Carbocationic polymerization combination

Terpenoid biosynthesis is a carbocationic polymerization, combining step-growth and chain-growth. 

The first diblock copolymer brushes synthesized in our group were made by a combination of carbocationic polymerization and ATRP (Scheme 1) [46]. Zhao and co-workers [47] synthesized diblock copolymer brushes consisting of a tethered chlorine-terminated PS block, produced using carbocationic polymerization, on top of which was added a block of either PMMA, poly(methyl acrylate) (PMA) or poly((Ar,M -dimethylamino)ethyl methacrylate) (PDMAEMA), synthesized using ATRP. The thickness of the outer poly(meth)acrylate block was controlled by adding varying amounts of free initiator to the ATRP media. It has been reported that the addition of free initiator is required to provide a sufficiently high concentration of deactivator, which is necessary for controlled polymerizations from the sur-... 

Tin Halides. Tin tetrachloride was the first Lewis acid used for carbocationic polymerizations [161]. It does not initiate polymerization of alkenes in the absence of cationogens and protonogens, and it is used most often in combination with alkyl chlorides and esters preformed by... 

The surest way toward desirable new polymer structures is by a systematic exploitation of the detailed mechanistic understanding of polymerization processes. The aim of this presentation is to examine in some depth the mechanism of carbocationic polymerizations and subsequently to apply this insight toward the preparation of new polymeric materials possessing advantageous combinations of processing and/or physical-mechanical characteristics. 

Since the appearance of the major review on the living carbocationic polymerization of olefins [1], a large body of pertinent additional data have been generated relative to this subject [2-17]. The significance of these data prompts us to combine this recently-acquired information with earlier data and to integrate all kinds of cationic olefin polymerizations into a comprehensive mechanism, be these induced by means of a purposely-added initiator or by an impurity, both of which can lead to conventional (presence of chain transfer and/or termination) or living (absence of chain transfer and irreversible termination) polymerizations. 

Regarding the comprehensive closed-loop model, a new methodology was developed to simulate kinetic responses of real-life carbocationic polymerizations to various events or combinations of events. Basic scenarios were set up to analyze numerically the above events and to demonstrate their effects on N and Mn vs Wp, and — ln(l — C) and C vs time diagnostic plots, respectively. 

A rather unexpected water- and alcohol-insensitive activator, namely boron trifluoride etherate, was developed by Sawamoto for the living polymerization of p-hydroxystyrene in combination with the water adduct of p-methoxystyrene as initiator [78], The polymerizations proceeded even in large excess of water, which is in large contrast with the absolutely dry conditions that are normally required for carbocationic polymerizations. It is proposed that acetonitrile, which is used as polymerization solvent, stabilizes the short-lived carbocationic propagating species. The same polymerization methodology could be applied for the preparation of statistical and block copolymers consisting ofp-hydroxystyrene and b-methoxystyrene [79], as well as for the homopolymerizations of styrene, p-chlorostyrene and p-methylstyrene in the presence of a proton trap [80]. 

Monomers active in carbocationic polymerization have been periodically reviewed over the years (26-30). Isobutylene remains the monomer with optimum combination of nucleophilicity, carbocation stability, and steric factors, 5delding high molecular weight elastomers. 

L.K. Breland and R.F. Storey, Polyisobutylene-based miktoarm star polymers via a combination of carbocationic and atom transfer radical polymerizations, Polymer, 49(5) 1154-1163, March 2008. 

Figure 5.13. Reactions involved in cationic addition polymerization. Shown are (a) generation of a carbo-cation intermediate from a Lewis acid initiator, (b) propagation of the polymer chain through the combination of the carbocationic polymer chain and additional monomers, and (c) termination of the polymer growth through either proton abstraction (i) or anionic attachment (ii) routes.

Novel Functional Copolymers by Combination of Living Carbocationic and Anionic Polymerizations... 

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 synthetic route for the synthesis poly(IB-i)-tBMA) developed by combining Hving carbocationic and anionic polymerizations involves metalation of 2-polyisobutylenyl-thiophene with n-butyUithium in THE at —40°C. The resulting stable macrocarbanion (PIB-T-, Li+) was successfully used to initiate living anionic polymerization of tBMA yielding poly(IB-i)-tBMA) block copolymers [235]. 

R. F. Storey, A. D. Scheuer, B. C. Achord, Amphiphilic poly(acrylic add-b-styrene-b-isobutylene-b-styrene-b-acrylic add) pentablock copolymers from a combination of quasiliving carbocationic and atom transfer radical polymerization. Polymer 200S. 46, 2141-2152. 

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