Polyisobutylene/polystyrene-based triblock and pentablock copolymers synthesized using a combination of quasiliving carbocationic polymerization and atom transfer radical polymerization
This research pertains to the synthesis of multiblock copolymers using a combination of quasiliving carbocationic polymerization (QCP) and atom transfer radical polymerization (ATRP), focusing on hydrophilic, poly(acrylic acid) (PAA) containing pentablock terpolymers (PTPs) grown from poly(styrene- b -isobutylene-b -styrene) (PS-PIB-PS) block copolymers (BCPs). In the first part of the study, tBA was grown via ATRP from well-defined PS-PIB-PS and poly(isobutylene-b -styrene) (PIB-PS) BCPs that were synthesized under QCP conditions. The poly(tert-butyl acrylate- b -styrene-bisobutylene-b -styrene-b-tert -butyl acrylate) (PtBA-PS-PIB-PS-PtBA) PTPs and poly(isobutylene- b -styrene-b-tert -butyl acrylate) BCPs had targeted molecular weights, narrow PDIs, and targeted copolymer compositions. Hydrophilic PTPs were achieved by deprotection of the tert -butyl ester functionality using TFA to form poly(acrylic acid-b -styrene- b -isobutylene-b -styrene-bacrylic acid) (PAA-PS-PIB-PS-PAA) PTPs. FT-IR, DSC, and 13 C-NMR were used to show the deprotection of the ester groups. DSC analysis confirmed the retention of phase-separation after the addition of the PtBA block segments and subsequent formation of PAA as evidenced by separate transitions from the PIB, PtBA, or PAA block segments. A water uptake study conducted on a series of PAA-PS-PIB-PS-PAA PTPs revealed that the hydrophilicity of the PTPs increased with an increase in the wt % of PAA block segments and was believed to be dependent on copolymer morphology. In the second study, triblock and PTPs having the basic structures of PIB-PS-X (X = poly(methyl acrylate) (PMA) or poly(2-(ethylhexyl) acrylate) (PEHA)) and Y-PS-PIB-PS-Y (Y = PMA, PEHA, poly(n -butyl acrylate) (PBA), poly(2-dimethylaminoethyl acrylate) (PDMAEA), or poly(methyl methacrylate) (PMMA)) were synthesized using a combination of QCP and ATRP. The polymerizations of most acrylates were controlled having targeted molecular weights and narrow PDIs. In contrast, the polymerization of DMAEA and MMA were uncontrolled. The thermal stabilities of the PTPs were slightly less than PS-PIB-PS, as evidenced by TGA. The final portion of the research discusses advancements in the field of aqueous carbocationic polymerization. Phenylphosphonic acid derivatives were used to initiate p -methoxystyrene (pMOS) in an aqueous medium in conjunction with a water tolerant Lewis acid, ytterbium trifluoromethanesulfonate (Yb(OTf)3 ). The polymerizations exhibited poor initiation, as evidenced by uncontrolled molecular weights, and the kinetics were affected by either the addition of cosolvents or increasing the reaction temperature.