Characterization of polyethylenes by x‐ray diffraction and <sup>13</sup>C‐NMR: Temperature studies and the nature of the amorphous halo

McFaddin, Douglas; Russell, K. E.; Wu, Gang; Heyding, R. D.

doi:10.1002/polb.1993.090310206

Cited by 70 publications

(81 citation statements)

References 26 publications

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“…In actual homogeneous copolymer systems, the content of comonomers lowers the crystallization temperature 48 and can be so high that the crystallization temperature may shift even below the glass transition temperature, then, only an amorphous state can be realized on cooling. 34,49 Such copolymers are usually named noncrystalline polymers or amorphous polymers. It has to be remarked that, in our simulations, no such vitrification is included, which is why the crystallinity curves can always go to high values on cooling even for those copolymers with high comonomer content, while in reality, they are usually intercepted by the glass transition.…”

Section: Discussionmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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We report a numerical study of crystallization and melting in bulk statistical homogeneous (random), homogeneous (slightly alternating), and heterogeneous (produced in a batch reaction) copolymers formed by crystallizable monomers and noncrystallizable comonomers. In our dynamic Monte Carlo simulations of lattice chains, the current model further assumes that the comonomers cannot move into crystalline regions by sliding diffusion of the chains. We find that both the overall composition and the statistical distribution of the monomers affect the phase-transition temperature, the resulting relative crystallinity, and the crystal morphology. However, the final absolute crystallinity of homogeneous copolymers seems insensitive to these parameters. Intramolecular segregation between monomers and comonomers is accompanied by crystallization, demonstrating the concept of sequence segregation or nanophase separation of statistical copolymers with assembling structures like in thermoplastic elastomers. Moreover, if crystallization of homogeneous copolymers has started but not yet completed on cooling, subsequent heating will show cold crystallization before melting, which can be attributed to insertion-mode lamellar growth. For heterogeneous copolymers, intermolecular segregation occurs on cooling before crystallization. On the basis of our observations, a pair of master melting and crystallization curves for the crystallinity of a statistical copolymer as a function of temperature are suggested to reflect the characteristic of the monomer-sequence-length distribution. This suggestion facilitates the clarification to the kinetic disturbance in local temperature regions and to the principle of some fractionation methods, such as temperature rising elution fractionation (TREF).

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Section: Discussionmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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“…The COCOCOC interactions would contribute to scattering at a higher angular range than the intermolecular contribution. 8,[13][14][15] With respect to the latter, an asymmetry in the shape of the high-angle portion of the LAH has been shown in a wide range of polyolefin melts, 8 nylon 6, PET, 5 ethylene copolymers, 16 and in the fiber patterns of ultrahigh molecular weight polyethylene (UHMWPE) 17 and PET. 18 Clarification of the relative contributions of the intramolecular and intermolecular scattering to the LAH through temperature variation has been shown, 19 but not addressed, relative to the problem of modeling of the amorphous state scattering for diffraction analysis in solidified systems.…”

Section: Introductionmentioning

confidence: 99%

Modeling the principal amorphous halo in quiescent melts of polyethylene and ethylene copolymers using wide-angle X-ray scattering and its implications

Monar

Habenschuss

1999

J. Polym. Sci. B Polym. Phys.

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Wide‐angle X‐ray scattering (WAXS) studies of the melts of polyethylenes indicate that the low‐angle amorphous halo (LAH) retains “sensible” information regarding the liquid state, which can be used to model the amorphous fraction in the semicrystalline state. The LAH was found to consist of a temperature‐independent and a temperature‐dependent region. A linear relationship was observed for the temperature dependence of the LAH peak value below 135 °C in branched ethylene copolymers, and was found dependent on comonomer concentration. When combined with group contribution theory, a simple model of average intermolecular separation determined from the WAXS–LAH peak value is consistent with free volume considerations, both with respect to predicting Tg(∞) and the free volume expansion coefficient. The polyethylene, without branches, shows a different behavior in the region 131–160 °C. A semiquantitative method is proposed to model the scattering from the LAH for use in the phase analysis of the copolymers through the separation of the temperature‐dependent (intermolecular) and temperature‐independent (intramolecular) fractions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3401–3410, 1999

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“…39 Accordingly, a melting process is observed in their calorimetric curves. Its location is practically constant independently of MCM-41 content in the nanocomposite, as seen in Table III.…”

Section: Thermal Analysismentioning

confidence: 99%

Self-Reinforced Hybrid Polyethylene/MCM-41 Nanocomposites: <I>In-Situ</I> Polymerisation and Effect of MCM-41 Content on Rigidity

Campos¹,

Lourenço²,

Pérez³

et al. 2009

J. Nanosci. Nanotech.

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The synthesis of self-reinforced polyethylene-based materials prepared by in-situ polymerisation is described. The methodology developed uses MCM-41 mesoporous material in a triple role: as catalyst carrier for ethylene polymerisation within its pores and channels in a first stage, as nanofiller of the formed polyethylene matrix during its useful lifetime and, finally, as promoter for long-term waste disposal. As evidenced by FTIR analysis, when the polymer is formed under these confined conditions different interactions between the MCM-41 material and the polyethylene matrix occur, when compared to simple blends. The influence of the filler content on the rigidity of the resulting nanocomposites is analysed by microhardness measurements and corroborated by the storage modulus values: a significant increase in rigidity is observed as the filler contents rises. In addition, thermogravimetric studies show interesting features concerning the degradability of these materials. The catalytic action of MCM-41 during degradation involves a reduction of the energetic requirements for their cracking and, therefore, a positive environmental impact.

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Characterization of polyethylenes by x‐ray diffraction and ¹³C‐NMR: Temperature studies and the nature of the amorphous halo

Cited by 70 publications

References 26 publications

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Modeling the principal amorphous halo in quiescent melts of polyethylene and ethylene copolymers using wide-angle X-ray scattering and its implications

Self-Reinforced Hybrid Polyethylene/MCM-41 Nanocomposites: <I>In-Situ</I> Polymerisation and Effect of MCM-41 Content on Rigidity

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Characterization of polyethylenes by x‐ray diffraction and 13C‐NMR: Temperature studies and the nature of the amorphous halo

Cited by 70 publications

References 26 publications

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Modeling the principal amorphous halo in quiescent melts of polyethylene and ethylene copolymers using wide-angle X-ray scattering and its implications

Self-Reinforced Hybrid Polyethylene/MCM-41 Nanocomposites: <I>In-Situ</I> Polymerisation and Effect of MCM-41 Content on Rigidity

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Characterization of polyethylenes by x‐ray diffraction and ¹³C‐NMR: Temperature studies and the nature of the amorphous halo