Structural Control of Fully Condensed Polysilsesquioxanes: Ladderlike vs Cage Structured Polyphenylsilsesquioxanes

Abstract

Through fine-tuning of the myriad of reaction conditions for an aqueous base-catalyzed hydrolysis−polycondensation reaction, a facile synthesis of structurally controlled polyphenylsilsesquioxanes was developed. Mechanism and kinetic studies indicated that the condensation reaction proceeded through a T 1 structured dimer, which was quantitatively and in situ formed through mild hydrolysis of a phenyltrimethoxysilane (PTMS) monomer, to give either the cage-structured polyhedral oligomeric silsesquioxanes (POSS) or the corresponding ladderlike silsesquioxane (LPSQ) with excellent yields. Ladderlike and POSS materials were selectively achieved at higher and lower initial concentrations of PTMS, respectively, and an in-depth spectroscopic analysis of both compounds clearly revealed their structural differences with different molecular weights.

Side-chain engineering of ladder-structured polysilsesquioxane membranes for gas separations

“…As represented in Table 3, the permeability of LMASQ was the highest and that of LPPSQ was the lowest among the all LPMAs. Those calculated permeabilities of homopolymers were confirmed by back calculation from Equation (14). The back calculated permeability results of all copolymers (i.e., LPMA64, LPMA73, and LPMA82) were in good agreement with the analogous experimental results (See Table 3).…”

“…The separation factor (α*) of the feed mixture (CO 2 /N 2 ) can be calculated using the following equation, The synthesis of LPSQs with various alkyl groups as well as copolymer ratios were carried out by following a modified literature procedure [14][15][16]. In this method, a high [28,29], as well as the various epoxy (908 cm -1 ), carbonyl (1748 cm -1 ), vinyl (1648 cm -1 ), and phenyl (1600 cm -1 ) groups (See Fig.…”

“…(14) where, P copolymer is permeability of copolymer, P A and P B are permeabilities of the homopolymers A and B, respectively, and φ A and φ B are the volume fraction of component A and B, respectively. It should be noted that the free-standing film formation of homopolymer LPSQ is very challenging due to the tandem limitations of mechanical properties and polymer state [62].…”

“…On the contrary, LPMAs with a phenyl group less than 60 mol% become a viscous liquid gel-state [24]. Thus we estimated the permeability of the respective homopolymer of LPMAs (i.e., ladder-like poly(phenyl)silsesquioxane (LPPSQ) and ladder-like poly(methacryloxypropyl)silsesquioxane (LMASQ)) by using the experimental permeability results for the copolymer and the volume fraction of each homopolymer in Equation (14). The volume fraction of each homopolymer was estimated by using van der Waals volume (See Table S8) instead of the actual volume.…”

“…Especially, ladderstructured polysilsesquioxanes (LPSQs), while relatively less known, may be unique enough to intrigue the interest of membrane scientists. They possess structural peculiarities in which the Si-O-Si bonds consist of double stranded ladder-like structure, with the organic functional groups radially stemming outwards [13][14][15]. Very recently, we investigated the first-ever free-standing LPSQ membrane as a proof of concept for gas separation [16].…”