Simultaneous wide‐angle X‐ray diffraction and differential scanning calorimetry analysis of the melting and recrystallization behavior of polyethylene and isotactic polypropylene containing cyclopentane units in the main chain

The melting and crystallization behavior of polyethylene and isotactic polypropylene containing 1,2‐ or 1,3‐disubstituted cyclopentane units in the main chain has been studied with simultaneous wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry. For the ethylene‐based copolymers, the position of a reflection peak in the WAXD patterns shifts to a low angle with the increasing acquired temperature. The temperature dependence on the axial length of the crystal lattice is more marked in the copolymers forming orthorhombic crystals (containing 1,2‐cyclopentane or 5.6 mol % 1,3‐cyclopentane units) than in those forming hexagonal crystals (containing 8.1 mol % 1,3‐cyclopentane units). For the isotactic propylene‐based copolymers, the position of the reflection peaks in the WAXD patterns is independent of the acquired temperature. The proportion of the γ form in the copolymer containing the 1,2‐cyclopentane units is higher than that in the copolymers containing the 1,3‐cyclopentane units. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1457–1465, 2004     

Copolymerization of propylene and disubstituted diallylsilanes involving intramolecular cyclization with stereoselective zirconocene catalysts

The copolymerization of propylene and disubstituted diallylsilanes [(CH₂ ?CH? CH₂? )₂R₂Si (R = CH₃ or C₆H₅)] was investigated with isoselective and syndioselective zirconocene catalysts with methylaluminoxane as a cocatalyst. The syndioselective catalyst showed a higher reactivity for disubstituted diallylsilanes than the isoselective catalysts. Diallyldimethylsilane was incorporated into the polymer chain via cyclization insertion preferentially and formed 3,5‐disubstituted dimethylsilacyclohexane units in the polypropylene main chain. In the copolymerization with diallyldiphenylsilane, diallyldiphenylsilane was copolymerized via both cyclization insertion and 1,2‐insertion, which formed a pendant allyl group. The structures of isolated silacyclohexane units, determined by ¹³C NMR and distortionless enhancement by polarization transfer spectroscopy, proved that the 1,2‐insertion of diallylsilanes proceeded with enantiomorphic site control; however, the diastereoselectivity of the cyclization reaction was independent of the stereoselectivity of the catalysts used, and cis‐silacyclohexane units were mainly formed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6083–6093, 2006     

Selective monolithiation of dibromobiaryls using microflow systems

Selective monolithiation of dibromobiaryls, such as 2,2'-dibromobiphenyl, 4,4'-dibromobiphenyl, 2,7-dibromo-9,9-dioctylfluorene, 2,2'-dibromo-1,1'-binaphthyl, and 5,5'-dibromo-2,2'-bithiophene, with 1 equiv of n-butyllithium followed by the reaction with electrophiles was achieved using a microflow system by virtue of fast micromixing and precise temperature control. Sequential introduction of two different electrophiles based on this method was also achieved using a microflow system composed of four micromixers and four microtube reactors.     

Synthesis of titanium(IV) complexes that contain the Bis(silylamide) ligand of the type [1,8-C10H6(NR)2], and alkene polymerization catalyzed by [1,8-C10H6(NR)2]TiCl2-cocatalyst system

[1,8-C₁₀H₆(NR)₂]TiCl₂ (3; R=SiMe₃, SiⁱBuMe₂, SiⁱPr₃) complexes have been prepared from dilithio salts [1,8-C₁₀H₆(NR)₂]Li₂ (2) and TiCl₄ in diethyl ether in moderate yields (60–63%). These complexes showed significant catalytic activities for ethylene polymerization and for ethylene/1-hexene copolymerization in the presence of methylaluminoxane (MAO), methyl isobutyl aluminoxane (MMAO), AlⁱBu₃– or AlEt₃–Ph₃CB(C₆F₅)₄ as a cocatalyst. The catalytic activities performed in heptane (cocatalyst MMAO) were higher than those carried out in toluene (cocatalyst MAO): 709 kg-PE/mol-Ti·h could be attained for ethylene polymerization by using [1,8-C₁₀H₆(NSiⁱBuMe₂)₂]TiCl₂–MMAO catalyst system.     

Synthesis of polyethylene and polypropylene containing fluorene units in the side chain

Copolymerizations of ethylene or propylene and allyl monomers containing 9‐fluorenyl group, diallyl‐di‐9‐fluorenylsilane (DAFS), 9,9‐diallylfluorene (DAF), and 9‐allylfluorene (AF), were investigated with various zirconocene catalysts using methylaluminoxane as a cocatalyst. The bridged zirconocene catalysts, especially a syndioselective catalyst, showed a higher reactivity for all the comonomers than the nonbridged catalysts. DAFS was mainly incorporated into the polymer chain via cyclization insertion, whereas DAF was copolymerized via both 1,2‐ and cyclization insertions. Cyclization selectivity, ratio of cyclized insertion unit, of DAF in the copolymerization with propylene was higher than that in the copolymerization with ethylene. Copolymerization with AF yielded low‐molecular weight copolymer because of frequent chain transfer reaction. Optical properties of the propylene based‐copolymers were investigated by UV‐vis and photoluminescence spectroscopy, and absorption‐ and emission‐derived from fluorenyl groups were detected in the copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3542–3552, 2010     

Morphosynthesis of poly(ether ketone) by reaction-induced crystallization during polymerization

Morphology control of poly(ether ketone) (PEK) was examined by using the crystallization during the nucleophilic aromatic substitution reaction of potassium salt of 4-fluoro-4′-hydroxybenzophenone. Polymerizations were carried out at 290 °C. The PEK was obtained as precipitates and its morphology was highly influenced by the polymerization condition such as the solvent, the concentration and the polymerization time. High crystalline spindle-like crystals were obtained by the polymerization in diphenyl sulfone (DPS) at a concentration of 5.0% for 2 h with the yield of 86%. The average length and width were 1.4 μm and 300 nm respectively, and the maximum thickness was 130 nm. The surface was not smooth and it was hilly. The spindle-like crystal was likely consisted of multilayered lamellae comprised of the microcrystallites. The molecules were oriented perpendicular to the lamella. The polymerization in DPS at a higher concentration of 10.0% afforded the networks of nanofibres, of which the diameter was 100–250 nm. The obtained PEK precipitates possessed excellent thermal properties.     

Effect of ligand in ethylene/styrene copolymerization by [Me2Si(C5Me4)(NR)]TiCl2 (R = tert-Bu, cyclohexyl) and (1,3-Me2C5H3)TiCl2(O-2,6-Pr2C6H3)-MAO catalyst system

Copolymerization of ethylene with styrene using linked cyclopentadienyl-amide titanium(IV) complexes, [Me₂Si(C₅Me₄)(R)]TiCl₂ [R=tert-Bu (1), cyclohexyl (2)], and non-bridged (1,3-Me₂C₅H₃)TiCl₂(O-2,6-ⁱPr₂C₆H₃) (3)-MAO catalysts have been explored. Although the catalytic activity by 2 was lower than 1, 2 showed more efficient styrene incorporation than 1 under the same conditions. Moreover, the resultant copolymer prepared by 2 possessed completely different microstructure from those by 1, indicating that the nature of amide ligand affects both styrene incorporation and monomer sequence.