Partial polycondensation of RSi(OMe) 3 (R = C 6 H 5 , CH 3 ) by the reaction with АсOH in the presence of HCl is studied. Oligoorganomethoxysiloxanes are obtained of the average composition [RSi(OMe)O] 4 , [RSi (OMe) 4/6 O 7/6 ] 6 , RSi(OMe) 0.5 O 1.25 ] 8 , and [RSi(OMe) 0.4 O 1.3 ] 10 . Using the method of 29 Si NMR spectroscopy they were shown to contain three types of structural fragments: RSi(OMe) 2 O-, RSiOMe(O-) 2 , RSi(O-) 3 . Based on the kinetic data, on the composition, properties, and the 29 Si NMR spectroscopy data of the products the conclusion is made that the obtained compounds have polycyclic structure with branched fragments. Using the GLC method the reaction was shown to have an induction period, whose duration can be substantially shortened by addition of HCl or methanol.Reactions of organoacetoxysilanes with alcohols [1, 2] and organoalkoxysilanes with organic acids [3][4][5][6][7][8][9][10][11][12][13] are an efficient method of synthesis of organosiloxanes of various composition and structure. A specific feature of these processes is the formation of the siloxane bond upon hydrolytic polycondensation in homogeneous environment due to the presence of water produced in the reaction of an acid with an alcohol. Thus, an industrial method for preparation of organosiloxane resins by the reaction of organoacetoxysilanes with methanol is described [1]. The synthesis of polyethylsiloxane liquids by the reaction of diethyldiethoxysilane with organic mono-and dicarboxylic acids in the presence of sulfuric acid as a catalyst is also described [3]. Depending on the ratio of the reagents cyclic or linear diethylsiloxanes can be obtained in quantitative yield. It was shown that carrying out the reaction of organoalkoxysilanes with acetic acid allows to substantially improve the control of the process, first of all as far as the control of the structure of the formed products is concerned [4]. This is connected with the fact that acetic acid and alcohol are an active medium of the reaction, which dissolve the reagents, the products, and are co-reagents.In the present work, we have investigated the partial polycondensation of phenyl-and methyltrimethoxysilanes RSi(OMe) 3 in the reaction with acetic acid in the presence of hydrogen chloride at different molar ratios of АсOH and RSi(OMe) 3 . The scheme of the reaction can be represented as follows [Eq. (1)].

No abstract

No abstract

Poly-(4,4′-oxydiphenylene) pyromellitimide or Kapton is the most widely available polyimide with high chemical and thermal stability. It has great prospects for use as a membrane material for filtering organic media due to its complete insolubility. However, the formation of membranes based on it, at the moment, is an unsolved problem. The study corresponds to the rediscovery of poly(4,4′-oxydiphenylene–pyromellitimide)-based soluble copoly(urethane-imides) as membrane polymers of a new generation. It is shown that the physical structure of PUI films prepared by the solution method becomes porous after the removal of urethane blocks from the polymer, and the pore size varies depending on the conditions of thermolysis and subsequent hydrolysis of the membrane polymer. The film annealed at 170 °C with a low destruction degree of polycaprolactam blocks exhibits the properties of a nanofiltration membrane. It is stable in the aprotic solvent DMF and has a Remasol Brilliant Blue R retention coefficient of 95%. After the hydrolysis of thermally treated films in acidic media, ultrafiltration size 66–82 nm pores appear, which leads to an increase in the permeate flow by more than two orders of magnitude. This circumstance provides opportunities for controlling the membrane polymer structure for further optimization of the performance characteristics of filtration membranes based on it. Thus, we proposed a new preparation method of ultra- and nanofiltration membranes based on poly(4,4′-oxydiphenylene–pyromellitimide) that are stable in aprotic solvents.

No abstract