SAXS and TEM studies on poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) in bulk and at various interfaces

Abstract

SAXS and TEM measurements are employed in order to study the morphology of poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) (SEBS) with 29 wt % styrene (Kraton G1652) in bulk and at interfaces to different polymers. Temperature-dependent SAXS measurements of the SEBS bulk sample reveal that PS cylinders are hexagonally packed in the EB matrix. The lattice constant increases during cooling from 200 to 120 degrees C from 27.5 to 29.5 nm and simultaneously an increase of the cylinder radius occurs from 7 to 7.5 nm. The lattice constant obtained by SAXS is in agreement with TEM measurements on ultrathin sections of the bulk sample. TEM tilting experiments confirm the existence of cylindrical microdomains in the SEBS bulk phase. Furthermore, the behavior of SEBS at the interface with various polymers is studied by TEM and peel tests. TEM: measurements show that SEBS forms one lamella at the interface PS homopolymer having a molecular weight much larger than the PS blocks. This results only in a very weak adhesion between SEBS and PS homopolymer measured by a peel test using bilayer specimens. In contrast there is a strong adhesion at the interface of SEBS with poly(3,5-dimethylphenylene ether) (PPE) or isotactic polypropylene (i-PP) after thermal annealing. This can be explained by the miscibility of the PS blocks with PPE and of the EB matrix of the block copolymer with i-PP, respectively. This leads to interfacial phase transitions, to cooperative orientation processes of PS cylinders, and finally to diffusion processes of disordered micelles as verified by TEM micrographs.