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Free-radical polymerizations of vinyl monomers under 60 Co γ-ray irradiation in the presence of benzyl 9H-carbazole-9-carbodithioate (BCCDT) have been studied. The polymers obtained were characterized by gel permeation chromatography (GPC) and 1 H nuclear magnetic resonance ( 1 H NMR) spectroscopy. The results for the polymerization of methyl acrylate show that the molecular weight increases linearly with monomer conversion, that the molecular weight distribution is fairly narrow (even equal to 1.01) and that a linear relationship exists between In([M) 0 /[M]) and polymerization time. All the evidence suggests that BCCDT is a good control agent and that the polymerization has excellent living characteristics. For styrene, the polymerization is a controlled process, although it is very slow, whereas the polymerization of methyl methacrylate is uncontrolled. To the best of our knowledge, this is the first time that dithiocarbamate has been used in γ-ray initiated living free radical polymerization.

Introducing isocyanate (NCO) groups onto the surface of expanded graphite (EG) was achieved by treatment of the EG with excess toluene-2,4-diisocyanate in dimethyl sulfoxide (DMSO). The reaction of NCO group on the EG with the hydroxyl group in the poly(ethylene oxide) methyl ether (MPEO) to yield MPEO-grafted EG was carried out for modifying the surface properties of graphite. The influence factors, such as reaction time, temperature and the ratio of the reactants, on the grafting reaction and grafting ratio were investigated.

Amphiphilic block comb-shaped copolymers, poly[poly(ethylene oxide) methyl ether acrylate]-block-polystyrene [P(A-MPEO)-block-PSt] with PSt as a handle, were successfully synthesized via a macromonomer technique. The reaction of MPEO with acryloyl chloride yielded a macromonomer, A-MPEO. The macroinitiator PSt capped with the dithiobenzoate group (PSt-SC(S)Ph) was prepared by reversible addition–fragmentation transfer (RAFT) polymerization of styrene in the presence of benzyl dithiobenzoate, and used as macroinitiator in the controlled radical block copolymerization of A-MPEO at room temperature under 60Co irradiation. After the unreacted macromonomer A-MPEO had been removed by washing with hot saturated saline water, block comb-shaped copolymers were obtained. Their structure was characterized by 1H NMR spectroscopy and gel permeation chromatography. The phase transition and self-assembling behaviour were investigated by atomic force microscope and differential scanning calorimetry. Copyright © 2004 Society of Chemical Industry

Monte Carlo simulations were used to investigate the compatibilizing effects of diblock copolymers in A/B/A–B diblock copolymer ternary blends and triblock copolymers in A/B/triblock copolymer ternary blends, respectively. The volume fraction of homopolymer A was 19% and was the dispersed phase. The simulation results show that diblock copolymers with longer A-blocks are more efficient as compatibilizers, and symmetric triblock copolymers with a shorter middle block length are easily able to bridge each other through the association of the end blocks. This kind of triblock copolymers have relatively high ability to retard phase separation as compatibilizers.

We have investigated systematically the morphology of thin films spin-coated from solutions of a semicrystalline diblock copolymer, poly(l-lactic acid)-block-polystyrene (PLLA-b-PS), in solvents with varying selectivity. In neutral solvents (chloroform and tetrahydrofuran (THF)), a spinodal-like pattern was obtained and the pattern boundary was sharpened by diluting the solution. Meanwhile, loose spherical associates, together with larger aggregates composed of these associates by unimer bridges, formed partly due to crystallization of the PLLA blocks in relatively concentrated solutions. In slightly PS-selective solvent (e.g., benzene), both loose and compact spherical micelles were obtained, depending on the polymer concentration, coexisting with unimers. When enhancing the selectivity with mixed solvents, for example, mixing the neutral solvent and the slightly selective solvent with a highly PS-selective solvent, CS2, loose assemblies (nanorods in CS2/THF mixtures and polydisperse aggregates in CS2/be...

The complex microstructures assembled by amphiphilic diblock copolymer in dilute solution have been investigated by the application of real-space self-consistent field theory in two-dimensional space. Different micelles, such as spherelike micelles, rodlike micelles, and vesicles are produced. The simulations show that vesicles are metastable in dilute solution within a certain range of some parameters. The mechanism for the formation of micromorphologies, especial vesicles, is discussed.

Poly(p-nitrophenyl acrylate)s (PNPAs) with different molecular mass and narrow polydispersity were successfully synthesized for the first time by reversible addition–fragmentation transfer (RAFT) polymerization with azobisisobutyronitrile (AIBN) as an initiator and [1-(ethoxy carbonyl) prop-1-yl dithiobenzoate] as the chain-transfer agent. Although the molecular mass of PNPAs can be controlled by the molar ratio of NPA to RAFT agent and the conversion, a trace of homo-PNPA was found, especially at the early stage of polymerization. The dithiobenzoyl-terminated PNPA obtained was used as a macro chain-transfer agent in the successive RAFT block copolymerization of styrene (St) with AIBN as the initiator. After purification by two washings with cyclohexane and nitromethane to remove homo-PSt and homo-PNPA, the pure diblock copolymers, PNPA-b-PSt's, with narrow molecular weight distribution were obtained. The structural analysis of polymerization products by 1H NMR and GPC verified the formation of diblock copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4862–4872, 2004

Poly(styrene- co -acrylonitrile)/expanded graphite composite sheets with very low in-plane (8.5 × 10 −3 Ω cm) and through-thickness (1.2 × 10 −2 Ω cm) electrical resistivities have been prepared. The expanded graphite was made by oxidation of natural graphite flakes, followed by thermal expansion at 600 °C. Microscopic results disclosed that the expanded graphite has a legume-like structure, and each “legume” has a honeycomb sub-structure with many diamond-shaped pores. After soaking the expanded graphite with styrene and acrylonitrile monomers, the polymer/expanded graphite composite granules were obtained by in situ polymerization of the monomers inside the pores at 80 °C. The functional groups and microstructures of the oxidized graphite, expanded graphite and composites in the forms of particles or sheets were carefully characterized using various techniques, including X-ray powder diffraction, thermogravimetry, optical and electron microscopy. It was found that the honeycomb sub-structure survived after hot-pressing, resulting in a graphite network penetrating through the entire composite body, which produces a composite with excellent electrical conductivity.

The free radical polymerizations of methyl acrylate have been studied under γ-ray irradiation in the presence of the dithiocarbamates with different N-groups. The results indicate that the conjugation structure of the N-group of dithiocarbamate plays an important role in living free radical polymerization. The polymerizations reveal good living characteristics in the presence of dithiocarbamates (benzyl 1H-imidazole-1-carbodithioate, benzyl 1H-pyrrole-1-carbodithioate, benzyl 1H-indole-1-carbodithioate, and benzyl 9H-carbazole-9-carbodithioate) with N-aryl group. In contrast, the polymerization with benzyl N,N-diethyldithiocarbamate cannot be controlled, and the obtained polymer has a broad molecular weight distribution or even crosslink occurs. Moreover, polymerization rate is influenced by the conjugation structure of the N-group of dithiocarbamate, and the aromatic polycyclic structure of the N-group leads to slow polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5670–5677, 2004

Well-defined diblock and triblock copolymers composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) were successfully synthesized through the reversible addition-fragmentation chain transfer polymerization ofN-isopropylacrylamide (NIPAM) with PEO capped with one or two dithiobenzoyl groups as a macrotransfer agent. 1 H NMR, Fourier transform infrared, and gel permeation chromatography instruments were used to characterize the block copolymers obtained. The results showed that the diblock and triblock copolymers had well-defined structures and narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight < 1.2), and the molecular weight of the PNIPAM block in the diblock and triblock copolymers could be controlled by the initial molar ratio of NIPAM to dithiobenzoate-terminated PEO and the NIPAM conversion.

Monte Carlo method was applied to simulate self-condensing vinyl polymerization (SCVP) in the presence of multifunctional initiator with unequal reactive rate constants. Simulations showed that, with the increase of reactivity of multifunctional initiator, the molecular weight distribution decreases, the fraction of multi-armed hyperbranched polymers increases, and the best reactivity ratio of multifunctional initiator to inimor is 10/1; the reactivity difference of two active sites in inimer has strong effects on the molecular weight distribution and degree of branching. The branch degree and fraction of branch-points depend on both the conversion of double bonds and reactivity difference of two active centers in inimer, and have no relation with the adding of multifunctional initiator. The density distribution of degree of branching further shows common self-similarity in SCVP.

Poly(4-vinylpyridine) (P4VP) and block copolymer, poly(4-vinylpyridine–b-styrene) (P4VP-b-PSt) were prepared by atom transfer radical polymerization (ATRP) using 1-phenylethyl chloride as initiator, CuCl and 5,5,7,12,12,14–hexamethyl-1,4,8,11-tetraazamacrocyclotetradecane (Me6[14]aneN4) as catalyst and ligand. The polymerization of 4VP was carried out in 2-propanol at 40 °C. GPC and NMR studies show that the plot of ln([4VP]0/[4VP]) against the reaction time is linear, and the molecular weight of the resulting P4VP increased linearly with the conversion. Within 3 h, the conversion can reach almost 90%. P4VP-b-PSt amphiphilic block copolymer with low polydispersity index (Mw/Mn ≈ 1.2) is also obtained by ATRP of St in DMF at 110 °C using P4VP–Cl as macroinitiator, CuCl/ Me6[14]aneN4 as catalyst.

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.

A two-armed polymer with a crown ether core self-assembles to produce macroporous films with pores perpendicularly reaching through the film down to the substrate. A possible assembling mechanism is discussed. The pore size can be conveniently adjusted by changing the solution concentration. These through-hole macroporous films provide a template for fabricating an array of Cu nanoparticle aggregates.

Block copolymers, poly(LLA- b -St)s and triblock copolymes, poly(LLA- b -St- b -MMA)s have been synthesized by the combination of the atom transfer radical polymerization (ATRP) with ring-opening polymerization (ROP) using bifunctional initiator β-hydroxylethyl α-bromoisobutyrate (HEBIB) without intermediate function transformation. The molecular weight (MW) and the molecular weight distribution (MWD) can be controlled. The structures of the copolymers were confirmed by 1 H NMR spectroscopy and GPC.

The copolymerization of styrene with maleic anhydride (MAh) in the presence of 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate was carried out under UV irradiation at room temperature, and showed ‘living’ polymerization nature which was evidenced by: linear evolution of molecular weight with conversion; and narrow molecular weight distribution (Mw/Mn = 1.08–1.20). The compositional analysis and the sequence structural information of the copolymer obtained from Distortionless Enhancement by Polarization Transfer (DEPT) NMR experiments demonstrated that the copolymers obtained possess strictly alternating structure. © 2003 Society of Chemical Industry

The miktoarm ABC star copolymer with three different branches, polystyrene (PS), poly(1,3-dioxepane) (PDOP), and poly(methyl methacrylate) (PMMA), was successfully prepared. PS with two transfer groups, hydroxyl and dithiobenzoate groups [PS-HECA-SC(S)Ph], was synthesized by the reaction of a dithiobenzoate group at the end of PS with hydroxyethylene cinnamate (HECA) in tetrahydrofuran solution. Then, the cationic ring-opening polymerization of 1,3-dioxepane was initiated by triflic acid in the presence of PS-HECA-SC(S)Ph and diblock copolymer, PS-PDOP, was formed. Finally, the diblock copolymer with the dithiobenzoate group situated between the two blocks was used in the reversible addition–fragmentation transfer (RAFT) process of methyl methacrylate (MMA). The miktoarm ABC star copolymer S(PS)(PDOP)(PMMA) was characterized by 1H NMR spectroscopy and gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1243–1250, 2003

Hyperbranched copolymers were synthesized by self-condensing vinyl copolymerization (SCVCP) of 2-[(2-bromopropionyl)oxy]ethyl acrylate (BPEA) and methyl acrylate (MA) in the presence of a tetrafunctional initiator, 6,6-bis[5-(α-bromoisobutyryloxy)-2-oxapentyl]-4,8-dioxaundecane-yl-1,11 dibromoisobutyrate (THABI). The structures of the polymers obtained were characterized by NMR and size exclusion chromatography/right-angle laser-light scattering/differential viscometry/differential refractometry. Molecular weight, molecular weight distribution and degree of branching were influenced by conversion and initial feed molar ratio of BPEA, MA and THABI. The addition of THABI can narrow the polydispersity of the hyperbranched copolymers obtained. The results are consistent with our previous simulation work. © 2003 Society of Chemical Industry

It is the first report on the atom transfer radical ring-opening copolymerizations of unsaturated cyclic acetal: 4,7-dimethyl-2-methylene-1,3-dioxepane (DMMDO) with conventional vinyl monomers, styrene (St), acrylonitrile (AN) and methyl acrylate (MA) in the presence of ethyl α-bromobutyrate as initiator and CuBr/2,2′-bipyridyl as catalyst/ligand at 110 °C. 1H, 13C NMR and IR data show that the copolymerizations of DMMDO with St (or AN or MA) yield the copolymers, poly(DMMDO-co-St) [or poly(DMMDO-co-AN) or poly(DMMDO-co-MA)] with narrow molecular weight distribution, and low content of DMMDO in the copolymers for electron-donor St, higher contents of DMMDO for electron-acceptor AN or MA are observed.

Polymer microspheres were prepared by dispersion copolymerization of styrene with poly(oxyethylene) (peo) macromonomer. A dispersion terpolymerization of styrene, PEO macromonomer and acrylic acid was also conducted to prepare polymer microspheres with both surface carboxyl groups and PEO polymer chains. The microspheres thus obtained were characterized with TEM, IR, and X-ray photoelectron spectroscopy analyses. Palladium nanoparticles were then formed on the surface of these copolymer microspheres forming polymer/metal nanocomposites which were then studied by TEM and X-ray diffraction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2732–2736, 2002

A new polymerization strategy, consisting of nucleophilic substitution reaction between CS32-, immobilized on a polymeric support, and dimethyl α,α′-dibromoalkylanedioate in solution, leads to the formation of polytrithiocarbonates. When n = 0, 1 in CH3OOCCHBr(CH2)nCHBrCOOCH3 (α,α′-dibromoalkylanedioate), only five- or six-membered cyclic trithiocarbonates were obtained; n ≥ 2 resulted in the formation of polytrithiocarbonates.

Styrene-rich copolymer/2-hydroxyethyl acrylate rich copolymer [P(St-co-HEA)] particles were prepared by emulsifier-free emulsion copolymerization of St with HEA. Fourier transform IR spectroscopy was used to follow the change of HEA content in the particles. The results of X-ray photoelectron spectroscopy measurements indicate that the HEA unit on the surface is richer than that inside the particles. Grafting of acrylamide (AAm) onto the surface of P(St-co-HEA) particles was carried out in an aqueous medium containing ceric ions. IR spectroscopy and laser light scattering were used to investigate the grafting polymerization. The morphologies of P(St-co-HEA) and P(St-co-HEA)AAm particles were observed using a transmission electron microscope. The amphiphilic properties of the particles were characterized by diesel oil and water.

Polystyrene-block-poly(5,6-benzo-2-methylene-1,3-dioxepane) (PSt-b-PBMDO), poly(methyl methacrylate)-block-PBMDO (PMMA-b-PBMDO) and poly(methyl acrylate)-block-PBMDO (PMA-b-PBMDO) were synthesized by two-step atom transfer radical polymerization (ATRP) of conventional vinyl monomers, then BMDO. First, the polymerization of St, or MMA, or MA was realized by ATRP with ethyl α-bromobutyrate (EBrB) as initiator in conjunction with CuBr and 2,2′-bipyridine (bpy). After isolation, polymers with terminal bromine, PSt-Br, PMMA-Br and PMA-Br, were obtained. Second, the ATRP of BMDO was performed by using macroinitiator, PSt-Br (or PMMA-Br, PMA-Br) in the presence of CuBr/bpy. The structures of block copolymers were characterized by 1 H NMR spectra. Molecular weight and polydispersity index were determined on gel permeation chromatograph. Among the block copolymers obtained, PMA-b-PBMDO shows the most narrow molecular weight distribution.

The copolymerization of styrene (St) with maleic anhydride (MAh) performed at 22 °C in the presence of dibenzyl trithiocarbonate exhibits controlled nature evidenced by: narrow molecular weight distribution, controlled molecular weight and first-order polymerization kinetics. The composition analysis of the copolymers obtained by 13 C NMR spectra shows the molar fraction of St in obtained copolymers is almost equal to 0.5 throughout the copolymerization. The sequence structure of the copolymer was obtained from DEPT experiments by recording the spectra at π/4 and 3π/4, and then combining them together, the results showed that the copolymers obtained possessed well-defined alternating structure. The experiment shows that charge-transfer-complex formed from St and MAh participates in both initiation and chain growth throughout the copolymerization.

The dynamic mean-field density functional method, driven from the generalized time-dependent Ginzburg–Landau equation, was applied to the mesoscopic dynamics of the multi-arms star block copolymer melts in two-dimensional lattice model. The implicit Gaussian density functional expression of a multi-arms star block copolymer chain for the intrinsic chemical potentials was constructed for the first time. Extension of this calculation strategy to more complex systems, such as hyperbranched copolymer or dendrimer, should be straightforward. The original application of this method to 3-arms block copolymer melts in our present works led to some novel ordered microphase patterns, such as hexagonal (HEX) honeycomb lattice, core–shell HEX lattice, knitting pattern, etc. The observed core–shell HEX lattice ordered structure is qualitatively in agreement with the experiment of Thomas et al. [Macromolecules 31, 5272 (1998)].

By using free-radical RAFT living polymerization, we successfully grafted linear poly(N-isopropylacrylamide) (PNIPAM) chains onto a spherical PNIPAM/HEA copolymer microgel to form a novel core−shell nanostructure. Both the tethered PNIPAM shell and the copolymer microgel core shrunk as the temperature increased, but in different temperature ranges. In the range ∼28−32 °C, the tethered PNIPAM chains underwent a coil-to-globule transition, while in the range ∼32−35 °C, the shrinking of the copolymer core induced a re-stretching of the collapsed PNIAPM chains on its surface to form a polymer brush in poor solvent. Our results showed that in the re-stretching process, the average hydrodynamic volume per tethered PNIPAM chain remained a constant, confirming a prediction made a long time ago that the collapsed chains in poor solvent were incompressible.

Cationic ring-opening polymerization of 3-ethyl-3-hydroxylmethyl oxetane was carried out using BF3·O(C2H5)2 as initiator, and a branched polyether was formed. Typical SEC curves show that the polymer consists of two fractions: one has higher molecular weight (11.7×104∼ 9.2×104) and the other has lower molecular weight (3.8×103∼4.0×103). This probably resulted from the chain-tran sfer reaction of two propagating polymer chains. The structure of the polyEHMO formed was characterized by 1H and 13C NMR spectra. The degree of branching is mainly affected by the propagation mechanism. As the molar ratio of [I]0/[EHMO]0 in feed increased, the degree of branching also increased.

The preparation and characterization of amphiphilic ABC miktoarm star copolymers based on polystyrene, and poly(ethylene oxide), poly(methyl acrylate) or poly(N-isopropylacrylamide) blocks are described in this paper. First, macrotransfer agent polySt-MAh-S-C(S)Ph with maleic anhydride and a dithio group at one end of polymer chain was synthesized by the reaction of a dithio group at the end of the polystyrene with maleic anhydride (MAh) in tetrahydrofuran solution. The second, reversible addition−fragmentation chain transfer polymerization of methyl acrylate or N-isopropylacrylamide was carried out in the prescence of polySt-MAh-S-C(S)Ph and benzoyl peroxide. Finally, the anhydride group at the joint of two blocks was reacted with terminal hydroxyl group of poly(ethylene glycol methyl ether). The obtained ABC star copolymers were characterized by 1H NMR spectroscopy and gel permeation chromatography.

Two functional crown ether initiator, bis[4′-(2-bromobutyryl)]dibenzo-18-crown-6 (BBDC) was synthesized through the condensation of dibenzo-18-crown-6 with 2-bromobutyric acid in the presence of polyphosphoric acid. Atom transfer radical polymerizations of styrene (St), methyl acrylate, methyl methacrylate and butyl acrylate were carried out in bulk to produce the polymers with well-controlled molecular weights and narrow molecular weight distributions (1.12–1.32). Based on 1H NMR results, both the two bromides of BBDC initiated the polymerizations. The well-defined two-armed polymers were self-assemblized in the presence of potassium cations. Their morphologies of the film obtained were studied by atomic force microscopy with tapping mode.

Controlled/“Living” Radical Ring-Opening Polymerization of 5,6-Benzo-2-Methylene-1,3-Dioxepane Based on Reversible Addition-Fragmentation Chain Transfer Mechanism

A two-stage gas-coupled Stirling-type pulse tube cryocooler (SPTC) driven by a linear dual-opposed compressor has been designed, manufactured and tested. Both of the stages adopted coaxial structure for compactness. The effect of a cold double-inlet at the second stage on the cooling performance was investigated. The test results show that the cold double-inlet will help to achieve a lower cooling temperature, but it is not conducive to achieving a higher cooling capacity. At present, without the cold double-inlet, the second stage has achieved a no-load temperature of 11.28 K and a cooling capacity of 620 mW/20 K with an input electric power of 450 W. With the cold double-inlet, the no-load temperature is lowered to 9.4 K, but the cooling capacity is reduced to 400 mW/20 K. The structure of the developed cryocooler and the influences of charge pressure, operating frequency and hot end temperature will also be introduced in this paper.

Polytetrahydrofuran (PTHF)/poly(1,3-dioxepane) (PDOP)/polystyrene (PSt) ABC miktoarm star copolymers were synthesized by combination of cationic ring-opening polymerization (CROP) and atom transfer radical polymerization. Two different functional groups, carboxylic acid and CHBr, were capped at one end of PTHF through the reaction of PTHF−OH with 2-bromosuccinic anhydride (BSA). After PTHF−OOCCHBrCH2COOH reacted with thionyl chloride, block copolymer PTHF-b-PDOP was synthesized by CROP of DOP at −30 to −35 °C with PTHF−OOCCHBrCH2COCl and AgClO4 as catalyst. Finally, (PTHF) (PDOP)−Br was used to initiate the polymerization of St in the presence of CuBr and bipyridine at 110 °C, and ABC miktoarm star polymer, s-[(PTHF) (PDOP) (PSt)] was successfully prepared. The copolymers obtained were characterized by 1H NMR and gel permeation chromatography measurements.

The polymerizations of styrene (St), methyl acrylate (MA), and butyl acrylate (BuA), carried out under UV irradiation at room temperature in the presence of dibenzyl trithiocarbonate (DBTTC) were found to display living free-radical polymerization characteristics as evidenced by: narrow molecular weight distribution, linear increase of molecular weight with increasing conversion, well-controlled molecular weight, and first-order polymerization kinetics. The triblock copolymer, PMA-PSt-PMA, with narrow polydispersity and well-defined structure was successfully prepared using PMA-S-C(=S)-S-PMA as macro-photoinitiator under UV irradiation at room temperature. Based on GPC, NMR and FT-IR analyses, the structures of the polymers were obtained and the mechanism of the polymerization was proposed.

The block copolymer polystyrene-b-poly[2-(trimethylsilyloxy)ethylene methacrylate] (PSt-b-PTMSEMA) was synthesized using atom-transfer radical polymerization (ATRP). The hydrolysis of PSt-b-PTMSEMA led to the formation of an amphiphilic block copolymer, polystyrene-b-poly(2-hydroxylethyl methacrylate) (PSt-b-PHEMA), which was characterized by GPC and H-1-NMR. TEM showed that the PSt-b-PHEMA formed a micelle, which is PSt as the core and PHEMA as the shell. Under appropriate conditions, the nickel or cobalt ion cause chemical reactions in these micelles and could be reduced easily. ESCA analysis showed that before reduction the metal existed as a hydroxide; after reduction, the metal existed as an oxide, and the metal content of these materials on the surface is more than that on the surface of the copolymer metal ion. XRD analysis showed that the metal existed as a hydroxide before reduction and existed as a metal after reduction.

Novel narrow distributed nanospheres with polystyrene shells and cross-linked poly(methacrylamide) (polyMMA) cores were fabricated. The cross-linking of the poly(p-nitrophenyl methacrylate) (polyNPMA) cores of micelles, formed by the self-assembly of well-defined block copolymer (poly(styrene-b-p-nitrophenyl methacrylate) (poly(St-b-NPMA))) in chloroform, was realized in the solutions directly through the reaction with ethylenediamine instead of in films as in other cases reported [3] , [8] , [9] , [10] , [11] . Further substitution of p-nitrophenol units with ammonia produced polyMMA cores. Dynamic light scattering was used to monitor the self-assembly process of poly(St-b-NPMA) in chloroform, the effects of the cross-linking and amino-substitution of the polyNPMA cores on the morphologies of the micelles, meanwhile, the changes in the chemical structures were verified by FTIR.

A series of hyperbranched polyacrylate copolymers have been synthesized by self-condensing vinyl copolymerization (SCVCP) of 2-(2-bromopropionyloxy)-ethyl acrylate (BPEA) and methyl acrylate (MA) in the presence of CuBr and bipyridine. The structures and properties of the polymers obtained are characterized by NMR and SEC/RALLS/DV/RI measurements. The effects of reaction conditions on molecular weight (MW), molecular weight distribution (MWD) and degree of branching (DB) are investigated. © 2002 Society of Chemical Industry

Gate-recessed AlGaN/AlN/GaN metal-oxide-semiconductor heterostructure high-mobility transistors (MOS-HEMTs) on SiC substrate are fabricated. The device with a gate length of 0.6 μm and a gate periphery of 100 μm exhibits a maximum dc drain current density of 1.59 A/mm at VGS = 3 V with an extrinsic transconductance (gm) of 374 mS/mm. An extrinsic current gain cutoff frequency (fT) of 19 GHz and a maximum oscillation frequency (fmax) of 50 GHz are deduced from S-parameter measurements. The output power density is 13 W/mm, and the associated power-added efficiency is 73% at 4-GHz frequency and 45-V drain bias. The power performance is comparable to state-of-the art AlGaN/GaN HEMTs, which demonstrates the great potential of gate-recessed MOS-HEMTs as a very promising alternative to GaN HEMTs.

A series of hyperbranched polyacrylates were synthesized by self-condensing vinyl polymerization (SCVP) of 2-[(2-bromobutyryl)oxy]ethyl acrylate (BBEA). A tetrafunctional atom transfer radical polymerization (ATRP) initiator (THABI) capped with bromoisobutyrate, which has higher reactivity than the initiating site of monomer, was used as core-forming molecules. The structure and properties of the obtained polymers were characterized by NMR and SEC/RALLS/DV/RI. The effect of the tetrafunctional initiator on molecular weight and molecular weight distribution of polymers was studied.

A series of hyperbranched polymers were synthesized in high yield by self-condensing vinyl polymerization (SCVP) of 2-[(2-bromobutyryl)oxy]ethyl methacrylate (BBEM) in the presence of an ATRP initiator: THABP (a tetrafunctional initiator)/CuBr/bpy. The structure and properties of the polymers obtained were characterized by NMR and SEC/RALLS/DV/RI. The effect of the tetrafunctional initiator on degree of branching (DB), molecular weight and molecular weight distribution of polymers was studied.

Self-assembly of symmetric diblock copolymers in confined state has been investigated by means of Monte Carlo simulation method. The symmetric diblock copolymers were confined in two- (parallel walls or circle) or in three-dimensional (spherical or cylindrical) space. There are interactions between these boundaries and the symmetric diblock polymers. These interactions and boundary shape resulted in the formation of novel self-assemble structures, e.g., strip, circle, core-multishell, and multibarrel-layer structures. Simulation results predicated that it is possible to design different phase structures for block copolymers by adjusting boundary shape and boundary-block copolymer interactions.

The polymerization of methyl acrylate and styrene was carried out under 60 Co γ-irradiation in the presence of dithiobenzoic acid (DTBA) and the kinetics of the polymerization of methyl acrylate was studied. The polymerizations are of a controlled free radical character. The molecular weight of the polymers increases with increasing monomer conversion, and the polydispersities of polystyrene and poly(methyl acrylate) are less than 1,4

Triblock copolymers were prepared under 60 Co γ-irradiation in the presence of a trithiocarbonate macroinitiator. The triblock copolymers, PSt-PMA-PSt and PMA-PSt-PMA have well-defined structures, controlled molecular weight and narrow molecular weight distribution. The reaction mechanisme is discussed

Poly(styrene-co-acrylic acid)metal (P(St-co-AA)metal) particles were prepared by chemical metal deposition. Characterization was carried out by transmission electron microscopy and X-ray diffraction. Dielectric behavior and determination of magnetic properties of P(St-co-AA)metal microspheres were investigated. Thermogravimetric analysis showed that the Curie temperature (TC) of P(St-co-AA)metal was lower than the TC of the corresponding block metal and fine metal particles. The susceptibility and hysteresis loop of P(St-co-AA)metal were studied. The results showed that the composite particles are soft magnetic materials.

Cationic ring-opening polymerization of 3,3-dimethyloxetane using C(CH 2 OCH 2 CH 2 CO - ClO 4 - ) 4 as initiator was examined, The results from 1 H NMR, FTIR and GPC measurements show that a star-shaped poly(3,3-dimethyloxetane) was obtained, and cyclo-oligomers were negligible. The polymerization process was followed by 1 H NMR. Polymerization kinetics were investigated, and the mechanism of the polymerization was discussed.

Polystyrene (PSt)/polytetrahydrofuran (PTHF) A 2 B 2 miktoarm star copolymers were prepared by transformation of cationic ring-opening polymerization (CROP) to atom transfer radical polymerization (ATRP). The synthetic approach involves the synthesis of PTHF with two secondary bromine groups in the center of a macromolecular chain, (PTHF) 2 Br 2 , by the CROP of THF with the symmetric tetrafunctional initiator α,ω-dibromosebasionyl dichloride [ClCOCHBr(CH 2 ) 6 CHBrCOCl] in conjunction with silver perchlorate; (PTHF) 2 Br 2 was used to initiate the polymerization of styrene to form (PSt) 2 (PTHF) 2 star copolymer. The copolymer obtained was characterized by gel permeation chromatography and 1 H NMR spectrum. The hydrolysis of (PTHF) 2 Br 2 was also investigated.

The Monte Carlo method is applied to simulate the copolymerization of a self-condensing vinyl monomer and a conventional vinyl monomer in the presence of a multifunctional initiator at equal rate constanits. With the increase of the molar ratio of self-condensing vinyl monomer in the monomer composition, the number average degree of polymerization decreases and the weight average degree of polymerization decreases at a lower conversion of double bonds but increases at a higher conversion of double bonds. The molecular weight distribution, PI, changes from 1.01 to 12.0 and the average degrec of branching, DB, increases from 0 to 0.456, We discovered that the addition of conventional vinyl monomer can modify the ratio of multi-arm hyperoranched macromolecules in the product, i.e., the content of macromolecules with core moiety will increase with the increase of the ratio of conventional vinyl monomer. The possibility of controlling PI and DB by changing the conversion and monomer compositions is demonstrated.

A new four-armed tetraol, poly(1,5,7,11-tetraoxaspiro [5,5] undecane) tetraol (poly(TOSU)), was prepared by the cationic ring-opening polymerization of TOSU using BF 3 ·OEt 2 as initiator. Its structure was characterized by 1 H, 13 C NMR and FTIR spectra. GPC curves showed that the polymer obtained had two fractions with higher and lower molecular weights; however, each had a relatively narrow molecular weight distribution. The molecular weights of the polycarbonate tetraols were controlled by the molar ratio of TOSU consumed to initial BHDU. The mechanism of the polymerization was discussed.

Seeded emulsion polymerization of methyl methacrylate (MMA) or styrene (ST) was carried in the presence of different vinyl-containing polysiloxane latices (SV- * ) and the core-shell particles with poly(methyl methacrylate) (PMMA) or polystyrene (PST), as the shells were obtained under different polymerization conditions. Besides the compatibility of the vinyl monomer and its polymer with polysiloxane and the reaction between vinyl monomer with vinyl group of polysiloxane, the content of vinyl group of seed polysiloxane has influence on the morphology and component of the resulted composite particles. The mechanism for the formation of core-shell structure is discussed.

The polymerization of acrylic acid (AA) was performed under 60 Co irradiation in the presence of dibenzyl trithiocarbonate at room temperature, and well-defined poly(acrylic acid) (PAA) with a low polydispersity index was successfully prepared. The gel permeation chromatographic and 1 H NMR data showed that this polymerization displays living free-radical polymerization characteristics: a narrow molecular weight distribution (M w /M n = 1.07-1.22), controlled molecular weight, and constant chain-radical concentration during the polymerization. Using PAA-S-C(=S)-S-PAA as an initiator, the extension reaction of PAA with fresh AA was carried out under 60 Co irradiation, and the results indicated that this extension polymerization displayed controlled polymerization behavior.