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Dhevi, D. M.,Anand Prabu, A.,Kim, K. J. Springer Science + Business Media 2016 Polymer bulletin Vol.73 No.10
<P>Hyperbranched polymers find applications in many fields such as biomedical, catalysis, commercial coatings, etc., owing to their many advantages such as ease of synthesis, more number of end functional groups, and low solution/melt viscosity. In our study, a previously unreported synthesis of A(2) + AB(2) type hyperbranched polyester (HBP) of three different generations (HBP-G1 to HBP-G3) using phenyl dichlorophosphate as a core and 2,2-dimethylol propionic acid as a monomer was carried out, and characterized using spectral, physical and thermal analyses. In situ FTIR was used to study the one-shot curing reaction between hexamethylene diisocyanate, polyethylene glycol and HBP-G3 at 60 A degrees C for two different NCO/OH ratios (1.2316 and 2.1042). Lower NCO/OH ratio (1.2316) was found to obey the second order, thereby indicating the occurrence of primary reaction between -OH and -NCO groups, whereas higher NCO/OH ratio (2.1042) follows third order due to auto-catalytic effect of urethane resulting from its reaction with excess isocyanate group. Non-isothermal curing kinetics of PU formation using in situ FTIR was accomplished to determine the percentage of urethane content formed using Factor Analysis program for the first time. Based on the above data, further curing kinetics studies were carried out at three different isothermal (70, 90, and 110 A degrees C) temperatures for lower NCO/OH ratio sample to extract its thermodynamic parameters.</P>
Dhevi, D. Manjula,Choi, Chang Woo,Prabu, A. Anand,Kim, Kap Jin Wiley Subscription Services, Inc., A Wiley Company 2009 Polymer composites Vol.30 No.4
<P>In this article, nylon 6,6 (NY66) and glass fiber-(30 wt%) reinforced NY66 (GFNY66) specimens were immersed in various aqueous calcium chloride (aq. CaCl<SUB>2</SUB>) mixture solutions at different thermal conditions for varying intervals of time, and analyzed using attenuated total reflection-infrared (ATR-IR) spectroscopy, inductively coupled plasma (ICP), energy dispersive X-ray (EDX), gel permeation chromatography (GPC), and mechanical studies. ICP data revealed increasing concentration of absorbed Ca<SUP>2+</SUP> ions with increasing immersion time resulting in disruption of intra- and intermolecular H-bonding as confirmed using ATR-IR results. From EDX data, the ratio of Ca<SUP>2+</SUP> and Cl<SUP>−</SUP> ions absorbed by NY66 was calculated and found to follow its stoichiometric equivalence. GPC data exhibited less reduction in M<SUB>n</SUB> and M<SUB>w</SUB> for aq. CaCl<SUB>2</SUB>-treated NY66 specimens suggesting the absence of any significant chemical degradation, but the occurrence of only physical changes involving H-bond breakage and the formation of new C&n.dbond;O···Ca<SUP>2+</SUP> dative bond in NY66 matrix. The mechanical properties of GFNY66 samples treated with various types of aq. CaCl<SUB>2</SUB> solutions exhibited pronounced deterioration, possibly due to the interfacial failure between glass fiber and NY66 matrix. The results obtained from this study were quite useful toward understanding the degradation mechanism in NY66 and GFNY66 caused by various aq. CaCl<SUB>2</SUB> mixture solutions, and will be helpful in improving the mechanical properties of recycled NY66. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers</P>
Lee, Jong Soon,Prabu, A. Anand,Chang, You Min,Kim, Kap Jin Wiley - VCH Verlag GmbH & Co. KGaA 2007 Macromolecular Symposia Vol.249 No.-
<P>Ultrathin ferroelectric P(VDF/TrFE(72/28) films were used in the fabrication of metal-ferroelectric polymer-metal single bit device with special emphasis on the formation of uniform film surface, faster dipole switching time under an external electric field, and longer memory retention time. FTIR-GIRAS and AFM were used complementarily in analyzing the changes in chain orientation and surface crystalline morphology with varying sample preparation methods. It was found that the magnitudes of remnant polarization and coercive field are highly related to the degree of chain orientation along the conductive substrate surface. The cast- annealed sample showed the highest polarization and the smallest coercive field. DC-EFM technique was successfully used to ‘write and erase’ the data bit on the ultrathin P(VDF/TrFE) film by applying a dc bias voltage much larger than coercive voltage with different polarities and the data bit state could be read by measuring the piezoelectric response of the cantilever with a lock-in amplifier by applying an ac modulating voltage whose V<SUB>pp</SUB> is much less than the coercive voltage.</P>