scholarly journals The activation efficiency of mechanophores can be modulated by adjacent polymer composition

RSC Advances ◽  
2021 ◽  
Vol 11 (13) ◽  
pp. 7391-7396
Author(s):  
Sourabh Kumar ◽  
Tim Stauch
Keyword(s):  
Polymer Composition ◽  
Rupture Force ◽  
Chemical Modifications ◽  
Polymer Backbone ◽  
Activation Efficiency

Chemical modifications of the linking units between a mechanophore and the polymer backbone can significantly enhance or reduce the rupture force of the mechanophore.

scholarly journals The Activation Efficiency of Mechanophores Can Be Modulated by Adjacent Polymer Composition

2020 ◽  
Author(s):  
Sourabh Kumar ◽  
Tim Stauch
Keyword(s):  
Structural Parameters ◽  
Polymer Composition ◽  
Polymer Backbone ◽  
Responsive Materials ◽  
Responsive Polymers ◽  
Quantum Chemical Methods ◽  
Mechanochemical Transformation ◽  
Activation Rate ◽  
Activation Efficiency ◽  
One Step

<div> <div> <div> <p>The activation efficiency of mechanophores in stress-responsive polymers is generally limited by the competing process of unspecific scission in other parts of the polymer chain. Here it is shown that the linker between the mechanophore and the polymer backbone determines the force needed to activate the mechanophore. Using quantum chemical methods, it is demonstrated that the activation forces of three mechanophores (Dewar benzene, benzocyclobutene and gem-dichlorocyclopropane) can be adjusted over a range of almost 300% by modifying the chemical composition of the linker. The results are discussed in terms of changes in electron density, strain distribution and structural parameters during the rupture process. Using these findings it is straightforward to either significantly enhance or reduce the activation rate of mechanophores in stress-responsive materials, depending on the desired use case. The methodology is applied to switch a one-step “gating” of a mechanochemical transformation to a two-step process. </p> </div> </div> </div>

scholarly journals The Activation Efficiency of Mechanophores Can Be Modulated by Adjacent Polymer Composition

2020 ◽  
Author(s):  
Sourabh Kumar ◽  
Tim Stauch
Keyword(s):  
Structural Parameters ◽  
Polymer Composition ◽  
Polymer Backbone ◽  
Responsive Materials ◽  
Responsive Polymers ◽  
Quantum Chemical Methods ◽  
Mechanochemical Transformation ◽  
Activation Rate ◽  
Activation Efficiency ◽  
One Step

<div> <div> <div> <p>The activation efficiency of mechanophores in stress-responsive polymers is generally limited by the competing process of unspecific scission in other parts of the polymer chain. Here it is shown that the linker between the mechanophore and the polymer backbone determines the force needed to activate the mechanophore. Using quantum chemical methods, it is demonstrated that the activation forces of three mechanophores (Dewar benzene, benzocyclobutene and gem-dichlorocyclopropane) can be adjusted over a range of almost 300% by modifying the chemical composition of the linker. The results are discussed in terms of changes in electron density, strain distribution and structural parameters during the rupture process. Using these findings it is straightforward to either significantly enhance or reduce the activation rate of mechanophores in stress-responsive materials, depending on the desired use case. The methodology is applied to switch a one-step “gating” of a mechanochemical transformation to a two-step process. </p> </div> </div> </div>

scholarly journals Hyperbranched Polycaprolactone through RAFT Polymerization of 2-Methylene-1,3-dioxepane

Polymers ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 318 ◽  
Author(s):  
Ping Xu ◽  
Xiaofei Huang ◽  
Xiangqiang Pan ◽  
Na Li ◽  
Jian Zhu ◽  
...  
Keyword(s):  
Chain Transfer ◽  
Raft Polymerization ◽  
Gel Permeation Chromatography ◽  
Chain Extension ◽  
Polymer Composition ◽  
Degree Of Crystallinity ◽  
Scanning Calorimetry ◽  
Radical Ring ◽  
Polymer Backbone ◽  
Controlled Structure

Hyperbranched polycaprolactone with controlled structure was synthesized by reversible addition-fragmentation chain transfer radical ring-opening polymerization along with self-condensed vinyl polymerization (SCVP) of 2-methylene-1,3-dioxepane (MDO). Vinyl 2-[(ethoxycarbonothioyl) sulfanyl] propanoate (ECTVP) was used as polymerizable chain transfer agent. Living polymerization behavior was proved via pseudo linear kinetics, the molecular weight of polymers increasing with conversion and successful chain extension. The structure of polymers was characterized by 1H NMR spectroscopy, tripe detection gel permeation chromatography, and differential scanning calorimetry. The polymer composition was shown to be able to tune to vary the amount of ester repeat units in the polymer backbone, and hence determine the degree of branching. As expected, the degree of crystallinity was lower and the rate of degradation was faster in cases of increasing the number of branches.

The Role of Stent Design and Polymers in Safety Outcomes – A Review

2012 ◽  
Vol 8 (1) ◽  
pp. 63
Author(s):  
Carlo Zivelonghi ◽  
Giulia Geremia ◽  
Michele Pighi ◽  
Flavio Ribichini ◽  
◽  
...  
Keyword(s):  
Clinical Performance ◽  
Drug Carrier ◽  
Chemical Properties ◽  
Vascular Wall ◽  
Radial Force ◽  
Vascular Trauma ◽  
Polymer Composition ◽  
Drug Eluting Stent ◽  
Stent Design ◽  
Drug Elution

Each component of a drug-eluting stent (DES) contributes to the safety of the device. Continuous efforts are being dedicated to the search of the optimal compromise between facility of use, safety and long-term efficacy. Shorter balloons reduce the vascular trauma beyond the stent struts; the metallic composition of the stent platform and the platform itself interact with the vascular wall in a long-lasting equilibrium between radial force, vessel patency and reparative cellular regrowth. The modality of drug elution is largely regulated by the chosen drug carrier, rather than by the chemical properties of the drug itself. Drug elution can be accomplished by permanent polymers that remain in the vessel wall forever, by biodegradable polymers that leave the naked metallic structure behind after their complete absorption, or even by direct release of the drug from stent reservoirs. The clinical performance of DESs has been exhaustively assessed in a large number of studies that have showed rapid and continuous improvements, from the first-generation DESs to the latest devices, based on substantial changes in stent design and polymer composition.

SuFExable Polymers with Helical Structures Derived from Thionyl Tetrafluoride (SOF4)

2019 ◽  
Author(s):  
Suhua Li ◽  
Gencheng Li ◽  
Bing Gao ◽  
Sidharam P. Pujari ◽  
Xiaoyan Chen ◽  
...  
Keyword(s):  
Functional Polymers ◽  
Polymer Chains ◽  
New Materials ◽  
Helical Structures ◽  
Polymer Backbone ◽  
Silyl Ethers ◽  
Helical Polymer ◽  
Key Characteristics ◽  
Post Modification ◽  
Individual Polymer

The first SuFEx click chemistry synthesis of SOF<sub>4</sub>-derived copolymers based upon the polymerization of bis(iminosulfur oxydifluorides) and bis(aryl silyl ethers) is described. This novel class of SuFEx polymer presents two key characteristics: First, the newly created [-N=S(=O)F-O-] polymer backbone linkages are themselves SuFExable and primed to undergo further high-yielding and precise SuFEx-based post-modification with phenols or amines to yield branched functional polymers. Second, studies of individual polymer chains of several of these new materials indicate the presence of helical polymer structures, which itself suggests a preferential approach of new monomers onto the growing polymer chain upon the formation of the stereogenic linking moiety.

Functional Poly(p-Xylylene)s via Chemical Reduction of Poly(p-Phenylene Vinylene)s

2019 ◽  
Author(s):  
Ain Uddin ◽  
Weifan Sang ◽  
Yong Gao ◽  
Kyle Plunkett
Keyword(s):  
Film Formation ◽  
Chemical Reduction ◽  
Water Soluble ◽  
Phenylene Vinylene ◽  
Polymer Modification ◽  
Polymer Backbone ◽  
Crosslinking Process ◽  
Conducting Membranes ◽  
In Situ Crosslinking

The synthesis of poly(p-xylylene)s (PPXs) with sidechains containing alkyl bromide functionality, and their post-polymer modification, is described. The PPXs were prepared by a diimide hydrogenation of poly(p-phenylene vinylene)s (PPVs) that were originally synthesized by a Gilch polymerization. The polymer backbone reduction was carried out with hydrazine hydrate in toluene at 80 °C to provide polymers with the sidechain-containing bromide functionality intact. To demonstrate post-polymer modification of the sidechains, the resulting PPX polymers were modified with trimethylamine to form tetraalkylammonium ion functionality and were evaluated as anion conducting membranes. While PPX homopolymers containing tetralkylammonium ions were completely water soluble and not able to form valuable films, PPX copolymers containing mixed tetraalkylammonium ions and hydrophobic chains were capable of film formation and alkaline stability. In addition, an in situ crosslinking process that used N,N,N',N'-tetramethyl-1,6-hexanediamine during the tetraalkylammonium formation of brominated PPX polymers was also evaluated and gave reasonable films with conductivities of ~10 mS-cm-1.

Functional Poly(p-Xylylene)s via Chemical Reduction of Poly(p-Phenylene Vinylene)s

2019 ◽  
Author(s):  
Ain Uddin ◽  
Weifan Sang ◽  
Yong Gao ◽  
Kyle Plunkett
Keyword(s):  
Film Formation ◽  
Chemical Reduction ◽  
Water Soluble ◽  
Phenylene Vinylene ◽  
Polymer Modification ◽  
Polymer Backbone ◽  
Crosslinking Process ◽  
Conducting Membranes ◽  
In Situ Crosslinking

The synthesis of poly(p-xylylene)s (PPXs) with sidechains containing alkyl bromide functionality, and their post-polymer modification, is described. The PPXs were prepared by a diimide hydrogenation of poly(p-phenylene vinylene)s (PPVs) that were originally synthesized by a Gilch polymerization. The polymer backbone reduction was carried out with hydrazine hydrate in toluene at 80 °C to provide polymers with the sidechain-containing bromide functionality intact. To demonstrate post-polymer modification of the sidechains, the resulting PPX polymers were modified with trimethylamine to form tetraalkylammonium ion functionality and were evaluated as anion conducting membranes. While PPX homopolymers containing tetralkylammonium ions were completely water soluble and not able to form valuable films, PPX copolymers containing mixed tetraalkylammonium ions and hydrophobic chains were capable of film formation and alkaline stability. In addition, an in situ crosslinking process that used N,N,N',N'-tetramethyl-1,6-hexanediamine during the tetraalkylammonium formation of brominated PPX polymers was also evaluated and gave reasonable films with conductivities of ~10 mS-cm-1.

Degradation Analysis of Thick Film Chip Resistors

2009 ◽  
Author(s):  
Bhanu Sood ◽  
Diganta Das ◽  
Michael H. Azarian ◽  
Michael Pecht
Keyword(s):  
Thick Film ◽  
Printed Circuit Board ◽  
Negative Resistance ◽  
Circuit Board ◽  
High Humidity ◽  
Circuit Boards ◽  
Chemical Modifications ◽  
Current Leakage ◽  
Printed Circuit ◽  
Degradation Analysis

Abstract Negative resistance drift in thick film chip resistors in high temperature and high humidity application conditions was investigated. This paper reports on the investigation of possible causes including formation of current leakage paths on the printed circuit board, delamination between the resistor protective coating and laser trim, and the possibility of silver migration or copper dendrite formation. Analysis was performed on a set of circuit boards exhibiting failures due to this phenomenon. Electrical tests after mechanical and chemical modifications showed that the drift was most likely caused by moisture ingress that created a conductive path across the laser trim.

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