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Molecularly asymmetric triblock copolymers progressively grown from a parent diblock copolymer can be used to elucidate the phase and property transformation from diblock to network-forming triblock copolymer. In this study, we use several theoretical formalisms and simulation methods to examine the molecular-level characteristics accompanying this transformation, and show that reported macroscopic-level transitions correspond to the onset of an equilibrium network. Midblock conformational fractions and copolymer morphologies are provided as functions of copolymer composition and temperature.

The phase behavior of an A–B diblock copolymer in a selective solvent of type A in thin films is examined by Monte Carlo simulations, using the coarse-grained lattice model with the Cooperative Motion Algorithm (CMA). This behavior is compared with that of the bulk (3-dimensional) and the 2-dimensional solutions. While we focus the simulations on symmetric 16–16 copolymers with a chain length of N = 32, we also simulate asymmetric 8–24 copolymers and chains with N = 48 and 64. At a relatively low copolymer volume fraction, approximately ϕ ≈ 0.3, the self-assembled micelles lose their long range order, and a solution of disordered micelles is obtained. We simulate the phase behavior of copolymer solutions both for thin films and 2-dimensional systems. Relevant properties, such as squared end-to-end distance, energy, specific heat and structure factor are measured as a function of the reduced temperature, T*. We also characterize the observed micelles by counting the average number of copolymer chains that constitute a single micelle. We observe three phases: layers, hexagonally packed disks and disordered micelles. The phase diagrams from ϕ = 1.0 to 0.1 in the (ϕ, T*) parameter space are shown for both the symmetric and asymmetric copolymer. We find that the phase behavior of the thin film solution is intermediate between that of the 3D and 2D solutions, but it is more similar to 2D because the film thickness is relatively small.

We extend Wertheim's first-order thermodynamic perturbation theory [J. Chem. Phys. 87, 7323 (1987)] to sticky chains and square-well chains. The predicted compressibility factors for square-well chains are found to agree with Monte Carlo data. We demonstrate that the effect of chain connectivity is to reduce the attraction contributions to the compressibility factor and to the critical temperatures.

The formation of lamella microphases in symmetric neutral-ionic block copolymers has been investigated by constant volume--constant temperature (NVT) molecular-dynamics computer simulations using a generic coarse-grain model. Computations of counterion diffusion, pressure tensor, and the anisotropy of the structure factor are used to characterize the order-disorder transition (ODT). There is strong counterion condensation on the ionic blocks at temperatures well above the ODT; this creates a slight imbalance in the volume composition of the two blocks and results in a perforated lamella structure in the microphase. Below the ODT counterion diffusion is decoupled from the chain motions but is strongly anisotropic due to the microphase morphology. The high counterion diffusional mobility is discussed in terms of the relatively low value of the glass transition for the ionic blocks.

On the basis of experimental batch-cell data, increasing short-chain branch density is found to reduce the cloud-point pressure of poly(ethylene-1-butene) solutions in propane, by as much as a factor of 3. This trend is captured by a SAFT approximation via an effective. segment energy that depends on the branch density. Increasing branch density is found to decrease the effective segment energy and, hence, to make it closer to that of propane, which is consistent with the enhanced miscibility of branchy poly(ethylene-1-butenes) in propane