Influence of number of functional groups of hyperbranched polyol on cure kinetics and physical properties of polyurethanes

Abstract

Curing of polyurethane prepolymer with three hyperbranched polyol was studied using FTIR spectroscopy. The disappearance of the strong isocyanate absorption peak was followed with time and temperature to determine the reaction kinetics. It was shown that all the hyperbranched polyols followed the second order kinetic equation and the reaction rate enhanced with increase in the number of the functional groups of the hyperbranched polyol. Activation energy, activation enthalpy, and activation entropy were also measured. The swelling character of the polyurethanes was investigated with the help of gel fraction, degree of crosslinking, and average molecular weight between crosslinks. Atomic force microscopy indicated phase separated morphology of the cured polyurethanes. The thermal, mechanical, and thermomechanical properties were enhanced when the number of the functional groups in the hyperbranched polyols was increased. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 731–745, 2009

Surface and thermomechanical characterization of polyurethane networks based on poly(dimethylsiloxane) and hyperbranched polyester

“…Polyurethane networks based on PDMS macrodiols and hyperbranched polyesters (HBP) as crosslinkers introduced into the hard segment domains can combine properties of all components, making these networks good candidates for coating applications. The large number of terminal hydroxyl groups present in Boltorn ® HBPs enables fast formation of networks that have good mechanical properties, as well as good resistance to chemicals [11][12][13][14], while the presence of PDMS contributes to the good thermal and surface properties, and to elasticity of the highly crosslinked materials. In our previous studies, we have investigated the influence of the content of !,"-dihydroxyethoxy propyl-poly(dimethylsiloxane) (EO-PDMS) and type of HBPs on the swelling behavior, morphological, thermal and thermomechanical properties of PU networks [15][16][17][18][19][20][21].…”

Simultaneous Measurement of Effective Chemical Shrinkage and Modulus Evolutions During Polymerization

“…The curing kinetics parameters were A=29.1/s, E a =35.8kJ/mol, n=2 with a curing temperature of 165°C [17]. They yield a polymerization rate of k c ≈0.002/s at the curing temperature [17,[22][23][24][25][26][27]. Polymers develop a small modulus at the end of the curing, especially when they are cured at elevated temperatures.…”

“…The average modulus over this segment, E s,j , can be determined using equation (25). Then, by substituting E s,j back into either one of equation (24), Δ" ch j can be calculated.…”

“…Considering a minimum of ten segments (ten data points) to describe the nonlinear nature of two property evolutions faithfully, the required minimum BW shift for each segment should be at least 20 pm (or a total of 200 pm) given the fact that a typical fiber Bragg grating interrogating system provides a measurement resolution of ≈1 pm. A simple material system following an nth order model [17,[22][23][24][25][26][27] is considered to illustrate the above criterion quantitatively. The model can be expressed as…”

Estudio de Nanocompuestos de Espumas de Poliuretano Reforzadas con Nanocargas en Base Carbono

“…[196,197] The kinetic data are determined taking into account the approximation of Li et al [198] to a n th order kinetics approach, widely used for the modelling of PUs. [199][200][201] (4.9)…”