Initiators, for acrylate polymerization

To date there are no reported examples of the above molecules catalyzing a reaction, however Lacote, Curran et al. recently demonstrated that their NHC-stabilized boryl radicals (85, vide supra) can serve as radical initiators for acrylate polymerizations, radical deoxygenation reagents, radical reductions of alkyl halides and radical chain homolytic substitution reactions. ... 

The depletion of O2 enhances the lifetime of PIf and, therefore, its effectiveness as an energy transfer agent for decomposing RO2H into alkoxy and hydroxy radicals, as shown in equation (10). In contrast to peroxy radicals, the resulting alkoxy and hydroxy radicals are effective initiators for acrylate polymerization. Thus, the overall process (Scheme 4) results in the use of O2 to produce initiator radicals. Evidence for photosensitized cleavage of peroxides and hydroperoxides, using ITX (8), in accordance with equation (10), has been reported. 

The use of single-site initiators for the polymerization of acrylates is attractive, since steric protection of the metal center should eliminate the unwanted side reactions described above, allowing living polymerization systems to be developed. Further, stereocontrol may be achievable by appropriate ligand selection. 

Group transfer polymerization allows the synthesis of block copolymers of different methacrylate or acrylate monomers, such as methyl methacrylate and allyl methacrylate [Hertler, 1996 Webster and Sogah, 1989]. The synthesis of mixed methacrylate-acrylate block copolymers requires that the less reactive monomer (methacrylate) be polymerized first. The silyl dialkylketene acetal propagating center from methacrylate polymerization is more reactive for initiation of acrylate polymerization than the silyl monoalkylketene acetal propagating center from acrylate polymerization is for initiation of methacrylate polymerization. Bifunctional initiators such as l,4-bis(methoxytri methyl si loxymethylene)cyclohexane (XXXIII) are useful for synthesizing ABA block copolymers where the middle block is methacrylate [Steinbrecht and Bandermann, 1989 Yu et al., 1988]. 

Enolate Initiators. In principle, ester enolate anions should represent the ideal initiators for anionic polymerization of alkyl methacrylates. Although general procedures have been developed for the preparation of a variety of alkali metal enolate salts, many of these compounds are unstable except at low temperatures (67,102,103). Useful initiating systems for acrylate polymerization have been prepared from complexes of ester enolates with alkali metal alkoxides (104,105). 

It is well known that primary amines are efficient initiators for the polymerization of Leuch s anhydrides (oxazolidinediones) and that initiation proceeds by the addition of the amine to the monomer. This pathway has been utilized recently to synthesize polypeptide macromonomers bearing a terminal p-vinylbenzyl group 88). Copolymerization of these macromonomers with a vinylic or acrylic comonomer yields graft copolymers with polypeptide grafts. Alternately, the monomer adduct (IV) was copolymerized with styrene, and the primary amine functions of this polymer were used to initiate the polymerization of an oxazolidinedione whereby polypeptide grafts are formed 89). Such graft copolymers may be of interest for biomedical applications. 

TABLE 3.14 Two-Photon Initiators for Radical Polymerization of Acrylates and Methacrylates = One-Photon Absorption Maxima, = Two-Photon... 

BPIC [PPG]. TM for technical grade of ter-butylperoxyisopropyl carbonate, a polymerization initiator for acrylic, ethylene, styrene, and other monomers, and a cross-linking agent for silicone and ethylene propylene elastomers. 

Looking at in line continuous production of initiators for the polymerization of acrylics and vinylics, the long-life cations and anions quoted here and the prepolymerization effects observed in many cases make it attractive to consider these intermediates for applicative purposes as well. 

Figure 6. Exotherm rate at peak, —dH/dt (peak), vs. incident light intensity for photoactivated Trigonal 14 initiated lauryl acrylate polymerizations (cf. Table TV). 0, Series VIII O, Series IX and Series X.

Lupersol. [Atochem N. Am.] Organic peroxide conqxls. initiator for vinyl polymerizations, curing polyester and acrylic resins crosslinl g agent... 

Aztec t-Butyl Peroctoate Aztec t-Butyl Peroctoate-50 OMS tert-Butyl 2-ethylperoxyhexanoate EINECS 221-110-7 Hexaneperoxoic acid, 2-ethyl-, 1,1-dimethylethyl ester Peroxyhexanoic acid, 2-ethyl-, tert-butyl ester Trigonox 21. Initiator for acrylates, styrenics, and LDPE polymerization used where presence of water is... 

Most studies have dealt either with the free radical polymerization of hydrophobic monomers—e.g., styrene [56-89], methyl methacrylate (MMA) [68,73,74,84,86,90-93] or derivatives [2,94,97], and butyl acrylate (BA) [98-100]—within the oily core of O/W microemulsions or with the polymerization of water-soluble monomers such as acrylamide (AM) within the aqueous core of W/O microemulsions [101-123]. In the latter case, the monomer is a powder that has to first be dissolved in water (1 1 mass ratio) so that the resulting polymer particles are swollen by water, in contrast with O/W latex particles, where the polymer is in the bulk state. The polymerization can be initiated thermally, photochemically, or under )>-radiolysis. The possibility of using a coulometric initiation for acrylamide polymerization in AOT systems was also reported [120]. Besides the conventional dilatometric and gravimetric techniques, the polymerization kinetics was monitored by Raman spectroscopy [73,74], pulsed UV laser source [72,78], the rotating sector technique [105,106], calorimetry, and internal reflectance spectroscopy [95]. 

Classification Organic peroxide Empirical C13H26O3 Properties M.w. 230.35 Uses Initiator for vinyl polymerization, bulk/sol n./suspension polymerization, for cure of polyester resins and acrylic syrup Manuf./Distrib. Akzo Nobel http //www.akzonobel.conr, Aztec Peroxides Trade Name Synonyms Aztec TAPEH [Aztec Peroxides] Esperox 570 [Crompton/Olefins Styrenics] Lupersol 575 [Atofina N. Am./Org. Peroxides Atofina SA http //www.atofina.com, Trigonox 121 4tAkzo Nobel http //www.akzonobel.com]-, Trigonox 121-BB75 [Akzo Nobel http //www.akzonobel.com] t-Amylperoxy 2-ethylhexyl carbonate CAS 70833-40-8... 

Uses Polymerization initiator, crosslinking agent for emulsion, bulk, sol n., and suspension polymerization, high temp, cure of polyester, and cure of acrylic syrup Trade Name Synonyms Luperox TAEC [Atofina SA http //www.atofina.com, Atofina http //www.atofinachemicals.com] Trigonox 131 f[Akzo Nobel http //www.akzonobel.com] t-Am yl peroxy neodecan oate CAS 68299-16-1 Empirical C15H30O3 Properties M.w. 258.40 Uses Initiator for vinyl polymerizations Manuf./Distrib. Akzo Nobel http //WWW. akzonobel. com Trade Name Synonyms Aztec TAPND-75-AL [Aztec Peroxides] t-Amylperoxyneoheptanoate Empirical C12H24O3 Properties M.w. 216.32 Uses Initiator for polymerizations... 

Properties M.w. 314.47 Uses Initiator for LDPE polymerization, styrenics, acrylates, PVC polymerization Trade Name Synonyms Aztec INP-37-AL t[Aztec Peroxides] Aztec INP-75-AL t[Aztec Peroxides] Peroyl 355 t[NOF http //www.nof.co.jp], Trigonox 36-W40 f[Akzo Nobel http //www.akzonobel.com]... 

Uses Catalyst, crosslinking agent for heated curing of unsat. polyester resin systems polymerization initiator for acrylates, PE, PS Trade Name Synonyms Aztec DHPEH f[Aztec Peroxides] Trigonox 141 f[Akzo Nobel http //www.akzonobel.com], USP -245 t[Crom pto n http //www. cromptoncorp. com]... 

Interpenetrating polymer network varnishes are composed of the phenolic resin, an epoxy resin, flame retardants, for example brominated epoxies or acrylates, and triphenylphosphate, polymerization initiators for radical polymerization of the acrylates and curing accelerators to catalyze the reaction between epor groups and phenolic groups. 

Ru complexes with a-haloester-functionalized ligands have been used as initiators for the polymerization of acrylates in the presence of Ni(PPh3)2Br2 as the catalyst. Hexafunctional Ru-centered complexes were also used as initiators for the s)mthesis of 6-arm poly(methyl methacrylate) stars. 

Sulfonyl halides have also proven to be effective initiators for the polymerization of styrenes, methacrylates, and acrylates by... 

In a later work, copolymers of PVC with various grafted chains like polyCbutyl acrylate), PMMA, PS, and poly(methyl acrylate) were synthesized (43). The backbone was a random copolymer of vinyl chloride and vinyl acetate. The carbonyl substituted alkyl halide groups were used as the initiator for the polymerization of these monomers by ATRP. 

The main role of the alkyl halide (RX) is to generate growing chains quantitatively. The structure of the alkyl group R preferably mimics the growing polymer chain. Therefore a-halopropionates are effective initiators for the ATRP of acrylates [288]. The main importance of the choice of the initiator for the polymerization of acrylates and methacrylates is based on the requirement of a fast initiation to obtain molecular mass control. A slow initiation results in higher moleeular masses than predicted and a higher polydispersity, which is specified in Table 9 for the polymerization of MMA [299]. Similar results were also observed for the phosphine-based Ni(II) eomplexes [301,302] and the Ni(0) complex. Here, well controlled radical polymerization was only possible with bromide initiators [303]. 

Similar polymerizations have been carried out at monomer concentrations of 0.2 M/liter using potassium persulfate as the initiator for the polymerization of methacrylic, acrylic, and itaconic acids at 50°C for 5 hr under reduced pressure. In this case, the solid acids were isolated by precipitation from the aqueous solution with ethyl acetate and reprecipitated from a methanol-ethyl acetate system [49]. 

Reetz and co-workers " first used metal-free carbon, nitrogen, or sulfur nudeophiles as initiators for the controlled anionic polymerization of nBA. It was thought that repladng the metal counterion in the polymerization would reduce the problem assodated with aggregation and improve the control over the polymerization. Tetrabutylammonium salts of malo-nate derivatives provided poly(n-butyl acrylate) (PnBA) of rdativdy narrow MWD at room temperature (Scheme 14). Many metal-free initiators for the polymerization of alkyl (meth) acrylates using a variety of anions and cations have been reported (Scheme 15) 208,220-224... 

Another innovative approach to initiating the polymerization of acrylic structural adhesives is illustrated by a family of adhesives that uses the adherend surface itself as part of the chemical reaction that generates the free radical initiator. The compositions contain an acidic material, a sulfonyl halide group, and a transition metal compound. Upon contact with a metal surface such as iron, zinc, copper, cadmium, and their alloys, the components react with the metal surface through a free radical pathway, producing effective initiators for the polymerization of the acrylic monomers. Later extensions of this concept provide two-part adhesives employing... 

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