A New Synthetic Method for the Preparation of Star‐Shaped Polyisobutylene with Hyperbranched Polystyrene Core

Abstract

Friedel–Crafts self‐grafting of polystyrene (PSt) under quasiliving carbocationic polymerization was utilized to develop a new rapid one‐pot method for the preparation of star‐shaped polyisobutylene (PIB). First, the polymerization of isobutylene led to PIB with predetermined molecular weight ($\overline M _{\rm n}$ = 2 000) and narrow molecular weight distribution ($\overline M _{\rm w} /\overline M _{\rm n}$ = 1.03). Then addition of relatively small amount of styrene after isobutylene consumption yielded PIB‐PSt diblocks. Multiple alkylation of the resulting PSt segments by the polystyryl cations led to hyperbranched PSt cores coupling PIB chains to form a star polymer in short reaction time (within an hour) compared to reported methods. The formation of star polymers by this self‐grafting mechanism was proved by gel permeation chromatography equipped with online viscosimeter and 1H NMR spectroscopy.

Star and Hyperbranched Polyisobutylenes via Terminally Reactive Polyisobutylene‐Polystyrene Block Copolymers

“…The first side reaction decreases the active chain end concentration and thus the branching efficiency. The alkylation of the monomer is negligible, because the reaction rate of chain propagation is much higher than that of the Friedel‐Crafts alkylation 34…”

“…Due to these special properties, several attempts have been reported on the synthesis of highly branched polyisobutylenes so far 12–16, 20–33. Previously, it was found that intra‐ and intermolecular Friedel‐Crafts alkylation of the benzene rings of styrene (St) units in polystyrene (PSt) segments might occur by carbocationic chain ends 13, 16–23, 34, 35. This undesired side reaction was observed not only during the cationic polymerization of pure St,35 but in the case of the preparation of thermoplastic elastomer block copolymers composed of PIB and PSt13–19 as well.…”

Precision synthesis of graft copolymers via living cationic polymerization ofp-acetoxystyrene followed by friedel-crafts-type termination reaction

“…Friedel–Crafts alkylation could be useful for polymer reactions in cationic polymerizations because an aromatic ring reacts with an electrophile or an electron‐deficient species. For example, the use of the electrophilic reactions of aromatic groups has been examined as a novel synthetic tool for producing star‐shaped polymers, hyperbranched polymers or end‐functional polymers via the cationic polymerization of isobutylene or vinyl ethers . More reactive aromatic rings such as a naphthyl group could allow more facile synthesis of well‐defined polymers in cationic polymerization.…”

“…To achieve an efficient reaction of living propagating cations with naphthalene rings, the propagating cations should have high reactivity, which allows the use of less reactive monomers for the synthesis. Highly reactive polyisobutylene or polystyrene carbocations were employed in the aforementioned synthesis using the Friedel–Crafts reaction . Another candidate for such less reactive monomers generating highly reactive species is p ‐acetoxystyrene (AcOSt).…”

Association, emulsifying, and solubilization properties of amphiphilic hyperbranched poly(acrylic acid) with short polystyrene stickers

“…On the other hand, in the aspect of preparation of “star‐like” polymers, hyperbranched/dendritic chains are usually acted as a multisites functional core to produce grafting chains via “graft‐onto” or “graft‐from” strategy. However, the as‐prepared “star‐like” amphiphilic or double‐hydrophobic/hydrophilic polymers are generally made of a very small core and much longer grafting chains, because the hyperbranched/dendritic cores are mainly prepared from small‐molecular polymerizable monomer, instead of long polymer chains (macromonomers) . One can image that hyperbranched topology, instead of star topology, will finally govern the physical properties of graft copolymers in solution if the branched core size is much larger than the grafting chain size.…”