Reactive extrusion Reactivity ratios

If both reactivity ratios are smaller than unity (k i < ki2 and k22 < 21), this implies that a monomer unit reacts more easily with a chain ending with the other monomer unit than with a chain ending with a same monomer unit. Therefore, the copolymerization is faster than the homopolymerization, which implies for reactive extrusion that a shorter extruder or a larger throughput can be used, compared to the homopolymerizations. Good micromixing will favor the formation of an alternating copolymer and will speed up the reaction. 

A more accurate method is the direct determination of the reactivity ratios. In literature, a number of studies is reported, where several copolymerizations are studied. Unfortunately, many of these studies are performed at low temperatures and therefore not applicable to reactive extrusion. 

It appears that copolymerization poses no significant problems in reactive extrusion. Similar to classical polymerization processes, the reactivity ratios play an important role in the composition of the copolymers and it... 

Example 3. Hydrolysis in an Extruder.69 PET reactive extrusion experiments were carried out on a 25-mm Berstorff ZE25 corotating twin-screw extruder with a barrel length-to-screw ratio of 28 1. The extruder consisted of six barrel sections equipped for heating, cooling, and controlling the temperature of each section of the extruder. Initially reaction extrusion of PET and water was performed with cold water at room temperature injected into the extruder. Typical operating conditions were reaction temperatures of 230-265° C, extruder speeds... 

Figures 20.13 and 20.14 describe the effect of dibutyltin dilaurate (DBTDL) on the tensile strength and tensile modulus for the 25/75 LCP/PEN blend fibers at draw ratios of 10 and 20 [13]. As expected, the addition of DBTDL slightly enhances the mechanical properties of the blends up to ca. 500 ppm of DBTDL. The optimum quantity of DBTDL seems to be about 500 ppm at a draw ratio of 20. However, the mechanical properties deteriorate when the concentration of catalyst exceeds this optimum level. From the previous relationships between the rheological properties and the mechanical properties, it can be discerned that the interfacial adhesion and the compatibility between the two phases, PEN and LCP, were enhanced. Hence, DBTDL can be used as a catalyst to achieve reactive compatibility in this blend system. This suggests the possibility of improving the interfacial adhesion between the immiscible polymer blends containing the LCP by reactive extrusion processing with a very short residence time.

Carr et al.119 investigated grafting via reactive extrusion of starch with cationic methacrylate, acrylamide and acrylonitrile monomers. Starch, monomer and CAN initiator were metered into a twin-screw extruder at starch contents of approximately 35% solids. The cationic methacrylate monomer showed poor reactivity during extrusion, with essentially no add-on. Acrylamide-starch systems (1 1 w/w) gave conversions of approximately 20% and add-ons of 16% to 18%. Acrylonitrile displayed the greatest reactivity during extrusion, with conversions of 74% and 63% for 1 1 and 1 2 w/w acrylonitrile/starch ratios, respectively. The corresponding add-ons were 27% and 42%. 

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... 

Extrusion of sulfur dioxide from oxidized thiophene derivatives is an exceptional method to prepare cis-dienes as components for Diels-Alder reactions. An example of this approach utilizes the Diels-Alder reactivity of the furan ring in substituted 4//,6ff-thieno[3,4-c]furan-3,S-dioxides to react with a variety of dienophiles such as DMAD, dimethyl maleate and dimethyl fumarate which then lose SO2 to form another reactive diene (Eq. 17) <94H961>. A review of the preparation and use of 4i/,6f/-thieno[3,4-c]furan-S,5-dioxides as well as other heteroaromatic-fused 3-suIfolenes is report <94H1417>. The preparation of dihydrothienooxazole 80 requires the careful control of the reaction time and temperature as well as the reactants molar ratio <94JOC2241>. Specific control of the alkylation conditions for 81 (X = COCH3) allows for the preparation of either 1,4-disubstituted or 1,6-disubstituted 4, 6//-thieno[3,4-c]furan-S,S-dioxides. These molecules could be used as intermediates for the preparation of novel pentacyclic compounds <94JCS(P1)1371>. 

Table 11.2 Comparison of two types of poly-L-lactide potymerized in glass ampoule bulk batch polymerization technology and using a single-stage reactive extrusion potymerization process, both catalyzed with an equimolar Sn(0ct]2 TPP complex with an initial monomer to tin molar ratio of 5000 at 180°C...

Takamura et al. [127] cross-linked PLLA using various types of peroxides under constant mole ratios of peroxide-derived radicals to PLLA during reactive extrusion in a single-screw extruder (D = 20 mm, L/D = 25) with a fixed temperature profile for the extruder (Zone 1/Zone 2/Zone 3/Die = 180 =C/185°C/190°C/190°C). 

Li et al. reported that immiscible high-density polyethylene (HDPE)/ poly(ethylene terephthalate) (PET) blends, prepared by means of melt extrusion with ethylene-butyl acrylate-glycidyl methacrylate (EBAGMA) terpoly-mer as a reactive compatibilizer, can exhibit shape memory effects [32]. They observed that the compatibilized blends showed improved shape memory effects along with better mechanical properties as compared to the simple binary blends. In the blend, HDPE acts as a reversible phase, and the response temperature in the shape recovery process is determined by of HDPE. The shape-recovery ratio of the 90/10/5 HDPE/PET/EBAGMA blend reached nearly 100%. Similar behavior was observed for immiscible HDPE/ nylon 6 blends [33]. The addition of maleated polyethylene-octene copolymer (POE-g-MAH) increases compatibility and phase-interfacial adhesion between HDPE and nylon 6, and shape memory property was improved. The shape recovery rate of HDPE/nylon 6/POE-g-MAH (80/20/10) blend is 96.5% when the stretch ratio is 75%. 

Aldehyde olefination reaction was carried out using 1.5 mmol of EDA, 1.2 mmol of PPhs, and 1 mol% of catalyst in toluene to give excellent to moderate yield. Although the catalyst 68-BAr exhibits lesser reactivity compared to 67-BAr, selectivity is not compromised. The reaction does not occur without PPhs. The diruthenium catalysts also catalyze cyclopropanation reactions. Cis or trans cyclopropanes are obtained using 1.5 mmol of EDA as added in a DCM solution of catalyst (0.5 mol%) and olefins (10 mmol) in room temperature. The dimerization of EDA was minimized by its slow addition to an excess of olefin solution. The trans to cis ratio in all these cases is found to be 75 25. Similar to aldehyde olefination reaction, 67-BAr was found to be superior. Insertion of EDA into N-H and O-H bonds were also studied with amines and alcohols to obtain amino acid derivatives and ethers, respectively. Catalyst 67-BAr affords higher yields than 68-BAj. The reaction of EDA with the diruthenium catalyst is accompanied by the extrusion of N2, which generates a diruthenium(I,I) species, [Ru -Ru =CH (COOEt)] (Scheme 41). This species is a common intermediate in all the reactions mentioned above. During aldehyde olefination reaction, the incipient carbene is... 

Three units of ethene/n-octene copolymers (I) were blended with a unit of isotactic polypropylene (II) grafted/crosslinked with mixtures of unsaturated silanes and (PhCMejO)jO under conditions of reactive extrusion at 170-190 °C and studied for mech cal properties, thermal stability and microstmcture. The composite materials consisted of a semicrystal II matrix and dispersed small pertides of cross-linked I. The best mechanical properties were when the II/I mass ratio was 55/45. 

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