Phase transitions involving molecular reorientation in a series of copoly(esterimide)s

A series of copoly(ester imide)s (CPEIs) was synthesized by the esterification of N, N'-dodecane-1, 12-diylbis(trimellitimide) to two different acetylated diols, 4, 4'-dihydroxybiphenyl and hydroquinone, in varying proportions. Six samples were prepared and are designated as CPEI(A-F). CPEI(A) is a homopolymer having 100% of incorporated 4, 4'-dihydroxybiphenyl and CPEI(F) is a homopolymer having 100% of incorporated hydroquinone. The composition ratios of the copolymers are 80/20 (Bi, 60/40 (C), 40/60 (D), and 20/80 (E). With the exception of CPEI(F), the copolymers show enantiotropic smectic C phases. All of the samples exhibit highly ordered crystalline phases in the solid state. The nature of these phases has been found to depend on the thermal history of the samples with the existence of two possible molecular orientations with respect to the smectic layers. The first arrangement involves an alignment of the molecules parallel to the layer normal while the second arrangement involves tilted molecular alignment. Both appear to possess the same lateral packing dimensions and symmetry within the layers which is rectangular in the plane perpendicular to the chain direction. The three-dimensional lattice is thus orthorhombic in the case of the parallel molecular alignment and monoclinic (beta not equal 90 degrees) in the case of the tilted molecular alignment. Of the two arrangements the orthorhombic one appears to be more stable than the monoclinic one. Therefore, the phase associated with the monoclinic arrangement is accessible through a monotropic transition. A transition between these two arrangements occurs via structural melting and new order development upon heating. The presence of these two arrangements provides a unique opportunity to assess the origin of the anomalous orientation found in this series of copolymers.