Synthesis And Morphology Of Amphiphilic AB₂ Copolymers, One-Pot Metathesis Polymeric Nanoparticles

A new amphiphilic AB2 star copolymer was synthesized by the combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Two different routes (methods A and B) were employed firstly to prepare the poly(oxanorbornene)-based monotelechelic polymers as the hydrophobic arm bearing dibromo-ended group via ROMP in the presence of two different terminal agents catalyzed by the first generation Grubbs catalyst RuCl2(PCy3)2(CHPh). The values of capping efficiency (CE) of the polymers were determined by 1H NMR, which were 94% and 67% for methods A and B, respectively. Then, the dibromo-ended ROMP polymers were used as the macroinitiators for ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to produce two hydrophilic arms. The prepared amphiphlic AB2 star copolymers poly(7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid dimethyl ester)-block-bis[poly (2-(dimethylamino)ethyl methacrylate)] (PONBDMn-b-(PDMAEMAm)2) with a fixed chain length of hydrophobic PONBDM and various hydrophilic PDMAEMA chain lengths can self-assembly spontaneously in water to form polymeric micelles, which were characterized by DLS, AFM and TEM measurements. An average micelle diameters of 130 nm and 330 nm with spherical morphology were observed for these two copolymers.Furthermore, a one-pot method was used successfully to prepare copolymeric nonoparticles. Under strictly oxygen-free and anhydrous conditions, living chains of poly(norborn-5-ene-exo, exo-2,3-dicarboxylic acid di(2'-bromo-2'-methylpropionyloxy methyl ester)) prepared via ROMP initiated by RuCl2(PCy3)2(CHPh) in the solvent of toluene, then the second and third monomers were sequentially added to this reaction mixture for the followed copolymerization. The resultant block copolymers formed aggregation of micelles in situ. The micelles were fixed by crosslinking under the irradiation of UV light. The micelles could exist in other unselective solvent such as CHCl3. The micellar characteristics of the copolymers were investigated by using DLS, AFM and TEM measurements. The spherical morphologies with diameter from 80 nm to 180 nm were obtained. The molecular characteristics of the copolymers were investigated by 1H NMR,EA and GPC techniques.