Degradation Of Ester Bonds Research Articles

A polyurethane integrating self-healing, anti-aging and controlled degradation for durable and eco-friendly E-skin

Two of the very important demands for the elastic matrix of electronic skin (E-skin) are durability and degradability, which ensure the stable performance in daily life and green end of the E-skin. Unfortunately, these two requirements are usually incompatible. Here, we proposed the idea of controlled degradation and synthesized a polyurethane, AL-PU-4, to solve such challenge. High crystalline hydroxy-terminated poly (1,4-butylene adipate) (HTPBA) and low crystalline polycaprolactone diol (PCL diol) were mixed and used as the degradable soft segment. The dynamic disulfide bond was chosen as the chain extender, which could simultaneously endow the polyurethane with anti-aging and self-healing properties. The AL-PU-4 didn’t show significant loss in mechanical and molecular weight after 12 days of accelerated aging experiment, which equaled to 12 months of daily use, and it owned a fast room temperature self-healing speed of 1.31 μm/min. With the steric protection of the hard segment, the degradation of ester bonds in HTPBA and PCL diol segments was seriously retarded under enzymatic and low pH conditions. Only when the pH reached 14, the ‘lock’ on degradation was opened. The above functionalities were also verified in an E-skin demo, which could response the external pressure quickly and show high stability in cyclic test.

Reactions at the lower potential limit in aprotic medium at a platinum cathode revisited: their role in indirect electrochemical reductive degradation of polymers

Abstract Formation of hydroxyl ions when reduction of residual water occurs at the lower potential limit at a Pt cathode in a tetrabutylammonium perchlorate solution in dimethylformamide (DMF), results not only in splitting of TBA + cations via the Hofmann reaction, but also in hydrolysis of the solvent through an intermediate charged complex into dimethylamine (DMA) and a formic acid anion. These solvent hydrolysis products can play a significant role in reactions, which may occur in electrochemical organic systems. For example, such products formed by electrochemical reduction of the background solution at a Pt cathode, interact with some electrophilic compounds present in the solution. In the case of polymers, it results both in dehydrohalogenation of halogenated polyolefins (polyvinyl chloride, poly(vinylidene fluoride), etc.) and in degradation of ester bonds in polycarbonates. That is, the solvent hydrolysis products are the active agents of the indirect electrochemical reductive degradation (ECRD) of polymers. The results obtained suggest that an intermediate charged complex of an aprotic solvent (DMF, MeCN) with OH − ions plays the governing role in the indirect ECRD of halogenated polyolefins. Furthermore, this complex and the DMA which appeared due to DMF hydrolysis are the agents of an indirect ECRD of polycarbonates. Undoubtedly, the electrochemically induced hydrolysis reactions can be minimized both in the thoroughly dried solutions, which have by our CV data a lower potential limit at Pt at about −3.0 V versus SCE, in the case of cathode materials with a high hydrogen overpotential.

Preparation and properties of poly(L-lactide)/hydroxyapatite composites

In this study, two different viscosity-average molecular weight (η = 4.0 and 7.8) poly(L-lactide) (PLLA) were synthesized by ring-opening polymerization and the poly(L-lactide)/hydroxyapatite composites (PLLA/HA) were prepared by blending HA particles (size range: 25-45 μm and Ca/P = 1.69) with a content of 10, 30, and 50 wt% in PLLA solution with further evaporation of the solvent. The plain PLLA polymers and PLLA/HA composites were compressionmolded and machined to yield 25×3×2 mm3 specimens. The molar mass of resulting specimens was decreased drastically due to the hydrolytic and thermal degradation of ester bonds. Scanning electron microscopy and thermal gravimetric results indicated that the compositions of HA in PLLA were well dispersed. With increasing HA content, the crystallinity of PLLA/HA composites are slightly increased due to the effect of HA as a nucleating agent. The dynamic mechanical analysis is useful in studying the viscoelastic behaviour of the PLLA/HA composites and no secondary relaxation was observed below the glass-to-rubber transition (60°C). The mechanical properties of the PLLA/HA composites were found to vary with HA content. Increased levels of HA resulted in increased bending modulus and strength.