Initiator effect, copolymerization

A perspective method for the production of HCP was proposed by Labarre et al 92-94) [t invo]ves radical graft-copolymerization of methyl methacrylate onto heparin effected by cerium salts (Ce4+). As well as other hydroxyl-containing polymers, heparin may react with cerium ions producing free radicals which may initiate graft-copolymerization of unsaturated compounds ... 

This deactivation of the amino group in (J-hydroxyalkylamines has already been proposed by Alvey 70) and is supported by the results of the initiation of copolymerization by quinoline and its 8-hydroxy derivative. Whereas a high initiation efficiency was found for quinoline, 8-hydroxyquinoline, a very effective chelating agent, does not initiate copolymerization 69). 

Table IV. Effect of Method of Initiation of Copolymerization Reaction on the Properties of Polyacrylonitrile—Cotton Copolymer Fabrics (Print Cloth)...

The same authors (5) showed also in another work that the presence of larger amounts of lignin in bisulfite pulps may have a favourable effect on grafting polyacrylonitrile using the cellulose xanthate-hydrogen peroxide redox system to initiate the copolymerization reaction. The plots of the total conversion as well as of polymer loading show a minimum centered around approximately 15% of lignin. 

Aryl-substituted enolizable keto compounds initiate the copolymerization of unsaturated polyesters with styrene. Gel times of the same order as those obtained with conventional peroxide initiators can be attained exotherms, however, are considerably lower, this latter effect being of technological interest—e.g., casting resins. Since a radical mechanism has been proved, it is postulated that radicals result from keto hydroperoxides which have been formed from the aryl-substituted enols via autoxidation. Steric effects and resonance may partly account for differences in the catalytic activity of some and for the inhibiting effect of other ketones and enols. NMR spectroscopy indicates further that cis-trans isomerism may influence the catalytic effectiveness of pure enols. 

T he initiating effect of phenylacetaldehyde on the copolymerization of unsaturated polyesters with vinyl monomers has been described (9). The copolymerization proceeds at approximately the same rate as with the usual peroxide catalysts, but the reaction is much less exothermic hence, the effects of too rapid a polymerization such as fissures, bubble formation, and volume contraction do not occur. Investigation of a series of compounds of the benzene family showed that only enolizable phenyl-keto compounds were initiators (7). 

The acrylate- and methacrylate-derivatized r 5-(benzene)tricarbonylchromium monomers 20 65,66,68,72 21,69>72 and 2273 (Scheme 1.2) were synthesized from benzyl alcohol or 2-phenylethanol when reacted with Cr(CO)6. The alcohols were esterified with either acrylyl or methacrylyl chloride in ether/pyridine and purified by multiple recrystallizations from CS2. Homopolymerizations proceeded in classic fashion with no special electronic effects from the rr-complexed Cr(CO)3 moiety.65,73 Acrylate 20 was copolymerized with styrene and methyl methacrylate and the reactivity ratios were obtained.65 Acrylate 21 and methacrylate, 22, copolymerized readily with styrene, methyl acrylate, acrylonitrile, and 2-phenylethyl acrylate to give bimodal molecular-weight distributions using AIBN initiation.69 Copolymerization of 20 with ferrocenylmethyl acrylate, 2, generates copolymers with varying mole ratios of two transition metals, Cr and Fe (see structure 34).65... 

In an early approach towards MIP-based sensors using capacitance measurement, thin MIP membranes were prepared by in situ polymerization of MAA/ EDMA and then sandwiched as a sensing layer in afield effect device a capacitance decrease was observed due to specific binding of the template L-phenylalanine anilide [103]. Recently, two promising alternative approaches towards ultrathin MIP films for capacitive sensors had been reported electropolymerization of phenol for imprinting of phenylalanine [74], and photo-initiated graft copolymerization of AMPS/MBAA for imprinting of desmetryn [82] and creatinine [83] (cf Sections III.C.2, III.C.3). 

Similarly, Liu et prepared graft copolymers comprising poly(acrylic add) (PAA) backbone and side-chain PNIPAAm grafts that exhibited pH-responsive (due to PAA) and thermo-responsive (due to PNIPAAm) behavior. The macromolecules were formed by AIBN-initiated direct copolymerization in solution. No effert of comonomer sequences on the phase behavior was reported, although the system would, in prindple, allow for probing this effect efficiently. 

The reactivities, i.e., the rate constants, are very different when at one instant it is the ion, and at another the ion pairs, which are the active species. Complex formation between ions and monomer also alters the reactivity. Since the solvent affects both dissociation of the ions and complex formation with the monomer, a strong solvent influence would be expected with the same initiator (Table 22-15) and a strong initiator effect with the same solvent (e.g., the monomer mixture itself) (Table 22-16). Table 22-15 also shows that copolymerization has to be used with great care as a diagnostic tool for distinguishing between mechanisms, since the copo-... 

Poly(dextran-g-acrylamides) from ferrous ion—hydrogen peroxide initiation Graft copolymerization of acrylamide onto dextran with ferrous ion-hydrogen peroxide initiation is being studied in detail. The effect of variation of each reaction parameter on graft copolymerization behavior may be measured by direct gel permeation chromatographic analysis of the final product polymer solution. 

BDCA is described in Eqn. 9 and the results of copolymerization of various perhaloacetaldehydes with phenyl-isocyanate are shown in Table 2. The copolymers are generally prepared with anionic initiators, for example with pyridine or Ph P, but LTB was also used as effective initiator, particularly for chloral copolymerizations. As in homopolymerizations, low temperature conditions must be employed for an effective copolymerization and yields of 30 % to nearly quantitative yields have been obtained. Most copolymers of a perhaloacetaldehyde and phenylisocyanate are insoluble when the copolymer contains only small amounts of phenylisocyanate, but polymers with more than 20 mole % of phenylisocyanate are normally soluble. A truly alternating copolymer of a perhaloacetaldehyde and phenylisocyanate has only been prepared with bromal as the monomer. Many attempts to prepare an alternating copolymer with chloral failed. This result seems to... 

Trllsobutylalumlnum, a very effective initiator for alkylene oxide-dibasic acid anhydride copolymerlzatlonr -was used to initiate the copolymerization of N-phenylazlrldine and phthalic anhydride (Table I). 

Copolymerization is effected by suspension or emulsion techniques under such conditions that tetrafluoroethylene, but not ethylene, may homopolymerize. Bulk polymerization is not commercially feasible, because of heat-transfer limitations and explosion hazard of the comonomer mixture. Polymerizations typically take place below 100°C and 5 MPa (50 atm). Initiators include peroxides, redox systems (10), free-radical sources (11), and ionizing radiation (12). 

AlkyUithium compounds are primarily used as initiators for polymerizations of styrenes and dienes (52). These initiators are too reactive for alkyl methacrylates and vinylpyridines. / -ButyUithium [109-72-8] is used commercially to initiate anionic homopolymerization and copolymerization of butadiene, isoprene, and styrene with linear and branched stmctures. Because of the high degree of association (hexameric), -butyIUthium-initiated polymerizations are often effected at elevated temperatures (>50° C) to increase the rate of initiation relative to propagation and thus to obtain polymers with narrower molecular weight distributions (53). Hydrocarbon solutions of this initiator are quite stable at room temperature for extended periods of time the rate of decomposition per month is 0.06% at 20°C (39). 

Styrene readily copolymerizes with many other monomers spontaneously. The styrene double bond is electronegative on account of the donating effect of the phenyl ring. Monomers that have electron-withdrawiag substituents, eg, acrylonitrile and maleic anhydride, tend to copolymerize most readily with styrene because their electropositive double bonds are attached to the electronegative styrene double bond. Spontaneous copolymerization experiments of many different monomer pair combiaations iadicate that the mechanism of initiation changes with the relative electronegativity difference between the monomer pairs (185). 

The effects of increasing the concentration of initiator (i.e., increased conversion, decreased M , and broader PDi) and of reducing the reaction temperature (i.e., decreased conversion, increased M , and narrower PDi) for the polymerizations in ambient-temperature ionic liquids are the same as observed in conventional solvents. May et al. have reported similar results and in addition used NMR to investigate the stereochemistry of the PMMA produced in [BMIM][PFgj. They found that the stereochemistry was almost identical to that for PMMA produced by free radical polymerization in conventional solvents [43]. The homopolymerization and copolymerization of several other monomers were also reported. Similarly to the findings of Noda and Watanabe, the polymer was in many cases not soluble in the ionic liquid and thus phase-separated [43, 44]. 

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