title: Synthesis of poly(poly(ethylene glycol) methacrylate)-polyisobutylene ABA block copolymers by the combination of quasiliving carbocationic and atom transfer radical polymerizations.
abstract: Systematic investigations are carried out on the synthesis of a series of new, unique ABA-type triblock copolymers consisting of the hydrophobic and chemically inert polyisobutylene (PIB) inner and the hydrophilic comb-shaped poly(poly(ethylene glycol) methacrylate) (PPEGMA) polymacromonomer as an outer block. Telechelic PIB macroinitiators with narrow molecular weight distributions (MWD) are synthesized by quasiliving carbocationic polymerization of isobutylene with a bifunctional initiator followed by quantitative chain end derivatizations. Atom transfer radical polymerization (ATRP) of PEGMAs with various molecular weights is investigated by using these macroinitiators. It is found that CuBr is an inefficient ATRP catalyst, while CuCl leads to high, nearly complete conversions of the PEGMA macromonomers. Gel permeation chromatography (GPC) analyses reveal slow initiation of PEGMA at relatively high PIB/PEGMA ratios or with PEGMAs of higher molecular weights due to steric hindrance between the macroinitiator and macromonomer. The occurrence of slow initiation, and not permanent termination, is proven by highly efficient ATRP of a low-molecular-weight monomer, methyl methacrylate, with the block copolymers as macroinitiators. Successful synthesis of PPEGMA-PIB-PPEGMA ABA block copolymers is obtained by using either low-molecular-weight PEGMA or relatively low macroinitiator/macromonomer ratios. Differential scanning calorimetry (DSC) indicates phase separation and significant suppression of the crystallinity of the pendant poly(ethylene glycol) (PEG) chains in these new block copolymers.
authors.affiliation: Polymer Chemistry Research Group, Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117, Budapest, Magyar tudósok krt. 2, Hungary.
authors.forename: Ákos
authors.initials: Á
authors.lastname: Szabó
authors.forename: Györgyi
authors.initials: G
authors.lastname: Szarka
authors.forename: Béla
authors.initials: B
authors.lastname: Iván
mesh_terms: D002152:Calorimetry, Differential Scanning; D002384:Catalysis; D002850:Chromatography, Gel; D009682:Magnetic Resonance Spectroscopy; D008689:Methacrylates / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D011090:Polyenes / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D058105:Polymerization; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D008689:Methacrylates; D011090:Polyenes; D011108:Polymers; C524499:polyethylene glycol methacrylate; D011092:Polyethylene Glycols; C008967:polyisobutylene
keywords: atom transfer radical polymerization; block copolymers; comb-shaped poly(poly(ethylene glycol) methacrylate); polyisobutylenes; quasiliving carbocationic polymerization