A thermomechanical investigation of highly cold‐drawn polycarbonate

Abstract

SynopsisA new technique detecting molecular motions in drawn polymers was applied to highly cold-drawn polycarbonate of bisphenol A. It is shown that the sample exhibits thermal shrinkage in three steps with the temperature increase up to above the glass transition temperature. The molecular relaxation at the highest temperature is due to the glass transition. The other two molecular motions a t the lower temperature are those of main chain in the glassy state and they correspond to the molecular motions as revealed in dielectric measurement by Sacher.' By using the general theory of the thermal analysis by Ozawa,2 the apparent activation energies of these molecular motions were obtained for the highest temperature 110 kcal/mole, and for the lowest temperature, 33.5 kcal/mole. The impact strength and the cold workability of this polymer are also discussed in relation to these molecular motions.

Elastic Yielding after Cold Drawing of Ductile Polymer Glasses

“…Below we would like to explore in further detail the characteristics of the elastic yielding. We also note that thermal shrinkage of a cold-drawn polymer glass, after unloading from the strain hardening regime, has been known to take place since 1950s. − ,− In our new understanding, such shrinkage is clearly another form of elastic yielding. We will discuss its effect on the elastic yielding in section .…”

“…Elastic yielding should be a universal phenomenon for all ductile polymer glasses. Apart from PC, 38,45,51 in this work we have also two other ductile glasses: PET 45 and PPE. Since they are ductile at room Figure 9 shows that all of them exhibit the elastic yielding phenomenon.…”

“…Elastic yielding should be a universal phenomenon for all ductile polymer glasses. Apart from PC, ,, in this work we have also two other ductile glasses: PET and PPE. Since they are ductile at room temperature, we performed cold-drawing of PPE as well as PET at 20 °C, as shown in the inset of Figure .…”

Multiple molecular relaxations of hot‐drawn and quenched polymers above their glass transition temperatures

“…We have presented a new technique detecting molecular motions in solid polymers using thermal contraction under uniform rate of heating. 5,6 One of the two objects of the present article is to show multiple molecular relaxations of highly hot-drawn and quenched poly(methy1 methacrylate) and polycarbonate of bisphenol A. Almost all the molecular relaxations associated with shrinkage are above their glass transition temperatures.…”

Aging of oriented polymer glasses

“…These last experiments on PC demonstrate that the chains have a great mobility even far below T g . Kato and Kambe [33] found that annealing at 140°C (10°C below T g ) permits the complete relaxation of the cold drawn sample. These experiments are not possible for PS; this polymer is fragile and the sample breaks during cold deformation, before yielding.…”