Synthesis Of Fast Responsive Polymer Hydrogels And Investigation Of Their Hydrogel Behavior

Polymer hydrogels are a class of functional materials that combine the functions of absorbent, water retention and release, and thus have a wide range of biomedical applications such as drug delivery and etc. Among all the hydrogels, PNIPAAm hydrogels are extensively studied by scholars and recognized as the standard material. Using the new controlled polymerization methods, the introduction of pro / hydrophobic components, the design of the gel structure favorable to produce nano-micro-zones are effective ways to modify the conventional PNIPAAm hydrogels to improve its LCST and swelling properties. Besides, by selecting materials that are more biocompatible (such as MEO₂MA) to prepare new aternatives of PNIPAAm hydrogel is a recent research focus.In this paper, RAFT / MADIX polymerization methods are employed to prepare a series of temperature-sensitive block copolymers and their crosslinked networks .Nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC) were employed to characterize these block copolymers and networks. The results from Differential scanning calorimetry showed the miscibility of the copolymers and the swelling, deswelling, reswelling experiments reflected the response rate of the hydrogels. The main works are as follows: 1. Poly (N-isopropyl acrylamide)-block-poly(ethylene oxide)-block- poly(N-isopropyl acrylamide) (PNIPAAm-b-PEO-b-PNIPAAm) triblock copolymer was synthesized via the reversible addition-fragmentation chain transfer-macromolecular design via the interchange of xanthate (RAFT/MADIX) process with xanthate-terminated poly(ethylene oxide) as the macromolecular chain transfer agent. This approach was successfully employed to prepare poly(N-isopropyl acrylamide)-block-poly(ethylene oxide) (PNIPAAm-b-PEO) copolymer networks whilst N,N'-methylenebisacrylamide was used as the crosslinking agent. With the RAFT/MADIX process, PEO chains were successfully blocked into PNIPAAm networks. The unique architecture of PNIPAAm-b-PEO networks allows investigating the effect of the blocked PEO chains on the deswelling and reswelling behavior. The hydrogel behavior of the PNIPAAm-b-PEO networks was investigated in terms of swelling, deswelling and reswelling tests. It was found that with the PEO chains into the PNIPAAm networks, the swelling ratios of the hydrogels were significantly enhanced. The PNIPAAm-b-PEO hydrogels displayed faster response to the external temperature changes than control PNIPAAm hydrogel. The accelerated deswelling and reswelling behaviors have been interpreted on the basis of the formation of PEO microdomains in the PNIPAAm networks, which could act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the PNIPAAm networks.2. Poly (2-(2-methoxyethoxy)ethylmethacrylate-co-oligo(ethylene glycol methacrylate) (ie. P(MEO₂MA-co-OEGMA300)) block copolymer and networks were synthesized via RAFT/MADIX process with xanthate-terminated P(MEO₂MA-co-OEGMA300) as the macromolecular chain transfer agent whilst ethyleneglycol dimethacrylate(EGDMA) was used as the crosslinking agent. P(MEO₂MA-co-OEGMA300) chains hang onto the copolymer networks of PMEO₂MA and OEGMA and formed unique architecture. The hydrogel behavior of the P(MEO₂MA-co-OEGMA300) networks was investigated in terms of swelling, deswelling and reswelling tests. It was found that compared with control P(MEO₂MA-co-OEGMA300), the swelling ratios and responsive rate of the hydrogels were enhanced. The accelerated deswelling and reswelling behaviors have been interpreted on the basis of the hydrophilic P(MEO₂MA-co-OEGMA300) dangling chains on the P(MEO₂MA-co-OEGMA300)networks, which are very active and act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the P(MEO₂MA-co-OEGMA300) networks. Also as the chemical structure of the macromolecular chain transfer agent(CTA) was the same with the matrix network, the system was homogeneous and exhibited unique biocompatibility. By synthesizing a series of CTAs with different molecular weight (ie. the chain length), we investigated the effect of chain length and chain number on swelling properties of the hydrogels.3.Poly(Vinylpyrrodinel)-block-poly(2-(2-methoxyethoxy)ethylmethacrylate-co-oligo(ethylene glycol methacrylate) (ie. PVP-b- P(MEO₂MA-co-OEGMA300)) block copolymer was prepared via the reversible addition-fragmentation chain transfer-macromolecular design via the interchange of xanthate (RAFT/MADIX) process with xanthate-terminated PVP as the macromolecular chain transfer agent. This approach was successfully employed to prepare PVP-b- P(MEO₂MA-co-OEGMA300) copolymer networks whilst Ethyleneglycol dimethacrylate was used as the crosslinking agent. With the RAFT/MADIX process, PVP chains hang onto the copolymer networks of PMEO₂MA and OEGMA and formed unique architecture. The hydrogel behavior of the PVP-b- P(MEO₂MA-co-OEGMA300) networks was investigated in terms of swelling, deswelling and reswelling tests. It was found that with the PVP chains into the P(MEO₂MA-co-OEGMA300) networks, the swelling ratios of the hydrogels were enhance. Also,the hydrogels displayed faster response to the external temperature changes than control hydrogel. The accelerated deswelling and reswelling behaviors have been interpreted on the basis of the hydrophilic PVP dangling chains on the P(MEO₂MA-co-OEGMA300) networks, which are very active and act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the P(MEO₂MA-co-OEGMA300) networks.