Thermodynamic properties of high polymers as a function of their pretreatment as determined by specific heat measurements

Dole, Malcolm

doi:10.1007/bf01797347

Cited by 43 publications

(6 citation statements)

References 23 publications

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“…where m is negative when u decreases with increasing time. Equation 3 can now be cast in the form of log [-(In (1 -uc))] = log g + log IV + n log u0 + n(m + 1) log t log [-(In (1 -oc))] = log K2* + n(m + 1) log t (7) where K2* = gNv0n, and n(m + 1) is the slope of log t. Such a slope is smaller than n since m is negative. If the crystal growth is diffusion-controlled, for instance, in which case v would scale as t"1/2,26 according to eq 7, the slope of log t becomes 0.5n, and it would be 0.5, 1, and 1.5 for one-, two-, and three-dimensional growth, respectively.…”

Section: Crystallization With Nonnegligible Volume Fraction Of Nucleimentioning

confidence: 99%

Modification of the Avrami treatment of crystallization to account for nucleus and interface

Cheng¹,

Wunderlich²

1988

Macromolecules

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Section: Crystallization With Nonnegligible Volume Fraction Of Nucleimentioning

confidence: 99%

Modification of the Avrami treatment of crystallization to account for nucleus and interface

Cheng¹,

Wunderlich²

1988

Macromolecules

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“…Recrystallization from the glassy state or supercooled liquid, which occurs upon heating up to the normal melting temperature, is referred to as cold-crystallization. For a given heating rate, the cold-crystallization depends on the number of nuclei existing in the amorphous material, − and reducing or avoiding nucleation would be expected to stabilize the amorphous pharmaceutical.…”

Section: Introductionmentioning

confidence: 99%

Nanoconfinement Effects on the Glass Transition and Crystallization Behaviors of Nifedipine

Cheng

McKenna

2019

Mol. Pharmaceutics

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The impact of nanoconfinement on the crystallization and glass transition behaviors of nifedipine (NIF) has been investigated using differential scanning calorimetry. Nanoconfinement was provided by imbibing the NIF into a porous medium (controlled pore glass, CPG), and results were compared with the unconfined bulk material. Consistent with previous results from the literature, both glass transition temperature T g and melting temperature T m decrease with decreasing pore size. The melting temperature was found to decrease with the reciprocal of pore diameter and could be analyzed with the Gibbs–Thomson equation. In addition, for confinement sizes of 7.5 and 12 nm, it was found that no cold-crystallization occurs upon heating from the glassy state to above the expected melting transition. Finally, at intermediate confinements we find evidence of a possible new, confinement-induced polymorph of NIF.

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“…The observed AC, at Tg is not proportional to the percent amorphicity as would be expected on the basis of a two phase (crystalline-amorphous) system. This was first reported many years ago for polyethylene terephthalate (32) and polycarbonate (33). It is unclear why a small amount of crystallinity in some polymers restricts the amorphous polymer chains from attaining their liquid-like motions and the corresponding heat capacity above Tg .…”

Section: Resultsmentioning

confidence: 92%

Thermal transitions of ethylene‐vinyl chloride copolymers and their blends

Bowmer

Tonelli

1986

J. Vinyl Addit. Technol.

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Differential Scanning Calorimetry (DSC) measurements were performed on a series of ethylene‐vinyl chloride copolymers (E‐V) prepared via reductive dechlorination of poly(vinyl chloride) with tributyltin hydride. The copolymers were identical in chain length and branching distribution; differing only in comonomer content, sequence distribution, and stereoregularity of adjacent —V— units. Extrapolation of glass transition temperatures, Tg, measured for our E‐V copolymers to pure polyethylene (PE) predicted a Tg = −85 ± 10°C for amorphous PE. E‐V copolymers with greater than 60 mol percent —E— units exhibited melting endotherms from 20 to 128°C and degrees of crystallinity from 12 to 63 percent. The melting point depressions observed for our E‐V copolymers were in agreement with Flory's theory, if the CH2CH2 moiety is considered to be the crystallizable unit and the moiety is assumed to prevent the CH2CH2 units attached on either side from being incorporated into the crystal. In general, the E‐V copolymer blends with PE were incompatible, while those with PVC were compatible only for E‐V copolymers with high V contents (>80 mol percent). Blends of the amorphous E‐V copolymers were found compatible if their V contents differed by less than 15 mol percent, while blends where one or both E‐V copolymers are crystalline were found to be incompatible. The properties of these copolymers will be discussed in terms of their microstructure.

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Thermodynamic properties of high polymers as a function of their pretreatment as determined by specific heat measurements

Abstract: Dieser Vorschlag wurde aber, da noch zu wenig entwickelt, als in der Diskussion seinerzeit nicht wciterbehandelbar betrachtet. Die weitere Entwicldung der Dinge scheint inzwischen mehr oder weniger tats~eh-tich auf /~hnliche Bctrachtungen hinauszukommen..

Cited by 43 publications

References 23 publications

Modification of the Avrami treatment of crystallization to account for nucleus and interface

Modification of the Avrami treatment of crystallization to account for nucleus and interface

Nanoconfinement Effects on the Glass Transition and Crystallization Behaviors of Nifedipine

Thermal transitions of ethylene‐vinyl chloride copolymers and their blends

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