Peroxides polymerisation initiators

Minor peaks in the chromatogram were associated with end groups derived from benzoyl peroxide polymerisation initiator or dodecane thiol chain transfer agent reactions. End-group data were related to molecular weight data. 

More frequently either methyl ethyl ketone peroxide or cyclohexanone peroxide is used for room temperature curing in conjunction with a cobalt compound such as a naphthenate, octoate or other organic solvent-soluble soap. The peroxides (strictly speaking polymerisation initiators) are referred to as catalysts and the cobalt compound as an accelerator . Other curing systems have been devised but are seldom used. 

Chemical compounds (usually an organic peroxide) which initiate polymerisation of a resin (also called hardeners). 

Vinyl acetate is normally inhibited with hydroquinone to prevent polymerisation. A combination of too low a level of inhibitor and warm, moist storage conditions may lead to spontaneous polymerisation. This process involves autoxidation of acetaldehyde (a normal impurity produced by hy droly sis of the monomer) to a peroxide which initiates exothermic polymerisation as it decomposes. In bulk, this may accelerate to a dangerous extent. Other peroxides or radical sources will initiate the exothermic polymerisation. 

Sebastian, D. H. et al., Polym. Eng. Sci., 1976, 16, 117-123 The conditions were determined for runaway/non-runaway polymerisation of styrene in an oil-heated batch reactor at 3 bar, using dibenzoyl peroxide as initiator at 3 concentrations. Results are presented diagrammatically. 

Though regarded as one of the more stable peroxides, it becomes shock-sensitive on heating, and self-accelerating decomposition sets in at 49° C [1]. One of the recently calculated values of 46 and 42°C for induction periods of 7 and 60 days, respectively, for critical ignition temperatures is closely similar to that (4577 days) previously recorded. Autocatalytic combustion of the polymerisation initiator is exhibited. Although not ordinarily shock sensitive, it responds to a detonator [2],... 

VI Galibey. Study of Acyl Peroxides as Initiators of Radical Polymerisation. Ph.D. thesis Dissertation, OGU, Odessa, 1965 [in Russian]. 

List C contains peroxidisable monomers, where the presence of peroxide may initiate exothermic polymerisation of the bulk of material. Precautions and procedures for storage and use of monomers with or without the presence of inhibitors are discussed in detail. Examples cited are acrylic acid, acrylonitrile, butadiene, 2-chlorobutadiene, chlorotrifluoroethylene, methyl methacrylate, styrene, tetraflu-oroethylene, vinyl acetate, vinylacetylene, vinyl chloride, vinylidene chloride and vinylpyridine [1]. 

Significantly endothermic AHf (1) 147 kJ/mole 2.8 kJ/g. The monomer is sensitive to light, and even when inhibited (with aqueous ammonia) it will polymerise exother-mally at above 200°C [1]. It must never be stored uninhibited, or adjacent to acids or bases [2]. Polymerisation of the monomer in a sealed tube in an oil bath at 110°C led to a violent explosion. It was calculated that the critical condition for runaway thermal explosion was exceeded by a factor of 15 [3]. Runaway polymerisation in a distillation column led to an explosion and fire [4]. Another loss of containment and fire resulted from acrylonitrile polymerisation in a waste solvent tank also containing toluene and peroxides (peroxides are polymerisation initiators) [5]. Use of the nitrile as a reagent in synthesis can lead to condensation of its vapour in unseen parts of the equipment, such as vent-pipes and valves, which may then be obstructed or blocked by polymer [6]. 

Tatemoto et al. used peroxides as initiators of polymerisation. Improvement is also possible by using diiodide and polyiodide compounds [316,382],... 

We originally suggested - that trauisfer to the polyvinyl alcohol could explain the effect of Elvanol 32-22 in reducing the rate of polymerisation of vinyl acetate solutions. The importance of this transfer reaction has recently been confirmed by Dimonie et al.(6) who use ferrous ion/hydrogen peroxide redox Initiation. However Okamura, Yamashlta, and Motoyama determined the transfer rate constant of vinyl acetate to polyvinyl acetate and polyvinyl alcohol in homogeneous solution they found for... 

Thus, for radical polymerisation initiated by hydrogen peroxide of a monomer, which gives termination exclusively by recombination, it is possible to obtain good hydroxy-telechelic polymers, useful in polyurethane fabrication (reactions 9.3 and 9.4). 

By far the greatest part of PVC production across the world is now made by the suspension process. Vinyl chloride monomer (derived from a reaction between ethylene (derived from oil) and chlorine (derived from common salt) is dispersed in deionised water with the help of small quantities of chemical dispersants and polymerisation initiators (typically peroxide compounds). At moderately raised temperature (50 C) and pressure (0.7 MPa) polymerisation proceeds and the polymer can be removed from the resulting slurry by de-watering and steam stripping the unconverted vinyl chloride monomer. 

Undissociated hydrogen peroxide also behaves as a nucleophile to some extent, being about 10 times as nucleophilic as water. For example, H2O2 readily adds to many carbonyl double bonds, giving hydroxyhydroper-oxides (peracetals and perketals). Compounds prepared thus are used as polymerisation initiators on account of their radical decomposition at moderate temperatures (—O—O— bond homolysis). However, they can be hazardous if formed accidentally in other synthesis reactions, for which ketones are therefore not recommended solvents. Neutral H2O2 can also... 

A substance (usually a peroxide) which initiates and accelerates the polymerisation reactions without being consumed itself. It is also known as a hardener. (See Initiator and Hardener)... 

Two-part acrylic adhesive An initiator, such as peroxides, polymerises acrylate groups of the main component... 

Peroxides of different types are important as polymerisation initiators in the manufacture of plastics. Knappe and Pbteri [39] have separated various technically important organic peroxides on silica gel G layers, using toluene-carbon tetrachloride (67 + 33) and toluene-acetic acid (95 + 5). 

Radical polymerisation is the most important method and this often employs a peroxide (ROOR) initiator containing a weak oxygen-oxygen bond. On homolysis (using heat or UV radiation) the resulting alkoxyl radical (RO ) adds regioselectively to the least hindered end of the alkene to form a carbon-centred radical. This radical then adds to the least hindered end of another molecule of the alkene to build the polymer by a chain reaction. The polymerisation is terminated by, for example, the coupling of two radicals. 

The first aromatic polycarbonates were prepared more than a century ago by reacting hydroquinone or resorcinol with phosgene in pyridine, but the crystalline polymers produced were brittle and difficult to process. After 50 years, a crosslinked resin was introduced, prepared by a free-radical polymerisation using a peroxide as initiator and an unsaturated carbonate derivative as a monomer. 

As a general rule, a greater degree of graft polymerisation takes place, when peroxy compounds are used as initiators, compared to circumstances involving the use of azo compounds. This is due to the greater potential for hydrogen abstraction when peroxides are used as initiators, than when azo compounds are employed as polymerisation initiators. 

Current Polymerisation Catalysts—Peroxide, and Other Initiators, muIti-cHent study. Catalyst Consultants, Inc., Spring House, Pa., Nov. 1991. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

---