Glass transition temperatures experimental values

Experimental glass-transition temperature (onset) values (closed symbols) and water contents (open symbols) for amorphous maltodextrin MlOO (circles) and M180 (triangles) matrices as a function of storage relative humidity at 25°C. The glass-transition temperatures and water contents for maltodextrin MlOO and M180 matrices stored at relative humidities of 66 and 54%, respectively, are shown by straight lines. 

In addition to thermodynamic appUcations, 62 values have also been related to the glass transition temperature of a polymer, and the difference 62-61 to the viscosity of polymer solutions. The best values of 6 have been analyzed into group contributions, the sum of which can be used to estimate 62 for polymers which have not been characterized experimentally. 

The TPX experimental product of Mitsubishi Petrochemical Ind. (221) is an amorphous, transparent polyolefin with very low water absorption (0.01%) and a glass-transition temperature comparable to that of BPA-PC (ca 150°C). Birefringence (<20 nm/mm), flexural modulus, and elongation at break are on the same level as PMMA (221). The vacuum time, the time in minutes to reach a pressure of 0.13 mPa (10 torr), is similarly short like that of cychc polyolefins. Typical values of TPX are fisted in Table 11. A commercial application of TPX is not known as of this writing. 

Moreover, the mesophase-volume fractions Oj for the same inclusion-contents were determined from the experimental values of heat-capacity jumps ACp at the respective glass transition temperatures T f by applying Lipatov s theory. Fig. 7 presents the variation of the differences Ars oi the radii of the mesophase and the inclusion (rf), versus the inclusion volume content, uf, for three different diameters of inclusions varying between df = 150 pm and df = 400 pm. 

The glass transition temperature is generally measured- by experiments that correspond to a time scale of seconds or minutes. If the experiments are done more rapidly, so that the time scale is shortened, the apparent Tg value is raised. If the time scale is lengthened to hours or days, the apparent Tg value is lowered. Thus, as generally measured, Tg is not a hue constant but shifts with the time scale of the experiment or observation. Moreover, Tg is masked by experimental difficulties, compounded by multiple and often inaccurate definitions of Tg in the literature. The least... 

Fig. 2. Correlation of experimental values of the Langmuir capacity parameter (Sq) for C02 at 35 °C with the glass transition temperature of the polymer25) [cf. Eq. (10)]. Pure polymers (PSF = a poly-sulphone 231 COP = a copolyester 26) remaining abbreviations as in the text). Miscible polymer blends O PPO-PS 65> O PC-COP 26>...

The temperature position of the secondary fi relaxation (about 290 K 1 Hz), generally attributed to partial rotations of the side chains COOR, is only slightly affected by the polarity and volume of the substituent R but decreases markedly (by 120 K) on removal of the a-methyl group on the main chain. The experimental data obtained contradict the assumption that there is a certain relationship between this temperature and the glass transition temperature. Nevertheless, we can infer that the pertinent molecular mechanism in polymethacrylates differs from that in polyacrylates, probably due to the different participation of the main chains. The values of the individual contributions to the activation energy were estimated by employing a procedure similar to that used in the y relaxation process, and their sum was found to agree approximately with the experimental values. 

At least two different glass transition temperatures have been reported for PVdF homopolymer. Owing to the large proportion of crystalline structure in this polymer and the rapid crystallization which occurs while heating quenched amorphous samples, it is difficult experimentally to obtain an unambiguous, well-defined second-order transition. Mandel-kem, Martin, and Quinn (16) reported a value below — 40°C based upon an extrapolation of the Tg data for vinylidene fluoride-chlorotri-fluoroethylene copolymers in accordance with the Fox equation (6),... 

The crystalline state configuration of polymeric selenium is a helix in which all the rotational angles are of the same sign with a value of 78°. This is fairly close to the expected value of 90°.52 The barrier to rotation about the Se-Se bond is thought to be roughly the same as that about S-S bonds. No reliable experimental results are available on the statistical properties of these chains. Some values of the glass-transition temperature of polymeric selenium have been reported15 and these could at least provide a measure of the dynamic flexibility of the chains. However, these results are probably compromised by the presence of cyclic selenium molecules that act as plasticizer. 

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