Subject homopolymerization

Aspects of thermal initiation have been reviewed by Moad et al., w Pryor and Laswell, 10 Kurbatov/" and Hall.312 It is often difficult to establish whether initiation is actually a process involving only the monomer. Trace impurities in the monomers or the reaction vessel may prove to be the actual initiators. Purely thermal homopolymerizations to high molecular weight polymers have only been demonstrated unequivocally for S and its derivatives and MMA. For these and other systems, the identity of the initiating radicals and the mechanisms by which they are formed remain subjects of controversy. 

Thus, the introduction effect of long-chain alkyl groups into the DAP resins was reflected in the improved flexibiiity. In particular, LMA and SMA as comonomers showed a remarkable effect for example, the DAP resin cocured with 10 mol% of LMA had the tensile strength of 600 kg/cm and the elongation of 9.0%, although the DAP resin obtained by homopolymerization was quite brittle and, therefore, could not even be subjected to the measurement of mechanical properties as mentioned above. 

The copolymerization equation is valid if all propagation steps are irreversible. If reversibility occurs, a more complex equation can be derived. If the equilibrium constants depend on the length of the monomer sequence (penultimate effect), further changes must be introduced into the equations. Where the polymerization is subjected to an equilibrium, a-methylstyrene was chosen as monomer. The polymerization was carried out by radical initiation. With methyl methacrylate as comonomer the equilibrium constants are found to be independent of the sequence length. Between 100° and 150°C the reversibilities of the homopolymerization step of methyl methacrylate and of the alternating steps are taken into account. With acrylonitrile as comonomer the dependence of equilibrium constants on the length of sequence must be considered. 

The actual amount and structure of this "bound" water has been the subject of debate (83), but the key factor is that in water, PVP and related polymers are water structure oiganizers, which is a lower entropy situation (84). Therefore, it is not unexpected that water would play a significant role in the homopolymerization of VP, because the polymer and its reactive terminus are more rigidly constrained in this solvent and termination k is reduced (85). 

While the cationic homopolymerization of isobutylene has been the subject of numerous books (9), recent book chapters (JO. 11) and review articles (12,13), and while the polymerization of P-pinene has also been studied by many authors (1-3,... 

Epoxy resins may be cured in the manner of polyadditions, i. e., homogeneously catalyzed by multifunctional amines and isocyanates, or cyclic anhydride, dicyan-diamide, or biguanide derivatives. On the other hand epoxy resins are also subject to homopolymerization. The catalysts represent Lewis bases, preferably tertiary amines, imidazoles, or ureas (the latter exclusively for the dicyandiamide curing)... 

Extension of macromonomer reinitiation led to copolymerizations with nonpolymerizable monomers .399 401 Methacrylate oligomers cannot be ho-mopolymerized due to the steric bulk of the substituents at what would be the radical center. Thus, they are subject only to reinitiation under CCT conditions. There are many other olefinically unsaturated species which do not undergo homopolymerization or copolymerization with normal free-radical monomers.402 These can by represented by the tetrasubstituted olefin in eq 45, though more often the desired olefin is 1,2-disubstituted. 

A further possibility consists of subjecting the catalyst to incipient polymerization with small quantities of styrene, isoprene, or butadiene (organic alkali compounds also can be used for this purpose), then adding dropwise a mixture of cyanoprene and selected monomers at low temperatures. If no incipient polymerization takes place, metallo-organic catalysts will only give a homopolymerization of the cyanoprene. 

The formation of alternating copolymer is attributed to the homopolymerization of a comonomer charge-transfer complex. The latter is formed spontaneously, subject to equilibrium considerations, with the interaction of a strong donor monomer and a strong acceptor monomer. 

The attachment of cymantrene groups to polymers has attracted interest for other reasons. Studies have shown, for example, that adherent, abrasion-resistant coatings are formed on metals when thin films of the Mn-containing polymer are subjected to irradiation with UV light. The polymerization of styrene tricarbonylchromium 47 has also been studied.This species is available from the reaction of styrene with Cr(CO)3(NH3)3. Although the Cr monomer 47 resisted attempts at homopolymerization, co-polymerizations with styrene, methyl acrylate, as well as with 41 to yield bimetallic polymers 48 were possible (Equation (17)). In addition, co-polymerization with vinyl-ferrocene afforded co-polymers of low molecular weight (Mn = ca. 4,000). A variety of other organometallic vinyl momomers 49 has been successfully polymerized to yield polymers 50 that contain pendant Gr, W, and Ir carbonyl moieties (Equation (18)). ... 

Probably most industrial homopolymerizations of vinyl acetate are carried out by suspension processes, since the resulting beads are readily converted to poly(vinyl alcohol). This is the major reason for producing the homopolymer. Surprisingly little has been published about the suspension polymerization of vinyl acetate, despite the fact that Lindemaim [1] cites nearly 1100 references on the subject of vinyl acetate and approximately 2(K) references on the higher vinyl esters. 

Probably the most noteworthy of comparatively recent developments connected with radical polymerization has been the discovery and exploitation of the substantial effects of Lewis acids upon certain systems. Many papers have refened to copolymerizations but the additives can also influence homopolymerizations, altering not only the kinetic characteristics of the reactions but also the molecular weights and, in some cases, structures of the resulting polymm. Further interesting papers on this subject were published in 1977 and 1978. 

Bulk thermal homopolymerization of TSL. TSL, 0.5g triply crystallized was subjected to high vacuum (10 torr) and warmed slightly to remove solvent and air. After back-filling with dry argon, the tube was heated in an oil bath at 124 for 16 hours. The monomer melted to a liquid and polymerization occurred immediately upon melting. 

Enhanced absorption and emission lines are detected in the NMR spectra of peroxides and azo compounds subjected to rapid decomposition.This phenomenon, referred to as chemically induced dynamic nuclear polarization (CIDNP), was first detected during the free-radical-initiated homopolymerization of CIDNP does not arise in reactions where radical transfer... 

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