An introduction to polymer science

Elias, Hans‐Georg

doi:10.1016/s0151-9107(99)80082-8

Cited by 80 publications

(109 citation statements)

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“…These values are identical with those reported for poly(ethylene), 23 indicating that LLDPE-BUT and LLDPE-OCT also belong to the orthorhombic crystal class. The determination of constant c could not be accomplished, since reflections with l 0 were not observed.…”

Section: Resultssupporting

confidence: 87%

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Grafting of tetrahydrophthalic and maleic anhydride onto polyolefins in solution

Campos

Fantini

Petri

2004

J. Braz. Chem. Soc.

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Polietileno de baixa densidade (LLDPE) com comonômeros 1-buteno e 1-octeno foram funcionalizados com anidrido tetrahidroftálico (THA) e anidrido maléico (MA) em solução na presença de peróxido de benzoíla (BPO), de acordo com planejamentos fatoriais. As variáveis testadas foram concentração de anidrido, concentração de peróxido, tempo de reação e tipo de comonômero. As formulações foram analisadas por espectroscopia vibracional no infravermelho FTIR. Na funcionalização com THA o efeito principal tempo de reação foi significativo, assim como, a interação deste com a concentração de THA, enquanto que no caso do MA as concentrações de BPO e MA foram significativas. Poliolefinas modificadas com teores semelhantes de THA e MA foram analisadas por calorimetria exploratória diferencial (DSC) e por difração de raios X (XRD). Amostras modificadas com THA e MA apresentaram redução na temperatura de fusão de 4,3 °C e 1,4 °C, respectivamente, com relação ao polímero original. Alterações devido à funcionalização também foram evidenciadas por forte redução nas áreas dos picos de difração relativos aos planos cristalinos (110) e (200), corroborando com os dados de calorimetria exploratória diferencial (DSC).Tetrahydrophthalic (THA) and maleic (MA) anhydrides were grafted onto linear low density polyethylene with comonomer 1-butene and 1-octene (LLDPE) in solution in the presence of benzoyl peroxide (BPO) following experimental designs, where anhydride and BPO concentrations, type of comonomer and reaction time were varied. The formulations were analyzed by Fourier transform infrared spectroscopy (FTIR). In the case of THA modified polyolefins, the time of reaction and the interaction between time of reaction and THA concentration influenced the process, whereas the MA and BPO concentrations influenced the grafting of MA onto polyolefins. THA and MA modified polyolefin samples with similar grafting contents were analized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). THA and MA functionalized polyolefins presented reduction in the melting temperature of 4.3 °C and 1.4 °C, respectively, comparing with the original polymer. These effects corroborate with the strong reduction in the areas of the diffraction peaks (110) and (200) after the grafting process.

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Section: Resultssupporting

confidence: 87%

“…Polyethylene crystallizes in the all-trans conformation and belongs to the orthorhombic crystal class. The corresponding lattice constants 23 amounts to a = 0.742 nm, b = 0.495 nm and c = 0.254 nm. Figure 5a shows typical curves of X-ray (Table 11).…”

Section: Resultsmentioning

confidence: 99%

Grafting of tetrahydrophthalic and maleic anhydride onto polyolefins in solution

Campos

Fantini

Petri

2004

J. Braz. Chem. Soc.

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“…1 Hence, the number of applications of the material is huge and many millions of tons are produced worldwide annually. However, PE has hardly played any role in the field of nanotechnology.…”

mentioning

confidence: 99%

Single Lamella Nanoparticles of Polyethylene

Weber¹,

Chiche²,

Krausch³

et al. 2007

Nano Lett.

117

142

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We present a complete analysis of the structure of polyethylene (PE) nanoparticles synthesized and stabilized in water under very mild conditions (15°C, 40 atm) by a nickel-catalyzed polymerization in aqueous solution. Combining cryogenic transmission electron microscopy (cryo-TEM) with X-ray scattering, we demonstrate that this new synthetic route leads to a stable dispersion of individual PE nanoparticles with a narrow size distribution. Most of the semicrystalline particles have a hexagonal shape (lateral size 25 nm, thickness 9 nm) and exhibit the habit of a truncated lozenge. The combination of cryo-TEM and small-angle X-ray scattering demonstrates that the particles consist of a single crystalline lamella sandwiched between two thin amorphous polymer layers ("nanohamburgers"). Hence, these nanocrystals that comprise only ca. 14 chains present the smallest single crystals of PE ever reported. The very small thickness of the crystalline lamella (6.3 nm) is related to the extreme undercooling (more than 100°C) that is due to the low temperature at which the polymerization takes place. This strong undercooling cannot be achieved by any other method so far. Dispersions of polyethylene nanocrystals may have a high potential for a further understanding of polymer crystallization as well as for materials science as, e.g., for the fabrication of extremely thin crystalline layers.Polyethylene (PE) is a commodity polymer that has become ubiquitous over the past several decades because of its low price and good mechanical properties. 1 Hence, the number of applications of the material is huge and many millions of tons are produced worldwide annually. However, PE has hardly played any role in the field of nanotechnology. This is due to the problem that PE is produced either by free radical polymerization under high pressure and temperature or with metal-organic catalysts working exclusively under strictly water-free conditions. Polymer nanoparticles and their composites with inorganic compounds, however, are very often produced in aqueous systems. 2 Recently, it was demonstrated that ethylene can be polymerized in aqueous systems in a catalytic fashion by Ni(II) complexes. [3][4][5][6] By virtue of this novel synthesis, long chains of polyethylene can be generated in a well-controlled environment and at ambient temperature. Thus, it could be shown that aqueous PE dispersions can be produced. This novel way of polymerization hence opens the way for the creation of nanostructures made from PE. Up to now, the particles synthesized in this way were semicrystalline and for the largest part consisted of stacks of several crystalline lamellae. 6

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“…However, several parameters have been reported to affect the reflowed photoresist and make the resulted channel profiles more complex, such as critical angle and boundary movement between the photoresist and the solid substrate, material evaporation during reflow baking, temperature and timing for the reflow process, outgassing, substrate uniformity, and resist properties [32][33][34] . For example, the reflow temperature and timing can result in a volume change causing the boundary movement and hence varying the critical angle and final reflowed resist profile 33 . As reported by our previous work 15 , the reflow process decreased the channel widths by 2% on average because of photoresist volume reductions and boundary movement.…”

Section: Master Mold Fabricationmentioning

confidence: 99%

Procedure for the Development of Multi-depth Circular Cross-sectional Endothelialized Microchannels-on-a-chip

Mearns

Martins‐Green

et al. 2013

JoVE

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Efforts have been focused on developing in vitro assays for the study of microvessels because in vivo animal studies are more time-consuming, expensive, and observation and quantification are very challenging. However, conventional in vitro microvessel assays have limitations when representing in vivo microvessels with respect to three-dimensional (3D) geometry and providing continuous fluid flow. Using a combination of photolithographic reflowable photoresist technique, soft lithography, and microfluidics, we have developed a multi-depth circular cross-sectional endothelialized microchannels-on-a-chip, which mimics the 3D geometry of in vivo microvessels and runs under controlled continuous perfusion flow. A positive reflowable photoresist was used to fabricate a master mold with a semicircular cross-sectional microchannel network. By the alignment and bonding of the two polydimethylsiloxane (PDMS) microchannels replicated from the master mold, a cylindrical microchannel network was created. The diameters of the microchannels can be well controlled. In addition, primary human umbilical vein endothelial cells (HUVECs) seeded inside the chip showed that the cells lined the inner surface of the microchannels under controlled perfusion lasting for a time period between 4 days to 2 weeks. Video LinkThe video component of this article can be found at

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An introduction to polymer science

Cited by 80 publications

References 0 publications

Grafting of tetrahydrophthalic and maleic anhydride onto polyolefins in solution

Grafting of tetrahydrophthalic and maleic anhydride onto polyolefins in solution

Single Lamella Nanoparticles of Polyethylene

Procedure for the Development of Multi-depth Circular Cross-sectional Endothelialized Microchannels-on-a-chip

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