Synthesis of thermally and mechanically improved polyurethane-urea elastomers by using novel diamines as chain extenders

e-Polymers ◽  
2016 ◽  
Vol 16 (5) ◽  
pp. 411-418 ◽  
Author(s):  
Muhammad Shoaib ◽  
Ali Bahadur
Keyword(s):  
Hard Segment ◽  
Mechanical Test ◽  
Reference Sample ◽  
Thermal Stabilization ◽  
Urea Group ◽  
Chain Extenders ◽  
Stabilization Effect ◽  
Hard Segments ◽  
Reflectance Ftir ◽  
Atr Spectroscopy

AbstractThis article reports the synthesis of novel diamines as chain extenders for the improvement of thermal and mechanical properties of polyurethane (PU). Three novel diamine, 1,2-di(p-aminophenoxy)ethane (BAE), 1,2-di(p-aminophenoxy)propane (BAP) and 2,2-bis(p-(p-aminophenoxy)phenyl)propane (BAPP) were synthesized as chain extenders. Formation of diamines and their reaction with PU prepolymer was analyzed by using Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The conversion of the free isocyanate group (NCO) into a urethane-urea group was confirmed through the disappearance of the isocyanate peak at 2244 cm-1. The thermogravimetric analysis (TGA) reveals the thermal stabilization effect of urethane-urea hard segments of the polyurethane system. From the SAXS investigations, the hard segment inter-domain spacing (d) was calculated, which was 24 nm for the reference sample, and 25, 26, and 28.5 nm for the synthesized PU systems. Mechanical test shows an increase in the Young’s modulus and yield strength with BAE and BAP diamines, while BAPP diamine based systems reveal lower modulus values as compared to the reference sample.

scholarly journals Stabilization of a G-Quadruplex from Unfolding by Replication Protein A Using Potassium and the Porphyrin TMPyP4

2011 ◽  
Vol 2011 ◽  
pp. 1-13 ◽  
Author(s):  
Aishwarya Prakash ◽  
Fabien Kieken ◽  
Luis A. Marky ◽  
Gloria E. O. Borgstahl
Keyword(s):  
Dna Replication ◽  
Protein A ◽  
Thermal Stabilization ◽  
Replication Protein A ◽  
Replication Protein ◽  
Unique Problem ◽  
Ssdna Binding ◽  
Binding Domains ◽  
G Quadruplex ◽  
Stabilization Effect

Replication protein A (RPA) plays an essential role in DNA replication by binding and unfolding non-canonical single-stranded DNA (ssDNA) structures. Of the six RPA ssDNA binding domains (labeled A-F), RPA-CDE selectively binds a G-quadruplex forming sequence (5′-TAGGGGAAGGGTTGGAGTGGGTT-3′called Gq23). In K+, Gq23 forms a mixed parallel/antiparallel conformation, and in Na+Gq23 has a less stable (TMlowered by ∼20∘C), antiparallel conformation. Gq23 is intramolecular and 1D NMR confirms a stable G-quadruplex structure in K+. Full-length RPA and RPA-CDE-core can bind and unfold the Na+form of Gq23 very efficiently, but complete unfolding is not observed with the K+form. Studies with G-quadruplex ligands, indicate that TMPyP4 has a thermal stabilization effect on Gq23 in K+, and inhibits complete unfolding by RPA and RPA-CDE-core. Overall these data indicate that G-quadruplexes present a unique problem for RPA to unfold and ligands, such as TMPyP4, could possibly hinder DNA replication by blocking unfolding by RPA.

Thermal stabilization effect of some 3,5-di-t-butyl-4-hydroxy derivatives of ethane and ethene

2002 ◽  
Vol 21 (3) ◽  
pp. 353-361 ◽  
Author(s):  
S. Jipa ◽  
T. Zaharescu ◽  
R. Setnescu ◽  
T. Setnescu ◽  
J. Herdan ◽  
...  
Keyword(s):  
Thermal Stabilization ◽  
Stabilization Effect ◽  
Derivatives Of

scholarly journals Modification of epoxy resins with thermoplastic segmented polycarbonate-based polyurethanes

2014 ◽  
Vol 68 (6) ◽  
pp. 755-765 ◽  
Author(s):  
Jelena Pavlicevic ◽  
Mirjana Jovicic ◽  
Vesna Simendic ◽  
Oskar Bera ◽  
Radmila Radicevic ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Epoxy Resin ◽  
Hard Segment ◽  
Crosslinking Agent ◽  
Polyurethane Elastomers ◽  
Hard Segment Content ◽  
Weight Content ◽  
Epoxy Curing ◽  
Hard Segments ◽  
Modified Epoxy

In this work, epoxy hybrid materials were synthesized by addition of thermoplastic segmented aliphatic polyurethanes with good elastic properties. The modified epoxy samples were obtained by curing of previously homogenized mixture of prepared polyurethane melts, epoxy resin and crosslinking agent Jeffamine D-2000. The influence of different weight content of polyurethanes (5, 10 and 15 wt. % compared to pure epoxy resin) as well the influence of different hard segments of elastomers (20, 25 and 30 wt. %) on the curing of modified epoxy systems was studied. The curing was followed by differential scanning calorimetry (DSC), in dynamic regime from 30 to 300?C, at three heating rates (5, 10 and 20?C/min). With the increase of hard segments content of polyurethanes added in higher concentration (10 and 15 wt. %) into epoxy matrix, the temperature of maximum ratio of curing was shifted to lower values (from 205 to 179?C). Obtained DSC data were analyzed using two integral methods (Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose) and one differential kinetic model (Friedman). The significant differences were observed in the second part of the epoxy curing (for the reaction degrees higher than 60 %), where the values of activation energies remarkably increase. The addition of polyurethane elastomers retarded the curing process due to decreased mobility of reactant molecules caused by higher viscosity of reaction mixture. By detailed analysis of determined kinetic parameters, it is concluded that the influence of slow diffusion is more pronounced in the presence of thermoplastic polycarbonate-based polyurethanes, which confirmed their effect on the mechanism of epoxy curing. The highest tensile strength and hardness showed the DGEBA modified with the polyurethane with highest hard segment content. Increasing the hard segment content of polyurethane and its concentration in matrix, the tensile strength of modified epoxy was increased. The elongation at break of modified epoxy samples was significantly improved by addition of polycarbonate-based polyurethanes with low hard segment content, due to higher content of flexible soft segment chains.

Time-dependent ammonia emissions from fumed oak wood determined by micro-chamber/thermal extractor (μCTE) and FTIR-ATR spectroscopy

Holzforschung ◽  
2019 ◽  
Vol 73 (2) ◽  
pp. 165-170
Author(s):  
Elfriede Hogger ◽  
Klaus Bauer ◽  
Eva Höllbacher ◽  
Notburga Gierlinger ◽  
Johannes Konnerth ◽  
...  
Keyword(s):  
Partial Least Square ◽  
Least Square ◽  
Partial Least Square Regression ◽  
Coefficient Of Determination ◽  
Gaseous Ammonia ◽  
Ammonia Content ◽  
Oak Wood ◽  
Customer Complaints ◽  
Reflectance Ftir ◽  
Atr Spectroscopy

AbstractThe ongoing preference for dark colours in parquet and furniture is a driving force for colour modification of bright wood species. The treatment of oak wood with gaseous ammonia (fuming) leads to dark colours, but residual ammonia in the wood may lead to bonding failures with resins, odour nuisance and thus customer complaints. The focus of the present paper is the determination and emission of remaining ammonia in fumed oak. A fast and convenient approach based on Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy was developed to replace the currently applied time-consuming and complex determination procedures. The integrated area of the infrared (IR) region between 1575 and 1535 cm−1shows a relationship with the coefficient of determination (R2=0.76) to the residual ammonia content determined by the micro-chamber/thermal extractor (μCTE) method. The prediction accuracy was further improved by partial least square regression calculations. Promising models with high R2(0.85), low root mean square error of cross-validation (RMSE-CV=1.08%) with five principal components were established and already integrated successfully into the production as input control. FTIR-ATR spectroscopy proved to be a simple and fast predictive method to estimate residual ammonia in fumed oak.

Chain Extender and Diisocyanate Amount Effects on the Thermal, Mechanical and Wettability Properties of Some Polyurethane Elastomers

e-Polymers ◽  
2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Stelian Vlad ◽  
Stefan Oprea
Keyword(s):  
Thermal Stability ◽  
Hard Segment ◽  
Chain Extender ◽  
Polyurethane Elastomers ◽  
Triple Bonds ◽  
Fine Control ◽  
Chain Extenders

AbstractThe aim of this study was to investigate the effect of chain extender and diisocyanate amount on the thermal, mechanical and wettability properties of some polyurethanes. The chain extender nature caused the increase of the thermal stability due to the higher stability of the double and triple bonds respectively in contrast to simple bonds. Tg of the polyurethanes based on PCL/MDI decreased when the unsaturated grade from chain extenders increased. The double and triple bonds content from polyurethane structure was responsible for this behavior. The hard segment contents and the chain extenders nature also influenced the wettability. The results showed that the thermal, mechanical and wettability properties of the final products might be controlled by fine control of the amount of the MDI and the nature of the chain extenders

Properties of Polyether-Polyester Thermoplastic Elastomers

1977 ◽  
Vol 50 (1) ◽  
pp. 1-23 ◽  
Author(s):  
A. Lilaonitkul ◽  
S. L. Cooper
Keyword(s):  
Melting Point ◽  
Hard Segment ◽  
Elevated Temperatures ◽  
Basic Structure ◽  
Thermoplastic Elastomers ◽  
Degree Of Crystallinity ◽  
Fabrication Procedure ◽  
Hard Segments ◽  
Average Block ◽  
Definition Of

Abstract The viscoelastic properties of polytetramethylene oxide—polytetramethylene terephthalate block polymers are strongly influenced by phase separation of the 4GT hard blocks into crystalline domains. Thermal analysis reveals a single Tg which increases with increasing 4GT content. This suggests that short sequences of hard segments form a compatible interlamellar amorphous phase with the polyether component. The Gordon-Taylor equation was found to model Tg behavior accurately, provided that the crystalline polyester component was not included in the definition of the hard segment. The melting point of the polytetramethylene terephthalate blocks depends on the average block length of crystallizable segment. Incorporating non-crystallizing polytetramethylene 1,4-cyclohexanedicarboxylate into the hard segment reduces the 4GT melting point and degree of crystallinity. The morphological features of the copolymers depend on sample composition and fabrication procedure. The basic structure is spherulitic. Three different types of spherulite were observed: positive and negative spherulites, as well as spherulites which have their optical axis 45° to their radial direction. The different spherulite types are relatively stable; annealing the samples at elevated temperatures does not alter their morphology. Annealing does increase the degree of crystallinity somewhat and produces crystallites in equilibrium at the annealing temperature. Infrared dichroism studies reveal that, at low deformations, the hard segment lamellae orient as a whole in the stretching direction. This is refleeted by the initial negative orientation of the hard segments. At this stage of elongation, the deformation of the crystallites is nearly reversible. At higher strain levels, the lamellae are disrupted and the hard segments orient positively with a high degree of orientational hysteresis. The soft segments, however, orient almost reversibly in the stress direction at all strain levels studied. It is concluded that the extensive stress softening is brought about by plastic deformation of the crystalline hard segments.

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