Multifunctional Coupling Agents for Living Cationic Polymerization. 7. Synthesis of Amphiphilic Tetraarmed Star Block Polymers with α-Methylstyrene and 2-Hydroxyethyl Vinyl Ether Segments by Coupling Reactions with Tetrafunctional Silyl Enol Ether

Abstract

By the polymer coupling reaction with a tetrafunctional silyl enol ether [1; C{CH2OC6H4C-(OSiMe3)dCH2}4], amphiphilic tetraarmed star polymers (6) with R-methylstyrene-2-hydroxyethyl vinyl ether (RMeSt-HOVE) block arm chains have been synthesized: C{CH2OC6H4COCH2-[CH(OCH2CH2-OH)CH2]n-[C(CH3)(C6H5)CH2]m-}4. The synthesis consisted of the following steps: (i) the sequential living cationic polymerization of RMeSt and 2-[(tert-butyldimethylsilyl)oxy]ethyl vinyl ether (SiVE) into an RMeSt-SiVE living block copolymer (4); (ii) the coupling of four chains of 4 with the quencher 1 into a tetraarmed polymer (5); and (iii) the transformation of the poly(SiVE) segment into the poly(HOVE) chain by the fluoride-catalyzed deprotection. In step i the living polymerization was carried out at -78°Cin methylene chloride with a binary initiating system comprising tin tetrabromide and the hydrogen chloride adduct of 2-chloroethyl vinyl ether. After step iii, the tetraarmed amphiphile 6 (RMeSt/HOVE ) 27/27 in DPn in each arm) was soluble in ethanol and chloroform, in which its 1 H NMR spectra changed dramatically by responding to solvent polarity. For example, in the former polar solvent, the signals of the hydrophobic RMeSt units were hardly detectable, whereas they were clearly observed in chloroform. This responsiveness was attributed to the rigidity of the poly(RMeSt) segment, which contrasts with the more flexible poly(vinyl ether) arm chains in the previously reported tetraarmed amphiphiles.

Amphiphilic Block Copolymers in Structure-Controlled Nanomaterial Hybrids

“…[41] The latter has been used to synthesize a number of new amphiphilic block copolymers [42±44] but only a minority of these has been characterized in detail in terms of their aqueous solution properties. [45] Such polymers included poly(isobutylene-b-methyl vinyl ether), [46] poly(styrene-b-hydroxyethyl vinyl ether), [47] poly(styrene-b-ionic acetylene), [48] poly(methyl tri(ethylene glycol) vinyl ether-b-isobutyl vinyl ether), [49] poly(amethylstyrene-b-2-hydroxyethyl vinyl ether), [50] poly(2-(1-pyrrolidonyl)ethyl vinyl ether-b-isobutyl vinyl ether). [51] Armes and coworkers [49,52] investigated the synthesis by living cationic polymerization of amphiphilic water-soluble diblock copolymers of methyl tri(ethylene glycol) vinyl ether and isobutyl vinyl ether and their aqueous solution behavior, including a systematic variation of block lengths.…”

Synthesis of Polyisobutylene-Based Block Copolymers with Precisely Controlled Architecture by Living Cationic Polymerization

“…This is a general method in living anionic polymerization. Several coupling agents for living poly(vinyl ethers) and PaMeSt have been reported in cationic polymerization [65][66][67], but quantitative coupling was limited to the living polymers with low molecular weight (DPn~10). We have recently extended the concept of capping reaction to coupling reaction of living PIB using bis-DPE and bis-furanyl compounds [68,69].…”

Synthesis of Oligo(isobutyl vinyl ether) with a Silyl Enol Ether End Group and their Aldol Reactions with Benzaldehyde

“…SEEs had been used previously in cationic polymerizations as end capping agents in living cationic polymerization, as a means of forming star and block copolymers, etc. [4][5][6][7][8][9] The alkylation of silyl enol ethers with carbocations has been widely applied for the synthesis of low molecular weight ketones. [10,11] Also, aldol condensation, which is often carried out using masked enolates such as silyl enol ethers, has long been recognised as a versatile synthetic tool in organic chemistry.…”