Mechanical Behavior of Lightly Crosslinked Polyurethanes

1977 ◽  
Vol 50 (5) ◽  
pp. 934-944 ◽  
Author(s):  
S. Dzierża ◽  
J. Janáček
Keyword(s):  
Mechanical Properties ◽  
Hydrogen Bonding ◽  
Elevated Temperatures ◽  
Van Der Waals ◽  
Crosslinking Agent ◽  
Polymeric Materials ◽  
Van Der Waals Forces ◽  
Branch Points ◽  
Chain Entanglement ◽  
Polyurethane Elastomers

Abstract Polyurethane elastomers are a numerous group of polymeric materials of wide practical application. They are usually formed by polyaddition of diisocyanates with hydroxyl-terminated polyesters or polyethers in the presence of low molecular weight diols or diamines as chain extenders. One may consider urethane elastomers to be block copolymers, consisting of moderately flexible long linear polyester or polyether segments and relatively stiff segments of aromatic and urethane groups. The length and structure of each block can be easily controlled. Crosslinking by an excess of diisocyanate can occur only at the stiff segments, and the number of branch points can also be controlled. The properties of these elastomers can be widely changed using components of different structures and varying their quantitative ratios. They are the results of a combination of segment flexibility, crosslinking, chain entanglement, orientation of segments, hydrogen bonding and other van der Waals forces, as well as rigidity of aromatic units. In the urethane systems, hydrogen bonding and other van der Waals forces, play a much more pronounced role than in familiar olefin-derived elastomers. Although polyurethane elastomers have very good mechanical properties at room temperature, their application is strongly limited by rapid deterioration of properties which takes place at elevated temperatures. The decay of mechanical properties of polyurethane is caused by the breaking of hydrogen and other secondary bonds, as well as by the presence of relatively weak crosslinks that make up their network. The properties of polyurethanes at elevated temperatures may, perhaps, be improved by forming additional crosslinks, besides the typical ones. Some efforts concerning this problem have been published. The aim of our study was to obtain and check the properties of polyurethane elastomers having unsaturated bonds, on which some additional crosslinks were expected to be formed in the presence of a suitable crosslinking agent.

scholarly journals Crystal structure of 2-(2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-ylidene)acetonitrile

2015 ◽  
Vol 71 (10) ◽  
pp. o792-o793
Author(s):  
K. Priya ◽  
K. Saravanan ◽  
S. Kabilan ◽  
S. Selvanayagam
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Crystal Packing ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Chair Conformation ◽  
Equatorial Orientation ◽  
Amino Group ◽  
Phenyl Rings

In the title 3-azabicyclononane derivative, C22H22N2, both the fused piperidine and cyclohexane rings adopt a chair conformation. The phenyl rings attached to the central azabicylononane fragment in an equatorial orientation are inclined to each other at 23.7 (1)°. The amino group is not involved in any hydrogen bonding, so the crystal packing is stabilized only by van der Waals forces.

Structure of Stretched Rubber

1938 ◽  
Vol 11 (3) ◽  
pp. 510-514
Author(s):  
C. J. B. Clews ◽  
F. Schossberger
Keyword(s):  
Mechanical Properties ◽  
Transverse Direction ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Original Model ◽  
Micellar Structure ◽  
X Ray

Abstract Investigations of the micellar structure of fiber substances have given rise to two theories. The older theory (Meyer and Mark, 1930; Mark, 1932; Siefriz, 1934; Meyer, 1930; and Nägeli, 1928) considers the micelles as separate crystallites, between which lie the intermicellar spaces. The micelles consist of “Hauptvalenzketten“ bound together along their length by homeopolar bonds and in the transverse direction by van der Waals' forces, the intermicellar binding being also attributed to van der Waals' forces. The original model suggested in work published by Meyer (1930) for cellulose depicts the micelles arranged like bricks in a wall (Fig. 1), and doubtless this is the simplest explanation of the x-ray results. But it is difficult to understand how such an arrangement can give a micellar structure its peculiar mechanical properties, and further how it is possible, when both inter- and intramicellar cohesion are attributed to the same type of force, to cause by swelling experiments an enlargement of the intermicellar spaces, while the “Hauptvalenzketten” remain unaffected.

scholarly journals The Green Approach to the Synthesis of Bio-Based Thermoplastic Polyurethane Elastomers with Partially Bio-Based Hard Blocks

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2334
Author(s):  
Ewa Głowińska ◽  
Paulina Kasprzyk ◽  
Janusz Datta
Keyword(s):  
Mechanical Properties ◽  
Thermoplastic Polyurethane ◽  
Viscoelastic Behavior ◽  
Polymeric Materials ◽  
Building Blocks ◽  
Chain Extender ◽  
Sustainable Chemistry ◽  
Polyurethane Elastomers ◽  
Thermoplastic Polyurethane Elastomers ◽  
Hard Segments

Bio-based polymeric materials and green routes for their preparation are current issues of many research works. In this work, we used the diisocyanate mixture based on partially bio-based diisocyanate origin and typical petrochemical diisocyanate for the preparation of novel bio-based thermoplastic polyurethane elastomers (bio-TPUs). We studied the influence of the diisocyanate mixture composition on the chemical structure, thermal, thermomechanical, and mechanical properties of obtained bio-TPUs. Diisocyanate mixture and bio-based 1,4-butanediol (as a low molecular chain extender) created bio-based hard blocks (HS). The diisocyanate mixture contained up to 75 wt % of partially bio-based diisocyanate. It is worth mentioning that the structure and amount of HS impact the phase separation, processing, thermal or mechanical properties of polyurethanes. The soft blocks (SS) in the bio-TPU’s materials were built from α,ω-oligo(ethylene-butylene adipate) diol. Hereby, bio-TPUs differed in hard segments content (c.a. 30; 34; 40, and 53%). We found that already increase of bio-based diisocyanate content of the bio-TPU impact the changes in their thermal stability which was measured by TGA. Based on DMTA results we observed changes in the viscoelastic behavior of bio-TPUs. The DSC analysis revealed decreasing in glass transition temperature and melting temperature of hard segments. In general, obtained materials were characterized by good mechanical properties. The results confirmed the validity of undertaken research problem related to obtaining bio-TPUs consist of bio-based hard building blocks. The application of partially bio-based diisocyanate mixtures and bio-based chain extender for bio-TPU synthesis leads to sustainable chemistry. Therefore the total level of “green carbons” increases with the increase of bio-based diisocyanate content in the bio-TPU structure. Obtained results constitute promising data for further works related to the preparation of fully bio-based thermoplastic polyurethane elastomers and development in the field of bio-based polymeric materials.

scholarly journals 11-[Bis(trimethylsilyl)amino]-2,4-bis(trimethylsilyl)-7,8,9,10-tetrahydro-6H-cyclohepta[1,2-b]quinoline

IUCrData ◽  
2017 ◽  
Vol 2 (6) ◽  
Author(s):  
Ísmail Çelik ◽  
Mehmet Akkurt ◽  
Makbule Ekiz ◽  
Ahmet Tutar ◽  
Salih Ökten ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Title Compound ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Chair Conformation ◽  
Ring System ◽  
Maximum Deviation ◽  
Compound C ◽  
Trimethylsilyl Groups

In the title compound, C26H48N2Si4, the cycloheptane ring adopts a chair conformation, while the quinolinyl ring system is almost planar [maximum deviation = 0.040 (3) Å for one of the C atoms carrying a Me3Si group]. In the crystal, in the absence of classical hydrogen bonding, the packing is dominated by van der Waals forces. One of the N-bound trimethylsilyl groups is disordered by rotation about the C—SiMe3bond, and was modelled over two sets of sites in the ratio 0.873 (8):0.127 (8).

OxycodoneN-oxide

2012 ◽  
Vol 68 (11) ◽  
pp. o436-o438 ◽  
Author(s):  
Vijayakumar N. Sonar ◽  
Sean Parkin ◽  
Peter A. Crooks
Keyword(s):  
Hydrogen Bonding ◽  
Title Compound ◽  
Crystal Packing ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Pure Form ◽  
Chiral Center

The title compound, (5R,9R,13S,14S,17R)-14-hydroxy-3-methoxy-17-methyl-4,5-epoxymorphinan-6-oneN-oxide, C18H21NO5, has been prepared in a diastereomerically pure form by the reaction of oxycodone with 3-chloroperbenzoic acid and subsequent crystallization of the product from chloroform. The crystal packing shows that the molecule exhibits intramolecular O—H...O [D...A= 2.482 (2) Å] hydrogen bonding. In addition, there are weak intermolecular C—H...O interactions which, along with van der Waals forces, stabilize the structure. The new chiral center at the 17-position is demonstrated to beR.

2-Diethylamino-6-ethyl-6-methyl-3-phenylthieno[2,3-d]pyrimidin-4(3H)-one

2006 ◽  
Vol 62 (7) ◽  
pp. o2862-o2863
Author(s):  
Zheng-Dong Fang ◽  
Ming-Wu Ding
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Title Compound ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Stacking Interactions ◽  
Intermolecular Hydrogen Bonding ◽  
Compound C ◽  
Hydrogen Bonding Interactions ◽  
Π Stacking

In the title compound, C19H23N3OS, the two fused rings of the thieno[2,3-d]pyrimidin-4(3H)-one system are almost coplanar. The packing of the molecules in the crystal structure is determined by van der Waals forces. No intermolecular hydrogen-bonding interactions or π–π stacking interactions are present in the crystal structure.

Effect of van der Waals Interaction Strength and Nanocluster Size on the Dynamical and Mechanical Properties of 1,4-cis-polybutadiene Melts

2012 ◽  
Vol 1424 ◽  
Author(s):  
Canan Atilgan ◽  
Ibrahim Inanc ◽  
Ali Rana Atilgan
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Bulk Modulus ◽  
Residence Time ◽  
Van Der Waals ◽  
Interaction Strength ◽  
Polymeric Materials ◽  
Van Der Waals Interactions ◽  
Increasing Trend ◽  
Dynamics Simulations

ABSTRACTUsing molecular dynamics simulations, we have investigated the effect of embedding nanoclusters of radius 3-7 Å on the dynamical and mechanical properties of 1,4-cispolybutadiene melts. To see the effect of polymer-nanocluster interaction strength on the bulk modulus, the van der Waals interactions (vdW) between the polymer chain and nanocluster have been varied from weak to very stong while keeping polymer-polymer and nanoclusternanocluster interactions constant. The modulus depends on the interaction strength, but not on nanocluster size. Residence time of chains on the surface of the nanocluster (τr) has an increasing trend that reaches to a plateau as the vdW strength is increased. τr also doubles from 100 ps to 200 ps as the nanocluster size is increased from 3 to 7 Å. Our findings give clues on how the properties of polymeric materials may be controlled by nanoparticles of different chemistry and size.

scholarly journals Computational analysis the relationships of energy and mechanical properties with sensitivity for FOX-7 based PBXs via MD simulation

2021 ◽  
Vol 8 (2) ◽  
Author(s):  
Jianbo Fu ◽  
Baoguo Wang ◽  
Yafang Chen ◽  
Yunchuan Li ◽  
Xing Tan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Hydrogen Bonding ◽  
Binding Energy ◽  
Bond Length ◽  
Energetic Materials ◽  
Crystal Surface ◽  
Van Der Waals ◽  
Length Distribution ◽  
High Energy ◽  
Experimental Fact

Molecular dynamics (MD) simulations have been applied to investigate 1, 1-diamino-2, 2-dinitroethene (FOX-7) crystal and FOX-7 (011)-based polymer-bonded explosives (PBXs) with four typical polymers, polyethylene glycol (PEG), fluorine-polymer (F 2603 ), ethylene-vinyl acetate copolymer (EVA) and ester urethane (ESTANE5703) under COMPASS force field. Binding energy ( E bind ), cohesive energy density (CED), initiation bond length distribution, RDG analysis and isotropic mechanical properties of FOX-7 and its PBXs at different temperatures were reported for the first time, and the relationship between them and sensitivity. Using quantum chemistry, FOX-7 was optimized with the four polymers at the B3LYP/6-311++G(d,p) level, and the structure and RDG of the optimized composite system were analysed. The results indicated that the binding energy presented irregular changes with the increase in temperature. The order of binding ability of different binders to the FOX-7 (011) crystal surface is PEG > ESTANE5703 > EVA > F 2603 . When the temperature increases, the maximum bond length ( L max ) of the induced bond increases and the CED decreases. This result is achieved in agreement with the known experimental fact that the sensitivity of explosives increases with temperature, and they can be used as the criterion to predict the sensitivity of explosives. The descending order of L max is FOX-7 > F 2603 > ESTANE5703≈EVA > PEG. The intermolecular interactions between FOX-7 and the four polymers were mainly weak hydrogen bonding and van der Waals interactions, and these interactions helped to reduce the bond length of C-NO 2 , leading to a decrease in the sensitivity of FOX-7. The addition of polymers can effectively improve the mechanical properties of explosives. Among the four polymers, EVA has the best effect on improving the mechanical properties of FOX-7 (011). At the same temperature, the modulus can be used to predict the sensitivity of high-energy materials. Cauchy pressure can predict the sensitivity of non-brittle energetic materials. The nature of the interaction between FOX-7 and the four polymers is hydrogen bonding and van der Waals force, of which hydrogen bonding is the main one. These studies are meaningful for the formulation design and sensitivity prediction of FOX-7 and its PBXs.

scholarly journals Aptamer-Based Diagnostics and Therapeutics

2019 ◽  
Vol 12 (1) ◽  
pp. 6 ◽  
Author(s):  
Sarah Shigdar
Keyword(s):  
Hydrogen Bonding ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Base Pairing ◽  
Research Papers ◽  
Rna Sequences

Aptamers were first described almost 30 years ago, with the publication of three separate research papers describing how a randomized library of RNA sequences could be incubated with a target to find a sequence that specifically binds via van der Waals forces, covalent and hydrogen bonding, and not Watson Crick base pairing [...]

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