Transition temperatures, measuring

Apparently, annealing was not impeded by crosslinks (Fig. 5.1). The density effects observed agree with the results of the glass transition temperature measurements (Sect. 4.2). There, the Tg of the annealed (and therefore denser) sample was consistently higher by about 2 K than the Tg of the quenched polymer. 

Fig. 9.15 HS fraction in the region of the transition temperature measured by NFS on [Fe(tpa) (NCS)2]. The values derived during a temperature scan with increasing (decreasing) temperature are marked with upward directed triangles (downward directed triangles). (Taken from [41])...

Probably most of these investigators were studying poly(dichlorophosphazene) in the partially crosslinked state. Most of this was summarized by Allcock (.9). More recently, highly purified, uncrosslinked II has been examined in the solid state (21). The unstressed polymer is amorphous at room temperature, but crystallization can be induced by cooling or stretching techniques. The glass transition temperature, measured by Torsional Braid Analysis, is -66°C (22). 

It was also found that the tensile heat distortion temperatures of films containing only a few mole per cent of these units were considerably higher than those found for bisphenol A polycarbonate. X-ray diffraction studies made on the test samples used in the tensile heat distortion apparatus could not demonstrate an increase in crystallinity of the samples. Only a slight indication of increase of orientation was apparent. Glass transition temperatures measured by the refracto-metric method were considerably lower than the heat distortion temperatures. 

Fernando A. Alvearex-Ninez, Leonard, M.R., and Crawford, L.F. Glass transition temperature measurement as predictors of the physical stability of a poorly soluble pharmaceutical agent formulated as solid dispersion. AAPS 2002, Toronto, ON. 

Thermal properties are measured and evaluated by some of the methods also mentioned in Chapter 2. For identification of transition temperatures, measurements of heats of fusion, and so on, differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are much used. Thermal stability is measured by thermogravimetric analysis (TGA), although this technique can give overly optimistic results unless used with great care. 

Parentheses represent a monotropic transition temperature. Measured at a reduced temperature of 0.96 x Tn-i- Extrapolated value from a 10% concentration in a nematic mixture. 

Figure 26.16 Glass transition temperature, measured from the tan<5 peak maximum at 10 rad/s, of ESP. (P/S) denots the propylene to styrene molar ratio...

Ritter et al. [147-155] have been studying side chain poiyrotaxanes. They synthesized side chain poiyrotaxanes by amide coupling of polymer-carrying carboxylic acid moieties with various semirotaxanes of methylated /l-CD(s) and an axle bearing an amine group at one end [147-154]. These works have been reviewed in an excellent review by Raymo and Stoddard [78]. Ritter et al. [155] reported recently a new type of side chain polyrotaxane. They polymerized inclusion complexes of di(meth)acrylates of butan-l,4-diol and hexan-l,6-diol with a-CD and with methylated /1-CD using a redox initiator system in aqueous media, and characterized the polyrotaxane structure by IR and glass-transition temperature measurements. 

It is common practice now to use the glass transition temperature measured by a very slow rate method as the reference temperature for master curve construction. Tlien the shift factor for most amorphous polymers is given fairly well by... 

The studied copolymer (DRl-MMA 35/65) is presented in Figure 11.8. It is obtained by free radical polymerization of a 65/35 molar mixture of methylmetacrylate (MMA) and N-ethyl-N-(metacryloxyethyl)-4 -amino-4-nitroazobenzene (DRl derivative). Its glass transition temperature, measured by Differential Scaiming Calorimetry (DSC), is found to be 130°C. Polymer films are prepared by spin coating the solution of DRl-MMA in 1,1,2-trichloroethane (50 g/1) onto clean glass substrates. 

Chi, M.S. Compatibility of cross-hnked polymers with plasticizers by glass transition temperature measurement and swelling tests. J. Polym. Sci. Pol. Chem. Ed. 1981, 19, 1767-1779. 

Synthetic lipid A analogues were used in FTTR investigations to study possible intermolecular conformations of neighboring molecules [79]. There is good evidence that the bisphosphory-lated /3-(l—>6)-linked GlcN disaccharide backbone of lipid A is inclined (20—40° relative to the membrane normal), thus, the phosphate linked to 01 is reaching to the outside and that at 04 is buried in the membrane. This model is supported by data from transition temperature measurements and calorimetric experiments. However, it should be noted that other authors reported the reverse conformation with the 04 phosphate on the surface and the 01 phosphate in the membrane [80,81]. 

A common practice is to reduce relaxation or creep data to the temperature Tg thus, the reference temperature is picked as the glass transition temperature measured by some slow technique such as dilatometry. The reason for choosing Tg as the reference temperature is founded on the idea that all amorphous polymers at their glass transition temperature will have similar viscoelastic behavior. This type of corresponding states principal is often expressed in terms of a hopefully universal mathematical relationship between the shift factor aT at a particular temperature and the difference between Tg and this temperature. Perhaps the most well known of these relationships is the WLF equation... 

Table 7.20. Comparison of Various Methods for Transition Temperature Measurement (10)...

David et al. (31) used a digital temperature readout device in conjunction with an analog recorder for transition temperature measurements. Temperature resolution was about 0.05°C at a heating rate of lO C/ min. 

TG (Glass transition temperature)—measured on adhesive samples using differential scanning calorimetry (DSC). Changes in TG most often relate to chemical changes in the polymer that makes up adhesives. 

FIGURE 12.3 Specific volume v plotted against temperature for poly(vinyl acetate) measured after rapid cooling from above the T. measured 0.02 h after cooling and measured 100 h after cooling. and 7 are the glass transition temperatures measured for the different equilibration times. (From Kovacs, A.J., J. Polym. Set, 30, 131, 1958. With permission.)... 

FIGURE 3.14 Glass transition temperatures measured by the change in thermal expansion coefficient (circles), from calorimetry (triangles), by Raman scattering (inverted triangles), and by relaxation spectroscopy for r, = 100 (square). The solid line is the fit to the Fox-FTory equation with kpT = 12 kg/mol and Tg oo = 174.4K (Bc oslovov et al., 2010). 

In 1956 Thompson and Woods reported that dynamic experiments in extension indicated that orientation increased the temperature of the p transition, about 80°C, for oriented crystalline fibres, and reduced the drop in modulus occurring at higher temperatures. Subsequently nuclear magnetic resonance was used to demonstrate that orientation reduced molecular mobility above the glass transition temperature. Measurements of dynamic extensional and torsional moduli of hot stretched filaments and films were reported in 1963 by Pinnock and Ward, who found that the relations between measured compliances below the glass transition temperature were consistent with the deformation of an incompressible elastic solid. 

Dynamic mechanical analysis (DMA) is a sensitive method for glass transition temperature measurement, for detection of side-chain and main-chain motions, and for local mode relaxation measurements. Loeal mode relaxation can not be measured by DSC. DMA can give information about the crosslinking process of modified phenolic prepolymer [218] and about the erosslinked material [132]. During DMA measurements, sinusoidally varying stress of frequency is applied to the sample. Frequency and the stress are connected by equation 57, where is the maximum stress amplitude and is the phase angle at which the stress proceeds the strain. 

The Tg s of the FIPN s, PDIPN s and linear blends are listed in Table I. The two glass transition temperatures measured by DSC and Rheovibron are quite close (within experimental error). 

A phase diagram is a graphical representation of the relationship between a given set of experimental parameters and the phase changes occurring in a material. Sample volume, transition temperature and enthalpy, pressure and composition of the material are commonly used parameters in phase diagrams. Transition temperatures measured by TA are not equilibrium values and vary with the experimental conditions, particularly the scanning rate. Therefore,... 

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