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The phase behavior of poly(styrene-b-butyl methacrylate), PS-b-PBMA, diblock copolymers was investigated by small-angle neutron scattering (SANS), neutron reflectometry (NR), and rheology. For a symmetrical P(dS-b-nBMA) diblock copolymer a lower critical order transition (LCOT) at 155°C was found by SANS and rheology. Furthermore, the temperature-dependent interaction parameter was determined in the temperature regime between 110 and 145°C from fits to the scattering curves in the disordered region. The interaction parameter increases with increasing temperature and shows a weak temperature dependence. The LCOT behavior thus is expected to be a large entropic contribution to . The interfacial width observed by NR is relatively large compared to other diblock copolymers. Different block copolymers were investigated with respect to the influence of miscibility on tensile properties. While poly(styrene-b-butyl methacrylate) diblock copolymers show significant synergistic effects on tensile properties, for poly(methyl methacrylate-b-butyl methacrylate) diblock copolymers no significant synergistic effects on tensile properties were observed due to the increased interaction parameter and the smaller interfacial width as compared to the case of PS-b-PBMA diblock copolymers.

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The deformation behavior of poly(styrene-b-butyl methacrylate) diblock copolymers, PS-b-PBMA, is studied by high-voltage electron microscopy (HVEM) with an in-situ tensile device. While in the first part the phase behavior of PS-b-PBMA diblock copolymers is investigated via small-angle neutron scattering (SANS), in the second part the deformation behavior depending on composition and molecular weight is discussed. Disordered block copolymers have the same deformation mechanism as the corresponding homopolymers, while microphase-separated block copolymers undergo a cavitation mechanism. At the order-disorder transition, ODT, a transition from crazing to cavitation mechanism is found via HVEM. Moreover, a sharp increase of the diameter of craze fibrils occurs at the ODT, demonstrating that the craze microstructure is strongly influenced by phase behavior. As the incompatibility increases with increasing molecular weight, deformation mechanisms such as diversion and termination of crazes are observed for intermediately segregated block copolymers. The discussed correlation between phase behavior and deformation mechanisms indicates the existence of a unified scheme for deformation behavior of diblock copolymers depending on the strength of segregation, N.

Block copolymers having different strengths of segregation are investigated with respect to their deformation behavior. Disordered block copolymers are deformed by the mechanism which corresponds to a glassy homopolymer. A crazing mechanism is observed for block copolymers with polystyrene as matrix. At the order−disorder transition (ODT), a change from crazing to cavitation mechanism is observed, confirming the change of deformation mechanism at the ODT. For intermediately and strongly segregated block copolymers, observed mechanisms of termination and diversion of crazes are caused by both the increased long-range order and larger grain size with increasing incompatibility. A novel scheme is proposed which summarizes the deformation behavior of block copolymers depending on strength of segregation, χN. It is now possible to predict the deformation mechanism of a diblock copolymer system only from strength of segregation. Since the mechanical properties are also influenced by strength of segregation, it is possible to create materials with tailored properties utilizing temperature or pressure. The property profiles of different block copolymer systems are summarized to demonstrate the exceptional combination of high strength and toughness of intermediately segregated block copolymers. The presented scheme only represents a qualitative picture of deformation behavior of block copolymers and is only a first step to a future predictive modeling.

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The compatibility of d8-poly(methyl methacrylate) (d8-PMMA) and a series of poly(n-alkyl methacrylate)s (PnAlkMA) is studied by systematic variation of the length of the n-alkyl group from ethyl (EMA) to n-pentyl (nPenMA). Simultaneously, a series of symmetric diblock copolymers comprised of d8-PMMA and of PnAlkMA ranging from ethyl to n-hexyl (nHMA) is synthesized. Small-angle X-ray data of bulk samples of d8-PMMA-b-PEMA show that this block copolymer is in the disordered state. A change in the χ over 1/T plot occurs between 120 and 130 °C owing to fluctuations. All other block copolymers are in the ordered state at any temperature. The neutron reflection data of d8-PMMA-b-PEMA show a damped cosine concentration depth profile characteristic for thin films of block copolymers in the disordered state. In contrast, the bilayer film of the respective homopolymer pair indicates immiscibility. Neutron reflection measurements on thin films of diblock copolymers ranging from d8-PMMA-b-PnPrMA to d8-PMMA-b-PnHMA and of bilayer films of d8-PMMA and the respective PnAlkMAs show a decreasing apparent interfacial width with increasing length of the n-alkyl group. Taking into account the contributions of capillary waves leads to the inherent interfacial width. By use of the theoretical approach of Matsen and Bates, it is possible to extract the Flory-Huggins χ-parameter between the blocks and the average segment length.