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37 MPa. These, according to the authors, allow the use of new materials as
artificial cartilage.
Preparation of hydrogels
to form between the polymer components of the
covalent bonds in the step of polymer synthesis techniques that are composed of
two sequential steps. In the first step of forming one of the polymer components,
of which the macromolecules contain reactive functional groups. In the second
step the reaction medium containing the polymer synthesized in Step 1 was
injected monomer (s) forming a second polymer covalently binds to the first.
This group includes a method for the synthesis of the graft, block - copolymers
and macromolecular structures, called in English literature "conetworks", which
are actually not linear and cross-linked block - copolymers (block - copolymer
nets). In the synthesis of these structures are used known methods, described in
monographs and reviews [24-26]. We know a lot of graft and block -
copolymers constructed of hydrophilic fragments [27-34]. But not all of them are
capable of producing hydrogels from - for complete solubility of the copolymers
in water. Hydrogels are formed either by inclusion in the composition of graft or
block - copolymer resin fragments, having a pronounced ability to form grids in
aqueous media, for example, by hydrogen bonds (gelatin) or by introducing into
the reaction mixture crosslinkers.
Example hydrogels based graft copolymers is given in [27], which
describes hydrogels - superabsorbents obtained by grafting of acrylamide and
sodium acrylate on gelatin; grafting said monomers in an aqueous medium was
carried out at 60 °C in the presence of an initiator - of ammonium persulfate. the
authors present a grafting mechanism in terms of hydrogen abstraction from the
functional groups of gelatin (-COOH, -NH
2
, -SH) and subsequent initiation of
the copolymerization of acrylamide and sodium acrylate arising macroradicals.
Such a process should be accompanied by the formation and the ungrafted
copolymer, but its amount was very small (3 %). For hardening of the hydrogel
in the copolymerization in the reaction medium is added to a small amount of a
crosslinking comonomer - methylene-bis-acrylamide (MBAA). Hydrogels
obtained under optimum synthesis conditions are capable of absorbing water up
to 275 g per 1 g of the polymer, indicating the desirability of their use as
effective sorbents. This type supersorbents easily regenerated, that is, the cycle
of water sorption - desorption can be carried out repeatedly, because of the
sensitivity of the hydrogel to the pH of the environment. After reaching
maximum adsorption at pH 7-8, followed by lowering pH to 2 frees up to 80
%
adsorbed water. It should be noted a fairly high rate of swelling and collapse of
the hydrogel. One such cycle is held for 20-30 minutes.
Another example of obtaining hydrogels based on graft polymers relates to
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