Toughened ternary and quaternary polymer alloys of core-shell morphology; correlations among processing, microstructure, micromechanics, and macroscopic mechanical performance in reactive systems

Polymer alloys are increasingly being used in engineering applications. These multicomponent polymeric sys-tems are one of the fastest growing segments of today's plastics industry. This review examines the state-of-the-art and recent developments in the field of high performance reactively toughened ternary and quaternary polymeric alloys of encapsulated (core-shell) morphology. These alloys consist of a functionalized elastomeric polymer that functions as both dispersant and impact modifier for the resulting multiphase system. The chemical reaction of the impact modifier during melt processing gives rise to its interfacial localization and development of a core-shell structure for dispersed components. It is well-established that the dispersed composite nano/micro-domains in these blends provide a superior stiffness-toughness balance with improved processability at lower rubber contents compared with traditional toughened binary blends containing homogeneous rubbery domains. The thermodynamic and kinetic issues governing the development of an encapsulated morphology are presented. The impacts of processing conditions, microstructural (molecular, architectural, rheological, and physical) characteristics of blend components, and various blending parameters on the formation and evolution of core -shell nano/micro-morphology are reviewed thoroughly in conjunction with their subsequent influences on the macroscopic mechanical response of the blends. Special focus is on detailed discussion of the involved nano-and micro-mechanics of deformations associated with different phase structures, interphase adhesions, and disper-sion states of core-shell nano/micro-structures during both high-speed impact and quasi-static fracture me-chanics tests. The use of volume-strain measurements for determining the relative contribution of various dilatational and non-dilatational nano/micro-deformations accompanying the failure process during macro-scopic mechanical loadings is examined profoundly. The theoretical models proposed for prediction of modulus and strength of multiphase systems comprising core-shell structured domains as well as the design criteria deduced from these models to develop high-performance materials of high impact resistance with low rigidity loss are highlighted. Finally, future research perspectives and possible directions for further progress in this field are outlined.