Long-lived propagating species

Interestingly enough, this process is effective in bulk, in water suspension and in aqueous miniemulsion . The long-lived propagating species can be derivatized into a series of functional groups by addition of properly substituted nitroxides or nonpolymerizable olefins". Moreover, PVac-fc/oc -PS diblock copolymers were synthesized successfully, which is an additional step in the macromolecular engineering of PVac. ... 

Acetylenes copolymerize with each other and with cycloalkenes under the influence of olefin metathesis catalysts, as summarized in Tables 10.6 and 10.7, respectively. Each table is divided into two sections according to whether the catalyst system gives long-lived propagating species or not. 

Tabata, M. Yang, W. Yokota, K. Polymerization of m-chlorophenylacetylene initiated by [Rh(norbornadiene)Cl]2-triethylamine catalyst containing long-lived propagation species. Polym. J. 1990, 22, 1105-1107. 

Table 9. Reported evidence for the formation of living/long-lived propagating species in cationic vinyl polymerization...

In 1975 we found that a long-lived propagating species forms in the polymerization of p-methoxystyrene (pMOS) initiated with iodine in nonpolar media Subsequently, similar results were obtained for the isobutyl vinyl ether (IBVE)/iodine system These monomers have strongly electron-donating substituents that stabilize the propagating carbocations derived from them, so that they are likely to form living polymers. 

It is therefore concluded that the iodine-initiated polymerizations of pMOS and IBVE involve long-lived propagating species in a non-dissociated state. However, these species are not truly living as judged from the M of the formed polymers being not directly proportional to conversion. 

This chapter has shown that there are two extremely different systems forming living (or at least long-lived) propagating species. Table 12 compares these two systems for vinyl ether polymerization. 

In more conventional copolymerization, where both monomers are present at the start of reaction, standard analysis methods are available which were developed for free radical initiation. It is first necessary to enquire whether the techniques will be applicable to anionic systems containing long lived active species. Four propagation steps can be recognized in the copolymerization of two monomers Ml and M2 ... 

All limitations described above do not apply for the systems, which seem to be of considerable practical interest, namely oxazolines. Polymerization of these monomers proceeds practically irreversibly on long-living active species and, as discussed in Section III.F., chain transfer to polymer does not interfere with propagation. On the other hand, due to the possibility of obtaining oxazolines (or 6-membered analogs) with different substituents R ... 

The appearance of an increasing number of processes with long-living active species, such as generation of Ziegler-Natta or lanthanide-based catalysts or new cationic and certain free radical polymerizations with controlled chain propagation, makes the results obtained especially important for polymerization engineering. 

One obvious test of the F-Cat theory was to try to synthesise the perchlorate ester of styrene and to find out whether it will act as a polymerisation initiator however, the ester is stable only in the presence of an excess of styrene. This proved to be the first instance of the stabilisation of a hyperactive ester by an electron donor to give a species which is sufficiently long-lived to be an effective propagator (C). 

Besides confirming that chain propagation involves 1,2 insertion, the simultaneous observation of acyl and alkyl intermediates in the flow cell has shown that both intermediates are relatively long-lived species under catalytic conditions and have also comparable lifetimes in the presence of both CO and styrene [6b]. 

GPC analyses of polymers indicated that the polymerizations proceeded with two kinds of propagation reactions in these systems at low temperatures (about 30° to — 30° C) one of which was suggested to be due to long-lived highly stereospecific propagating species. 

When the propagating species are long-lived it is possible to make block copolymers of controlled chain length by sequential addition of monomers, for example with ClC=CC4H9/ClC=CCi4H29686 693 and with acetylene/norbornene396,628. 

It was found in this experiment that both anionic and cationic species reacted efficiently with methanol in bulk styrene. The bonded dimer cations and the radical anions were converted to long-lived benzyl radicals, which initiated the radical polymerization. The G value of the propagating benzyl radical was only 0.7 in pure styrene, but it increased up to 5.2 in the presence of methanol. A small amount of methanol converted almost all the charge carriers to propagating free radicals this explains why the mechanism of radiation-induced polymerization is changed drastically from cationic to radical processes on adding methanol. 

Under certain conditions, polymerizations of cationic cyclic ethers show the characteristics of living polymerizations in that the propagating species are long-lived and narrow MWDs are obtained. The rate and degree of polymerizations are then given by expressions previously described [Eqs. (10.15) and (10.16)]. Living polymerizations occur when initiation is fast relative to propagation and there is an absence of termination processes. Such conditions are found for polymerizations initiated with acylium (I) and... 

This result is still somewhat complicated but now depends only on the concentrations of long-lived species. The first term in the rate equation for CH3CHO is due to consumption by the initiation reaction and is presumed to be small compared to consumption by the propagation reactions. Thus the second term dominates, and the overall reaction has the form... 

The propagating species involved is not living but long-lived. Catalyst 30 [(1,5-cyclooctadiene) RhCl]2. 

---