Controlled synthesis of poly(dimethylsiloxane) homopolymers using high‐vacuum anionic polymerization techniques

Abstract

The controlled synthesis of poly(dimethylsiloxane) homopolymers (PDMS) using hexamethyl(cyclotrisiloxane) monomer (D 3 ), a mixture of ciclohexane/tetrahydrofuran 50/50 v/v and sec-Bu -Li þ as initiator was studied using different experimental conditions, and whole-sealed glass reactors according to standards procedures in high-vacuum anionic polymerization. It was observed that polydispersity indexes (PD) and conversions strongly depend on temperature and reaction times. For PDMS homopolymers with molar masses below 100,000 g/mol, high conversion ([90%) and PD \ 1.1 can be achieved at long reaction times (24 h) and mild temperature conditions (below or up to 30 C). On the other hand, to synthesize PDMS homopolymers with molar masses higher than 100,000 g/mol and PD \ 1.1 it is necessary to increase the temperature up to 50 C and decrease the reaction time (8 h). However, under these reaction conditions, it was observed that the conversion decreases (about 65-70% conversion is achieved). Apparently, the competition between propagation and secondary reactions (redistribution, backbiting, and reshuffling) depends on the molar masses desired. According to the results obtained in this study-which were compared with others found in the scientific literature-propagation is favored when M n \ 100,000 g/mol, whereas secondary reactions seem to become important for higher molar masses. Nevertheless, model PDMS homopolymers with high molar masses can still be obtained increasing the reaction temperature and shortening the total reaction time. It seems that the combined effect of these two facts favors propagation against secondary reactions, and provides model PDMS homopolymers with molar masses quite close to the expected ones. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4774-4783, 2009

Enhancement of mechanical and optical performance of commercial polystyrenes by blending with siloxane‐based copolymers

“…PS‐ b ‐PDMS copolymers were synthesized by employing anionic polymerization and sequential addition of monomers, in a Schlenk‐type reactor (Figure ) by following the classical methodology reported in the literature . For such a purpose, two main objectives were imposed: (i) a proper purification of monomers and reagents; and (ii) the precise methodology for controlling D 3 polymerization . By following these objectives, three different PS‐ b ‐PDMS copolymers were synthesized.…”

“…In addition, their polydisperisity index ( M w / M n ) are lower than 1.3. The reason why M w / M n is higher than conventional anionic polymerization (high vacuum techniques) can be explained by taking into account that the experimental procedure employed in this work involves only a vacuum manifold (no purified nitrogen or argon gas was employed), and the closing and opening of vacuum stopcocks (Rotaflo ® ) from different devices that are attached and de‐attached from the main reactor. These manipulations might contaminate, in some extent, the vacuum by introducing air inside the reactor.…”

“…Ciclohexane (Dorwill) and methanol (Química Industrial) were used as solvent and terminating agent, respectively. Tetrahydrofuran (THF, Ciccarelli) was added as solvating agent in order to promote D 3 polymerization according to previously reported procedures …”

“…Polymerizations were carried out in a specially designed Schlenk‐type reactor (Figure ), following the methodology reported in previous works . In this sense, the general procedure for the synthesis of PS‐ b ‐PDMS copolymers is briefly described as follows.…”

Organic–inorganic rod–coil block copolymers comprising substituted polyacetylene and poly(dimethylsiloxane) segments

“…The catalyst was only able to prepare block copolymers comprising two substituted polyacetylene segments with different side groups. 74,75 In this study, we synthesized rod-coil block copolymers consisting of substituted polyacetylene and PDMS segments via an anionic polymerization approach. [68][69][70] This approach was employed to prepare the well-defined polyacetylene containing the block copolymer and star-branched copolymer.…”