ANTI-REVERSION AGENT

Reversion characteristics of NR are of great concern. Lot of novel chemicals have been introduced to increase the reversion resistance of NR. Examples of these are zinc soap activator (Structol-A73), silane couphng agent (Si-69), anti-reversion agent (Perkalink 900), and post-vulcanization stabilizer (Durahnk HTS and Vulcuren KA 9188 Figure 32.7). These materials will enhance the life of the tire, enable the users for more retreading, and thereby reduce the material demand. " ... 

Schotman and co-workers tentatively assigned the new Raman peaks at 1625 and 1592 cm 1 observed during sulfur vulcanisation of squalene, to the formation of conjugated dienes and trienes, respectively [70]. When vulcanisation was carried out in the presence of l,3-di(citraconimidomethyl)benzene, this resulted in a reduced intensity of these two new peaks, corroborating that conjugated dienes and trienes, formed as a result of reversion, react with the diimide. Obviously, the diimide is not an anti-reversion agent in the sense that it prevents reversion, but it is in the sense that it repairs crosslinks when reversion has occurred. 

Rubber and Plastics News 28, No. 17, 22nd March 1999, p.16/9 ANTI-REVERSION AGENTS WORK TOGETHER... 

It is explained that if extreme heat builds up in aircraft tyres it can lead to reversion of the compounds and tyre failure. This paper traces the development of work done in which the combination of two anti-reversion agents used in an aircraft carcass compound provided a synergistic improvement in reversion resistance. Materials and methods are detailed, results are presented and discussed, and conclusions drawn. 

An examination is made of the range of mbber chemicals produced by Flexsys, including accelerators, anti-reversion agents and antidegradants. Particular attention is paid to Perkalink 900, an anti-reversion agent based on biscitraconimidomethylbenzene. Reference is made to investments by the Company in environmental protection, the constmction of a plant in Antwerp for the production of intermediates for antiozonants, and the acquisition of Kali Chemie s activities in the production of insoluble sulphur. FLEXSYS KALI CHEMIE AG... 

The effect of the above compound (Perkalink 900), as an anti-reversion agent, in a passenger tyre tread based on SBR/BR blends was investigated with the aim of increasing cure temp, such that cure times can be reduced, thus improving productivity. It was found that this compound reacted by scavenging dienes and trienes in the reverted network, thereby compensating for a reduced level of sulphidic crosslinks observed at increased cure temps. It did not affect compound cure characteristics or compound viscosity. 15 refs. 

Nashville, Tn., 29th Sept.-2nd Oct. 1998, paper 17. 012 USE OF TWO ANTI-REVERSION AGENTS TO GREATLY ENHANCE COMPOUND REVERSION RESISTANCE... 

The effect of Perkalink 900 anti-reversion agent is studied in tread cap and base compounds of truck tyres, and the advantages it affords regarding the performance of truck tyres are discussed. Its use is shown to bring about a reduction or elimination of the reversion process when determined from the cure characteristics in a rheometer, and a higher retention of modulus and tensile strength after extended cure and hot air aging. 14 refs. 

The anti-reversion agent l,3-bis(citraconimidomethyl) benzene (Perkalink 900) reacts by a unique crosslink compensation mechanism. In doing so, the crosslink density of vulcanisates can be maintained during overcure or during ageing as encountered during service life. As a result, the mechanical properties are stabilised, thereby controlling heat build-up. The anti-reversion effect of Perkalink 900 can be applied in tread compounds in which... 

Rubber Chemistry and Technology 70, No.l, March/April 1997, p. 129-45 BISCITRACONIMIDES AS ANTI-REVERSION AGENTS FOR DIENE RUBBERS SPECTROSCOPIC STUDIES ON CITRACONIMIDE-SQUALENE ADDUCTS Datta R N Schotman A H M Weber AIM van Wijk F G H van Haeren P J C Hofsraat J W Talma A G Bovenkamp-Bouwman A G V D Flexsys BV Akzo Nobel Central Research... 

Biscitraconimidomethylbenzene and hexamethylene bisthiosulphate disodium dihydrate, alone and in combination, were evaluated as anti-reversion agents in thick sectioned NR articles cured at high and low temperatures. Effects on cure characteristics and the mechanical properties of vulcanisates were investigated. 

There are currently six major antiretroviral drug families (Table 5). Nucleoside reverse transcriptase inhibitors (NRTI) are nucleoside analogs (discussed in more detail in chapter by De Clercq and Neyts, this volume) and were the first approved antiretroviral agents. They include drugs such as AZT, didanosine (ddl), stavudine (d4T), abacavir (ABC), and lamivudine (3TC), the latest used at doses of 300 mg daily as anti-HIV agent (lOOmg/day is the dosing approved for treatment of HBV... 

Obviously the best treatment for cirrhosis is removal of the injurious event. In the case of viral hepatitis, viral load can at least be temporarily reduced with anti-viral agents such as lamivudine, ribavirin and/or IFNa [76]. Unfortunately, complete removal of the injurious event is frequently not possible. Moreover, by the time cirrhosis is diagnosed the fibrotic process has usually progressed beyond the point of no return and removal of the injurious event will have little effect. Successful pharmacological treatment to reverse the fibrotic... 

The use of so-called reversal agents to block P-gp in order to decrease multi-drug resistance, will therefore also affect the elimination rate of those anti-cancer agents that are substrates for this transport system [19]. 

The development of antiretroviral therapy has been a major challenge since the discovery of the human inununodeficiency virus (HIV). Early successes with nucleoside and non-nucleoside reverse transcriptase (RT) inhibitors, as well as the development of protease inhibitors have facilitated, in recent years, a highly active antiretroviral therapy (HAART), where a combination of drugs is simultaneously administered. In spite of significant improvements in the morbidity and mortality of HIV-infected patients, the rapid appearance of resistant HIV-variants, as well as adverse effects and high cost of contemporary drugs necessitate the continuous development of independent classes of anti-HIV agents. ... 

Alkaloids such as berberine are known to be anti-microbial. They inhibit estarases as well as DNA and RNA polymerases. Moreover, berberine inhibits cellular respiration and acts in DNA intercalation. As a strong anti-microbial agent, berberine may be used in the treatment of AIDS, as it inhibits HIV-I reverse transcriptase. Berberine also has uses in the treatment of infections, specifically eye infections and hepatitis. 

Zidovudine (ZDV or AZT) is a nucleoside reverse transcriptase inhibitor (NRTI) and it was the first anti-HIV agent to be introduced. Other NRTIs include stavudine (d4T), lamivudine (3TC), didano-sine (ddl), abacavir (ABC) and zalcitabine (ddC). Recent additions to this class are emtricitabine (FTC) which has a molecular structure similar to 3TC and tenofovir (TDF) a nucleotide reverse transcriptase inhibitor. 

It is non-nucleotide reverse transcriptase inhibitor extensively metabolized by the CYP3A P450 isoform to hydroxylated metabolites and excreted in urine. It is indicated in combination with other anti-retroviral agents in a dose of 200 mg OD-BD for first 14 days. It is also been shown to be effective in the prevention of transmission of HIV from mother to new bom. 

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