Low ceiling temperature, thermodynamically unstable polymers have been troublesome to synthesize and keep stable during storage. In this study, stable poly(phthalaldehyde) has been synthesized with BF 3 -OEt 2 catalyst. The role of BF 3 in the polymerization is described. The interaction of BF 3 with the monomer is described and used to maximize the yield and molecular weight of poly(phthalaldehyde). Various Lewis acids were used to investigate the effect of catalyst acidity on poly(phthalaldehyde) chain growth. In situ nuclear magnetic resonance was used to identify possible interactions formed between BF 3 and phthalaldehyde monomer and polymer. The

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Knowledge of the ceiling temperature and thermodynamic variables for low ceiling temperature polymers is critical to understanding the material's synthesis and use. Synthesis of the polymer below its ceiling temperature is the routine polymerization route. In situ 1H NMR of the equilibrium polymerization reaction can provide critical information for determining the enthalpy and entropy of polymer formation. Three polyaldehydes were synthesized with in situ 1H NMR, and their energies of formation were determined for the linear region of ceiling temperature. Insights into the mechanism of polymerization were also found using this method. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 221–228

The study and development of transient devices is an emerging field where the disposal of a device after use is desired to avoid reverse engineering and minimize the environmental impact. Polyaldehydes with phototriggers have been investigated because the radiation wavelength can be adjusted to meet the transient application. Polynuclear aromatic hydrocarbons (PAHs) were used as the optical sensitizer for photoacid generators (PAGs). Photoinduced electron transfer (PET) with an iodonium-based PAG was used to expand the spectral sensitivity range. Anthracene, tetracene, and pentacene derivatives were synthesized with appended phenylethynyl groups to improve the solubility of the sensitizer and adjust the absorption wavelength. Sensitization of the iodonium-based PAG with the PAH derivatives was found to have thermodynamically favorable PET reactions for depolymerization of poly(propylene carbonate) and poly(phthalaldehyde) (PPHA). The Rehm-Weller equation and Stern-Volmer analysis were used to study the electron transfer and the fluorescence quenching rates of the PAHs with the iodonium salts, respectively. The photosensitivity, efficiency, and byproducts of the PET reactions in the decomposable polymer films are reported. A rapid photoreaction is reported for the depolymerization of PPHA exposed to a sunlight dose of <6 J cm −2 (i.e., 1 min of direct sunlight) with a pentacene-based sensitizer.

Polymers can be used as temporary place holders in the fabrication of embedded air gaps in a variety of electronic devices. Embedded air cavities can provide the lowest dielectric constant and loss for electrical insulation, mechanical compliance in devices where low-force deformations are desirable, and can temporarily protect movable parts during processing. Several families of polymers have been used as sacrificial, templating polymers including polycarbonates, polynorbornenes (PNBs), and polyaldehydes. The families can be distinguished by chemical structure and decomposition temperature. The decomposition temperature ranges from over 400 °C to below room temperature in the case of low ceiling temperature polymers. Overcoat materials include silicon dioxide, polyimides, epoxy, and bis-benzocyclobutene (BCB). The methods of air-gap fabrication are discussed. Finally, the use of photoactive compounds in the patterning of the sacrificial polymers is reviewed.

Low ceiling temperature polyaldehydes are of interest for transient materials because the temperature of depolymerization can be at or below room temperature. There is interest in expanding the number of aldehydes which can be copolymerized so as to change the vapor pressure and other properties of the depolymerized products. Although fast depolymerization has been achieved with polyaldehydes, the rate of monomer evaporation after depolymerization can be controlled by incorporating lower molecular weight monomers into the polymer. High vapor pressure aliphatic aldehydes have been copolymerized with low vapor pressure and high reactivity phthalaldehyde to create stable, high molecular weight polymers with high vapor pressure. A method for measuring the depolymerization time by quartz crystal microbalance has been developed. The copolymer of phthalaldehyde and butanal improves the evaporation time for the polymer by a factor of 11. The onset of thermal decomposition of the copolymer was increased from 107 C for the phthalaldehyde homopolymer to 141 C for the copolymer. The tensile strength of the copolymer was 0.8-1.6 GPa.

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A low permittivity, positive tone, polynorbornene dielectric has been developed that exhibits excellent lithographic and electrical properties. The polymer resin is a random copolymer of a norbornene hexafluoroalcohol (NBHFA) and a norbornene tert-butyl ester (NBTBE). High optical sensitivity and contrast were achieved using a chemically amplified solubility switching mechanism through the acid-catalyzed deprotection of the tert-butyl ester functionality. After developing in aqueous base, the film was thermally cured through a Fischer esterification reaction, resulting in a cross-linked permanent dielectric. The effect of the photoacid generator (PAG) concentration on the lithographic patterning and curing reactions was studied. Higher PAG loading was favorable for both sensitivity and dielectric constant. The sensitivity of a formulation was measured as low as 8.09 mJ/cm 2 . The molar ratio of the two monomers composing the polymer was varied. A higher NBHFA content was favorable because it resulted in a lower modulus, lower shrinkage, and lower dielectric constant and loss. A formulation with 70 mol% of the NBHFA had a modulus of 2.60 GPa, a 12.2% volume decrease during cure, and a dielectric constant of 2.23. The direction-dependent coefficient of thermal expansion was measured, and it was found that the anisotropy of the PNB films decreased with higher NBTBE content. Permanent dielectric materials are used in microelectronic devices and packages to separate and insulate components and interconnect. Low dielectric constant (low-k) insulators are desirable for on-chip, chip-to-chip, chip-to-package, and on-package wiring to avoid electrical delay and lower the energy consumed in the signal interconnect. [1][2][3] Polymers are widely used for these purposes because they offer a low-stress, easily processed alternative to inorganic dielectrics. [2][3][4][5] In addition, photosensitive dielectrics are desirable because they can be directly patterned by photolithographic means. Lithographically printed dielectrics do not require the use of photoresist or additional pattern transfer steps, which can be costly and expose the device to aggressive wet or dry etch process steps.Positive tone dielectrics are especially attractive because they result in sloped sidewalls that are generally favored for void-free electroplating of copper. Positive tone materials also exhibit better process yield because exposures through dark-field masks are less susceptible to particle defects. The ability to develop the latent image in an aqueous base developer mitigates the need for environmentally unfriendly organic solvent developers. High sensitivity is very important since it directly leads to higher throughput and tool utilization since less optical energy is required for the solubility switching reaction. The sensitivity of the photopatternable material is coupled to the quantum efficiency of the photoactive compound. Poor quantum efficiency often requires a high loading of the photoactive compounds to effect the inhibition or solu...