Reactive melt processing

Ghosh, R, Dev, D., Chakrabarti, A. Reactive melt processing of polyethylene Effect of peroxide action on polymer structure, melt rheology and relaxation behavior. Polymer (1997) 38, pp. 6175-6180... 

Acrylonitrile copolymeri2es readily with many electron-donor monomers other than styrene. Hundreds of acrylonitrile copolymers have been reported, and a comprehensive listing of reactivity ratios for acrylonitrile copolymeri2ations is readily available (34,102). Copolymeri2ation mitigates the undesirable properties of acrylonitrile homopolymer, such as poor thermal stabiUty and poor processabiUty. At the same time, desirable attributes such as rigidity, chemical resistance, and excellent barrier properties are iacorporated iato melt-processable resias. 

The competition at 200°C between an aliphatic and an aromatic amine toward the formation of an imide is a very selective reaction (Fig. 5.1) for the formation of an aliphatic imide.141 This reaction suggests that the reactive processing in extruder, for example, could be used to transform a melt-processable polyimide with an oligomer end capped with an aliphatic amine. In order to get a perfecdy alternate block polyimide-block siloxane, Rogers et al. used low-temperature transimidization.142 An oligomeric aromatic imide was end capped... 

Several models relating the isotopic effects of U-series disequilibria to the timescales of the melting process have now been proposed (e.g., McKenzie 1985 Williams and Gill 1989 Spiegelman and Elliott 1993 Qin 1992 Iwamori 1994 Richardson and McKenzie 1994). While these models differ mainly in their treatment of the melt extraction process (i.e., reactive porous flow vs near fractional melting), because they incorporate the effect... 

II) melt processing, where the high shearing action during the processing operation is utilised to promote the reaction between the reactive function of the modifier and the polymer often in the presence of an initiator. 

REACTIVE MODIFIERS FOR IMPROVING ADDITIVE PERFORMANCE-REACTIONS DURING MELT PROCESSING... 

Another example where antioxidant performance can be improved dramatically lies in the mechanochemlcally initiated addition of reactive antioxidants on rubbers (5.10) or unsaturated thermoplastics such as ABS (12). For example, using thiol antioxidants 2 and 3 as the reactive antioxidants, Kharasch-type addition of the thiol function to the polymer double bond takes place during melt processing to give bound antioxidant adduct (see Equation 1) the polymer becomes much more substantive under aggressive environments. 

Enhancing the properties of the relatively cheap commodity plastics through the use of small amounts of reactive modifiers during melt processing (as in method 2(10 above) is both attractive and rewarding. 

Radiation chemistry in polymer research, 168-169 Reactive macroalkyl radicals, formation, 409 Reactive modifiers addition of reactive antioxidants on rubbers, 417 adhesion, 420,422 demanding applications, 414,416 improving additive performance during melt processing, 412 polymer bound antioxidant, 418-419/ Reduced poly(vinyl chloride),... 

Melt-state testing, of polymers, 19 575 Melt-to-mold thermoforming, 18 49 Melt viscosities (MVs), 21 712-714 of ethylene oxide polymers, 10 680 of FEP resin, 18 306, 308 Membrane-based reactive separation processes, 15 848... 

Cyanamides - Cyanamides also represent a class of materials where reactive oligomers have been prepared. A representative example of the type of modification done to cyanamides to moderate the initial reaction to obtain linear soluble melt-processable oligomers 1s shown in Eq. 2. A bis(aryl sulfonyl cyanamide) was initially reacted with two moles of a bis (cyanamide) to yield an oligomeric mixture (ideally represented in Eq. 2 as a simple compound). These fire-resistant materials have shown promising properties as composite resin matrices (6). 

The ability to predict the behavior of a chemical substance in a biological or environmental system largely depends on knowledge of the physical-chemical properties and reactivity of that compound or closely related compounds. Chemical properties frequently used in environmental assessment include melting/boiling temperature, vapor pressure, various partition coefficients, water solubility, Henry s Law constant, sorption coefficient, bioconcentration factor, and diffusion properties. Reactivities by processes such as biodegradation, hydrolysis, photolysis, and oxidation/reduction are also critical determinants of environmental fate and such information may be needed for modeling. Unfortunately, measured values often are not available and, even if they are, the reported values may be inconsistent or of doubtful validity. In this situation it may be appropriate or even essential to use estimation methods. 

Reactive polymer processing modifies or functionalizes the macromolecular structure of reactor polymers, via chemical reactions, which take place in polymer processing equipment after the polymer is brought to its molten state. The processing equipment then takes on an additional attribute, that of a reactor, which is natural since such equipment is uniquely able to rapidly and efficiently melt and distributively mix reactants into the very viscous molten polymers. The operation is shown schematically in Fig. 1.3. 

There are many polymer chain modification reactions of different types that have been carried out on polymer melts processed in single and twin rotor extruders. This activity, (4-6) in the analysis of polymerization reactors, driven by market forces seeking to create value-added polymers from commodity resins, started in the mid-1960s in industrial research laboratories (7). Indeed much of the early work is to be found in the patent literature.1 Although in recent times more publications, both industrial and academic can be found in the open literature, there is still a good deal of industrial secrecy, because the products of reactive polymer processing are of significant commercial value to industry. Below we will deal briefly with two important examples of such reactions. 

Recalling the profound differences in the melting mechanisms in SSEs and in corotating twin-screw extruders (Co-TSE) (Chapter 5), we see that the latter one creates all of the melt almost instantaneously, resulting in a very narrow melt age distribution, while in SSE the age distribution is very broad. Thus, Co-TSEs and twin rotor melting devices [e.g., continuous mixers (CMs)] are better suited to be reactors of polymer melts, as is reflected in the current industrial reactive polymer processing practice. 

---