Distribution of Long and Short Branches in Low-Density Polyethylenes

Otocka, E. P.; Roe, Ryong‐Joon; Hellman, M. Y.; Muglia, P. M.

doi:10.1021/ma60022a029

Cited by 54 publications

(9 citation statements)

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“…Long-chain branching (LCB) has major implications on the melt strength of polymers. − The introduction of LCB reduces melt viscosity of high molecular weight polymers at a given processing temperature. ,, Furthermore, LCBs improve shear thinning and extensional flow over linear analogues at equivalent molecular weights. ,, This improvement over linear polymers makes LCB polymer systems a source of interest in applications involving molding strategies, where molten polymer flows into a desired shape at high frequencies. Much of the current literature reveals the impact of long-chain branches in polyolefins and polyesters, where branch molecular weights ( M b ) are orders of magnitude larger than the molecular weight of entanglement ( M e ). ,,− The low concentration of branching points in LCB polyolefins causes difficulties in the characterization of critical parameters, e.g., M b , of the branched polymers. − Despite this challenge, many correlations between rheological properties and degree of branching exist. ,− Generally, the presence of branches decreases viscosity at low shear rates (typically within the Newtonian plateau) as a result of the smaller random coil size compared to linear chains of the same molecular weight. , However, many also report an increase in viscosity with low incorporation of LCBs and attribute the increased density of chain entanglements and extensive chain–chain coupling to this phenomenon. , In detail, Manaresi et al systematically control polymerization conditions and trifunctional monomer concentration to elucidate the influence of branch density and length on viscosity of poly(ethylene terephthalate) (PET) . At constant M w , the zero-shear viscosity and intrinsic viscosity are lower than those of the linear analogue.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A₃ Comonomers

Dennis

Mondschein

Wolfgang

et al. 2020

ACS Appl. Polym. Mater.

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The synthesis of an aromatic trisamine enabled the generation of long-chain branched poly(ether imide)s (LCB-PEIs). The nucleophilic aromatic substitution of 1-chloro-4-nitrobenzene with 1,1,1-tris(4-hydroxyphenyl)ethane resulted in tris((p-nitrophenoxy)phenyl)ethane, and a subsequent reduction afforded tris((p-aminophenoxy)phenyl)ethane (TAPE) in high yields (>90%). Introducing TAPE at low percentages with m-phenylenediamine and bisphenol A dianhydride enabled synthesis of high molecular weight, branched poly(ether imide)s with varied branch lengths. The stoichiometric imbalance and phthalic anhydride end-capping controlled molecular weights. Complementary 1H NMR spectroscopy and size exclusion chromatography (SEC) identified average branch length as a function of TAPE incorporation and provided comparisons in molecular weights and distributions. The melt viscosity and thermal stability at elevated temperatures (∼340 °C) probed the feasibility of melt processing of LCB-PEIs in comparison to linear analogues. At equivalent molecular weight and below 1.5 mol % TAPE, melt viscosities increased at low shear rates. However, increasing TAPE above 1.5 mol % decreased melt viscosities at low shear rates, suggesting a correlation of branch length and polydispersity with melt viscosity. Mechanical testing of injection-molded samples demonstrated minimal changes in tensile and impact properties with branching. The LCB-PEIs herein establish their potential role in molding processes such as blow molding that requires high melt strength and advantageous shear thinning.

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Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A₃ Comonomers

Dennis

Mondschein

Wolfgang

et al. 2020

ACS Appl. Polym. Mater.

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“…of polydisperse samples are larger than those of monodisperse samples having the same weight-average molecular weights. 23 Moreover, the effect of polydispersity on <S 2 ). is more remarkable than that on [17].…”

Section: Discussionmentioning

confidence: 99%

Gel Permeation Chromatography of Comb-Shaped Branched Polymers

Kato

Itsubo

Yamamoto

et al. 1975

Polym J

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Comb-shaped branched polystyrenes prepared by anionic polymerization are fractionated carefully. The molecular weight, degree of branching and radius of gyration of those fractions are determined by light scattering. Gel gram (GPC) of those fractions are observed on toluene. If the radms of gyratiOn. of comb-shaped polystyrenes is plotted against retention volume, the data fit. the same lme as monodisperse linear polystyrenes. If the GPC data are replotted m the form of log [7J]M vs. retention volume, clear disagreement is found between both data, _though the disagreement is not so large. A discussion is given to the reason for the disagreement. KEY WORDS Gel Permeation Chromatogram I Comb-Shaped Polystyrenes 1 Calibration Curve I Hydrodynamic Volume I Radius of Gyration I

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“…Differential scanning calorimetry analyses were carried out in duplicate with a TA DSC 2920 instrument (heating rate = 10 °C min −1 ), and the data based on the second heat are reported 5. Molecular weight determinations were made with viscosity measurements in decahydronaphtalene at 135 °C with a Cannon‐Fenske viscometer, and literature constants were applied 6. Every polymer sample was weighed and measured twice to reduce the error.…”

Section: Methodsmentioning

confidence: 99%

Metallocene derivatives as active supports of zirconium‐based catalysts for ethene polymerization

Mortara

Fregonese

Bresadola

et al. 2001

J. Polym. Sci. A Polym. Chem.

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Cyclopentadienyl magnesium chloride (MgClCp) and its functionalized derivatives represent original and interesting supporting materials to heterogenize metallocene catalysts for olefin polymerizations. The synthesis of MgClCp, its functionalization, and the preparation of a catalytic system in which the ZrCl 2 (Flu) ϩ moiety is joined on the support through a cyclopentadienyl ligand are reported. This catalyst was tested in ethene polymerization, and both the catalytic activity and properties of the produced polymer were measured. Its performance was compared with that shown by the catalyst ZrCl 2 CpFlu employed under the same conditions for both unsupported and conventional supports, such as MgCl 2 . The results showed a remarkable improvement in terms of the activity and polymer properties with these heterogenized catalysts. Moreover, this system showed stability toward leaching processes and was characterized by good morphological control of the growing polymer. Finally, catalysts in which [HB(3,5-Me 2 pyrazolyl) 3 ]ZrCl 2 ϩ and [HB(3,5-Me 2 pyrazolyl) 3 ]ZrClOtBu ϩ moieties were bonded to a functionalized MgClCp Ϫ support were also synthesized and tested. The results showed that the proposed supports could be usefully used to heterogenize tailored metallocene homogeneous catalysts. In fact, new catalysts were prepared that combined the peculiar advantages of both heterogeneous and homogeneous catalysts and overcame the disadvantages of the latter, such as a lack of morphology and reactor fouling.

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Distribution of Long and Short Branches in Low-Density Polyethylenes

Cited by 54 publications

References 2 publications

Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A₃ Comonomers

Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A₃ Comonomers

Gel Permeation Chromatography of Comb-Shaped Branched Polymers

Metallocene derivatives as active supports of zirconium‐based catalysts for ethene polymerization

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Distribution of Long and Short Branches in Low-Density Polyethylenes

Cited by 54 publications

References 2 publications

Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A3 Comonomers

Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A3 Comonomers

Gel Permeation Chromatography of Comb-Shaped Branched Polymers

Metallocene derivatives as active supports of zirconium‐based catalysts for ethene polymerization

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Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A₃ Comonomers

Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A₃ Comonomers