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.

Understanding the dynamics of nanosheets in polymer matrices is crucial for the processing of polymer nanocomposites and their applications in drug delivery. In this work, we investigate the diffusion of thin nanosheets in unentangled polymer melts using molecular dynamics simulations. We show that for nanosheets smaller than a characteristic size l_c, which is a few times the polymer chain size, the continuum hydrodynamic theory based on macroscopic viscosity breaks down and significantly underestimates the diffusion coefficients. For nanosheets with sizes l < l_c, we derive scaling relationships for both translational and rotational diffusion coefficients as functions of l and further reveal the dynamical coupling between nanosheet motion and the modes of the polymer melt. For l > l_c, the continuum theory is recovered. Our findings reconcile the continuum and scaling theories for the diffusion of nanoparticles in polymer melts.

The oxidative coupling of amines is a useful way to prepare many diverse compounds for the pharmaceutical and chemical industries. Covalent organic frameworks (COFs), a crystalline class of porous polymers, have emerged as promising heterogeneous photocatalysts that can accomplish this transformation under metal-free conditions due to their excellent photochemical stability and tunable electronic properties. Herein, we report the optoelectronic and photocatalytic properties of an olefin-linked COF containing thienothiophene (TT) and 2,4,6-trimethyl-1,3,5-triazine (TMT) units. The TT-TMT-COF exhibited a narrow band gap with extended light absorption and excellent charge separation, making it useful for the oxidative coupling of various benzylamines. The TT-TMT-COF exhibited fast reaction times, excellent recyclability, and conversions as high as ∼99%. The reactivity of TT-TMT-COF was on par or significantly better than that of a few small molecule 2,4,6-tris((E)-2-(thieno[3,2-b]thiophen-2-yl)vinyl)-1,3,5-triazine (TT-TMT) and 2,4,6-tris((E)-2-(thiophen-2-yl)vinyl)-1,3,5-triazine (Thio-TMT) homogeneous catalytic systems containing similar functional units. This work further highlights the ability of the COF to perform useful and efficient catalytic transformations in a sustainable manner.

Achiral dynamic helical polymers, poly(quinoxaline-2,3-diyl)s (P1 and P2) bearing achiral carboxylic acid side chains, i.e., carboxymethoxymethyl (in P1) and carboxyethoxymethyl (in P2), with different polymerization degrees were synthesized. They exhibited induced circular dichroism (ICD) in the presence of chiral amines such as 1-phenylethylamine and nicotine, 1,2-amino alcohols such as valinol, leucinol, and prolinol, and the basic amino acid, arginine, in response to the induction of right- or left-handed helical conformation. The efficiency of helix induction depends on the compatibility of the structures of amines and polymers, with no clear structural correlation. The highly sensitive and formulated nature of ICD with the helical polymer-based poly(carboxylic acid)s allowed their use as CD-based sensors to detect and quantify minute imbalances of the enantiomeric excess of chiral molecules. We determined 0.2%–0.6% ee in the commercially available 1-phenylethylamine from three different suppliers, which have the label of “dl” or no indication of enantiopurity using P1 as a chemosensor.

Entanglement dynamics in polyelectrolyte solutions remain a challenging topic, particularly in capturing the entire dynamic spectrum, from single entanglement relaxation (τ_e) to reptation time (τ_rep), and aligning these observations with scaling predictions in the semidilute entangled (SE) and fully entangled (FE) neutral regimes. Using piezo compressional and classic rotational rheometry, we investigate the scaling behaviors of key viscoelastic properties over several decades of time scales in ten million Mw cationic polyacrylamide solutions. Specific viscosity (η_sp) and τ_rep scale as predicted within Fuoss, SE, and FE regimes, defining crossover concentrations between these regimes (C_e and C_D). More importantly, τ_e, the rubbery plateau width (τ_rep/τ_e), and the high-frequency modulus (G_e) scale as C^{–1.14±0.02}, C^1.25±0.07, and C^1.32±0.05, aligning with SE prediction in the early SE regime before transitioning to neutral scaling of C^–2.7±0.14, C^3.1±0.15, and C^2.35±0.07 at an intermediate concentration between C_e and C_D labeled C_D^e. These results indicate that electrostatic interactions affect single entanglements and reptation differently, leading to a transition to neutral behavior at C_D^e for the former and at C_D for the latter.