Simultaneous small-angle scattering and in situ dynamic mechanical measurements offer an excellent opportunity to relate the macroscopic dynamical mechanical response of block copolymers and their mesoscopic structural behavior. We use small-angle neutron scattering and rheology to examine the ordered phases and the order−order transitions exhibited by a poly(ethylene-alt-propylene)−poly(dimethylsiloxane) diblock copolymer. An intermediate structurevery similar to the hexagonal perforated layer (HPL) phase reported in other diblock systemsproves to be metastable, and we study the kinetics and epitaxy of its relaxation to the “gyroid” phase of Ia3̄d symmetry. Likewise we study the relaxation of a supercooled hexagonal phase to the gyroid structure and also observe that the gyroid phase is bypassed in a slow cool from the hexagonal phase to the HPL-like structure. The origin of a typical scattering pattern obtained from a highly oriented crystal structure of a sample in the gyroid phase is investigated and related to real space projections of the gyroid morphology. Synchrotron small-angle X-ray scattering is used for high-resolution studies of the ordered phases. Reversibility of transitions between different mesoscopic structures is studied, especially to and from the gyroid phase, and puzzling patterns of the HPL-like structure are observed.

Crystallization in oriented diblock copolymers containing poly(ethylene) (PE) has been investigated using simultaneous small-angle and wide-angle X-ray scattering (SAXS/WAXS). The orientation of the crystallized PE stems was deduced from the orientation of peaks in the WAXS pattern with respect to those in the SAXS to be parallel to the lamellar interface for symmetric diblocks containing PE and either a rubbery or glassy amorphous block. For a symmetric diblock with a poly(vinylcyclohexane) block that is glassy at room temperature we observe diffuse scattering parallel to the meridian in the SAXS pattern that is consistent with lateral correlations between PE crystallites within the layers of semicrystalline PE. In contrast, in all the samples containing an amorphous component, PE crystallization occurred with no lateral positional correlations of crystallites. Crystallization in asymmetric diblocks with compositions fPE ) 0.35 and 0.46 was also investigated. It was found that a lamellar structure is the stable solid structure and that this melts epitaxially to a hexagonal-packed cylinder structure in the fPE ) 0.35 sample. For the fPE ) 0.46 sample that forms a perforated layer phase in the melt, chainfolded PE stems were found to be parallel to the lamellar interface, as for the symmetric diblocks.

The morphological behavior of a series of well-defined A2B simple graft or “Y” architecture block copolymers is characterized via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). This model architecture is formed by grafting a polystyrene block onto the center of a polyisoprene backbone. The volume fraction windows in which specific strongly segregated microphase-separated morphologies are observed are shifted to higher volume fractions of the PS graft material than in the corresponding linear diblock copolymers. These findings are in good agreement with recently calculated theoretical phase behavior for simple graft, A2B, block copolymers. However, a new morphology, not found in neat linear diblock copolymers, is also observed. This A2B material is microphase separated into wormlike micelles but not ordered on a lattice. This morphology is found at high PS graft volume fraction (φs = 0.81), where the two PI chains per molecule are initially forced to the concave side of the PS/PI interface.

Unsolvated block copolymers and surfactant solutions are "soft materials" that share a common set of ordered microstructures. A set of polyethyleneoxide-polyethylethylene (PEO-PEE) block copolymers that are chemically similar to the well-known alkane-oxyethylene ( C, EO, ) nonionic surfactants was synthesized here. The general phase behavior in these materials resembles that of both higher molecular weight block copolymers and lower molecular weight nonionic surfactant solutions. Two of the block copolymers exhibited thermally induced order-order transitions and were studied in detail by smallangle scattering. The fundamental microstructural spacing was determined to be a crucial parameter in these transitions. Transitions from one ordered state to another occur only when the lattice spacing is nearly matched. These materials highlight the importance of epitaxy and molecular conformation in the phase transformations of soft material.AmDhiDhilic molecules such as surfactants, L A phospholipids, and ionic soaps self-assemble into micelles in dilute aqueous solution because of the hvdro~hobic effect. As the concentration of ;he akphiphile increases, thermodynamically stable supramolecular aggreeates form with a varietv of ordered-state

The chain folding behavior of oxyethylene/oxybutylene (E/B) diblock copolymers, with one crystallizable E block and one noncrystallizable B block, has been studied by simultaneous SAXS and WAXS, low-frequency Raman spectroscopy, and differential scanning calorimetry. Two models, normal density (ND) and crystal/liquid-crystal (CLC) models were used to explore the results, consideration being given to the difference in the cross-sectional area of the two chains and the need to fill space at approximately normal density. It was found that both models can describe the data for the longer copolymers, but the CLC model is better for the shorter copolymers.