Acid-sensitive polymeric micelles have great potential as carriers for target drug delivery systems.In this work

a methacrylate monomer with cyclic orthoester group

(2-ethoxy-5-methyl-1

3-dioxan-5-yl)methyl methacrylate (EDMM)

was synthesized.Two acidsensitive amphiphilic block copolymers

PEO-b-PEDMM17 and PEO-b-PEDMM34

were prepared by the atom transfer radical polymerization of EDMM using a PEO macroinitiator (molecular weight ca. 2000 Da).The compositions and molecular weights of the two block copolymers were measured by using 1H-NMR and GPC

respectively.Both polymers are not water soluble due to the hydrophobicity of PEDMM segments.However

micellar aggregates with sizes of 60～200 nm were obtained by slowly adding excessive phosphate buffer (10 mmol/L

pH 7.4) to the polymer solutions in tetrahydrofuran (THF) and then evaporating THF.The micellar aggregates were characterized by dynamic light scattering

transmission electronic microscopy and Nile Red fluorescence probe.PEO-b-PEDMM17

the polymer with a shorter hydrophobic chain length

had a lower critical aggregation concentration(cac) and formed micellar aggregates with smaller size compared with PEO-b-PEDMM34.pH-Dependent hydrolysis of the aggregates were monitored by Nile Red(NR)probe and 1H-NMR approaches

showing that the polymer aggregates were stable at pH 7.4

but the polarity of the micellar core increased with time at pH 5.0 due to the acid-triggered hydrolysis of the orthoester groups.This type of acid sensitive micellar aggregates may find applications as carriers for tumor tissue and/or intracellular drug delivery.