Study On Synthesis Of Amphiphilic Block Copolymer By Transfer Radical Polymerization

Amphiphilic block copolymers have great potential application in varieties of fieldsbecause of self-assembled behaviour in the selective solvents. So it is significant tosynthesize the block copolymers with specific property and well-defined structure forobtaining the uniform morphology of the aggregates. As atom transfer radicalpolymerization(ATRP) have powerful ability of molecular design, it is one of the mosteffective methods to synthesize the block copolymers with controlling molecular weightand narrow molecular weight distribution. For this reason, with water and ionic liquidsrespectively as reaction medium, Macroinitiator PMMA-Cl of halogen end-group polymerwas firstly synthesized by ATRP, which then initiated the second monomer styrene topolymerize by ATRP to gain block copolymer PMMA-b-PSt with comparatively lowpolydispersity.The effects of each factor on the controlled polymerization of MMA and the stabilityof emulsion system were examined in detail. The results indicated that the reaction systemhad the best stability and the conversion of MMA was95.6%with narrow molecularweight distribution, under the condition that the dosage of emulsifier Tw-80is4.0%, themolar ratio CuCl/EDA is1:2, the amount of initiator BzCl is0.2g, the reactiontemperature is70℃and the reaction time is2h. However, stable system was obtainedonly if the dosage of emulsifier added to5.0%in the block polymerization process. Thepolymerization rate of styrene was rapid with low molecular weight macroinitiator and theconversion of St could reach to86.3%at2h. Block copolymer PMMA-b-PS with narrowmolecular weight distribution(＜1.5) may be obtained according to GPC. Thepolymerization system was well controlled and consistent with characteristics of livingpolymerization. The structure of block copolymer was characterized by FT-IR,1H-NMRand TGA.The ionic liquids1-butyl-3-methylimidazolium hexafluorophosphate([Bmim]PF6)and1-allyl-3-methylimidazolium chloride([Amim]Cl) offered homogeneous condition forcatalyst system. Nevertheless, The polymerization of MMA in [Bmim]PF6and [Amim]Clwas formed homogeneous system and heterogeneous system, respectively. The effects ofinitiator type BzCl and CCl4on the control and polymerization rate of MMA wereinvestigated in ionic liquids. The results showed that the reaction in the two ionic liquidspresented the linear first-order kinetic relationship. Conversion and polymerization rate with CCl4as initiator were higher than that of BzCl. Heterogeneous system presentedbetter controlled than homogeneous system and molecular weights distribution of theobtained polymers was at range1.3～1.4. ATRP reaction characteristic and mechanism in[Amim]Cl was discussed. Polymerization occurred in the phase of ionic liquid and organicphase only was a storage of monomer and polymers. Similarly, ATRP reaction of St in thetwo ionic liquids was occurred with PMMA-Cl as macroinitiator, but the monomerconversion was very low.The self-assembled behaviour of block copolymers in the acetone solvent werestudied. The morphology of self-assembled microspheres were observed by TEM. Itfounded that typical spherical micelles were formed. Micelles dimensions were increasingwith the increasing amount of PS and the decreasing block ratio of PMMA/PS. Themorphology change could depended on block copolymers concentration in acetone,because of it had been a shift from spheres going through reticulars to irregular rodlike.