Novel Possibilities by Cationic Ring‐Opening Polymerisation of Cyclodextrin Derivatives: Preparation of a Copolymer Bearing Block‐Like Sequences of Tri‐O‐methylglucosyl Units

Abstract

Summary: Equimolar mixtures of O‐permethylated and O‐perdeuteromethylated cyclodextrins were submitted to cationic ring‐opening polymerisation (CROP) with Et3OPF6 or BF3 · Et2O as initiator in dichloromethane. Reaction started after an incubation time and yielded a polymeric product, which was partially degraded again during competing chain transfer reaction. Average block length was determined by ESI‐MS after partial methanolysis and was found to be close to the theoretical value of 14 for β‐cyclodextrin in the early stage of the reaction, but decreased to 2–5 during further chain transfer reactions accompanied by an equilibration of α‐ and β‐configurated glucosidic linkages to a ratio of 64:36. Molecular weight was estimated from end group analysis and GPC to reach about 29 000 as a maximum. From 31P NMR spectra of the initiator it was obvious that PF is partly hydrolysed to PO2F under participation of the glass surface. magnified image

Mechanistic studies on cationic ring-opening polymerisation of cyclodextrin derivatives using various Lewis acids

“…In preliminary investigations of Suzuki [Suzuki et al 2001] and our laboratory [Adden et al 2004], a lag phase of the polymerisation reaction has been observed. This has also been reported for CROP of simple acetals as 1,3-dioxolane.…”

“…Disaccharides obtained from random methanolysis of the polymeric product are analysed by ESI-MS [Adden et al 2004 …”

“…As has been reported, disappearance of α-H1 of CDs and occurrence of α,β-H1 of the polymer can be evaluated [Suzuki et al 2001, Adden et al 2004]. …”

“…Permethylation and perdeuteromethylation of β-CD was carried out with NaOH and CH 3 I ( 1) or CH 3 I-d 3 ( 2) according to Ciucanu and Kerek [1984] as previously described [Adden et al 2004]. Further purification was achieved by column chromatography on Sephadex LH 20 with methanol/dichloromethane (2:1 v/v).…”

“…We developed a concept for the synthesis of block-copolymers from differently substituted or protected cyclodextrins. In our model studies with permethylated (Me 21 -β-CD, 1) and perdeuteromethylated β-CDs ((Me-d 3 ) 21 -β-CD, 2) we obtained the desired products with average block length of 14, which fast decreased due to interfering chain transfer reactions [Adden et al 2004]. To get more insight into the mechanism and side reactions of cyclodextrin polymerisation, we performed some mechanistic studies under the influence of various Lewis acids.…”