Polymerization methods polyisobutylene

Preparations of macro-initiators or telechelic polymers by cationic methods have been executed primarily by polymerizing isobutylene in the presence of a co-initiator that also functions as a chain transfer agent. A typical reaction sequence is shown in Scheme 1, outlining the synthesis of difunctional polyisobutylene (PIB), which is then used to initiate the polymerization of a-methyl styrene (ffi-MS) to produce an A-B-A type block copolymer. By similar methods, polyisobutylenes with phenol, phenyl, cyclopentadiene, and olefin termini have been synthesized. 

Harada et al. explored the compatibility of CD with various polymeric backbones including polyethylene oxide) (PEG), polypropylene oxide) (PPG), polyisobutylene (PIB), and polyethylene (PE) [77-87]. The corresponding polyrotaxanes (36 to 47) were prepared by Method 2, simply by mixing a solution of CD and the polymer. The cavity size of CD was found to be the main factor in the threading process. While one a-CD (20) was threaded per two repeat units in PEG (m/n=0.50) and every three repeat units for PE (m/n=0.333), it was too small for PIB and PPG. On the other hand, two PPG units complexed per /(-CD (21). Because the upper limit of the min value is controlled by the depth of the CD cavity, the m/n value remained constant for the same type of backbone, irrespective of the end group. However, the nature and concentration, i.e., polymer... 

A method for preparing polyisobutylene-g-acrolein and then converting into polyisobutylene-g-alkylamines is described. These polymeric agents are designed for binding biomacromolecules and metal ions to the amine surface. 

Fundamental studies directed toward the elucidation of the mechanism of olefin i.e.f isobutylene, polymerizations yielded a new method for the synthesis of novel linear and tri-arm star telechelic polymers and oligomers [1,2]. The synthesis involves the use of bi- or tri-functional initiator/transfer agents, so called inifers (binifers and trinifers), in conjunction with BCI3 coinitiator and isobutylene, and gives rise to polyisobutylenes carrying exactly two or three terminal -CH2-C(CH3)2Cl groups. These liquid telechelic polyisobutylene chlorides can be readily and quantitatively converted to telechelic polyisobutylene di- or tri-olefins [2,3] which in turn can quantitatively yield by hydroboration/oxidation telechelic polyisobutylene di- and triols [4,5]. 

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. 

A new method for the synthesis of polyisobutylene-based block copolymers, involving living carbocationic polymerization of isobutylene and subsequent living anionic polymerization of methacrylic monomers has been demonstrated. Di- and triblock copolymers nearly free of PIB precursor and with narrow and unimodal MWD were synthesized under well-controlled conditions. 

Polymerization by the inimer technology has received much attention from Kennedy and Puskas, specifically for the synthesis of hyperbranched polyisobutylenes (PIB)s and copolymers thereof in a one-pot method [67]. While this convergent approach complicates the structural analysis of the branched polymers, fragmentation of the resulting polymer is possible in some cases to allow such analysis [68]. Branching ratios (BR) can be calculated directly from the molecular weight of the branched polymer as per Equation 30.9, to give an indication of the number of branches contained within the molecules, as the ratio of the measured for the polymer obtained to the theoretical... 

The discovery of living cationic polymerization has provided methods and technology for the synthesis of useful block copolymers, especially those based on elastomeric polyisobutylene (Kennedy and Puskas, 2004). It is noteworthy that isobutylene can only be polymerized by a cationic mechanism. One of the most useful thermoplastic elastomers prepared by cationic polymerization is the polystyrene-f -polyisobutylene-(>-polystyrene (SIBS) triblock copolymer. This polymer imbibed with anti-inflammatory dmgs was one of the first polymers used to coat metal stents as a treatment for blocked arteries (Sipos et al., 2005). The SIBS polymers possess an oxidatively stable, elastomeric polyisobutylene center block and exhibit the critical enabling properties for this application including processing, vascular compatibility, and biostability (Faust, 2012). As illustrated below, SIBS polymers can be prepared by sequential monomer addition using a difunctional initiator with titanium tetrachloride in a mixed solvent (methylene chloride/methylcyclohexane) at low temperature (-70 to -90°C) in the presence of a proton trap (2,6-dt-f-butylpyridine). To prevent formation of coupled products formed by intermolecular alkylation, the polymerization is terminated prior to complete consumption of styrene. These SIBS polymers exhibit tensile properties essentially the same as those of... 

The original commercial methods for preparing high molecular weight polyisobutylene by cationic polymerization in good yields were reported in 1940. The reaction was carried out at 40 to 80°C in a diluent with BF3 catalysis [72]. This developed into current commercial practices of polymerizing isobutylene at 80 to 100°C, using liquid ethylene or methyl chloride as a diluent [73,74]. Even at these low temperatures the reaction is quite violent. Methods were developed, therefore, to dissipate... 

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 ... 

Other Methods. Seqnential living cationic polymerization is primarily used to prepare block copol5uners containing a vinyl ether block, or polyisobutylene (18-20). It can also be conpled with other techniques (18,20). However the range of monomers that may be pol5unerized by this method is comparatively limited and consequently living cationic pol5unerization is only used in prescribed circumstances. 

Graft Polymerization. The most effective method for graft polymerization of VF is radiation polymerization (80). VF has been grafted to low density polyethylene, polyisobutylene, and polyamides (85-87). The density of the graft copolymers is higher than that of the starting homopolymer. Typically, VF is brought in contact with the polymer simultaneously with irradiation. 

---