Designing of polyhedral oligomeric silsesquioxane (POSS)-based dithiol/dimethacrylate nano-hybrids

Enhancing the Thermal Resistance of UV-Curable Resin Using (3-Thiopropyl)polysilsesquioxane

This study delineates a methodology for the preparation of new composites based on a photocurable urethane-acrylate resin, which has been modified with (3-thiopropyl)polysilsesquioxane (SSQ-SH). The organosilicon compound combines fully enclosed cage structures and incompletely condensed silanols (a mixture of random structures) obtained through the hydrolytic condensation of (3-mercaptopropyl)trimethoxysilane. This process involves a thiol-ene "click" reaction between SSQ-SH and a commercially available resin (Ebecryl 1271®) in the presence of the photoinitiator DMPA, resulting in composites with significantly changed thermal properties. Various tests were conducted, including thermogravimetric analysis (TGA), Fourier transmittance infrared spectroscopy (FT-IR), differential scanning calorimetry (Photo-DSC), and photoreological measurement mechanical property, and water contact angle (WCA) tests. The modification of resin with SSQ-SH increased the temperature of 1% and 5% mass loss compared to the reference (for 50 wt% SSQ-SH, T5% was 310.8 °C, an increase of 20.4 °C). A composition containing 50 wt% of SSQ-SH crosslinked faster than the reference resin, a phenomenon confirmed by photorheological tests. This research highlights the potential of new composite materials in coating applications across diverse industries. The modification of resin with SSQ-SH not only enhances thermal properties but also introduces a host of functional improvements, thereby elevating the performance of the resulting coatings.

Modified POSS nano-structures as novel co-initiator-crosslinker: Synthesis and characterization

OBJECTIVE

To synthesize an amine-modified polyhedral oligomeric silsesquioxane (POSS) nano-structure as a novel co-initiator-crosslinker (co-Ini-Linker) and to determine the effect of the co-Ini-linker on the physical and mechanical behavior of an experimental dental composite.

METHODS

The amine-methacrylate POSS nano-structures (AMA-POSS) were chemically synthesized by anchoring a tertiary amine functionality on the methacrylate POSS (MA-POSS) branches. Three types of AMA-POSS, having different amine branches in their structures, were synthesized through the Aza Michael reaction. The chemical structure of AMA-POSSs were evaluated by¹H-NMR spectroscopy. Afterward, the AMA-POSS was incorporated into a dental resin system composed of Bis-GMA, TEGDMA, and photo-initiator. Three resin systems with different AMA-POSS types were then prepared, and their properties were compared with a resin containing DMAEMA as a conventional co-initiator. The degree of conversion evaluated by FTIR spectroscopy and the shrinkage kinetics of the resins were determined through the bonded-disk technique. The flexural properties of the photopolymerized resins were also investigated. The distribution of nano-structures in the matrix resin was analyzed using EDX analysis.

RESULTS

The modified POSS structure and the number of amine branches were confirmed with¹H-NMR spectroscopy. The resin containing 8 amine branches (P8) showed the same degree of conversion (DC%) as the resin containing DMAEMA (P > 0.05). Decreasing the amine branches in the POSS structure, however, revealed an increasing trend in DC%. The resin containing P8 showed the lowest shrinkage strain. By incorporating AMA-POSS into the resin system, the water sorption significantly decreased (P < 0.05). The flexural strength and modulus increased by adding P3 into the resin system (P < 0.05). EDX Si-map revealed that the co-Ini-linker was well dispersed in the resin matrix.

SIGNIFICANCE

The synthesized novel amine-methacrylate POSS nanostructures not only act as an amine co-initiator but also work as a reinforcing filler and a cross-linking agent.

Anchor Effect in Polymerization Kinetics: Case of Monofunctionalized POSS

The effect of the anchoring group on the detailed polymerization kinetics was investigated using monomethacryloxy-heptaisobutyl POSS (1M-POSS). This compound was copolymerized with lauryl methacrylate (LM) as the base monomer, at various molar ratios. The process was initiated photochemically. The polymerization kinetics were followed by photo-DSC and photorheology while the polymers were characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). For comparison, a methacrylate containing the branched siloxy-silane group (TSM) was also studied. It was found that the modifiers with a bulky substituent have a dual effect on the termination process: (i) At low concentrations, they increase the molecular mobility by increasing the free volume fraction, which leads to an acceleration of the termination and slows the polymerization; while (ii) at higher concentrations, they retard molecular motions due to the “anchor effect” that suppresses the termination, leading to acceleration of the polymerization. The anchor effect can also be considered from a different point of view: The possibility of anchoring a monomer with a long substituent (LM) around the POSS cage, which can further enhance propagation. These conclusions were derived based on kinetic results, determination of polymerization rate coefficients, and copolymer analysis.