Poly polymeric radical

Polymeric ion-radicals are usually formed as a result of one-electron redox modifications of uncharged polymers containing electrochemically active groups. They attract an enhanced attention in the sense of possible practical applications. Because polymeric ion-radicals contain many spin-bearing groups, a similarity emerges between polymeric ion-radicals and poly(ion-radicals). 

The polymeric radicals resulting from the mechanical scission of poly(methyl methacrylate) are ... 

The catalytic or initiated reaction involves heating the poly(diene) in an aromatic solvent to temperatures between 120-150 °C in the presence of free radical initiators such as peroxides, hydroperoxides and azo compounds. The ensuing reaction involves addition of maleic anhydride to a polymeric radical which was formed by abstraction of an allylic hydrogen by initiator radicals. Four modes of addition are possible leading to partial structures such as (175)-(178) illustrated with poly(isoprene). It can readily be seen that some crosslinking is an inherent problem because of structures (177) and (178). The amount of gel formed, however, is found to be largely dependent on the initiator employed and can be minimized, especially with hydroperoxide initiators. 

The relative reactivity of the macromonomer in copolymerization with a common comonomer, A, can be assessed by l/rA=kAB/kAA> i-e-> the rate constant of propagation of macromonomer B relative to that of the monomer A toward a common poly-A radical. In summarizing a number of monomer reactivity ratios in solution copolymerization systems reported so far [3,31,40], it appears reasonable to say that the reactivities of macromonomers are similar to those of the corresponding small monomers, i.e., they are largely determined by the nature of their polymerizing end-group, i.e., essentially by their chemical reactivity. 

Various patents on the homopolymerization of BD in the presence of styrene are available [581-590]. According to these patents, St is used as a solvent in which BD is selectively polymerized by the application of NdV/DIBAH/EASC. At the end of the polymerization a solution of BR in St is obtained. In subsequent reaction steps the unreacted styrene monomer is either polymerized radically, or acrylonitrile is added prior to radical initiation. During the subsequent radical polymerization styrene or styrene/acrylonitrile, respectively, are polymerized and ris-l,4-BR is grafted and partially crosslinked. In this way BR modified (or impact modified) thermoplast blends are obtained. In these blends BR particles are dispersed either in poly(styrene) (yielding HIPS = high impact poly(styrene) or in styrene-acrylonitrile-copolymers (yielding ABS = acrylonitrile/butadiene/ styrene-terpolymers). In comparison with the classical bulk processes for HIPS and ABS, this new technology allows for considerable cost reductions... 

We have observed similar effects in the TREPR spectra of the polymeric radical of poly(adamantyl methacrylate) (PAMA, spectrum not shown). Earge ester side chains such as the adamantyl and fluorinated alkyl groups experience a larger amount of hydrodynamic friction than do smaller side chains such as methyl and ethyl groups. ... 

The decay time constants for the polymeric radicals clearly vary from solvent to solvent, ranging over an order of magnitude from about 2 ps in tetrahydrofuran (THF) to 200 ns in methylene chloride. A similar solvent dependence of NMR Ti values has been reported by Spyros et al. They studied poly(naphthyl methacrylate) using the inversion recovery technique and found that the spin-lattice relaxation time of... 

This picture is also consistent with the fact that, in general, to becomes shorter on increasing the content of tertiary amine co-units in the copolymer [118]. The observation that Rcmax decreases in poly(MBA-co-DAPA) and poly(MBA-co-DEPA) on increasing the content of tertiary amine co-units and that the minimum activity is observed in poly(MBA-co-DMEA) and poly(MBA-co-DEEA) in correspondence with the highest content of tertiary amine co-imits [118] can easily be explained. In fact, due to the mechanism proposed in Scheme 29, as soon as the traces of oxygen are consumed, the residual amine co-units, in excess with respect to MBA units, continue the conversion of the substituted benzyl-type polymeric radicals into the alkylamino radicals, which are known to display lower reinitiation constants for acrylic monomers. 

Dithienothiophenes give cation polymeric radicals capable of further copolymer addition" while polystryene with a narrow polydispersity has been prepared through the use of an end-capped photoactive anthryl group. ° Large differences in radical termination rates have been found to be responsible for the marked variations in molecular weights of polymer from the UV flash polymerisation of 1,3-butadiene. tra 5-l,2-bis(5-Phenyl-2-oxazolyl)ethene has been found to exhibit low laser conversion efficiency due to preferential dimerisation while thermally activated patterns can be formed on the surface of poly(methyl methacrylate) by coating with photodimerisable 9-anthraldehyde. " ... 

Some papers report on the influence of aromatic compounds on the polymerization of vinyl compounds other than vinyl acetate. Mayo et al.48 found that bromo-benzene acts as a chain transfer agent in the polymerization of styrene, although no fragments of bromobenzene are incorporated into the polymer. They concluded that a complex is formed between the solvent molecule and either the propagating poly-styryl radical or hydrogen atom derived from the latter. 

Some special reaction with a particularly designed route can be used to synthesize azo BCs. For instance, a series of poly(vinyl ether)-based azo LCBCs were synthesized by using living cationic polymerization and free-radical polymerization techniques (Serhatli and Serhatli, 1998). As shown in Scheme 12.8, 4.4 -azobis(4-cyano pentanol) (ACP) was used to couple quantitatively two well-defined polymers of LC living poly(vinyl ether), initiated by the methyl trifluor-omethane sulfonate/tetrahydrothiophene system. Then the ACP in the main chain was thermally decomposed to produce polymeric radical, which was used to initiate the polymerization of MMA or styrene to obtain PMMA-based or PS-based azo BCs (AB or ABA types). 

Tlie simplest model for the polymerization of MAN is that of the decomposition of AIBN. The cyanoisopropyl radical mimicks the action of a propagating poly(methacrylonitrile) radical. 

Poly(methyl methacrylate) Polyacrylonitrile Poly(vinyl acetate) CO2CH3 / CH2=C CHa CH2=CHCN 0 CH2=CHOCCHa radical-chain addition polymerization radical-chain addition polymerization in aqueous suspension radical-chain addition polymerization... 

Finally, according to basic equilibrium principles, additional Co favors recombination with propagating radicals. Consequently, in spite of the low propensity of Co(acac)2 to deactivate poly(acrylate) radicals, the successful controlled polymerization of acrylates was demonstrated when using a substantial excess of Co(acac)2 [30]. The drawback of this approach, however, was an ampHfied contamination of the final material by the metal. 

In the radical polymerization of styrene, the attack on the fi-C atom is unhindered, and the poly(styrene) radical—CH(C6H5) is, in addition, resonance-stabilized. In the polymerization of vinyl acetate, CH2==CH(0C0CH3), there are weak dipole-dipole interactions between the —COO— groups in the transition state, which facilitates an occasional attack on the a-C atom despite steric hindrance by these groups. Poly(vinyl acetate) therefore contains 1-2% head-to-head structures. The attack of the a position is furthermore the easier, the smaller the substituents. Poly-(vinyl fluoride), therefore, has up to 30% head-to-head sequences. 

Delayed-Action Accelerated Vulcanization. If cross-link formation is by a free radical mechanism, delayed action could be the result of a quenching action by the monomeric polysulfldes formed by reactions between accelerator and sulfur. If the polymeric poly-thiyl radicals (cross-link precursors) are rapidly quenched by an exchange reaction before they are able to form cross-links, cross-link formation would be impeded until substantial depletion of the monomeric polysulfldes. This is illustrated in Scheme 4. 

A matrix polymerization was reported to proceed through a living radical mechanism, where methacrylic add(MAA) was polymerized in water in the presence of chitosan(CTS) The poly(MAA) radicals were considered to survive due to com-... 

DBPOX, a low temperature initiator, decomposes easily at room temperature into t-butoxy radicals and carbon dioxide (Eq. (1)) The t-butoxy radical undergoes both addition to the monomer (Eq. (2)) and hydrogen-abstraction from the N-methyl group (Eq. (3)) Radicals 1 and II attack the monomer and propagate yielding poly(NMAAm) radicals (Eq. (4)). The stable poly(NMAAm) radic was similarly formed in the photo-sensitized polymerization with azo-bis-isobutyronitrile(AIBN) or di-tert-butyl peroxide(DBPO). In the latter system, the concentration of living radical III reached 1 x mol/1... 

The five line spectrum (b) observed in the MAm polymerization is closely similar to that of the poly(NMMAm) radical (Fig. lb), although the former is more sharp compared with the latter. 

Next, polymerizations of vinyl monom s were attempted by using poly(NMMAm) radicals as initiator. The poIy(NMMAm) radicals were prepared by polymerization in benzene with DBPOX at room temperature for 2 days. The polymerization system was heated for additional 3 h at 50 °C to decompose the unreacted initiator. To this solution, a second monomer was added and then allowed to stand without stirring at room temperature for a day. The results are summarized in Table 1. Thus, the living poly(NMMAm) radicals can readily initiate vinyl polymerization. 

Table 1. Polymerization of vinyl monomers with poly(NMMAm) radicals in benzene at room temperature ...

Fig. 10a. ESR spectrum change of the polymerization mixture with time at 44 °C in benzene [NMMAm] = 2.45 mol/1, [AIBN] = 1.21 x 10" mol/1. b. Relationship between [poly(NMMAm) radical] and time in the polymerization of NMMAm at 44, SO and SS °C in benzene [NMMAm] = 2.45 mol/1, [AIBN] = 1.21 x 10" mol/1...

A benzene solution of NMAAm (3.73 mol/1) and DBPO (0.175 mol/1) was irradiated at room temperature for 3 h by using a high pressure mercury lamp (100 W) to yield poly(NMAAm) radicals. A separate experiment revealed that the polymerization proceeded quantitatively and the resulting poly(NMAAm) had a weight-average molecular weight of 1.85 x 1 O . ... 

Table 4 shows the results obtained when the poly(NMAAm) radical was allowed to react with MA for five days at room temperature. The added MA was polymerized... 

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