Rheology of rigid–flexible liquid crystalline polymer/poly(methyl methacrylate) blends

Abstract

AbstractThe random liquid crystalline copolymer poly(4,4′‐biphenylene azelate)‐co‐(2‐methyl‐1,4‐phenylene azelate), synthesized by condensation polymerization, was found to be soluble in chloroform and methylene chloride. DSC, rheology, and optical microscopy indicated that this LCP broadly melts at ca. 160°C to a weakly birefringent melt that becomes isotropic at approximately 180°C. DSC and optical microscopy of blends with poly(methyl methacrylate) (PMMA) at wLCP = 0.06, 0.16, 0.34, and 0.69, indicated little compatibility between the polymers at middle compositions. Dynamic and steady shear flow rheological measurements, using cone/plate geometry, showed the PMMA‐rich (6 wt % LCP) and LCP‐rich (69 wt % LCP) blends to be essentially homogeneous, and dominated by the properties of the major component. However, at 16 wt % and 34 wt %, the resulting phase separation led to lower dynamic moduli (than either LCP or PMMA separately), and increased shear thinning. This behavior supports the notion that the LCP acts as a lubricant by promoting the flow of the non‐LCP. The results reported in this article show that these rheological effects, which were previously observed in blends of insoluble, rigid LCPs and engineering thermoplastics, still exist with a much less rodlike LCP mixed with a commodity polymer.