Glass transition temperature measurements

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. 

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. 

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. 

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... 

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). 

Part of the work performed on a sample will be converted irreversibly into random thermal motion by movement of the molecules or molecule segments. This loss passes through a maximum at the appropriate transition temperature or relaxation frequency in the associated alternating mechanical field (torsion pendulum test). A similar effect is obtained by the delayed response of the dipoles with dielectric measurements. Therefore, dielectric measurements can be made only on polar polymers. According to the frequency used, the glass-transition temperatures measured with dynamic methods lie higher than those obtained by quasistatic methods (see Section 10.5.2). 

Table 1. Glass transition temperatures measured by DSC, thermomechanical and AC dielectric methods on filled and nonfilled epoxy resins (after Ref.[6]).

When the kinetics of the final polymerization of higher methacrylates are compared with that of methyl methacrylate, the most Important difference is the size of the molecule and thus its diffusibility. Table 2 presents a summary of the monomers investigated and provides information on the glass transition temperatures measured by DSC, the molar volumes, and the final conversions achieved after 2 hours at temperatures 5K above T. In Figure 8... 

Glass transition temperature measurements on the solutions of Zdol in PFOM were performed in a temperature-modulated differential scanning calorimeter. 

The glass transition of amorphous polymeric films was investigated by SPM imder various conditions. We established, using lateral force measurements, that the pressure exerted by the tip does not have an effect similar to a hydrostatic pressure on the properties of the polymer. Instead, an apparent transition is observed due to the viscoelastic nature of the sanq)le. We confirm the existence of a critical load and scan speed, which need to be determined to obtain accurate glass transition temperature measurements. 

Specific volume and I is the sample length). Therefore, DMA is the most frequently used technique in the fiber/film technology field. A single measurement will provide the temperature dependence of the modulus and the glass transition temperature and will characterize possible second-order transitions of the material. It is important to remember, however, that the glass transition temperature measured by DSC always will be different from that determined by relaxation methods, such as DMA or DEA (due to the frequency excitation effect). Details of DMA measurements of fibers and films can be found in several references [e.g., Murayama (1978), Jaffe et al. (1997) Menczel et al. (1997b)]. Here we briefly summarize the most important aspects of this type area of DMA measurement. 

Riesen, R., Schawe, J. (2003). The glass transition temperature measured by different TA techniques. Part 2 Determination of glass transition temperatures. UserCom, 18(2), 2-5. 

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