Differential scanning calorimetry properties

Most hydrocarbon resins are composed of a mixture of monomers and are rather difficult to hiUy characterize on a molecular level. The characteristics of resins are typically defined by physical properties such as softening point, color, molecular weight, melt viscosity, and solubiHty parameter. These properties predict performance characteristics and are essential in designing resins for specific appHcations. Actual characterization techniques used to define the broad molecular properties of hydrocarbon resins are Fourier transform infrared spectroscopy (ftir), nuclear magnetic resonance spectroscopy (nmr), and differential scanning calorimetry (dsc). 

The compositional distribution of ethylene copolymers represents relative contributions of macromolecules with different comonomer contents to a given resin. Compositional distributions of PE resins, however, are measured either by temperature-rising elution fractionation (tref) or, semiquantitatively, by differential scanning calorimetry (dsc). Table 2 shows some correlations between the commercially used PE characterization parameters and the stmctural properties of ethylene polymers used in polymer chemistry. 

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

In order to optimize each embedding material property, complete cure of the material is essential. Various analytical methods are used to determine the complete cure of each material. Differential scanning calorimetry, Fourier transform-iafrared (ftir), and microdielectrometry provide quantitative curing processiag of each material. Their methods are described below. 

The procedures of measuring changes in some physical or mechanical property as a sample is heated, or alternatively as it is held at constant temperature, constitute the family of thermoanalytical methods of characterisation. A partial list of these procedures is differential thermal analysis, differential scanning calorimetry, dilatometry, thermogravimetry. A detailed overview of these and several related techniques is by Gallagher (1992). 

Many papers deal with the crystallization of polymer melts and solutions under the conditions of molecular orientation achieved by the methods described above. Various physical methods have been used in these investigations electron microscopy, X-ray diffraction, birefringence, differential scanning calorimetry, etc. As a result, the properties of these systems have been described in detail and definite conclusions concerning their structure have been drawn (e.g.4 13 19,39,52)). 

We analyzed the embedded particles with differential scanning calorimetry to identify the property of polystyrene. As shown in Fig, 1, fhe embedded particles show a small peak around 100 °C, which is typical in atactic polystyrene [7]. It is desirable that embedding polymer has a similar melting tempeiature as the final polymer (polyethylene) because a big difference in the melting temperatures between the two polymers may cause a gel problem and poor mechanical properties. 

Thermal Analysis - Differential Scanning Calorimetry (DSC) and thermal gravimetric analysis (TGA) were used to characterize the thermal properties of the polymers synthesized. DSC analysis was performed on a Perkin-Elmer Differential Scanning Calorimeter, Model 2C with a thermal analysis data station. Thermal gravimetric analysis (TGA) was carried out on a DuPont thermal gravimeter, Model 951. From the DSC and TGA plots of poly (N-pheny 1-3,4-dimethylene-... 

Chemical structure of monomers and intermediates was confirmed by FT-IR and FT-NMR. Molecular weight distribution of polymers was assessed by GPC and intrinsic viscosity. The thermal property was examined by differential scanning calorimetry. The hydrolytic stability of the polymers was studied under in vitro conditions. With controlled drug delivery as one of the biomedical applications in mind, release studies of 5-fluorouracil and methotrexate from two of these polymers were also conducted. 

We use differential scanning calorimetry - which we invariably shorten to DSC - to analyze the thermal properties of polymer samples as a function of temperature. We encapsulate a small sample of polymer, typically weighing a few milligrams, in an aluminum pan that we place on top of a small heater within an insulated cell. We place an empty sample pan atop the heater of an identical reference cell. The temperature of the two cells is ramped at a precise rate and the difference in heat required to maintain the two cells at the same temperature is recorded. A computer provides the results as a thermogram, in which heat flow is plotted as a function of temperature, a schematic example of which is shown in Fig. 7.13. 

One such property, as has been demonstrated (see [26]), is the change in partial heat capacity of the copolymer solution upon the heat-induced conformational transition of macromolecules. Such a change was detected by high-sensitivity differential scanning calorimetry (HS-DCS). The DSC data for the NVCl/NVIAz-copolymers synthesized at initial comonomer ratios of 85 15 and 90 10 (mole/mole) are given as thermograms in Fig. 4. 

X-ray diffraction studies are usually carried out at room temperature under ambient conditions. It is possible, however, to perform variable-temperature XPD, wherein powder patterns are obtained while the sample is heated or cooled. Such studies are invaluable for identifying thermally induced or subambient phase transitions. Variable-temperature XPD was used to study the solid state properties of lactose [20], Fawcett et al. have developed an instrument that permits simultaneous XPD and differential scanning calorimetry on the same sample [21], The instrument was used to characterize a compound that was capable of existing in two polymorphic forms, whose melting points were 146°C (form II) and 150°C (form I). Form II was heated, and x-ray powder patterns were obtained at room temperature, at 145°C (form II had just started to melt), and at 148°C (Fig. 2 one characteristic peak each of form I and form II are identified). The x-ray pattern obtained at 148°C revealed melting of form II but partial recrystallization of form I. When the sample was cooled to 110°C and reheated to 146°C, only crystalline form I was observed. Through these experiments, the authors established that melting of form II was accompanied by recrystallization of form I. 

Hydration of phospholipid head groups is essential properties not only for stabilizing bilayer structures in an aqueous environment, but also for fusion or endocytosis of biological membranes including protein transfers [33-35]. Hydration or swelling behavior has only been studied by indirect methods such as X-ray diffraction [36], differential scanning calorimetry (DSC) [37], and H-NMR [38,39]. 

The mechanical properties also depend on the relative block lengths. For instance, Fluoro-PSB-II is a soft, elastic material. Differential scanning calorimetry (DSC) measurements and wide-angle X-ray scattering (WAXS)... 

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