Construction And Rheological Behavior Of Triblock Copolymer Based Supra-amphiphilic Systems

Supramolecular self-assembly refers to a complex and orderly aggregation process via non-covalent interactions.Compared with conventional polymer assembly,supramolecular polymer assembly benefits a lot.The polymer-based supramolecular assemblage is highly controllable,and not only enrich the micro-nano structures,but also can be used to prepare functional materials,thus still having research value and application prospects.Commonly used non-covalent interactions for constructing supramolecules include hydrogen bonding,electrostatic interaction,hydrophobic interaction,host-guest recognition,etc.Electrostatic interaction as a simple and convenient approach is strong enough,thus the construction of polymeric supramolecules via electrostatic interaction has received extensive attention.However,most researches in this field focus on molecular design and recognition,and little attention is paid to the aggregation,gelation and rheological behaviors.For this reason,we have designed and constructed several different types of block copolymer based supramolecular systems,and the self-assembly and rheological properties have been discussed respectively.This work has significance for the construction of supramolecular polymer hydrogel and better understanding of the supramolecular network structure and rheological behavior.The main research contents and results are as follows:1.An ABA type of supra-amphiphilic triblock associative polymer（supra-amphiphilic TAP）was designed and prepared between a triblock double-hydrophilic polyelectrolyte of poly（3-sulfopropylmethacrylate potassium salt）-b-poly（ethylene glycol）-b-poly（3-sulfopropylmethacrylate potassium salt）（PKSPMA-b-PEG-b-PKSPMA）and a cationic surfactant,dodecylamine hydrochloride（DAHC）.The aggregation behavior between the two components showing that the supra-amphiphilic TAP formed via electrostatic interaction between DAHC and PKSPMA blocks can self-assemble into micelles,which can further associate into network leading to gelation behavior.This is similar to the aggregation of traditional TAP molecules.The rheological studies of the supra-amphiphilic TAP aqueous solution show that the viscoelastic behavior depends not only on the concentration,but also the stoichiometric ratio of two components,salt concentration,p H values and temperature.The solution relaxation dynamics follows the time-concentration,time-salt and time-p H superposition and is dominantly controlled by the electrostatic interaction in the form of ion-ion pairs rather than the hydrophobic association in the core of micelles.This result provides not only a new approach to understanding of the solution behaviors of the supra-amphiphilic associative polymers but also to construction of supramolecular viscoelastic gel.2.A type of supramolecular polymer hydrogel was designed and prepared using a triblock copolymer of poly（acrylic acid）-b-poly（ethylene glycol）-b-poly（acrylic acid）(PEG-(PAA₂₂)₂ or PEG-(PAA₃₅)₂)and an aliphatic primary amine of octylamine（OA）or dodecylamine（DA）.Four complex systems were built.The self-assembly and aggregation behavior between the two components show that the critical aggregation concentration（CAC）is the smallest for the complex of PEG-(PAA₃₅)₂/OA,while the largest for PEG-(PAA₃₅)₂/DA.And the composite micelles with OA are easier to associate into aggregates than that with DA,especially for PEG-(PAA₃₅)₂/OA.The rheological behaviors show that PEG-(PAA₃₅)₂/OA solutions have the largest elastic chains’density and plateau modulus（G₀）values.The high hydrophobicity and long PAA blocks help PEG-(PAA₃₅)₂/OA to form a strong physical network with a slow relaxation process.It is worth mentioning that no gelation behavior occurs when PEG-（PAA）₂is mixed with n-hexylamine（HA）for the weak hydrophobicity of short C6 side chain in PEG-（PAA）₂/HA.These results will be of value not only for the fundamental research of self-assembly of polymeric supra-amphiphiles in aqueous solutions but also for the potential applications of hydrophilic triblock ionomer in soft materials,functional materials,etc.3.A supramolecular polymer hydrogel based on a triblock copolymer of poly（acrylic acid）-b-poly（ethylene glycol）-b-poly（acrylic acid）（PAA-b-PEG-b-PAA）and a homopolymer of branched poly（ethyleneimine）（bPEI）was designed and prepared.The self-assembly and aggregation behavior between the two components in aqueous solution were studied.The results show that the critical aggregation concentration（CAC）of PAA-b-PEG-b-PAA/bPEI complex（f=[-NH-]/[-COOH]=1）is lower than that of PAA-b-PEG-b-PAA suggesting that micelles are formed via ionic coacervation.And at a relatively low concentration,the micelles can associate into aggregates,while no isolated micelles exsit.The rheological behaviors were further studied,and it was found that the modulus and viscosity of the concentrated solutions not only depend on the total polymer concentration,but also the value of f and temperature.In summary,this supramolecular hydrogel system is simple and easy to control,and there is no interference of other ions on electrostatic interaction,so that we can better understand the aggregation and rheological behavior between the polyelectrolytes.