By G.-H. Hu, J.-J. Flat, M. Lambla (auth.), S. Al-Malaika (eds.)
Chemical amendment of polymers by means of reactive modifiers is not any longer a tutorial interest yet a advertisement fact that has introduced a various variety of speciality fabrics for area of interest markets: reactively grafted styrenic alloys, maleated polyolefins, super-tough nylons, silane changed and moisture-cured polyolefins, and thermoplastic elastomers, are yet few examination ples of industrial successes. even if the strategy of reactive amendment of polymers has been principally completed both in answer or within the sturdy nation (through in situ reactions in polymer melts), it's the latter course that has attracted so much cognizance within the final twenty years due to its flexibility and economical ness. This direction, known as reactive processing, makes a speciality of using appropriate reactive modifier(s) and the adoption of traditional polymer processing equipment, an extruder or a mixer, as a chemical reactor, to accomplish in situ certain reactions for chemical amendment of preformed polymers. This quite easy, even though scientifically hugely hard, method of reactive amendment bargains targeted possibilities in exploiting quite a few reactive modifiers for the aim of changing and reworking in a managed demeanour the houses of preformed advertisement polymers into new/speciality fabrics with tailored houses and custom-designed functionality for goal functions. Such an economically beautiful course constitutes an intensive diversion clear of the normal practices of producing new polymers from monomers which contains tremendous in vestments in refined applied sciences and chemical plants.
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Example text
Therefore, higher reactivity would be expected, as observed experimentally [36,37]. Detailed reactions involved in a free-radical grafting process are still poorly understood. Based on the IR spectra of MA-modified PP in the presence of BP as free-radical initiator, Ide, Kamada and Hasegawa [24] suggested that the probable termination reaction was the recombination between macroradicals PP-MA* and primary radicals R* and that the termination by disproportionation between macro radicals PP-MA* is improbable.
Many speculations are involved in the mechanisms and/or microstructure of grafts proposed in the literature. 5 Recent advances in melt free-radical grafting In what follows, we discuss recent advances in melt free-radical grafting upon taking two systems investigated in our Reactive Extrusion Laboratory as examples: the grafting of MA [48-50] and glycidyl methacrylate (GMA) [51-53] onto PP. 3. GMA bears a double bond (free-radical reactivity) and an epoxy group (functional reactivity). This epoxy group possesses reactivity toward various functional groups such as -COOH, -OH, -SH, and -NH 2 • The reason for choosing these two systems is that the MA grafting system reveals mainly the chemical aspect of the melt free-radical grafting whereas in the case of the GMA grafting system both the chemical and the processing aspects of the problem are addressed.
Those that are not consumed for grafting will cause degradation by p-scission. Because of the instability of PP tertiary macroradicals associated with their tertiary character, the degradation process is extremely fast and important at elevated temperatures. Therefore, low MA grafting yields together with severe PP degradation must be attributed to the weak free-radical reactivity of MA. In fact, the low free-radical reactivity of MA is a well-known fact. It results from the following inherent structural characteristics of MA: • a strong steric hindrance arising from the di-substitution of the two adjacent carbonyl groups at positions 1 and 2 of the double bond, • a deficiency of electron density around the C=C double bond of MA because of the electron-attracting nature of the carbonyl groups, and • the symmetry of the double bond and the corresponding electron cloud.