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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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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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In an until now widest study of the penultimate effect the reactivity ratios of 66 published styrene copolymerization systems showing a non-classical behaviour have been reviewed. For the alternating systems a simplified two-parameter penultimate model with r2 = r i = 0 was applied.The systems were classified into 2 groups: 1. alternating and 2. non-alternating systems. 32 systems of the first group have been reevaluated. r-Values, together with their 95% confidence limits have been calculated. The confidence parameter 6' and the "efficiency factor" of planning Q, suitable for classification of the systems, have been applied. In this number 23 (72%) systems yielded linear Kelen-TiidBs-plots (13 belong to class I, 10 to class I!). 5 (16%) systems were assigned to class I1 (non-adequacy of the penultimate model possible) and 4 (12%) to class 111, where the experimental data are inconsistent and the r-values meaningless. 0 1992, Hiithig & Wepf Verlag, Basel CCC 0025-1 16X/92/$05.00

SynopsisA combined (chemical and infrared (IR) spectrophotometric) method is discussed for the simultaneous determination of concentrations of carboxyl (A), ketone (K), and ester (E) groups formed in the oxidation of polyethylene (PE). The IR absorptivities of these functional groups were determined by using model compounds [stearic acid, stearone, poly-(1,4-butylene sebacate)]. The integral absorption of the C=O band of polymer samples which contained several 0x0 groups of different types was found to be additive. This method was applied to the determination of the carboxyl, ester, and ketone content of samples oxidized at different oxygen pressures.