SynopsisPolyethyloxazoline (PEOx) is a new water-soluble, thermoplastic polymer. It has a glass temperature of 56°C which increases to about 72'C on storage at room temperature. This increase is a manifestation of physical aging, and it occurs relatively fast with PEOx in comparison to other polymers. Also, the extent of this aging, as measured by the amount of enthalpy relaxation, is high for PEOx. It was shown that PEOx can be brought to 320°C without reduction of glass temperature, indicating an exceptional thermal stability.
INTRODUCTIONPolyethyloxazoline (PEOx) is a new water-soluble thermoplastic polymer which can be easily melt fabricated, and has excellent thermal stability.It is also miscible with a number of other thermoplastic polymers.2It is well known that amorphous polymers are not in thermodynamic equilibrium in their glassy state.3r4 At storage temperatures below T , , continuous reduction of free volume takes place due to molecular relaxation, and eventually an equilibrium state will be reached. The degree of such relaxation can be most conveniently followed by measuring the changes in the enthalpy by differential scanning calorimetry (DSC). This reduction of free volume or physical aging also manifests itself by changes in mechanical properties. Accordingly, it was of interest to study the thermal properties and behavior of PEOx in some detail and to make comparisons with some polymers which have been previously studied. The results of this study are presented in this paper.
EXPERIMENTALPEOx is an experimental polymer from The Dow Chemical Co. It is a linear, amorphous polymer of the following structure:
942KESKKULA AND PAUL lycarbonate sheet was also used for some comparative thermal measurements. Glass transition temperatures and other thermal characteristics were determined using a Perkin-ELmer DSC-2 equipped with a Thermal Analysis Data Station (TADS). The computer-plotter combination permits storage and recall of data for manipulation such as subtraction and integration. The DSC was calibrated with Indium. The thermal behavior of PEOx was studied over a wide range of heating rates and storage times. However, in most cases a heating rate of 20°C min was used, and quenching was done at the fastest setting on the instrument,. 320°C min.-'The T , was defined as the intersection of the heat capacity slopes from the glass to the transition region. Endothermic peak area ( A H ) was determined by integration of the area above the extension of the line representing the liquid state of the polymer. Specimens for the DSC experiments were prepared by placing the polymer (10-20 mg) in a tared DSC aluminum pan, transferring to a hotplate and then melting in the specimen pan at about 200-230°C for a short time (30 s). Sample weight was determined by difference.
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