The Preparation of Acryloxyl Group Functionalized Siloxane Polymers and the Study of Their Ultra Violet Curing Properties

Polysiloxane with multiple acryloxyl groups at the terminal site of the polymer chain was synthesized by the condensation reaction between hydroxyl-terminated polysiloxane and acryloyl chloride and used to improve the cross-linking density of UV-curable silicone materials initiated from dual acryloxy-terminated symmetric polysiloxane or single acryloxy-terminated asymmetric polysiloxane with the mixture of Irgacure 1173 and Irgacure 184 at a mass ratio of 1:1 as the photoinitiator. The effects of factors such as initiator composition, UV irradiation time, structure, and molecular weight of linear dual acryloxy-terminated or single acryloxy-terminated asymmetric siloxane oligomers on the gelation yield, thermal properties, water absorption, and water contact angle of UV-cured film were investigated. The synthesized cross-linking density modifier can be copolymerized with acryloxy-functionalized linear polysiloxanes under the action of a photoinitiator to increase the cross-link density of UV-cured products effectively. Both linear dual acryloxy-terminated or single acryloxy-terminated asymmetric siloxane oligomers can be copolymerized with cross-link density modifiers within 20 s of UV irradiation. The gelation yields of the UV-cured products obtained from the dual acryloxy-terminated siloxane oligomers were greater than 85%, and their surface water contact angles increased from 72.8° to 95.9° as the molecular weight of the oligomers increased. The gelation yields of UV-cured products obtained from single acryloxy-terminated asymmetric siloxane oligomers were less than 80%, and their thermal stabilities were inferior to those obtained from the dual acryloxy-terminated siloxane oligomers. However, the water contact angles of UV-cured products obtained from these single acryloxy-terminated asymmetric siloxane oligomers were all greater than 90°.

Photopolymerization of Macroscale Black 3D Objects Using Near-Infrared Photochemistry

The efficiency of the photopolymerization technology significantly decreases when the color of materials blackens, which is contributed by the limitations of light penetration. Herein, we demonstrate rapid generation of black 3D objects up to the centimeter level in size based on melanin using near-infrared (NIR) photochemistry. Melanin, of a low absorption coefficient in the NIR range, allows thorough penetration of the 980 nm light to induce emission from upconversion nanoparticles (UCNPs) for initiating UCNP-assisted photopolymerization (UCAP). A model that describes light-attenuation gradients and dose-dependent kinetics in UCAP-guided NIR photochemistry is developed. Notably, the established model for the UCAP concept provides sufficient vertical light penetration to form scale-predictable black materials and instructs 3D printing applications. The critical control parameters were evaluated, and it was shown that complex macroscale black objects can be processed within dozens of minutes. The modeling methodologies integrated with rich functional fillers will further extend the versatility of UCAP technology in device design and manufacturing.

Delayed Thiol-Epoxy Photopolymerization: A General and Effective Strategy to Prepare Thick Composites

Photoinduced thiol-epoxy click polymerization possesses both the characteristics and advantages of photopolymerization and click reactions. However, the photopolymerization of pigmented or highly filled thiol-epoxy thick composites still remains a great challenge due to the light screening effect derived from the competitive absorption, reflection, and scattering of the pigments or functional fillers. In this article, we present a simple and versatile strategy to prepare thick composites via delayed thiol-epoxy photopolymerization. The irradiation of a small area with a light-emitting diode (LED) point light source at room temperature leads to the decomposition of a photobase generator and the released active basic species can uniformly disperse throughout the whole system, including unirradiated areas, via mechanical stirring. No polymerization was observed at room temperature and therefore the liquid formulations can be further processed with molds of arbitrary size and desired shapes. It is only by increasing the temperature that base-catalyzed thiol-epoxy polymerization occurs and controllable preparation of thick thiol-epoxy materials can be achieved. The formed networks display excellent uniformity in different radii and depths with comparable functionality conversions, similar T _g values, and thermal decomposition temperatures. The presented strategy can be applied to prepare thick composites with glass fibers possessing improved mechanical properties and dark composites containing 2 wt % carbon nanotubes.

Cellulose-based polyacetals by direct and sensitized photocationic ring-opening polymerization of levoglucosenyl methyl ether

Polyacetal homopolymers and block copolymers are produced by photochemically initiated cationic ring-opening polymerization (CROP).

Photopolymerization processes of thick films and in shadow areas: a review for the access to composites

The state of the art for the access to thick samples by photopolymerization processes as well as some perspectives are provided.