Glass transition of undrawn and drawn copolyetherester thermoplastic elastomers

Abstract

The phase and deformation behaviour of two types of copolyetheresters (the block copolymers E and P) were studied by means of DSC, dynamic mechanical spectroscopy and X-ray diffraction. The block copolymers E and P based on poly(butylene therephtalate) (PBT) as a hard block have poly(tetramethylene oxide) (PTMO) and triblock copolymer (PEO-PPO-PEO) with a middle poly(propylene oxide) (PPO) block and two end poly(ethylene oxide) (PEO) as a soft block, respectively. The complex investigation shows that the studied copolyetheresters are microphase separated polymer systems in the amorphous matrix of which the PBT crystallites are embedded. The volume fraction of PBT crystallites depends on the block copolymer composition and changes from 5 to 20%. In the amorphous matrix that is the mixed PBT/ the soft block phase the soft block acts as a PBT plasticizer reducing the glass transition temperature of the amorphous mixed phase. The most interesting aspect of the phase behaviour of the copolyetheresters consists in the fact that, in comparison with PTMO, the triblock is characterized by a more pronounced PBT plasticization effect. A special emphasis was placed in this work on the investigation of an increased glass transition temperature of drawn copolyetheresters. It was found that this process depends on the volume fraction of PBT crystallites and chemical structure of the soft blocks. The first factor characterizes the interaction between the amorphous mixed phase and PBT crystallites and, therefore, the higher value of the volume fraction of PBT crystallites the higher is the glass transition temperature of drawn copolyetheresters. The second factor determines the PBT plasticization effect of the soft blocks and a level of the interaction of chains in the amorphous mixed phase. Because of a weaker PBT plasticization effect of PTMO in comparison with that of the triblock, the deformation of the block copolymer E is accompanied by a more pronounced elevation of the glass transition temperature in comparison with the block copolymer P.