Reactive extrusion polymerization

Wang used reactive-extrusion polymerization with 2,5-di-methyl-2,5-di-t-bu-tylperoxy hexane to prepared a graft copolymer, (11), by free radically grafting polyethylene-glycol malonic acid onto the biodegradable substrate of poly((3-hydroxybutyrate-co- p-hydroxy valerate). 

Figure 11.3 Processing and screw concept used for reactive extrusion polymerization of polylactide. Reproduced from ref. 90 with permission of Elsevier.

Table 11.3 Influence of different processing parameters during reactive extrusion polymerization on the resulting molecular polymer parameters...

Schmack et al. [126] spun PLA fibers through the reactive extrusion polymerization of L-lactide (92 wt%) and meso-lactide (8 wt%). In many potential textile technological applications (e.g., for nonwoven materials) the fiber forming process is of general importance. An effective polymer synthesis requires also an effective spinning process to reduce the still high cost of the PLA fibers compared with those of established synthetic fibers. 

A new process has been developed for the production of PLA using reactive extrusion polymerization based on a new catalytic system, which not only enhances the ROP kinetics of L-lactide but also suppresses side and degradation reactions such as intermole-cular transesterification reactions. Co-rotating closely intermeshing twin-screw extruders have often been used for polymerization reactions, but in any case, the reaction time was sufficiently smaller than the residence time in the extruder. In the case of ROP of lactide, the extraordinary effect of triphenylphosphine on the efficiency of Sn[Oct)2 as a catalyst was the key point to ensure further enhancement of the polymerization reaction. Thus, it was feasible... 

Jacobsen et al. reported a new catalytic system and a reactive extrusion polymerization process, which can be used to produce PLA continuously in larger quantities and at lower costs than before. This extrusion polymerization process has been developed and tested with laboratory scale machines and the possibilities to extend this polymerization process to lactide-based block copolymers have been investigated [11]. 

Elucidation of degradation kinetics for the reactive extrusion of polypropylene is constrained by the lack of kinetic data at times less than the minimum residence time in the extruder. The objectives of this work were to develop an experimental technique which could provide samples for short reaction times and to further develop a previously published kinetic model. Two experimental methods were examined the classical "ampoule technique" used for polymerization kinetics and a new method based upon reaction in a static mixer attached to a single screw extruder. The "ampoule technique was found to have too many practical limitations. The "static mixer method" also has some difficult aspects but did provide samples at a reaction time of 18.6 s and is potentially capable of supplying samples at lower times with high reproducibility. Kinetic model improvements were implemented to remove an artificial high molecular weight tail which appeared at high initiator concentrations and to reduce step size sensitivity. 

While starch copolymers are typically prepared by batch polymerization methods, reactive extrusion of starch has been studied. Mixtures of starch, polystyrene, styrene, sodium hydrogen carbonate, citric acid and water were extruded at temperatures between 100°C and 200°C.118 It was reported that expanded graft copolymers... 

During the past few decades, the mechanisms for reactive extrusion have become much better understood, and the residence times needed for complete conversion have come within reasonable limits. A large variety of polymerization reactions have been investigated in different types of extruders, and reactive extrusion has been implemented on an industrial scale [7]. 

Reactive extrusion takes place when the twin screw system is designed to incorporate one or more chemical reactions during the process, such as grafting or even polymerization. Grafting is the process of attaching pendant molecules onto the backbone of a polymer chain. For example, a small concentration of maleic anhydride can be incorporated into polypropylene to make the... 

The ring-opening polymerization of PLA is traditionally realized during a discontinuous batch-process, but recently continuous processes have been developed. As another alternative to continuous polymerization processes the reactive extrusion of PLA was realized. By combining Lewis-acid catalysts with cocatalysts it is possible to increase the catalytic activity and to reduce the polymerization time [18]. 

Xanthos, M. (1992) Process analysis from reaction fundamentals.Examples of polymerization and controlled degradation in extruders, in Xanthos, M. (Ed.) Reactive Extrusion Principles and Practice, Munich Hanser-Verlag. 

In principle, the CL from polyolefins could be used as a monitor of the extent of oxidation during reactive extrusion in the presence of peroxides to decrease the molar mass (Brown, 1992), but this has not been reported. Attention has been paid to the effect that change in viscosity of a polymerizing network has on the CL profile, as described in the following section. 

A large range of polymers can be obtained by polymerization in reactive extrusion, and the techniques involved and polymers produced include the following (Fink, 2005) ... 

Choulak et al. (2004) Polymerization of caprolactone A one-dimensional dynamic model of a twin-screw reactive extrusion Predicts pressure, filling ratio, temperature, molar conversion profiles and residencetime distributions under various operating conditions... 

CORl s are the prime machines for polymer blending and reactive extrusion [Brown, 1992]. They have been used as reactors for the addition polymerization (polyacrylates, SAN, S-MMA, PA-6, POM, or TPU) and for the polycondensation (PA-66, polyarylates, PEST, PEI). Polymer grafting (polyolefin + silane, maleic anhydride, acetic anhydride, etc.) as well as mechanical and chemical degradation of polypropylene have also been carried out. 

The term reactive processing is used to describe a polymer processing that involves chemical reactions. In principle, any processing operation can be conducted as a reactive process, viz. reactive injection molding (RIM). However, most often the term refers to reactive extrusion, and in particular, to the reactive compatibilization of immiscible polymer blends, usually conducted in a TSE. During the last 50 years, the latter machines have been used as chemical reactors for the polymerization, depolymerization (chemical recycling), polymer modification and compatibilization [Brown, 1992, Xanthos, 1992 Utracki, 1989, 1991, 1994, 1997]. 

It has been reported that neo-alkoxy titanates or zirconates can re-polymerize polymers or joint several polymers into compatibilizing copolymers. These compounds have been used to repair degraded PEST or PC during reactive extrusion. For example, phosphato titanate (Ken-React Lica-12 from Kenrich Petrochemicals, Inc.) was used to ... 

The data on the rheological behavior of molten (PP/PE)-g-IA systems suggest a complex nature of influence of the polymers on the course of free-radical chain transformations taking place during reactive extrusion. Small amounts of one or another polymeric component, introduced into a blend, cause some changes in the rheological properties of the molten (PP/PE)-g-IA systems. For instance, a low (below 25 wt%) quantity of PE, contrary to the expectations, would increase MFI while low amounts of PP would decrease MFI for (PP/PE)-g-IA systems against... 

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