Organolithium Structure on the Propagation Stereochemistry
    Polymer Journal, 1995
    Co-Authors: Tamaki Nakano, Yoshio Okamoto, Koichi Hatada
    Abstract:

    Asymmetric anionic Polymerization and oligomerization of triphenylmethyl methacrylate (TrMA) were carried out with the complexes of (–)-sparteine (Sp) with 9-methyl-9-fluorenyllithium (MeFlLi) and 9-ethyl-9-fluorenyllithium in toluene at −78°C in conjunction with the Polymerization of TrMA with Sp–9-fluorenyllithium (FlLi) complex. As well as Sp–FlLi complex, Sp–MeFlLi complex gave an optically active ([α]_D+360°), highly Isotactic Polymer with one-handed helical conformation; the Polymer had a higher molecular weight than that obtained by Sp–FlLi under the same reaction conditions. The oligomers obtained at the feed ratio of monomer to initiator of two, three, and five were converted to oligo(methyl methacrylate) [oligo(MMA)]; the oligo(MMA)s were first separated in terms of degree of Polymerization and then into diastereomers. The dimer meso ( m ) and racemo ( r ) and the trimer mm and mr were resolved into enantiomers to determine the ratio of isomers for each oligomer. On the basis of the change in isomer content of the dimer with the change in the feed ratio of monomer to initiator, it was concluded that the dimer anion having S absolute configuration is more active toward TrMA monomer than that having R configuration in both the systems with MeFlLi and EtFlLi in contrast to the reaction with Sp–FlLi where the R -dimer anion is more active. The stereochemistry in the propagation of a trimer anion to a tetramer anion and thereafter appeared similar to the reaction system with Sp–FlLi where ---RRR--- isomers predominantly propagate. The predominant propagation of the S -dimer anion results in a larger amount of the isomeric anions which do not propagate to the optically active Polymer.

  • Highly Isotactic and Living Polymerization of Ethyl Methacrylate with t-C_4H_9MgBr in Toluene and the Preparation of Block and Random CoPolymers with High Stereoregularity
    Polymer Journal, 1990
    Co-Authors: Tatsuki Kitayama, Masanori Yamamoto, Nobutaka Fujimoto, Koichi Hatada
    Abstract:

    The Polymerization of ethyl methacrylate (EMA) with t -C_4H_9MgBr in toluene at low temperature gave a highly Isotactic Polymer as in the case of living and highly Isotactic Polymerization of methyl methacrylate (MMA) with t -C_4H_9MgBr. Although the molecular weight distribution (MWD) of the poly(EMA) was bimodal, both species giving higher and lower molecular weight fractions contributed to the formation of highly Isotactic block coPolymers with bimodal MWD, indicating the living nature of both species. The Polymerization of EMA with the living anion of Isotactic PMMA formed with t -C_4H_9MgBr gave a highly Isotactic block coPolymer with unimodal MWD. This suggests that the multiplicity of active species observed in the Polymerization of EMA with t -C_4H_9MgBr was caused by the initiation of EMA with t -C_4H_9MgBr. Conventional coPolymerization of EMA and MMA afforded a highly Isotactic coPolymer with bimodal MWD, confirming the above consideration. ^13C NMR spectrum of the coPolymer indicated the comonomer sequence to be random. Glass transition temperatures of the Isotactic and syndiotactic coPolymers of EMA and MMA could be changed from 8 to 120°C by changing composition and tacticity.

  • Highly Isotactic and living Polymerization of ethyl methacrylate with t-C4H9MgBr in toluene and the preparation of block and random coPolymers with high stereoregularity.
    Polymer Journal, 1990
    Co-Authors: Tatsuki Kitayama, Masanori Yamamoto, Nobutaka Fujimoto, Koichi Hatada
    Abstract:

    The Polymerization of ethyl methacrylate (EMA) with t-C4H9MgBr in toluene at low temperature gave a highly Isotactic Polymer as in the case of living and highly Isotactic Polymerization of methyl methacrylate (MMA) with t-C4H9MgBr. Although the molecular weight distribution (MWD) of the poly(EMA) was bimodal, both species giving higher and lower molecular weight fractions contributed to the formation of highly Isotactic block coPolymers with bimodal MWD, indicating the living nature of both species. The Polymerization of EMA with the living anion of Isotactic PMMA formed with t-C4H9MgBr gave a highly Isotactic block coPolymer with unimodal MWD. This suggests that the multiplicity of active species observed in the Polymerization of EMA with t-C4H9MgBr was caused by the initiation of EMA with t-C4H9MgBr. Conventional coPolymerization of EMA and MMA afforded a highly Isotactic coPolymer with bimodal MWD, confirming the above consideration. 13C NMR spectrum of the coPolymer indicated the comonomer sequence to be random. Glass transition temperatures of the Isotactic and syndiotactic coPolymers of EMA and MMA could be changed from 8 to 120°C by changing composition and tacticity.

Giulio Natta - One of the best experts on this subject based on the ideXlab platform.

  • Some aspects of the Polymerization mechanism of α‐olefins to Isotactic Polymers
    Journal of Polymer Science Part C: Polymer Symposia, 2014
    Co-Authors: I. Pasquon, Giulio Natta, Adolfo Zambelli, A. Marinangeli, A. Surico
    Abstract:

    Data on the behavior of different heterogeneous catalyst systems in the Polymerization of α-olefins to Isotactic Polymer are reported and compared. The effect of substituents on the kinetic behavior of the catalyst complexes, which in the different systems yield Polymeric chains having comparable steric regularities, was investigated. Moreover, hypotheses are put forth on the factors influencing the stereospecificity of the catalyst systems studied. Des resultats concernant le comportement de differents systemes catalytiques heterogenes pour les Polymerisations d'α-olefines en vue d'obtenir des Polymeres isotactiques sont rapportes et compares entre eux. L'effet des substituants sur le comportement cinetique des catalyseurs complexes qui dans differents systemes fournissent des chaines Polymeriques ayant des regularites steriques comparables a ete etudie. En outre, des hypotheses sont presentees concernant les factuers qui influencent la stereospecificite des systemes catalytiques etudies. Daten uber das Verhalten verschiedener heterogen-katalytischer Systeme bei der Polymerisation von α-Olefinen zu isotaktischen Polymeren werden mitgeteilt und verglichen. Der Einfluss von Substituenten auf das kinetische Verhalten der Katalysatorkomplexe welche in den verschiedenen Systemen Polymerketten mit vergleichbarer sterischer Regelmassigkeit liefern, wurde untersucht. Hypothesen uber die Faktoren, welche die Stereospezifitat der untersuchten Katalysatorsysteme beeinflussen, werden aufgestellt.

  • THE INFLUENCE OF HYDROGEN ON COORDINATED ANIONIC PolymerIZATION OF PROPYLENE AND ETHYLENE
    Stereoregular Polymers and Stereospecific PolymerizationsThe Contributions of Giulio Natta and His School to Polymer Chemistry, 2013
    Co-Authors: Giulio Natta, G. Mazzanti, P. Longi, F. Bernardini
    Abstract:

    ABSTRACT It has been observed that the presence of hydrogen during the Polymerization of propylene, carried out with catalysts consisting of aluminum alkyls and titanium trichloride, exerts a considerable influence on both the rate of Polymerization and the molecular weight of the Polymer. On the other hand, by operating under suitable experimental conditions, the presence of hydrogen does not decrease the percentage of the Isotactic Polymer. It is also possible to minimize the hydrogenation reaction of propylene.

  • KINETICS OF PROPYLENE PolymerIZATION WITH HIGHLY STEREOSPECIFIC HETEROGENEOUS CATALYSTS. NOTE III: CHAIN TERMINATION PROCESSES DEPENDING ON CATALYST CONCENTRATION
    Stereoregular Polymers and Stereospecific PolymerizationsThe Contributions of Giulio Natta and His School to Polymer Chemistry, 2013
    Co-Authors: Giulio Natta, Italo Pasquon, E. Giachetti
    Abstract:

    ABSTRACT Results are here reported on further research on the production of Isotactic Polymers through coordinated anionic catalysis. By operating at constant pressure and temperature, the molecular weight of the Isotactic Polymer, obtained with a catalyst prepared from titanium trichloride (violet modification), and trialkyl aluminum, decreases with the increase of the relative quantity of any of these two compounds. The decrease of the molecular weight has been attributed to processes involving the termination of growing molecules, depending on the concentration of the organometallic compounds in solution. The termination process of the Polymeric chains, is interpreted as an exchange process of alkyls between the growing Polymeric chains and the triethyl aluminum. The observed processes of termination of the Polymeric chains are kinetically equivalent to chain transfer reactions. Within our limits of investigation, the molecular weights and the stereoisomeric composition of the Polymer do not depend on the time of Polymerization.

  • KINETICS OF THE STEREOSPECIFIC PolymerIZATION OF PROPYLENE TO Isotactic PolymerS
    Stereoregular Polymers and Stereospecific PolymerizationsThe Contributions of Giulio Natta and His School to Polymer Chemistry, 2013
    Co-Authors: Giulio Natta, Italo Pasquon, E. Giachetti
    Abstract:

    ABSTRACT The kinetics of the Polymerization of propylene to an Isotactic Polymer was studied with a heterogeneous catalytic system prepared from α-TiCl3 (violet modification characterized by a layer lattice) and Al (C2H5)3 in n-heptane. The catalytic system adopted here possesses a good stereospecificity. In runs carried out at constant temperature and pressure of olefin, the Polymerization rate kept constant even for several tens of hours. The catalytic activity was also unaltered when the catalyst was kept under different operating (or not operating) conditions and subsequently brought back to its original starting conditions. The Polymerization rate was first order with respect to the partial pressure of the olefin, and with respect to the amount of α-TiCl3 present in the system, while it was independent of the ratio of Al(C2H5)3 to TiCl3, and of the concentration of the Al(C2H5)3. The apparent activation energy of the overall Polymerization process, measured between 30° and 70°C, was about 14,000 cal/mol (referred to the concentration of the olefin in the liquid phase). The results obtained demonstrate that the Polymerization process of propylene is really catalytic with respect to TiCl3. This differentiates this type of Polymerization from the Polymerization processes characterized by a free radical mechanism. In these last processes the initiator is not actually a true catalyst, because, at the end of the Polymerization it is found bound to the Polymeric chains.