Relative Chain Flexibility Determines the Spatial Arrangement and the Diffusion of a Single Ring Chain in Linear Chain Films

Crystalline Nanoflowers Derived from the Intramolecular Cyclization-Induced Self-Assembly of an Amorphous Poly(amic acid) at High Solid Content

The investigation of the amorphous to crystalline transformation and the corresponding influence on the self-assembly behavior of amphiphilic polymers are of significant interest in this field. Herein, we propose the concept of intramolecular cyclization-induced self-assembly (ICISA) to prepare crystalline nanoflowers at a high solid content of 15% on the basis of the amorphous to crystalline transformation of poly(amic acid) (PAA). Taking advantage of the reactive property of the PAA, rigid and crystalline polyimide (PI) segments are introduced to the backbone of the PAA to give P(AA-stat-I) induced by the intramolecular cyclization reaction upon thermal treatment, leading to the in situ formation of crystalline nanoflowers. Revealing the formation mechanism of the nanoflowers, we found that the nanosheets are formed at the early stage and then stacked to form the nanoflowers at high concentrations. The relationship between the degree of imidization and incubation temperature is quantitatively analyzed, and the effects of temperature on the morphology, degree of imidization, and crystallinity of the assemblies are also investigated. Furthermore, computer simulations demonstrate the optimized temperature of ICISA of 160 °C, which ensures the match between the intramolecular cyclization reaction rate, the self-assembly process, and the lowest energy state of the self-assembly system, resulting in the formation of nanoflowers with high crystallinity. Overall, a facile one-step strategy is proposed to prepare crystalline nanoflowers based on the in situ thermally triggered intramolecular cyclization reaction of a PAA, which may bring fresh insights into the dynamic amorphous to the crystalline transformation of polymers.

Rheological Role of Stiff Nanorings on Concurrently Strengthening and Toughening Polymer Nanocomposites

Nanorings, which are increasingly uncovered in natural systems and synthesized in man-made materials, exhibit dynamics distinct from those known for linear chains. We show in this study that, when immersed in a polymer melt matrix, segments of a stiff nanoring (SNR) have more facilitated subdiffusion, i.e., with a larger scaling exponent in the mean squared displacement, than those belonging to one flexible counterpart, while the whole SNR is more suppressed by its surroundings. It is revealed that adding SNRs contributes to achieving the long-anticipated rheological objective of sol- and gel-like characteristics at high and low shearing frequencies, respectively. This study suggests the promising prospect of exploiting SNRs to concurrently strengthen and toughen target polymer nanocomposites.

To thread or not to thread? Effective potentials and threading interactions between asymmetric ring polymers

We use computer simulations to study a system of two unlinked ring polymers, whose length and bending stiffness are systematically varied. We derive the effective potentials between the rings, calculate the areas of minimal surfaces of the same, and characterize the threading between them. When the two rings are of the same kind, threading of a one ring through the surface of the other is immanent for small ring-ring separations. Flexible rings pierce the surface of the other ring several times but only shallowly, as compared to the stiff rings which pierce less frequently but deeply. Typically, the ring that is being threaded swells and flattens up into an oblate-like conformation, while the ring that is threading the other takes a shape of an elongated prolate. The roles of the threader and the threaded ring are being dynamically exchanged. If, on the other hand, the rings are of different kinds, the symmetry is broken and the rings tend to take up roles of the threader and the threaded ring with unequal probabilities. We propose a method how to predict these probabilities based on the parameters of the individual rings. Ultimately, our work captures the interactions between ring polymers in a coarse-grained fashion, opening the way to large-scale modelling of materials such as kinetoplasts, catenanes or topological brushes.

Impact of Chain Conformation on Structural Heterogeneity in Polymer Network

Polymer networks generally consist of an ensemble of single chains. However, understanding how chain conformation affects the structure and properties of polymer networks remains a challenge for optimizing their functionality. Here, we present the fabrication and comparative study of a polymer network composed of collapsed self-entangled chains (intrachain entangled network) and a standard polymer network in which random-coil chains are entangled with each other (interchain entangled network). For poly(methyl methacrylate) thin films composed of these networks, we coupled solvent vapor swelling and single-molecule tracking techniques to examine the anomalies in the dynamics of a small-molecular probe included in the system. We demonstrate that when compared to the interchain entangled network the intrachain one exhibits a more substantial structural heterogeneity, particularly under highly crowded conditions. This network also exhibits physical compactness, which keeps the heterogeneous network structure frozen over time and impedes network plasticization through solvent uptake by the film.