Synthesis Of CO₂-responsive Amphiphilic Block Polymers And Study On CO₂-response Behavior

Physical or chemical prosperities of stimulus-response materials could be changed after being stimulated by changes environmental conditions,and after withdrawal of these stimuli,the properties will return to its original state.As a new natural and harmless stimulus,CO2 has attracted the attention of researchers in recent years.Atom transfer radical polymerization(ATRP)is an advanced polymerization method that has been developed in recent years and has been used in small-scale industrial applications.Compared with conventional free radical polymerization,ATRP is much easier to carry out and obtain polymers with determined molecular weight and low molecular weight distribution.Due to the advantages of controlling of polymers with functional groups and specific topology,ATRP has become today’s research Hot spots on polymer science.Based on these ideas,ATRP method was used to synthesize block polymers with CO2 responsive ability;further,the responsive ability and self-assembled morphological changes were studied.The main research included the following aspects:(1)In this paper,PEG2000,PEG6000,PEG20000 and a-bromoisobutyryl bromide were used as raw materials for esterification,and then the macroinitiator were obtained.FT-IR and 1H NMR were adopted for characterization;the results of 1H NMR integral areas were used to calculate the three macromolecules and the number of repeating units of polyoxyethylene ether were 50,165 and 500,respectively.Then,the "ABA" type symmetrical polymers PDM200-PEG50-PDM200,PDM,65-PEG165-PDM165,PDM57-PEG500-PDM57,PDM100-PEG500-PDM100 and PDM133-PEG500-PDM133 were synthesized by ATRP method for by using the three macroinitiators and 2-(Dimethylamino)ethyl methacrylate.EGBIB was synthesized by esterification of ethylene glycol with a-bromoisobutyryl bromide,and then a macroinitiator Br-PDM100-Br was obtained;further,three "BAB" type polymers PAM22-PDM100-PAM22,PAM70-PDM100-PAM70,PAM125-PDM100-PAM125 were obtained.(2)The linear triblock polymers have similar stimulus response to CO2 in aqueous solution;after introducing CO2 into its aqueous solution,the conductivity and viscosity increases and the pH decreases.After the CO2 was expelled by N2,the properties of the solution can be restored to the initial state.Once CO2 was introduced into the aqueous solution,the conductivity and viscosity increase,and the pH decrease.The properties of the solution can be restored to the initial state.The self-assembled structures of the polymers were all vesicular-network structure before and after the introduction of CO2,and the mechanism was protonation and deprotonation of the tertiary amines in the PDM segments.However,due to the proportion of hydrophilic/hydrophobic segments in the polymer,the vesicle structures formed by the polymer in the aqueous solution are different.It was found that due to the longer hydrophobic segments in PEG200-PEG50-PDM200,the polymer molecular formed a"hairpin" type,and a large number of "hairpin" molecules formed a double-layer vesicle structure.For those polymers with shorter hydrophobic length,PDM blocks tend to aggregate while longer PEG chains form a "petal" structure in the outer layer,polymer molecular self-assembled into unilamellar vesicle.On the other hand,since the hydrophobic chains in "BAB" type polymers are fixed in the middle of the polymer molecule and the length is fixed,the self-assembled structure changes from unilamellar vesicle to network structure after CO2 is introduced.It was found that the vesicles had a lower drug release rate,and if CO2 was introduced,the release rate of RhB will be accelerated.(3)A four-armed initiator was synthesized and then(PAMPS50)4 and(PDM50)4 were synthesized by using 2-acrylamido-2-methyl-1-propanesulfonic acid(AMPS)and DM as monomers,respectivily.(PAMPS50-PDM50)4 and(PDM50-PAMPS18)4 were synthesized by using(PAMPS50)4 and(PDM50)4 as macroinitiator.The viscosity of(PAMPS50)4 will be reduced significantly in the presence of inorganic salts,showing an anionic polyelectrolyte effect;there is no CO2-responsive ability of(PAMPS50)4 in pure water or saline.The viscosity of the(PDM50)4 aqueous solution will increases with the addition of CO2.In the(PDM50)4 saline solutions after the introduction of CO2,the viscosity decreased,showing a polyelectrolyte effect.(4)After introducing CO2 into the aqueous solution of(PAMPS50-PDM50)4,the polymer will precipitate due to the equal number of quaternary ammonium groups in PDM and anions sulfonic acid groups in PAMPS;as a result a strong Coulomb force,the precipitate could not be recovered by bubbling N2.The block polymer(PAMPS50-PDM50)4 retains the properties of hydrophobic polymer(PAMPS50)4 and the hydrophobic polymer(PDM50)4.After adding NaCl to the(PAMPS50-PDM50)4 solution,the solution viscosity will decrease and showing polyelectrolyte effect.As the salt concentration increased further,the viscosity of the solution increased and showed the properties of the hydrophobic polymer.Owing to the charge shielding effect,(PAMPS50-PDM50)4 did not precipitate when bubbling CO2 in brine and has CO2 reversibility.In this paper,(PDM50-PAMPS50)4 was not obtained but only to get(PDM50-PAMPS18)4.After the introduction of CO2,due to the higher proportion of PDM,the solution pH deviation far from the isoelectric point,the polymer have more positive net charge,so the polymer is mainly expressed as the nature of PDM and with some extent of CO2 reversibility.