Sıcaklığa duyarlı N-izopropilakrilamit (NIPAAm)in nötral ve, hidrofobik dimetilitakonat (DMI),
hidrofilik itakonik asit (IA), hidrofilik/hidrofobik monoester komonomerlerini içeren NIPAAm/DMI,
...NIPAAm/IA veNIPAAm/monoitakonat hidrojelleri, çapraz bağlayıcı bileşen olarak hem hidrofilik N,N'-
metilenbis(akrilamid) (BIS) hem de hidrofobik vinil sonlu poli(dimetilsiloksan) (VTPDMS) varlığında,
potasyum persulfat (KPS)-N,N,N',N'-tetrametiletilendiamin (TEMED) redoks başlatıcı çifti ve AIBN
kullanılarak su/metanol karışımında ve dioksanda serbest radikal çözelti polimerizasyonu ile sentezlendi
ve bunların sıcaklığa bağlı şişme özellikleri ve sıkıştırma modülleri hesaplandı. Hidrofobik makro
çapraz bağlayıcı VTPDMS kullanılarak elde edilen nötral NIPAAm hidrojellerinin mekanik dayanımlarının,
BIS gibi dört fonksiyonlu çapraz bağlayıcılar kullanılarak elde edilen jellere göre yaklaşık 10 kat
daha fazla olduğu gözlendi. Hidrofobik komonomerler (monobutil itakonat (MBuI), mono oktil itakonat
(MOcI) ve mono setil itakonat (MCeI) ile iki farklı çapraz bağlayıcı BIS konsantrasyonunda NIPAAm
hidrojelleri sentezlendi ve bunların mekanik dayanım deneyleri yapıldı. BIS kullanılarak sentezlenen
NIPAAm hidrojellerinin sıkıştırma modülleri ve çapraz bağ yoğunlukları, alkil zincirlerinin uzunluğunun
artmasına paralel olarak MCeI>MOcI>MBuI sıralamasına göre beklendiği şekilde artış gösterdi.
Elde edilen bu sonuçlar doğrultusunda ilaç salımında kullanılmak için çapraz bağlayıcı olarak BIS ve
VTPDMS kullanılarak sentezlenen NIPAAm, NIPAAm/IA, NIPAAm/monoitakonat homopolimer ve kopolimer
hidrojelleri seçildi. IA, DMI, MMI, MBuI, MOcI ve MCeI komonomerlerini kullanılarak, AIBN
ve KPS/TEMED redoks başlatıcı çifti eşliğinde 1,4-dioksan ve metanol/su çözücü karışımında toplam
monomer konsantrasyunu 0.7 mol/L sabit tutularak, NIPAAm in doğrusal kopolimer ve terpolimerleri
serbest radikal çözelti polimerizasyonu ile sentezlendi ve bu kopolimerlerin alt kritik çözelti sıcaklıkları
incelendi.
Poly(N-isopropyl acrylamide) (PNIPAAm) has become
the most popular member of a class of polymers
that exhibits inverse solubility in aqueous solutions.
This property is contrary to the solution behavior
of most polymers in organic solvents under
atmospheric pressure near room temperature. Its
macromolecular transition from a hydrophilic to a
hydrophobic structure occurs at a temperature
which is known as the Lower Critical Solution Temperature
(LCST). This temperature, being a function
of the micro-structure of the polymer chains lies between
$30^0C$ and $35^0C$. PNIPAAm has been used in
many forms including single chains, macroscopic
gels, micro gels, latexes, thin films, membranes,
coatings and fibers. Moreover, wide ranges of disciplines
have examined PNIPPAm, encompassing
chemistry, physics, rheology, biology and photography.
PNIPAAm has been synthesized by a variety of
techniques. Free radical initiation in organic solvents
and aqueous media is only one of these experimental
methods. Various initiators and solvents
such as potassium persulfate (KPS), Ammonium persulfate
(APS), azobis(isobutyronitrile) (AIBN), benzoylperoxide,
laurylperoxide and water, methanol,
benzene, 1,4-dioxane, tetrahydrofuran (THF), respectively,
have been used in free radical polymerization
produced in organic solvents and in aqueous
media.Redox polymerization of NIPAAm typically
uses APS or KPS as the initiator and either
N,N,N',N' tetramethylethylenediamine (TEMED) as
the accelerator.
In this study, taking into account the above literature
results, we have attempted to investigate the effect of
initiator type and concentration, hydrophobic and
ionizable comonomers, and synthesis-solvent composition
on the swelling behaviour of NIPAAM gels. For
this purpose, NIPAAM gels, initiated with two different
initiator concentrations, in water, and
NIPAAM/DMI (dimethyl itaconate) and NIPAAM/
IA and NIPAAm/monoesters of IA copolymer gels in
water/methanol mixtures and 1,4-dioxane were synthesized
and their volume phase transitions were examined.
Conventional swelling theory is used to
characterize the interactions between the polymer
and solvent molecules.
Monoitaconates containing methyl, butyl, octyl and
cetyl groups were synthesized. The copolymers
containing these monoitaconates, IA and DMI were
obtained by free-radical solution polymerization of
NIPAAm.
Hydrogels composed of NIPAAm, BIS, vinyl terminated
poly(dimethyl siloxane) (VTPDMS) (commercial
product) and IA as hydrophobic monomer, hydrophilic
crosslinker, hydrophobic crosslinker and
weakly ionizable comonomer, respectively, were
prepared to investigate the effect of hydrophobic
component, i.e., VTPDMS on the compression moduli
of the samples attained equilibrium swollen state
in distilled-deionized water at $25^0C$. For the NIPAAm/
monoitaconate copolymer hydrogels crosslinked
with BIS, the effects of hydrophobic component
i.e., monobutyl itaconate (MBuI), monooctyl
itaconate (MOcI) and monocetyl itaconate (MCeI)
on the compression moduli of the samples attained
equilibrium swollen state in distilled-deionized water
at $25^0C$ were investigated. Compression moduli
and crosslinking densities of NIPAAm hydrogels
containing 2.50 and 5.0 mole % of monoesters of IA
in the feed and crosslinked with BIS increased with
alkyl chain length in the order of MCeI > MOcI >
MBuI.
Theophylline was used as a drug for controlledrelease
of PNIPAAm, NIPAAm/IA and NIPAAm/
monoitaconate copolymer hydrogels crosslinked
with BIS and VTPDMS. PNIPAAm hydrogel
crosslinked with VTPDMS has the lowest drug
release capacity because of the unresemble
structures to each other. The presence of hydrophilic
and ionizable IA molecules in the structures of
NIPAAm hydrogels increases the release capacities
and rates of hydrogels crosslinked with BIS or
VTPDMS because repulsive forces between the -
COO- groups controls the shrinking rate at $37^0C$ and
so the drug molecules do not trap in the polymeric
network.
PNIPAAm, poly(dimethyl itaconate) (PDMI) and,
copolymers of NIPAAm with IA, DMI, MMI, MBuI,
MOcI and MCeI were obtained by free radical
solution polymerization using AIBN and
KPS/TEMED redox pair, as initiator, in 1,4-Dioxane
and in MetOH/DDW with a total monomer
concentration of 0.7 mol/L. The sensitivity of
NIPAAm copolymers to change in pH and
temperature suggest that they could be useful in
biotechnology and drug delivery applications where
small changes in pH and temperature.
