Cationic chain polymerization living

Cationic Polymerization. For decades cationic polymerization has been used commercially to polymerize isobutylene and alkyl vinyl ethers, which do not respond to free-radical or anionic addition (see Elastomers, synthetic-BUTYLRUBBEr). More recently, development has led to the point where living cationic chains can be made, with many of the advantages described above for anionic polymerization (27,28). 

Surface-initiated living cationic polymerization of 2-oxazolines on planar gold substrates has been reported by Jordan et al (Fig. 9). SAMs of initiators on a planar gold substrate have been used to initiate the living cationic ringopening polymerization of 2-ethyl-2-oxazoline. The polymer chain end was functionalized with an alkyl moiety by means of a termination reaction in order to form an amphiphilic brush-type layer. The resulting layers (thickness... 

P-Pinene which is a main component of natural turpentine can be polymerized by living cationic isomerization polymerization [82] (Scheme 10) using TiCl3(OfPr) as a Lewis acid in conjunction with rc-Bu4NCl in CH2C12 at -40 °C. When initiator 31 was used, polymerization led to a poly(P-pinene) macromonomer with a methacrylate function at the a end and a chlorine atom at the co chain end [83]. Three macromonomers were prepared with DPn=8,15, and 25 respectively they had narrow MWD (Mw/Mn= 1.13-1.22) and the reported functionality was close to 1 (Fn=0.90-0.96). 

Since the appearance of the major review on the living carbocationic polymerization of olefins [1], a large body of pertinent additional data have been generated relative to this subject [2-17]. The significance of these data prompts us to combine this recently-acquired information with earlier data and to integrate all kinds of cationic olefin polymerizations into a comprehensive mechanism, be these induced by means of a purposely-added initiator or by an impurity, both of which can lead to conventional (presence of chain transfer and/or termination) or living (absence of chain transfer and irreversible termination) polymerizations. 

The differences between the step-growth and the chain polymerization mechanisms are summarized in Table 1.2. Notice that chain polymerizations may include bimolecular termination reactions (as in the free radical mechanism) or may not (as in living anionic or cationic polymerizations). 

Moreover, the absence of unsaturations in the resulting polymers clearly indicated the absence of chain transfer reactions. Similar living polymerization characteristics were reported for cationic isobutene polymerizations initiated with cumyl methyl ethers (Scheme 8.6) with BCI3 as activator [29, 30] as well as with cumyl ethers and cumyl esters as initiators together with titanium tetrachloride as activator [31],... 

Classification of Polymers Properties 1223 Addition Polymers A Review and a Preview 1225 Chain Branching in Free-Radical Polymerization 1227 Anionic Polymerization Living Polymers 1230 1 Cationic Polymerization 1232... 

One of the most important breakthroughs in cationic polymerization is the discovery of living cationic polymerization. The inherent and serious drawback of cationic vinyl polymerization is instability of the carbocationic intermediates, which causes the chain transfer leading to the formation of polymers of broad molecular weight distribution. Higashimura, Sawamoto, and coworkers proposed and verified experimentally that living cationic polymerization can be attained by stabilizing the carbocationic intermediate by nucleophilic interaction with a suitably nucleophilic counter anion or an externally added Lewis base (B) (Scheme 3) [96-98]. 

The kinetics of free radical polymerization and the molecular weight distribution of the polymer were already discussed in Section 1.6.2 of Chapter 1. To improve the chemical and mechanical properties of the polymer great efforts were undertaken a number of years ago to achieve narrow distributions. This is possible with anionic or cationic — so-called living — polymerization, in which chains can not terminate or transfer and grow at a rather uniform rate, thus yielding a polymer with a polydispersity close to one. This type of polymerization requires very special operating conditions and high purity of the feed, however. 

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