The Study On The Structure Of Polymer Hydrogel And The Rheological Properties Of HPAM Aqueous Solution

Hydrogels are widely used in many fields, such as biochemistry, medicineand so on, because of their excellent biocompatibility and physicochemicalproperties. The field and the range of hydrogels be used are usually different fortheir different microstructures and properties, so the problem that control thestructures of the hydrogel to make use of hydrogels in more widely field is wemust deal with now.The curing theory of polymer is one of the most important parts of thepolymer statistic theory. The critical gel points, the distribution of sol/gel and thenetwork structure of gels in process of cross-linking reaction have been madefurther studied and discussed in polymer statistic theory and some importantachievements have been got. But there are still have some deviations between thetheoretical prediction and the experimental results in polymer statistic theory. Oneof the most important reasons for the deviations is that we cite an importanthypothesis in the theories' calculation: intramolecular cyclization only exists in thegel molecules, and there is no intramolecular cyclization before the gel points. Infact, it is inevitable that the intramolecular cyclization reaction will happen beforethe gel points in the real reaction, so further studies were necessary.There are three ways to prepare hydrogels: 1, hydrogels can be prepared bythe reaction of linear polymer with cross-linker. 2, hydrogels can be prepared bythe monoene/diene radical copolymerization. 3, hydrogels can be got by thepolycondensation of multi-functional groups.There are many theory models about the cross-linking reaction in polymerstatistic theory, but most of them are deal with the polycondensation. Relatively,there are fewer studies on the long chain polymer cross-linking and free radicalcopolymerization reaction. It is because the mechanisms of the free radicalcopolymerization reaction are more complicatedly and there are too manyparameters in the system. So the system of long chain cross-linking of polymersand the A4 -A2 random copolymerization reaction have been studied base on thepolymer statistic theory, discussing about the gel fraction, sol/gel distribution,critical gel point and the network structure of gels of these two reaction systems.The results will provide the relationship of the structure and properties of gels withcorresponding theories for the further study.In this paper, we obtain some new results through the study of thecross-linking reaction of the polyvinyl alcohol (PVA) with glutaraldehyde (GA)and the copolymerization of N, N'-methylene-bis-acrylamide (BIS) .The resultsare:For the long-chain of polymers cross-linking system: 1, both inner cyclizationfractions and mixture ratios at the critical gel points will decreased with theincreasing of polymer concentrations. The bulk gels do not form when PVAconcentration is below a certain value. 2, in a certain range of PVA concentrations,inner cyclization fractions are basically independent of the increase of gel fractionsabove the critical gel points and keep constant. 3, the increasing rate of thefractions of gels' is influenced by the concentration of the polymer, in a certainrange, the lower polymer concentration is the higher increasing rate of gels is. 4,the swelling ratio decreases with the increasing of the polymer concentration andcross-linker content.As for the system of the polyacrylamide gels synthesized by free radicalcopolymerization: 1, the increase of the gel fractions will be divided into threesteps with the increase of the concentration of the cross-linking. 2, the analysis ofdynamic in the process of the addition reaction demonstrate that the probability ofchain propagating is not consistent with the assumption of that it is a constant inthe literature, it will decreased with the increase of monomer conversion .3, themole fractions of cross-linker at the critical gel points were proportional to the[M]-1/2(M is moment concentration of monomer). The mole fraction of cross-linkerat the critical gel points increased with the decrease of the initial monomerconcentration caused by the effect of dilution, which lead to the increase of theprobability of termination by intramolecular combination. 4, the ways of the gelsincrease affect by the concentration of the initial monomer. 5, the tendency ofphase separation decreased with the increase of the cross-linker in the AM/BIScopolymerization system. The swelling ratios of the polyacrylamide gels got themax value where the behaviors of phase separation vanish. Correspondingly, theconcentration of cross-linker and the max swelling degree decreased with theincrease of the initial concentration. The tendency of the physical entanglement ofthe polymer increased and the swelling degree of its gel decreased with theincrease of the initial concentration, 6, the ratios of cross-linker to monomer at thecritical gel points are affected by the chain transfer agent. The higher theconcentration of the chain transfer is, the bigger the ratio of cross-linker tomonomer at the critical gel points is .It has a linear relation with the ratio ofcross-linker to monomer on the concentration of the chain transfer reagent.Otherwise, as for the water-soluble polymers have been used in manyindustrial applications, the rheologic behaviour of its solution has been studied. Inthis paper, distilled water and simulant salt water have been taken as solventsrespectively. Steady shear viscosity (η ), the first normal stress difference (N1),modulus (G ), loss tangent (tgδ) and complex viscosity ( η *) and the othersrheologic behaviors have been studied by using Haake rheometer under variousconcentration, temperature and the added salt of electrolyte. The results showedthat:1, the steady shear viscosity of HPAM solution decreased with the increase ofshear rate and HPAM showed a shear-thinning behavior. 2, in a certain shear rate,the relationship of the first normal stress difference with the shear rate of HPAMsolution obey a power-law relation;At the same shear rate, the higher theconcentration of the polymer is, the greater the first normal stress difference is. 3,the elastic behaviour of the polymer is results of the orientation and theconformation of polymer chain's. The elastic behaviour caused by orientation atthe low shear rate and caused by conformation of polymer chains at higher shearrate. The flexibility of the chains' increased and the first normal stress differencedecreased with the increase of temperature. 4, the result of the dynamic showedthat, the elastic behaviour of HPAM solution became more apparently with theincrease of the frequency and concentration within the range of measuringfrequency. 5, complex viscosities are higher than the steady shear viscosities ofHPAM solution at a higher shear rate for the influence of the hydrogen bond.In a word, the synthesis and the characterization of hydrogel as well as theproperties of HPAM aqueous solution were studied in this paper, moreover, theresults were more significantly for the synthesize and the application ofwater-soluble polymer as well as its hydrogel.