Dibenzoyl peroxide chain transfer

Biesenberg, J. S. etal., J. Polym. Eng. Sci., 1976,16, 101-116 Polymerisation of methyl methacrylate initiated by oxygen or peroxides proceeds with a steady increase in velocity during a variable induction period, at the end of which a violent 90°C exotherm occurs. This was attributed to an increase in chain branching, and not to a decrease in heat transfer arising from the increasing viscosity [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of methyl methacrylate, initiated by azoisobutyronitrile, dibenzoyl peroxide or di-ferf-butyl peroxide [2],... 

On a commercial scale, a variation of this procedure, involves the extrusion of the finished product onto a moving belt. The molecular weight may be maintained within fairly narrow limits by this procedure, particularly when propio-naldehyde is used as a chain-transfer agent. In a typical formulation, 3140 lb of vinyl acetate, 27 lb of dibenzoyl peroxide, and 11.8 lb of propionaldehyde give rise to a product with an average molecular weight of about 40,000 [82]. 

According to another patent, heating 100 parts of diallyl o-phthalate with 2 parts of methanol, 2 parts of carbon tetrachloride, and 0.4 parts of dibenzoyl peroxide for 3.5 hr at 1 lO C results in the isolation of 27 gm of a prepolymer by precipitation with an excess of methanol [105]. After heating 30 gm of the monomer with 10 gm of hexachloroethane for 18 hr with 0.3 gm of dibenzoyl peroxide at 80 C, 12.3 gm of a prepolymer is isolated which could readily be molded. This process affords a greater than 30% yield of prepolymer [106]. Evidently by using a rather large quantity of chain-transfer agent, substantial... 

Kajtna and Sebenik described the synthesis of pressure-sensitive adhesives based on polyacrylates by suspension polymerization. The monomers used were 2-ethylhexyl acrylate (2-EHA) and ethyl acrylate (EA), and dibenzoyl peroxide (DBF) was used as initiator. Surface-active agents [modified ester of sulfocarboxylic acid (SCA) and ethoxylated oleyl alcohol (EOA)], chain transfer agent (w-dodecanethiol) (CTA) and suspension stabilizer [poly(vinyl alcohol) (PVA)] were also used. Various organically modified montmorillonites were used as fillers. It was observed that the kinetics of suspension polymerization were independent of the presence of the montmorillonite in the system, as shown in Figure 1.8. 

The rather stable diacyl peroxides such as dibenzoyl or phthaloyl peroxide have attracted special interest as some of their reactions, mostly not chain reactions, are chemiluminescent. Triplet-singlet energy transfer is very often involved, and emission generally occurs only when a fluorescer is present since the primary excited products cannot emit in the visible range of the spectrum. 

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