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The copolymerization equation considering the penultimate unit effect, the so called penultimate model, takes a simplified shape in the case of rz = 0 (monomer 2, M,, does not homopolymerize). For this case a method analogous to the conventional KT(Ke1en-Tiid&transformation for estimation of r , and rl' is proposed. The new method was verified by literature data for the system styrene/fumarodinitrile, polymerized with benzoyl peroxide at 70"C, yielding rl = 0,062 and r,' = 0,812. Classification of copolymerization curves by means of the classical copolymerization model permits to distinguish between three curve-types: rl < 2 (alternation with respect to M3, rl = 2 (linear diagram with slope 0,5) and rl > 2 (non alternating system). The penultimate model permits to generate further curve-types of ''S'khape with r, < 2 and r,' > 2 or rl > 2 and r,' < 2 (rl = rl' for classically behaving systems and r, =k rl' for non-classically behaving systems).

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Investigation of the morphology and properties of ternary composites of polypropylene, ethylene-propylene-diene terpolymer, and filler has shown that in such systems two kinds of structures can be formed: separate dispersion of the components or encapsulation of the filler by the elastomer. A thermodynamic analysis of the two structures revealed that encapsulation is the thermodynamically favored process. The final structure is determined by the stability of the encapsulated units, which depends on the relative magnitude of adhesion and shear forces. The former depends on the reversible work of adhesion and on the particle size of the filler, while the latter depends on the viscosity and shear rate. Surface treatment of the filler decreases the work of adhesion, resulting in extensive de-encapsulation. The developed tentative explanation is in agreement with the observed phenomena and experimental results.EPDM elastomer (Buna AP 331, Huls, FRG). Elasto-POLYMER COMPOSITES, APRIL 1990, Yo/. 11, No. 2

A thorough examination of some cationic copolymerization systems by a new method has shown that many published r values have to be corrected significantly and that some are erroneous and meaningless, because for these systems the conventional copolymer compositions equation does not hold. Available information in regard of cationic copolymerizations has been treated in terms of three classes: (a) Systems in which the conventional copolymer composition equation adequately describes the copolymerization mechanism and previous authors justifiably used the two parameter model to calculate reactivity ratios. Our results show that the discrepancy between published r values and the more precise values obtained in this work is about ±23%. (b) Systems in which the approximations implicit in the conventional copolymer composition equation do not hold and the calculated r values are erroneous and misleading. Monomer pairs comprising monomers of significantly different reactivities belong to this class indicating that in copolymerizations in general and in cationic copolymerizations in particular a strong cast system exists, i.e., copolymerization can readily occur within the cast (between monomers of similar reactivities); however, only with difficulty if at all between casts (between monomers of differing reactivities). (c) Systems in which the use of the copolymer composition equation is completely unjustified, the calculated r values are meaningless and in some cases the existence of true copolymers is questioned.

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