BCMO polymerization

Table III shows the increase of molecular weight of BCMO polymerization with conversion, although the polymer tends to precipitate. The monomer reactivity ratios of DOL-BCMO copolymerization were previously determined as rx (DOL) = 0.65 0.05, r2 (BCMO) = 1.5 0.1 at 0°C. by BF3 Et20 (8). Table IV shows a preparation of block copolymer of DOL, St, and BCMO. In the first step we polymerized DOL and St in the second step we added BCMO to this living system. The copolymer obtained showed an increase of molecular weight, and considerable BCMO was incorporated in the copolymer still remaining soluble in ethylene dichloride. The solubility behavior together with the increase of molecular weight with addition of BCMO shows that this polymer consists of block sequences of DOL-St and (St)-DOL-BCMO. This we call block and random copolymer of DOL-St—BCMO. We can deny the presence of BCMO, St, or DOL homopolymers in this system, but some chain-breaking reactions are unavoidable, leading to copolymer mixtures. Thus, the principle of formation of block copolymers by cationic system is partly substantiated.

Usually, [l]o is of the order of 10 mole 1 . Thus, if [M]q = 1.0 mole 1 and kj/kp 10 (conditions used for BCMO polymerization) then the limited conversion, when all of the active species are transformed into the PJ[ species (considered inactive), Aould be close to 0.8, As it was reported, the kinetic curves indeed level off (rates approach zero) at the plateau corresponding to approx. 80% of conversion under these conditions. Since the slope of the plateau is not perfectly equal to zero, there is probably some reinititation which has not been taken into account in the formulation of the kinetic Scheme (138). 

In 1969 Penczek and Kubisa [59] reported an exhaustive study of the kinetics and mechanism of BCMO polymerization initiated by the (i-C4H9 )j AI/H2O system and carried out in chlorobenzene solution at 55—95°C. This system produced homogeneous conditions for the polymerization and the whole process could be described as a non-stationary reaction with slow initiation, fast propagation, and slow degradative chain transfer to polymer. 

A complete kinetic scheme, involving slow initiation, propagation, and termination by chain transfer to polymer, has been developed 29,30) and it was conclusively shown that it is applicable for BCMO polymerization. The pertinent kinetic equations were given in Vol. I (Adv. Polymer Sci. 37). The rate constant of termination by chain transfer to polymer was kt = 1.2 10 3 mol-1 - I s-1 (C6H5C1, 70 °C)18). 

Another approach for the preparation of BCMO graft copolymers was based on the use of macromolecular initiators 38). Polystyrene or polyTHF containing dioxole-nium groups in the chain were prepared and used as initiators of BCMO polymerization as shown for polystyrene ... 

The following scheme of reactions will explain the course of the BCMO polymerization. 

Figure 5. nmr spectrum of BCMO polymerization mixture by EtOSO CFs in nitrobenzene after 180 min at 63°C (12)... 

Table VI. Rate Constants and Activation Parameters in the BCMO Polymerization in Nitrobenzene )...

The transition state of the BCMO polymerization by Et0S02CF3 is probably formulated as XII, in which two neutral molecules of... 

The mechanistic difference of these two cases Is well recognized by the observation that the transition state XII differs much from XIII since going from the Initial to transition state the charge Is developed at XII whereas it is despersed at XIII. This was further supported by the examination of the solvent effect on the rate of BCMO polymerization (12). 

New findings specific to the THF and BCMO polymerizations Initiated by superacid esters are described. In the THF polymerization the oxonium (I) and ester (II) species of the propagating end were involved In equilibration, which were directly observed by F nmr spectroscopy. Thus, kp(ap) and kp(i) were separately determined, In which the contribution of the propagation due to the ester species (II) was estimated to be very small. In the BCMO polymerization, however, the ester species (IV and V) were actually the propagating chain-ends. This provides... 

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