Selectivity Control By Temperature Variation in the Formation of Isotactic vs. Syndiotactic Polypropylene with a Titanocene/Alumoxane Catalyst

✍ Scribed by Prof. Dr. Gerhard Erker; Dipl.-Chem. Cornelia Fritze

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 526 KB
• Volume: 31
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.199201991

✦ Synopsis

along a part of the chain and would be much easier to carry out. The nicotinoyl group was chosen as a blocking group since it is sufficiently hydrophilic. After the reaction of nicotinoyl chloride. HCI 3 with 1 a . 2b the reaction mixture was dialyzed. The optical rotation of the mixture did not approach zero but rather stabilized at 0.065 (Fig. 3). Thus permanently bound a-cyclodextrin is present in product 4 a. The integration of the signals of the 'H NMR spectrum of 4a (Fig. 3 d) indicates a concentration of 10 mol YU cyclodextrin and 2.5 mol% nicotinoyl groups. The absence of the signal at 6 = 5.04 indicates that all the a-cyclodextrin units are threaded. All the cyclodextrin signals are sharp and identical to those of 1 a . 2 a. Since the structure of these rings is retained and since the rings are bound permanently, we believe that 4a is a polyrotaxane.

Only those rings on the chain between the two blocking groups remain threaded. The probability of finding at least two blocking groups on one chain increases with the conversion x of the blocking reaction. Thus the relative amount y of permanently bound rings should increase with x. This is the case. From the reaction of l a 2b with 3 polyrotaxane 4b is obtained in 43% yield with x = 25 mol% blocking groups and y = 67 mol% cyclodextrin rings per basic unit. The molecular mass of 4b"I M , = 55000 & 5000 gmol-' was found by light scattering; this corresponds to a degree of polymerization P, = 55 & 5, in good agreement with that of 2b (P,, = 60 &12). Thus 37 cyclodextrin rings are permanently threaded in 4b. By this synthesis of polyrotaxanes 4a and 4 b we demonstrate not only the threading of rings 1 a on the chains 2a and 2 b but also a promising new approach to polyrotaxanes.

Experimental Procedure

2a: Reprecipitated[h] Nylon 11 (6.0 g, 32.8 mmol, Aldrich) was suspended in dry THF (100 mL) and heated to reflux under inert gas. A 2 M solution of BH, . Me,S in THF (55 mL, 110 mmol, Aldrich) was added dropwise over 1 h. The reaction mixture was heated 1 d at reflux. The THF was distilled off, water (100 mL) added, and the mixture heated at reflux 1 h. The reaction mixture was allowed to cool to 20" and glacial acetic acid (60 mL) was added. The mixture was stirred 1 h at room temperature and heated 3 h at reflux. The cooled solution was added dropwise to a 10% NaOH solution (2 L). The precipitate was removed by filtration, washed with water, dried in vacuum, and extracted with CHCI, in a Soxhlet apparatus. The extract was added dropwise to diethyl ether (1 L). Polymer 2a precipitated and was filtered and dried in vacuum. Yield 5.2 g (94%), white powder, m.p.