Hydroperoxide groups polyesters

A broad peak at 3200-3500 cm appears as a result of hydroxy/ hydroperoxide group formation. The peak at 1720 cm- emerges and it can be attributed to the formation of carbonyl groups. Formation of these bands is characteristic for the photo-oxidation of both polystyrene (15,23) and polyester (14) samples. 

In polyethylene the proportion of vicinal hydroperoxides is lower than in PP and random chain scission is initially the dominant process. However, a variety of low molar mass oxidation products are formed via vicinal hydroperoxides (Scheme 1). The alkoxyl radicals formed by decomposition of the hydroperoxides contain weak carbon-carbon bonds in the a positions to the hydroperoxide groups which lead to the formation of low molecular weight aldehydes and alcohols that further oxidise rapidly to abiotically stable carboxylic acids. These are biodegradable species, similar to those formed by hydrolysis of aliphatic polyesters and they provide an environment for rapid biofilm formation (Section 5.5). 

Ketone Peroxides. These materials are mixtures of compounds with hydroperoxy groups and are composed primarily of the two stmctures shown in Table 2. Ketone peroxides are marketed as solutions in inert solvents such as dimethyl phthalate. They are primarily employed in room-temperature-initiated curing of unsaturated polyester resin compositions (usually containing styrene monomer) using transition-metal promoters such as cobalt naphthenate. Ketone peroxides contain the hydroperoxy (—OOH) group and thus are susceptible to the same ha2ards as hydroperoxides. 

Another approach is to use an easily oxidized substance such as acetaldehyde or methylethyl ketone, which, under the reaction conditions, forms a hydroperoxide. These will accelerate the oxidation of the second methyl group. The DMT process encompasses four major processing steps oxidation, esterification, distillation, and crystallization. Figure 10-16 shows a typical p-xylene oxidation process to produce terephthalic acid or dimethyl terephthalate. The main use of TPA and DMT is to produce polyesters for synthetic fiber and film. 

The photooxidation rates of nylon polymers have been monitored using Fourier Transform Infra-red spectroscopy. Norrish type-II reactions of carbonyl groups were considered to be the most important process. Another group of workers have studied the photooxidations rates of a nylon 6- polypropylene glycol copolymerIn this case polyether sequences are the major source of free radical attack resulting in high levels of hydroperoxides. Irradiation of nylon and polyester fibres with an excimer laser resulted in... 

The photo-oxidation takes place when UV irradiation causes formation of free radicals that in turn absorb oxygen molecules. Most double bond structures in mbbers and aromatics readily absorb photo-energy at 200 to 360 nm. Hydroperoxides (formed in thermo-oxidative reactions during or after processing) are also powerful chromofors, e.g., for PE and especially for PP. Polyester groups in aromatic PEST or PC may also undergo... 

The synthesis of ABA blocks from a glassy thermoplastic A and an elastomeric B produces other elastoplastics with attractive properties. Polyester chains can be extended with di-isoeyanate, which is then treated with cumene hydroperoxide to leave a peroxide group at both ends of the chain. By heating this in the presence of styrene, a vinyl polymerization is initiated and an ABA block created. The modulus-temperature curves show how the mechanical properties can be modified in this way (Figure 15.7). These block copolymers are known as thermoplastic elastomers. 

The cure reaction in polyester gel coat systems makes them particularly useful model coatings materials since the cure kinetics can be studied by several analytical techniques. The initiation of cure in polyester gel coat resins begins with the decomposition of hydroperoxide (MEKP is predominately hydroperoxide) and the subsequent copolymerization of styrene with the unsaturated groups, either fumarate or maleate, incorporated into the resin backbone. ... 

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