Macromolecules最新文献

Star polymers are attracting intense interest as functional materials because their three-dimensional topology affords tunable physicochemical properties. Yet the widely used arm-first route to star synthesis still struggles to precisely control arm number and its distribution. Simulation can reveal microscopic events that are inaccessible experimentally, but models often fail to reproduce measurements when key factors are neglected. Here, we investigate the macroinitiator-based, arm-first synthesis of polyethylene glycol star polymers by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). We develop a kinetic Monte Carlo model that explicitly incorporates steric congestion between growing arms─an effect frequently overlooked in prior work. Using this framework, we systematically examine how cross-linker feeding profiles, catalyst-to-reducing-agent ratios, and initial concentrations govern the evolution of molar mass and composition (core proportion) distributions during star formation. In addition, we establish a procedure for quantitatively comparing simulations with experimental data acquired by size-exclusion chromatography coupled to multiangle light scattering (SEC-MALS). Together, these advances highlight the central role of steric effects in shaping star-formation kinetics and dispersity, as demonstrated by the good agreement to the experimental results, and provide practical tools for optimizing synthesis and rigorously benchmarking simulations against experiment in polymers with complex architectures.

The control and design of the semicrystalline structure of polymer binders within nanopapers based on graphene-related materials (GRM) may have a significant impact on the nanopapers’ physical properties, including thermomechanical resistance and thermal conductivity. In this article, biopolyesters differing in methylene chain length between ester groups were studied, specifically using poly(ε-caprolactone) (PCL) and poly-4-hydroxybutyrate (P4HB), with additional comparisons to polyglycolide (PGA). The crystallization behavior and crystalline structure of the polymers embedded in GRM nanopapers were studied by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). In particular, high melting point crystals originating from strong nucleation and strong molecular interactions with the GRM were observed with thermal stability dependent on the chemical structure of the polymer. The crystals having the highest melting temperatures, well above the equilibrium melting points of PCL and P4HB, are of particular interest. Besides their high thermal stability, these crystals cannot be fractionated through successive self-nucleation and annealing. At the same time, WAXS revealed distinct crystal diffraction reflections and relatively broad rings, suggesting the formation of crystals stabilized up to high temperatures by their interfacial adsorption onto GRM. These findings offer new insights into the mechanism of polymer crystallization at the interface with nanoparticles and may have implications for the development and application of hybrid organic/inorganic flexible nanopapers in electronic devices.

To improve the sensitivity of i-line photoresists, we investigated the structure–sensitivity relationship of six base self-amplifying photoresists. In this work, six base self-amplifying polymers with different core structures (piperidine, pyrrolidine, and morpholine) and substitution positions were synthesized. Their degradation properties were studied through thermal decomposition, solution decomposition, and evaluation of photoresist sensitivity. The results indicated that the P(3-Pyrrolidine) exhibited the best sensitivity, with an E₀ of 7.9 mJ/cm² (γ = 10.2) at a postexposure bake (PEB) temperature of 100 °C for 3 min. A sharp increase in sensitivity was observed at higher PEB temperatures or longer PEB times. The study revealed the following key findings regarding the structure–sensitivity relationship: 1) basicity, which accelerates hydrogen abstraction by lowering the activation barrier; 2) hydrogen bonding, where a strategically placed H-bond kinetically traps the system and inhibits the reaction; and 3) steric hindrance, which physically blocks reactant approach. This trend held true for all derivatives, including both the 2-substituted and the 3- or 4-substituted series, where stronger basicity resulted in higher sensitivity. Density functional theory (DFT) studies revealed a novel six-membered ring elimination mechanism for the Fmoc deprotection reaction, and the energy barriers for each step were also determined. We computed the energy barriers for monomers with different backbones and substituents. Based on these results, the rate-determining step of the reaction was identified, and weaker basicity of the parent core and greater steric hindrance led to a higher energy barrier, which in turn corresponded to lower photoresist sensitivity.