Radical polymerization, of acrylate

These materials are obtained through free-radical polymerization of acrylic or methacrylic monomers, or of fumarates. 

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. 

The free-radical polymerization of acrylic monomers follows a classical chain mechanism in which the chain-propagation step entails the head-to-tail growth of the polymeric free radical by attack on the double bond of the monomer. 

Cobalt porphyrin complexes are involved in the chain transfer catalysis of the free-radical polymerization of acrylates. Chain transfer catalysis occurs by abstraction of a hydrogen atom from a grow ing polymer radical, in this case by Co(Por) to form Co(Por)H. The hydrogen atom is then transferred to a new monomer, which then initiates a new propagating polymer chain. The reaction steps are shown in Eqs. 12 (where R is the polymer chain. X is CN), (13), and (14)." ... 

Polyacrylate Formation Investigated in Micro Reactors Organic synthesis 61 [OS 61] Radical polymerization of acrylates... 

Figure 4.74 Radical polymerization of acrylates in a iaboratory-scaie experimentai set-up with a Sulzer-type pre-mixer. Fouling at the feeding point of the static mixer (top) and molecular weight distribution (bottom) [125],...

Polymerization employing Co complexes as catalysts or else polymers incorporating functionality that includes Co ions represent aspects of polymerization reactions of interest here. Cobalt-mediated free-radical polymerization of acrylic monomers has been reviewed.55 Co11 porphyrins act as traps for dialkylcyanomethyl radicals.1098 Alkyl complexes of Co(TMesP)... 

Much work on the preparation of nonaqueous polymer dispersions has involved the radical polymerization of acrylic monomers in the presence of copolymers having the A block the same as the acrylic polymer in the particle core 2). The preparation of polymer dispersions other than polystyrene in the presence of a PS-PDMS diblock copolymer is of interest because effective anchoring of the copolymer may be influenced by the degree of compatibility between the PS anchor block and the polymer molecules in the particle core. The present paper describes the interpretation of experimental studies performed with the aim of determining the mode of anchoring of PS blocks to polystyrene, poly(methyl methacrylate), and poly(vinyl acetate) (PVA) particles. 

Cobalt complexes are used for the living radical polymerization of acrylates to give a high molecular weight polymer with a narrow molecular weight distribution (Mw/Mn 1.2) (Eq. 71), whereas the complex is applied to the introduction of an unsaturated group into the methacrylate polymers with a high efficiency via a reaction mechanism illustrated in Eq. (72) [27,28,267,268]. 

Ladaviere C, Dorr N, Claverie IP (2001) Controlled radical polymerization of acrylic acid in protic media. Macromolecules 34 5370-5372... 

Couvreur L, Lefay C, Belleney 1 (2003) First nitroxide-mediated controlled free-radical polymerization of acrylic acid. Macromolecules 36 8260-8267... 

These superabsorbents are synthesized via free radical polymerization of acrylic acid or its salts in presence of a crosslinker (crosslinking copolymerization). Initiators are commonly used, water-soluble compounds (e.g., peroxodi-sulfates, redox systems). As crosslinking comonomers bis-methacrylates or N,hT-methylenebis-(acrylamide) are mostly applied. The copolymerization can be carried out in aqueous solution (see Example 5-11 or as dispersion of aqueous drops in a hydrocarbon (inverse emulsion polymerization, see Sect. 2.2.4.2). 

In contrast to the above polymerizations via anionic and/or coordination anionic mechanisms, radical polymerization initiated with metalloporphyrins remains to be studied. The only example of controlled radical polymerization by metalloporphyrins has been reported by Wayland et al. where the living radical polymerization of acrylic esters initiated with cobalt porphyrins was demonstrated. In this section the radical polymerization of MMA initiated with tin porphyrin is discussed. 

Triphenylphosphine sensitizes the radical polymerization of acrylic monomers, such as methyl acrylate or methyl methacrylate (MMA), whereas styrene and vinyl acetate are not photosensitized. Complex formation between MMA and (C6H6)3P was spectroscopically observed. 

Controlled Free Radical Polymerization of Acrylic Monomers... 

The goal of producing low cost ( 1—5/lb.) acrylic block, comb, star, and telechelic polymers by GTP and anionic polymerization has not been met. Free radical polymerization of acrylics and other vinyl monomers on the other hand requires little purification of materials, works in water and other protic solvents, and is low cost. Considerable efforts are presently under way therefore to develop controlled free radical polymerization methods. 

Figure 5.11 Radical polymerization of acrylates using a static mixer-reactor without (left) and with (right) a micromixer as premixer. Top molecular weight distribution down appearance ofthe static mixer to illustrate the degree offou ling (by courtesy of Springer) [42],...

Of these, the most commonly used in letterpress printing is photo-initiated free-radical polymerization of acrylates. 

The free radical polymerization of acrylic anhydride has been shown (37) to proceed predominantly by alternating intramolecular and intermolecular propagation steps. The product after hydrolysis and methylation has been found to yield a polymethyl acrylate exhibiting considerable crystallinity (37). 

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. 

Kabanov et al. have studied the radical polymerization of acrylic acid in aqueous solutions [61] (see Chap. 4, Sect. 1.4). A crystaline, syndiotactic polymer was formed at pH 10.2-10.8. The kinetics of the photosensitized polymerization of acrylic acid was studied by Galperina et. al. [62], They observed a strong solvent dependence for the rate constant of propagation. At 293 K, kp[mol-1 dm3 s-1] = 22 500 in water, 4 200 in formamide, and 500 in dimethylsulphoxide. 

The mechanism of Co(acac)2-mediated polymerization of Vac is still an open question. On the basis of an early work by Wayland and coworkers on the controlled radical polymerization of acrylates by complexes of cobalt and porphyrins, Debuigne and coworkers proposed a mechanism based on the reversible addition of the growing radicals P to the cobalt complex, [Co(II)], and the establishment of an equilibrium between dormant species and the free radicals (equation 8). Maria and coworkers, however, proposed that the polymerization mechanism depends on the coordination number of cobalt . Whenever the dormant species contains a six-coordinated Co in the presence of strongly binding electron donors, such as pyridine, the association process shown in equation 8 would be effective. In contrast, a degenerative transfer mechanism would be favored in case of five-coordinated Co complexes (equation 9). 

Radical polymerization of acrylates can be used to make low-molecular-weight oligomers under high dilution conditions with a relatively large concentration of chain transfer reagent. These conditions were extended to the intramolecular cycli-zation of two acrylate entities tethered by a chiral diol in the formation of a remote stereocenter and a medium-sized ring (Eq. (13.38)) f49J. 

A kinetic study of living radical polymerizations of acrylates initiated by the (tetramesitylporphyronato)-cobalt(III) organo complexes (TMP)Co—CH(CH3)C02-Me and (Br8TMP)Co—CH(CH3)C02Me has been reported by Wayland et al.122 They applied an initial excess of the free cobalt complex and obtained the equilibrium constant for the reversible dissociation of the complex—poly(methyl acrylate) bond as K = 4.2 x 10 10 M for (TMP)Co and K= 1.3 x 10 8 M for (BrgTMP)Co from the rate of monomer consumption at 50 °C. The temperature dependence led to a bond... 

The polystyrene obtained by living cationic polymerization with R—Cl/Lewis acid possesses a carbon-chlorine terminal that is subsequently used for the living radical polymerizations of acrylates and methacrylates to give block copolymers such as B-65 to B-67 376-378... 

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

Figure 3.73. Volume size of voxels assuming ellipsoid structure as a function of the inverse of the scan speed. The voxels were obtained by TP initiated crosslinking radical polymerization of acrylates in the presence of poly (styrene-co-acrylonitrile) as binder and an amino-substituted distyrylbenzene as TP active initiator using a pulsed laser (150-fs pulses at a 76-MHz repetition rate or 85-fs pulses at a repetition rate of 82 MHz). (From Ref. [133] with permission of the Technical Association of Photopolymers, Japan.)...

A photonic crystal-type stack of logs was obtained by TP initiated cross-linking radical polymerization of acrylates in the presence of poly(styrene-co-acrylonitrile) as binder and an amino substituted distyrylbenzene (58) as two-photon active initiator (Fig. 3.93) [133]. This photonic crystal-type microstructure has an average periodicity of 1 pm, a base area of 60 pm x 60 pm, and a height of 8 pm. The lines are about 200 nm wide, which is considerably smaller than the fabrication wavelength (Fig. 3.93) [133]. 

The concept of controlled hydrolytic stability based on substituted phospha-zenes can be extended to organic polymers. Free radical polymerization of acrylic acid in aqueous solution in presence of 39 yields a degradable hydrogel with imidazolyl groups as controlling sites with respect to the hydrolytic stability. ... 

---