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Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation.

ABSTRACT: The polymerization of octamethylcyclotetrasiloxane (D4) is investigated using several five-, six- and seven-membered N-heterocyclic carbenes (NHCs). The catalysts are delivered in situ from thermally susceptible CO2 adducts. It is demonstrated that the polymerization can be triggered from a latent state by mild heating, using the highly nucleophilic 1,3,4,5-tetramethylimidazol-2-ylidene as organocatalyst. This way, high molecular weight PDMS is prepared (up to >400 000 g/mol, 1.6 < Ð M < 2.5) in yields >95%, using low catalyst loadings (0.2-0.1 mol %). Furthermore, the results suggest that a nucleophilic, zwitterionic mechanism is in operation, in preference to purely anionic polymerization.

SUBMITTER: Naumann S

PROVIDER: S-EPMC4660969 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation.

Naumann Stefan S Klein Johannes J Wang Dongren D Buchmeiser Michael R MR

Beilstein journal of organic chemistry 20151120

The polymerization of octamethylcyclotetrasiloxane (D4) is investigated using several five-, six- and seven-membered N-heterocyclic carbenes (NHCs). The catalysts are delivered in situ from thermally susceptible CO2 adducts. It is demonstrated that the polymerization can be triggered from a latent state by mild heating, using the highly nucleophilic 1,3,4,5-tetramethylimidazol-2-ylidene as organocatalyst. This way, high molecular weight PDMS is prepared (up to >400 000 g/mol, 1.6 < Ð M < 2.5) in ...[more]

PMID: 26664650

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Project description:AbstractPoly(dimethylsiloxane) (PDMS)-based nanocomposites have attracted increasing attention due to their inherent outstanding properties. Nevertheless, the realization of high levels of dispersion of nanosilicas in PDMS represents a challenge arising from the poor compatibility between the two components. Herein, we explore the use of ionic interactions located at the interface between silica and a PDMS matrix by combining anionic sulfonate-functionalized silica and cationic ammonium-functionalized PDMS. A library of ionic PDMS nanocomposites was synthesized and characterized to highlight the impact of charge location, density, and molecular weight of ionic PDMS polymers on the dispersion of nanosilicas and the resulting mechanical reinforcement. The use of reversible ionic interactions at the interface of nanoparticles-polymer matrix enables the healing of scratches applied to the surface of the nanocomposites. Molecular dynamics simulations were used to estimate the survival probability of ionic cross-links between nanoparticles and the polymer matrix, revealing a dependence on polymer charge density.Impact statementPoly(dimethylsiloxane) (PDMS) has been widely used in diverse applications due to its inherent attractive and multifunctional properties including optical transparency, high flexibility, and biocompatibility. The combination of such properties in a single polymer matrix has paved the way toward a wide range of applications in sensors, electronics, and biomedical devices. As a liquid at room temperature, the cross-linking of the PDMS turns the system into a mechanically stable elastomer for several applications. Nanofillers have served as a reinforcing agent to design PDMS nanocomposites. However, due to significant incompatibility between silica and the PDMS matrix, the dispersion of nanosilica fillers has been challenging. One of the existing strategies to improve nanoparticle dispersion consists of grafting oppositely charged ionic functional groups to the nanoparticle surface and the polymer matrix, respectively, creating nanoparticle ionic materials. Here, this approach has been explored further to improve the dispersion of nanosilicas in a PDMS matrix. The designed ionic PDMS nanocomposites exhibit self-healing properties due to the reversible nature of ionic interactions. The developed synthetic approach can be transferred to other kinds of inorganic nanoparticles dispersed in a PDMS matrix, where dispersion at the nanometer scale is a prerequisite for specific applications such as encapsulants for light-emitting diodes (LEDs).Graphical abstractSupplementary informationThe online version contains supplementary material available at 10.1557/s43577-022-00346-x.

Project description:Growth factors have been shown to be potent mediators of osteogenesis. However, their use in tissue-engineered scaffolds not only can be costly but also can induce undesired responses in surrounding tissues. Thus, the ability to specifically induce osteogenic differentiation in the absence of exogenous growth factors through manipulation of scaffold material properties would be desirable for bone regeneration. Previous research indicates that addition of inorganic or hydrophobic components to organic, hydrophilic scaffolds can enhance multipotent stem cell (MSC) osteogenesis. However, the combined impact of scaffold inorganic content and hydrophobicity on MSC behavior has not been systematically explored, particularly in three-dimensional (3D) culture systems. The aim of the present study was therefore to examine the effects of simultaneous increases in scaffold hydrophobicity and inorganic content on MSC osteogenic fate decisions in a 3D culture environment toward the development of intrinsically osteoinductive scaffolds. Mouse 10T½ MSCs were encapsulated in a series of novel scaffolds composed of varying levels of hydrophobic, inorganic poly(dimethylsiloxane) (PDMS) and hydrophilic, organic poly(ethylene glycol) (PEG). After 21 days of culture, increased levels of osteoblast markers, runx2 and osteocalcin, were observed in scaffolds with increased PDMS content. Bone extracellular matrix (ECM) molecules, collagen I and calcium phosphate, were also elevated in formulations with higher PDMS:PEG ratios. Importantly, this osteogenic response appeared to be specific in that markers for chondrocytic, smooth muscle cell, and adipocytic lineages were not similarly affected by variations in scaffold PDMS content. As anticipated, the increase in scaffold hydrophobicity accompanying increasing PDMS levels was associated with elevated scaffold serum protein adsorption. Thus, scaffold inorganic content combined with alterations in adsorbed serum proteins may underlie the observed cell behavior.

Dataset Information

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation.

Publications

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation.

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