Free-radical polymerisation initiation

The utility of a novel intra-ion-pair electron transfer cleavage reaction has been reported by Schuster et al. [128] for free radical polymerisation initiation... 

Solomon, D.H., Rizzardo, E., and Cacioli, P. (1985) Substd. alkyl-amine cpds.— useful as controlled growth free radical polymerisation initiators for unsaturated monomers. Patent Number EP135280-A2. 

Figure 4c illustrates interfacial polymerisation encapsulation processes in which the reactant(s) that polymerise to form the capsule shell is transported exclusively from the continuous phase of the system to the dispersed phase—continuous phase interface where polymerisation occurs and a capsule shell is produced. This type of encapsulation process has been carried out at Hquid—Hquid and soHd—Hquid interfaces. An example of the Hquid—Hquid case is the spontaneous polymerisation reaction of cyanoacrylate monomers at the water—solvent interface formed by dispersing water in a continuous solvent phase (14). The poly(alkyl cyanoacrylate) produced by this spontaneous reaction encapsulates the dispersed water droplets. An example of the soHd—Hquid process is where a core material is dispersed in aqueous media that contains a water-immiscible surfactant along with a controUed amount of surfactant. A water-immiscible monomer that polymerises by free-radical polymerisation is added to the system and free-radical polymerisation localised at the core material—aqueous phase interface is initiated thereby generating a capsule sheU (15). 

Eree-radical initiation of emulsion copolymers produces a random polymerisation in which the trans/cis ratio caimot be controlled. The nature of ESBR free-radical polymerisation results in the polymer being heterogeneous, with a broad molecular weight distribution and random copolymer composition. The microstmcture is not amenable to manipulation, although the temperature of the polymerisation affects the ratio of trans to cis somewhat. 

A further feature of anionic polymerisation is that, under very carefully controlled eonditions, it may be possible to produee a polymer sample which is virtually monodisperse, i.e. the molecules are all of the same size. This is in contrast to free-radical polymerisations which, because of the randomness of both chain initiation and termination, yield polymers with a wide molecular size distribution, i.e. they are said to be polydisperse. In order to produce monodisperse polymers it is necessary that the following requirements be met ... 

A certain free-radical polymerisation reaetion is described by the following sequence of initiation, addition and termination... 

At pressures above 6000 bar, free radical polymerisation sometimes proceeded explosively [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of acrylonitrile initiated by azoisobutyronitrile, dibenzoyl peroxide or di-/er/-butyl peroxide [2],... 

Dartnell, R. C. et al., Loss Prev., 1971, 5, 53-56 MCA Case History No. 1649 A batch of 8 t of material accumulated in storage at 154°C during 72 h decomposed explosively. Stability tests showed that thermal instability developed when 3-methyl-4-nitrophenol is stored molten at temperatures above 140°C. Decomposition set in after 14 h at 185° or 45 h at 165°, with peak temperatures of 593 and 521°C, respectively. In a closed vessel, a peak pressure of 750 bar was attained, with a maximum rate of increase of 40 kbar/s. Thermal degradation involves an initially slow exothermic free radical polymerisation process, followed by a rapid and violently exothermic decomposition at take-off. 

Figure 1 Reaction scheme for the free-radical polymerisation (I is the initiator, R the fragment of initiator, M the monomer and AH the chain transfer agent).

In this section, we review the properties of a series of PNIPAM-b-PEO copolymers with PEO blocks of varying length, with respect to the PNIPAM block. Key features of their solutions will be compared with those of PNIPAM-g-PEO solutions. PNIPAM-b-PEO copolymers were prepared by free-radical polymerisation of NIPAM initiated by macroazoinitiators having PEO chains linked symmetrically at each end of a 2,2/-azobis(isobutyronitrile) derivative [169,170]. The polydispersities of PEOs were low, enabling calculations of the number-average molar mass for each PNIPAM block from analysis of their H-NMR spectra (Table 2). 

This technique is extensively used for the free radical polymerisation of vinyl monomers containing water soluble initiators. The monomers like vinyl chloride, butadiene, chloroprene, vinyl acetate, acrylates and methacrylates are polymerised by this technique. 

Only very few results are available on the variation of DP with temperature, but they indicate that between -63.5° and -95.5° the DP does not vary significantly and hence EDP = 0 2 kcal/mole [76]. The obvious interpretation of the small EDP, and the large positive Er is that Er is essentially , which means that initiation is slow compared with propagation and termination, and that one is dealing here with a system which has kinetics resembling those of free-radical polymerisations. 

With free-radical polymerisation B (now equivalent to R ) is shortlived and is usually generated continuously by the decomposition of an initiator... 

The normal dispersants used for both kaolin and calcium carbonate pigments are aqueous solutions of sodium polyacrylate. These are prepared by free radical polymerisation using various combinations of initiators and terminators which may be proprietary to the manufacturer. Number average molecular weights are... 

Free radical polymerisation can also be promoted by a mixture of ferrous sulphate and hydrogen peroxide (FeS04 + H2O2). These two compounds react to produce hydroxyl radicals. (OH ) which act as chain initiators. They are used as catalyst in the manufacture of Orion and Teflon. 

When the decomposition is performed in the presence of unsaturated monomers (styrenic, acrylic...) a free-radical polymerisation can be initiated and grafting occurs ... 

Later, other authors utilized the differences found in the optical activity of monomer and polymer to carry out kinetic investigations on the free-radical polymerisation (70,72,120) and copolymerization (71), and tried to achieve the steric control of the propagation step of free-radical polymerization and copolymerization (13, 14, 39, 73, 98) using optically active monomers and initiators. 

Qualitative evidence that ionic species were significant intermediates was obtained from a study of the radiation induced polymerisation of isobutene28,29. Since this monomer was known to be readily polymerised by ionic initiators, polymerisation by 2 MeV electrons at —80 °C seemed to indicate the existence of ionic intermediates. However, the polymerisation was inhibited by oxygen and benzoquinone which are known to be inhibitors for free radical polymerisations. It was subsequently suggested30 that polymerisation was caused by the positive ion (CH3)3C+ produced by the reactions... 

The details of the reaction model will be given subsequently, but it is noted here that whilst, in principle, the free radicals which initiate the polymerisation may be generated either within the external phase or within the reation loci, in all the cases to be considered in this paper the new radicals are assumed to be generated exclusively with the external phase. The reaction loci then acquire the radicals by absorption from the external phase. 

The reaction model assumed is one in which free-radical polymerisation is compartmentalised within a fixed number of reaction loci, all of which have similar volumes. As has been pointed out above, new radicals are generated in the external phase only. No nucleation of new reaction loci occurs as polymerisation proceeds, and the number of loci is not reduced by processes such as particle agglomeration. Radicals enter reaction loci from the external phase at a constant rate (which in certain cases may be zero), and thus the rate of acquisition of radicals by a single locus is kinetic-ally of zero order with respect to the concentration of radicals within the locus. Once a radical enters a reaction locus, it initiates a chain polymerisation reaction which continues until the activity of the radical within the locus is lost. Polymerisation is assumed to occur almost exclusively within the reaction loci, because the solubility of the monomer in the external phase is assumed to be low. The volumes of the reaction loci are presumed not to increase greatly as a consequence of polymerisation. Two classes of mechanism are in general available whereby the activity of radicals can be lost from reaction loci ... 

A comprehensive kinetic model for the free-radical polymerisation of vinyl chloride in the presence of monofunctional and bifunctional initiators,... 

Redox- and photo-initiation of free radical polymerisation found (Melville, Logemann, Kern, et al.)... 

A high-molecular-weight, insoluble polymer is obtained when perfluoro-2-butyne is subjected to various initiators for free-radical polymerisation (Figure 7.87). The off-white colour of this material is remarkable for a polyacetylene [307, 308]. Indeed, it is largely ignored in discussions on polyacetylenes because, of course, the fact that it is not coloured also means that the system is not conjugated the trifluoromethyl groups keep the TT-systems out of plane relative to each other. 

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