Strong Hydrogen Bonds Sustain Even-Odd Effects in Poly(ester amide)s with Long Alkyl Chain Length in the Backbone

The number of methylene groups between strongly interacting functional groups within polymer repeating units induces even-odd effects on thermal and mechanical properties. However, detailed studies correlating the even-odd effect with structural changes are still lacking. In this work, we establish correlations between the structure and thermal properties of poly(ester amide)s containing long alkyl chain lengths. The even-odd effect impacts the thermal properties, including the melting temperature and crystallinity degree. It influences the spherulitic morphology of poly(ester amide)s, controlling the appearance of banding. We demonstrate that even-odd effects in poly(ester amides)s persist even with 27 CH2 groups within the repeating unit, an effect due to strong hydrogen bonds caused by the amide groups. Our X-ray studies reveal that the even-odd effect originates from changes in the crystalline structure of the materials. This work helps elucidate the role of strong intermolecular interactions (i.e., hydrogen bonding) on the even-odd effect in long-chain poly(ester amides).

High ion barrier hydrogel with excellent toughness achieved by directional structures

Owing to their nontoxicity, environmental friendliness, and high biocompatibility, physically cross-linked hydrogels have become popular research materials; however, their high water content and high free volume, along with the weak bonding interactions inherent to ordinary physically cross-linked hydrogels, limit their application in fields such as flexible devices, packaging materials, and substance transport regulation. Here, a structural barrier approach based on directional freezing-assisted salting out was proposed, and the directional structure significantly enhanced the barrier performance of the hydrogel. When the direction of substance diffusion was perpendicular to the pore channel structure of the directional freezing-PVA hydrogel (DFPVA), the Cl- transmission rate was 57.2% for the uniform freezing-PVA hydrogel (UFPVA). By adjusting the concentration of the salting-out solution and the salting-out time, the crystallinity and crystal domain size of the hydrogel could be further changed, optimizing and regulating the barrier performance of the hydrogel, with the best Cl- unit permeability being 36.02 mg mm per cm2 per day. Additionally, DFPVA had excellent mechanical properties (stress of 6.47 ± 1.04 MPa, strain of 625.85 ± 61.58%, toughness of 25.77 ± 3.72 MPa). Due to the barrier and mechanical properties of the direct structure, DFPVA is suitable as a drug carrier for slow drug release in vitro.

Effect of the TrFE Content on the Crystallization and SSA Thermal Fractionation of P(VDF-co-TrFE) Copolymers

In this contribution, we study the effect of trifluoro ethylene (TrFE) comonomer content (samples with 80/20, 75/25, and 70/30 VDF/TrFE molar ratios were used) on the crystallization in P(VDF-co-TrFE) in comparison with a PVDF (Poly(vinylidene fluoride)) homopolymer. Employing Polarized Light Optical Microscopy (PLOM), the growth rates of spherulites or axialites were determined. Differential Scanning Calorimetry (DSC) was used to determine overall crystallization rates, self-nucleation, and Successive Self-nucleation and Annealing (SSA) thermal fractionation. The ferroelectric character of the samples was explored by polarization measurements. The results indicate that TrFE inclusion can limit the overall crystallization of the copolymer samples, especially for the ones with 20 and 25% TrFE. Self-nucleation measurements in PVDF indicate that the homopolymer can be self-nucleated, exhibiting the classic three Domains. However, the increased nucleation capacity in the copolymers provokes the absence of the self-nucleation Domain II. The PVDF displays a monomodal distribution of thermal fractions after SSA, but the P(VDF-co-TrFE) copolymers do not experience thermal fractionation, apparently due to TrFE incorporation in the PVDF crystals. Finally, the maximum and remnant polarization increases with increasing TrFE content up to a maximum of 25% TrFE content, after which it starts to decrease due to the lower dipole moment of the TrFE defect inclusion within the PVDF crystals.