Copolymers living systems

Sawamoto et al. have revealed that the ruthenium complex induces the living radical polymerization of MMA [30,273-277]. For example, RuCl2(PPh)3 provided poly(MMA) with Mw/Mn 1.1 and the block copolymers. This system has a unique characteristic in that it is valid not only for MMA and other methacrylates, but also for acrylates and St derivatives. 

They obtained moderately monodispersed (1.2 + 0.1) polymacromonomers with 30% initiator efficiency when short macromonomers (DP = 21 to 75) are polymerized. Higher MW macromonomers polymerized only partially. Evidence for interaction of the PEO ether groups with the catalytic center is given and assumed to be responsible for the shortcomings of the living system. Random and block copolymers of PS and PEO macromonomers, as well as of P(EO-b-S) and P(S-b-EO) macromonomers have also been made [112], The same group successfully prepared PS macromonomers with a norbornene group in the a position [113]. 

Unlike in radical or anionic polymerizations, in ROMP with single-component metathesis catalysts the growing polymer chain remains able to further grow even after consumption of the monomer. This enables the manufacture of block copolymers with interesting physicochemical properties by sequential addition of different monomers to such living systems. 

In a living system, if Mi is much more reactive than M2 and polymerization is allowed to proceed to completion, the end-product is a tapered block copolymer, in which only the middle section contains units of both monomers, e.g. with anti-1-methylnorbomene (Mi)/syw-7-methylnorbomene (M2), see Section VIII.C.4 also with norbornene (Mi)/cyclooctatetraene (M2), catalysed by 8W (R = Me)360. In the extreme case the cross-propagation reactions may be so slight that the product is indistinguishable from a perfect block copolymer, e.g. with bicyclo[3.2.0]hept-2-ene (Mi)/norbornene (M2) catalysed by 18109,597, or with awft -7-methylnorbornene (Mi) syn-1 -methylnorbomene (M2), catalysed by 7 (R = Me)128. The successive polymerization of the two monomers can be readily followed by NMR. 

B. Block Copolymers by Sequential Addition of Monomers to Living Systems... 

Much work has been carried out on phenylacetylene and its derivatives631,648-674. Of particular interest are the ori/io-substituted phenyl derivatives because, unlike their met a and para isomers, they generally give living systems when initiated by MoOCl4/Bu4Sn/EtOH (1/1/1), allowing the preparation of block copolymers. This is the... 

The synthesis of PP-fr-EPR can be accomplished by a stopped-flow polymerization method, whose polymerization time is very short and which is a quasi-living system, in the presence of a MgCl2-supported titanium catalyst [132-135]. The results of GPC, 13C NMR, CFC, DSC, and optical microscopic observation indicated the formation of a block copolymer having a chemical linkage between PP and EPR segments. 

The coordination-insertion type of polymerization has been thoroughly investigated since it may yield well-defined polyesters through living polymerization [20]. When two monomers of similar reactivity are used,block copolymers can be formed by sequential addition to the living system [63]. 

Table III shows the increase of molecular weight of BCMO polymerization with conversion, although the polymer tends to precipitate. The monomer reactivity ratios of DOL-BCMO copolymerization were previously determined as rx (DOL) = 0.65 0.05, r2 (BCMO) = 1.5 0.1 at 0°C. by BF3 Et20 (8). Table IV shows a preparation of block copolymer of DOL, St, and BCMO. In the first step we polymerized DOL and St in the second step we added BCMO to this living system. The copolymer obtained showed an increase of molecular weight, and considerable BCMO was incorporated in the copolymer still remaining soluble in ethylene dichloride. The solubility behavior together with the increase of molecular weight with addition of BCMO shows that this polymer consists of block sequences of DOL-St and (St)-DOL-BCMO. This we call block and random copolymer of DOL-St—BCMO. We can deny the presence of BCMO, St, or DOL homopolymers in this system, but some chain-breaking reactions are unavoidable, leading to copolymer mixtures. Thus, the principle of formation of block copolymers by cationic system is partly substantiated.

Some of these living systems, especially those which generate block copolymers and polymers with reactive end groups, should be commercialized in the near future. 

The inclusion of apparently dead polymer into block copolymer is of interest (Table II). Certainly less of the first PMDS polymer was incorporated in this system than in the corresponding living system, because all the... 

In the study of anionic copolymerization it is possible to use two types of approach. The first method is the use of the classical copolymer composition equations developed for free radical polymerization. The second is unique to anionic polymerization and depends on the fact that for living systems it is possible to prepare an active polymer of one monomer and to study its reaction with the second monomer. The initial rate of disappearance of one type of active end, or the appearance of the other type (usually determined spectroscopically) or the rate of monomer consumption gives directly the reactivity of polymer-1 with monomer-2. It is in principle possible to compare the two methods to see if additional complications occur when both monomers are present together. 

The synthetic copolymers described in the previous section are particularly simple molecules compared to the macromolecules that occur in living systems. Virtually all bio-polymers exhibit some amphiphilic character, due to the presence of polar and lipophilic patches in the single molecule. 

Kunitake and Takarabe" as 2—30 ms. This result seems reasonable since the presence of the methoxy substituent would be anticipated to stabilize a positive charge on the a carbon atom in the case of p-methoxystyrene. Equally interesting is the observation that propagating intermediates are generated most slowly with 12 as catalyst, but once formed these are the longest lived. Perhaps not surprisingly therefore the system displays some of the characteristics of a living system, and allows block copolymer synthesis to be achieved with isobutyl ether. 

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