Synthesis And Properties Of Four-arm Amphiphilic Block Copolymers

In this paper, a solution atom transfer radical polymerization (ATRP) of ethyl methacrylate (EMA) was first studied. The 4-arm initiator was prepared by the esterification reaction between pentaerythritol and 2-bromoisobutyryl bromide. The 4-arm poly(ethyl methacrylate) (PEMA-Br) was prepared by ATRP using the 4-arm initiator, CuCl and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst and ligand in N,N′-dimethylformamide (DMF). The molecular weight of PEMA-Br was characterized by gel permeation chromatography (GPC). It was found that the number average molecular weight (Mn) of PEMA-Br could be controlled from 1.30×10~4 to 3.92×10~4g/mol by varying the ratio of EMA monomer to initiator in range of 1:160 to 1:320, and distribution of molecular weight (Mw/Mn) kept low than 1.40. The structure of the 4-arm PEMA-Br was characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (1H-NMR). It was found that the obtained PEMA-Br had a specific structure.A solution ATRP of tert-butylmethacrylate (tBMA) and poly(ethylene glycol) methacrylate (PEGMA) was then studied using resulting 4-arm PEMA-Br as macroinitiator, CuCl as catalyst, PMDETA as ligand to form 4-arm block copolymer poly(ethyl methacrylate)-b-poly(tert-butylmethacrylate) (PEMA-b-PtBMA) and poly(ethyl methacrylate) -b-poly(poly(ethylene glycol) methacrylate) (PEMA-b-PPEGMA). Then the 4-arm amphiphilic block copolymer of poly(ethyl methacrylate)-block-poly(methyl acrylic acid) (PEMA-b-PMAA) was obtained from 4-arm PEMA-b-PtBMA copolymer by hydrolysis in trifluoroacetic acid solution. The structure and properties of block copolymer were characterized by FTIR, 1H-NMR, GPC and differential scanning calorimeter (DSC). Furthermore, the 4-arm PEMA-b-PMAA could self-assemble to form spherical micelles in the selective solvent. The diameters of the micelles was investigated with different concentration and pH by using dynamic laser light scattering (DLS), while the aggregates morphologies were observed by transmission electron microscopy (TEM).The eugenol-loaded micelles were prepared by self-assembly. The release curves of eugenol from micelles were investigated in ethanol and ethanol/water (1:1, v/v). It was found that the copolymer micelle may provide as an effective perfume carrier for perfume control and release.