Synthesis Of Amphiphilic Block Copolymer By Mechanism Transformation

A novel amphiphilic block copolymer of polybutadiene(PB)-b- poly[2-(dimethylamino) ethyl methacrylate] (PDMAEMA) was synthesized by transformation of living anionic polymerization into atom transfer radical polymerization (ATRP). The macroinitiator, PB containing the 2-bromoisobutyryl end group(PB-Br or Br-PB-Br) was attempted by anionic polymerization of butadiene with Butyllithium or Dilithium initiator, then the living PB was chain extended with propylene oxide (PO) and terminated by 2-bromoisobutyryl bromide (BriBBr). By using this macroinitiator with high bromine content(85%-95%) and low polydispersities(Mw/Mn<1.2), ATRP of hydrophilic DMAEMA was realized. The properties of the PB-Br(Br-PB-Br) and amphiphilic block copolymers PB-b-PDMAEMA(PDMAEMA-b-PB-b-PDMAEMA) were characterized by SEC, H-NMR, FT-IR, DSC in detail. The results show that well-defined target products with controlled molecular weight and low dispersities were obtained.In this thesis, the effects of reaction conditions on capping efficiency and esterification efficiency of the macroinitiators have been examined. The results show that: the excess amount of PO(PO/Li=5) and the slight excess(a 1.05-fold excess) of BriBBr were enough for a complete capping and esterification reaction of living PB. On the other hand, the polymerization kinetics of DMAEMA is determined by HNMR method. Then initiator efficiency of macroinitiator(IE%) was also discussed. It was found that: Kinetics studies reveal a controlled/living polymerization for DMAEMA. With anisole as solvent, [macroinitiator]₀: [Cu(I)]₀:[ligand]₀=1:1:1, the ATRP of DMAEMA catalyzed by CuCl/1,1,4,7,10,10- Hex amethyltriethylenetetramine (HMTETA) at 50℃gave higher initiator efficiencies than others.The solution properties of the PDMAEMA-b-PB-b-PDMAEMA and PB-b-PDMAEMA in aqueous solvents were investigated by using HNMR. Emission and excitation fluorescene spectra of pyrene show that the critic micelle concentration is about 0.00501mg/ml (PDMAEMA-b-PB-b-PDMAEMA), 0.00316 mg/ml (PB-b-PDMAEMA). The Scanning electron microscope picture of the micelles is shown that aggregates of nano-sized rugby micelles with 200-250nm and spherical micelles with 100-200nm diameters are respectively discernible. It reveals their polydisperse nature.