Polymerization of deuterated

Powells et al. pdymerized stereospecifica% deuterated acrylic and methr acrylic esters to h y isotactic polymers tmder several conditions with a number of anionic initiators. They analyzed the polymers by NMR spectroscopy to get the information on the mode of monomer approach to the growing anion. The results of the polymerization initiated with fluorenyllithium suggest that there are two transition states leading to an isotactic placement which differ in the degree of solvation. One is derived from a naked contact ion pair and forms the polymer of threo-meso configuration. The other is apparently formed by the specifically solvated contact ion pair and forms erythro-meso. A very similar study was reported on the anionic polymerization of deuterated ntethyl acrylate. " ... 

Polymer (B) Characterization Solvent (A) ethylene/l-bntene copolymer (denterated) 2000BY1 M /kg.mor = 55,MJkg.moT = 169, 3 mol% 1-butene, synthesized from polymerization of deuterated 1,3-butadiene with controlled 1,2-addition, Polymer Source, Inc., Dorval, Quebec ethane C2H6 74-84-0 ... 

The most famous mechanism, namely Cossets mechanism, in which the alkene inserts itself directly into the metal-carbon bond (Eq. 5), has been proposed, based on the kinetic study [134-136], This mechanism involves the intermediacy of ethylene coordinated to a metal-alkyl center and the following insertion of ethylene into the metal-carbon bond via a four-centered transition state. The olefin coordination to such a catalytically active metal center in this intermediate must be weak so that the olefin can readily insert itself into the M-C bond without forming any meta-stable intermediate. Similar alkyl-olefin complexes such as Cp2NbR( /2-ethylene) have been easily isolated and found not to be the active catalyst precursor of polymerization [31-33, 137]. In support of this, theoretical calculations recently showed the presence of a weakly ethylene-coordinated intermediate (vide infra) [12,13]. The stereochemistry of ethylene insertion was definitely shown to be cis by the evidence that the polymerization of cis- and trans-dideutero-ethylene afforded stereoselectively deuterated polyethylenes [138]. 

The polymerization of St with 56 as the initiator is considered to proceed via a reaction mechanism in Eq. (56), being identical to the models in Eqs. (18) and (20). The structure of both chain ends of the resulting polymer was confirmed by NMR using the deuterated St as the monomer. The polymerization with BPO and TEMPO without isolation of the adduct would also proceed via a similar path. In the absence of BPO, it has been reported that the radicals produced by spontaneous initiation according to the Mayo mechanism react with TEMPO to yield the adducts, and then they initiate polymerization [206]. 

The same type of addition—as shown by X-ray analysis—occurs in the cationic polymerization of alkenyl ethers R—CH=CH—OR and of 8-chlorovinyl ethers (395). However, NMR analysis showed the presence of some configurational disorder (396). The stereochemistry of acrylate polymerization, determined by the use of deuterated monomers, was found to be strongly dependent on the reaction environment and, in particular, on the solvation of the growing-chain-catalyst system at both the a and jS carbon atoms (390, 397-399). Non-solvated contact ion pairs such as those existing in the presence of lithium catalysts in toluene at low temperature, are responsible for the formation of threo isotactic sequences from cis monomers and, therefore, involve a trans addition in contrast, solvent separated ion pairs (fluorenyllithium in THF) give rise to a predominantly syndiotactic polymer. Finally, in mixed ether-hydrocarbon solvents where there are probably peripherally solvated ion pairs, a predominantly isotactic polymer with nonconstant stereochemistry in the jS position is obtained. It seems evident fiom this complexity of situations that the micro-tacticity of anionic poly(methyl methacrylate) cannot be interpreted by a simple Bernoulli distribution, as has already been discussed in Sect. III-A. 

Polymerization of MM in the presence of syndiotactic PMM was also reported. In this case, PMM of mostly isotactic structure was produced. Interaction between growing chains and the template is rather weak. The template influence is not as pronounced as in the case of isotactic template. Matsuzaki at al used deuterated syndiotactic PMM as template for polymerization of MM. The measurements of tacticity by NMR were... 

This model had been proposed by Fowells et al. (17) on the basis of NMR measurements of partially deuterated polymers prepared in the system THF/Li, and it was applied by Fisher and Szwarc (3o) and Sigwalt and coworkers (31,32)to the polymerization of 2-vinyl pyridine. 

The propylene oxide complex not only dissociated into its components but also transformed to either an oligomer or a polymer of propylene oxide when it was allowed to stand in solution. This transformation could be followed by H-NMR techniques with the use of a-deuterated propylene oxide instead of the non-deuterated one. Its rate depended on the nature of solvent and on the temperature. This experimental result implies that the monomer liberated by dessociation of the complex is polymerized by the catalyst, that only a minute fraction of the organozinc component of the complex actually acts as a catalyst for polymerization, and that the rate of propagation is far faster than that of initiation. These implications together with the evidence that coordination of the monomer to the catalyst is a prerequisite for the stereospecific polymerization led us to the detailed studies of the bulk polymerization, that is, the polymerization of propylene oxide in propylene oxide solution. 

Oguni,N., Fujita,T., Tani.H. Stereospecific polymerization of propylene oxide and its a-deuterated derivative by bis(ethylzinc) t-butylamine in the presence of water as a catalyst (in preparation). 

NMR studies of polymers made with deuterated monomers provide additional information on the cyclic isotactic transition state. Miyazawa and Ideyuchi (97) have shown that the isotactic polymerization of propylene takes place with cis opening of the olefinic double bond. This shows that the 4-membered cyclic transition occurs with reaction of the new monomer on the front side of the propagating ion as illustrated in Fig. 12. 

In the polymerization of allyl acetate, transfer to monomer produces an unreactive radical which fails to re-initiate growth of the polymer chain. Bartlett and Tate (31) compared the rates of polymerization for the unlabelled monomer and.the deuterated monomer CH2 CH-CD2 0-CO CH3. The deuterated monomer polymerized more rapidly giving a product of higher molecular weight. These observations suggest that the rate of polymerization and the molecular weight of the polymer are controlled by the reaction... 

Rp k 2 (10), and thus the relative change in rate should be proportional to the square root of the isotope effect. We felt that synthesis and polymerization of two partly deuterated vinyl acetates, trideuterovinyl acetate (D CD - OAc) and vinyl trideuteroacetate =CH-0-C-CD ) cou settle the question... 

Bulk Polymerization The conversion versus time plot for the bulk polymerizations of vinyl acetate and its deuterated analogues is shown in Figure 1. Vinyl tridueteroacetate has a conversion rate of 9.9 x 10 3/min which is identical with that of vinyl acetate (9.5 x 10 3/min) within the experimental error. However, trideuterovinyl acetate has a much higher conversion rate (1.69 x 10 2/min). The ratio of the rate of polymerization of tridueterovinyl acetate to the average of the other two monomers is 1.74 -. 03. 

The adoption of reaction models available for the polymerization of conjugated dienes by Ni- and Ti-catalysts to the polymerization of BD by Nd catalysis is justified by the similarities of the respective metal carbon bonds. In each of these mechanistic models the last inserted monomer is bound to the metal in a 3-allyl mode. The existence of Ni- -allyl-moieties was demonstrated by the reaction of the deuterated nickel complex [ rf- C4D6H)NiI]2 with deuter-ated BD (deuterated in the 1- and 4-position). After each monomer insertion a new 3-allyl-bond is formed [629]. As TT-allyl-complexes are known for Ti and Ni this knowledge has been adopted for Nd-based polymerization catalysts [288,289,293,308,309,630-636,638-645]. 

Fig. 33. a Volume fraction of deuterated poly(ethylenepropylene), dPEP (full dots) and pro-tonated PEP (open circles) versus depth, for a degree of polymerization N-2300 for both constituents, after a 4 h quench to T=294 K (Tcb 365 K). Profiles are obtained with the time of flight forward recoil spectrometry (TOF-FRES). The dashed line indicates the surface domain thickness l(t). b Plot showing the growth of the surface domain thickness (t) vs t1/3. From Krausch et al. [136]... 

One of the well documented examples for these exchange reactions is due to studies of the polymerization of jwopylene sulfide . A mixture of non-dmterated and deuterated preformed polymers gives a copolymer, in which the deuterated and non-deuterated units are distributed at random. 

The above mechanisms for cis-1,4 polymerization of isoprene or isotactic polymerization of acrylates assume that the configuration of each unit is fixed at the moment of reaction and that no racemization occurs between additions of monomer molecules. Little evidence for the validity of the mechanisms was available when suggested. Recently it has been possible to obtain information, from NMR studies, on the reaction path. This evidence is of two types and depends on the polymerization of stereospecifically deuterated monomers to determine the mode of approach of monomer molecules and on direct observations of NMR spectra of the terminal monomer unit in the polymer. 

Copolymers have been prepared using (tt-CsHj )2TiCl2/AlEtj. The rates of polymerization at constant concentration of catalyst and monomer increase with increase of deuterated styrene in the monomer mixture [162], but without differences in the molecular weights of the polymers. Similar findings were obtained with the TiCl4/AlEt3(Al/Ti = 3) catalyst at 60°C [78a]. The explanation for the rate increase was considered to be an increase in the concentration of active species in the presence of the deuterated monomer. 

Structural studies of polymer materials often use neutron scattering techniques. In such circumstances the use of deuterated chains can be necessary because it overcomes problems associated with inelastic scattering. In this example, a commercial sample of polystyrene-d7 is polymerized in such a way as to maximize yield due to the high cost of the monomer. There is lillle advantage in polymerizing styrene in solution unless large quantities are required (where heat transfer becomes a problem). Polystyrene can be polymerized in the... 

The peak at 0.97 ppm in the spectrum in Fig. 7 should be due to the proton of this partially deuterated methyl group. As mentioned above, the Tx for this peak was much longer than those for other two peaks. The longer should be due to the loss of dipolar relaxation from the two protons in the methyl group. The amount of CHD2 group was determined to be 0.71 per polymer molecule. On the other hand, some coinitiator is usually necessary for the cationic polymerization of styrene by metal halide.52 In this work the coinitiator was a small amount of water which was admitted incidentally into the reaction mixture. 

Polymerizations of MMA with Grignard reagents were also studied using the totally deuterated monomer technique.26,27,63,65-68 n-Butylmagnesium chloride reacts with the C=0 double bond of MMA as well as the C=C double bond... 

Table 11. Polymerization rate and elementary rate constants in the free radical polymerization of methyl methacrylate and vinyl acetate in benzene and deuterated benzene at 30 °C17 ...

The structure of this unique radical was confirmed later by irradiation of deuterated polymers [83, 92]. Fischer [88, 89], studying the transient radical formed during redox polymerization of methylmethacrylate, was able to confirm the non-equivalence of the two 3-protons and the free-rotation of the methyl group. 

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