A lower critical ordering transition in a diblock copolymer melt

Russell, Thomas P.; Karis, T. E.; Gallot, Yves; Mayes, Anne M.

doi:10.1038/368729a0

Cited by 166 publications

(216 citation statements)

References 26 publications

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“…63 Such LCOT behavior is quite uncommon in polymer blends; the system that has been most widely characterized and shows similar behavior is poly(styrene)/poly(butyl methacrylate). [64][65][66] This behavior has been suggested to depend on a weak overall immiscibility and originate from a positive volume change on demixing (ordering) of the two block segments, increasing the number of available configurations and therefore the entropy of the system. 64 Considering the structural similarity between PS/PnBMA and PbnMA/PnBA, it is perhaps not surprising that the latter should also show LCOT-type behavior.…”

Section: Resultsmentioning

confidence: 99%

Phase Behavior of Complementary Multiply Hydrogen Bonded End-Functional Polymer Blends

et al. 2010

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Blends of diamidonaphthyridine (Napy) end-functional poly(n-butyl acrylate) (PnBA) and ureidopyrimidinone (UPy) end-functional poly(benzyl methacrylate) (PbnMA) were studied as a function of the component molecular weights to compare with prior theoretical predictions.1 Macroscopic phase separation was observed to be prevented by the reversible association of end-functional polymers to form supramolecular diblock copolymers, resulting in stabilization of the interface between the polymers. At low molecular weights homogeneous microstructures were observed, in contrast to nonfunctional homopolymer blends of the same molecular lengths, which rapidly phase separate over macroscopic length scales. At higher molecular weights, the blend structure was reminiscent of compatibilized homopolymer blends, with the phase-separated domain size rapidly increasing with temperature. To compare with theoretical phase diagrams, the temperature-dependent Flory-Huggins χ parameter was measured, and it was found that PnBA/PbnMA covalent diblock copolymers show unusual lower critical ordering (LCOT) behavior with χ slightly increasing with temperature (χ(T) = 0.036 -0.56/T).

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Section: Resultsmentioning

confidence: 99%

Phase Behavior of Complementary Multiply Hydrogen Bonded End-Functional Polymer Blends

et al. 2010

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“…It is even conceivable that vibrational entropy could induce a transition from a disordered to an ordered phase with increasing temperature, if the vibrational entropy difference between the ordered and disordered phases is larger and opposite to the configurational entropy difference. While this phenomenon has, so far, not been observed in metallic alloys, presumably because of the large configurational entropy associated with disordering, it does occur in molecular systems, such as in diblock copolymer melts, where the configurational entropy (per monomer) is small (Russell et al, 1994).…”

Section: ␣→␤mentioning

confidence: 99%

The effect of lattice vibrations on substitutional alloy thermodynamics

2002

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A long-standing limitation of first-principles calculations of substitutional alloy phase diagrams is the difficulty in accounting for lattice vibrations. A survey of the theoretical and experimental literature seeking to quantify the effect of lattice vibrations on phase stability indicates that they can be significant. Typical vibrational entropy differences between phases are of the order of 0.1 to 0.2k B /atom, which is comparable to the typical values of configurational entropy differences in binary alloys (at most 0.693k B /atom). This article presents the basic formalism underlying ab initio phase diagram calculations, along with the generalization required to account for lattice vibrations. The authors review the various techniques allowing the theoretical calculation and the experimental determination of phonon dispersion curves and related thermodynamic quantities, such as vibrational entropy or free energy. A clear picture of the origin of vibrational entropy differences between phases in an alloy system is presented that goes beyond the traditional bond counting and volume change arguments. Vibrational entropy change can be attributed to the changes in chemical bond stiffness associated with the changes in bond length that take place during a phase transformation. This so-called ''bond stiffness vs bond length'' interpretation both summarizes the key phenomenon driving vibrational entropy changes and provides a practical tool to model them. CONTENTS

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“…%). [9,10] Also amorphous polystyrene has been modified by reacting with diisocyanates to form semi-crystalline polyurethane.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of Poly (urethane-urea) based on Functionalized Polystyrene and MDI

Kayalvizhi¹,

Vakees²,

Suresh³

et al. 2014

IOSRJAC

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A lower critical ordering transition in a diblock copolymer melt

Cited by 166 publications

References 26 publications

Phase Behavior of Complementary Multiply Hydrogen Bonded End-Functional Polymer Blends

Phase Behavior of Complementary Multiply Hydrogen Bonded End-Functional Polymer Blends

The effect of lattice vibrations on substitutional alloy thermodynamics

Synthesis and Characterization of Poly (urethane-urea) based on Functionalized Polystyrene and MDI

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