Influences of Ligand Backbone Substituents on Phosphinecarbonylpalladium and -nickel Catalysts for Ethylene Polymerization and Copolymerization with Polar Monomers.

A series of phosphinecarbonylpalladium and -nickel catalysts bearing various substituents on the ligand backbone were prepared, characterized, and used in ethylene polymerization and copolymerization with polar monomers. The Pd and Ni catalysts can achieve high activities as well as high polymer molecular weights in both ethylene polymerization and copolymerization with polar monomers. The electron-donating group from the carbonyl side can effectively increase the polymer molecular weights. Utilization of a cyclic backbone structure can increase the catalytic activities at the expense of the polymer molecular weights. Moreover, installation of a pyridyl moiety in the ligand backbone can enable Lewis acid responsiveness and can enhance the polymerization activities. These results suggest the importance of the ligand backbone for the properties of catalysts in ethylene polymerization and copolymerization reactions.

Ortho-Functionalized Dibenzhydryl Substituents in α-Diimine Pd Catalyzed Ethylene Polymerization and Copolymerization.

Sterically bulky diarylmethyl-based ligands have received increasing attention in the field of late-transition-metal catalyzed olefin polymerization. Ortho-substituents may have a significant impact on the performance of diarylmethyl-based α-diimine Pd catalysts. In this contribution, a series of α-diimine Pd catalysts bearing ortho-methoxyl/hydroxyl functionalized dibenzhydryl units were prepared, characterized, and investigated in ethylene polymerization and copolymerization with methyl acrylate (MA). The catalytic performances were improved by introducing more ortho-substituents. The catalysts exhibited good thermal stabilities at high temperatures, producing branched polyethylenes. The catalysts bearing hydroxyl groups possessing intramolecular H-bonding, resulted in slightly higher incorporation ratios of MA unit when compared with the catalysts bearing methoxyl groups.

Phosphine phosphonic amide nickel catalyzed ethylene polymerization and copolymerization with polar monomers.

The phosphine phosphonic amide ligand platform is highly versatile, with three positions that can be independently tuned. In this contribution, we wish to study the nickel complexes based on this ligand system. Interestingly, the nickel dibromide and nickel allyl complexes are not active in ethylene polymerization. In contrast, the nickel phenyl chloride complexes are highly active in ethylene polymerization in the presence of a sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate cocatalyst. In addition, these nickel complexes can initiate ethylene copolymerizations with polar functionalized comonomers including methyl 10-undecenoate, 6-chloro-1-hexene and 5-acetoxy-1-pentene. More interestingly, these nickel complexes can oligomerize 1-hexene and 6-chloro-1-hexene.

Influence of Ligand Backbone Structure and Connectivity on the Properties of Phosphine-Sulfonate Pd(II)/Ni(II) Catalysts.

Phosphine-sulfonate based palladium and nickel catalysts have been extensively studied in ethylene polymerization and copolymerization reactions. Previously, the majority of the research works focused on the modifications of the substituents on the phosphorous atom. In this contribution, we systematically demonstrated that the change of the ligand backbone from benzene to naphthalene could greatly improve the properties of this class of catalysts. In the palladium system, this change could increase catalyst stability and polyethylene molecular weights. In the nickel system, this change could dramatically increase the polyethylene molecular weights. Most interestingly, the change in the connectivity of phosphine and sulfonate moieties to the naphthalene backbone could also significantly influence the catalyst properties.

Photochemical control of microphase structure in biocompatible polyester membranes generated by ultraviolet irradiation.

The morphologies of PEMA-RB/PHEMA semi-interpenetrating polymeric network (semi-IPN) blended membranes prepared via ultraviolet (UV) promoted in situ photopolymerization were investigated using laser scanning confocal fluorescence microscopy (LSCFM). The results show that the semi-IPN morphology generated through UV light irradiation-induced microphase separation is considerably dependent on the relative rates of the photochemical reaction and microphase separation in the reactive precursor mixtures, which are determined by reactive dynamic factors. Changing the dynamic conditions, such as the UV light intensity, content of cross-linker and concentration of HEMA photopolymerization monomer resulted in a corresponding alteration of the morphological structure in the semi-IPN membranes. The hierarchical morphology appearing in the PEMA-RB/PHEMA semi-IPN should be related to the inhomogeneous photoreaction dynamics of the mixed system. Desired morphologies of the semi-IPN blend membranes can be obtained by controlling the corresponding dynamic conditions of both the photochemical reaction and microphase separation.

One-step functionalization of multi-walled carbon nanotubes with Ag/polymer under γ-ray irradiation.

We reported an easy strategy of using γ-ray irradiation to functionalize multi-walled carbon nanotubes (MWCNTs) without the use of aggressive acid treatment, all in a single processing step. In this paper, we tried to decorate MWCNTs with Ag nanoparticles relying on covalently bonded polymers, via one-step covalent grafting of the polymer to the surface of MWCNTs, and simultaneous reducing of Ag(+) ions to Ag which are then efficiently anchored onto the MWCNTs. Herein, the polymer involved was the commercially available polymer poly(vinyl alcohol) (PVA) and two of its derivatives, polyvinylacetone with ketalization degree D(H) = 0.22 and 0.53. It is envisioned that this simple but efficient method could be extended to fabricate other CNT-based hybrids for both theoretical study and applications in biological and technological fields.

Morphology and properties of organic-inorganic hybrid materials involving TiO2 and poly(epsilon-caprolactone), a biodegradable aliphatic polyester.

The novel biodegradable poly(epsilon-caprolactone)/titanium dioxide hybrid materials were prepared via in situ sol-gel process of tetrabutyl titanate (TBT) as inorganic precursor in the presence of PCL. The relationships between morphology, microphase separation, crystalline structure, and properties were investigated by means of XPS, SEM, XRD, DSC, and in vitro degradation test. The microstructures of the bulk hybrids display two-phase microscopic separation on the nanometer scale, which domain is 20-80 nm. The surface morphology and intermolecular bonding interaction are significantly dependent on inorganic component. The relative crystalline degrees of PCL/TiO(2) hybrid nanocomposite materials were controlled by both inorganic component and hydrogen bonding special interaction. The hybrid nanocomposite materials with TiO(2) showed faster biodegradation rate than that of pure PCL itself, and the transparency corresponding to microstructure increase with increase of inorganic component content.

Propeller-like multicomponent microstructures: Self-assemblies of nanoparticles of poly(vinyl alcohol)-coated Ag and/or Cu2O.

Novel propeller-like multicomponent microstructures, which are actually self-assemblies of nanoparticles of poly(vinyl alcohol) (PVA)-coated Ag and/or Cu2O, were synthesized in aqueous solution of amphiphilic polyvinylacetone (PVKA) (ketalization degree D(H) = 0.549), via one-step in situ reduction of Ag+ and Cu2+ under gamma-ray irradiation, utilizing the low hydrolysis rate of PVKA in the dilute acidic solution. Herein, PVA chains are obtained from hydrolyzed PVKA. The reaction mechanism and the formation mechanism are proposed. The room temperature photoluminescence spectrum has also been applied to explore the optical property.

Synthesis and characterization of water-soluble multiwalled carbon nanotubes grafted by a thermoresponsive polymer.

Water-soluble multiwalled carbon nanotubes (MWNTs) with temperature-responsive shells were successfully prepared by grafting poly (N-isopropylacrylamide) (PNIPAM) from the sidewalls of MWNTs, via surface reversible addition-fragmentation chain transfer (RAFT) polymerization using RAFT agent functionalized MWNTs as the chain transfer agent. Thermogravimetric analysis (TGA) measurements showed that the weight composition of the as-grown PNIPAM polymers on the MWNTs can be well controlled by the feed ratio (in weight) of NIPAM to RAFT agent functionalized MWNTs (MWNT-SC(S)Ph). The MWNT-g-PNIPAM has good solubility in water, chloroform, and tetrahydrofuran (THF). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images also showed that the MWNT-g-PNIPAM was dispersed individually and eventually bonded with the polymer layer by surface RAFT polymerization. The PNIPAM shell is very sensitive to a change of temperature. This method could find potential applications by grafting other functional polymer chains onto MWNTs.

[Spectral study on intermolecular coupling interaction and relation to microstructure in polyester/inorganic hybrid materials].

The coupling form of the polymeric-inorganic component and the relation between intermolecular special hydrogen bonding interaction and the microstructure of crystallizable polymer, as well as micro-phase separation scale in non-covalently coupled poly (epsilon-caprolactone) (PCL)/silica (SiO2) hybrid materials were investigated by means of Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results show that the coupling form between PCL and SiO2 mainly depend on a strong intermolecular hydrogen bonding interaction in the hybrid system. The hydrogen bonding strength increases with increasing TEOS content, while the crystallization of PCL decreases, and the optical transparency of hybrid materials increases. In addition, it affects the scale of micro-phase separation in hybrid materials.

In situ formation of Ag flowerlike and dendritic nanostructures in aqueous solution and hydrolysis of an amphiphilic block copolymer.

Silver flowerlike and dendritic nanostructures were synthesized in an aqueous solution of a hydrolysable amphiphilic block copolymer polyvinylacetone (PVKA) via in situ reduction of Ag(+) and hydrolysis of PVKA at room temperature. Compared with a previous result, the complete hydrolysis time of PVKA is greatly shortened in this process.