Department of Applied Chemistry

A new ansa-fluorenylamidodimethyltitanium complex 1 was synthesized and applied for ethylene-dicyclopentadiene copolymerization using modified methylaluminoxane (MMAO) as a cocatalyst at 50 C. 1-MMAO exhibited the remarkable catalytic activity for the copolymerization and gave a copolymer with high glass-transition temperature of 191 C. Single-site catalysts 1 are effective catalysts for the copolymerization of-olefins and cycloolefins. 2 Cycloolefin copoly

The dynamics of the photochemical phase transition process of guest/host liquid crystals (LCs) containing an azobenzene derivative as a photosensitive chromophore was studied. We proposed a model for the photochemical phase transition of the guest/host LCs and simulated the change in transmittance through LCs due to the phase transition on the basis of this model. Upon irradiation at 366 nm, the cis isomer was generated randomly in the irradiated site, and then the transmittance of the probe light was slightly decreased because of the disturbance of the alignment of the nematic (N) phase by the cis isomers. Upon further irradiation, the N-to-isotropic (I) phase transition took place in local domains, and the transmittance of the probe light decreased with the growth of these local I domains. In the simulations, three factors were found to affect significantly the dynamics of the photochemical phase transition and the change in transmittance of light: the number of I domains formed by irradiation, the growth rate of the I domains, and the threshold size of the I domains detected with the probe light.

Polymer/liquid crystal (LC) composite films possessing an azobenzene LC as a photoresponsive molecule (AzoCFs) were prepared by the thermal polymerization-induced phase separation method. The composite films (AzoCFs) showed a strong light-scattering state after polymerization, and their optical properties were strongly affected by the compositional ratio of the liquid crystals in the composite film. Change in the transmittance between a light-scattering and a transparent state could be induced isothermally by photoirradiation. Upon irradiation at 366 nm, AzoCFs changed from the light-scattering state to the transparent state. This is ascribed to nematic (N)-isotropic (I) phase transition due to transcis isomerization of the azobenzene molecules in the LC domains within the polymer matrix. Furthermore, restoration of the initial state could be achieved by visible-light irradiation (>420 nm), resulting from the IN phase transition induced by cis-trans back-isomerization of the azobenzene guest molecules.

Dynamic holographic grating by means of photochemical nematic-to-isotropic phase transition has been studied in a polymer liquid crystal containing an azobenzene moiety with strong donor-acceptor substituents in the side chain. Periodical change in the phase structure was caused reversibly by trans-cis photoisomerization and cis-trans thermal backisomerization of the azobenzene moiety and led to formation of the dynamic grating following change in refractive index on the order of 10-2. The production and removal of the grating with a narrow fringe spacing of 1.4 µm was achieved within ∼150 and ∼190 ms, respectively. Moreover, the optical switching behavior of the holographic diffraction was observed repeatedly by turning on and off the writing beams.

In this article, we cover the development of L-lactide (L-LA) random copolymers into which useful compounds, such as repellents and antibacterial agents, were impregnated by high concentration. Outstanding controlled release materials were developed with statistical random copolymers of L-LA with cyclic carbonate (CC) [2,2-dimethyltrimethylene carbonate (2,2-DTMC) or tetramethylene carbonate (TEMC)] with tin 2-ethyL-hexanoate as a catalyst at 150 C (2,2-DTMC) or 120 C (TEMC) for 24 h without solvent. The preparation of improved controlled release materials was performed with useful organic compounds with low boiling points and synthetic L-LA random copolymers containing CCs as base materials under supercritical carbon dioxide (scCO 2). Low-boiling-point compounds, such as d-limonene and hinokitiol, were used. In impregnation experiments with scCO 2 , the amounts of low-boiling-point compounds increased with increasings L-LA content. The compound content impregnated into poly(L-lactide-ran-cyclic carbonate) [poly(L-LAran-CC)] was greater than that of the experiment with poly(L-lactide-ran-e-caprolactone) previously studied. When the enzymatic degradation of poly(L-LA-ran-CC) was performed with proteinase K, copolymers with a greater L-LA content degraded more rapidly than did copolymers with a greater CC content. In a controlled release experiment with poly(L-lactide-ran-2,2-dimethyltrimethylene carbonate) (76/24) or poly(L-lactide-ran-tetramethylene carbonate) (81/19), the rate of polymer degradation and the rate of impregnated compound release were almost the same. V

Ring-opening polymerization of x-pentadecalactone (PDL) by tetrahydroborate complexes of rare earth metals, Ln(BH 4) 3 (THF) 3 (Ln ¼ La (1), Nd (2), Y (3)), was studied. These complexes showed high activity for PDL polymerization in THF at 60 C. Among the complexes 1-3, the neodymium complex 2 was most active. The obtained poly(PDL) was demonstrated to be hydroxytelechelic by 1 H-NMR and MALDI-TOF MS spectroscopy. Biodegradation of the poly(PDL) in compost at 60 C was investigated, where 18% weight loss of the samples was observed after 280 days. V

A series of anilinonaphthoquinone-based nickel complexes, Ni(C 10 H 5 O 2 NAr)(Ph)(PPh 3) (Ar = C 6 H 3-2,6-Me (1c); Ar = C 6 H 3-2,4,6-Me (2c); Ar = C 6 H 3-2,6-Et (3c)), were synthesized and the structures of 1c-3c were confirmed by single crystal X-ray analyses. The anilinonaphthoquinone-ligated nickel complexes activated with B(C 6 F 5) 3 showed high activities for ethylene polymerization at 40 °C under atmospheric pressure of ethylene and gave polyethylene with long chain branches and short chain branches. The activity of these systems was decreased by lowering polymerization temperature accompanied by increase in molecular weight. The number of the chain branches was also decreased with lowering polymerization temperature and increasing the bulkiness of the ligand.

L-Lactide (L-LA) was polymerized in the presence of N-methyldiethanolamine as an initiator and Sn(Oct) 2 as a catalyst to give hydroxy-telechelic poly(L-lactide) (PLLA-diol) bearing a tertiary amine group at the center of the polymer chain. Successive chain extension of the PLLA-diol with hexamethylene diisocyanate afforded PLLA-based poly(ester-urethane)s (PEU) with equally spaced tertiary amine groups. Treatment of the PEU with iodomethane converted tertiary amine groups to quaternary ammonium groups to give cationic ionomers (PEU-MeI). The thermal, mechanical, hydrophilic, and biodegradation properties of the obtained polymers were investigated. The thermal properties of the PEUs and the PEU-MeIs were similar each other. The PEU-MeIs exhibited higher tensile modulus than those of the starting PEUs. The contact angles of water on the PEU-MeIs were lower than those of the PEUs with similar NMDA content indicating their higher hydrophilicity. In compost degradation tests, the PEU-MeIs showed slower degradation than those of the PEUs. V

A-B-A block copolymers which consist of poly(norbornene-co-1-octene) and atactic polypropylene (PP) segments were synthesized by using ansa-fluorenylamidotitanium complex as a catalyst varying the ratio of norbornene, 1-octene, and propylene. The copolymer was obtained quantitatively with high molecular weight (>100,000) and narrow molecular weight distribution (polydispersity index, <1.5). A-B block copolymers of poly(norbornene-co-1-octene) and poly(methyl methacrylate) (PMMA) was also obtained by the same procedure. Mechanical and optical properties of these copolymer films, which were obtained by solution casting process, were also investigated. Introduction of PP soft segment greatly improved mechanical properties, keeping their high transparency. Introduction of PMMA block also increased the tensile strength. V

The copolymerization of propylene and 3-buten-1-ol protected with alkylaluminum [trimethylaluminum (TMA) or triisobutylaluminum] was conducted with an isospecific zirconocene catalyst [rac-dimethylsilylbis(1-indenyl)zirconium dichloride], combined with methylaluminoxane as a cocatalyst, in the presence of additional TMA or H 2 as the chain-transfer reagent if necessary. The results indicated that endhydroxylated polypropylene was obtained in the presence of the chain-transfer reagents because of the formation of dormant species after the insertion of the 3-buten-1-ol-based monomer followed by chain-transfer reactions. The selectivity of the chain-transfer reactions was influenced by the alkylaluminum protecting the comonomer and the catalyst structure.

A series of titanium complexes with ansa-(fluorenyl)(cyclododecylamido) ligands, Me 2 Si(g 3-R)(N-cC 12 H 23)TiMe 2 [R ¼ fluorenyl (5), 2,7-t Bu 2 fluorenyl (6), 3,6-t Bu 2 fluorenyl (7)], was synthesized. The crystal structure of complex 6 revealed g 3-coordination of the fluorenyl moiety to the metal. Upon activation with trialkylaluminum-free modified methylaluminoxane, complexes 5-7 as well as the corresponding t Bu amide complexes, Me 2 Si(g 3-R)(N t Bu)TiMe 2 [R ¼ fluorenyl (2), 2,7-t Bu 2fluorenyl (3), 3,6-t Bu 2 fluorenyl (4)], were adopted as the catalysts for the copolymerization of ethylene (E) and isobutylene (IB). Among these complexes, complex 6 was found to achieve the highest IB incorporation to produce alternating E-IB copolymers. Complex 6 system also achieved copolymerization of E and limonene. V

Norbornene copolymers functionalized with methyl ester group or carboxy group are facilely synthesized by the copolymerization of norbornene and 7-octenyldiisobutylaluminum (ODIBA) with ansa-dimethylsilylene(fluorenyl)(t-butylamido)dimethyltitanium (1) activated by Ph 3 CB(C 6 F 5) 4 , and the sequential CO 2 /methanolysis reactions or CO 2 /hydrolysis reactions, respectively. The methanolysis and the hydrolysis are simply switched by engaging acidic methanol or acidic aqueous acetone as the quenching/washing solution, respectively. Meanwhile, the increase of ODIBA in the copolymerization abruptly decreases the yield and number-average molecular weight (M n) of the product. However, the addition of triisobutylaluminum (8 mM) and the use of excess Ph 3 CB(C 6 F 5) 4 (twofold of 0.4 mM of 1) significantly increase the yield, accompanying the increase in the M n and the narrowing of the molecular weight distribution (M w /M n), especially in the case of the use of excess Ph 3 CB(C 6 F 5) 4. The yield (g polymer/g monomers), M n , and M w /M n reach up to 0.82, 341,000, and 1.46, respectively, at a copolymerization condition. The carboxy groups in the norbornene copolymers are controlled in the range of 0-1.8 mol % in high polymer yields with high M n and narrow M w /M n accompanied by the decrease in the contact angle with water from 104 to 89. V

Reactions of CrCl 3 (thf) 3 with bis(imino)pyridines gave a series of {bis(imino) pyridine}chromium(III) trichloride complexes, {2,6-(RN¼ ¼CMe) 2 C 5 H 3 N}CrCl 3 [R ¼ C 6 H 3 i Pr 2-2,6 (1), C 6 H 3 Et 2-2,6 (2), C 6 H 3 Me 2-2,6 (3), C 6 H 2 Me 3-2,4,6 (4), C 6 H 3 Me 2-3,5 (5), C 6 H 5 (6), cyclohexyl (7), 2-methyl-1-naphthyl (8), C 6 H 3 F 2-2,6 (9), C 6 H 3 Br 2-2,6 (10), C 6 F 5 (11)]. Pseudo-octahedral geometries of 6, 10, and 11 were revealed by Xray crystallography. The complexes having bulky substituents such as 1-4 showed high activity for ethylene polymerization in combination with modified methylaluminoxane (MMAO) to give linear polyethylenes. In sharp contrast, the pentafluorophenyl complex 11/modified methylaluminoxane system was found to be moderately active for ethylene homopolymerization to give moderately branched polyethylene with only ethyl branches. V

i Bu, n Oct]. The activity of 1 in the absence of R 3 Al was approximately double of that of 2 and became two-to fourfold by the addition of R 3 Al depending on the amount and R of R 3 Al. Et 3 Al increased the activity most effectively and the number-average molecular weight (M n) of the produced polymer was decreased from 100,000 g/mol to 25,000 g/mol according to the amount of Et 3 Al added. On the other hand, the M n value was increased by the addition of i Bu 3 Al from 100,000 g/mol to 209,000 g/mol accompanied by the increase of the activity with approximately 2.5-fold. Consequently, 1 was found to be one of the most promising complexes for synthesis of alternating E-N copolymers, of which M n value is widely controlled by the kind and the amount of R 3 Al added accompanied by the increase in the copolymerization activity.

Both propene polymerization and ethylene/propene copolymerization were conducted with an Al,O,-supported CpTiC1, (Cp: cyclopentadienyl) catalyst using a common alkylaluminium as cocatalyst. The catalyst system gave atactic polypropene with frequently inverted propene units which are randomly distributed over the polymer chain. The structure of poly(ethy1ene-co-propene) produced with the catalyst system was found to be very different from that obtained with ordinary titanium based catalysts.