synopsisThe heats of fusion and the melting transitions of the crystallinity present in the side chains were determined for selected copolymers incorporating n-octadecyl acrylate or vinyl stearate. A major purpose of this investigation was to ascertain the effect of INTRODUCTIONMuch interest has centeredl8.2 on the crystallization phenomenon in copolymers in which one co-unit of the main chain is capable of crystallizing. The Flory theory of the equilibrium crystallization of polymers3 required that sequence length distribution, and not the chemical nature of the amorphous component, determbed the melting point depression. A very broad distribution of crystal sizes and lowered crystallinities were 3349 0

Electron spin resonance spectra have been recorded for model Ziegler-Natta catalysts prepared by depositing alkylmagnesium butoxide (AMB) and titanium tetrachloride onto a silica support. Depending on the reagent stoichiometry and loading, one or more of four different singlet resonances are observed which account for no more than 17% of all the titanium present. By examining trends in the spectra as a function of Mg to Ti ratio and of temperature, one ESR site (g = 1.895) is proposed to arise from an interaction between [Ti(3+)]" clusters and TiCl4. In situ dosing experiments and wet chemistry titanium oxidation state determinations support this proposal, while ethylene polymerization experiments on selected preparations show that catalyst activity increases by increasing the Ti(4+) content. In the case of the in situ dosing experiments, the g = 1.895 signal can be created or eliminated by exposing the catalyst to TiCl4 or diethylaluminum chloride vapors, respectively. The titanium oxidation state determinations show that even under the most extreme reducing conditions used (AMB/TiCl4 molar ratio 10/1), only a negligible fraction (0.8%) of all titanium is reduced to Ti(2+). All Ti(3+) determinations by cyclic voltammetry on filtrates of extracted catalysts show that there is two to nine times more Ti(3+) present than is detected by ESR. All of the above findings are consistent with the equilibrium process shown below: [ Ti (3 +)]" + rnTiCI* ;=i [Ti (3 + )]"( TiCI4)" ESR silent ESR activeThrough comparisons with ESR spectra reported for other similar catalysts, it is proposed that these or related cluster sites exist in many titanium Ziegler-Natta catalysts on magnesium-based supports. Ironically, then, ESR can be used to detect the presence of the diamagnetic molecule TiCl4 in these catalysts.

Magnetic susceptibility data (4‐290 K) are reported for four supported catalysts of general formulation SiO2/xAMB/yTiCl4, where AMB is an alkylmagnesium butoxide reagent.

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