Search

Long-standing conventional synthetic methods limit the scope of polymer architectural design such as connectivity, sequence and symmetry. Herein, we report a series of star gradient copolymers with variable grafting densities and backbone lengths. These star copolymers were obtained by one-shot ring-opening metathesis polymerization (ROMP) of an ω-norbornenyl polystyrene macromonomer (PS) and an endo-norbornenyl penta-fluorophenyl ester monomer (PFP), mediated by the highly active Blechert's type three-arm olefin metathesis catalyst. The kinetic studies of the copolymerization process revealed that a gradient sequence distributed along the star backbone and the tapered structure changed with the feed ratio between the PS and PFP. These copolymers were further modified with the activated ester chemistry to afford novel star-polymer-based functional materials.

The binuclear half-sandwich scandium aminobenzyl/chloride complex [(Cp′)Sc(THF)Cl]2[p-(CH2C6H3(o-NMe2)−)2] (Cp′ = C5Me4SiMe3) (2) was synthesized by linking two scandium centers through a bis(amino...

We present a new cyclooctene monomer with abundant biorenewable limonene oxide as side group via simple esterification, which could be polymerized by ring-opening metathesis polymerization (ROMP) using Hoveyda-Grubbs second-generation catalyst (H2) to afford polymer with remarkably high head-to-tail regioregularity and high trans-stereoregularity, as well as precisely placed ether branches on every eighth backbone carbon. Due to the presence of easily functional oxirane in limonene oxide side chain, the polymer can be efficiently modified by thiol, or dibutyl phosphate that shows impart flame-resistant property, even bearing pendent cyclic carbonate groups by CO2 insertion catalyzed by tetrabutylammonium bromide. In all cases, the main chains of the polymer remain intact. Differential scanning calorimetry (DSC), thermal gravimetric analyzer (TGA) and the microscale combustion calorimeter test (MCC) were used to study the thermal properties and flame retardancy.

Hydrogenolysis of the scorpionate-supported barium alkyl complex (Tp^Ad,iPr)Ba[CH(SiMe3)2](THF) (Tp^Ad,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) afforded the dinuclear barium hydrido complex [(Tp^Ad,iPr)Ba(µ-H)]2 (2), which was characterized by NMR spectroscopy and single crystal X-ray analysis. Exposure of 2 with 1 atm of CO resulted in a reductive coupling process to form the cis-ethendiolate dianion (3). Reaction of 2 with one equivalent of PhCC-CCPh gave barium 1,4-diphenyl-2-butyne-1,4-diyl complex {[(Tp^Ad,iPr)Ba]2(PhCH-CC-CHPh) (4).

Norbornene macromonomers (MMs) with polystyrene (PS) or poly(tert-butyl acrylate) (PtBA) side chains were synthesized by a combination of atom-transfer radical polymerization (ATRP) and click reactions. A series of amphiphilic linear and star-shaped brush block copolymers were obtained through sequential ring opening metathesis polymerization (ROMP) of MMs by the use of the highly active olefin metathesis Blechert's catalyst and tri-functionalized Blechert's catalyst respectively, followed by hydrolysis reaction. These well-defined diblock molecular brushes can undergo further self-assembly to form spherical micelles in solution, which have been characterized using DLS, AF4-MALLS, AFM, TEM and fluorescence spectra. The dynamic diameter increases as the hydrophilic backbone content increases for the vast majority of the linear and star copolymers. Brush-arm star diblock amphiphilic copolymers have smaller hydrodynamic diameter and aggregation number than the corresponding linear analogues. Moreover, the critical micelle concentration (CMC) values of star diblock copolymers show less sensitive to the variety of composition.

A series of PB-g-SAN impact modifiers (polybutadiene particles grafted by styrene and acrylonitrile) are synthesized by seed emulsion copolymerization initiated by oil-soluble initiator, azobisiobutyronitrile (AIBN). The ABS blends are obtained by mixing SAN resin with PB-g-SAN impact modifiers. The mechanical behavior and the phase morphology of ABS blends are investigated. The graft degree (GD) and grafting efficiency (GE) are investigated, and the high GD shows that AIBN has a fine initiating ability in emulsion grafting of PB-g-SAN impact modifiers. The morphology of the rubber particles is observed by the transmission electron microscopy (TEM). The TEM photograph shows that the PB-g-SAN impact modifier initiated by AIBN is more likely to form subinclusion inside the rubber particles. The dynamic mechanical analysis on ABS blends shows that the subinclusion inside the rubber phase strongly influences the Tg, maximum tan δ, and the storage modulus of the rubber phase. The mechanical test indicates that the ABS blends, which have the small and uniform subinclusions dispersed in the rubber particles, have the maximum impact strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Three series of MBS core–shell impact modifiers were prepared by grafting styrene and methyl methacrylate onto PB or SBR seed latex in emulsion polymerization. All the MBS modifiers were designed to have the same total chemical composition, and MMA/Bd/St equals 30/42/28, which is a prerequisite for producing transparent blends with PVC. Under this composition, there were three different ways of arrangement for styrene in MBS, which led to the different structure of MBS modifier. The concentration of MBS in PVC/MBS blends was kept at a constant value of 20 wt.%. The effects of arrangement of St in MBS on the mechanical and optical properties of PVC/MBS blends were studied. The notched Izod impact test results showed that the MBS with a PB homopolymer core grafted with St had a lowest brittle–ductile transition (BDT) temperature and BDT temperature increased with the amount of St copolymerized with Bd in the core of MBS. The transparency of blends also increased with the amount of St copolymerized with Bd in the core. TEM results showed that the arrangement of St in MBS influenced the deformation behavior. Two deformation modes were observed in the blends: cavitation and shear yielding. When all St was grafted onto the PB rubber, both cavitation and debonding were observed, which relieve the triaxial tension and promote the shear yielding of the PVC matrix. When all St was copolymerized with Bd in MBS, no cavitation could be observed and only the shear yielding of the PVC matrix took place.