Shinichi Yachigo

Studies on polymer stabilisers: Part I—A novel thermal stabiliser for butadiene polymers☆

Abstract 2-Tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (Sumilizer GM) is shown to be a very effective stabiliser for thermal degradation of butadiene type polymers under an oxygen-free atmosphere. The stabilising mechanism is confirmed to be a unique bifunctional mechanism, which consists of polymer radical trapping by the acrylate group, followed by fast hydrogen transfer from intramolecular hydrogen-bonded phenolic hydroxyl groups to result in stable phenoxyl radicals.

Studies on polymer stabilizers: Part II. A new concept of a synergistic mechanism between phenolic and thiopropionate type antioxidants☆☆☆

Abstract 3,9-Bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1, 1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5] undecane (Sumitomos new antioxidant: Sumilizer GA-80) is shown to have a very effective synergistic stabilizing effect in combination with thiopropionate type antioxidants. For synergistic stabilization, association of phenolic antioxidants with thiopropionate type antioxidants through hydrogen bonding is shown, by IR analyses and estimation of association equilibrium constant of a model system, to be an important factor.

Studies on polymer stabilizers: Part V—Influences of structural factors on oxidative discoloration and thermal stability of polymers

Abstract 2- tert -Butyl-6-(3- tert -butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (GM, Sumilizer® GM) is known as an effective thermal stabilizer which protects polymers against thermal degradation caused by heat or mechanical stress especially under oxygen-deficient atmosphere. Its unique bifunctional stabilizing mechanism has been reported recently. 1 Further studies on the influences of structural factors of related phenols on oxidative discoloration and thermal stability of polymers has shown that 2-(1-(2-hydroxy-3,5-di- tert -pentylphenyl)ethyl)-4,6-di- tert -pentylphenyl acrylate (GS, Sumilizer® GS) not only has a more effective thermal stabilizing effect than GM but also has much higher resistance to oxidative discoloration.

Studies on polymer stabilizers: Part IV—Prevention of oxidative discoloration☆

By a model accelerated oxidative reaction and product analysis, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (Sumilizer® GM) was found to give a stilbene quinone-type colored product through a quinone methide-type intermediate. The resistance of GM and its analogs against oxidative discoloration was remarkably improved by substitution with a bulky group at the para position to the phenolic OH group.

Studies on polymer stabilizers: Part VI—Relationship between performance and molecular conformation

Abstract 2- tert -Butyl-6-(3- tert -butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (GM, Sumilizer® GM) is known as an effective thermal stabilizer for butadiene type polymers especially under an oxygen-free atmosphere. Further studies on this range of thermal stabilizers has recently shown that 2-(1-(2-hydroxy-3,5-di- tert -pentylphenyl)ethyl)-4,6-di- tert -pentylphenyl acrylate (GS, Sumilizer® GS) is a more effective thermal stabilizer and has resistance to discoloration. In this study, the molecular structures of GM, GS and some of their substituted analogs were determined by X-ray crystallography, and were found to be very similar to each other except for the conformation of the acrylate group. These compounds were found to have an intramolecular hydrogen bonding between the phenolic hydroxyl group and the oxygen atom of the acrylate carbonyl group. IR spectra at various temperatures showed that the performance of the bisphenol monoacrylate type compounds was correlated with the strength of the intramolecular hydrogen bonding. The substitution on the bridged methylene group may restrict the bond rotation and stabilize the molecular conformation which can form the intramolecular hydrogen bonding at high temperatures. This will result in a more effective hydrogen transfer from the phenolic OH groups to enolate radical inducing improved performance in the stabilizing mechanism.

Studies on polymer stabilizers: Part III—Prevention of NOx gas discoloration with a new antioxidant

Abstract 3,9-Bis(2-(3-(3- tert -butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1, 1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5·5]undecane (Sumitomos new antioxidant: Sumilizer® GA-80) was shown to have extremely high discoloration resistance against nitrogen dioxide. This might be due not to the inertness of GA-80 to nitrogen dioxide but to the fact that the GA-80 structure allows an energy favorable reaction pathway to give stable colorless products. This proposition was supported by product analyses and computer calculation of molecular orbitals.