Monomer stabilization copolymerization

Of course, it is possible to first copolymerize the macromonomer and vinyl monomer and then use this as a stabilizer in dispersion polymerization. As mentioned earlier, HSM is a stabilizer copolymerized from a methyl methacrylate and a macromonomer that is a maleic ester of 12 hydroxystearic acid pentamer (17). 

A factor that affects the kinetics of the polymerization, and, more critically, the utility of the monomer in copolymerizations with other monomers, e.g., methyl methacrylate, is the stability of the radical formed from addition of the growing polymer chain to the vinyl terminus. In order to gauge the stabilizing effect of the phcnylethynyl group, and the sensitivity of the stabilization to substitution at the para position of the aromatic ring, Ochiai and co-workers carried out calculations at the UHF/3-21G level to evaluate... 

VIKON FPB is a unique copolymer emulsion in which a blend of monomers is copolymerized with vinyl acetate to yield a film which has permanent flexibility. The emulsion is nonionic and has excellent stability in textile processing. 

Coming back to Table 7, it should be emphasized that the simple cases shown there are the most important. None of the numerous derivatives obtained hitherto via monomer modification, copolymerization or codeposition of dispersed solids to form composites [258] showed improved properties relevant to batteries. Therefore the basic systems shown in Table 7 represent the optimum in terms of redox capacity, potential and long-term stability. 

Tests of the light stabilizing activity of monomeric HAS and the corresponding homo- and copolymers reveal mostly better properties of the monomers if physical persistence is not the decisive testing factor [8]. This was found e.g. in comparison of the functionalized urethane 182 and its copolymers with styrene or methyl methacrylate [303], The macromolecular architecture is expressed very distinctly. For example, a PP photografted HAS-functionalized acrylate was more efficient than the respective monomer or homopolymer. Another observation performed with A-(2,2,6,6-tetramethyl-4-piperidyl)methacry-lamide, piperidyl acrylate and methacrylate, their homopolymers and copolymers with dodecyl methacrylate and octadecyl acrylate revealed that the stabilizing effect in PP was in favour of copolymers [304]. Similar HAS-functionalized monomers were copolymerized with styrene. In this case, the copolymers were substantially less efficient in PS than the monomers. Masterbatches of PP-bound HAS prepared by reactive processing imparted a comparable effectivity as conventional HAS when tested at an equimolar basis [298]. 

Biomaterials must be free from elutable impurities, such as additives and residual substances. Additives include stabilizers, antioxidants, plasticizers, and fillers which are added to commercial polymers to impart specific physical or mechanical properties. Since long- and short-term migration of these components to the adjacent tissues and biological fluids is highly undesirable, additives must be eliminated before use. In addition, favorable polymer properties can be achieved without using additives via block or random copolymerization of the candidate homopolymer with other monomers. Graft copolymerization is also used to obtain polymer surfaces with... 

UF resins are susceptible to hydrolytic d radation. Rank the following monomers in order of the expected increase in the hydrolytic stability of UF resins modified by the incorporation of these monomers through copolymerization of their urea derivatives. Explain the basis of your ranking order. 

In the g - e scheme, Q characterizes the resonance stabilization of a monomer during copolymerization and e is the factor reflecting the degree of the polar effect of substituents at a multiple bond. These parameters are associated with the constants of relative activity of monomers by the known... 

Other methods that have been reported include inducing the cyclization reaction by incorporating thioamide groups [491], copolymerized AF-vinylpyrrolidone [492], or vinyl halogen monomers in copolymerized or grafted form [493]. Stabilizers based on maleic acid are also effective [494,495]. Reviews on the subject have been published by Brown [496] and Krcma [497]. 

Electron-withdrawing substituents in anionic polymerizations enhance electron density at the double bonds or stabilize the carbanions by resonance. Anionic copolymerizations in many respects behave similarly to the cationic ones. For some comonomer pairs steric effects give rise to a tendency to altemate. The reactivities of the monomers in copolymerizations and the compositions of the resultant copolymers are subject to solvent polarity and to the effects of the counterions. The two, just as in cationic polymerizations, cannot be considered independently from each other. This, again, is due to the tightness of the ion pairs and to the amount of solvation. Furthermore, only monomers that possess similar polarity can be copolymerized by an anionic mechanism. Thus, for instance, styrene derivatives copolymerize with each other. Styrene, however, is unable to add to a methyl methacrylate anion, though it copolymerizes with butadiene and isoprene. In copolymerizations initiated by w-butyllithium in toluene and in tetrahydrofuran at-78 °C, the following order of reactivity with methyl methacrylate anions was observed. In toluene the order is diphenylmethyl methacrylate > benzyl methacrylate > methyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > t-butyl methacrylate > trityl methacrylate > a,a -dimethyl-benzyl methacrylate. In tetrahydrofuran the order changes to trityl methacrylate > benzyl methacrylate > methyl methacrylate > diphenylmethyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > a,a -dimethylbenzyl methacrylate > t-butyl methacrylate. 

If, however, one polymer free radical is resonance stabilized and the other is not, the resonance-stabilized monomer is preferentially added on to the resonance stabilized free radical, since, a new resonance species is formed. That is why styrene has a copolymerization parameter much greater than unity and vinyl esters have copolymerization parameters of much less than unity when these two monomers are copolymerized together. 

For stabilization with macromonomers, the dependence of the particle size with respect the operation variables can be obtained using Equation 4.20 in which 1/C is substituted by Tj, where is the reactivity ratio of the monomer in copolymerization with the macromonomer [131],... 

Thiols may be used as transfer agents in a wide variety of free radical polymerization processes. Scheme 1.12 shows the general reaction mechanism for this class of transfer agents. Nucleophilic radicals react more readily with thiols than electrophilic radicals, so transfer coefficients are higher for vinyl esters and styrene than for acrylates and methacrylates. Aromatic thiols react more readily than aliphatic ones, i.e., the chain transfer constant is higher, but they also show a stronger retardation effect as the resulting S-centered radicals are less prone for monomer addition due to their increased stability. The product of the transfer reaction is a thiyl radical, which is electrophilic and will react preferably with the more electron rich monomer in copolymerizations. 

Emulsion Process. The emulsion polymerization process utilizes water as a continuous phase with the reactants suspended as microscopic particles. This low viscosity system allows facile mixing and heat transfer for control purposes. An emulsifier is generally employed to stabilize the water insoluble monomers and other reactants, and to prevent reactor fouling. With SAN the system is composed of water, monomers, chain-transfer agents for molecular weight control, emulsifiers, and initiators. Both batch and semibatch processes are employed. Copolymerization is normally carried out at 60 to 100°C to conversions of - 97%. Lower temperature polymerization can be achieved with redox-initiator systems (51). 

The aqueous phase into which the monomer mix is dispersed is also prepared in a separate tank before transferring to the copolymerization ketde. It contains a catalyst, such as benzoyl peroxide [94-36-0], to initiate and sustain the polymerization reaction, and chemicals that aid in stabilizing the emulsion after the desired degree of dispersion is achieved. Careful adherence to predeterrnined reaction time and temperature profiles for each copolymer formulation is necessary to assure good physical durabiHty of the final ion-exchange product. 

Butadiene—Acrylonitrile Latices. Nitrile latices are copolymers of butadiene and acrylonitrile ia which those copolymerized monomers are the main constituents (see Elastomers, synthetic-nitrile rubber). The latices differ mainly ia ratio of comonomer and stabilizer type. They can be classified as low and medium acrylonitrile (ACN) types. The latter contain 35—40 wt % nitrile mbber, and low types ca 27—29 wt %. 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

Alkyl cyanoacrylate monomers have been copolymerized with a variety of monomers, both by radical and anionic initiation. The radical-initiated copolymerization with acrylic monomers was performed with a sufficient amount of an acid stabilizer present to suppress polymerization by anionic means [19]. This investigation has been covered extensively elsewhere. 

Styrene monomer was also copolymerized with a series of functional monomers by using a single-step dispersion copolymerization procedure carried out in ethanol as the dispersion medium by using azobisizobu-tyronitrile and polyvinylpyrollidone as the initiator and the stabilizer, respectively [84]. The comonomers were methyl methacrylate, hydroxyethyl acrylate, metha-crylic acid, acrylamide, allyltrietoxyl silane, vinyl poly-dimethylsiloxane, vinylsilacrown, and dimethylamino-... 

Cationic polymerizations work better when the monomers possess an electron-donating group that stabilizes the intermediate carbocation. For example, isobutylene produces a stable carbocation, and usually copolymerizes with a small amount of isoprene using cationic initiators. The product polymer is a synthetic rubber widely used for tire inner tubes ... 

All this evidence suggests that the radical produced from 2-vinylfuran is a rather strongly stabilized entity, compared with those of more common monomers, and is therefore, not very active in homopolymerization. On the other hand, because of its relative stability, it does not add easily to monomers like styrene, vinylidene chloride or butadiene, and thus the copolymerization rates are also low. Aso and Tanaka86) calculated the values of Q and e as 2.0 and 0.0, respectively. 

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