Method INIFER

Inhibitory activity INID codes Inifer method InipolEAP22 Initiators... 

For PIB, a method resulting in end-reactive polymers, however, based on chain transfer reactions during polymerization, was addressed as the cationic inifer method (54). 

A special case of controlled initiation is the inifer method. The word inifer (front initiator transfer agentsl describes compounds that function simultaneously as initiators and as chain transfer agents. The inifer technique provided the first carbocationic route toward the synthesis of telechelic ta. to functional) polymers. 

The Inifer Method. A special case of controlled initiation is the inifer method (17). The word inifer (from initiator trans/t / agents) describes compounds that function simultaneously as initiators and as chain-transfer agents. Chain transfer to inifer regenerates R+. The inifer technique provided the first carbocationic route toward the synthesis of telechelic (a,G) functional) polyisobutylenes and more recendy telechelic poly( >-chlorostyrenes) (18). To prepare telechelic products chain transfer to monomer must be absent, and with BC13 as coinitiator this requirement is fulfilled. 

Nevertheless, a few years ago, Kennedy 66 69) developed a method yielding co-functional polymers by cationic polymerization of vinyl monomers. The principle of the socalled inifer method is to kinetically favor transfer to the initiating species with respect to all other kinds of transfer reactions (especially the transfer to monomer). A typical initiating system is composed of an allyl or benzyl halide and boron trichloride BCl3. This mixture behaves like an alkenium tetrachloro-borate and readily initiates the polymerization of monomers such as isobutene or a-methylstyrene. The efficiency of the halide as a transfer agent depends on the lability of the C—Cl bond and on the molar ratio [RC1]/[BC13],... 

Techniques derived from anionic or cationic living polymerization methods have widely been used. They are efficient because of the long lifetime of the active sites. Once polymerization is completed these sites are used for functionalization purposes. Alternately, unsaturated ionic initiators have been used but to a lesser extent because of the requirement involved that the polymerizable groups remain unscathed during the macromonomer formation. The versatile inifer method has also been applied to the synthesis of macromonomers. 

By reactions (82)-(84), 8 wt. % Br was introduced into the oligomers, an average of 1.95 Br atoms per chain. This work was extended by Kennedy and Smith [91] who selected the co-initiator from a group of transfer agents, which thus had a double function. This new technique they called the inifer method (from co-initiator-trans/er agent). When the rate of transfer to monomer is much less than to the inifer, the formation of the reactive macromer end groups can be better controlled. Macromer formation can be represented by the scheme... 

In addition to the sequential living polymerizations, block copolymers may be synthesized by various reactions of end-functionalized polymers. The method may be subdivided into two classes, as discussed in Section III. A. Most of the examples via living cationic polymerizations are based on vinyl ethers, and Fig. 8 lists the second monomers used in these vinyl ether-based block copolymers. Similar syntheses based on the inifer methods are discussed elsewhere [1,3]. 

Rather interestingly, most of the end-functionalized polyisobutenes have been prepared by the inifer method, in sharp contrast to that those... 

As pointed out already, rather few end-functionalized poly isobutenes have been obtained from isobutene via living cationic polymerization, whereas abundantly via the inifer method followed by various chemical reactions to convert the resulting tertiary chloride terminal (Section IV.A.3) [3],... 

Apart from the syntheses by living cationic polymerizations, a variety of polyisobutene macromonomers have been prepared by converting the chloride terminal derived from the inifer method (Section IV.A.3) [166-170] and more recently from living cationic polymerization... 

In conclusion, these experiments indicate the possibility of synthesizing polyurethanes with polyisobutylene soft segments. The polyisobutylene diols have been synthesized by the inifer method and careful characterization techniques indicate Fn = 2.0. It is anticipated that polyurethanes with polyisobutylene soft segments will exhibit superior thermal, UV, oxidative and chemical resistance to conventional polyurethanes having polyester, polyether, or polybutadiene soft segments. 

Kennedy and Carter used the inifer method to prepare polyisobutylene (PIB) macromonomers with phenol end-groups [186]. The method involves the polymerization of IB with BCl3 andp-hydroxycumylchloride as the initiation system. This system gives rise to transfer reactions but both these reactions and the ion splitting of the BCI4 anion produce the same species, as shown in the following Scheme 54. 

Three methods were developed to overcome transfer to monomer. These are (1) use of inifers (2) use of proton traps and (3) establishing conditions under which the rate of termination is much faster than the rate of transfer to monomer. The first one, the inifer method, is particularly useful in formation of block copolymers. It allows the preparation of head and end (a and to) functionalized telechelic polymers. Bifunctional initiators and transfer agents (inifers) are used. The following illustrates the concept ... 

Macromers can be prepared not only by anionic polymerization, but also by cationic and radical polymerization. Kennedy and his coworkers utilized the inifer method of cationic polymerization in synthesizing polyisobutylene macromers, as follows ... 

Polystyrene and Derivatives. Telechelic polystyrene, poly(2,4,6-trimethylst5Tene), poly(p-methylstyrene), and poly(p-chlorostyrene) can be prepared by living carbocationic polymerization (269-271) or by inifer method (272). While end-quenching the living carbocationic polsrmerization gave quantitatively polymers with sec-benzylic termini, the diciunyl chloride/BClg inifer system yielded a,with olefine end groups were also prepared by dehydrochlorination (272,273). 

Macromonomers from 2-isobutylene have been prepared by the inifer method... 

From the viewpoint of polymer synthesis, the multiplicity of the propagating species provides a possibility to synthesize polymers with varying structures from the different intermediates. In fact, the steric structure of, e.g., polystyrene, polyfvinyl ether)s, and poly(a-methylstyrene) can be controlled by selecting counteranions Recently, Kennedy and his associates studied in detail the control of chain transfer and termination by counteranions (initiators) in isobutene polymerization, and opened a new field of block and graft polymer synthesis (especially by their inifer method)... 

The story of star polyisobutylene (PIB) began with the synthesis of three-arm star PIBs via the inifer method [14]. Over the years the process has been refined... 

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