Synthesis and characterization of graft and block copolymers using hydroboration

[摘要] Graft and block copolymers were synthesized using multifunctional andmonofunctional macroinitiators to produce the copolymers. The process involvedhydroboration of commercially available unsaturated rubbers and chain-endunsaturated macromonomers with 9-borabicyclo [3.3.1] nonane (9-BBN). Theresulting secondary alkyl 9-BBN moieties in the starting materials were subsequentlyexposed to oxygen in the presence of free radical polymerizable monomers tofacilitate the formation of graft and block copolymers.This research was initiated by first studying the hydroboration of a model compound,2-hexene, in order to determine the optimal conditions for the graft reactions. Themodel compound was subsequently used as a macroinitiator to initiate thepolymerization of methylmethacrylate (MMA). The same borane chemistry wasextended to the synthesis of polystyrene (PS) block copolymers. Chain-endunsaturated PS macromonomers, synthesized by anionic polymerization, wereeffectively hydroborated and then polymerized to produce PS-b-PMMA blockcopolymers.The synthesis of polyolefin graft copolymers was subsequently achieved byhydroboration. Several commercial rubbers with different levels of unsaturatedsegments were efficiently grafted with vinyl monomers MMA and styrene (St)following the 'graft from approach. The grafted reactions were carried out undervarious reaction conditions to determine the effect of the following factors:concentration of oxygen, amount of borane and monomer concentration. Bycontrolling these factors, different graft densities were achieved with high graftefficiencies. All reactions produced mixed products including unreacted(non-functional) macroinitiator, homopolymer, graft copolymer and in case of thehighly unsaturated polymer a crosslinked gel.Finally, the chemical compositions as well as the molar mass distribution of the graftcopolymers were fully characterized by different chromatographic techniques.1H-NMR and FTIR were also used to confirm the structure of these copolymers.Gradient HPLC was developed and extensively used to characterize the graftcopolymers.

[发布机构] Stellenbosch University