Preparation And Property Analysis Of The Zwitterionic Agarose-g-PDMAPS Copolymers

Thermo-sensitive polymers have become very important in academic and applied polymer science over the last decades. The UCST of all known examples is based on either thermally reversible hydrogen bonding or electrostatic interaction. For the electrostatic forces induced UCST behavior, the most studied examples are zwitterionic polymers, such as sulfobetaine-based (meth) acrylic polymers. These zwitterionic polymers are considered to be in a collapsed coil in water below UCST due to intra-and/or inter-chain associations, while in the form of non-associations above UCST. Agarose is a natural polysaccharide extracted from the cellular walls of agarophyte seaweed and exhibits the UCST behavior. Agarose forms the hydrogel due to the helix conformation of the large amount of hydroxyl. Agarose-g-PDMAPS combines the properties of the agarose main chain and that of the PDMAPS graft chain which have great potential useness in biomedical sciences.A novel polysaccharide based zwitterionic copolymer, agarose-graft-poly(3-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate)(agarose-g-PDMAPS) with UCST depending both on hydrogen bonding and electrostatic interaction, is synthesized by ATRP and its properties including solution and aggregation behavior, thermo-sensitive behavior, sol-gel transition and protein-resistence properties are investigated in detail.A series of copolymers were synthesized by varying the graft degrees and graft lengths. As the molecular weight is not only in good correlation with the theoretical molecular weight, but also with narrow polydispersity (1.03<PDI <1.3), we confirm that the copolymerization is well-controlled.1H NMR, FT-IR and GPC are performed to characterize the copolymer. The so called “antipolyelectrolyte effect” is investigated by Ubbelohde viscosity meter. Thermo-sensitive behaviors of the copolymers in water, NaCl and urea solution are tracked by UV, DLS and TEM analysis. The thermo-sensitive aggregation mechanism of the copolymer in aqueous media is proposed and confirmed in detail. In pure water, the copolymer exhibits an UCST behavior. With the addition of NaCl or urea, the cloud point shifts to lower temperature with the increase of their concentrations. And it finally disappears after reaching the critical NaCl or urea concentration. The aggregation mechanism of the copolymer along with the decrease of temperature has been confirmed: the copolymers are first heated into the isolated molecular chains. After the hydrogen bonding from the agarose backbone leads to the “core” building in self-assembly stage, the copolymer turns to isolated sphere during cooling. Then the isolated spheres collide with adjacent ones to form the final aggregates below UCST. Furthermore, UCST of the copolymer can be tuned in a wide range by adjusting the side chain lengths. The sol-gel transition of the copolymer is investigated by inverting the tube. It comes to the conclusion that the gel temperature could be tuned by adjusting the concentration for use as microcarrier for cell encapsulation. Furthermore, the physical copolymer hydrogels show better protein-resistant properties comparing with the pure PDMAPS hydrogel, agarose hydrogel and tissue culture polystyrene (TCPS) samples by ELISA.