Search

A series of poly(sodium methacrylate) hydrogels, also called superabsorbents, having a theoretical degree of neutralization of 100 mol%, and degree of crosslinking varying from 0.6 to 20 mol%, are synthesized via conventional free radical polymerization. The networks are characterized in detail by inverse size-exclusion chromatography and 1H-NMR relaxometry in order to place particular emphasis on the investigation of the pore size distribution (PSD) and the chain mobility, respectively. The two previously mentioned parameters are compared to understand the correlation between the elastic chain mobilities and the average pore size of the hydrogel. From the resulting data, a new empirical equation is proposed, which is valid under the given experimental conditions and permits a rough estimation of the average PSD from the relaxation data. Thus, the equation permits to reduce the number of analytical techniques needed for the characterization of complex systems such as polymer networks.

An in-depth investigation of the network topology for a series of sodium acrylate hydrogels synthesized via conventional free radical polymerization (FRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization is conducted. The role of the RAFT agent on the crosslinking process is demonstrated on a model system upon analysis of the reaction mixture via size-exclusion chromatography before the gelation point. For a comprehensive study, both the impact of the amount of RAFT agent and of the degree of crosslinking on the microstructure of the final product are systematically investigated. In addition to swelling experiments and oscillatory shear rheology measurements, the resulting networks are analyzed via low-field proton nuclear magnetic resonance (1H-NMR) techniques such as transverse relaxation and double-quantum coherence to evaluate the network mobility, which is then correlated to structural inhomogeneity. A broader mobility distribution is observed for the RAFT mediated networks compared to the FRP samples, which can be assigned to a higher content of dangling ends in the former case. The results are further elaborated to propose a mechanism for network formation in presence of a RAFT agent. Special Issue: 100 Years of Macromolecular Chemistry and Physics

Scaffolds based on bioconjugated hydrogels are attractive for tissue engineering because they can partly mimic human tissue characteristics. For example, they can further increase their bioactivity with cells. However, most of the hydrogels present problems related to their processability, consequently limiting their use in 3D printing to produce tailor-made scaffolds. The goal of this work is to develop bioconjugated hydrogel nanocomposite inks for 3D printed scaffold fabrication through a micro-extrusion process having improved both biocompatibility and processability. The hydrogel is based on a photocrosslinkable alginate bioconjugated with both gelatin and chondroitin sulfate in order to mimic the cartilage extracellular matrix, while the nanofiller is based on graphene oxide to enhance the printability and cell proliferation. Our results show that the incorporation of graphene oxide into the hydrogel inks considerably improved the shape fidelity and resolution of 3D printed scaffolds because of a faster viscosity recovery post extrusion of the ink. Moreover, the nanocomposite inks produce anisotropic threads after the 3D printing process because of the templating of the graphene oxide liquid crystal. The in vitro proliferation assay of human adipose tissue-derived mesenchymal stem cells (hADMSCs) shows that bioconjugated scaffolds present higher cell proliferation than pure alginate, with the nanocomposites presenting the highest values at long times. Live/Dead assay otherwise displays full viability of hADMSCs adhered on the different scaffolds at day 7. Notably, the scaffolds produced with nanocomposite hydrogel inks were able to guide the cell proliferation following the direction of the 3D printed threads. In addition, the bioconjugated alginate hydrogel matrix induced chondrogenic differentiation without exogenous pro-chondrogenesis factors as concluded from immunostaining after 28 days of culture. This high cytocompatibility and chondroinductive effect to, Peer Reviewed, Postprint (author's final draft)

Assessing the stability of molecular bonds in polymer architectures is of critical importance for determining conditions for extrusion, molding, and processing. The topological complexity of branched polymers defines their strain hardening and consequently their melt strength properties, critical parameters for their exploitation in applications. Their molecular architecture is defined by the grafting density and the chain length of the backbone as well as branches. Herein, we introduce a set of polymer combs to establish an understanding of the above parameters on the stability of the popular triazole linkage—often exploited in tethering the branches to the backbone—during thermal treatment and shearing. We exploit a combination of reversible deactivation radical polymerization (RDRP) and copper-catalyzed alkyne–azide cycloaddition (CuAAC) to construct comb polymers (ranging in backbone number-average molecular weight from 39.9 to 55.6 kg mol–1 and a branch length from 3.3 to 18 kg mol–1) with statistically located branches tethered via triazole-based ligation to the backbone. These polymer combs were subsequently thermally challenged at 150 °C (or 180 °C) in an inert atmosphere as well as subjected to shearing at the same temperature. The resulting molecular cleavage processes were analyzed via size exclusion chromatography (SEC) as well as SEC coupled to high-resolution electrospray ionization mass spectrometry (SEC-HR ESI MS) to establish a mechanistic image of branch debonding when it occurs. In addition, by virtue of this approach, we establish an in-depth understanding of how the comb architecture dictates its stability under otherwise unchanged chemical bonding conditions via triazole units, allowing to adopt design criteria for generating thermally and mechanically stable comb structures.

The German Nutrition Society raised in 2012 the recommended daily vitamin D intake from 200 to 800 international units (IU) to achieve 25-hydroxyvitamin D (25 (OH) D) levels of at least 50 nmol/L, even when endogenous vitamin D synthesis is minimal such as in winter. We aimed to evaluate this recommendation in women of childbearing age. This is a single-center, randomized, open trial conducted from 8 January to 9 May 2016 in Esslingen, Germany. We randomized 201 apparently healthy women to receive for 8 weeks a daily multimicronutrient supplement containing either 200 IU (n = 100) or 800 IU vitamin D3 (n = 101). Primary outcome measure was serum 25 (OH) D. 196 participants completed the trial. Increases in 25 (OH) D (median with interquartile range) from baseline to study end were 13.2 (5.9 to 20.7) nmol/L in the 200 IU group, and 35.8 (18.2 to 52.8) nmol/L in the 800 IU group (p < 0.001 for the between group difference). At study end, levels of ≥50 nmol/L were present in 70.4% of the 200 IU group and in 99% of the 800 IU group. Participants on hormonal contraceptives had higher baseline levels and a stronger increase in 25 (OH) D. In conclusion, daily supplementation of 800 IU vitamin D3 during wintertime in Germany is sufficient to achieve a 25 (OH) D level of at least 50 nmol/L in almost all women of childbearing age, whereas 200 IU are insufficient.

Procter & Gamble Company, Schlumberger-Doll Research Center

We describe a simple and facile method for quantitatively converting bromine end-groups of well-defined polystyrene (PS, Mn,SEC = 4000 Da, D = 1.08) prepared by activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) into terminal alkenes by heating at 100 °C in dimethylformamide (DMF) without additional reagents. Subsequently, a facile quantitative post-functionalization of the terminal double bonds to various end functional polymers was performed via light-induced thiol-ene reactions. The quantitative end-group modifications as well as their thermal stability were assessed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS), nuclear magnetic resonance (1H NMR) spectroscopy and size-exclusion chromatography (SEC), evidencing the generated functional polystyrenes to be highly stable up to 200 °C for extended periods of time (24 h). © The Royal Society of Chemistry.

A novel adaptable network based on the reversible hetero Diels-Alder reaction of a cyanodithioester and cyclopentadiene is presented. Reversible between 50-120 °C, the adjustable and self-healing features of the network are evidenced via temperature dependent rheology experiments and repetitive tensile tests whereas the network's chemical structure is explored by temperature dependent 1H MAS-NMR spectroscopy. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A novel adaptable network based on the reversible hetero Diels-Alder reaction of a cyanodithioester and cyclopentadiene is presented. Reversible between 50-120 °C, the adjustable and self-healing features of the network are evidenced via temperature depe

Although controlled/living radical polymerization processes have significantly facilitated the synthesis of well-defined low polydispersity polymers with specific functionalities, a detailed and systematic knowledge of the thermal stability of the products-highly important for most industrial processes-is not available. Linear polystyrene (PS) carrying a trithiocarbonate mid-chain functionality (thus emulating the structure of the Z-group approach via reversible addition-fragmentation chain transfer (RAFT) based macromolecular architectures) with various chain lengths (20 kDa ≤ Mn,SEC ≤ 150 kDa, 1.27 ≤ Crossed D sign = Mw/Mn ≤ 1.72) and chain-end functionality were synthesized via RAFT polymerization. The thermal stability behavior of the polymers was studied at temperatures ranging from 100 to 200 C for up to 504 h (3 weeks). The thermally treated polymers were analyzed via size exclusion chromatography (SEC) to obtain the dependence of the polymer molecular weight distribution on time at a specific temperature under air or inert atmospheres. Cleavage rate coefficients of the mid-chain functional polymers in inert atmosphere were deduced as a function of temperature, resulting in activation parameters for two disparate Mn starting materials (Ea = 115 ± 4 kJ·mol-1, A = 0.85 × 109 ± 1 × 109 s-1, M n,SEC = 21 kDa and Ea = 116 ± 4 kJ·mol -1, A = 6.24 × 109 ± 1 × 109 s-1, Mn,SEC = 102 kDa). Interestingly, the degradation proceeds significantly faster with increasing chain length, an observation possibly associated with entropic effects. The degradation mechanism was explored in detail via SEC-ESI-MS for acrylate based polymers and theoretical calculations suggesting a Chugaev-type cleavage process. Processing of the RAFT polymers via small scale extrusion as well as a rheological assessment at variable temperatures allowed a correlation of the processing conditions with the thermal degradation properties of the polystyrenes and polyacrylates in the melt. © 2013 American

The rheological behavior of a poly(styrene)-poly(L-lactide) (PS-PLLA) block copolymer was investigated in the viscoelastic linear and nonlinear regime. Large amplitude oscillatory shear (LAOS) experiments in the nonlinear regime led to an exponential decay of the G moduli and the nonlinearity parameter I-3/1. During LAOS, the lamellar microstructure of a low molecular weight PS-PLLA copolymer was orientated parallel to the shear field to achieve a macroscopically ordered material. The degree of orientation was analyzed via small angle X-ray scattering (SAXS) measurements. The crystallization kinetics could be accurately described by the Avrami equation as determined by DSC and rheology. These experiments revealed that the crystallization process was slower for the PS-PLLA copolymers than for the PLLA homopolymers. SAXS was also used to monitor the crystallization of the PS-PLLA copolymers. When the temperature of the crystallization experiments, T-c, was lower than the glass transition temperature of the amorphous PS block, 7; (hard confinement), the lamellar microstructure of the low molecular weight PS-PLLA was maintained apart from a small increase in the domain spacing. When T-c was higher than T-g(a) of PS (soft confinement), the block copolymer also retained its lamellar structure, but the increase in the domain spacing was unexpectedly increased compared to what occurred for crystallization under hard confinement conditions. In addition, two-dimensional (2-D) SAXS diffractograms indicated a loss of the structure periodicity during crystallization under soft confinement.

The detailed characterization of poly(styrene)-b-poly(tetrahydrofuran) (pS-b-pTHF) multiblock copolymers (17800 g mol -1≥ M n ≥ 46800 g mol -1) generated via urethane linkages is presented. The synthesis of the block copolymers is enabled via a mechanistic switch of the thiocarbonyl thio end group of a poly(styrene) to dihydroxyl terminated polymers that subsequently react with a diisocyanate terminated polytetrahydrofuran based prepolymer to form multiblock copolymer structures. The characterization of the multiblock copolymers and their substructures includes size exclusion chromatography (SEC), liquid chromatography at critical conditions (LCCC), nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy as well as matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. To obtain even further details of the polymer size and its composition, SEC with triple detection as well as newly developed SEC coupled online to IR spectroscopy was carried out. The quantification of the average block fractions via online SEC-IR (41-61 mol % pTHF) is in very good agreement with the results obtained via NMR spectroscopy (39-66 mol % pTHF). © 2012 American Chemical Society.

Liquids composed of small-molecule monohydroxy alcohols are demonstrated to display rheological behavior typical for oligomeric chains. This observation was made possible by rheological experiments in which more than seven decades in frequency and more than five decades on the mechanical modulus scale are covered. The singly hydrogen-bonded monohydroxy alcohols were chosen because they display significant, but surprisingly poorly understood effects of intermolecular association. Based on the present shear study, one can apply theoretical concepts of polymer science to understand the anomalous physical behavior of a wide range of hydrogen-bonded liquids.