Preparation And Properties Of Functional Polyacrylamide Based Gels

Functional hydrogels are three-dimensional hydrophilic polymer network or IPN that exhibit characteristic response to external stimuli (such as temperature, pH, solvents, light, electric field, etc), or possess some specific features.Currently, there are some problems existing in the study of functional hydrogels which will hinder their potential applications. First, the equilibrium swelling rate of hydrogels is not high. Second, the hydrogels usually do not have sufficient mechanical strength to fulfill the practical application. Third, the response speed of hydrogels is slow and chemical initiator is often used in the synthesis which have much detriment on the biomedical applications. Finally, the majority of functional hydrogels have only a single stimulus-response performance which can not meet the requirements of a multiple response of system. Therefore it is an important issue to develop high-strength, fast response, good biocompatibility and multi-functional hydrogels.In the first part of this paper, N-isopropylacrylamide (NIPA) and acrylamide(AM) was used as monomer to prepare high mechanical strength and conductivity hydrogels by introducing functional nano carbon nanotubes (MWNT). The temperature sensitivity, swelling dynamics, mechanical properties and electric properties of the hydrogels were analyzed in detail. In the second part, copolymerization hydrogels were synthesized from acrylamide (AM) and methyl-2-hydroxy ethylmethacrylate (HEMA), which have good biocompatibility, with clay as physical cross-linking agent. The pH sensitivity, swelling dynamics and mechanical properties were also studies and the promising applications in chemical equipment, tissue engineering, drug release system, etc could be expected. The main results are as follows:1.Temperature-sensitive PNIPA/MWNT/Clay composite hydrogelA novel gel, PNIPA/MWNT/Clay, was prepared via in situ free radical aqueous polymerization from NIPA in the presence of Clay, and MWNT was added as fillers. The gels showed a porous structure and the size of porous became large with increasing content of MWNTs. The volume phase transition temperature (VPTT) was increased with the increasing content of MWNT. When MWNT content reached 1.12%, the VPTT reached to 37℃(close to body temperature), and the swelling properties were improved to some extent.The mechanical properties of the gels were also increased with the adding of MWNT. When the content of MWNTs was increased from 0 to 1.19wt%, the tensile strength of the gels increased from 0.15 to 0.35 MPa, and the gel with high content of MWNT could be elongated to more than 900% when the content of water reached 500%, which increased 0.5 times on breaking elongation and 1.3 times on tensile strength compared with NC gel without MWNT.Due to the good electrical properties of carbon nanotube, the conductive properties of hydrogels increased slightly. The conductivity of the the gel with high content of MWNT attained to 1.09 ms/cm when the content of water reached 700% and the lower water content made it further increase.2. PAM/MWNT/Clay composite hydrogelPAM/MWNT/Clay was prepared via in situ free radical aqueous polymerization. In the hybrid gels, the clay acted as functional crosslinker and BIS played the role of chemical crosslinker.The gels had good compression performance and were able to recovery instantly after removing the load. It was found that, in the high ratio of water, AC gels appeared low tensile strength and elongation. While the mechanical properties of the AC gels tended to be increased with the decreasing of water.The results of conductivity showed that MWNT formed a internal conductive network in the case of low water content.3. Copolymerization PAM/HEMA/Clay gelsA series of pH sensitive hydrogels were prepared. The gels possessed obvious porous structure and the distribution of pores was uniform which resulted in the high swelling ratio. The gel with high content of AM had a high swelling ratio as a result of the amide group (-CONH2) in AM is easier to form hydrogen bonds than the hydroxyl group (-OH) in HEMA. The copolymer gel showed the lowest degree of swelling ratio in the pH value of 7, which indicated it had a sensitive response of pH.The gels had good compression performance and were able to recovery instantly after removing the load. The tensile strength of the gel with high content of AM was 0.5 MPa and the breaking elongation could be more than 400% when the content of water reached 350%.