Importance of interfacial mixed layer to determine the middle block Tg in lamellar structures of uncross-linked and cross-linked hard-b-soft-b-hard triblock copolymers

Abstract

We here discuss the importance of interfacial mixed layer on determination of the middle block Tg (Tg,B) of lamellar-forming hard-b-soft-b-hard ABA triblock copolymers. The detailed morphological characterization is first conducted by scattering measurements and model analyses, which provides the length fraction of B segments (fint,B) existing in the interfacial mixed layer to the overall B block chain. By investigating Tg for the neat triblock copolymers with various middle block lengths and volume fractions of the A blocks (φA), the variation of Tg,B is found to have a correlation with (fint,B). In the later section, the discussion related to Tg,B is made for the samples with cross-linked A block domains prepared via photo reaction. In this design, the original morphology is finely retained after the cross-linking, thereby enabling the extraction of the pure effects of the domain cross-linking on the physical properties. After the domain cross-linking, interestingly, the glass transition temperature of the B middle block (Tg,B) decreases, especially for the sample with φA > 0.5, where the reduction degree of Tg,B is determined by both the segmental density in the interface and fint,B.