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. Anahtar Kelimeler: Poli(NIPAAm) jelleri, NIPAAm/IA, LCST, poli(dimetilsiloksan), mekanik dayanım, sıkıştırma modülü, kontrollü ilaç salınımı.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 30oC and 35oC. 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 25oC. 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 25oC 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 controlled-release 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 37oC 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. Keywords: poly(NIPAAm) gels, poly(NIPAAm-co-IA), LCST, Poly(dimethylsiloxane), mechanical strength, compression module, drug delivery systems
