Heat Capacity Study of Isotactic Polystyrene:  Dual Reversible Crystal Melting and Relaxation of Rigid Amorphous Fraction

Xu, Hongyao; Cebe, Peggy

doi:10.1021/ma035961n

Cited by 134 publications

(142 citation statements)

References 66 publications

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“…Both cold crystallization and double-melting behavior are well-known phenomena. [43][44][45][46] However, the observation of a single melting peak for the macroemulsion prepared from iPS is somewhat unexpected. As we did not fi nd any tabulated values for the enthalpy of cold crystallization for iPS, the degree of cold crystallization was not calculated.…”

Section: Crystallinity Of the Particlesmentioning

confidence: 99%

Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers

Staff

Lieberwirth

Landfester

et al. 2012

Macro Chemistry & Physics

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The synthesis of colloidally stable submicron particles of syndiotactic polystyrene (sPS) and isotactic polystyrene (iPS) is reported. Model particles based on poly‐L‐lactic acid (PLLA), atactic polystyrene (aPS), sPS, and iPS are prepared by the evaporation of a solvent present in miniemulsion droplets. The degree of crystallinity of the particles is found to decrease with their size, as shown by DSC and WAXS measurements. Remarkably, nonspherical particles can be formed in the dispersed state with sPS and iPS, whereas PLLA and aPS particles always display spherical morphologies.

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Section: Crystallinity Of the Particlesmentioning

confidence: 99%

Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers

Staff

Lieberwirth

Landfester

et al. 2012

Macro Chemistry & Physics

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“…Data such as those in Figure 4(c) show that the oriented segments relax at a higher temperature (T g $ 80-90 8C) than the unoriented segments (T g $ 30-50 8C). 62 The higher T g fraction is called the rigid amorphous fraction (RAF), [63][64][65] and the lower T g fraction corresponds to the conventional amorphous fraction. It is sometimes thought that the RAF is at the fold surface of the lamellae.…”

Section: Glass Transitionmentioning

confidence: 99%

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

Murthy

2006

J Polym Sci B Polym Phys

215

197

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Some salient results in nylon research are reviewed to identify the fundamental principles that are applicable to other strongly interacting or hydrogenbonded polymers, including proteins. The effects of hydrogen bonds on stress-, heat-, and solvent-induced changes in macroscopic properties are discussed. These data provide a window into the chain mobility and linkages between the crystalline and amorphous domains, both of which are important for any predictive model. The changes in the characteristics of the amorphous phase with the crystallinity and orientation require that it be modeled with at least two components: a rigid/immobile/ anisotropic component and a soft/ mobile/isotropic component. The deformation and shrinkage behavior of these polymers are discussed in terms of the relative contributions of the amorphous and crystalline domains and of the interactions between them. The premelting crystalline transition is accompanied by the merging of intersheet and intrasheet diffraction peaks in some nylons, as observed by Brill, and not in others even though the underlying mechanism that gives rise to these transitions, the onset of volume-increasing librational motion of the crystalline stems, is the same. Because the effects of the temperature, deformation, and solvent have a common origin associated with mobility, a fictive temperature can be associated with a given solvent activity or stress level. The magnitude of this fictive temperature is the amount by which the glass or Brill transition temperature is reduced in the presence of solvents ($50 8C) or stress or by which the annealing temperature can be reduced in the presence of a solvent (or active stress) to achieve the same structural state as that of a dry (or static) polymer.

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“…In Zhuravlev et al [15], the influence of the temperature history on the creation of crystal nuclei is also investigated. In [15] and [16], detailed insights into the temperature-dependent relaxation behaviour of the rigid amorphous phase are provided. All experimental results demonstrate that the current degree of crystallinity of a semicrystalline polymer is a functional of the entire temperature history.…”

Section: Introductionmentioning

confidence: 99%

A thermodynamic approach to model the caloric properties of semicrystalline polymers

Lion

Johlitz

2015

Continuum Mech. Thermodyn.

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It is well known that the crystallisation and melting behaviour of semicrystalline polymers depends in a pronounced manner on the temperature history. If the polymer is in the liquid state above the melting point, and the temperature is reduced to a level below the glass transition, the final degree of crystallinity, the amount of the rigid amorphous phase and the configurational state of the mobile amorphous phase strongly depend on the cooling rate. If the temperature is increased afterwards, the extents of cold crystallisation and melting are functions of the heating rate. Since crystalline and amorphous phases exhibit different densities, the specific volume depends also on the temperature history. In this article, a thermodynamically based phenomenological approach is developed which allows for the constitutive representation of these phenomena in the time domain. The degree of crystallinity and the configuration of the amorphous phase are represented by two internal state variables whose evolution equations are formulated under consideration of the second law of thermodynamics. The model for the specific Gibbs free energy takes the chemical potentials of the different phases and the mixture entropy into account. For simplification, it is assumed that the amount of the rigid amorphous phase is proportional to the degree of crystallinity. An essential outcome of the model is an equation in closed form for the equilibrium degree of crystallinity in dependence on pressure and temperature. Numerical simulations demonstrate that the process dependences of crystallisation and melting under consideration of the glass transition are represented.

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Heat Capacity Study of Isotactic Polystyrene: Dual Reversible Crystal Melting and Relaxation of Rigid Amorphous Fraction

Cited by 134 publications

References 66 publications

Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers

Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

A thermodynamic approach to model the caloric properties of semicrystalline polymers

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