Effects of Transreactions on the Compatibility and Miscibility of Blends of Condensation Polymers

Abstract

Principles of blend compatibilisationFew polymers form truly miscible blends characterised by a single glass transition temperature (Tg) and homogeneity on a 5-10nm scale with domain sizes comparable to the dimension of a macromolecular statistical segment. The majority of blends are immiscible, i e . , possess a phase separated morphology. Blends of this type are often preferred over the miscible ones since they combine some of the important characteristics of both blend constituents. Blend composition, viscoelastic properties of the components, and interfacial adhesion are among the parameters known to control the size and morphology of the dispersed phase and its stability to coalescence. Heterogeneous blends of technological importance are termed "compatible" and they constitute the majority of the commercial blends introduced in the past 30 years. In such blends, often known also as alloys, satisfactory physical and mechanical properties are related to the presence of an interphase modified through compatibilisation and the formation of a fine dispersed morphology resistant to phase separation.Polymer compatibility, which may lead ultimately to complete thermodynamic miscibility, may be enhanced by various methods. In addition to cocrystallisation and cocrosslinking, strong interactions such as acidbase or ion-dipole, hydrogen bonding and transition metal complexation Transreactions in Condensation PolymersStoyho Fahirov copyright 0 WILEY-VCH Verlag GrnbH. 1999 412 M. Xanthos, H. Warth between suitably functionalised components, have been shown to improve compatibility. More commonly, compatibility is promoted through interfacially active copolymers (e.g., block, graft, random) with segments capable of specific interactions and/or chemical reactions with the blend components. The copolymers may be added separately, or formed in situ through chemical reactions, often catalysed by the addition of low molecular weight (MW) compounds. Reactive and non-reactive compatibilisation of polymer blends has been the subject of numerous reviews [l-71.During blending of a pair of suitably functionalised polymers A and B, interchain block, graft, or random copolymers may be formed at various concentrations through covalent or ionic bonding. According to Brown [3] , the following are five general types of chemical processes/reactions by which interchain copolymer formation has been achieved in extruder reactors: 1. Chain cleavage/recombination (main chain of A/main chain of B or 2. End-group of A/end-group of B; block. 3. End-group of A/pendant functionality of B; graft. 4. Covalent cross-linking: pendant functionality of Alpendant functionality of B or main chain of A/main chain of B; graft (crosslinked network). Ionic bond formation between A and B; usually graft (usually crosslinked).The compatibilisers formed in situ have segments that are chemically identical to those in the respective unreacted homopolymers and are thought to be located preferentially at the interface, thus lowering interfacial tension, and also promo...

Influence of the Activity of Transesterification Catalysts on the Phase Behavior of PC-PET Blends

“…[41] The miscibility is induced by transreactions and, for this reason, the catalyst activity plays a crucial role on the control of the phase behavior and hence on the properties of the blends prepared by reactive blending.…”

Structural Characterization of Copolyamides Synthesized via the Facile Blending of Polyamides

“…Widespread interest in the development of polymer blends with useful properties has resulted in numerous studies on the exchange reactions occurring in the melt mixing of polymer systems containing reactive functional groups. − …”

“…In the melt mixing process, variable amounts of random, block, and grafted copolymers are formed, which often act as partial compatibilizers of the initial blend, affecting the mechanical properties and the thermal stability of the resulting material. − …”

“…Reactive functional groups, besides being located inside the polymer chains, may also be placed at the chain ends. Both inner and outer reactive groups may therefore be responsible for the chemical exchange reactions occurring in molten polymer blends. − Traditionally, workers have addressed the issue of reactive blending considering only the inner functional groups of the homopolymers repeat units, often forgetting about the role of reactive chain ends. − , …”

Accelerating Reactive Compatibilization of PE/PLA Blends by an Interfacially Localized Catalyst

“…Past work has identified variables that strongly affect coupling kinetics, including Flory–Huggins interaction parameter, flow, , coupling reaction type, and catalyst. Several reports have utilized catalysts to improve conversion to copolymer, but results have been mixed. − Most studies select catalysts based on their activity toward analogous small molecule reactions and stability at melt processing temperatures, with little regard for surface activity or localization. The sole report of catalyst localization came from Legros et al, where tin distannoxane catalyst preferentially localized in poly(butylene terephthalate) (PBT) portions of PE/PBT reactive blends.…”