Peroxides, initiation with

The choice of initiators for polymerizations is an important problem. MCMs can affect the initiator dissociation and initiation rate, and sometimes a chemical interaction of the MCM with an initiator occurs. Thus, MCMs based on Ti(IV) effectively interact with peroxide initiators, with the formation of titanium acrylates. In this connection the polymerization of (BuO)3TiOCOC(CH3)=CH2 does not compete with the acylation reaction, while in the presence of azobisisobutyronitrile (AIBN) it can be avoided completely. Such examples are numerous, as are variants in which the MCM serves as a co-initiator , increasing or decreasing the polymerization rate. 

For reactive extrusion of butylmethacrylate the influence of the rotation rate of the screws and the throughput on the product were also investigated by Jongbloed et al. (11) in a self-wiping corotating twin-screw extruder. The inhibited monomer was mixed with a combination of two peroxide initiators with different half-life values. A combination of initiators was used to prevent a deficiency of radicals towards the end of the reactive extrusion process, where due to the reaction, the temperature increased significantly. The total initiator concentration was 0.07mol/l. The mixture of monomer and initiators was fed to the extruder at room temperature. 

Addition to vinyl ethers and vinyl esters is regioselective, leading to the corresponding j8-alkyloxy/acyloxy sulfone. Addition to alkynes gives vinyl sulfones via a radical pathway. These reactions can be carried out in the presence of peroxide initiators, with Lewis acids such as copper(II) bromide (eq 4), or thermally (eq 5). - ... 

Vinyl ester resins are related to UPRs. They consist of a styrene monomer and the addition products of epoxy resins with methacrylic acid. The vinyl esters are usually cured using a peroxide initiator at elevated temperature [62] or at ambient temperature using a peroxide initiator with a cobalt promoter. Vinyl ester resin can also be photopolymerized [63]. Photocurable vinyl ester systems with methacrylic acid/phenyl glycidyl ether addition product as a diluent were used with ( )-camphorquinone photoinitiator and N,N,3,5-tetramethylaniline photoreducer [64]. The effect of the monomethacrylate... 

For the production of a boat hull or an automobile body, layers of glass cloth or mat can be placed on a form and then impregnated by pouring activated resin from a pail. The activation usually consists of a peroxide initiator with an accelerator such as cobalt naphthenate. The resin is spread out with rollers and polymerization takes place after an induction period (pot life) of an hour or so at room temperature. If production volume justifies the added cost, a matched metal compression mold can be used to give a denser, stronger finished product. The hand layup may still be used. A more uniform product is obtained if the glass fibers are sprayed onto the form or if resin and glass are sprayed on simultaneously. 

Usually, free-radical initiators such as azo compounds or peroxides are used to initiate the polymerization of acrylic monomers. Photochemical (72—74) and radiation-initiated (75) polymerizations are also well known. At a constant temperature, the initial rate of the bulk or solution radical polymerization of acrylic monomers is first order with respect to monomer concentration and one-half order with respect to the initiator concentration. Rate data for polymerization of several common acrylic monomers initiated with 2,2 -azobisisobutyronittile (AIBN) [78-67-1] have been determined and are shown in Table 6. The table also includes heats of polymerization and volume percent shrinkage data. 

Polymerization. The first successful polymerizations of VDE in aqueous medium using peroxide initiators at 20—150°C and pressures above 30 MPa were described in a patent issued in 1948 (73). About a year later, the first copolymerizations of VDE with ethylene and halogenated ethylenes were also patented (74). After a hiatus of over 12 years a commercially feasible process was developed and PVDE was ready for market introduction (2). 

Solution polymerization of VDE in fluorinated and fluorochlorinated hydrocarbons such as CEC-113 and initiated with organic peroxides (99), especially bis(perfluoropropionyl) peroxide (100), has been claimed. Radiation-induced polymerization of VDE has also been investigated (101,102). Alkylboron compounds activated by oxygen initiate VDE polymerization in water or organic solvents (103,104). Microwave-stimulated, low pressure plasma polymerization of VDE gives polymer film that is <10 pm thick (105). Highly regular PVDE polymer with minimized defect stmcture was synthesized and claimed (106). Perdeuterated PVDE has also been prepared and described (107). 

The decomposition kinetics of an organic peroxide, as judged by 10-h HLT, largely determines the suitabiUty of a particular peroxide initiator in an end use appHcation (22). Other important factors ate melting point, solubiUty, cost, safety, efficiency, necessity for refrigerated storage and shipment, compatibihty with production systems, effects on the finished product, and potential for activation. 

Eor apphcation temperatures below 10°C or for acceleration of cure rates at room temperature, nonredox systems such as ben2oyl peroxide initiated by tertiary amines such as dimethylaruline (DMA) have been appHed widely. Even more efficient cures can be achieved using dimethyl- -toluidine (DMPT), whereas moderated cures can be achieved with diethylaruline (DEA). 

Bulk polymerization has been studied at relatively low temperatures and in toluene and carbon tetrachloride solutions carried to low conversions (12). The effects of temperature and different organic peroxide initiators have been observed. The molecular weight of soluble polymer after 3% conversion is ca — 19,000 and is somewhat dependent on initiator concentration or temperature between 35 and 65 °C. With di-2-methylpentanoyl... 

Scratch resistance of polymer from DADC is improved by novel mixtures of peroxide initiators such as 5% isopropyl percarbonate with 3.5% benzoyl peroxide (16). In order to force completion of polymerization and attain the best scratch resistance in lenses, uv radiation is appHed (17). Eyeglass lenses can be made by prepolymerization in molds followed by removal for final thermal cross-linking (18). 

Telomerization. Polymerization of DAP is accelerated by telogens such as CBr, which are more effective chain-transfer agents than the monomer itself (65) gelation is delayed. The telomers are more readily cured in uv than DAP prepolymers. In telomerizations with CCl with peroxide initiator, at a DAP/CCl ratio of 20, the polymer recovered at low conversion has a DP of 12 (66). 

The reaction is particularly effective with alkenes with electron-attracting substituents such as diethyl maleate. When the reaction is conducted thermally with a peroxide initiator at 160°C, the product mixture is much more complex ... 

The cure reaction of structural acrylic adhesives can be started by any of a great number of redox reactions. One commonly used redox couple is the reaction of benzoyl peroxide (BPO) with tertiary aromatic amines. Pure BPO is hazardous when dry [39]. It is susceptible to explosion from shock, friction or heat, and has an autoignition temperature of 79°C. Water is a very effective stabilizer for BPO, and so the initiator is often available as a paste or a moist solid [40], The... 

Qiu et al. [11] reported that the aromatic tertiary amine with an electron-rich group on the N atom would favor nucleophilic displacement and thus increase the rate of decomposition of diacyl peroxide with the result of increasing the rate of polymerization (Table 1). They also pointed out that in the MMA polymerization using organic peroxide initiator alone the order of the rate of polymerization Rp is as follows ... 

The effect of the decomposition products of the polymerization initiator incorporated at the beginning of the chain is a controversial one. If the polymerization of vinyl chloride is initiated with organic peroxides, which decompose according to Eqs. (13) and (14) ... 

Peroxide initiators may also undergo primary radical transfer to produce unsaturated end groups, which may result in a less stable polymer. In the case of benzoyl peroxide, an additional possibility is initiation by phenyl radicals to give a polymer with terminal phenyl groups [Eq. (17)] ... 

An alternating copolymer of a-methyl styrene and oxygen as an active polymer was recently reported [20]. When a-methyl styrene and AIBN are pressurized with O2, poly-a-methylstyreneperoxide is obtained. Polymerization kinetic studies have shown that the oligoperoxides mentioned above were as reactive as benzoyl peroxide, which is a commercial peroxidic initiator. Table 1 compares the overall rate constants of some oligoperoxides with that of benzoyl peroxide. 

Unsaturated polyester finishes of this type do not need to be stoved to effect crosslinking, but will cure at room temperature once a suitable peroxide initiator cobalt salt activator are added. The system then has a finite pot life and needs to be applied soon after mixing. Such a system is an example of a two-pack system. That is the finish is supplied in two packages to be mixed shortly before use, with obvious limitations. However, polymerisation can also be induced by ultra violet radiation or electron beam exposure when polymerisation occurs almost instantaneously. These techniques are used widely in packaging, particularly cans, for which many other unsaturated polymers, such as unsaturated acrylic resins have been devised. 

Many types of peroxides (R-O-O-R) are known. Those in common use as initiators include diacyl peroxides (36), pcroxydicarbonatcs (37), peroxyesters (38), dialkyl peroxides (39), hydroperoxides (40), and inorganic peroxides [e.g. persulfate (41)1, Multifunctional and polymeric initiators with peroxide linkages are discussed in Sections 3.3.3 and 6.3.2.1. 

In general, aliphatic diacyl peroxide initiators should be considered as sources of alkyl, rather than of aeyloxy radicals. With few exceptions, aliphatic acyloxy radicals have a transient existence at best. For certain diacyl peroxides (36) where R is a secondary or tertiary alkyl group there is controversy as to whether loss of carbon dioxide occurs in concert with 0-0 bond cleavage. Thus, ester end groups observed in polymers prepared with aliphatic diaeyl peroxides are unlikely to arise directly from initiation, but rather from transfer to initiator (see 3.3,2.1.4),... 

---