M. Padmanabha Raju

Synthesis and Characterization of GAP-PEG Copolymers

ABSTRACT A series of glycidylazide–poly(ethylene glycol) (GAP-PEG) copolymers were synthesized by cationic ring-opening polymerization of epichlorohydrin (ECH) in the presence of poly(ethylene glycol) (PEG) using borontrifluoride etherate (BF3-etherate) as catalyst, followed by the conversion of the CH2Cl groups of poly(epichlorohydrin) (PECH) to CH2N3 groups. The formation of PECH-b-PEG-b-PECH triblock copolymers was confirmed by IR, 1H NMR, and 13C NMR spectroscopy. The corresponding GAP-b-PEG-b-GAP triblock copolymers were characterized by UV, IR, 1H NMR, and 13C NMR spectroscopy. The copolymers have shown an increment in their molecular weights as the higher analogue molecular weight PEGs were used in the polymerizations. The thermogravimetry-differential thermogravimetry (TG-DTG) and differential scanning calorimetry (DSC) studies of the GAP triblock copolymers indicate an increase in the decomposition temperature of the azide groups of GAP block in the copolymers caused by the introduction of higher molecular weight PEG blocks. GAP-PEG copolymers have shown lower glass transition temperatures than the homo glycidylazide polymer. The nitrogen content of the GAP-PEG copolymers was estimated by various methods and the value was in good agreement with the estimated values.

SYNTHESIS AND SWELLING BEHAVIOR OF SUPERABSORBENT POLYMERIC MATERIALS

A series of novel crosslinked copolymers based on the monomers acrylamide (AM), calcium acrylate (CA), and sodium methacrylate (SMA) were prepared by aqueous solution polymerization using ammonium persulfate (APS) as initiator and N, N-methylene-bis-acrylamide (MBA) as crosslinking agent. The synthetic variables monomer concentration, crosslinker concentration, initiator concentration were also studied. The experimental results of SAPs show good absorbency in both water and NaCl solutions. The copolymers were characterized by IR spectroscopy. The water retention of SAPs was studied in an oven at 60 and 100°C.

Swelling and Diffusion Properties of Poly(acrylamide-co-maleic acid) Hydrogels: A Study with Different Crosslinking Agents

Crosslinked hydrogels comprising acrylamide (AAm) and maleic acid (MA) were synthesized by free radical polymerization in presence of a crosslinker using ammonium persulfate (APS) and N,N,N1,N1-tetramethylethylenediamine (TMEDA) as initiator and activator, respectively. The crosslinked hydrogel formation was confirmed by IR analysis. The swelling/de-swelling characteristics were studied in detail for crosslinked poly(acrylamide-co-maleic acid) [poly(AAM-co-MA)] hydrogels containing different amounts of maleic acid. Four different crosslinkers such as 1,2-ethyleneglycol dimethacrylate (EGDMA), 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), and diallyl phthalate (DP) were utilized to study their influence on the swelling behavior of the hydrogels. The effect of reaction parameters such as the concentration of crosslinker and initiator on swelling capacity of the crosslinked poly(AAm-co-MA) hydrogels was also investigated. Further, the influence of various salts, simulated biological fluids, and pH solutions on the swelling pattern of hydrogels was studied extensively. Phase separation morphology of crosslinked hydrogels was also studied by differential scanning calorimetry. The morphology of crosslinked hydrogels were revealed using scanning electron microscopy (SEM).

Synthesis of Polyimide Nanocomposites

A series of polyimide nanocomposite (PINC) films were prepared by using poly(amic acid) and Ba, Sr, Sn, TiO3 nanoparticles via in-situ polymerization method. Poly(amic acid) was synthesized from benzophenone tetracarboxylic anhydride and diamino diphenyl ether by ring-opening polyaddition reaction. The PINC films were characterized by FTIR spectroscopy. The thermal properties of PINC films were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods. The prepared PINC showed major weight loss in the range of 550–600°C in nitrogen atmosphere. These had char yield in the range of 50–60% at 800°C. The morphological studies of PINC films were carried out using SEM method.