Investigations on the kinetics of copolymerization of vinyl acetate with acrylonitrile by Co(acac)3–Al(C2H5)3 catalyst system

Vinyl acetate and acrylonitrile were copolymerized with Co(acac)₃-Al(C₂H₅)₃ catalyst system in benzene at 40°C. The rate of copolymerization is linearly proportional to monomer concentration and catalyst concentrations up to a certain value. The overall activation energy was found to be 11.3 kcal/mole. The effect of hydroquinone on the rate of copolymerization indicates the presence of free radicals in this system. The possibility of simultaneous formation of coordinate anionic and free radical active sites has been proposed.     

Transformation of “living” carbocationic and other polymerizations to controlled/“living” radical polymerization

Transformation of “living” carbocationic polymerization of styrene and isobutene to controlled atom transfer radical polymerization (ATRP) is described and formation of the corresponding AB and ABA block copolymers with styrene (St), methyl methacrylate (MMA, methyl acrylate (MA) and isobornyl acrylate (IBA) was demonstrated. A similar approach was applied to the cationic ring opening polymerization of tetrahydrofuran leading to the AB and ABA block copolymers with St, MMA and MA using ATRP. Site transformation approach was also used for the ring opening metathesis polymerization of norbornene and polycondensation systems using polysulfone as an example. In both cases, AB and ABA block copolymers were efficiently formed with styrene and acrylates.     

Study of (π-C5H5)2Ti(CH3)Cl and (π-C5H5)2Ti(C6H5)Cl in soluble Ziegler catalysts

Soluble ethylene polymerization catalysts derived from (π-C₅H₅)₂Ti(R)Cl and R ′AlCl₂, where R = methyl or phenyl and R ′ = methyl or ethyl, were studied both by polymerization kinetics at 0°C and by diagnostic experiments. It was found that the first insertion of ethylene into the Ti? R bond is difficult when R = methyl or phenyl, and for this reason these catalysts show a different overall behavior than when R = ethyl or higher alkyl.     

Block copolymers by transformation of “living” carbocationic into “living” radical polymerization. II. ABA-type block copolymers comprising rubbery polyisobutene middle segment

A general method for the transformation of “living” carbocationic into “living” radical polymerization, without any modification of chain ends, is reported for the preparation of ABA block copolymers. For example, α,ω-difunctional polyisobutene, capped with several units of styrene, Cl-St-PIB-St-Cl, prepared cationically (M_n = 7800, M_w/M_n = 1.31) was used as an efficient difunctional macroinitiator for homogeneous “living” atom transfer radical polymerization to prepare triblock copolymers with styrene, PSt-PIB-PSt (M_n = 28,800, M_w/M_n = 1.14), methyl acrylate, PMA-PIB-PMA (M_n = 31,810, M_w/M_n = 1.42), isobornyl acrylate, PIBA-PIB-PIBA (M_n = 33,500, M_w/M_n = 1.21), and methyl methacrylate, PMMA-PIB-PMMA (M_n = 33,500, M_w/M_n = 1.47). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3595–3601, 1997     

Anionic polymerization of methyl methacrylate with Cr(C5H7O2)3–Al(C2H5)3 catalyst system

A homogeneous catalyst system, Cr(C₅H₇O₂)₃–Al(C₂H₅)₃, was used for the polymerization of methyl methacrylate. The yield of polymer increased up to an Al/Cr ratio of 12 and thereafter remained almost constant with increasing Al/Cr. The rate of polymerization increased linearly with increasing catalyst and monomer concentrations at Al/Cr = 12. The molecular weight, however, decreased with increasing catalyst concentration and increased with increasing monomer concentration, indicating anionic polymerization reaction. NMR studies of the polymers indicated the presence of a stereoblock structure, which changed to heteroblock structure in presence of triethylamine and hydroquinone as additives in the catalyst. In the light of these observations, the mechanism of the polymerization is discussed.     

Die Strukturen der 1,3,5-Trisilacyclohexan-Eisendicarbonyl-cyclopentadienylkomplexe C3H6Si3Cl5Fe(CO)2πcp und C3H6Si3Cl4(Fe(CO)2πcp)2

Structures of the l,3,5-Trisilacyclohexane-Iron Dicarbonyl-cyclopentadienyl Complexes and C₃H₆Si₃Cl₅Fe(CO)₂πcp and C₃H₆Si₃Cl₄(Fe(CO₂)πcp)₂ Trisilapentachlorocyclo-hexyl-dicarbonylcyclopentadienyliron C₃H₆Si₃Cl₅Fe(CO)₂πcp 1 and Trisilatetrachlorocyclohexyl-bis(dicarboncyclopentadienyliron)C₃H₆Si₃Cl₄(Fe(CO)₂πcp)₂ 2 are 1,3,5-Trisilacyclohexane complexes substituted by dicarbonylcyclopentadienyliron at one and two silicon atoms of the six-membered ring, respectively. The crystal and molecular structures were determined from single crystals ( 1 ; space group P2₁/a (No. 14); a = 1100.5 pm; b = 2033.9 pm; c = 843.3pm; β = 98.58°; Z = 4; MoKα-radiation; 3142h k l; R = 0.036. 2 ; space group P1 ; (No. 2); a = 1231.1 pm; b = 1267.3 pm; c = 1045.9 pm; α = 113.23°; β = 83.93°; γ = 115.00°; Z = 2; Mokα-radiation; 4196 h k 1; R = 0.065). In both complexes the six-membered rings of the carbosilane ligands are in skew-boat conformation. The bond lengths Fe? Si are 226.4 pm and 228.1 pm, respectively. The distances Si? C and Si? Cl are 186 pm and 206 pm in 1 and 187 pm and 209 pm in 2 . Their different lengths depend on the position in the ligand system and can be explained with the concept of bond orders.     

New prospects for “living” anionic polymerization of (meth) acrylic esters

The living low temperature polymerization in polar solvents of most methacrylates, even functional ones, can now be performed by direct and experimentally convenient anionic methods, thanks to the use of α-methylstyrene and of complex-purified monomers. A diversified family of block copolymers has thus been generated, that are used as compatibilizing agents in the designing of interesting heterophase materials: i.e. blends of polymers and inorganic fillers, and liquid-solid dispersions. The living polymerization of acrylates (or of methacrylates under more drastic conditions) raises additional requirements: they have been met to a large extent by the use of specific ligands of the growing ion-pair. Resulting structures such as f.i. block copolymers and end-functionalized oligomers of a low dispersity, should have a great interest in the molecular engineering of (meth)acrylate-based products. Finally, these new initiators lend themselves to structural and mechanistic studies which should shed some light on the critical features of these living propagation processes.     

Block copolymerization of alkoxyallenes by the living coordination system with a π-allylnickel catalyst

Block copolymers of alkoxyallenes were obtained in high yield by the two-stage living coordi-nation polymerization of two kinds of alkoxyallenes using an allylnickel catalyst. The resulting copolymers had narrow molecular weight distributions (～ 1.1), regardless of the order of the monomer additions. When an alkoxyallene-bearing hydrophilic substituent was used as a co-monomer for the block copolymerization with that bearing a hydrophobic one, the resulting copolymer showed amphiphilic properties. For example, a block copolymer obtained by the copolymerization of n-hexyloxyallene with diethylene glycol allenyl methyl ether was soluble in water as well as n-hexane. © 1995 John Wiley & Sons, Inc.     

Zur Polyreaktion von Äthylen mit dem löslichen Ziegler-Natta-Katalysator (C5H5)2Ti(C2H5)Cl/Al(C2H5)Cl2

Ohne Zusammenfassung     

Molecular engineering of liquid crystalline polymers by “living” polymerization. XXXII. Synthesis and “living” cationic polymerization of 3-fluoro-4′-(ω-vinyloxyalkoxy)-4-biphenylyl (2r,3s)-2-fluoro-3-methylpentanoate with undecanyl and octyl alkyl groups

The synthesis and “living” cationic polymerization of 3-fluoro-4′-(11-vinyloxyundecany-loxy)-4-biphenylyl (2R,3S)-2-fluoro-3-methylpentanoate ( 12-11 ) and 3-fluoro-4′-(8-vi-nyloxyoctyloxy)-4-biphenylyl (2R,3S)-2-fluoro-3-methylpentanoate ( 12-8 ) are presented. Poly ( 12-11 )s and poly ( 12-8 )s with degrees of polymerization from 4.0 to 16.5 and poly-dispersities ≤ 1.13 have been synthesized and characterized by differential scanning cal-orimetry (DSC) and thermal optical polarized microscopy. Over the entire range of molecular weights poly ( 12-11 )s and poly ( 12-8 )s exhibit an enantiotropic S_A and an unidentified S_X phase. In addition, regardless of its molecular weight, poly ( 12-8 ) exhibits a S^*_c phase in between the S_A and S_x phases. Poly ( 12-11 ) and poly ( 12-8 ) show lower transition tem-peratures and broader temperature ranges of all their mesophases as compared to the corresponding polymers without a fluorine atom on the biphenyl group. The role of the connecting group between the biphenyl and chiral group of the mesogenic unit on the phase behavior of these polymers is also discussed. Copolymers of 12-8 with (2R,3S)-2-fluoro-3-methylpentyl 4′-(11-vinyloxyundecanyloxy)biphenyl-4-carboxylate ( 13-11 ) {i.e., poly-[( 12-8 )-co-( 13-11 )] (X/Y), where X/Y represents the molar ratio of monomer 12-8 to monomer 13-11 } with DP of ca. 11 and polydispersities lower than 1.23 were also syn-thesized and characterized. Their S_A and S^*_c mesophases exhibit continuous dependences of composition and this support the assignment of the mesophases exhibited by poly ( 12-8 ). © 1995 John Wiley & Sons, Inc.     

Influence of SeOCl2 on the polymerization of propylene by TiCl3–Al(C2H5)3

The influence of SeOCl₂ on the polymerization of propylene by TiCl₃–Al(C₂H₅)₃, and the temperature dependence of the stereospecificity of the catalyst, TiCl₃–Al(C₂H₅)₃, have been investigated. SeOCl₂ decreases the rate of polymerization and increase the stereospecificity of the catalyst, which could be explained on the basis of a decrease of the concentration of Al(C₂H₅)₃ accompanied by a reaction between Al(C₂H₅)₃ and SeOCl₂. On the other hand, the stereospecificity of the catalyst, TiCl₃–Al(C₂H₅)₃, increases gradually with a decrease in polymerization temperature from 40 to 0°C. From these results, we conclude that SeOCl₂ exerts no essential influence on the polymerization of propylene by TiCl₃–Al(C₂H₅)₃, and that the stereospecificity of the catalyst is attributed mainly to the reducing ability of the organometallic compound.     

Block copolymerization of allene derivatives with isocyanides by the coordination polymerization with π-allylnickel catalyst

A living block copolymerization of allene derivatives with 1-phenylethyl isocyanide ( 3 ) using [(allyl)NiOCOCF₃]₂ ( 1 ) is described. After complete polymerization of allene monomers such as n-octyloxyallene ( 2A ) with 1 , further addition of 3 to the reaction system yielded the corresponding block copolymers in high yield. For instance, a block copolymer ( 4A , M_n = 39,600, M_w/M_n = 1.20) was obtained in 96% yield by the addition of 3 ([ 3 ]/[ 1 ] = 250) to the living solution of poly(n-octyloxyallene) (M_n = 14,400, M_w/M_n = 1.03) prepared by the polymerization of 2A in the ratio of [ 2A ]/[ 1 ] = 90. The resulting copolymer was a brownish orange gum or a solid, depending on the length of each of the segments. The solubility of the block copolymers could be controlled by the allene components. The copolymer of 2A with 3 having appropriate length of segments was soluble in n-hexane, while that of methoxyethoxyethoxyallene ( 2D ) with 3 was soluble in methanol. © 1997 John Wiley & Sons, Inc.     

New 1,1′-Ring-substituted Vanadocene Dichlorides. Crystal structures of [V(η5-C5H4SiMe3)2Cl2] and [V(η5-C5H5)2Cl2]

The 1,1′-ring-substituted vanadocene dichlorides [V(η⁵-C₅H₄R)₂Cl₂] (R = CMe₃, SiMe₃, SiEt₃) have been prepared from VCl₄ and the appropriate lithiated cyclopentadiene, C₅H₄RLi, in 1 : 2 ratios. All complexes were characterized by elemental microanalysis and IR spectroscopy. The crystal structures of [V(η⁵-C₅H₄SiMe₃)₂Cl₂] 3 and the parent compound [V(η⁵-C₅H₅)₂Cl₂] 1 have been determined by X-ray diffraction and are in accordance with expectations. Compound 1 crystallizes with two crystallographically independent molecules in its monoclinic unit cell. These two molecules are quite similar in their essential structural features. Compound 3 crystallizes in the triclinic space group P1 . The trimethylsilylcyclopentadienyl rings are bound in a staggered relative orientation.