AIBN as initiator

Figure 3.3 Cumulative ( ) and instantaneous ( ) initiator efficiency (/) of AIBN as initiator in S polymerization (50% v/v toluene, 70 °C) as a function of monomer conversion (lines are a polynomial fit to the datapoints).1,32...

Olaj et /.124 proposed that termination of S polymerization involves substantial disproportionation. They analyzed the molecular weight distribution of PS samples prepared with either BPO or AIBN as initiator at temperatures in the range 20-90 °C and estimated kJkK to be ca 0.2. In a more recent study, Olaj et a/.149 determined the molecular weight distribution of PS samples prepared with photoinitiation at 60 and 85 °C and estimated values of kxproblems associated with estimating k-.vk , on the basis of dispersity measurements and determined that kxiiklc should be "substantially smaller" than suggested by Olaj et til.m... 

In addition to heat and light, generation of free radicals can be accomplished by using 7-rays, X-rays or through electrochemical means. In general, however, these methods do not tend to be so widely used as those involving benzoyl peroxide or AIBN as initiators. 

Radical polymerizations of vinyl-substituted ultraviolet stabilizers were accomplished with azobisisobutyronitrile (AIBN) as initiator, with careful exclusion of oxygen. Copolymerization was also readily achieved. The following sections describe in detail the preparation of polymeric ultraviolet stabilizers from salicylate esters, 2-hydroxybenzophenones, a-cyano-p-phenyl-cinnamates and hydroxyphenylbenzotriazoles. 

Each of the derivatives may be regarded as a substituted styrene, and classical styrene syntheses have been employed. Radical polymerization of the phenolic monomers (salicylate esters, 2-hydroxybenzophenones and hydroxyphenylbenzotriazoles) proceeds normally with AIBN as initiator, at least when oxygen is carefully excluded. It is expected that polymeric ultraviolet stabilizers, perhaps in combination with conventional stabilizer will make an important contribution to photostabilization technology. 

The experiments on emulsion cumene oxidation with AIBN as initiator proved that oxidation proceeds via the chain mechanism inside hydrocarbon drops [17]. The presence of an aqueous phase and surfactants compounds does not change the rate constants of chain propagation and termination the ratio (fcp(2fct)-1/2 = const in homogeneous and emulsion oxidation (see Chapter 2). Experiments on emulsion cumene oxidation with cumyl hydroperoxide as the single initiator evidenced that the main reason for acceleration of emulsion oxidation versus homogeneous oxidation is the rapid decomposition of hydroperoxide on the surface of the hydrocarbon and water drops. Therefore, the increase in the aqueous phase and introduction of surfactants accelerate cumene oxidation. 

The rare example of synergistic action of a binary mixture of 1-naphthyl-A-phcnylaminc and phenol (1-naphthol, 2-(l,l-dimethylethyl)hydroquinone) on the initiated oxidation of cholesterol esters was evidenced by Vardanyan [34]. The mixture of two antioxidants was proved to terminate more chains than both inhibitors can do separately ( > /[xj). For example, 1-naphtol in a concentration of 5 x 10 5 mol L-1 creates the induction period t=170s, 1 -naphthyl-A-phenylamine in a concentration of 1.0 x 10-4 mol L 1 creates the induction period t = 400s, and together both antioxidants create the induction period r = 770 s (oxidation of ester of pelargonic acid cholesterol at 7= 348 K with AIBN as initiator). Hence, the ratio fs/ZfjXi was found equal to 2.78. The formation of an efficient intermediate inhibitor as a result of interaction of intermediate free radicals formed from phenol and amine was postulated. This inhibitor was proved to be produced by the interaction of oxidation products of phenol and amine. 

Emulsion copolymerization of EUP and comonomers may be initiated in the aqueous (persulfate) or in the non-aqueous phase (AIBN). On the decomposition of persulfates, sulfate and hydroxyl groups are introduced into macromolecules and microgels, thus influencing their surface properties [118,123-125]. By using AIBN as initiator a change of the chemical character of the surface and of the properties of the microgels is avoided. 

Because the composition of microgels prepared by micro-ECP of EUP and styrene with AIBN as initiator remains constant and irrespective of the reaction... 

Funke and coworkers extensively studied the conditions for the synthesis of 1,4-DVB microgels in dilute solutions of toluene, using AIBN as initiator [209,212]. They prepared homologous series of 1,4-DVB microgels by a systematic variation of the polymerization temperature, the monomer and the initiator concen-... 

Scheme 3. Initiation of Vinylidene Chloride Polymerization Using AIBN as Initiator.

Copolymers of styrene with 4-vinylpyridine (II) and N-viny1imizado1e (III) were obtained by copolymerization for one day at 60°C in 25 wt% comonomer solutions in toluene, using AIBN as initiator. In all cases the degrees of substitution, a, of the functionalized polymers with ligand groups were derived from the nitrogen contents found by elemental analyses. 

HPMA [36] and a vinyl metal-chelating monomer A-(A/, A/ -dicarboxy-methylaminopropyl)methacrylamide synthesized [35]. Chemical structures of HPMA and DAMA are given in Figure 4. Poly(HPMA-co-DAMA) was prepared by free radical copolymerization in methanol with AIBN as initiator. Molecular weight distribution was determined by size exclusion chromatography and content of side-chain carboxylic group by acid-base titration. 

Radical-initiated allylic bromination using NBS, and catalytic AIBN as initiator or NBS under photolysis. 

The inhibiting effect of NaHC03 on chain oxidation was established by studying the effect of ions on the oxidation of cyclohexanol. The latter was oxidized at 75°C. with AIBN as initiator (R = 6.9 X 107 mole liter"1 sec."1). To dissolve NaHC03, 9% of water was added to cyclohexanol. The rate of oxidation was measured volumetrically. 

Another type of multimonomer was prepared from poly(methacryloyl chloride) and allilamine, and was used in order to examine copolymerization process with sty-rene. ° The copolymerization was carried out in dioxane with AIBN as initiator. The basic reaction leads to the product with ladder-type blocks of allylmethacrylamide units, and blocks consist of styrene units ... 

In this laboratory we have studied the interaction of methyl methacrylate, methyl acrylate, methacrylic acid, and acrylic acid with the goal of positively identifying the site of addition to the polymer and hence proving the type of reaction. A comparison of the results for both BPO and AIBN as initiators is suggestive of the actual mechanism and site of attachment but it is not conclusive proof of the actual site of attachment. 

The terpolymerization of CPT-SO2 and acrylonitrile is shown in Table II. It was necessary to accelerate the polymerization by adding azobisisobutyronitrile (AIBN) as initiator. The nature of the propagating species may not be different with a different initiator. Polymerization ceased at a low conversion at 40 °C in toluene. The terpolymer composition calculated from elemental analysis of C, H, N, and S showed an equimolar ratio of CPT and S02. The terpolymers are white powders, soluble in DMF, can be cast into transparent film different from the CPT-SO2 copolymer, and showed melting temperature without decompo-... 

Binary copolymerization of the CPT-AN system was carried out at 40°C using AIBN as initiator. From the Finemann-Ross plot of the copolymer composition and monomer feed ratios, the monomer reactivity ratios were determined. (CPT) = 0, r2 (AN) = 1.97. The increase of the relative reactivity of CPT by forming a complex with SC is calculated as follows. 

In particular, crude polymerizates prepared in the presence of AIBN as initiator, which yield resonance stabilized radicals (17) that are unable to extract hydrogen from hydrocarbon supports (I, 18) show the same content of non-extractable rubber as that of the polymerizates prepared in the presence of active radicals in the hydrogen extraction from hydrocarbon polymers, such as those derived from the decomposition of benzoyl peroxide. 

Table VI. Effect of Initiator Concentration on Grafting Reaction with AIBN as Initiator...

Tables IX and X and Figure 12 show the dependence of percent grafting and grafting efficiency on methyl methacrylate concentration. It can be seen that the percent grafting increased with the monomer concentration in the initial stages and after reaching a maximum remained almost constant. In BPO-initiated reaction, grafting efficiency increased initially and then decreased with increase in monomer concentration. With AIBN as initiator, high values of grafting efficiency were obtained even at very low monomer concentrations, and then the grafting efficiency decreased with the increase of monomer concentration.

Methods The polymer beads were synthesized by suspension polymerization in concentrated aqueous NaCl solution using 0.1% (of monomers) AIBN as initiator, a monomer/aqueous phase ratio of 2/5 and freshly precipitated Mg(0H)2 as suspending agent (9). The beads were Soxhlet extracted with ethanol for 24 hours and after drying classified into mesh sizes. The 30 mesh (0.59-0.70 mm ) and 18 mesh (1.00-1.19 mm 4>) fractions were used for release experiments (30 mesh for DC1 18 mesh for OX). 

Miniemulsion copolymerization of a 50 50 styrene/methyl methacrylate monomer mixture, using hexadecane as hydrophobe, was carried out by Rodriguez et al. [78]. The mechanism of mass transfer between miniemulsion droplets and polymer particles in the miniemulsion copolymerization of styrene-methyl methacrylate (AIBN as initiator, hexadecane as hydrophobe) was studied, analyzing the mass transfer of highly water-insoluble compounds from miniemulsion droplets to polymer particles by both molecular diffusion and collisions between droplets and particles [79,80]. 

As a comparison and reproduction to recent works done by DeSimone and coworkers [2], attempts were made in the free radical polymerization of acrylic acid (AA) in supercritical carbon dioxide (SCCO2) with Azoisobutyronitrile (AIBN) as initiator. 

A similar experiment is reported in (60) in-situ polymerization of PMMA in presence of MWCNT at analogous experimental conditions (in methanol, using PVP as stabilizer and AIBN as initiator) produced monodisperse PMMA/MWCNT microspheres only with the help of mechanical stirring. The spheres diameters decreased from about 11.6 pm to 6.0 pm as the content of MWCNT increased from 0 to 0.03 wt%. Additional analyses identified carbon nanotubes to be present both in the interior and on the surface of the particles. 

In the first step, the hydrophobic monomer was partially polymerized in bulk, using AIBN as initiator, by heating at 50 °C until a small conversion was reached. Then the inhibitor methylhydroquinone (MEHQ) was introduced to terminate polymerization. In the second step, the partially polymerized monomer was injected at room temperature into a small amount of a stirred aqueous solution of SDS to generate a concentrated emulsion. 

A further useful application of SC-CO2 as a reaction medium is the free-radical side-chain bromination of alkylaromatics, replacing conventional solvents such as tetra-chloromethane or chlorofluorohydrocarbons having no abstractable hydrogen atoms [920]. For example, bromination of ethylbenzene in SC-CO2 at 40 °C and 22.9 MPa yields 95 cmol/mol (1-bromoethyl)benzene, with practically the same regioselectivity as obtained in conventional tetrachloromethane as the solvent. Even the classical Wohl-Ziegler bromination of benzylic or allylic substrates using A-bromosuccinimide (NBS) can be conducted in SC-CO2 [920]. Irradiation of a solution of toluene, NBS, and AIBN (as initiator) in SC-CO2 at 40 °C and 17.0 MPa for 4 hours gave (bromomethyl)-... 

Since the initiation by y-irradiation is unsatisfactory for AAm-TAA system, the suspension polymerization procedure is adopted using isopropanol as solvent and AIBN as initiator to obtain a resin having a capacity of 0.63 meq/g. When vinylacetate (26 % by weight based on AAm) is used as a third monomer, the capacity is improved from 0.63 to 0.9 meq/g. For the MAAm-TAA system the chemical initiation is not preferred since the yields of the resins obtained by this method are lower than those obtained by y-irradiation. 

Fig. 5 gives electron micrographs of latexes prepared with AIBN as initiator from emulsions with a constant styreneiHoO weight ratio = 1 3, a constant amount of OPB and with HD 0PB molar ratios of 0, 1 1,... 

---