Synthesis of structurally well-defined telechelic polymers by organostibine-mediated living radical polymerization: in situ generation of functionalized chain-transfer agents and selective omega-end-group transformations.

Several organostibine chain-transfer agents possessing polar functional groups have been prepared by the reactions of azo initiators and tetramethyldistibine (1). Carbon-centered radicals thermally generated from the azo initiators were trapped by 1 to yield the corresponding organostibine chain-transfer agents. The high yields observed in the synthesis of the chain-transfer agents strongly suggest that distibines have excellent radicophilic reactivity. As the reactions proceeded under neutral conditions, functional groups that are incompatible with ionic conditions were incorporated into the chain-transfer agents. The chain-transfer agents were used in living radical polymerization to synthesize the corresponding alpha-functionalized polymers. As the functional groups in the chain-transfer agents did not interfere with the polymerization reaction, well-controlled polymers possessing number-average molecular weights (M(n)s) predetermined by the monomer/transfer agent ratios were synthesized with low polydispersity indices (PDIs). The organostibanyl omega-polymer ends were transformed into a number of different functional groups by radical-coupling, radical-addition, and oxidation reactions. Therefore, it was possible to synthesize well-controlled telechelic polymers with the same and also with different functional groups at their alpha- and omega-polymer ends. Distibine 1 was also found to increase PDI control in the living radical polymerization of styrene and methyl methacrylate (MMA) using a purified organostibine chain-transfer agent. Well-controlled poly(methyl methacrylate)s with M(n) values ranging from 10 000 to 120 000 with low PDIs (1.05-1.15) were synthesized by the addition of a catalytic amount of 1. The results have been attributed to the high reactivity of distibine 1 towards polymer-end radicals, which are spontaneously deactivated to yield organostibine dormant species.

Control of extremely fast competitive consecutive reactions using micromixing. Selective Friedel-Crafts aminoalkylation.

Friedel-Crafts reactions of aromatic and heteroaromatic compounds with an N-acyliminium ion pool were studied. The reaction of 1,3,5-trimethylbenzene in a batch reactor gave rise to the selective formation of a monoalkylation product (69%). Presumably, the second alkylation is slower than the first alkylation because of the protonation of the monoalkylation product that decreases its reactivity. The reaction of 1,3,5-trimethoxybenzene, however, gave rise to the formation of both monoalkylation (37%) and dialkylation (32%) products. Disguised chemical selectivity due to faster reaction than mixing seems to be responsible for the lack of selectivity. The use of micromixing was found to be quite effective to solve this problem to increase the selectivity. The monoalkylation product was obtained in 92% yield together with a small amount of the dialkylation product (4%). The reaction with various aromatic and heteroaromatic compounds revealed that the low mono/dialkylation selectivity was observed only for highly reactive aromatics. In such cases, the use of micromixing was quite effective to improve the selectivity. On the basis of micromixing, the selective sequential dialkylation using two different N-acyliminium ions was achieved. CFD simulations using a laminar flow and finite-rate model are consistent with the experimental observations and clearly indicate the importance of mixing.