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SUMMARY: The silylation of cellulose with hexamethyldisilazane (HMDS) in liquid ammonia at elevated temperature has been extended to the synthesis of partly silylated trimethylsilylcellulose. Predictable degrees of silylation (DS) were obtained either with excess ammonia or in a nearly 1 : 1 ratio of NH 3 /AGU (anhydroglucose unit) or with toluene as co-solvent. Complete reaction of the silylating agent allows to adjust the DS directly by simple variation of the ratio of OH groups to trimethylsilyl groups of the silylating agent. With chlorotrimethylsilane more than the stoichiometric amount of silylating agent is required to obtain a desired DS and the work up is more tedious. A simple method to determine the DS of trimethylsilylcellulose based on infrared spectroscopy is proposed. It is applicable to cellulose with a DS greater than 1.3.

Eight samples of trimethylsilyl cellulose (TMSC) with different degrees of substitution (DS) were investigated by static and dynamic light scattering in tetrahydrofuran at 25 °C. Six of these sample were prepared from Avicel cellulose (DPw = 221) by controlled silylation with stoichiometric amounts of hexamethyldisilazane in liquid ammonia at elevated temperature in an autoclave. The two others were obtained by controlled desilylation of the sample with DS = 2.72. The TMSC samples were soluble in tetrahydrofuran, but in all cases strong aggregation was observed with aggregation numbers of 80 for DS = 1.96 up to 270 for DS = 2.72. Surprisingly, the aggregation number considerably increased for the samples obtained by desilylation. These very large aggregates permitted a detailed analysis of the angular dependencies which resulted in rather rigid structures with Kuhn segment lengths of l K = 122−174 nm, about 6 times the segment length of molecularly dissolved cellulose derivatives. This increase in chain stiffness is caused by a side-by-side alignment of 2−4 chains, which further increased to about 13−14 chains for the samples obtained by partial desilylation. The structure of the aggregates resembles that of branched macromolecules built up from stiff chains in which the junction zones of 2−4 aligned chains act as branching points.

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Desilylation of trimethylsilyl cellulose with stoichiometric amounts of water has been achieved in THF/ammonia in the presence of saccharin as catalyst. Experimental degrees of silylation are in close agreement with calculated ones. Deviations occur if the desired DS is near 1. These are due to the insolubility of silyl cellulose with DS 1 in THF/ammonia and to the heterogeneous character of the reaction at this point. Hydrolysis of 1,2‐bis(trimethylsiloxy)propane in THF/ammonia showed that the secondary siloxy group is more readily cleaved than the primary. It also proved that the slow conversion of trimethylsilanol to hexamethyldisiloxane is responsible for the rather long reaction times required.

High molecular weight vinyl‐type polynorbornene was obtained by polymerization of norbornene initiated by [NiBr(NPMe3)]4/B(C6F5)3. Polymerization in the presence of olefins resulted in termination of polynorbornene chains by olefinic moieties. Molecular weights of polynorbornenes terminated by vinylidene compounds are lower than those terminated by vinyl and vinylene compounds. Corresponding polymerizations with polybutadiene and polyisoprene yielded graft copolymers with polynorbornene as grafts without contamination by homopolymerized polynorbornene. Grafting reactions were proved by spectroscopy, GPC, and degradation experiments using OsO4. GPC traces (refractometer detector) of PN obtained for the polymerizations of 2 in the presence of 4d.magnified imageGPC traces (refractometer detector) of PN obtained for the polymerizations of 2 in the presence of 4d.

Acylation of partially trimethylsilylated cellulose, glycerol (1), 1,3‐bis(trimethylsiloxy)‐2‐propanol (2), methyl‐2,3,4,6‐tetrakis‐O‐trimethylsilyl‐α‐D‐glucopyranoside (10) and methyl‐2,3,4‐tris‐O‐trimethylsilyl‐α‐D‐glucopyranoside (11) either with acyl chlorides/triethylamine at room temperature or with acyl chlorides at elevated temperature in the absence of an acid scavenger has been studied. Selective acylation of free hydroxy groups has been found with acyl chloride/amine, though complete conversion of free hydroxy groups of cellulose could not be achieved under these conditions. High temperature acylation, however, results in an unselective reaction of free hydroxy groups and trimethylsilyloxy groups. Trans‐silylation takes place and chlorination is found in the reaction of 1 and 2. Carbohydrates were not chlorinated under these conditions, silyl cellulose, however, is strongly depolymerized.