Polymer Chemistry最新文献

The structural understanding of catalysts is essential for achieving efficient and selective polymerization. In this study, we designed a series of bifunctional catalysts based on squaramide, carboxylates, and alkali cations for the ring-opening polymerization (ROP) of lactide. These catalysts exhibited controlled polymerization behavior with narrow dispersity (Đ_M = 1.08–1.12). Kinetic evaluations revealed a linear relationship between the catalyst's chain length and activity for short CH₂ chains (X = 1–4). However, as the CH₂ segments lengthened, an “odd-even” effect on the kinetics was found, suggesting that the chain length alternately enhances or diminishes catalytic activity. The catalytic activity was significantly influenced by the counter cation (Li⁺, Na⁺, K⁺, and Cs⁺) of carboxylate, with larger radius cations showing higher rate constants (k_{obs Cs⁺} > k_{obs K⁺} > k_{obs Na⁺} > k_{obs Li⁺}). Computational studies demonstrated that this correlation resulted from varying binding energies. Moreover, the k_obs value of the catalyst can be tuned by adding different ratios of the crown ether. An interpretable machine learning method was introduced to link physical properties and activities, guiding the further design of effective catalysts for ROP.

Effects of solvent quality on block copolymer (BCP) self-assembly in flow are investigated. Stable kinetically trapped nanoaggregates are created using a continuous flow technique with turbulent mixing under systematically changing THF/water ratios. To elucidate particles morphologies, small angle neutron scattering (SANS) is used as an online analytical method. At high organic solvent contents, elongated particles are observed while at low contents shorter particles are formed. The method can hence be used in a versatile way to control particle morphologies without changing the BCP block lengths used for self-assembly. This offers a more efficient and flexible approach in drug delivery and biomedical applications where particle morphologies directly influence the cell uptake capabilities and reduces the need to resynthesize BCPs with varying block lengths to control size and morphology.

Maintaining the high mechanical properties of degradable polyesters is crucial for their practical application. In this work, tricyclodecanedimethanol (TCD) with a rigid ring structure was introduced into the synthesis of polybutylene succinate (PBS) to form PBTCDS copolyester. The addition of TCD significantly improved the glass transition temperature (T_g), mechanical properties, and barrier properties of the copolyester. The inherent toughness of PBS is limited by its poor elongation at break, which restricts its application range. However, the tensile strength of PBTCDS5 synthesized in this study is 42 MPa, with an elongation at break of 687%. It is noteworthy that the elongation at break of PBTCDS15 reaches 860%, greatly improving the mechanical properties of PBS. Compared with PBS (T_g −31.4 °C), the T_g of the copolyester increased from −29.2 °C to −22.8 °C, thereby improving its thermal properties. The water vapor barrier test showed that the water vapor transmission rate had improved. In addition, water degradation experiments showed that changing the TCD content resulted in different degradation rates, leading to copolyesters with different degradation rates. Ultimately, this method significantly improves mechanical properties while maintaining degradability, thereby broadening the application scope of PBS.

From a practical perspective, it is important to maintain or increase the mechanical properties of functional ethylene copolymers to those of nonpolar polyethylene (PE). In this contribution, we report the enhanced mechanical properties of acrylate- and 5-vinyl-2-norbornene (VNB)-based ethylene terpolymers. Originally, phosphine-sulfonate Pd1 and Pd2 with methyl and phenyl installed para to the sulfonic group were synthesized and characterized. Subsequently, long-chain (but more challenging) polar monomers in which the polar groups combined linearly with double bonds (butyl acrylate (BA) and ethylene glycol monomethyl ether acrylate (EGMA)) were chosen to obtain more flexible chain structures. Crosslinkable and cyclic VNB were used, targeting at rapid crosslinking and enhanced material properties. Ethylene copolymerization and terpolymerization could be efficiently achieved using this strategy, and polymers exhibited improved surface and similar or enhanced mechanical properties compared with those of PE. High activity (2.9 × 10⁷ g (mol h)⁻¹) and high molecular weight (3.8 × 10⁵) were simultaneously observed in ethylene homopolymerization. E-BA(0.64) and E-EGMA(0.87) had a strain-at-break as high as 1016% and 974%, respectively, and stress-at-break up to 45 MPa compared with those of ethylene homopolymer. VNB-based terpolymers E-BA(0.68)–VNB(0.94) and E-EGMA(0.73)–VNB(1) displayed better tensile elongations (723% and 714%) than those of ENB- and DCPD-based terpolymers. Furthermore, though similar thermoplastic properties to PE (strain recovery (SR) = 10%) were observed, enhanced mechanical properties of teropolymers were obtained after sulfur vulcanization, with SR = 19–23% and Δσ (stress differences) = 3.3–10.3 MPa.

Nano-objects generated via a scalable polymerization-induced self-assembly (PISA) process can serve as organic nanofillers, replacing the widely used inorganic nanofillers in composites. In this contribution, polyisoprene (PI)-b-polystyrene (PS) (PI-b-PS) or PI-b-PS/PS nano-objects were prepared via a living anionic polymerization-induced self-assembly (LAPISA) process or a derived process of living anionic polymerization-induced cooperative assembly (LAPICA) using nonpolar n-heptane as a solvent, which facilitated the control over morphologies and sizes. After the living species in the core region were in situ crosslinked by divinylbenzene (DVB) monomers, stabilized PDVB@(PI-b-PS) or PDVB@(PI-b-PS/PS) nano-objects were generated. After hydroxylated or epoxidized nano-objects were obtained through thiol–ene or epoxidation reactions on the double bonds of the PI stabilizer, the miscibility between the nano-objects and epoxy resin was improved, and the functionalized nano-objects could be introduced into epoxy resin. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and thermomechanical analysis (TMA) results affirmed that the organic nano-objects could improve the thermal properties of the composites, which were obviously superior to commercial inorganic silica nano-objects. In particular, the composites with smaller spherical nano-objects had a higher glass transition temperature (T_g) than those with larger spherical ones or worm-like ones. Transmission electron microscopy (TEM) measurements verified the uniform distribution of organic nano-objects and the formation of sufficiently integrated interfaces between the epoxy resin and nano-objects, thereby improving the thermal properties of the composites.

The properties of waterborne polymer dispersions synthesized by emulsion radical polymerization are influenced by reactions in both the aqueous medium and the growing particles. Mathematical models representing the process often do not consider the difference in the propagation rate coefficient (k_p) of monomers in the two phases, despite the body of evidence demonstrating that solvent polarity influences monomer–monomer and monomer-solvent hydrogen-bonding that affects both k_p homopropagation values and copolymerization reactivity ratios. Therefore, it is vital to develop experimental approaches to systematically measure the influence of solvent on the copolymerization kinetics of hydrophobic monomers under conditions that are similar to emulsion systems. In this work, we study the copolymerization of methyl acrylate (MA) with di(ethylene glycol) methyl ether methacrylate (DEGMEMA) as models for the common emulsion monomers butyl acrylate and methyl methacrylate. As well as varying solvent choice and monomer concentration, MA/DEGMEMA copolymerization kinetics are compared to those of MA with methacrylic acid (MAA) to determine the influence of monomer functionality on its relative reactivity. The findings suggest that the copolymer composition of all methacrylate–acrylate systems – whether involving functional or non-functional monomers – converge to a single curve in protic polar aqueous solution.

The readily prepared CF₃TMS adduct of anthraquinone is shown to be an efficient monomer for superacid-catalysed step-growth polymerisations, as exemplified by its reaction with diphenyl ether. The resulting polymer (BTFMA-DPE) is produced rapidly, with high molecular mass, and shows promise as a gas separation membrane material.

The properties, applications, and end-of-life considerations of plastics are fundamentally linked to the structure of the polymer backbones at the core of these materials. With that in mind, editing the polymer backbone composition offers exciting opportunities to transform the plastics economy; yet, few examples of such transformations utilize commodity plastics as starting materials. In this work, we describe the development of a tandem C–H oxidation/hydroxyalkyl azide mediated rearrangement strategy that converts polyethylene into “polyethylene-like” materials with iminium ethers, esters, amides, and other pendant chemical functionality. Control over formation of esters or amides is achieved by variation of the hydroxyalkyl azide reagent, as well as processing conditions. By targeting specific functionalities, a variety of thermal and mechanical properties can be accessed. For example, incorporation of iminium ethers decreases the Young's modulus of post-consumer PE from 196 MPa to 69–83 MPa, but conversion of the iminium ethers to esters and amides produces materials with moduli of 212–287 MPa—values higher than the original material. Thus, the demonstration of a modular backbone editing methodology for polyethylene showcases the broader value of this emerging strategy for polymer modification.