Damage and Repair in Informational Poly(N-substituted urethane)s

The degradation and repair of uniform sequence-defined poly(N-substituted urethane)s was studied. Polymers containing an ω-OH end-group and only ethyl carbamate main-chain repeat units rapidly degrade in NaOH solution through an ω→α depolymerization mechanism with no apparent sign of random chain cleavage. The degradation mechanism is not notably affected by the nature of the side-chain N-substituents and took place for all studied sequences. On the other hand, depolymerization is significantly influenced by the molecular structure of the main-chain repeat units. For instance, hexyl carbamate main-chain motifs block unzipping and can therefore be used to control the degradation of specific sequence sections. Interestingly, the partially degraded polymers can also be repaired; for example by using a combination of N,N′-disuccinimidyl carbonate with a secondary amine building-block. Overall, these findings open up interesting new avenues for chain-healing and sequence editing.     

Linear polyamides from L‐malic acid and alkanediamines

A series of linear polyamides (PnMLM) derived from O‐methyl‐protected L ‐malic acid and 1,n‐alkanediamines with even n values ranging from 4 to 12 were prepared and fully characterized. L ‐Malic acid entered in the chain with a random orientation rendering essentially aregic polymers. PnMLM displayed optical rotation consistent with the content of the polymer in malic units, and they all were crystalline with melting points ranging from 158 to 188 °C and glass‐transition temperatures varying from 37 to 70 °C. PnMLM appeared to be fairly stable to heat with thermal decomposition starting close to 300 °C. Hydrolytic degradation of PnMLM at 37 °C was slow, but the process was significantly faster at 70 °C. Thermal degradation took place with the formation of cyclic malimides in the residual polymer and released the 1,n‐alkanediamine. However, hydrolytic degradation took place in a first stage with the formation of open chains of carboxylic‐ and amine‐ended oligomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1566–1575, 2004     

Dual stimuli‐responsive microgels based on photolabile crosslinker: Temperature sensitivity and light‐induced degradation

The synthesis and characterization of a new photocleavable crosslinker is presented here. Dual stimuli‐responsive P(VCL‐co‐NHMA) microgels were prepared by precipitation polymerization of vinylcaprolactam (VCL) with N‐hydroxymethyl acrylamide (NHMA) and the new crosslinker. The microgels had distinct temperature sensitivity as observed in the case of PVCL‐based particles and their volume phase transition temperature (VPTT) shifted to higher temperature with increasing NHMA content. Photolytic degradation experiments were investigated by irradiation with UV light, which led to microgel disintegration caused by cleavage of the photolabile crosslinking points. The degradation behavior of the microgels was conducted with respect to degradation rates by means of the relative turbidity changes. Hence, the microgels could totally degrade into short linear polymers by UV light, thus representing a great potential as new light and temperature dual responsive nanoscale materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1676–1685     

Degradation Mechanisms of Biodegradable Poly(DL-lactide-co-glycolide)1000 Diacrylate Network as Studied by Proton Solid-State Flow NMR Relaxometry

Summary: Degradation mechanisms of biodegradable photo-polymerised poly(DL-lactide-co-glycolide)1000 diacrylate {[(DL-LA/GA)DA]} matrices or films were studied by proton solid-state NMR relaxometry. A flow NMR unit cell was developed for this purpose. The (DL-LA/GA)DA-network was degraded in PBS buffer solution of pH = 7.4. A real-time proton NMR method provided information about the staged break down of the network during continuous circulation of the buffer solution through the NMR tube. The current study shows that degradation of the network proceeds in three stages: 1 - extraction of a sol fraction that causes substantial immobilization of the material, 2 - scissions of network chains producing network defects without formation of extractable products, and 3 – finally, chain scissions that cause formation of a sol fraction and complete degradation of the material. It was shown that the [(DL-LA/GA)DA-network was composed of rigid and viscoelastic domains on all stages of degradation. This heterogeneity could be due to heterogeneous spatial distribution of network junctions in the initial network and/or nano-scale phase separation of polyacrylate chains that form multifunctional network junctions and poly(lactide-co-glicolide) network chains. A combination of bulk and surface erosion both on nano- and macroscopic scales could explain the observed degradation mechanisms. It is shown that knowledge of weight loss upon hydrolytic degradation is not sufficient for understanding degradation mechanisms in the relation to functional properties of this type of hydrogels.     

Effect of degradation on electronic properties of polymer solar cells

We present here the effect of degradation on electronic properties of polymer solar cells. Investigations were performed on two types of solar cells based on the bulk‐heterojunction network of poly(3‐hexylthiophene) and phenyl [6,6] C₆₁ butyric acid methyl ester, one with slow degradation whereas other with faster degradation. Samples were prepared in identical conditions with controlled atmosphere, but for faster degradation, one of the samples was exposed to ambient air (rich in O₂ and H₂O molecules) before deposition of top metal electrode. The sample with slow degradation showed linear degradation in short circuit current density (J_sc), whereas the sample with faster degradation exhibited exponential degradation in J_sc. Linear degradation happens due to degradation in the active layer only whereas the exponential degradation is because of through degradation of the solar cell. The effect of degradation is investigated on different diode parameters. Because of different degradation processes in the two samples, the variations in diode parameters with time are different. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal characterization of carbonate rocks,Kozani area,North-western Macedonia,Greece

The curing of a thermoreactive alkyd-melamine-formaldehyde resin system was investigated by rheologycal, TG and TMA-analysis, in order to construct the time-temperature-transformation diagram. The points of the gelation curve were determined by measuring the increase in viscosity during isothermal curing at different temperatures. A power-function could be fitted to the gelation curve, which is suitable to estimate gelation at any curing conditions, as well as to establish storage conditions. The reaction in the resin matrix was followed by monitoring the loss of mass during isothermal curing at different temperatures. The final section of the resulted iso-curing temperature (iso-T _cure) diagrams could be fitted with logarithmic functions, which may be used for estimating the conditions needed to a given, desirable mass loss, i.e. conversion. The steepness of the curves increases with temperature suggesting the forthcoming of degradation during cure with increasing temperature. From these data the iso-mass loss curves of the TTT-diagram were constructed. For determining the iso-Tg curves of the TTT-diagram isothermal curing was carried out in a drying oven at different temperatures, followed by TMA measurements. The iso-Tcure diagrams served to determine T _{g ￥}, and to construct the iso-T _g curves of the TTT diagram. Vitrification curve is far beyond conditions of storage, curing and degradation, meaning that the resin matrix is in rubbery physical state before, during and after the cure. Curing conditions resulting degradation can also be estimated from the TTT-diagram. This revised version was published online in August 2006 with corrections to the Cover Date.     

The transformation of phenyltin species during sample preparation of biological tissues using multi-isotope spike SSID-GC-ICPMS

A multi-isotope spike species-specific isotope dilution (MI-SSID) calibration strategy in connection with gas chromatography-inductively coupled plasma mass spectrometry was applied to evaluate different extraction procedures for the speciation analysis of phenyltin (PhT) compounds in biological materials: mussel tissue BCR CRM-477 and fish tissue NIES-11. Three different isotope-enriched PhT compounds, ¹¹⁸Sn-enriched monophenyltin (MPhT), ¹²²Sn-enriched diphenyltin (DPhT), and ¹²⁴Sn-enriched triphenyltin (TPhT), were used for the preparation of spikes to follow and correct for six possible interconversion reactions between PhT species that can take place in a sample. The acidity of the extractant, the presence of complexing reagents, and the use of ultrasonic or microwave agitation were found to affect the degradation of PhT compounds. No formation of PhTs through phenylation and negligible degradation of MPhT to inorganic tin were observed under the conditions investigated. The degree of degradation increased with increased acidity of extractant and when ultrasonication or microwave agitation was used. Under relatively mild extraction conditions, the degradation factors for DPhT and TPhT in the two reference materials studied were found, using MI-SSID, to be between 10 and 55% and 2 and 10%, respectively. Using the degradation factors, we calculated corrected concentration values for the organotin species. When microwave extraction at high power output was used, hydrogen radicals were formed that can enhance the degradation of DPhT and TPhT. The hydrogen radicals were trapped using N-tert-butyl-α-phenylnitrone and detected by electron spin resonance spectrometry. The effect of different extraction parameters on the degradation of PhT compounds in biological samples is discussed.     

Quercetin enhances vitamin D2 stability and mitigate the degradation influenced by elevated temperature and pH value

Vitamin D₂ (vit. D₂) is a nutraceutical essentially needed for good health. However, it is susceptible to oxygen and high temperature. The use of natural products such as bioflavonoids possessing anti-degradative effect of vit. D₂ degradation has not been described before. A combinational effect of vit. D₂ with quercetin showed a positive effect and inhibited vit. D₂ degradation when exposed to high temperature (50 ℃ and 75 ℃) at different time points. The results obtained revealed vit. D₂ degradation was drastically increased with longer incubation under thermal treatment. However, quercetin and vit. D₂ groups were able to significantly inhibit the degradation of vit. D₂ and stabilize it, evaluated through the retention percentage. We also exposed vit. D₂ at solutions with different pH values (1, 4, 5, 7, 10). Quercetin exerted vit. D₂ anti-degradation at different pH values as well as under thermal pressure at different time points. Conclusively, quercetin can be an effective way to reduce temperature and pH induced degradation of vit. D₂.     

Activation energies for the thermodegradation process of an epoxy-diamine system

The study of the degradation of a polymer is important because it can determine the upper temperature limit, the mechanism of a solid-state process, and the life-time for this system. Since the behavior of thermosets is affected by the selection of the curing cycle, it is important to investigate the changes which take place during the thermal degradation of these materials when a change on the sequence of time and temperature is introduced during the curing reaction. In this work, the thermal degradation of two epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) cured through different sequences of time and temperature was studied by thermogravimetric analysis in order to determine the reaction mechanism of the degradation processes, and also to check the influence of the curing cycle on this mechanism. Values obtained using different kinetic methods were compared to the value obtained by Kissinger’s method (differential method which do not require a knowledge of the n-order reaction mechanism), and to that obtained through Flynn–Wall–Ozawa method in a previous work.     

Thermal degradation and kinetic analysis of biodegradable PBS/multiwalled carbon nanotube nanocomposites

In this study, carbon nanotubes (CNTs) were first modified using N,N′‐ dicyclohexylcarbodiimide (DCC) dehydrating agents. Subsequently, the poly(butylene succinate)/multiwalled carbon nanotube (PBS/MWNTs) nanocomposites were prepared through facile melt blending. Thermal degradation of these PBS/MWNT nanocomposites was investigated; the kinetic parameters of degradation were calculated using the Coats and Redfern, Ozawa, and Horowitz and Metzger methods, respectively. It was found that the degradation reaction mechanism of PBS and the CNT‐C18 containing nanocomposites at lower temperature was likely to produce an F1 model through reaction of random chain cleavage (cis‐elimination). However, the reaction mechanism at higher temperature was likely to be a D1 model because of the dominant diffusion control effect. Moreover, it was found that the activation energies of CNT‐C18‐containing PBS nanocomposites were first increased with the content of CNT‐C18, but then decreased after the content was larger than 0.5 wt % for all models at differing heating rates. This may be due to the formation of a conductive network of CNTs in the polymer matrix at higher content of CNTs, which lead to better heat and electrical conductivity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1231–1239, 2009     

Stability of doripenem in reconstituted solution – thermal and oxidative decomposition kinetics and degradation products by LC–MS

A ultra‐fast liquid chromatography method applied to quantitation of doripenem in powder for injection was validated. Validation parameters were assayed and a rapid analysis was established by a reversed‐phase system comprising a C₁₈ column endcapped (50 × 4.0 mm, 2.0 μm), mobile phase consisting of phosphoric acid 0.01% (pH 3.8) and acetonitrile (98:02, v /v) and a flow rate of 0.4 mL min⁻¹. Drug stability was studied through submission to forced conditions, allowing the major degradation products to be detected and the kinetics parameters to be established. Thermal and oxidative degradation were determined, and indicated a kinetic decomposition following first and second order, respectively. The main degradation products were identified by LC–MS analysis, and the results were evaluated in order to suggest the chemical structures corresponding to respective masses and fragmentations. Six compounds were identified, with m/z 411, 427, 437, 634, 650 and 664. All of them resulted from cleavage of β ‐lactam ring and alcoholic chain and/or dimerization. These experimental results provide valuable information about the stability of doripenem reconstituted solution and procedures for its handling and storage.     

Preparation, characterization and hydrolytic degradation of poly[p-dioxanone-(butylene succinate)] multiblockcopolymer

A series of poly[p-dioxanone-(butylene succinate)] (PPDOBS) copolymers were prepared from p-dioxanone (PDO), 1,4-butanediol and succinate acids through a two-step process including the initial prepolymer preparation of poly(p-dioxanone)diol (PPDO-OH) and poly(butylene succinate)diol (PBS-OH) and the following copolymerization of the two kinds of prepolymers by coupling with hexamethylene diisocyanate (HDI). The molecular structures of the prepared PPDO-OH, PBS-OH and PPDOBS were characterized by hydrogen nuclear magnetic resonance spectroscopy (¹H NMR). The crystallization of the copolymers was investigated by using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). It has been shown that the crystallization rate and the degree of crystallization increases with the increase of the weight fraction of poly(butylene succinate) (PBS) blocks in the copolymers. In phosphate buffer solution with pH 7.4 at 37 °C for 18 weeks, the hydrolytic degradation behaviors of the copolymers were studied. The changes of retention weight, water absorption, pH value, and surface morphologies with the degradation time showed that the hydrolytic degradation rate of PPDOBS could be controlled by adjusting the weight fraction of poly(p-dioxanone) (PPDO) and PBS blocks in the copolymers. The changes of the thermal properties of PPDOBS during the degradation were also investigated by DSC.     

Exploration of the Photodegradation of Naphtho[2,3‐g] quinoxalines and Pyrazino[2,3‐b]phenazines

Nitrogen‐containing polycyclic aromatic hydrocarbons are very attractive compounds for organic electronics applications. Their low‐lying LUMO energies points towards a potential use as n‐type semiconductors. Furthermore, they are expected to be more stable under ambient conditions, which is very important for the formation of semiconducting films, where materials with high purity are needed. In this study, the syntheses of naphtho[2,3‐g]quinoxalines and pyrazino[2,3‐b]phenazines is presented by using reaction conditions, that provide the desired products in high yields, high purity and without time‐consuming purification steps. The HOMO and LUMO energies of the compounds are investigated by cyclic voltammetry and UV/Vis spectroscopy and their dependency on the nitrogen content and the terminal substituents are examined. The photostability and the degradation pathways of the naphtho[2,3‐g]quinoxalines and pyrazino[2,3‐b]phenazines are explored by NMR spectroscopy of irradiated samples affirming the large influence of the nitrogen atoms in the acene core on the degradation process during the irradiation. Finally, by identifying the degradations products of 2,3‐dimethylnaphtho[2,3‐g]quinoxaline it is possible to track down the most reactive position in the compound and, by blocking this position with nitrogen, to strongly increase the photostability.     

Freshwater quality in urban areas: a case study from Rome, Italy

Water quality in streams running in urban areas can be strongly altered by the impact of human activities. Different kinds of water quality degradation were investigated in the streams running in the ‘Appia Antica’ Regional Park, placed in the southern suburbs of Rome. Water quality was assessed in 21 sampling points located in eight streams by the analysis of chemical [chemical oxygen demand (COD), nitrates, ammonia, total phosphorus], biological (IBE index), microbial (total coliforms, faecal coliforms, Escherichia coli, faecal streptococci, sulphite-reducing clostridia) ecosystemic (IFF index), and hydrological (flow) parameters. On the whole the results indicate an in depth degradation of water quality. However, IBE and IFF showed local condition of water stress that were not individuated by chemical parameters. A multidisciplinary approach is necessary to highlight the different pressures on water quality of urban freshwaters. The presence of buffer zones in urban green areas does not avoid the impact arising from the surrounding urban area.     

On the Mechanism of Polyamide Degradation in Chlorinated Water

Experiments were performed in an attempt to identify the reactive intermediate(s) involved in the degradation of a polyamide, Nylon 66, in chlorinated water. According to previous studies, N‐chlorination is certainly one reaction that ultimately contributes to polyamide degradation. In this case, the intermediates involved could either be Cl₂ or HClO. Available information also indicates that, for many polymers, singlet molecular oxygen (a¹Δ_g), chemically generated from HClO, could likewise be involved as an intermediate in a degradation reaction. Thus, tests were undertaken to specifically address this latter issue with respect to polyamide degradation. The degradation of Nylon 66 was monitored under a variety of conditions by FT‐IR spectroscopy. The rate of degradation was pH‐dependent, and degradation was most pronounced at pH<5. Characteristic tests for the intermediacy of singlet oxygen, however, were negative. Rather, the data strongly pointed to Cl₂ as the key intermediate in the degradation. The presence of compounds capable of being oxidized by Cl₂ arrested the degradation reaction. These results should be pertinent in an attempt to stabilize polymers exposed, e.g., to water that has been chlorinated to kill bacteria (i.e., drinking water).     

Graft Copolymerization of Vinyl Monomers onto Silk Fibers

Modification of the properties of textile fibers in order to get a fiber of improved textile performance is the subject of study of several groups of scientists and technologists [1–4]. Of the several methods available, grafting promises to be a potentially effective means of altering the fiber properties through the added polymer formed in situ without destroying the basic properties of the parent fiber. Copolymerization is attractive to chemists as a means of modifying macromolecules since, in general, degradation can be minimized. The desirable properties of the polymer are retained and copolymerization provides additional properties through the added polymer. The added polymer may be formed in situ by polymerization of a monomer or monomers, by condensation of reactants, or by the deposition of preformed polymer.     

The influence of processing conditions on the properties and the degradation of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)

The influence of melt-extrusion on the degradation behavior of poly(3-hydroxybutyrate-co-7% 3-hydroxyvalerate) in a small-scale compost and in salt media with Aspergillus fumigatus has been studied. The degradation has been monitored by Size Exclusion Chromatography (SEC), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and X-ray analysis. During the first 9 weeks of composting the degradation proceeds through surface erosion without any significant change in molecular weight or weight crystallinity. After 10 months the weight average molecular weight, Mw, has decreased by approximately 15–50%. It is suggested that degradation mechanism is converted from enzymatic to chemical hydrolysis as the porosity of the samples increases which facilitates water penetration. In addition, the acidic degradation products would accelerate the chemical hydrolysis inside the sample due to lowering of the pH. During degradation in media containing A. fumigatus the sample processed at low temperature exhibited extensive surface degradation and a 12% reduction of the Mw. In contrast the sample processed at high temperature showed an homogeneous surface degradation and no reduction in molecular weight. The differences in degradation are attributed to variations in the initial morphology of the samples caused by the processing conditions. Further investigations are, however, required to separate effects attributed to local differences in the compost environment and the structure of the samples.     

6-Desoxy-L-idose, 6-Desoxy-L-sorbose und 6-Desoxy-L-psicose. Desoxyzucker, 41. Mittelung [1]

Although crystalline 6-deoxy-L -idose ( 2 ) and crystalline 6-deoxy-L -sorbose ( 3 ) have similar melting points and specific rotations, they can be conclusively differentiated from one another through paper chromatography and paper electrophoresis. 6-Deoxy-L -idose cannot be converted into 6-deoxy-L -sorbose on short heating in very dilute aequeous mineral acids. The synthesis of amorphous 6-deoxy-L -psicose ( 17 ), through oxidative fermentation of 6-deoxy-L -allitol with Acetobacter suboxydans, has been described.     

Multi-arm Star Polyisobutylenes. V. Characterization of Multi-arm Polyisobutylene Stars by Viscometry,Pour Points,Electron Microscopy,and Ultrasonic Shear Degradation

Abstract

Structure/property relationship of multi-arm star polyisobutylenes [?-(PIB) _n s] were characterized by a variety of techniques, including vis-cometry, pour points, electron microscopy, and ultrasonic degradation. The intrinsic viscosity of ?-(PIB) _n s changes very little with temperature in the 30 to 100°C range, whereas that of linear PIBs of the same molecular weight increases strongly with temperature. Kinematic viscosity measurements of select ?-(PIB) _n s gave viscosity indices in excess of 130. The viscosity of ?-(PIB) _n s is mainly determined by the molecular weight of the arms and much less by the number of arms or overall molecular weights. Electron microscopy of ?-(PIB) _n s indicates a compact spherical morphology, a conclusion that was substantiated by radius of gyration measurements. Pour points of ?-(PIB) _n s are ?27°C. Ultrasonic studies gave insight into the mechanism of shear degradation of ?-(PIB) _n s. These characteristics render ?-(PIB) _n s of interest as rheology control additives for motor oils.     

Fast Cyclization of a Proline-Derived Self-Immolative Spacer Improves the Efficacy of Carbamate Prodrugs

Self-immolative (SI) spacers are sophisticated chemical constructs designed for molecular delivery or material degradation. We describe herein a (S)-2-(aminomethyl)pyrrolidine SI spacer that is able to release different types of anticancer drugs (possessing either a phenolic or secondary and tertiary hydroxyl groups) through a fast cyclization mechanism involving carbamate cleavage. The high efficiency of drug release obtained with this spacer was found to be beneficial for the in vitro cytotoxic activity of protease-sensitive prodrugs, compared with a commonly used spacer of the same class. These findings expand the repertoire of degradation machineries and are instrumental for the future development of highly efficient delivery platforms.