Preparation and characterization of long chain branched polycarbonates with significantly enhanced environmental stress cracking behavior through gamma radiation with addition of difunctional monomer

Abstract

In this study a series of long chain branched polycarbonates (LCB-PCs) was prepared from linear PC precursors through gamma radiation with addition of a difunctional monomer, divinyl benzene (DVB) of varying amounts. The topological structures of the linear PCs and LCB-PCs were measured by size-exclusion chromatography coupled with a multiangle light scattering detector (SEC-MALLS) and rheology. SEC-MALLS measurements showed that the topological structures of the PCs were changed with the introduction of LCB structures. Rheological measurements showed that the LCB structures of the LCB-PCs contributed to enhancements of storage modulus, complex viscosity, shear-thinning behavior, and the deviation of phase angle, δ, from the “standard” curve of linear PCs in the δ − |G*| plots (van Gurp–Palmen plot). Modulated differential scanning calorimetry (MDSC) measurements showed that the glass transition temperature, T_g, of LCB-PCs decreases with increasing LCB degree, which is attributed to the combined effects of both increased branching density and free chain ends. LCB structures introduced into PCs did not apparently weaken the tensile properties of the PC materials, whereas the notched Izod impact strength could be obviously improved by the LCB structures. More importantly, the influence of LCB structures on the environmental stress cracking (ESC) behavior of LCB-PCs was explored and the results indicated that the ESC properties of LCB-PCs could be significantly enhanced with the introduction of LCB structures, which makes the application of LCB-PCs as the window view materials for helmets worn by astronauts while in outer space a possibility.