Autoxidative crosslinking

Alkyds, oils and oil/alkyd mixtures have been emulsified and subsequently autoxidatively crosslinked in the emulsion form to a near-gel or gelled state within the polymer particles. During the emulsification, the emulsifier type was carefully... 

Control of Autoxidative Crosslinking with the Swelling Ratio... 

Stable emulsions may be prepared from soya oil. The autoxidative crosslinking of the emulsified soya oil was slow and produced films of poor tensile strength which were slow to dry. These results were encouraging from the viewpoint that vegetable oil derived materials of higher molecular weight such as alkyds autoxidized faster and films formed from them dried more completely. 

J. W. Gooch, "Autoxidative Crosslinking of Emulsions Prepared from Vegetable Oil Materials," Ph.D. Dissertation, University of Southern Mississippi, May 1980. 

Autoxidative crosslinking of emulsified vegetable oils and vegetable oil derived... 

Polyester-based networks are typically prepared from polyester prepolymers bearing unsaturations which can be crosslinked. The crosslinking process is either an autoxidation in the presence of air oxygen (alkyd resins) or a copolymerization with unsaturated comonomers in the presence of radical initiators (unsaturated polyester resins). It should also be mentioned that hydroxy-terminated saturated polyesters are one of the basis prepolymers used in polyurethane network preparation (see Chapter 5). 

Gooch (1997, 2002) emulsified fatty acids and oils and autoxidized them under greater than atmospheric pressure of oxygen or air to produce a network polymer or gel that did not flow after applying the emulsion to a surface and allowing the aqueous phase to evaporate. By this method, the viscosity and crosslink density was adjusted to control rheological properties, including viscosity and flow-out. 

Zhu M, Spink DC, Yan B, Bank S, DeCaprio AP. 1994. Formation and structure of crosslinking and monomeric pyrrole autoxidation products in 2,5-hexane-dione-treated amino acids, peptides, and protein. Chem. Res. Toxicol. 7 551-58... 

One of the drawback of radiation crosslinking of NR latex is the poor ageing property of the film. This poor ageing property may be coming from two causes natural antioxidant degrade under radiation and autoxidation due to the presence of trapped radical in NR matrix. 

Several more complex species may also result from addition of H- to the polymer, especially on the aromatic rings. The presence of oxygen will lead to an autoxidation cycle to be established. The relative importance of chain scission versus crosslinking in PET will be very dependent on conditions, e.g., humidity, oxygen levels, crystallinity, dosage, dosage rate and temperature. 

Autoxidation of polymers n. The reaction of oxygen with polymers to form peroxides, etc., which can result in crosslinking and/ or degradation. Zaiko GE (ed) (1995) Degradation and stabilization of polymers. Nova Science Publishers Inc., New York. 

Malonic Aldehyde, This dialdehyde is preferentially formed by autoxidation of fatty acids with three or more double bonds. The compound is odorless. In food it may be bound to proteins by a double condensation, crosslinking the proteins (cf. 3.7.2.4.3). Malonic aldehyde is formed from a-linolenic acid by a modified reaction pathway, as outlined under the formation of hydroperoxide-epidioxide (cf. 3.7.2.1.3). However, a bicyclic compound is formed here as an intermediary product that readily fragments to malonic aldehyde ... 

The "swelling ratio" of the emulsified particles was determined at frequent intervals to monitor the autoxidative reaction. In each determination, a 0.2 gram sample of emulsified solids was added to a deciliter of reagent grade acetone to swell the crosslinked particles. Density, viscosity... 

It would be obvious to increase the catalyst concentration in order to further reduce autoxidation time required to densely crosslink the alkyd polymer particles. However, formidable effects arise from increasing the concentration of zirconium maphthenate to 0.05% and cobalt naphthenate to 0.05%. When the emulsion was subjected to 80.0 psi, the autoxidation reaction was uncontrollable. Therefore, the concentration of catalysts is critical. 

As indicated in Figure 1, the oxygen must diffuse from the aqueous phase through the emulsifier region and into the alkyd particle phase in order to initiate autoxidation. If the emulsifier is capable of retarding the diffusion of oxygen by radical stabilization or a formidable intermolecular reaction, then the crosslinking reaction by autoxidation is slowed. A total explanation of how emulsifiers retard the reaction is not within the scope of this research, but demonstration that the factor exists is clearly made here. 

Many emulsifier variations have been used during the course of this research effort. The effect of emulsifiers has been observed on numerous properties of the emulsions generated. A study was initiated to determine the effect of emulsifier structure on the autoxidation rate of reaction. Figure 5 represents the oxygen pressure variation during successive reactions as a function of the time required to reach a densely crosslinked state. The Gafac RE-960 system is dramatically slower relative to the autoxidation rate when T-Det and dodecyl sodium sulfate or Igepal CO-850 and dodecyl sodium sulfate surfactants are employed. 

FTIR techniques in combination with or as complement to other measurement techniques have been used in a wide range of photochemistry studies on polymers. These include bisphenol-A polycarbonate [173], polycarbonate coatings on mirrors [174], PMMA [175], poly( -butyl acrylate) [176] and polypropylene [177]. DSC and FTIR studies have been used in conjunction to investigate the nature of y-radiation-induced degradation and its effect on the 19°C and 30°C phase transitions in PTFE [178]. IR studies of the hydrolysis of melamine-formaldehyde crosslinked acrylic copolymer films have shown that copolymer-melamine formaldehyde crosslinks are broken and that crosslinks between melamine molecules are formed [179]. The thermal and photo-degradation mechanisms in an IR study of cured epoxy resins were found to be related to the autoxidative degradation processes for aliphatic hydrocarbons [180]. 

Kienle recognized that the condensation of difunctional reactants produced linear polymers and trifunctional reactants produced crosslinked, infusible network polymers. Accordingly, he used a reaction of ethylene glycol and phthalic anhydride in the presence of drying oils to obtain linear polymers that could undergo autoxidation polymerization like that described for oleoresinous paints. Kienle used syllables from the reactants alcohol and acid to coin the word alkyd. 

The mechanism of drying is not yet fully understood. Hydroperoxides, cyclic peroxides and dimerization lead to crosslinking through the formation of C-C, C-O-O-C and C-O-C bonds. The reaction with oxygen is catalyzed by dryers, which are also called siccatives. They are oil-soluble salts of Co, Fe, Mn, Ce, Pb, Zr (order of decreasing activity) with mainly - linoleic, naphthenic or isooc-tanoic acids. Secondary or auxiliary dryers are the salts of Ca, Ba and Zn. They do not catalyze the autoxidation but enhance the efficiency and stability of primary dryers. 

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