Living isobutylene

D.L. Morgan and R.F. Storey, End-quenching of quasi-living isobutylene polymerizations with alkoxybenzene compounds, Macromolecules, 42(18) 6844-6847, September 2009. 

FT-NIR spectroscopy in combination with a fiber-optic probe was successfully used to monitor living isobutylene, ethylene oxide and butadiene polymerizations using specific monomer absorptions. In the case of EO a temperature dependent induction period was detected when 5ec-BuLi/ BuP4 were used as an initiating system. This demonstrates the usefulness of this technique because this phenomenon had not been observed so far by other methods. We have also successfully conducted experiments in controlled radical polymerization. Then we were able to monitor the RAFT polymerization of A -isopropylacrylamide (NIPAAm). Thus it can be expected that with the help of online NIR measurements detailed kinetic data of many polymerization systems will become available which will shed more light onto the reaction mechanisms. Consequently, FT-NIR appears to be a method, which can be applied universally to the kinetics of polymerization processes. 

M. Krombholz, J. E. Puskas, Real-Time Fiber Optic FTIR Monitoring of Sequential Living Isobutylene and Styrene Block Copolymerization, Polymer Preprints 42(1), 339-340(2001). 

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). 

A living cationic polymeriza tion of isobutylene and copolymeriza tion of isobutylene and isoprene has been demonstrated (22,23). Living copolymerizations, which proceed in the absence of chain transfer and termination reactions, yield the random copolymer with narrow mol wt distribution and well-defined stmcture, and possibly at a higher polymerization temperature than the current commercial process. The isobutylene—isoprene copolymers are prepared by using cumyl acetate BCl complex in CH Cl or CH2CI2 at —30 C. The copolymer contains 1 8 mol % trans 1,4-isoprene... 

Thus with aMeSt, the kinetic chain is relatively short, monomer is consumed mainly by initiation and propagation, and chain transfer by the HSiCCHj CH H C Q initiator is unfavorable (see Sect. III.B.3.b.i.). In contrast, with isobutylene the kinetic chain may live longer because it is sustained by thermodynamically favorable chain transfer by the initiator. Scheme 5 illustrates the mechanism of isobutylene polymerization by the HSi(CH3)2CH2CH29>CH2Cl/Me3Al system. The kinetic chain is sustained by chain transfer loops shown on the left margin of the Scheme. 

In view of the great structural similarity between the propagating sites in the cationic polymerization of P-PIN and isobutylene and their respective polymers (4), and our considerable experience accumulated with the LC Pzn of isobutylene [1-3], efforts have been made to adapt LC Pzn conditions found to yield living polyisobutylenes for the polymerization of p-PIN. 

Thus a variety of P-PIN polymerizations have been carried out under conditions isobutylene yields living polymer. Table 1 shows the results of representative experiments. 

Living polymerization of isobutylene (IB) by di- and trifunctional initiators to make the nearly uniform rubber mid-block... 

Poly(styrene-/7-isobutylene-/ -styrene) (PS-PIB-PS), triblock copolymers can be prepared via coupling of living PS-PIB diblock copolymers in a one-pot procedure [12]. 

Cao X. and Faust R., Polyisobutylene based thermoplastic elastomer 5. Poly(styrene-b-isobutylene-b-styrene) tri-block copolymers by coupling of living poly(styrene-b-isobutylene) di-block copolymers. Macromolecules, 32, 5487, 1999. 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

Nagy, A., Qrszagh, I., and Kennedy, J.P. Living carbocationic copolymerizations. II. Reactivity ratios and microstructures of isobutylene/p-methylstyrene copolymers, J. Phys. Org. Chem., 8, 273, 1995. Puskas, J.E. and Paulo, C. Synthesis and Characterization of Hyperbranched Polyisobutylenes. Proceedings of the World Polymer Congress (lUPAC Macro 2000), 384, 2000. 

Song, J., Bodis, J., and Fhiskas, J.E. Direct functionalization of poly isobutylene by living initiation with alpha-methylstyrene epoxide, J. Polym. Set, Polym. Chem., 40, 1005, 2002. 

However, chain end functionalization does not occur when these reagents are added to living polymerization of less reactive monomers such as isobutylene (7). 

The synthesis of A2B miktoarm star polymers has been discussed and exemplified using PIB as a component. The synthesis involves a quasi living cationic polymerization of isobutylene from a monofunctional cationic initiator. This initiator also contains a blocked hydroxyl group. Eventually, the blocked hydroxyl group of the initiator is deblocked, and functionalized with a branching agent. This activated reagent is then used for an atom transfer radical polymerization process of /erf-butyl acrylate (18). 

In the course of quasi living carbocationic isobutylene polymerization it is possible to functionalize the polymer at their end groups by quenching with reactive compounds. The various possibilities are shown in Table 6.2. 

R. Faust and J.P. Kennedy, Living carbocationic polymerization. XXI, Kinetic and mechanistic studies of isobutylene polymerization initiated by trimethylpentyl esters of different acids, J. Macromol. Sci.-Chem., 27(6) 649-667,1990. 

As seen in Scheme 2 (A), the most of the syntheses have been carried out with the HI/I2 and HX/ZnX2 (X = halogen) initiating systems, because these systems can effectively polymerize a large variety of vinyl ethers, including those with pendant functions, into well-defined living polymers [1]. In this way, the sequential living cationic polymerizations of two vinyl ethers are mostly "reversible i.e., both A - B and B - A polymerization sequences are operable. This is in sharp contrast to the block copolymerization of a vinyl ether with a styrene derivative or isobutylene (see below), where such reversibility often fails to work. 

As the range of styrene derivatives for living cationic polymerization expands (Chapter 4, Section V.C), a variety of block copolymers with sty-renic segments have been synthesized. Most of the reported examples involve combinations of styrene derivatives with vinyl ethers or isobutene. Some examples of styrene derivative-vinyl ether block copolymers are listed in Fig. 6 [16,87-89]. Monomers that can form similar block copolymers with isobutylene are listed in Fig. 7 (Section III.B.3). 

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