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Advanced communication technology using millimeter waves (mmWaves) requires new polymeric materials with low dielectric properties to minimize signal transmission losses. The dielectric polarization of polymers, including electronic, vibrational, orientational, ionic, and interfacial contributions, as well as the water molecules absorbed within them, is strongly related to their dielectric properties in the mmWave region. This has led to the emergence of liquid crystal polymers (LCPs) and fluoropolymers as candidate materials for mmWave communication. However, their poor secondary processability and adhesion to copper wiring often limit their practical application. This focus review describes two types of thermoplastic films developed via formulation design technology for mmWave communication. A crystalline polyaryletherketone-based film, compounded with a plate-like, low-polarity filler and blended with miscible noncrystalline polymers to control the crystallization behavior, exhibits a low transmission loss capability comparable to that of LCPs. Additionally, this film offers solder reflow heat resistance, a low coefficient of thermal expansion (CTE), and excellent multilayer processing capabilities at low temperatures, making it suitable for use in multilayer substrates for mmWave communication applications. A polyolefin-based film demonstrates ultralow dielectric properties comparable to those of fluoropolymers and strong adhesion to copper foil. Furthermore, this film offers customizable functionalities, including laser processability, transparency, a low CTE, and flame retardancy, enabling its application in flat, flexible cables and transparent antennas. Owing to their unique characteristics, these films are promising candidates for mmWave communication materials.

Background: The inhibitory effects of N-(4-hydroxyphenyl)-retinamide (4HPR) on tumorigenesis and tumor growth may result from its ability to induce apoptosis (programmed cell death). Since antioxidants inhibit 4HPR-induced apoptosis, experiments were planned to determine whether the levels of reactive oxygen species increase in cells undergoing apoptosis after exposure to 4HPR. Methods: Cells of the human cervical carcinoma cell line C33A and normal human cervical epithelial cells were treated with 4HPR and analyzed for survival, induction of apoptosis, generation of reactive oxygen species, and expression of the apoptosis-related proteins Bcl-2 and Bax. Results: Treatment with 4HPR decreased C33A cell number by inducing apoptosis in a time- and dose-dependent fashion. DNA fragmentation typical of apoptosis was observed in cells exposed to 4HPR at concentrations of 3 [mu]M or higher for 6-24 hours. The generation of reactive oxygen species was enhanced by 1.85-fold to 4.5-fold after a 1.5-hour treatment with 0.4-10 [mu]M 4HPR. Pyrrolidine dithiocarbamate, an oxygen radical scavenger, suppressed the rate of generation of reactive oxygen species and inhibited 4HPR-induced apoptosis. 4HPR failed to modulate cellular levels of the Bcl-2 and Bax proteins. N-(4-Methoxyphenyl)-retinamide, the major 4HPR metabolite, and several other retinoids that bind to nuclear retinoic acid receptors or retinoid X receptors failed to enhance the generation of reactive oxygen species and to induce apoptosis. 4HPR was much less effective in generating reactive oxygen species and in inducing apoptosis in normal human cervical epithelial cells than in C33A cervical carcinoma cells. Conclusions: Enhancement of the generation of reactive oxygen species may be involved in apoptotic pathway induction by 4HPR. [J Natl Cancer Inst 1997;89:1191-8]