Synthesis and thermal decomposition kinetics of tri-block copolymer ε-caprolactone / polybutadiene (PCL-PB-PCL); preparation of polyurethane network-based tri-block copolymer

In this research, tri-block copolymer polycaprolactone-polybutadiene-polycaprolactone (PCL-PB-PCL) (Mn = 2382 g.mol−1) was synthesized via cationic ring-opening polymerization of caprolactone in the presence of hydroxyl-terminated polybutadiene (HTPB) as macroinitiator and different catalysts such as dibutyltin dilaurate, tin (II) 2-ethyl hexanoate, and tetra-n-butyl orthotitanate. This copolymer has a potential application in the propellant industries as a binder. The obtained products were characterized by FT-IR, and 1HNMR spectroscopy gel permeation chromatography (GPC). The thermal behavior of the tri-blockcopolymer was studied by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). The result was approved that the glass transition temperature of the tri-block copolymer (Tg =  −72.1 °C) is lower than homopolymer PCL (Tg =  −65 °C). The effect of heating rate (5,7,10 and 15◦C min−1) on the decomposition of the copolymer was investigated. The kinetic parameter (activation energy for the thermal decomposition of tri-block copolymer) was calculated by the Flynn–Wall–Ozawa (FWO) and Kissinger methods. The polyurethane elastomers were synthesis by the reaction of triblock copolymer and toluene-2,4-diisocyanate diisocyanate(TDI) or isophorone diisocyanate(IPDI) isocyanates with different NCO/OH ratios and in the presence of the plasticizer. The plasticized elastomer with TDI and NCO/OH = 1.2 showed better mechanical properties than IPDI with 0.44 MPa strain and 483% elongation. The average value of the three tensile tests reported as the final result. The effect of 1,4 butanediol as chain extender on mechanical properties of polyurethane-based PCL-PB-PCL was investigated using a tensile test. According to the results, chain extenders caused increasing strength of plasticized elastomer (0.593 MPa) and decreasing its elongation at break (349%).