SynopsisTorsional braid analysis (TBA) ( 4 . 3 Hz) and differential thermal analysis (DTA) data are presented for the temperature region 0-200°C for two series of atactic polystyrenes with narrow molecular weight distributions: (a) anionic series, M n = 6O0-2X1O6, MW/Mn N 1.1; (b) fractionated thermal series, @, , = 2,000-l.lX105, Mw/M ,, (1.25. Preliminary results on bimodal blends are also reported. Heating and cooling cycles were employed with TBA; only the heating mode was used with DTA. In addition to a dynamic mechanical loss peak a t T,, a higher temperature loss peak was also found. Designated the Tu or liquid-liquid transition (relaxation), its temperature is 1.1 to 1.2 T, ( O K ) for polymers with molecular weight below the critical molecular weight (M,) for chain entanglements. Above M, a? 35,000, it rises steeply, being c=2OO0C for @, , = 110,000. The common dependence of T, and Tii on &f,,-l below M, suggests a common molecular origin. The two facts, (a) that Ti1 > Tg and (b) that Ti1 reflects chain entanglements, further suggest that Ti1 involves a longer chain segment length and possibly the entire molecule. Comparison of 7 ' " versus log M plots with T versus log M isoviscous state plots based on zero-shear melt viscosity data from the literature implies that Tii-as measured by the TBA technique corresponds to an isoviscous state of 104-105 poises. The employment of narrow molecular weight polymers is presumably responsible for both the linear variation of the Ti1 transition with & f n -l (which suggests a free volume basis for the relaxation) and the form of the variation of the Ti1 transition with log M (which suggests an isoviscous basis for the relaxation). The sharpness of the Ti1 loss peak by TBA decreases with increasing molecular weight and dispersity. The DTA endothermic event corresponding to Ti! is clearly related to the occurrence of flow since the fused films which result from heating granules to 200'C and cooling to R.T. do not reveal a Tli on reheating. If a fused film is crushed, a Ti1 event is observed on heating. For bimodal blends with M,, < M, for both components, the Ti1 transition was averaged; with one component less than and one greater than M,, the Ti1 transitions of the components appeared to occur independently at temperatures corresponding to those of the isolated components. In accordance with Ueberreiter and Orthmann, T, appears to separate a glassy state from a fixed liquid state, whereas T11separates the fixed liquid from a true liquid state. Possible molecular interpretations for the Ti1 process are discussed. Systematic bodies of data from the literature which indicate the presence of the Ti1 process in other polymers are summarized.

SynopsisA computerized and automated torsional pendulum has been used to characterize amorphous poly(methy1 methacrylates) a t about 1 Hz in the temperature sequence 473' -93" -473°K. The effects of thermal prehistory, temperature cycling, water content, and tacticity are demonstrated. In particular, a comparison of the out-of-phase shear modulus (G") versus temperature for "syndiotactic," "atactic," and "isotactic" polymer specimens shows that the intensity of the glassy-state 6 loss peak decreases with increasing isotactic content while the temperature of its location remains the same. Extrapolation suggests that completely isotactic polymer would not display a 6 loss peak.The shape and location of the G " data a t low temperatures indicate that the basic mechanism of the 6 process is the same for the three polymer samples and support the validity of the extrapolation.The effect of tacticity is reflected also in the glass transition region; the isotactic sample has its Tx about 65°C lower with greater intensity than the syndiotactic polymer.

synopsisTwelve polyimides which differ systematically in chemical structure were investigated in nitrogen through the temperature range -190" + 500°C by torsional braid analysis.The degrdative regions were also examined in nitrogen by thermogravimetric analysis. Relationships between chemical structure/thermal history, processibility, thermomechanical behavior, and weight loss are discussed. A logical thermal program for converting the precursor polyamic acid solutions to solid polyimides was developed. High-temperature, thermdly induced chemical reactions could be regulated so as to preferentially freeze out longer-range relaxations and extend the glass state behavior to well above its original load-limiting T,. Materials made from more flexible molecules had lower glass transit,ions, softened more through the To, and had simpler damping spectra and lower thermal stability than materids made from more rigid molecules. A commercially available polyimide film and polyimideforming varnish of undisclosed structures were examined by torsional pendulum and torsional braid analyses, respectively. The thermomechanical spectra of the f i l m and cured varnish were similar to the spectra of one structural type of polyimide.