PIB-based block copolymer

PIB based block copolymers are of interest for biomedical applications due to their superior biostability and biocompatibility (30). 

In this chapter, synthetic methodologies for PIB-based block copolymers, as outlined in Scheme 1, are reviewed with examples developed mainly in our laboratory. 

A new synthetic route for the preparation of polyisobutylene (PIB) based block copolymers was developed by combining living carbocationic and anionic polymerizations. Living PIB chains were quantitatively end-capped with 1,1-diphenylethylene (DPE) leading to 1,1-diphenyl-l-methoxy (DPOMe) and/or 2,2-diphenyl vinyl (DPV) termini. This end-capping process is very sensitive to temperature, and retroaddition of DPE occurs in an equilibrium reaction above about -70 °C. Both the DPOMe and DPV terminated PIBs, and the mixtures of the two endgroups were quantitatively metalated with K/Na alloy, Cs metal and Li dispersion in THF at room temperature. 

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. 

The concept was further extended to the preparation of PtBA-l7-PIB-l7-PSt (ABC) triblock and amphiphilic penta-block copolymers based on PIB. ° ... 

Table 1 a Results of a droplet size determination for the PDMS/PIB system /t43, , using LAOS measurements and the relation according to Eq. 13 compared to radii from a microscopic analysis / 43,M- In the first series of blends, PDMS/PIB was prepared using manual mixing with a spatula, PDMS/PIB-100 and PDMS/PIB-300 rpm with an electrical stirrer at the designated rotation speed. In the second series the blends differed in their block-copolymer content, as stated in wt% of block-copolymer in the PDMS phase, b Estimation of the interfacial tension F using Eq. 13 based on additional information about the radius from microscopic droplet size determination... 

The carbocationic polymerization of ND proceeds with transannular rearrangement, where both double bonds are involved. Thus, a product polymer has a rigid and high-Tg ( 320 °C) tricyclic repeat stmcture, suitable for thermoplastic applications. Peetz et al. examined cationic polymerization of ND using the 2-chloro-2,4,4-trimethylpentane (TMP-Cl)/TiCl4 initiating system. The use of a proton trap or an added base at -35 to -60 °C rendered the reaction controlled, and the inaeased linearly with conversion up to approximately 45%. The produrt polymer chain consisted of approximately equal amounts of exo/exo and exo/endo connected tricyclic repeat units. Furthermore, a set of three-arm star block copolymers, t-cumyl(PIB- -PND)3 and t-cumyl (PND-b-PIB)3, were prepared and characterized. ... 

Kennedy s group also extended its work on the synthesis of octa-arm star block copolymers [40]. The synthetic strategy is very similar to the method described above for the synthesis of allyl group-terminated octa-arm star PIB. The synthesis involved the use of an octafimctional calix(8)arene-based initiator to initiate the polymerization of isobutylene to desirable molecular weights then st)n ene or / -chlorostyrene was polymerized to obtain the sought stars,... 

In a more recent study [88], the chlorine end groups of PIB were quantitatively converted to bromoester groups to facilitate ATRP from end-positioned activated ester groups (Scheme 11.21). In this way, the capping with short blocks of PSt observed in the earlier method could be avoided. The concept was further extended to the preparation of PIB-h-PMMA diblock [89], poly(t-butyl acrylate)-b-polyisobutylene-b-polystyrene triblock [90], and amphiphilic pentablock copolymers based on PIB [91]. 

Many examples of active-site transformations, from cation to anion, to prepare block and graft copolymers based on PIBs have been reported [62, 63],... 

PB base polymers are semicrystalUne isotactic thermoplastic polyolefins. They are derived from the polymerization of butene-1 monomer with or without other alpha-olefin monomers utilizing a Ziegler-Natta type of catalyst. Their unique crystallization behavior means longer open times of adhesive and sealant formulations compared to other commonly used polymers such as polyethylene and ethylene-vinyl acetate copolymer (EVA). Polybutylene (PB), also called polybutene-1 or poly-1-butene, is different from polybutene or polyisobutylene (PIB). PIB is amorphous and rubbery, and comes in the form of a viscous liquid or big, hard block (6 in. in length and width or could be larger). PB base polymers are sup-pUed in the form of small pellets (about 0.25 in. in diameter) or nibs. 

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