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the synthesis of comb graft - PIP-PEO copolymer [28]. Hydrogels of these
polymers have the ability to collapse at 32-34 ° C [29]. This property finds a
number of uses - the use of hydrogels as carriers of drugs, drug-releasing when
the temperature rises above 32-34 ° C, i.e. at temperatures close to human body
temperature. To date, much research done by modifying the properties of PIPA
to vary the temperature of the hydrogel and rate of collapse. Hydrogels IPA graft
copolymers differ significantly higher rate compared to collapse homopolymer
hydrogels IPA. Differences in the kinetics of hydrogels compression samples
having the same geometrical dimensions. If the compression rate of conventional
PIPA hydrogels is inversely proportional to the square of the sample size, in the
case of graft copolymers IPA collapse rate is inversely proportional to the size of
the sample in the degree of 1.58. The authors [28] observed effects for graft
copolymers explain:
- strong hydrophobic interactions comb grafted chains after PIP their
dehydration;
- Acceleration of the release of water from the hydrogel through the channels
formed by the PEO macromolecules.
Grafting hydrophilic monomers PIP increases the collapse temperature to
body temperature [30], and if the grafting monomer is an ionic compound as the
hydrogel becomes pH-sensitive. Such a case is implemented in [31] by grafting
itaconic acid to PIP. The presence of carboxyl groups in the copolymer, on the
one hand, provides specific sorption substances hydrogel containing a basic
functional group, on the other hand, to release the sorbed substance in a
controlled manner. Thus, the lidocaine drug substance containing a tertiary
amino group is released from the hydrogel in three stages. lidocaine released
initially, sorbed nonspecific manner (pores containing water), followed by
lowering the pH to 5.5 (pKC1OOH 5.44) is released the second portion of
material while further lowering the pH to 2.0, which is significantly lower pK a
second carboxyl group itaconic acid (pKC2OOH 3. 85), leading to the explosive
nature of the release of lidocaine. In [32], a type of heat-sensitive hydrogels
based on block-poly (block-glycidol-block-ethylene oxide-block-glycidol).
Synthesis of block-copolymers was carried out under the scheme:
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