| With the rapid development and progress of society,stricter ecological protection demands were being putting up accordingly.Environmental-friendly water solvent is becoming more and more important in many industrial processes.Double-hydrophilic block copolymer is a special class of water-soluble block copolymer.This kind of copolymer is typically composed of a solubility-promoting block with permanent hydrophilicity in water,and a functional block with stimuli-responsiveness.Compared with conventional amphiphilic polymers,double-hydrophilic block copolymers can exhibit a wide range of aggregating structures and properties in water,and are more flexible in switching the functions to meet more requirements.Thus,double-hydrophilic block copolymers have wide ranges of applications in many fields.In recent years,heavy oil resource is attracting more and more attention with the exploration and development of oil and gas gradually shifting to the unconventional oil and gas.China is abundant of heavy oil resources.However,the high viscosity,high density and poor fluidity often make the heavy oil difficult to extract.Many studies have been carried out on the structure of heavy oils,and it was found that the high content of resins and asphaltenes is the most important reasons for the high viscosity of heavy oils.These polar molecules can form huge aggregating networks inside the heavy oil,and prevent the free slips between molecules in heavy oil.Many water-soluble heavy oil viscosity reducers have been developed to reduce the high viscosity of heavy oil.They could be combined with the thermal recovery technology to achieve better recovery of heavy oil.However,most of the viscosity reducers developed till now often showed relatively rudimentary properties,and could not meet the requirement for functional adjustment as required during the mining process.Therefore,the designing of functional molecules possessing tunable interactions with heavy oil,and development of efficient heavy oil viscosity reducers that can adjust the emulsion stability reversibly are the main directions of the research in the field of heavy oil viscosity reduction.In this work,various stimuli-responsive double-hydrophilic block copolymers with different molecular structures and responding modes were designed and synthesized basing on the understanding of composition of heavy oil.These block copolymers possess controllable polymeric structures and clear functional divisions.The aggregating behaviors of the block copolymers were investigated in aqueous solutions.Interactions between copolymers and asphaltenes and resins in heavy oil were also explored,and the viscosity reduction performances were evaluated.The main content includes the following five parts:1.A series of dual-temperature and ethonal solvent-responsive poly(Nacryloylmorpholine)-b-poly(N-isopropylacrylamide)(PNAMO-b-PNIPAm)doublehydrophilic block copolymers were prepared by reversible addition-fragmentation chain transfer(RAFT)polymerization in aqueous solution.The structure and molecular weight of these block copolymers were characterized by 1H NMR spectra and GPC measurements.The aggregating behavior and phase-transition behavior of PNAMO-b-PNIPAm block copolymers were studied by DLS,TEM,light tranmittance method and DSC measurements in solvents with various ethonal contents.It was found that the copolymers could be greatly responsive to the variation of temperature and ethanol conten in solvent,and the temperature-induced phase transition behavior of these copolymers would become more obvious with the addition of ethonal.The copolymer samples showed great viscosity reduction performance when applied to heavy oil systems with asphaltenes and resins.These copolymers had obvious interactions with asphaltene and resin aggregates,and could reduce the viscosity of heavy oil with relatvely smaller dosages than the products in existing studies.Therein,PNAMO100-bPNIPAm50 achieved degree of viscosity reduction(DVR)of 92%for heavy oil(ηapp,50℃=4165 mPa·s)with the polymer dosage of 30 mg·L-1.This part of work investigated the heavy oil viscosity reduction performance of double-hydrophilic block copolymers preliminarily,and confirms their promising application in the field of viscosity reduction in heavy oil.2.A series of poly(N-acryloylmorpholine)-b-(N,N-dialkylacrylamide)double-hydrophilic block copolymers with different side chain lengths were prepared as heavy oil viscosity reducers by RAFT polymerization method.The copolymers could interact with asphaltenes and resins in heavy oil,and greatly reduce the viscosity of heavy oils with various viscosities.The structure and molecular weight of these block copolymers were characterized by]H NMR spectra and GPC measurements.The aqueous solution properties of these doublehydrophilic block copolymers were investigated through light transmittance methods and interfacial tension tests.The results showed the side chains in N,N-dimethylacrylamide(DMAm)polymers were short,and the heavy oil viscosity reduction performance of the PDMAm-containing copolymers were relatively poor due to their weak amphiphilicity.While N,N-diethylacrylamide(DEAm)polymers had longer alkyl side chains and showed significant thermo-responsive properties in water.At high temperatures,PDEAm block in copolymer chains would dehydrate and act better outside the asphaltene polar aggregates at the heavy oil/water interface.Block copolymers containing PDEAm block could achieve DVR of 92%for conventional heavy oil(ηapp,50 ℃=4165 mPa·s)at the dosage of 25 mg·L-1,achieve DVR of over 95%for super-heavy oil(ηapp,50℃=22430 mPa·s)with polymer dosage of 50 mg·L-1,and achieve DVR of 98%for extra-heavy oil(ηapp,50 ℃=85820 mPa·s)at the dosage of 200 mg·L-1.The obtained block copolymer products showed low dosages,high viscosity reduction effects and great gcneralisabilities in the viscosity reduction for conventional heavy oil,superheavy oil and extra-heavy oil,showing great potentials for industrial application.3.A series of pH-responsive poly(N-acrylomorpholine)-b-poly(acrylic acid-co-N,Ndimethylacrylamide)(PAADM)double-hydrophilic block copolymer as heavy oil viscosity reducers were prepared by RAFT polymerization.The structure and molecular weight of these block copolymers were characterized by 1H NMR spectra and GPC measurements.Results of interfacial tension tests and heavy oil viscosity reduction tests showed that the addition of polyacrylic acid in the block copolymers could enhance the interfacial activity and viscosity reduction effect of the polymers on heavy oil.Besides,the aggregating behavior of PAADM block copolymers were investigated using DLS measurement.The carboxylic acid groups in the polymer chains could combine with metal cations in aqueous solution through electrostatic interaction and form self-assembled structures accordingly.Thus,the aggregating behaviour of copolymer would be less affected by the salts and show better tolerance in mineralized water.To further enhance the interfacial activity of polymer solutions,the polymer products were combined with organoamines with different chain length through electrostatic interactions.These copolymers combined with organoamines were characterized by surface tension tests,interfacial tension tests,contact angle tests and heavy oil viscosity reduction tests.The results showed that the organoamine-combined copolymers would have better surface/interfacial activity and heavy oil viscosity reduction performance with the growth of chain lengths and combination ratio of the organoamines.With the combination of n-orthodecylamine,contact angle between heavy oil and aqueous solution of PAADM-5 copolymer with concentration of 1000 mg·L-1 was reduced from 28.6° to 13.9°,and the interfacial tension(IFT)was reduced from 12.26 mN·m-1 to 8.46 mN·m-1.The addition of organoamines significantly improved the heavy oil viscosity reduction effect of the polymer.It provided a convenient method to regulate heavy oil viscosity reduction properties of polymers.4.A series of star-[poly(N-hydroxyethylacrylamide)-b-poly(dimethylaminoethyl methacrylate)]4(S-PHEDM)double-hydrophilic star block copolymers with different degree of polymerization of monomers were prepared as heavy oil emulsifiers through RAFT polymerization method.The structure and molecular weight of these star copolymers were characterized and analyzed by 1H NMR spectra and GPC measurements.The heavy oil emulsification behaviors of these star copolymers were investigated using optical microscopy and Turbiscan Lab analysis.At ambient temperature,the heavy oil emulsification ability of the star block copolymers increased and then decreased with the growth of poly(dimethylaminoethyl methacrylate)block in copolymer chains.Therein,S-PHEDM-2 star copolymer could emulsify the heavy oil greatly and form emulsions with small and uniform oil droplets at the dosage of 500 mg·L-1.Based on the pH-responsiveness of the copolymers,cyclic regulations of emulsion stability were achieved through the regular changes in pH values of oil/water mixing systems.Afterwards,the polymers were applied to the field of heavy oil viscosity reduction.Under alkaline condition,S-PHEDM-2 copolymer could achieve DVR of 99.88%for heavy oil(ηapp,50℃=85820 mPa·s)at the dosage of 1000 mg·L-1.The dehydration rate of the heavy oil emulsion was 25.58%after standing for 1h.When the heavy oil mixing system was adjusted to acidic,heavy oil emulsion demulsified rapidly and achieved the dehydration rate of 90.7%within 1 hour.The heavy oil emulsification ability of these copolymers exhibited great pH-responsiveness.They could achieve transformation between emulsification and demulsification of heavy oil by adjusting pH values of oil/water mixing systems.This work provided a new idea to enhance the efficiency and reduce the costs in heavy oil recovery.5.A series of double-hydrophilic star block copolymers with different block sequences were obtained by RAFT polymerization by changing the feeding sequence of Nhydroxyethylacrylamide(HEAm)and dimethylaminoethyl methacrylate(DMEAMA)monomers based on the structure of star block copolymer.Structures and molecular weight of thses star block copolymers with different block sequences were characterized by 1H NMR spectra and GPC measurements.The aggregating behavior of the star copolymers with different block sequences and their pH-responsiveness were investigated uding DLS,TEM,fluorescence spectra and interfacial tension tests.The results showed that the block sequence had significant effects on the polymer properties in solution.For S-PDMHE star copolymers with PDMAEMA block near the star core,the pH-responsive groups were exhibited at a higher density compared to S-PHEDM copolymers with PDMAEMA at the end of the star arms.Under alkaline conditions,S-PDMHE block copolymers showed higher interfacial activity,which allowed it to exhibit better performance of heavy oil viscosity reduction.Therein,S-PDMHE-a block copolymer in weak alkaline aqueous solution achieved DVR of 99.2%for heavy oil(ηapp,50℃=85820 mPa·s)at the dosage of 70 mg·L-1.While S-PHEDM-a copolymer with the same composition as S-PDMHE-a required a dosage of 200 mg·L-1 to achieve the same DVR.Besides,S-PDMHE copolymers possessed relatively stronger pHresponsiveness,and could rapidly turn to be hydrophilic and achieve the oil-water separation at acidic conditions.This part of the work revealed the importance of block sequences in star block copolymers on their properties and applications.It provided great basis for understanding the structure-property relationships of complex block copolymers and regulate polymer properties through the precise designing of molecular structures. |
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