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Self-Etching, Polymerization-Initiating Primers for Dental Adhesion
Published in Raphael M. Ottenbrite, Sung Wan Kim, Polymeric Drugs & Drug Delivery Systems, 2019
Chetan A. Khatri, Joseph M. Antonucci, Gary E. Schumacher
The use of strongly acidic conditioners such as nitric or phosphoric acid may excessively demineralize dentin and create a highly decalcified collagenous zone that is not optimal for bonding because it may not be completely infiltrated with the primer and adhesive resin. A less-aggressive decalcifying agent is the chelating acid ethylenediamine tetraacetic acid (EDTA), which is used in the form of a soluble salt because of its poor solubility. It would be desirable to have a soluble analog of EDTA that can also act as a primer and, thereby, reduce the usual three-step bonding protocol to two steps by combining etchant and primer functions in one compound. In previous studies it was shown that N-phenyliminodiacetic acid (PIDAA) has these properties and also can self-initiate polymerization of several acrylic monomers [3,4]. PIDAA has a structure intermediate between NPG and EDTA as shown in Figure 3, and this unique structure enables it to function as a self-etching primer with the ability to initiate and co-initiate the polymerization of dental monomers. Chemical structures of N-phenylglycine, N-phenyliminodiacetic acid, and ethylenedi-aminetetraacetic acid.
Polypeptides
Published in Stanislaw Penczek, H. R. Kricheldorf, A. Le Borgne, N. Spassky, T. Uryu, P. Klosinski, Models of Biopolymers by Ring-Opening Polymerization, 2018
Different results were obtained, when N-phenylglycine-NCA was reacted with excess ammonia, aniline (or N-methylaniline). In this case, N-phenylglycine amides were the main products because the phenyl groups reduce the nucleophilicity of the nitrogen to such an extent that initiation is faster than propagation. However, other NCAs also yield mainly amino acid amides when the reaction with a less basic amine is conducted in water at the acidic pH. The salts of aromatic amines are hydrolyzed so that part of the amine is free. The free amino groups react with the NCA, and because the amino group generated from the NCA is more basic, it is preferentially protonated, and thus protected against oligomerization. In this way, α-amino acid derivatives of aromatic amino acids were prepared86 (Equation 55).
Polymeric Materials as a Holographic Recording Medium
Published in Asit Baran Samui, Smart Polymers, 2022
Asit Baran Samui, Alips Srivastava
However, acrylamide suffers from the drawback of low photosensitivity. Also, these photopolymers tend to absorb water from the surrounding atmosphere when the humidity level exceeds 60%, resulting in excessive light scattering which deteriorates the product quality. The addition of a secondary photo-initiator like N-phenylglycine,41 or the addition of a cross-linking agent, such as glutaraldehyde, for the binder, serves to overcome this shortcoming. Hologram recording on polyvinyl alcohol (PVA)/acrylamide-based photopolymer compositions has been widely studied.34,6 These holograms have been used even as humidity and temperature sensors.
An overview of HPDLC films and their applications
Published in Liquid Crystals, 2022
Katariya-Jain Anuja, Rajendra R. Deshmukh
In order to improve the wavelength sensitivity of a HPDLC grating, Wang et al. proposed mixing of two photo-initiators, methylene blue (MB)/p-toluenesulfonic acid (PTSA) system and rose Bengal (RB)/N-phenylglycine (NPG) system. By doing this, the holographic grating becomes responsive to all visible wavelengths, including red, green and blue. This volume H-PDLC grating consists of three different period volume H-PDLC sub-gratings. The application of this tri-colour Composite Volume HPDLC Grating is in three-dimensional (3D) colour autostereoscopic display [26,27]. To induce photo-polymerisation PI, co-initiators and sometimes chain initiators are also needed. The selection of PI is based on the wavelength of laser beam used for writing. Table 2 shows the list of PI and co-initiators used with acrylate or thio-lene monomers and corresponding laser beam employed for writing [2]. Peng et al. investigated the effect of the photoinitibitor (simultaneous initiation and inhibition functions) on the formation of HPDLC films [28].
Enhanced wavelength-sensitivity of volume holographic grating with dual-photoinitiation system in polymer-dispersed liquid crystal
Published in Liquid Crystals, 2019
Kangni Wang, Jihong Zheng, Linyong Qian, Yourong Liu
Photoinitiation system within H-PDLC gratings plays a crucial role for photopolymerisation because it decides the wavelength of the recording light and its concentration also influences the quality of hologram [13]. Photoinitiators postpone the polymerisation gelation and also increase the gelation time difference between the bright and dark areas of the holographic patterns [14]. If the time of the LC molecules diffusion is faster than their nucleation and the nucleation occurs much faster than gelation, a well-defined grating is formed and affords high DE. Commonly used photoinitiators for fabricating H-PDLC gratings include Ingacure 1173 for ultraviolet light [15], Rhodamine 6G dye, rose bengal (RB), Ingacure 784 for green and blue light [16], methylene blue (MB), H-Nu-Blue 640 used for red light [17,18], and Cyanine dye IR-140 for near infrared light [19]. The photoinitiator requires good absorption at the recording wavelength and their coordination with coinitiators to induce photopolymerisation. Despite the diversity and wide applications of each photoinitiation system, little has been reported about the combination of two or more photoinitiators for the formation of H-PDLC gratings. Previously, our group proposed a multi-colour composite grating, especially for its application within autostereoscopic display [20]; however, the electro-optical features and holographic characteristic parameters compared with the gratings exposure upon a single photoinitiation system, such as sensitivity and refractive index modulation remain unclear. Herein, we mix two groups of photoinitiation systems including RB/N-phenylglycine (NPG) and MB/p-toluenesulfonic acid (PTSA) for both green and red laser beams, which enable the fabrication of H-PDLC gratings upon two different visible laser lights with an output wavelength of 532 and 632.8 nm. Distinct from previous reports, a detailed comparative analysis between dual- and single photoinitiation system for H-PDLC grating fabrication is carried out by experiment. In addition, three-dimensional (3D) images of a coin have been reconstructed within a single-layer H-PDLC hologram by using both green and red laser source.