Design, synthesis and characterization of polyhedral oligomeric silsesquioxane based hybrid macroamphiphiles achieved via reversible deactivation radical polymerization

Abstract

Three series of well-defined polyhedral oligomeric silsesquioxane (POSS) based hybrid polymers have been successfully synthesized by reversible deactivation radical polymerization (RDRP), namely atom transfer radical polymerization (ATRP) and nitroxide mediated radical polymerization (NMP) for potential biomedical applications. In first series, POSS-PGMA tadpole shaped amphiphilic hybrid polymers of different molecular weights having polyhedral oligomeric silsesquioxane (POSS) nanocage as the hydrophobic head and poly(glycerol methacrylate) (PGMA) as the hydrophilic tail (POSS-PGMA) have been synthesized via atom transfer radical polymerization (ATRP). Synthesis of POSS PGMA was obtained in two steps, (1) first POSS-poly(solketal methacrylate) was obtained by ATRP of solketal methacrylate (the precursor monomer for GMA) using bromo functionalized aminopropylIsobutyl POSS as initiator and CuCl/N,N,N,N,N-pentamethyldiethylenetriamine as the catalyst system. In the second step, the obtained POSS-PSMA was transformed into amphiphilic POSS-PGMA by acid hydrolysis. The successful transformation was verified by 1H NMR and FTIR spectroscopy. Finally, the solution behaviors of these polymers were studied in aqueous medium using laser light scattering and fluorescence spectroscopy. The CAC was found to increase with increasing the PGMA chain length. The large hydrodynamic size of the self assembled structures, as determined by the laser light scattering data, however, suggests that the aggregates are not of typical core-shell type micelles Second series consists of Poly(POSS-methacrylate-co-styrene)-b-Poly(acryloyl morpholine)x P(POSS-MA-co-S)x-b-P(ACM)y block copolymers which differs in chain length of polyacryloyl morpholine blocks. For the synthesis of P(POSS-MA-co-S)x-b-P(ACM)y block copolymers, bulky methacryloisobutyl-polyhedral oligomeric silsesquioxane (POSS-MA) was first polymerized by nitroxide-mediated radical polymerization (NMP) at 110 oC using 10 mol % styrene as comonomer and BlocBuilder as the NMP initiator. The synthesized P(POSS-MA-co S)x with a molecular weight of ~8000 g/ mol and dispersity Ð = 1.2 was extended with N-acryloyl morpholine (ACM) via NMP to obtain amphiphilic hybrid P(POSS-MA-co-S)x-b-P(ACM)y block copolymers, where the subscript “y” represents the degree of polymerization of (ACM) block (182 < x < 695). The size exclusion chromatography (SEC) of the synthesized diblock copolymers xvii reveals the presence of some dead chains in P(POSS-MA-co-S)x macroinitiator. Kinetic investigations reveal first-order kinetics for the polymerization of ACM using P(POSSMA-co-S)x as the macroinitiator under NMP conditions. The kinetic and SEC data confirms the controlled nature of the NMP of ACM. Being amphiphilic, the synthesized P(POSS-MA-co-S)x-b-P(ACM)y block copolymers self-assembled in aqueous solution as revealed by the fluorescence spectroscopy and dynamic light scattering studies. Third series consists of (PEG5k-b-P(MA-POSS)x diblock copolymers (3.7 < x < 21) obtained via ATRP with two objective (1) to study the effect of POSS nanocage on the crystallization of poly(ethylene glycole) chains in the synthesized block copolymers and (2) to study the layer/film formation behaviours of the block copolymers at air / water interface. The result obtained with various techeniques shows that POSS nanocages could hinder chain mobility and hence the crytallization of PEG chains in the block copolymers. The attachment of POSS to poly(ethylene glycole) chain results in the formation of a very stable film on the water surface, however AFM, Brewster angle microscopy (BAM) and infrared reflection absorption spectroscopy investigations revealed a significant increase in film thickness with increase in surface pressure that is attributed to multilayer formation by the POSS nanogages on the water surface. Moreover crystallization of POSS cages of the block copolymers was also observed on the water surface upon several compressions and expansions. For potential biomedical applications, several of synthesized hybrid polymers were investigated for their pore / channel activity in a lipid bilayer (a model membrane that serves as a good model for biomembrane). Only highly amphiphilic (PEG5k-b-P(MA-POSS)3.7 and P(POSS MA-co-S)8-b-P(ACM)695 with relatively small POSS content were found to have the ability to penetrate the model lipid bilayer membrane generating pores/channels. The synthesized POSS based hybrid polymers can also find potential applications in water treatment as P(POSS-MA-co S)8-b-P(ACM)695 modified PVDF membranes revealed enhanced hydrophilicity, water flux efficiency and antifouling properties.