ACS Macro Letters最新文献

Sequence-controlled polymerization aims to bridge the gap between biopolymers and synthetic macromolecules. In a kinetically controlled approach, the inherent reactivity differences among monomers determine the primary structure or sequence of the monomers linked within the resulting copolymer chains. This report outlines a one-pot synthesis of polypeptide-b-polypeptoid by choosing a suitable pair of N-carboxy anhydride (NCA) monomers with significant reactivity differences. We have demonstrated the preparation of well-defined block copolymers, including polyproline-b-polysarcosine (PLP-b-PSar) and poly(propargyl proline)-b-polysarcosine (PLPP-b-PSar) in a single step. ¹H NMR kinetic studies confirmed the sequence-controlled primary structures of these block copolymers. The NMR analysis indicated a striking reactivity ratio difference (r_PLP = 925 and r_PSar = 0.0014; r_PLPP = 860 and r_PSar = 0.0015) between the selected monomer pairs, which was crucial for a one-pot block copolymer synthesis. Notably, these sequence-controlled copolymers’ secondary structures and stability were remarkably similar to those of block copolymers synthesized through conventional sequential addition methods. This further underscores the practicality of this kinetically controlled approach.

Vitrimers are sustainable cross-linked polymers characterized by an associative bond exchange mechanism within their network. A well-known feature of vitrimers is the Arrhenius dependence of the viscosity or relaxation time. Another important aspect is the existence of a topology-freezing temperature (T_v), which represents a transition between the viscoelastic solid state and the malleable viscoelastic liquid state. Various methods, including viscosity-temperature plots and temperature-ramp creep (or dilatometry), have been proposed for determining the T_v. In this study, we complementarily employ X-ray scattering-based structural analysis and rheological analysis to assign T_v in phase-separated vitrimer-like materials undergoing trans-N-alkylation bond exchange. Note that the trans-N-alkylation progresses via the dissociative bond exchange pathway, whereas our previous studies demonstrated that the temperature-dependence of relaxation time followed the Arrhenius dependence, which was the reason for the classification as a vitrimer-like material. Specifically, we identify T_v as the temperature at which an anomalous increase in domain distance occurs during the rubbery state in the structural analysis. In the rheological analysis, T_v corresponds to the transition temperature marking the shift from the Williams–Landel–Ferry dependence to the Arrhenius dependence in the shift factors used to create master curves for frequency sweep rheology data. Importantly, both methods yield nearly the same T_v, validating the accuracy of the proposed assignment and, thus, providing valuable insights into the specific properties of vitrimers.

In complex networks and fluids such as the extracellular matrix, the mechanical properties are substantially affected by the movement of polymers both part of and entrapped in the network. As many cells are sensitive to the mechanical remodeling of their surroundings, it is important to appreciate how entrapped polymers may inhibit or facilitate remodeling in the network. Here, we explore a molecular-level understanding of network remodeling in a complex hydrogel environment through successive compressive loading and the role that noninteracting polymers may play in a dynamic network. We find that this is a highly localized and time-dependent effect, with one of the major driving factors of hydrogel matrix remodeling the interaction and movement of water within the network in calcium-cross-linked alginate. Our results suggest a more general mechanistic understanding of hydrogel remodeling, with implications for tissue transformations in disease, biomaterials, and food science formulation.

Stimuli-responsive polymers have demonstrated significant potential in the development of smart materials due to their capacity to undergo targeted property changes in response to external physical or chemical stimuli. However, the scales of response in most existing stimuli-responsive polymer systems are mainly focused on three levels: functional units, chain conformations, or polymer topologies. Herein, we have developed a covalent polymer network (CPN) capable of converting into a supramolecular polymer network (SPN) within bulk materials directly at the scale of polymer network types. This transformation is enabled by specifically designed covalent moieties that upon UV exposure reveal quadruple hydrogen bonding sites, allowing the formation of a supramolecular network. This network-type transition from CPN to SPN induces pronounced intrinsic changes in material properties, including a substantially increased breaking elongation, lower Young’s modulus, reduced fracture strength, and decreased creep resistance, marking a shift from a stable, rigid structure to a dynamic, adaptable one. These findings provide new insights into the design of advanced stimuli-responsive polymer materials through network-type transformations, opening new avenues for applications in smart and multifunctional materials.

We developed a unique water droplet templating method to fabricate polymer films with three-dimensionally ordered porous structures. This technique is based on a polymer/solvent/H₂O ternary system, and the key is to choose a volatile and hydrophobic solvent that is slightly miscible with H₂O. With the fast evaporation of the solvent, water droplets separate from the casting solution and condense from the air to act as pore templates inside the film and on the surface, respectively. According to this law, nitrocellulose (NC) films were produced from the NC/methyl acetate (MA)/H₂O system in which the solubility of H₂O in MA is 8.1 wt %. By modulating the solution concentration (density) from 3% to 9% NC, the distribution of separated water droplets (pores) in the solution can be flexibly controlled from sinking to floating. On the other hand, substantial ordered honeycomb pores, originated from condensed water droplets, distribute uniformly on the surface of NC films. This water droplet templating technique can be extensively applied in various polymer films, providing an effective pathway to designing polymer films with a desirable porous structure and diverse functionalities.

We investigate the impact of poly adenine (poly-A) sequences on the type and stability of liquid crystalline (LC) phases formed by concentrated solutions of gapped DNA (two duplex arms bridged by a flexible single strand) using synchrotron small-angle X-ray scattering and polarizing optical microscopy. While samples with mixed sequence form layered (smectic) phases, poly-A samples demonstrate a columnar phase at lower temperatures (5–35 °C), not previously observed in GDNA samples, and a smectic-B phase of exceptional stability at higher temperatures (35–65 °C). We present a model that connects the formation of these LC phases with the unique characteristics of poly-A sequences, which manifest in various biological contexts, including DNA condensation and nucleosome formation.