Polyolefins

Whiteley, K. S.; Heggs, T. Geoffrey; Koch, Hartmut; Mawer, Ralph L.; Immel, Wolfgang

doi:10.1002/14356007.a21_487

Cited by 37 publications

(34 citation statements)

References 112 publications

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“…Polyolefins made with metallocene catalysts will not, in principle, be adequate for some types of processing. However, various methods have been proposed for the production of polymers with multimodal MWDs and controlled molecular weights: (1) the use of physical polymer mixtures of different weight‐average molecular weights ( M w 's); (2) the use of reactors in series, each reactor being maintained at different polymerization conditions, including the temperature and pressure; (3) the variation of the operation conditions, such as the temperature and concentrations of the comonomer and hydrogen, in a single reactor during polymerization; and (4) the simultaneous use of more than one type of metallocene complex during polymerization 1, 3, 4…”

Section: Introductionmentioning

confidence: 99%

Polypropylene reactor mixture obtained with homogeneous and supported catalysts

Bastos

Marques

2004

J. Polym. Sci. A Polym. Chem.

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Propylene polymerizations were performed with homogeneous ϕ2C(Flu)(Cp)ZrCl2 and SiMe2(Ind)2ZrCl2 catalyst mixtures and with mixtures supported on the zeolite acid mordenite. The polymerizations were performed in toluene and hexane/triisobutylaluminum at different temperatures and Al(MAO)/Zr concentration ratios. The effects of these variables on the catalyst activity were investigated with statistical experimental planning. The average molecular weights, molecular weight distributions, melting temperatures, and crystallinities of the obtained polymers were examined. The results showed lower activities for the homogeneous catalyst mixture than for the isolated systems. On the other hand, high activities were obtained for the syndiospecific heterogeneous system, but very low values were obtained for the supported isospecific metallocene, although both catalysts were prepared under the same conditions. The supported binary system showed intermediary catalyst activity in comparison with the syndiospecific and isospecific supported catalysts. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 263–272, 2005

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Section: Introductionmentioning

confidence: 99%

Polypropylene reactor mixture obtained with homogeneous and supported catalysts

Bastos

Marques

2004

J. Polym. Sci. A Polym. Chem.

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“…Ethylene copolymers such as poly(ethylene‐ co ‐vinyl acetate) (EVA) are produced by free‐radical polymerization in a bulk process, like that used for low‐density polyethylene (LDPE) production, involving high pressures and temperatures 1. Because the vinyl acetate monomer has the same reactivity with the ethylene monomer, a variety of copolymers, containing different vinyl acetate contents, can be produced.…”

Section: Introductionmentioning

confidence: 99%

Compatibility of low‐density polyethylene/poly(ethylene‐co‐vinyl acetate) binary blends prepared by melt mixing

Takidis

Bikiaris

Papageorgiou

et al. 2003

J of Applied Polymer Sci

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ABSTRACT:The compatibility of low-density polyethylene and poly(ethylene-co-vinyl acetate) containing 18 wt % vinyl acetate units (EVA-18) was studied. For this purpose, a series of different blends containing 25, 50, or 75 wt % EVA-18 were prepared by melt mixing with a single-screw extruder. For each composition, three different sets of blends were prepared, which corresponded to the three different temperatures used in the metering section and the die of the extruder (140, 160, and 180°C), at a screw rotation speed of 42 rpm. Blends that contained 25 wt % EVA-18 were also prepared through mixing at 140, 160, or 180°C but at a screw speed of 69 rpm. A study of the blends by differential scanning calorimetry showed that all the prepared blends were heterogeneous, except that containing 75 wt % EVA-18 and prepared at 180°C. However, because of the high interfacial adhesion, a fine dispersion of the minor component in the polymer matrix was observed for all the studied blends with scanning electron microscopy. The tensile strengths and elongations at break of the blends lay between the corresponding values of the two polymers. The absence of any minimum in the mechanical properties was strong evidence that the two polymers were compatible over the whole range of composition. The thermal shrinkage of the blends at various temperatures depended mainly on the temperature and EVA-18 content.

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“…While crosslinking can present challenges from the perspective of recyclability, it is advantageous in applications where chemical, biological or electrical degradation are concerns (2,3). Crosslinked polyethylene, for example, is used for medical devices (4), insulation for electrical wires (5,6), and containers for corrosive liquids (7).…”

mentioning

confidence: 99%

A broadly applicable cross-linker for aliphatic polymers containing C–H bonds

Lepage

Simhadri

Liu

et al. 2019

Science

126

133

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Addition of molecular cross-links to polymers increases mechanical strength and improves corrosion resistance. However, it remains challenging to install cross-links in low-functionality macromolecules in a well-controlled manner. Typically, high-energy processes are required to generate highly reactive radicals in situ, allowing only limited control over the degree and type of cross-link. We rationally designed a bis-diazirine molecule whose decomposition into carbenes under mild and controllable conditions enables the cross-linking of essentially any organic polymer through double C–H activation. The utility of this molecule as a cross-linker was demonstrated for several diverse polymer substrates (including polypropylene, a low-functionality polymer of long-standing challenge to the field) and in applications including adhesion of low–surface-energy materials and the strengthening of polyethylene fabric.

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Polyolefins

Cited by 37 publications

References 112 publications

Polypropylene reactor mixture obtained with homogeneous and supported catalysts

Polypropylene reactor mixture obtained with homogeneous and supported catalysts

Compatibility of low‐density polyethylene/poly(ethylene‐co‐vinyl acetate) binary blends prepared by melt mixing

A broadly applicable cross-linker for aliphatic polymers containing C–H bonds

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