Miscibility in poly(L-lactide)- b -poly( $ \upvarepsilon$ -caprolactone) double crystalline diblock copolymers
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Miscibility
Caprolactone
Miscibility
Transition temperature
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Thermomechanical properties of polymers highly depend on their glass transition temperature (T g). Differential scanning calorimetry (DSC) is commonly used to measure T g of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring T g in such type of polymers. The changes in specific heat capacity (Δc ₚ) at T g were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc ₚ from flexible polymer (0.28 J g⁻¹ K⁻¹ for polystyrene) to rigid CPs (10⁻³ J g⁻¹ K⁻¹ for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc ₚ at T g by a factor of 10, confirming that backbone rigidity reduces the Δc ₚ. Additionally, an increase in the crystalline fraction of the CPs further reduces Δc ₚ. We conclude that the difficulties of determining T g for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1635–1644
Polystyrene
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The glass transition behaviour of the four metallic glasses La55 Al25 Ni20, Zn65Mg35, and Nd60Fe30Al10 and Zr30Y30Al15Ni25 has been studied by temperature-modulated differential scanning calorimetry (MDSC). It is clearly demonstrated that the glass transition can be separated from crystallization by MDSC. Two glass transitions have been observed for Zn65Mg35, Nd60Fe30Al10 and Zr30Y30Al15Ni25. Owing to the clearer observation of the glass transition, calculation of the reduced glass temperatures Trg (glass transition temperature divided by the melting point) can now be made with greater confidence.
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Poly(N-isopropylacrylamide)
Miscibility
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The glassy and rubbery states have an important influence on the physical-chemical and structural properties of food, such as viscosity crispness,crystallization,collapse and ice formation.Differential Scanning Calorimetry(DSC)was used to study glass transition and determine the Tg,some examples were given to in this article.
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Thermogravimetric analysis
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Miscibility
Polyvinylpyrrolidone
Flory–Huggins solution theory
Methyl cellulose
Hydroxypropyl cellulose
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Transition temperature
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This research has been carried out in order to demonstrate the use of differential scanning calorimetry (DSC) in detecting and measuring α- and β-relaxation processes in amorphous pharmaceutical systems. DSC has been employed to study amorphous samples of poly (vinylpyrrolidone) (PVP), indomethacin (InM), and ursodeoxycholic acid (UDA) that are annealed at temperature (Ta) around 0.8 of their glass transition temperature (Tg). Dynamic mechanical analysis (DMA) is used to measure β- relaxation in PVP. Yet, the DSC has been used to study the glassy indomethacin aged at 0 and -10 oC for periods of time up to 109 and 210 days respectively. The results demonstrate the emergence of a small melting peak of the α-polymorph after aging for 69 days at 0°C and for 147 days at -10°C (i.e., ~55°C below the glass transition temperature) that provides evidence of nucleation occurring in the temperature region of the β-relaxation.
Supercooling
Characterization
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