Propagation acrylic polymers

SCHEME 14.1 The general stmcture of an acrylic polymer and the estahhshed photodegradation mechanism via Norrish I a-cleavage of the carhonyl side chain, leading to main-chain polymeric radical a and oxo-acyl radical b. The secondary P-scission rearrangement reaction leading to the propagating radical c is also shown. 

Titanium hydroxide, 129 Wollastonite, 129 Wood flour, 129 Mold and spores, 412,413 Mold growth, 27, 412-416 Mold propagation, 26,412 16 Mold shrinkage, 105, 131 Nucleation, effect of, 131 Plastic crystalllinity, effect of, 131 Moldable thermoset acrylic polymer, 80 Molecular weight distribution (MWD), 63, 636, 649-651... 

The immediate objective of this work was to characterize quantitatively the microstructure of polyphase acrylic polymers. The long-term aim was to relate microstructure to selection of materials, processing conditions, and service properties. This report is confined to preliminary observations on crack propagation and tensile strength. More detailed accounts are being published elsewhere (9). 

J. PojMAN, J. Willis, A. Khan, and W. West, The true molecular weight distributions of acrylate polymers formed in propagating fronts, J. Polym. Sci. Part A Polym Chem., 34 (1996), pp. 991-995. 

Pojman, J. A. Willis, J. R. Khan, A. M. West, W. W. 1996d. The True Molecular Weight Distributions of Acrylate Polymers Formed in Propagating Fronts, J. Polym. Sci. Part A Polym. Chem. 34, 991-995. 

In these equations I is the initiator and I- is the radical intermediate, M is a vinyl monomer, I—M- is an initial monomer radical, I—M M- is a propagating polymer radical, and and are polymer end groups that result from termination by disproportionation. Common vinyl monomers that can be homo-or copolymeri2ed by radical initiation include ethylene, butadiene, styrene, vinyl chloride, vinyl acetate, acrylic and methacrylic acid esters, acrylonitrile, A/-vinylirnida2ole, A/-vinyl-2-pyrrohdinone, and others (2). 

A few studies have appeared on systems based on persistent nitrogen-centered radicals. Yamada et al.2"1 examined the synthesis of block polymers of S and MMA initiated by derivatives of the triphenylverdazyl radical 115. Klapper and coworkers243 have reported on the use of triazolinyl radicals (e.g. 116 and 117). The triazolinyl radicals have been used to control S, methacrylate and acrylate polymerization and for the synthesis of block copolymers based on these monomers [S,243 245 tBA,243 MMA,243 245 BMA,245 DMAEMA,24 5 TMSEMA,247 (DMAEMA-Wbc/fc-MMA),246 (DMAEMA-Woc -S)246 and (TMSEMA-6/ocfc-S)247]. Reaction conditions in these experiments were similar to those used for NMP. The triazolinyl radicals show no tendency to give disproportionation with methacrylate propagating radicals. Dispcrsitics reported arc typically in the range 1.4-1.8.2"43 246... 

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)." ... 

The susceptibility of the polymerization of a given monomer to autoacceleration seems to depend primarily on the size of the polymer molecules produced. The high propagation and low termination constants for methyl acrylate as compared to those for other common monomers lead to an unusually large average degree of polymerization (>10 ), and this fact alone seems to account for the incidence of the decrease in A f at very low conversions in this case. 

The lanthanocene initiators also polymerize EtMA, PrMA and BuMA in a well-controlled manner, although syndiotacticity decreases as the bulk of alkyl substituent increases. Reactivity also decreases in the order MMA EtMA > PrMA > BuMA. Chain transfer to provide shorter polymer chains is accomplished by addition of ketones and thiols.460 The alkyl complexes (190) and (191) also rapidly polymerize acrylate monomers at 0°C.461,462 Both initiators deliver monodisperse poly(acrylic esters) (Mw/Mn 1.07). An enolate is again believed to be the active propagating species since the model complex (195) was also shown to initiate the polymerization of MA. 

Abstract. Auto-accelerated polymerization is known to occur in viscous reaction media ("gel-effect") and also when the polymer precipitates as it forms. It is generally assumed that the cause of auto-acceleration is the arising of non-steady-state kinetics created by a diffusion controlled termination step. Recent work has shown that the polymerization of acrylic acid in bulk and in solution proceeds under steady or auto-accelered conditions irrespective of the precipitation of the polymer. On the other hand, a close correlation is established between auto-acceleration and the type of H-bonded molecular association involving acrylic acid in the system. On the basis of numerous data it is concluded that auto-acceleration is determined by the formation of an oriented monomer-polymer association complex which favors an ultra-fast propagation process. Similar conclusions are derived for the polymerization of methacrylic acid and acrylonitrile based on studies of polymerization kinetics in bulk and in solution and on evidence of molecular associations. In the case of acrylonitrile a dipole-dipole complex involving the nitrile groups is assumed to be responsible for the observed auto-acceleration. 

Both methyl acrylate and butyl acrylate have been used to prepare vinylidene chloride copolymers with sufficient stability to permit thermal processing. The presence of alkyl acrylate units in the polymer mainchain limits the size of vinylidene chloride sequences and thus the propagation of degradative dehydrochlorination. More importantly it lowers the melt... 

Polymerizations of vinyl ketones such as methyl vinyl ketone are also complicated by nucleophilic attack of the initiator and propagating carbanion at the carbonyl group although few details have been established [Dotcheva and Tsvetanov, 1985 Hrdlovic et al., 1979 Nasrallah and Baylouzian, 1977]. Nucleophilic attack in these polymers results in addition, while that at the ester carbonyl of acrylates and methacrylates yields substitution. The major side reaction is an intramolecular aldol-type condensation. Abstraction of an a-hydrogen from a methyl group of the polymer by either initiator or propagating carbanion yields an a-carbanion that attacks the carbonyl group of the adjacent repeat unit. 

Deviations are also observed in some copolymerizations where the copolymer formed is poorly soluble in the reaction medium [Pichot and Pham, 1979 Pichot et al., 1979 Suggate, 1978, 1979]. Under these conditions, altered copolymer compositions are observed if one of the monomers is preferentially adsorbed by the copolymer. Thus for methyl methacrylate (M1 )-/V-vinylcarbazole (M2) copolymerization, r — 1.80, r2 = 0.06 in benzene but r — 0.57, > 2 0.75 in methanol [Ledwith et al., 1979]. The propagating copolymer chains are completely soluble in benzene but are microheterogeneous in methanol. /V-vinylcarba-zole (NVC) is preferentially adsorbed by the copolymer compared to methyl methacrylate. The comonomer composition in the domain of the propagating radical sites (trapped in the precipitating copolymer) is richer in NVC than the comonomer feed composition in the bulk solution. NVC enters the copolymer to a greater extent than expected on the basis of feed composition. Similar results occur in template copolymerization (Sec. 3-10d-2), where two monomers undergo copolymerization in the presence of a polymer. Thus, acrylic acid-2-hydroxyethylmethacrylate copolymerization in the presence of poly(V-vinylpyrrolidone) results in increased incorporation of acrylic acid [Rainaldi et al., 2000]. 

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