Radical ring-opening polymerization (RROP) of 2methylene-1,3-dioxepane (MDO) leads to a polymer that is structurally similar to poly(ε-caprolactone) (PCL). Despite the similarities, polymerized MDO (PMDO) is known to exhibit little or no semicrystallinity, which is often explained by the branching of PMDO caused by the free-radical polymerization. Branching in RROP can arise from intramolecular 1,7-H-transfer to result in short-chain branching or from intermolecular H-transfer, resulting in long-chain branching. In this study, we performed UV-initiated RROP to isolate several PMDO samples with varying amounts of branching while keeping the molar mass below 30,000 g/mol and the dispersity below 2.0. A detailed analysis by NMR spectroscopy clarified which signals belong to the ring-retaining structure of PMDO and that branching originated from the α-carbon next to the carbonyl unit of the ester group. A deeper insight into the viscosity of PMDO solutions following a size exclusion chromatography analysis suggested that both long-chain branching and short-chain branching existed but could not discriminate between both of them. It did, however, show that the K η and the α values of the Kuhn−Mark−Houwink−Sakurada (KHMS) plot vary systematically with the branching density of PMDO. Thermal analysis by differential scanning calorimetry exposed a semicrystalline behavior with more than one melting peak for all investigated samples. Both the degree of crystallization and the melting temperature of the investigated melting peaks again correlated with the branching density of PMDO. Altogether, this study shed light on how macroscopic properties like viscosity and thermal behavior correlate with the branching density of PMDO and thus provides insights into the structure−property relationships of this polymer. It lays the basis to synthesize branched PCL analogues with fine-tuned stability for biomedical applications.

In this paper, we report on the use of amorphous lignin, a waste by-product of the paper industry, for the production of high performance carbon fibers (CF) as precursor with improved thermal stability and thermo-mechanical properties. The precursor was prepared by blending of lignin with polyacrylonitrile (PAN), which was previously dissolved in an ionic liquid. The fibers thus produced offered very high thermal stability as compared with the fiber consisting of pure PAN. The molecular compatibility, miscibility, and thermal stability of the system were studied by means of shear rheological measurements. The achieved mechanical properties were found to be related to the temperature-dependent relaxation time (consistence parameter) of the spinning dope and the diffusion kinetics of the ionic liquids from the fibers into the coagulation bath. Furthermore, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical tests (DMA) were utilized to understand in-depth the thermal and the stabilization kinetics of the developed fibers and the impact of lignin on the stabilization process of the fibers. Low molecular weight lignin increased the thermally induced physical shrinkage, suggesting disturbing effects on the semi-crystalline domains of the PAN matrix, and suppressed the chemically induced shrinkage of the fibers. The knowledge gained throughout the present paper allows summarizing a novel avenue to develop lignin-based CF designed with adjusted thermal stability.

Polystyrene/polyolefin elastomer (PS/POE) (90/10 and 80/20 wt/wt) blends containing 1, 3, and 5 phr halloysite nanotubes (HNTs) in the presence and absence of a compatibilizer (polypropylene-graft-maleic anhydride) were prepared using the meltmixing technique. Scanning electron microscopic studies confirmed a matrix-droplet morphology. Energy dispersive spectroscopy (EDS) mapping indicated that the blends containing 5 phr HNTs possessed aggregates, while no agglomeration was observed after incorporating 5 phr compatibilizer. Thermal stability and thermal degradation kinetics were investigated using thermogravimetry analysis (TGA). The results demonstrated that the PS/POE blend (90/10) containing 5 phr HNTs and compatibilizer (90/10/5/5) has the best thermal stability. Different methods such as Friedman, Flynn-Ozawa-Wall, and Kissinger-Akahira-Sunose were applied to calculate the degradation activation energy. The 90/10/5/5 nanocomposite exhibited the highest degradation activation energy, indicating that this sample is more difficult to degrade thermally than other samples. A correlation was obtained between the activation energy and the intensity of the TGA-fourier-transform infrared spectroscopy (TGA/FTIR) peaks of the evolved products. The Criado method was used to determine the changes in the thermal degradation mechanism of the samples.

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Thermotropic liquid crystalline polyesters with varied chemical structure are synthesized by melt transesterification polycondensation. They are employed as matrix for blends with lignin materials to obtain melt-spinnable precursors for carbon fibers. The lignin samples are carefully purified by fractionation, enzymatic removal of reducing sugars, and subsequent modification of the terminal OH groups. Effective melt blending is achieved with liquid-crystalline aromatic-aliphatic polyesters having melting ranges that match the softening temperature of the lignin fractions, which is necessary to prevent thermal decomposition of the lignin. Polyester/lignin blends are partially compatibilized, phase-separated materials. The polyester/lignin materials are melt-spun successfully. The fiber properties depend on the lignin purification process. X-ray scattering reveals that orientation in lignin-containing fibers is maintained. First experiments show that the fibers can be converted successfully to carbon fibers by thermal annealing procedures.In the past, many efforts were undertaken to improve the spinnability of lignin either from the melt or from solution, in particular including: (1) chemical modification of the lignin, and (2) mixing lignin with synthetic polymers to ease processability. The chemical modification of the terminal aliphatic and aromatic OH groups interrupts the hydrogen bonds and reduces T g which Additional Supporting Information may be found in the online version of this article.