Kinetics study on melt grafting copolymerization of LLDPE with acid monomers using reactive extrusion method

Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetics studies on reactive extrusion were carried out for the difficulties as expected. In this work, the macromolecular peroxide-induced grafting of acrylic acid and methyl methacrylate onto linear low density polyethylene by reactive extrusion was chosen as the model system for the kinetics study; the samples were taken out from the barrel at five ports along screw axis and analyzed by FTIR, H-1 NMR, and ESR. For the first time, the time-evolution of reaction rate, the reaction order, and the activation energy of graft copolymerization and homopolymerization in the twin screw extruder were directly obtained. On the basis of these results, the general reaction mechanism was tentatively proposed. It was demonstrated that an amount of chain propagation free radicals could keep alive for several minutes even the peroxides completely decomposed and the addition of monomer to polymeric radicals was the rate-controlled step for the graft copolymerization.

Syntheses, crystal structures and magnetic properties of two heterometallic coordination polymers

Two heterometallic chain coordination polymers with the chemical formula {[Cu2Mn2L2(CH3OH)(H2O)] center dot 0.5CH(3)OH center dot 0.5CH(3)CH(2)OH}(n) (1) and {[Cu2Co2L2(H2O)(2)] center dot H2O}(n) (2) have been synthesized and characterized by IR, UV spectroscopy and single-crystal X-ray structural analysis, where H4L = 2-hydroxy-3-[(E)-({2-[(2-hydroxybetizoyl)amino]ethyl}imino)methyl] benzoic acid. Magnetic measurements showed that the two compounds exhibit antiferromagnetic coupling exchange interactions, and satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a linear four-spin arrangement with two isotropic magnetic exchange interactions.

Fabrication of arrays of silver nanoparticle aggregates by microcontact printing and block copolymer nanoreactors

A combination of microcontact printing and block copolymer nanoreactors succeeded in fabricating arrays of silver nanoparticle aggregates. A complex solution of polystyrene-block-poly(4-vinylpyridine) micelles and silver salt was used as an ink to form thin films or droplets on polydimethylsiloxane stamp protrusions. After these complex aggregates were printed onto silicon substrates under controlled conditions, highly ordered arrays of disklike, dishlike, and dotlike complex aggregates were obtained. A Subsequent oxygen reactive ion etching treatment yielded arrays of silver nanoparticle aggregates.

Reactive blending of modified polypropylene and polyamide 12: Effects of compatibilizer content on crystallization and blend morphology

The crystallization behavior and morphology of nonreactive and reactive melt-mixed blends of polypropylene (PP) and polyamide (PA12; as the dispersed phase) were investigated. It Was found that the crystallization behavior and the size of the PA12 particles were dependent on the content of the compatibilizer (maleic anhydride-modified polypropylene) because an in situ reaction occurred between the maleic anhydride groups of the compatibilizer and the amide end groups of PA12. When the amount of compatibilizer was more than 4%, the PA12 did not crystallize at temperatures typical for bulk crystallization. These finely dispersed PA12 particles crystallized co-incidently with the 1313 phase. The changes in domain size with compatibilizer content were consistent with Wu's theory. These investigations showed that crystallization of the dispersed phase Could not be explained solely by the size of the dispersion. The interfacial tension between the polymeric components in the blends may yield information on the fractionation of crystallization.

Neodymium oxide-assisted melt free-radical grafting of maleic anhydride on isotactic-polypropylene by reactive extrusion

Rare earth oxide, neodymium oxide (Nd2O3), -assisted melt free-radical grafting of maleic anhydride (MAH) on isotactic-polypropylene (i-PP) was carried out by reactive extrusion. The experimental results reveal that the addition of Nd2O3 into reactive system leads to an enhancement of the grafting degree of MAH, along with an elevated degradation of i-PP matrix. When Nd2O3 content is 4.5 mmol %, the increment of the grafting degree of MAH (maximally) is up to about 30% compared with that of the related system without adding Nd2O3, while the severest degradation of i-PP matrix simultaneously occurs. On the basis of the reaction mechanism of PP-g-MAH proposed before, the sequence of beta-scission and grafting reaction is discussed in detail. It is found that, for the reactive system studied, most tertiary macroradicals first undergo beta-scission, and then, grafting reaction with MAH takes place at the new radical chain ends. The imported Nd2O3 has no effect on the aforementioned reaction mechanism, whereas it enhances the initiating efficiency of the initiator, dicumyl peroxide (DCP).

Synthesis, characterization, properties and crystal structure of heterometallic 1D coordination polymers {[CuLZn center dot CuLZn(H2O)]center dot H2O}(n)

Copper-zinc heterometallic 1D chain coordination polymer has been synthesized and characterized by elemental analysis, and IR spectra etc. The crystal structure was determined by single-crystal X-ray diffraction analyses. The title complex is 1 D chain coordination polymer with the chemical formula {[CuLZn center dot CuLZn(H2O)]center dot H2O}(n), where H4L=N-(2-hydroxybenzamido)-N'-(3-carboxylsalicylidene)ethylenediamine. Its structural unit is comprosed of two tetranuclear cycles formed by two dissymmetrical tetranuclear units. These units polymerized each other to form 1 D chain coordination polymer.

Synthesis, structure and reactive mechanism of intermetallic W3Mg

Assisted by mechanical alloying and high-pressure technique, a new W3Mg intermetallic was formed. W3Mg amorphous mixture was obtained by mechanically alloying the pure metal powder mixtures at designated composition for 20 h. A new compound was found after the Subsequent high pressure and high temperature treatment. W3Mg intermetallic was identified as a tetragonal structure and the lattice parameter was a = 0.7880 nm, c = 0.7070 nm. The synthesis mechanism is also discussed in this paper.

Synthesis, structure and reactive mechanism of intermetallic W4Mg

Assisted by a mechanical alloying and high-pressure technique, a new W4Mg intermetallic was formed. W4Mg amorphous mixture was obtained by mechanically alloying the pure metal powder mixtures at designated composition for 20 h. A new compound was found after the subsequent high-pressure and high-temperature treatment. W4Mg intermetallic was identified as a cubic structure and the lattice parameter was a=0.4150 nm. The synthesis mechanism is also discussed in this paper.

Novel PPV-based light-emitting polymers containing siloxane moiety

Two PPV-based copolymers consisting siloxane linkage have been synthesized by melt condensation of bisphenol and dianilinodimethylsilane. The rigid PPV segments act as chromosphere and allow fine turning of band gap for blue-light emission, while the flexible siloxane units lead to the effective interruption of conjugation and the enhancement of solubility. The UV-vis absorption, photoluminescent and eletroluminescent properties have been studied.

Enhanced efficiency of light-emitting polymers through intra-molecular energy transfer

To enhance the photoluminescence and electroluminescence efficiency, light-emitting polymers with energy transferring chromophores including N,N,N'N'-phenylene-diamine, naphthalene-imide, oxadiazole, meta-phenylene vinylene are designed and synthesized.

AFM study of the self-assembly behavior of hexa-armed star polymers with a discotic triphenylene core

The size-armed polystyrenes and poly-(methyl methacrylate)s with a triphenylene core showed different self-assembling patterns, isolated cylinders for polySt on mico and highly ordered cylindrical pores for polyMMA on a silicon water. With a decrease of polymer concentration in tetrahydrofuran (HHF), the size and height of cylinders decreased for polySt, but fur polyMMA, the size and depth of the cylindrical pores increased. Slow evaporation of the solvent and a low molecular weight favored the formation of regular patterns.

Embossing of polymers using a thermosetting polymer mold made by soft lithography

In this article we present a mechanical pattern transfer process where a thermosetting polymer mold instead of a metal, dielectric, ceramic, or semiconductor master made by conventional lithography was used as the master to pattern thermoplastic polymers in hot embossing lithography. The thermosetting polymer mold was fabricated by a soft lithography strategy, microtransfer molding. For comparison, the thermosetting polymer mold and the silicon wafer master were both used to imprint the thermoplastic polymer, polymethylmethacrylate. Replication of the thermosetting polymer mold and the silicon wafer master was of the same quality. This indicates that the thermosetting polymer mold could be used for thermoplastic polymer patterning in hot embossing lithography with high fidelity.

Brittle-ductile transition of polymers and its percolation model

The brittle-ductile transition (BDT) of particle toughened polymers was extensively studied in terms of morphology, strain rate, and temperature. The calculation results showed that both the critical interparticle distance (IDc) and the brittle-ductile transition temperature (T-BD) of polymers were a function of strain rate. The IDc reduced nonlinearly with increasing strain rate, whereas T-BD increased considerably with increasing strain rate. The effects of temperature and plasticizer concentration on BDT were discussed using a percolation model. The results were in agreement with the experiments.

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 degreesC were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R-g and hydrodynamic radius, R-h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 degreesC were discussed according to the scaling relationships between R-g, R-h and M and the rho-ratio (p = R-g/R-h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.

Reactive compatibilization of polyamide 6 with isocyanate functionalized ethylene-propylene copolymer

Reactive compatibilization of ethylene-propylene copolymer functionalized with allyl (3-isocyanato-4-tolyl) carbamate (TAI) isocyanate (EPM-g-TAI) and polyamide 6 (PA6) was investigated in this paper, FTIR analysis revealed the evidence of a chemical reaction between the end groups of PA6 and EPM-g-TAI. Thermal, rheological, morphological, and mechanical properties of the resultant system were examined, DSC analysis indicated that the crystallization of PA6 in Pa6/EPM-g-TAI blends was inhibited, due to the chemical reaction that occurs at the interface of PA6 and EPM-g-TAI. Rheological measurement showed that complex viscosity and storage modulus of PA6/EPM-g-TAI were both dramatically enhanced compared to those of PA6/EPM at the same blending composition. After examining the morphology of both blending systems, smaller particile sizes, more homogeneous distribution of domains and improved interfacial adhesion between matrix and domains were observed in the compatibilized system. Mechanical properties such as tensile strength. Young's modulus, flexural strength and modulus, as well as notched and un-notched impact strength of PA6/EPM-g-TAI blends were also found to improve gradually with increasing the content of grafted TAI.