Inifer

Inhibitory activity INID codes Inifer method InipolEAP22 Initiators... 

Interest in anionic polymerizations arises in part from the reactivity of the living carbanionic sites4 7) Access can be provided to polymers with a functional chain end. Such species are difficult to obtain by other methods. Polycondensations yield ro-functional polymers but they provide neither accurate molecular weight control nor low polydispersity. Recently Kennedy51) developed the inifer technique which is based upon selective transfer to fit vinylic polymers obtained cationically with functions at chain end. Also some cationic ring-opening polymerizations52) without spontaneous termination can yield re-functional polymers upon induced deactivation. Anionic polymerization remains however the most versatile and widely used method to synthesize tailor made re-functional macromolecules. 

The former possibility previously described could be refuted by the spin-trap-ping experiments and the living radical polymerization of St with 46. Therefore, 13 was added to the polymerization system to conserve the active site of the inifer-ter. It was expected to reproduce the iniferter site due to the formation of DC radicals which can function as primary radical terminators and/or the effective chain transfer ability of 13. It was pointed out that the DC radical generated from 13 had high selectivity for monomers, i.e., 13 acted as an initiator for the polymerization of St, but did not as an initiator for the polymerization of MA, VAc, and AN [72,175,177]. 

Inifer controlled initiation method, 14 269 Iniferters, 14 297 Inipol EAP22, 3 765 Initial breeding, in nucleation, 3 105 Initial modulus, 19 743 Initial reacting species, in pulp bleaching, 21 32-33... 

New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator-Transfer Agents (Inifers) End Reactive Polyisobutylenes by Semicontinuous Polymerization... 

The inifer technique is a most convenient route for the preparation of well-defined end-reactive polyisobutylenes (PIB)(1). These materials may be linear or three-arm star telechelics carrying exactly 2.0 or 3.0 end-functions, respectively. The inifer technique yields tert.-chlorine-telechelic product, for example,... 

A thorough investigation of the products obtained by the inifer technique has shown that sometimes low molecular weight materials (Mn = from 500 to 6000) may carry "unfired" or "once-fired" end-groups ... 

Semicontinuous polymerization experiments were carried out in a stainless steel enclosure (dry box) under a dry nitrogen atmosphere in three neck flasks (11) equipped with overhead stirrer and an inlet for the continuous introduction of precooled inifer/isobutylene/ solvent feeds to stirred, dilute BCI3/solvent charges. Experiments with binifer were performed at -80°C by the use of CH3Cl/n-hexane solvent mixtures (80/20 v/v), with trinifer at -40°C using CH3CI... 

Conventional polymerizations were carried out by rapidly adding the BCI3 coinitiator to stirred inifer/isobutylene/solvent charges. The composition of the final charges was identical to the final composition of the corresponding semicontinuous runs. Heat evolution could often be observed in conventional batch polymerization upon BCI3 addition. 

Kinetic Considerations. The following elementary reactions describe the polymerization of isobutylene by the inifer/BCl3 system ... 

The dispersion ratio for polymers obtained by bifunctional inifers (binifers) is (6) ... 

Thus when k T [I ]+kf kp [M], the polymer formed at each time element will exhibit M /Mn = 1.5 in polymerization by binifers and Mjj/Mn = 1.33 in polymerization by trinifers. The number average degree of polymerization in inifer polymerization systems is ... 

According to Equation 9 polymers with close to theoretical molecular weight distributions could be prepared even at very high conversions provided [M] and [I] remain constant throughout the polymerization. This condition can be fulfilled by continuously adding a mixed monomer/inifer feed at a sufficiently low constant rate to a coinitiator charge, making certain that the rate of monomer/inifer addition and that of monomer/inifer consumption are equal over the course of the polymerization. 

In semicontinuous polymerization under stationary conditions the concentration of monomer and inifer are constant ... 

Comparing Equations 14 and 19 the rates of polymer formation and inifer addition are equal under stationary conditions ... 

Since the feed contains both the monomer and the inifer dissolved in a common solvent ... 

This simple DPn equation is generally valid for mono- or multifunctional inifers however with multifunctional inifers ktr> j and kt in Equation 21 correspond to one inifer/polymer molecule, i.e., the parameters are not normalized to one functional group. 

The stationary concentration of monomer can be calculated by the following considerations. Comparison of Equations 13, 18 and 19 shows that the rate of cationation is equal to the rate of inifer addition ... 

The above expression contains the three rate constants involved in initiation, k (in C), kc and k, whose values are not known. (Recent attempts failed to determine the value of k due to experimental difficulties [10]). The value of [M] depends on both the relative and the absolute addition rates A and Aj, which means that at a given [M]/[I] in the feed, the [M] would increase with increasing addition rate. It is important therefore that the addition rate be sufficiently low so as to achieve stationary conditions rapidly, i.e., the time to reach stationary conditions should be negligible compared to the polymerization time. Unless this precaution is taken monomer/ inifer may accumulate in the system which may lead to short or in worse cases even to an absence of stationary periods which in turn... 

BC13 IB in initial charge M x 10 Inifer in feed M Feed rate time ml/min min n VMn... 

Table II. Comparison between Conventional Batch and Semicontinuous Inifer Techniques for the Preparation of End-Reactive Polyisobutylenes...

Possibility of unfired and/or once-fired end groups Broad or bimodal and molecular weight distribution Mjj control by nature of inifer (Cj), very reactive or un-reactive inifer unsuitable 100% conversion of both I and M only in specific cases Reactor control difficult, danger of heat jump on rapid BClj introduction... 

The molecular weights of polymers formed in semicontinuous experiments are controlled by the concentration ratio [M]/[I] in the feed, while in batch polymerizations the molecular weights are controlled mostly by the reactivity of the inifer (i.e., the value of the chain transfer constant Cj rendering too reactive or unreactive inifers unsuitable). In batch polymerizations complete depletion of... 

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). 

J.P. Kennedy and R.A. Smith, New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers). II. Synthesis and characterization of a, a>-di(ferf-chloro)polyisobutylenes,. Polym. Sci., Part A Polym. Chem., 18(5) 1523-1537,1980. 

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