Reactivity ratio product

Depending on the grade, the unsaturation is between 0.5 and 2.5 mol per 100 mol of monomer. The low content of isoprene and a reactivity ratio product near unity (see and iu Table 1) iadicate a random distribution of unsaturation along the chain. The mol wt distribution of butyl mbber depends on the grade, but many products have a M /M of 3—5. 

Table XXII.—Monomer Reactivity Ratio Products (50 to 80°) (From Mayo and Walling )... 

The first to attempt this were Tosi, Valvassori and Ciampelli [284] who observed a relationship between infrared methyl group absorptions in the region 900—1000 cm and the reactivity ratio product rjTj. These infrared bands were shown to contain characteristic propene absorptions for isolated units at 935 cm and for sequences at 973 cm , and a distribution index containing the rates of these absorptions was found to correlate well with the fractions of E—P(fi2) and E—E(fj i) bonds given by [285]... 

TaUe 8. Reactivity ratio products in the case of the fottr-component system styrenef 1)-methyl methacrylate(2)-acrylonitrik(3)-vinylidene cUoride(4) (ref. 11)... 

Table IV shows the reactivity ratios rG and r, derived from the probabilities in Table III in accord with a first-order Markov model (2), where it is assumed that the more likely propagating terminal radical structure is 1 (—CHF-) and not 0 (—CH2). This assumption is consistent with gas phase reactions of VF with mono-, di-, and trifluoromethyl radicals, which add more frequently to the CH2 carbon than to the CHF carbon (20). The reactivity ratio product is unity if Bernoullian statistics apply, and we see this is not the case for either PVF sample, although the urea PVF is more nearly Bernoullian in its regiosequence distribution. Polymerization of VF in urea at low temperature also reduces the frequency of head-to-head and tail-to-tail addition, which can be derived from the reactivity ratios according to %defect — 100(1 + ro)/(2 + r0 + r,). Our analysis of the fluorine-19 NMR spectrum shows that commercial PVF has 10.7% of these defects, which compares very well with the value of 10.6% obtained from carbon-13 NMR (13). Therefore the values of 26 to 32% reported by Wilson and Santee (21) are in error.

A detailed study of the reactivity ratios of the isobutylene and 0-pinene system has been undertaken. We found that the reactivity ratio product is dose to unity over the whole temperature range studied from —50° to —130°, indicating a random copolymer system. Further, we discovered that while the reactivity ratios are quite insensitive to the particular Lewis acid used, they can be controlled by temperature and that the individual reactivity ratios become equal to unity below about —110°. In other words, at very low temperatures the copolymerization becomes azeotropic (the composition of the feed and that of the copolymer become equal). 

It should be noted, too, that the r values for this system do not permit an azeotropic polymerization, as predicted by Eq. (2.39). With respect to the distribution of styrene monomer units in the copolymer, the monomer reactivity ratio product, rers = 0.8, is close to a value of 1.0, which would correspond to an ideal copolymerization (Odian, 2004b) which would correspond to a random distribution of styrene units along the chain. For an ideal copolymerization, the relative rates of incorporation of the two monomers are independent of the chain end unit as predicted by Eq. (2.42). 

Table 22-10. Reactivity Ratio Products r V2 in Free Radical Copolymerizations (60°C)... 

Fig. 3. Stockmayer s distribution for chains with Fi = 0.5 and Nn = 1000 as a function of reactivity ratio product. Alternating rir2 = 0.01 random rir2 = 1 and block rir2 = 10-----rir2 = 0.01 --------rir2 = 1.0 ------rir2 = 10.

Composition, Microstructure, Reactivity Ratio Product, and Melting Enthalpy for EP Copolymers Prepared Using Various ... 

Fig. 6 Chemical composition distribution as a function of reactivity ratio product...

Table I lists monomer feed compositions, copolymer compositions and conversions obtained in the copolymerization experiments. The copolymerization diagram of the system (Fig. 4) shows a tendency towards alternation with an azeotropic point at 70 mole % MA. Reactivity ratios for the aFS-MA copolymerization system, determined by the Kelen-Tudos method were r =0.26 and The KT-plot is shown in Figure 5. Average monomer feed compositions were used for this determination whenever the conversion was above 10 wt. percent. Almost identical values of the reactivity ratios were obtained when calculated by the Tidwell-Mortimer method. The reactivity ratio product for this copolymerization system ( MA aFS" 2) indicates a tendency for alternation.

In so called block copolymers, the reactivity ratio product < . 

The values of the reactivity ratio products are the parameters of main significance for the statistic description of the copolymer structure, which is why these parameters are so carefully evaluated. 

Scattering amplitude Reactivity ratio product Radius of gyration... 

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