Synthesis Of Thermo-Responsive Polymers And Their Interactions With Surfactants

Due to the excellent properties and controllable response characteristics,thermo-sensitive polymers show potential applications in drug delivery,gene therapy,sensors and separation engineering,etc.In this paper,a series of thermo-sensitive polymers are synthesized.Their thermo-sensitive aggregation behaviors and their intercactions with surfactants are studied systematically,in order to provide both theoretical and experimental data for the further application of thermo-sensitive polymer/surfactant composite system.The main content is as follows:Random copolymers of 2-（2-methoxyethoxy）ethyl methacrylate（MEO₂MA）and oligo（ethylene glycol）methacrylate（OEGMA）were synthesized by atom transfer radical polymerization（ATRP）.The results indicate that the copolymers have an appreciably reversible thermal responsivity that can be attributed to a delicate balance between hydrogen bonds between the copolymers and water molecules and hydrophobic interactions of polymer segments.The lower critical solution temperature（LCST）correlates linearly with the mole fraction of OEGMA units in the copolymer,and can be adjusted by changing the mole ratio of the two monomers.The interactions between copolymer P(MEO₂MA₉₀-co-OEGMA₁₀)and surfactant（sodium dodecyl sulfate（SDS）and dodecyl trimethyl amonium bromide（DTAB））in aqueous solutions with and without salt were explored using dynamic light scattering（DLS）,pyrene fluorescence spectroscopy and nuclear magnetic resonance（NMR）technology.The results have suggested that the self-aggregation of polymer chains is hindered causing the LCST increases due to the electrostatic repulsion and the "locking water" effect caused by surfactant head groups.The addition of inorganic salt（ammonium bromide（NH4Br））has little effect on the interaction between P(MEO₂MA₉₀-co-OEGMA₁₀)and SDS.Organic salts（tetra-n-propylammonium bromide（Pr4NBr）and tetra-n-butylammonium bromide（Bu4NBr））can retard the interactions between P(MEO₂MA₉₀-co-OEGMA₁₀)and SDS by electrostatic interaction,thus resulting less resistance between the aggregation of polymer chains and the LCST decreases correspondingly.A series of star-shaped block copolymers（CDPDPM）of 2-（dimethylamino）ethyl methacrylate（DMAEMA）and MEO₂MA were synthesized via ATRP.The results have shown that CDPDPM exhibits both pH-and thermo-responsive behaviors in aqueous solutions.The star-shaped copolymers with the nearly equal mole fraction of DMAEMA and MEO₂MA show two-step thermo-induced aggregation behavior in water at a pH near the isoelectric point,which corresponds to the formation of branch aggregates and large aggregates consisting of clustered branch aggregates,respectively.Moreover,the micellar behaviors of the synthesized copolymers in aqueous solution are explored.The aggregation process of the copolymer can be generalized into intramolecular aggregation of the hydrophobic chains（corresponding to C1）,formation of premicelles,the aggregation and rearrangement of the premicelles（namely CMC）,as well as the formation of multicore structures.The C1 and CMC values depend on both the MEO₂MA molar fraction and the carbon backbone length of polymers.The interactions between star-shaped copolymer CDPDPM2 and SDS in aqueous solutions were investigated.The effects of nonionic surfactant dodecyl β-D-maltopyranoside（C12G2）and salts including inorganic salt NH4Br and organic salt Bu4NBr on the interaction between CDPDPM2 and SDS have been explored systematically.The results have suggested that SDS molecules can bind on CDPDPM2 by electrostatic interaction and thus weaken the binding ability of CDPDPM2 to water molecules.The LCST decreases with the increase of SDS concentration correspondingly.The introduction of C12G2 changes the interaction between CDPDPM2 and SDS significantly by participate the formation of complexes and the stability of the CDPDPM2/SDS complexes declines leading to the chance of forming larger complexes is deprived at higher temperature.The addition of NH4Br to the CDPDPM2/SDS system can retard the binding of SDS on the polymer chains because of electrostatic shielding.Correspondingly,LCST is higher.For CDPDPM2/Bu4NBr/SDS system,the phenomenon is similar to that of the CDPDPM2/C12G2/SDS system.This should be attributed to the nature of Bu4N+,possesses not only positive charges but also certain hydrophobicity,and thus Bu4N+has the ability to participate and facilitate the formation of SDS micelles.The linear polymer P(MEO₂MA₉₀-co-OEGMA₁₀)and star-shaped polymer CDPDPM2 were introduced to the sodium deoxycholate（NaDC）/L-Aspartic acid（Asp）supramolecular hydrogels.The results have shown that the addition of polymer does not change the gelation route of NaDC/Asp hydrogels though it incorporates in the network structure of the hydrogels.The special structure enables the CDPDPM2 to provide more binding sites for hydrogen bonding and the stronger hydrophobicity endows CDPDPM2 the ability to inhibit the entry of water,thus avoiding the swelling and dissolution of hydrogels.Therefore,the star-shaped polymer CDPDPM2 has more advantages in strengthening the network structure of the hydrogels than the linear polymer P(MEO₂MA₉₀-co-OEGMA₁₀).Furthermore,due to the excellent dye adsorption property and mechanical strength,NaDC/Asp/CDPDPM2 hydrogel has potential to be used in the field of water purification.