Copolymer radical

It was recently found that j3-PCPY can also be used as a radical initiator to obtain an alternate copolymer of MMA with styrene [35], which was only possible in the presence of Lewis acids [36,37] in the past. The kinetics of the system has been formulated as Rp a[/3-PCPY] a[MMA] (l/a[Styrene] The values of kp /k, and AE were evaluated as 1.43 x 10 L mol -s and 87 kJ/ mol, respectively, for the system. NMR spectroscopy was used to determine the structure composition and stereochemistry of copolymers. Radical copolymerization of AN with styrene [38] by using /3-PCPY as the initiator at 55-65°C also resulted in an alternate copolymer. Rp is a direct function of /3-PCPY and AN, and is inversely related to styrene. 

The coupling constants for the initial copolymer radicals are given in Table III together with those of the corresponding monomer radicals. The monomer radicals included give coupling constants, which are in... 

Figure 8. Concentration of different radicals measured from ESR spectra during copolymerization of vinyl acetate (VAc) with maleic acid (MA) ana of VAc with fumaric acid (FA) at different molar concentrations of MA in the VAc-MA system and FA in the VAc-FA system, respectively. (VAc-) and (MA-) refer to monomer radicals and (VAc-MA-) and (VAc-MA-) to the copolymer radicals observed. [VAc] = 5.5 X 10 2M ...

AZBN, in contrast to various peroxides, to crosslink EVA copolymers radically, which means that the formation of radicals at the macromolecules does not take place to a sufficient extent. 

Since the decay behaviors of polymer radicals is mainly governed by nmlecular motions of the polymer matrix (79, Si), the fact that the decay behavior raths resembles to that of the pire PTFE suggests that the mcdecular motion of this PMMA radicals is rather same to that of PTFE polymer. This is also good support for the copolymerization of MMA with PTFE. Moreover, this PTFE-PMMA copolymer radical decays more rapidly than either one of the hotnopolymers does. This rapid decay seems to be interpreted as that the PMMA branch of the copolymer is not so long as to retard the molecular motion in the range of lower temperature. 

Figure 7.3. shows the ESR spectrum obtained for the polymerization system vinyl acetate-acrylnitrile (VAc-AN), the spectram is due to three kinds of free radicals, the VAc monomer radical, (OH)CH2-(C )—CH—(OCOCH3). VAc-AN copolymer radical, (OH)CH2—CH (OCOCH3) CH2—(C ) H(CN), and the AN... 

The equation given in Table 1 is quite useful in designing "A" segments of different molecular weight. This is the key to the control of solution viscosity and spray solids in finishes applications of the block copolymers. Radical combination to form tetramethyl succinonitrile is the likely cause of the efficiency factor of 0.5 for azobisisobutytonitrile. 

If the reactor fluid contains two different monomers Mi and M2, both monomers can react with radical sites to form copolymer radicals. If there is no template for the monomer preference to react with the radical site, then the sequence of monomer addition will be based on monomer reactivity rules. Description of copolymerization kinetics differs from that in Fig. 1.3.1 (homopolymerization kinetics) during chain propagation, as shown in Fig. 1.3.4... 

Specifically, the copolymer mechanism expressed in Fig. 1.3.4 is the so-called terminal model, because identification and reactivity of copolymer radicals are solely based on which monomeric unit contains the radical site. Based on the rate coefficients shown above the reaction arrows, the following reactivity ratios are defined ... 

In the first case, radical sites from a particular monomer have the preference of reacting with monomers of the other type that is why the copolymer chain has an alternating sequence between the two monomers. In the second case, radical sites from a particular monomer prefer to react with monomers of the same type. Thus, once a particular monomer is incorporated, the same monomer is added into the copolymer chain in subsequent reactions as long as it is available. One note of caution here is that these copolymerization reactions are also based on statistical rules. For example, if r = 10 and the copolymer radical site comes from monomer 1, then if monomer 2 in the vicinity of the radical site outnumbers monomer 1 by 10 1 there is an equal likelihood for either monomer type to be incorporated in the copolymer chain. 

Fig. 1.3.4 Reaction kinetics mechanism of propagation for free-radical based copolymerization from monomers Mi and Mi, Species Mi- and M2- are copolymer radicals with end-groups coming from monomers Mi and M2, respectively...

For the styrene (S)/acrylic acid (AA) system, the average reactivity ratios for AA (1) and S (2) are r = 0.21 and r2 = 0.33 (Brandrup et al., 1999). This means that both S and AA do not want to react with copolymer radicals of the same moiety. The extent at which this happens is pretty much the same for both monomers thus, with almost equal charges of S and AA, alternating copolymers will be formed. Fiowever, if S outnumbers AA in the initial charge, more S will be added into the copolymer chain. 

In a more recent work (Caneba, 2007a), the FRRPP process was shown to be capable of producing dispersions of VDC copolymer radicals that we were able to maintain their activity prior to reaction with a new set of monomers to form block copolymers. Note that in Table 1.1.2, the LCST of VDC copolymers have been found to be of reasonable values. 

Attempts were made to carry out C-NMR spectroscopy of monomeric components, intermediate, and final copolymer products. Problems include long NMR runs (8-12 h per sample) and the difficulty in completely dissolving the VDC segments of the copolymer samples. Still, it was possible to conclude that the second-stage monomers were incorporated into the intermediate copolymer radicals from the Stage 1 reactor (Fig. 4.3.6). 

Fig. 33. Concentrations of different radicals in copolymerization of VAc with AN at different molar concentrations of AN . VAc and AN, monomer radicals VAc-AN, copolymer radical. [VAc] = 5.5...

When a small amount of a second monomer was added to VAc, the ESR spectrum for the copolymer radical HO-VAc-M2 and that for the monomer radical of the comonomer, i.e., HO—M2 overlapped on that for the monomer radical. As an example, the ESR spectrum obtained for the polymerization system VAc-AN is shown in Fig. 32. The relative concentrations of the three radical species as functions of [AN], shown in Fig. 33, indicate that with the addition of small amounts of the comonomer M2(M2/Mi < 0.5), the concentration of VAc decreases sharply and that of VAc-M correspondingly increases. The concentration ratio [VAc-M ]/(VAc ] plotted against comonomer concentration [M2] gives the characteristic slopes as shown in Fig. 34. 

While living polymerizations can be exploited to produce block copolymers, a copolymerization should give polymer chains that contain both monomers distributed throughout. You might expect that a radical chain polymerization would give a truly random copolymer. Radicals are quite reactive and not known for their selectivity. In fact, though, radical copolymerizations are not totally random, and some quite distinctive polymer compositions can be achieved. Consider a radical polymerization progressing in the presence of two different monomers. 

Limonene can also be copolymerized with acrylonitrile (in DMF at 70°C, initiator AIBN) [69], MMA (xylene, 80°C, BPO) [70], styrene (xylene, 80°C, AIBN) [71], A(-vinylpyrrolidone (dioxane, 80°C, AIBN) [72], and (V-vinyl acetate (dioxane, 65°C, AIBN) [73], always producing alternating copolymers. Radical addition of limonene occurs via the exocyclic isopropenyl group (in contrast to the cationic system, see above). Also, a terpolymer of limonene, MMA, and styrene has been prepared by free-radical copolymerization (xylene, 80°C, BPO) [74]. Poly (limonene-co-MMA) can be converted into a LC polymer (cf. Scheme 2) [75]. 

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