A. Anand Prabu

Studies on the toughening of epoxy resin modified with varying hyperbranched polyester-toluene diisocyanate content

Epoxy resins have long been used in many fields like structural, coating, aerospace industries, etc., but their main drawback is brittleness which can be improved by using toughening agents. In the present study, a novel pathway for the toughening of diglycidyl ether of bisphenol-A based epoxy resin has been carried out using hydroxyl terminated hyperbranched polyester of third generation (HBP-G3) that have been covalently linked to the epoxy resin through toluene diisocyanate (TDI) which serves as a linkage between the hydroxyl groups on the epoxy resin and HBP resulting in the formation of HBP-Polyurethane/Epoxy (HBP-PU/Epoxy) blends. The synthesized HBP-G3 was characterized using spectral and physical methods. Though the thermal stability, glass transition temperature and flexural properties of the HBP-PU/Epoxy blends are declined, a significant gain in the impact behavior (up to 30xa0%) was observed with increasing content of HBP-TDI (upto 12.5xa0wt.%) in epoxy matrix, which is further confirmed by the existence of heterogeneous morphology from SEM micrographs.

FTIR studies on polymorphic control of PVDF ultrathin films by heat-controlled spin coater

AbstractnThe performance of organic polymer-based memory devices based on polyvinylidene fluoride (PVDF) ultrathin films depends on the extent of its ferroelectric crystalline phase content. In the present study, the changes in polymorphs of PVDF ultrathin films prepared by using heat-controlled spin coater are examined. The polymorphic changes were analyzed by using FTIR-transmission (TS) and FTIR-grazing incidence reflection–absorption spectroscopy (GIRAS) as a function of varying (i) spin-coating temperatures (SCT-30 to 80xa0°C), (ii) spin-coating substrates (KBr, ITO and Gold) and (iii) thermal treatments [as-cast (AC) at 30xa0°C, annealed at 130xa0°C (AN130) and melt (200xa0°C)-slow cooled (MSC)] conditions. Compared to MSC samples, the AC and AN130 samples exhibited higher β-crystalline (polar, all-trans) phase along with the complete absence of α-crystalline (non-polar, tgtg′) phase at lower SCT-30 and 40xa0°C irrespective of the substrates used, thereby avoiding the need of high-temperature SCT conditions. Among the three substrates used, FTIR-GIRAS data obtained using ITO and Gold substrates were more favored than the FTIR-TS data obtained using KBr window due to their real-time usage as the substrate for electronic applications.

Hyperbranched polyester as a crosslinker in polyurethane formation: real-time monitoring using in situ FTIR

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 A2xa0+xa0AB2 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 60xa0°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 110xa0°C) temperatures for lower NCO/OH ratio sample to extract its thermodynamic parameters.