The Chemoenzymatic Synthesis of a Novel CBABC-Type Pentablock Copolymer and Its Self-Assembled “Crew-Cut” Aggregation

Abstract

A symmetric linear CBABC pentablock copolymer consisting of poly(ethylene oxide) (PEO), polycaprolactone (PCL), and polystyrene (PSt) was synthesized by the combination of enzymatic ring-opening polymerization (eROP) and atom transfer radical polymerization (ATRP). Dihydroxyl-capped PEO first initiated eROP of -CL in the presence of biocatalyst Novozyme 435. Subsequently, the resulting dihydroxyl-terminated copolymer PCL-b-PEO-b-PCL was converted to bromine-ended triblock macroinitiator by the esterification with R-bromopropionyl bromide. Pentablock copolymer PSt-b-PCL-b-PEO-b-PCL-b-PSt was obtained via a subsequent ATRP of styrene(St), and its kinetics analysis indicated a "living"/controlled radical polymerization. The selfassembly behavior of pentablock copolymer was investigated in aqueous media. The "crew-cut" aggregates of various morphologies were observed, such as normal spherical micelles, rodlike micelles, vesicles, lamellae, and large compound micelles (LCMs). In addition, it was found that both the copolymer composition and the copolymer concentration in THF had a great influence on the morphologies of the aggregates.

Enzymes in the Synthesis of Block and Graft Copolymers

“…Based on this successful strategy also GMA was polymerized from the PCL macroinitiator to yield amphiphilic bock copolymers, which assemble into nanoscale micelles [33] . Pentablock copolymers where also obtained by combining this approach with the enzymatic macroinitiation of CL from PEG diol (Figure 12.11 ) [34] . The obtained PCL diol was modifi ed with α -bromopropionyl to yield a telechelic ATRP macroinitiator.…”

Chemoenzymatic Synthesis of H-shaped Amphiphilic Pentablock Copolymer and Its Self-assembly Behavior

“…39 Our group has reported the synthesis of block copolymers by chemoenzymatic method, such as AB-type block copolymers PCL-b-PSt, ABA-type block copolymers PSt-b-PCL-b-PSt, and the pentablock copolymers PHFMA-b-PCL-b-PEG-b-PCL-b-PHFMA and PSt-b-PCL-b-PEG-b-PCL-b-PSt. [40][41][42] Two pairs of building blocks were aligned along the same axle in a symmetry distribution, compared to traditional linear polymers, so the selfassembly of a H-shaped block copolymer into micelles in selective solvent (i.e. water) would exhibit more stable structures.…”

“…41,43 The resulting pentablock copolymers (PSt) 2 -b-PCL-b-PEO-b-PCL-b-(PSt) 2 are especially interesting because PCL has features like crystallizability, lack of toxicity, printability, and good mechanical properties. On the other hand, the also crystallizable PEO has superior properties for being nontoxic, flexible, hydrophilic, weakly immunogenic, and biocompatible.…”

“…In fact, the linear pentablock copolymers comprised of PSt, PEO, and PCL have been reported. 41 Nevertheless, no reports have been published on their analogous synthesis of H-shaped block copolymers (PSt) 2 …”

Chemoenzymatic synthesis amphiphilic H-shaped copolymer and its self-assembly behavior

“…Thus, the combination of the eROP and ATRP has been one of the most promising techniques and a large number of functional polymers could be synthesized effectively. Our laboratories have reported the synthesis of block copolymers by the combination of eROP and ATRP, including AB-type block copolymers PCL-b-PSt, ABA-type block copolymers PSt-b-PCL-bPSt [8] and the pentablock copolymers PSt-b-PCL-b-PEG-b-PCL-b-PSt [9] . Because two building blocks have been linked to single junction point, compared to traditional linear polymers, H-shaped block copolymer selfassembly formation of micelles exhibits more stable structure, excellent performance, such as solution properties, mechanical properties and special morphology.…”