Copolymerization block formation

It was also discovered at Phillips. that the four rate constants discussed above can be altered by the addition of small amounts of an ether or a tertiary amine resulting in reduction or elimination of the block formation. Figures 13 and 14 illustrate the effect of diethyl ether on the rate of copolymerization and on the incorporation of styrene in the copolymer. Indeed, random copolymers of butadiene and styrene or isoprene and styrene can be prepared by using alkyllithium as initiator in the presence of small amounts of an ether or a tertiary amine. 

The measured values of the reactivity ratios for copolymerization reactions involving olefins (particularly those with four or more carbon atoms) where polymerization has been initiated by co-ordination catalysts has been examined by Kissin. In general there is a tendency for block formation to take place and the distribution of monomer units in the copolymers is in general accord with... 

Polymerization with the monollinctional monomers (4 and 6) was used to estimate the reactivity ratios for copolymerization with NVP (rs = 0.32, riwp = 0.97 and = 0.61, rNvp = 1.31). This study showed that both these allyl carbonate and isopropenyl carbonate monomers copolymerize in an almost statistical manner and that copolymerization with 5 and 7 could be predicted to produce random copolymer networks without significant block formation. We produced materials containing 5, 10, 15 and 20 wt% of 5-FU by copolymerization with 5 and 7. However, degradation of the allyl carbonate crosslinks in copolymers with 5 appears to be very slow and these materials were... 

To deepen these results, the same OA alkyl a-olefins already mentioned were also copolymerized in addition to styrene, with 1-vinyl-naphthalene or 2-methylstyrene with the same Ziegler-Natta catalyst. Fractionation by solvent extraction as well as the optical properties and X-ray spectra demonstrate the formation of an isotactic copolymer which is, at the first sight predominantly random but also block formation seems to occur, depending on the reactivity of vinyl aromatic monomers with respect to the a-olefin and on the composition of the starting co-monomer mixture. The remarkable contribution to optical rotation by aromatic units observed in their copolymers with (/ )3,7-dimethyl-l-octene is at least 10—15% larger than predictable from the corresponding model. The CD spectra relative to the formally forbiden electronic transition of lowest energy (with very low ellipticity) of aromatic nuclei show that, when inserted in OA copolymers, they assume a preferential chiral conformation [171]. (see chapter of Chiellini etd.). 

GopolymeriZation Initiators. The copolymerization of styrene and dienes in hydrocarbon solution with alkyUithium initiators produces a tapered block copolymer stmcture because of the large differences in monomer reactivity ratios for styrene (r < 0.1) and dienes (r > 10) (1,33,34). In order to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such as tetrahydrofuran or an alkaU metal alkoxide (MtOR, where Mt = Na, K, Rb, or Cs). In contrast to Lewis bases which promote formation of undesirable vinyl microstmcture in diene polymerizations (57), the addition of small amounts of an alkaU metal alkoxide such as potassium amyloxide ([ROK]/[Li] = 0.08) is sufficient to promote random copolymerization of styrene and diene without producing significant increases in the amount of vinyl microstmcture (58,59). 

To elaborate a theory of interphase copolymerization at an oil-water boundary the necessity arises to consider initially the growth of an individual polymer chain near the surface separating the organic and water phases. By the model introduced in paper [74], molecules of only one of the monomers are presumed to be solved inside either of these two phases. A theoretical examination of the formation of macromolecules turns out here to be substantially simpler, since their chemical structure under such an approximation is the same as that of a traditional block copolymer. 

Thus, the problem on the growth of a block copolymer chain in the course of the interphase radical copolymerization may be formulated in terms of a stochastic process with two regular states corresponding to two types of terminal units (i.e. active centers) of a macroradical. The fact of independent formation of its blocks means in terms of a stochastic process the independence of times ta of the uninterrupted residence in every a-th stay of any realization of this process. Stochastic processes possessing such a property have been scrutinized in the Renewal Theory [75]. On the basis of the main ideas of this theory, the set of kinetic equations describing the interphase copolymerization have been derived [74],... 

The overall rate V of the interphase copolymerization equals the sum of rates of the formation of homopolymer blocks in each phase... 

The exclusive formation of the block copolymer has been confirmed by selective fractionation, NMR spectroscopy, and SEC analysis. For instance, the copolymerization of eCL and 6VL has been followed by SEC. Figure 2 compares the SEC chromatograms of the first PCL block and the final poly(eCL-h-6VL) diblock copolymer. The molecular weight of the macroinitiator is shifted towards higher values in close agreement with the theoretical value expected from the comonomer-to-Al(OzPr)3 molar ratio, and the MWD remains very narrow during the copolymerization process (PDI=1.10). 

It is highly unlikely that the reactivities of the various monomers would be such as to yield either block or alternating copolymes. The quantitative dependence of copolymer composition on monomer reactivities has been described [Korshak et al., 1976 Mackey et al., 1978 Russell et al., 1981]. The treatment is the same as that described in Chap. 6 for chain copolymerization (Secs. 6-2 and 6-5). The overall composition of the copolymer obtained in a step polymerization will almost always be the same as the composition of the monomer mixture since these reactions are carried out to essentially 100% conversion (a necessity for obtaining high-molecular-weight polymer). Further, for step copolymerizations of monomer mixtures such as in Eq. 2-192 one often observes the formation of random copolymers. This occurs either because there are no differences in the reactivities of the various monomers or the polymerization proceeds under reaction conditions where there is extensive interchange (Sec. 2-7c). The use of only one diacid or one diamine would produce a variation on the copolymer structure with either R = R" or R = R " [Jackson and Morris, 1988]. 

Deters (14) vibromilled a blend of cellulose and cellulose triacetate. The acetic acid content of cellulose acetate decreased with grinding time (40 h) while that of the cellulose increased, suggesting the formation of a block or graft copolymer or of an esterification reaction by acetic acid developed by mechanical reaction. Baramboim (/5) dissolved separately in CO polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). After mixing equal volumes of solutions of equivalent polymer concentration, the solvent was evaporated at 50° C under vacuum and the resultant product ball-milled. The examination of the ball-milled products showed the formation of free radicals which copolymerized. 

Copolymerization is a facile method to diversify the structure of polymer materials. However, if the polymerizabiHties of comonomers are far from each other, copolymerization is essentially difficult, resulting in the formation of a mixture of the homopolymers and/or the copolymer with block sequences. This is the case for the anionic copolymerization of epoxide and episulfide, where the po-lymerizabihty of episulfide is much higher than that of epoxide, and the copolymer consisting mostly of -S-C-C-S- and -O-C-C-O- homo sequences is formed [87]. As mentioned in the previous sections, the zinc complex of /-methylpor-phyrin brings about polymerization of both epoxide and episulfide. 

Chemical processes are far more varied and may involve either the formation of radicals or ions along a polymeric backbone. Both cationic processes3 as well as radical processes have been widely used for graft copolymerization of vinyl monomers onto various polymers. Radical graft copolymerization has been reported for many polymers including styrene-butadiene block copolymers, and acrylonitrile-butadiene-styrene terpolymer, ABS.3 7 9... 

A typical procedure for the synthesis of a propylene-MMA diblock copolymer is as follows. A living polypropylene (Mn = 16,000, Mw/Mn = 1.2) was prepared at —78 °C in a toluene solution of the V(acac)3/A1(C2H5)2C1 catalyst, followed by the addition of MMA. The block copolymerization with MMA was carried out for 5 h at 25 °C, resulting in the formation of an almost monodisperse block copolymer (K I0 = 18,000, Mw/Mn = 1.2). The block copolymer was treated with acetic acid in which the homopolymer of MMA would be soluble. No soluble polymer was detected. In addition, the insoluble polymer was treated with boiling acetone. Again, no soluble polymer was found. These results indicate the formation of a diblock copoly-... 

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