A two-phase method is exploited to prepare many kinds of nearly monodisperse, highly crystalline, size- and shape-controlled, surface-property-tunable inorganic nanocrystals, such as metal, semiconducting, magnetic, dielectric, and rare earth nanocrystals. The reaction of the two-phase system happens at the interface between the oil (nonpolar) and water (polar) phases and the interface is an exclusive site for both nucleation and growth. Interestingly, many solvent pairs with a clear interface can be applied to synthesize inorganic nanocrystals successfully. Generally, as-prepared nanocrystals with organic ligands are soluble in nonpolar solvents. Furthermore, exchange of ligands can also be realized readily and the final nanocrystals can be soluble in polar solvents. This two-phase method is a simple, reproducible, and general route and is becoming as powerful an approach as other solution-based synthetic approaches to high-quality inorganic nanocrystals.

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In this work, two industrial bimodal high density polyethylene resins, resin A and resin B, having similar molecular weight (M w ), molecular weight distribution (M wD ), and short-chain branching (SCB) content but different mechanical properties, were fractionated through cross-fractionation. The fractions were further characterized by GPC, 13 C NMR, DSC and FT-IR techniques. These two resins were firstly fractionated into two fractions, i.e., high-temperature and low-temperature fractions, via preparative solution crystallization fractionation. Resin A with much better mechanical properties contains more hightemperature fractions with longer crystallizable sequences. The SCB content in the low-temperature fraction of resin A is lower than that of resin B. Both low-temperature fractions were then further fractionated using solvent gradient fractionation (SGF). The characterization of SGF fractions indicates that most of the branches fall into the high molecular weight chains in both low-temperature fractions. However, the high molecular weight chains in the low-temperature fraction of resin A contain less SCB than that of resin B.KEY WORDS: Polyethylene (PE) / Fractionation of Polymers / Microstructure / Bimodal high density polyethylene (HDPE) resins benefit from their bimodality by having the strength and stiffness of HDPE, whilst retaining the high-stress-crack resistance and processability of a unimodal medium density polyethylene. 1Such bimodal HDPE resins are ideally suited to the application demands of pipes for gas and water distribution.Bimodal HDPE resins are produced by tandem processes that use reactor combinations of loop, slurry, and gas-phase by themselves or in combination with one another. In the first reactor, high amounts of hydrogen are fed with ethylene. This process leads to the formation of low-molar-mass polyethylene. The second reactor is loaded with much less hydrogen to form a high-or very high-molar-mass polyethylene.2 This process allows for further essential product modification, specifically the incorporation of comonomer in the long polymer chains within the second reactor. There is also a reversed mode wherein the high-molar-mass component is produced firstly, followed by a low-molar-mass component. These products build up a polymer alloy in solid state with crystalline and amorphous regions in between. The crystalline regions are mainly formed by low-molar-mass homo-polyethylene. The high-molar-mass copolymers form the amorphous regions and act as tie molecules that connect the crystal lamellae ( Figure 29 in ref 2). These tie molecules that possess short-chain branching (SCB) effectively hinder the pullout of the polymer chains from the crystallites. In this manner, the strength and resistance to slow crack growth of the resin are greatly improved finally.Recently, there has been an emphasis in developing relations between microstructure and end-use physical/mechanical properties of bimodal HDPE resins. Many investigators have pointed out that the amount and distribution of S...

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Three Polypropylene/Poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys produced by a two-stage slurry/gas polymerization had different ethylene contents and mechanical properties, which were achieved by controlling the copolymerization time. The three alloys were fractionated into five fractions via temperature rising dissolution fractionation (TRDF), respectively. The chain structures of the whole samples and their fractions were analyzed using high-temperature gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), 13 C nuclear magnetic resonance ( 13 C NMR), and differential scanning calorimetry (DSC) techniques. These three in-reactor alloys mainly contained four portions: ethylenepropylene random copolymer (EPR), ethylene-propylene (EP) segmented and block copolymers, and propylene homopolymer. The increased copolymerization time caused the increased ethylene content of the sample. The weight percent of EPR, EP segmented and block copolymer also became higher. The more EPR content indeed improves the toughness of the alloy but lowers its stiffness. Increasing the ethylene content in the EPR fraction and EP segmented and block copolymer, as well as the suitable content of EPR, is believed to be the key factors resulting in the excellent toughnessstiffness balance of in-reactor alloys.KEY WORDS: PP/EPR In-Reactor Alloy / Fractionation / Microstructure / Isotactic polypropylene (iPP) is a thermoplastic material widely used as it offers interesting combinations of good mechanical performance, heat resistance, and fabrication flexibility. However, it has relatively poor impact resistance, especially at low temperatures. Its toughness could be improved by a variety of elastomers, 1-3 by adding a nucleating agent that reduces the average dimensions of the spherulites. 4The toughness could also be improved by copolymerization of propylene with ethylene or other olefins, 5-10 among which the copolymerization with ethylene is one of the most useful and effective methods. Polypropylene/poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys have been industrialized on a large scale.The in-reactor blending technology was developed by Montell Company, hence opening up new horizons for polyolefin materials. The technology involves bulk polymerization of propylene and gas-phase copolymerization of ethylene and propylene using spherical superactive TiCl 4 /MgCl 2 based catalyst systems.11-14 The use of a spherical catalyst allows a wider range of rubber content in the alloy and better control over phase structure to be achieved. The resulting spherical granules can be directly processed, eliminating the need for pelleting.The mechanism of the two-stage in-reactor blending technology is very complicated, depending on the nature of active species in the catalysts and polymerization process. Xu et al. had proposed that the iPP with active center still can copolymerized with propylene and ethylene in the second stage.6 A previous investigation of the composition and chain structure of the PP/EPR in-reactor ...

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