Rheological and thermal degradation properties of hyperbranched polyisoprene prepared by anionic polymerization

Abstract

Hyperbranched polyisoprene was prepared by anionic copolymerization under high vacuum condition. Size exclusion chromatography was used to characterize the molecular weight and branching nature of these polymers. The characterization by differential scanning calorimetry and melt rheology indicated lower Tg and complex viscosity in the branched polymers as compared with the linear polymer. Degradation kinetics of these polymers was explored using thermogravimetric analysis via non-isothermal techniques. The polymers were heated under nitrogen from ambient temperature to 600°C using heating rates from 2 to 15°C min−1. Three kinetics methods namely Friedman, Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose were used to evaluate the dependence of activation energy (Ea) on conversion (α). The hyperbranched polyisoprene decomposed via multistep mechanism as manifested by the nonlinear relationship between α and Ea while the linear polymer exhibited a decline in Ea at higher conversions. The average Ea values range from 258 to 330 kJ mol−1 for the linear, and from 260 to 320 kJ mol−1 for the branched polymers. The thermal degradation of the polymers studied involved one-dimensional diffusion mechanism as determined by Coats–Redfern method. This study may help in understanding the effect of branching on the rheological and decomposition kinetics of polyisoprene.

Bio-elastomer nanocomposites reinforced with surface-modified graphene oxide prepared via in situ coordination polymerization

“…47,48 Note that we relate our values of E a to the viscous dissipation of the PF-GO composite and not the thermooxidative processes and hemolytic dissociation of crosslinked bridges between PF and GO as reported otherwise. 49 Comparing the rheological response of our PF/m-GO samples to petroleumbased elastomers, such as styrene-butadiene rubbers and hyperbranched polyisoprene, our values of G 0 over the corresponding unshied frequency range and h are found in a good agreement to the studies, 47,50,51 reporting shear thinning behavior and strong elastic response as shown in Fig. 6.…”

Hyperbranched Copolymers Forming Polymersome-like Structures Used for Encapsulation and Controlled Release of α-Tocopherol Succinate (TOS): Drug Transport Modeling

“…Both P1 and P2 showed a greater dependency on angular frequency because of less branching and more chain entanglements. On the other hand, with short molecular chains and more branching in P3, it was difficult for the molecules to entangle; thus, they were less sterically hindered during flow and hence exhibited the lowest or no dependence on the angular frequency . It appeared to be more Newtonian than both P1 and P2.…”

Investigation of nonisothermal fusion bonding for extrusion additive manufacturing of large structural parts

“…[64,65] Moukinha [64] suggests using model-free analyses to obtain a satisfactory decomposition model for either separated-step or single-step processes. The widely accepted Friedman method [66,67] investigates degradation kinetics at heating rates not achievable in TGA measurements, as presented in additive manufacturing. It is based on a set of multiple linear heating rates and derives a semi-empirical rate law to predict degradation behavior.…”