Synthesis of Ladder Polymers Via Soluble Precursor Polymers

1988 ◽  
Vol 134 ◽  
Author(s):  
Larry R. Dalton ◽  
Luping Yu
Keyword(s):  
Thermal Processing ◽  
Elevated Temperatures ◽  
Electrochemical Polymerization ◽  
Van Der Waals Interactions ◽  
Open Chain ◽  
Polymer Backbone ◽  
Langmuir Blodgett ◽  
Poor Solubility ◽  
Ladder Polymers ◽  
Rigid Rod

ABSTRACTAlthough ladder polymers have been known for some time, poor solubility and low molecular weights have prevented processing and have discouraged consideration of these materials for structural and electronic applications. Poor solubility can be associated with strong Van der Waals interactions between delocalized π-electron clouds on adjacent chains. The optimum orbital overlap along the polymer backbone existent for ladder polymers has motivated reexamination of these systems for electronic applications. We have pursued alternatives to the tradiational acid-catalyzed polycondensation of underivatized monomers at elevated temperatures by reacting derivatized (e.g., with alkyl or vinylamine substituents) monomers at reduced temperature in organic solvents (e.g., DMF) to produce open-chain precursors to ladder polymers. These are converted to fully-fused ladder polymers by thermal processing either in solution or as solid state (e.g., thin film) materials. The preparation of precursors of improved solubility greatly enhances processing options and has permitted the utilization of both Langmuir-Blodgett methods and the perparation of optical quality films by casting (including spin casting). By control of thermal processing conditions, both derivatized and underivatized ladder polymers have been prepared. Our approach offers obvious advantages for the investigation of the effect of conformation and of substituents upon electronic properties. The preparation of copolymers with rigid rod and flexible chain segments incorporated in the polymer backbone has also been investigated. For such materials, polymers with fully fused ladder segments can exhibit improved solubility in DMF relative to polymers with open chain segments due to the absence of favorable hydrogen bonding stuctures in the former. Finally, we are investigating the effect of electrochemical polymerization of Langmuir-Blodgett films prepared with derivatized diaminobenzene. Such an approach clearly takes advantage of improved solubility of the derivatized monomer and improved molecular order which can be realized with the Langmuir-Blodgett method. Free radical polymerization may facilitate the realization of improved molecular weight distributions.

Highly Thermal Stable Lambda-Shaped Main-Chain Nonlinear Optical Polyimide

2005 ◽  
Vol 889 ◽  
Author(s):  
Hsieh-Chih Tsai ◽  
Wen-Jang Kuo ◽  
Ging-Ho Hsiue
Keyword(s):  
Glass Transition ◽  
Elevated Temperatures ◽  
Main Chain ◽  
Molecular Design ◽  
Polymer Networks ◽  
Temporal Stability ◽  
Two Dimensional ◽  
Transient Time ◽  
Polymer Backbone ◽  
Rigid Rod

ABSTRACTIn poled electro-optical (E-O) polymer systems, the relaxation of oriented chromophores is maintained by either introducing the guest chromophores into host polymers with high glass transition temperatures, or by confining the chromophores in polymer networks. Various highly stable NLO polymers have been prepared by grafting NLO-active chromophores onto aromatic polyimide backbones. The pendent chromophores of side chain polyimides can be stabilized at low temperature because they have rigid rod-like structures. However, the orientation decays quickly at elevated temperatures because the local free volumes that surround the chromophores increase. Taking advantage of the multifunctional characteristics of carbazole along with rational molecular design, a new NLO-active lambda-shape main-chain polyimide that comprises the two-dimensional carbazole chromophore was synthesized. This polyimide exhibits high thermal and temporal stability. it can endure as high as 240 °C in a transient time and maintain large SH signal at 100 °C for a long time. The high-glass transition polyimide as a matrix and embedding the two-dimensional chromophore into the polymer backbone are the major reasons that effectively restrict randomization of the oriented dipole.

Ultra-thin two-dimensional molecular crystals grown on a liquid surface for high-performance phototransistors

2021 ◽  
Author(s):  
Shuyuan Yang ◽  
Yu Zhang ◽  
Ying Wang ◽  
Jiarong Yao ◽  
Lijuan Zhang ◽  
...  
Keyword(s):  
Organic Semiconductor ◽  
High Performance ◽  
Elevated Temperatures ◽  
Liquid Surface ◽  
Molecular Crystals ◽  
Two Dimensional ◽  
Poor Solubility

Bilayer 2D molecular crystals of an organic semiconductor with poor solubility were grown on a liquid substrate at elevated temperatures. The molecularly thin crystals exhibited superior mobility and photoresponse.

Spectroscopic and morphological studies of highly conducting ion-implanted rigid-rod and ladder polymers

1992 ◽  
Vol 25 (21) ◽  
pp. 5828-5835 ◽  
Author(s):  
John A. Osaheni ◽  
Samson A. Jenekhe ◽  
Andrew Burns ◽  
Gang Du ◽  
Jinsoo Joo ◽  
...  
Keyword(s):  
Morphological Studies ◽  
Ladder Polymers ◽  
Rigid Rod ◽  
Ion Implanted

Network Changes in Nitrile Rubber at Elevated Temperatures

1973 ◽  
Vol 46 (2) ◽  
pp. 483-503 ◽  
Author(s):  
T. C. P. Lee ◽  
S. H. Morrell
Keyword(s):  
Heat Resistance ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Essential Feature ◽  
Nitrile Rubber ◽  
Polymer Backbone ◽  
Thermal Changes ◽  
Effective Antioxidant ◽  
Cleavage Reactions ◽  
Crosslinking Reactions

Abstract The network analysis of the aged sulfur vulcanizates of nitrile rubber serves to re-emphasize the complexity of the structural changes which can occur at elevated temperatures. Three factors control the rate and degree of crosslinking in these systems. First there is the crosslink structure. An essential feature for heat resistance in sulfur compounds is that they should contain, as near as possible, 100 per cent monosulfide crosslinks. Systems which contain polysulfide crosslinks, and probably to a lesser extent disulfide crosslinks, are prone to purely thermal crosslink shortening or cleavage reactions. The physical effect of these thermal changes would be superimposed on the effects brought about by thermooxidative changes. Despite their thermal stability monosulfide crosslinks can oxidize and cleave, a process which will result in stress relaxation if the sample is held in tension or compression. Hence for truly inert systems one will have to turn to non-sulfur cure in conjunction with a suitable stabilizer. Because the results indicate that scission associated with chemistry at the monosulfide crosslink is reversible, this cleavage does not contribute to the change in modulus or hardening during aging. This brings in the second controlling factor. The degree and rate of hardening depends on the nature of the products of vulcanization, and also possibly on those species intermediate between crosslink and accelerator, the pendent accelerator groups. In acting as an antioxidant ZDMC is apparently oxidized to a new source of sulfur. The more heat resistant cadmate system contains no such products and also a minimum of pendent accelerator groups. This leads to the third factor—the added antioxidant. For its heat resistance the cadmate system relies on an antioxidant. It is this which stops crosslinking reactions through autooxidation of the polymer backbone. The efficiency with which the antioxidant (dioctyldiphenylamine) works suggests that there is a synergistic effect in operation, which in some way involves cadmium. Thus the best heat resistance will be obtained where the compound yields monosulfide crosslinks, an uncomplicated network structure, unreactive vulcanization products, and contains a highly effective antioxidant system. Many facets of the aging of nitrile rubber are still open to explanation. Not the least of these is why crosslinks formed during the aging of the TMTD/S vulcanizate, which, by reason of their reactivity to methyl iodide, are thought to be sulfidic, are not themselves oxidized in a manner similar to the original monosulfide crosslinks. Model compound studies would answer this and other questions.

scholarly journals Primary Investigation into the Occurrence of Hydroxymethylfurfural (HMF) in a Range of Smoked Products

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Laura-Artemis Bouzalakou-Butel ◽  
Pantelis Provatidis ◽  
Keith Sturrock ◽  
Alberto Fiore
Keyword(s):  
Thermal Processing ◽  
Elevated Temperatures ◽  
Food Products ◽  
Mitigation Strategies ◽  
Processed Meat ◽  
Thermal Processes ◽  
Preparation Process ◽  
Product Categories ◽  
Smoke Generation

5-Hydroxymethylfurfural (HMF) is produced in foods through many different pathways. Recently, studies have revealed its potential mutagenic and carcinogenic properties. Determination of HMF was originally used as an indicator of both the extent of thermal processing a food had undergone and food quality. It has been identified in a variety of food products such as bread, breakfast cereals, fruit juices, milk, and honey. In addition to the thermal processes that lead to the formation of HMF during thermal treatment, food smoking also creates conditions that result in the formation of HMF. This can take place within the food due to the elevated temperatures associated with hot smoking or by the proximity of the products of the pyrolysis of the wood matrix that is used for smoking (cold smoking). This may lead to further contamination of the product by HMF over and above that associated with the rest of the preparation process. Until now, there have been no studies examining the relation between the smoking procedure and HMF contamination in smoked food. This study is a primary investigation measuring HMF levels in three categories of smoked food products, cheese, processed meat, and fish, using HPLC-UV. The amount of HMF found in all three product categories supports our hypothesis that HMF levels are due to both internal pathways during processing and external contamination from the smoke generation matrix (wood) employed. The results ranged from 1 ppb (metsovone traditional Greek smoked cheese) to 4 ppm (hot-smoked ready-to-eat mackerel). Subsequently for smoked cheese products, a correlation was found between HMF and phenolic compounds generated by the smoking procedures and identified by SPME-GCMS. It was observed that cheese samples that had higher concentrations of HMF were also found to have higher concentrations of syringol and cresols. It is important therefore to understand the smoking procedure’s effect on HMF formation. This will aid in the development of mitigation strategies to reduce HMF formation while retaining the flavour of the smoked products.

On the origin of main chain orientation of rigid-rod macromolecules during the Langmuir-Blodgett process

1992 ◽  
Vol 210-211 ◽  
pp. 6-8 ◽  
Author(s):  
S. Schwiegk ◽  
T. Vahlenkamp ◽  
G. Wegner ◽  
Y. Xu
Keyword(s):  
Main Chain ◽  
Chain Orientation ◽  
Langmuir Blodgett ◽  
Rigid Rod

Rigid-rod Langmuir-Blodgett films from [n]staffane-3-carboxylates

Langmuir ◽  
1992 ◽  
Vol 8 (11) ◽  
pp. 2740-2746 ◽  
Author(s):  
Huey C. Yang ◽  
Thomas F. Magnera ◽  
Chongmok Lee ◽  
Allen J. Bard ◽  
Josef Michl
Keyword(s):  
Langmuir Blodgett ◽  
Langmuir Blodgett Films ◽  
Rigid Rod

Stability of Partially Hydrolyzed Polyacrylamides at Elevated Temperatures in the Absence of Divalent Cations

SPE Journal ◽  
2009 ◽  
Vol 15 (02) ◽  
pp. 341-348 ◽  
Author(s):  
R.S.. S. Seright ◽  
A.R.. R. Campbell ◽  
P.S.. S. Mozley ◽  
Peihui Han
Keyword(s):  
Dissolved Oxygen ◽  
Oil Recovery ◽  
Elevated Temperatures ◽  
Divalent Cations ◽  
Oxidative Degradation ◽  
Reservoir Rock ◽  
Oxygen Scavengers ◽  
Polymer Backbone ◽  
Polymer Injection ◽  
The Stability

Summary At elevated temperatures in aqueous solution, partially hydrolyzed polyacrylamides (HPAMs) experience hydrolysis of amide side groups. However, in the absence of dissolved oxygen and divalent cations, the polymer backbone can remain stable so that HPAM solutions were projected to maintain at least half their original viscosity for more than 8 years at 100°C and for approximately 2 years at 120°C. Within our experimental error, HPAM stability was the same with and without oil (decane). An acrylamide-AMPS copolymer [with 25% 2-acrylamido-2-methylpropane sulphonic acid (AMPS)] showed similar stability to that for HPAM. Stability results were similar in brines with 0.3% NaCl, 3% NaCl, or 0.2% NaCl plus 0.1% NaHCO3. At temperatures of 160°C and greater, the polymers were more stable in brine with 2% NaCl plus 1% NaHCO3 than in the other brines. Even though no chemical oxygen scavengers or antioxidants were used in our study, we observed the highest level of thermal stability reported to date for these polymers. Our results provide considerable hope for the use of HPAM polymers in enhanced oil recovery (EOR) at temperatures up to 120°C if contact with dissolved oxygen and divalent cations can be minimized. Calculations performed considering oxygen reaction with oil and pyrite revealed that dissolved oxygen will be removed quickly from injected waters and will not propagate very far into porous reservoir rock. These findings have two positive implications with respect to polymer floods in high-temperature reservoirs. First, dissolved oxygen that entered the reservoir before polymer injection will have been consumed and will not aggravate polymer degradation. Second, if an oxygen leak (in the surface facilities or piping) develops during the course of polymer injection, that oxygen will not compromise the stability of the polymer that was injected before the leak developed or the polymer that is injected after the leak is fixed. Of course, the polymer that is injected while the leak is active will be susceptible to oxidative degradation. Maintaining dissolved oxygen at undetectable levels is necessary to maximize polymer stability. This can be accomplished readily without the use of chemical oxygen scavengers or antioxidants.

scholarly journals Reduced Coefficients of Linear Thermal Expansion of Colorless and Transparent Semi-Alicyclic Polyimide Films via Incorporation of Rigid-Rod Amide Moiety: Preparation and Properties

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 413
Author(s):  
Gang-lan Jiang ◽  
Dong-yang Wang ◽  
Hao-peng Du ◽  
Xiao Wu ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Thermal Expansion ◽  
Elevated Temperatures ◽  
Linear Thermal Expansion ◽  
Optical Transparency ◽  
Aromatic Diamines ◽  
Good Thermal Stability ◽  
Glass Substrates ◽  
Rigid Rod ◽  
Pyromellitic Anhydride

Semi-alicyclic colorless and transparent polyimide (CPI) films usually suffer from the high linear coefficients of thermal expansion (CTEs) due to the intrinsic thermo-sensitive alicyclic segments in the polymers. A series of semi-alicyclic CPI films containing rigid-rod amide moieties were successfully prepared in the current work in order to reduce the CTEs of the CPI films while maintaining their original optical transparency and solution-processability. For this purpose, two alicyclic dianhydrides, hydrogenated pyromellitic anhydride (HPMDA, I), and hydrogenated 3,3’,4,4’-biphenyltetracarboxylic dianhydride (HBPDA, II) were polymerized with two amide-bridged aromatic diamines, 2-methyl-4,4’-diaminobenzanilide (MeDABA, a) and 2-chloro-4,4’-diaminobenzanilide (ClDABA, b) respectively to afford four CPI resins. The derived CPI resins were all soluble in polar aprotic solvents, including N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). Flexible and tough CPI films were successfully prepared by casing the PI solutions onto glass substrates followed by thermally cured at elevated temperatures from 80 °C to 250 °C. The MeDABA derived PI-Ia (HPMDA-MeDABA) and PI-IIa (HBPDA-MeDABA) exhibited superior optical transparency compared to those derived from ClDABA (PI-Ib and PI-IIb). PI-Ia and PI-IIa showed the optical transmittances of 82.3% and 85.8% at the wavelength of 400 nm with a thickness around 25 μm, respectively. Introduction of rigid-rod amide moiety endowed the HPMDA-PI films good thermal stability at elevated temperatures with the CTE values of 33.4 × 10−6/K for PI-Ia and 27.7 × 10−6/K for PI-Ib in the temperature range of 50–250 °C. Comparatively, the HBPDA-PI films exhibited much higher CTE values. In addition, the HPMDA-PI films exhibited good thermal stability with the 5% weight loss temperatures (T5%) higher than 430 °C and glass transition temperatures (Tg) in the range of 349–351 °C.

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