Journal of Polymer Science最新文献

This study utilizes the homopolymer, poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPSNa₉₀) to synthesize the thermo-responsive ionic liquid polymer P[AMPS][P₄₄₄₈]₉₀ by exchanging the counter cation, sodium (Na⁺) of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) with tributyl(octyl)phosphonium bromide ([P₄₄₄₈ ⁺]Br). Furthermore, a two-step synthesis approach was employed to create a dual thermo-responsive water-soluble diblock copolymer PAMPSNa₉₀-b-PNIPAM₂₇₉ composed of PAMPSNa₉₀ and poly(N-isopropylacrylamide) (PNIPAM) via reversible addition-fragmentation chain transfer polymerization. Later a modification was carried out to exchange the counter cation Na⁺ in PAMPSNa₉₀-b-PNIPAM₂₇₉ with [P₄₄₄₈ ⁺], resulting in the P[AMPS][P₄₄₄₈]₉₀-b-PNIPAM₂₇₉. The individual synthesized polymers were extensively characterized using proton nuclear magnetic resonance spectroscopy and gel permeation chromatography to infer their correct synthesis composition and molecular weight. Turbidity, measured by the percentage transmittance, revealed the thermo-responsive behavior of these synthesized blocks. The hysteresis phenomenon of heating/cooling for each synthesized polymer was identified as single or dual cloud point temperature, depending on the applied stimuli such as polymer concentration, temperature rate, and sonication. Scattering techniques, such as dynamic light scattering and small-angle neutron scattering, were employed to obtain insight into the size/shape of the self-aggregates formed in an aqueous solution environment, which is supported using transmission electron microscopy.

High temperature resins are of interest in many applications including use in extreme environments including atmospheric reentry. Finding methodology to reduce additives while increasing processability for these resins while simultaneously relying less on petroleum-based products is of high importance so that large-scale manufacturing becomes more accessible. Herein, we report the synthesis of a series of new vanillin-oxydianiline (Vn-ODA) based phthalonitrile (PN) resins. These resins contain the bio-based monomer, vanillin, along with internal initiators via an imine linkage formed by the vanillin and ODA molecules, eliminating the requirement for additives to initiate curing. The resulting resins exhibit good thermo-oxidative properties with char yields under N₂ above 75% and thermolytic degradation above 490°C under air. Furthermore, the meta- and para- resins exhibit promising processing windows with low melt temperatures and a T _g above final cure temperature.

For the proton exchange membrane (PEM) applying in vanadium flow battery (VFB), it is difficult to separate the electrolyte ions at two electrodes while conducting protons. In this work, a novel composite membrane is developed, organically modified-MXene (MDP) filled sulfonated poly(ether ether ketone) (SPEEK) membrane, where MDP is prepared through co-coating the polydopamine (PDA) and polyethyleneimine (PEI) on the surface of MXene. The two-dimensional structure of MXene can effectively reduce the vanadium ions permeation, while the surface functional groups from the coating layer can assist in proton transport, thus enhancing the membrane selectivity. The membrane with only 1.0 wt% MDP (SPEEK/MDP-1) achieves maximum selectivity of 7.1 × 10⁷ S min cm⁻³. Furthermore, the energy efficiency (EE) of the VFB loaded with SPEEK/MDP-1 reaches ~92.5% at 40 mA cm⁻² current density. This work provides a new direction for enhancing the properties of PEM used in VFB applications.

The widespread use of polycaprolactone (PCL) in electrospun scaffolds for biomedical applications is often hindered by the reliance on toxic halogenated solvents such as chloroform and dichloromethane. In this study, an innovative green solvent system based on acetone and dimethyl carbonate (DMC) is proposed for the electrospinning of PCL, aiming to reduce environmental and health risks while preserving fiber quality for biomedical applications. The acetone: DMC mixture was optimized for solubility, volatility, and electrospinnability to produce bead-free, uniform nanofibers with morphological tunability. Physicochemical properties, including mechanical properties, percentage of swelling, degradation, and Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis, were conducted on the electrospun membranes. Initial in vitro experiments confirm the biocompatibility of the resultant membranes, supporting their application in tissue engineering and drug delivery. This green solvent method offers a sustainable and safer approach for electrospinning PCL, without compromising its functional properties.

Poly(L-lactic acid) (PLLA) is one of the most popularly utilized plant-based polymers, as PLLA can be synthesized from renewable sources such as sugar, carbohydrate, etc. In recent several decades, scientists have been interested in PLLA because of its environment-friendly characteristics. However, there exist some big problems with PLLA, which are low crystallization rate and low crystallinity. In order to overcome such drawbacks, nucleation agents have been incorporated into PLLA. On the contrary, we have reported that plasticizers (both of biobased (organic acid mono-glyceride; OMG) and oil-based (dioctylphthalate)) can improve the crystallizability of PLLA [Polymer Journal 2019; 51(2): 283–294]. The results are significant because plasticizers are believed to delay crystallization of polymers by reducing the thermodynamical driving force of crystallization. We now recognize that the lowering of the activation energy for the PLLA crystallization may be the main effect of a plasticizer with small-amount loading. In this study, we confirm that in the presence of the plasticizer molecules, better folding of the PLLA chains results, which has been experimentally confirmed by the fact that the surface free energy (σ _e ) of the crystallites plane, on which the folds of the PLLA chains exist, becomes lower upon the loading of plasticizers. The free energy change upon the formation of a primary nucleus is then drawn as a function of the thickness of the primary nucleus using the values of σ _e (which were evaluated in the framework of the Hoffman-Lauritzen theory through the growth rate of spherulite from the polarizing optical microscopic observation) and it was found that the energy barrier (activation energy) for the crystallization is decreased by the loading of plasticizers. This explains the enhancement of the crystallizability by the presence of plasticizer.

The study investigates the influence of scaffold architecture and postprocessing, specifically heat treatment, on the mechanical and biological effectiveness of 3D-printed polylactic acid (PLA) scaffolds. Cross-patterned PLA scaffolds were printed at infill densities of 50%, 60%, and 70% and heat-treated (HT) at varying temperature–time combinations to enhance crystallinity. The optimum condition was found to be 90°C for 120 min (HT-120), which was chosen for further study. MTT assays using MG 63 osteoblast cells indicated that HT scaffolds, particularly with 70% infill density (HT90(120)-70), showed significantly greater cell viability for 15 days than untreated scaffolds (UT-70). The exchange of growth-promoting nutrients among cells and heat treatment-induced surface roughness enhances biocompatibility and cellular proliferation, crucial for bone regeneration. Mechanical tests showed that HT90(120)-70 had nearly 20% higher yield strength than UT-70 due to its enhanced crystallinity. Immersion of HT90(120)-70 in physiological fluid for 15 days at 37°C did not significantly change yield strength compared to dry conditions, but post-yield softening was observed in immersed scaffolds due to hydrolytic aging. Cyclic unloading-reloading experiments under physiological conditions also demonstrated that HT90(120)-70 shows greater resistance to deformation. The study reveals HT90(120)-70 as a promising alternative scaffold for load-bearing bone tissue engineering.