Improved Elastomers through Control of Network Chain-Length Distributions

1999 ◽  
Vol 72 (3) ◽  
pp. 465-483 ◽  
Author(s):  
J. E. Mark
Keyword(s):  
Chain Length ◽  
Addition Reaction ◽  
Condensation Reaction ◽  
Bimodal Distribution ◽  
Polymer Chains ◽  
Network Chain ◽  
End Linking ◽  
Chain Lengths ◽  
Bimodal Elastomers

Abstract Methods are described for obtaining elastomers of controlled network chain-length distributions by restricting the reactivity of the polymer chains to their ends, and then end linking these chains with a multi-functional reactant. The networks of this type that have proved to be of greatest interest consist of short chains end linked with long chains to yield a bimodal distribution of network chain lengths. These bimodal elastomers have unusually high extensibility for their values of the modulus and ultimate strength, and thus considerable toughness, even in the unfilled state. Most such elastomers have been prepared from chains of poly(dimethylsiloxane), by carrying out either a condensation reaction between hydroxyl-terminated chains and tetraethoxysilane, or an addition reaction between vinyl-terminated chains and a poly(methylhydrogen siloxane) oligomer. The material presented in this review discusses the preparation of such elastomers, the characterization of some of their properties, and the interpretation of some of these properties in terms of the molecular theories of rubber-like elasticity.

Networks Having Multimodal Chain-Length Distributions

1997 ◽  
Author(s):  
Burak Erman ◽  
James E. Mark
Keyword(s):  
Free Radical ◽  
Chain Length ◽  
Length Distribution ◽  
Bimodal Distribution ◽  
High Energy ◽  
Chain Length Distribution ◽  
Network Chain ◽  
Ultimate Properties ◽  
Non Gaussian ◽  
Chain Lengths

As was mentioned in chapter 10, end-linking reactions can be used to make networks of known structures, including those having unusual chain-length distributions. One of the uses of networks having a bimodal distribution is to clarify the dependence of ultimate properties on non-Gaussian effects arising from limited-chain extensibility, as was already pointed out. The following chapter provides more detail on this application, and others. In fact, the effect of network chain-length distribution, is one aspect of rubberlike elasticity that has not been studied very much until recently, because of two primary reasons. On the experimental side, the cross-linking techniques traditionally used to prepare the network structures required for rubberlike elasticity have been random, uncontrolled processes, as was mentioned in chapter 10. Examples are vulcanization (addition of sulfur), peroxide thermolysis (free-radical couplings), and high-energy radiation (free-radical and ionic reactions). All of these techniques are random in the sense that the number of cross-links thus introduced is not known directly, and two units close together in space are joined irrespective of their locations along the chain trajectories. The resulting network chain-length distribution is unimodal and probably very broad. On the theoretical side, it has turned out to be convenient, and even necessary, to assume a distribution of chain lengths that is not only unimodal, but monodisperse! There are a number of reasons for developing techniques to determine or, even better, control network chain-length distributions. One is to check the “weakest link” theory for elastomer rupture, which states that a typical elastomeric network consists of chains with a broad distribution of lengths, and that the shortest of these chains are the “culprits” in causing rupture. This is attributed to the very limited extensibility associated with their shortness that is thought to cause them to break at relatively small deformations and then act as rupture nuclei. Another reason is to determine whether control of chain-length distribution can be used to maximize the ultimate properties of an elastomer. As was described in chapter 10, a variety of model networks can be prepared using the new synthetic techniques that closely control the placements of crosslinks in a network structure.

scholarly journals Preparation of Tri(alkenyl)functional Open-Cage Silsesquioxanes as Specific Polymer Modifiers

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1063
Author(s):  
Katarzyna Mituła ◽  
Michał Dutkiewicz ◽  
Julia Duszczak ◽  
Monika Rzonsowska ◽  
Beata Dudziec
Keyword(s):  
Condensation Reaction ◽  
Polyhedral Oligomeric Silsesquioxanes ◽  
Double Decker ◽  
Application Potential ◽  
Synthetic Routes ◽  
High Yields ◽  
Chain Lengths ◽  
Tga And Dsc ◽  
Melting And Crystallization Temperatures

The scientific reports on polyhedral oligomeric silsesquioxanes are mostly focused on the formation of completely condensed T8 cubic type structures and recently so-called double-decker derivatives. Herein, we report on efficient synthetic routes leading to trifunctionalized, open-cage silsesquioxanes with alkenyl groups of varying chain lengths from -vinyl to -dec-9-enyl and two types of inert groups (iBu, Ph) at the silsesquioxane core. The presented methodology was focused on hydrolytic condensation reaction and it enabled obtaining titled compounds with high yields and purity. A parallel synthetic methodology that was based on the hydrosilylation reaction was also studied. Additionally, a thorough characterization of the obtained compounds was performed, also in terms of their thermal stability, melting and crystallization temperatures (TGA and DSC) in order to show the changes in the abovementioned parameters dependent on the type of reactive as well as inert groups at Si-O-Si core. The presence of unsaturated alkenyl groups has a profound impact on the application potential of these systems, i.e., as modifiers or comonomers for copolymerization reaction.

Synthesis and characterization of some octaalkyl substituted lead phthalocyanines and unexpected variations in lead lability arising from the position of substituents and their chain length

2013 ◽  
Vol 17 (06n07) ◽  
pp. 511-521 ◽  
Author(s):  
Lydia X. Sosa-Vargas ◽  
Isabelle Chambrier ◽  
Colin J. MacDonald ◽  
Simon J. Coles ◽  
Graham J. Tizzard ◽  
...  
Keyword(s):  
Chain Length ◽  
Alkyl Chain ◽  
Lead Ion ◽  
X Ray ◽  
H Nmr ◽  
Alkyl Groups ◽  
Nmr Spectrometry ◽  
Acid Catalyzed ◽  
Chain Lengths

The preparation of some peripherally substituted (2,3,9,10,16,17,23,24) and non-peripherally substituted (1,4,8,11,15,18,22,25) octaalkyl lead(II) phthalocyanines with different alkyl chain lengths (6, 7, 8 or 9 carbons) is described and a comparison of some of their properties reported. X-ray structure analyses of the isomeric peripheral and non-peripheral octakis(octyl)phthalocyaninato lead(II) compounds reveal a greater degree of distortion of the ligand ring system from planarity in the former derivative. The series of peripherally substituted octaalkyl lead(II) phthalocyanines exhibit columnar liquid crystal behavior whereas the non-peripherally substituted isomers do not. The lability of the lead ion was investigated using 1 H NMR spectrometry under a specific set of conditions (8.8 × 10-4 M solutions of the phthalocyanine in d8-toluene containing d4-acetic acid 2.06 × 10-5 M). All the compounds underwent acid catalyzed demetalation at rates dependent upon the location of the substituents and, more surprisingly, the chain length of the alkyl groups. Under these conditions the lead ion within each of the peripherally substituted octaalkyl lead phthalocyanines was more labile than that in the non-peripherally substituted isomer.

Approaching the size limit of organometallic layers: synthesis and characterization of highly ordered silver–thiolate lamellae with ultra-short chain lengths

2016 ◽  
Vol 45 (47) ◽  
pp. 18954-18966 ◽  
Author(s):  
Zichao Ye ◽  
Lito P. de la Rama ◽  
Mikhail Y. Efremov ◽  
Jian-Min Zuo ◽  
Leslie H. Allen
Keyword(s):  
Single Crystal ◽  
Chain Length ◽  
Short Chain ◽  
Synthesis And Characterization ◽  
Size Limit ◽  
Chain Conformations ◽  
Chain Lengths

Synthesis of single crystal silver alkanethiolate (any chain length) lamellae with highly ordered chain conformations, interlayer interfaces and intralayer lattices.

Chain Extension Studies Relevant to the Completeness of End-Linking in Elastomeric Polyurethane Networks

1982 ◽  
Vol 55 (5) ◽  
pp. 1464-1468 ◽  
Author(s):  
J. E. Mark ◽  
P. H. Sung
Keyword(s):  
Propylene Oxide ◽  
Relevant Information ◽  
Polymer Chains ◽  
Chain Extension ◽  
Polyurethane Elastomers ◽  
Molecular Weights ◽  
Before And After ◽  
End Linking ◽  
Poly Propylene

Abstract Polyurethane elastomers may be prepared by end-linking hydroxyl-terminated (atactic) poly(propylene oxide) chains with an aromatic triisocyanate. As is invariably the case, networks thus formed are insoluble and very difficult to analyze with regard to the completeness of the end-linking reaction. Relevant information can, however, be obtained by studying the products of the analogous reaction, between a structurally similar diisocyanate and the same polymer chains, under identical conditions. Since both reactants now have functionalities less than three, the reaction gives chain extension rather than crosslinking (gelation), and it is now possible to measure molecular weights before and after the reaction. Such experiments were carried out using diphenylmethane-4,4′-diisocyanate with poly(propylene oxide) chains which had viscosity-average molecular weights ranging from 10−3Mv=1.15−4.50 g mol−1. Values of Mv were found to increase by factors of 20–30, which indicates high extents of reaction. These results are relevant with regard to the probable efficiency of polyurethane curing techniques, and also for the characterization of “model” networks used in the quantitative evaluation of the molecular theories of rubberlike elasticity.

scholarly journals Phenylalkylammonium passivation enables perovskite light emitting diodes with record high-radiance operational lifetime: the chain length matters

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yuwei Guo ◽  
Sofia Apergi ◽  
Nan Li ◽  
Mengyu Chen ◽  
Chunyang Yin ◽  
...  
Keyword(s):  
Chain Length ◽  
Quantum Efficiency ◽  
External Quantum Efficiency ◽  
Light Emitting Diodes ◽  
Surface Defects ◽  
Theoretical Modelling ◽  
Ion Migration ◽  
Light Emitting ◽  
Operational Lifetime ◽  
Chain Lengths

AbstractPerovskite light emitting diodes suffer from poor operational stability, exhibiting a rapid decay of external quantum efficiency within minutes to hours after turn-on. To address this issue, we explore surface treatment of perovskite films with phenylalkylammonium iodide molecules of varying alkyl chain lengths. Combining experimental characterization and theoretical modelling, we show that these molecules stabilize the perovskite through suppression of iodide ion migration. The stabilization effect is enhanced with increasing chain length due to the stronger binding of the molecules with the perovskite surface, as well as the increased steric hindrance to reconfiguration for accommodating ion migration. The passivation also reduces the surface defects, resulting in a high radiance and delayed roll-off of external quantum efficiency. Using the optimized passivation molecule, phenylpropylammonium iodide, we achieve devices with an efficiency of 17.5%, a radiance of 1282.8 W sr−1 m−2 and a record T50 half-lifetime of 130 h under 100 mA cm−2.

scholarly journals Responsive Polyesters with Alkene and Carboxylic Acid Side-Groups for Tissue Engineering Applications

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1636
Author(s):  
Stella Afroditi Mountaki ◽  
Maria Kaliva ◽  
Konstantinos Loukelis ◽  
Maria Chatzinikolaidou ◽  
Maria Vamvakaki
Keyword(s):  
Carboxylic Acid ◽  
Chain Length ◽  
Main Chain ◽  
Alkyl Chain ◽  
Click Reaction ◽  
Irradiation Time ◽  
Alkyl Chain Length ◽  
Polymer Chains ◽  
Condensation Polymerization ◽  
L929 Fibroblast

Main chain polyesters have been extensively used in the biomedical field. Despite their many advantages, including biocompatibility, biodegradability, and others, these materials are rather inert and lack specific functionalities which will endow them with additional biological and responsive properties. In this work, novel pH-responsive main chain polyesters have been prepared by a conventional condensation polymerization of a vinyl functionalized diol with a diacid chloride, followed by a photo-induced thiol-ene click reaction to attach functional carboxylic acid side-groups along the polymer chains. Two different mercaptocarboxylic acids were employed, allowing to vary the alkyl chain length of the polymer pendant groups. Moreover, the degree of modification, and as a result, the carboxylic acid content of the polymers, was easily tuned by varying the irradiation time during the click reaction. Both these parameters, were shown to strongly influence the responsive behavior of the polyesters, which presented adjustable pKα values and water solubilities. Finally, the difunctional polyesters bearing the alkene and carboxylic acid functionalities enabled the preparation of cross-linked polyester films by chemically linking the pendant vinyl bonds on the polymer side groups. The biocompatibility of the cross-linked polymers films was assessed in L929 fibroblast cultures and showed that the cell viability, proliferation, and attachment were greatly promoted on the polyester surface, bearing the shorter alkyl chain length side groups and the higher fraction of carboxylic acid functionalities.

Degrees of order of solubilized alkanes, alcohols, carboxylates, and carboxylic acids in oriented lyomesophases

1977 ◽  
Vol 55 (12) ◽  
pp. 2404-2410 ◽  
Author(s):  
Douglas M. Chen ◽  
Fred Y. Fujiwara ◽  
Leonard W. Reeves
Keyword(s):  
Carboxylic Acids ◽  
Chain Length ◽  
Linear Increase ◽  
Short Chain ◽  
Appreciable Amount ◽  
Linear Region ◽  
Short Chain Length ◽  
Chain Lengths ◽  
Degree Of Order ◽  
Limiting Value

The degree of order of solubilized molecules and ions in oriented lyomesophases has been determined at specifically deuterated C—D bond axes from the quadrupole splitting of the deuterium magnetic resonance. Mixtures at low concentration of specifically deuterated alkanes, alcohols, carboxylic acids, and carboxylates of different chain length have been observed in host cationic and anionic lyomesophases. The degree of order of a given C—D position in alcohols increases strongly with chain length up to a length comparable with the host detergent. A broad series of carboxylic acids and carboxylate ions from C2 to C16 have been deuterated in the α position. The α-C—D bond axis in the solubilisate increases in order with chain length, the anion having lower order than the parent acid. An accurately linear increase in the degree of order of the α position is observed for intermediate chain lengths. At chain lengths approximately equal to the host chain lengths the α position reaches a limiting value in the degree of order and further segments do not influence the order. At short chain lengths the degree of order is less than that predicted from extrapolation of order in the linear region. This has been interpreted in terms of distribution into the aqueous compartment by the solubilisates of short chain length. Acetic acid and the acetate, propionate, butanoate, and pentanoate ions spend an appreciable amount of time in the aqueous region. An estimate has been made of these distributions based on reasonable assumptions.

Synthesis and characterization of periphery-functionalized porphyrazines containing mixed pyrrolyl and pyridylmethylamino groups

2009 ◽  
Vol 13 (02) ◽  
pp. 223-234 ◽  
Author(s):  
Tomasz Goslinski ◽  
Ewa Tykarska ◽  
Wojciech Szczolko ◽  
Tomasz Osmalek ◽  
Aleksandra Smigielska ◽  
...  
Keyword(s):  
Electrochemical Properties ◽  
Chemical Sensors ◽  
Electronic Materials ◽  
Condensation Reaction ◽  
Synthesis And Characterization ◽  
X Ray ◽  
Coordination Properties ◽  
Perpendicular Orientation ◽  
Selective Sensor

The condensation reaction of 2-amino-3-[(3-pyridylmethyl)amino]-2(Z)-butene-1,4-dinitrile with a series of diketones led to novel dinitriles, of which 2-(2,5-dimethyl-1H-pyrrol-1-yl)-3-[methyl(3-pyridylmethylene)amino]-2(Z)-butene-1,4-dinitrile, the product of the Paal-Knorr reaction, was successfully utilized in the Linstead macrocyclization towards symmetrical and unsymmetrical porphyrazines. NMR and X-ray study revealed an almost perpendicular orientation of the pyrrolyl groups in relation to the porphyrazine platform. The newly synthesized macrocycles with different peripheral groups show interesting spectroscopic and electrochemical properties. Due to selective sensor/coordination properties they are expected to find applications as chemical sensors and electronic materials.

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