Low dielectric constant fluorinated

Synthesis and Structure-Property Relationships of Low-Dielectric-Constant Fluorinated Polyacrylates ... 

Ma Y, Yang H, Guo J, Sathe C, Agui A, Nordgren J (1998) Structural and Electronic Properties of Low Dielectric Constant Fluorinated Amorphous Carbon Films, Appl Phys Lett 72(25) 3353-3355... 

S. Sheng, D. Li, T. Lai, X. Liu, C. Song, Organosoluble, low-dielectric-constant fluorinated polyimides based on 9,9-( w[4-(4-amino-2-trifluoromethyl-phenoxy)phenyl]xanthenes, Polym. Int. 60 (8) (2011) 1185-1193. 

C.P. Yang, S.H. Hsiao, C.L. Chung, Organo-soluble, low-dielectric-constant fluorinated polyimides based on 2,6- w(4-amino-2-triflu-oromethylphenoxy)naphthalene, Polym. Int. 54 (4) (2005) 716-724. 

Decafluorobiphenyl [434-90-2] C F C F (mol wt, 334.1 mp, 68°C bp, 206°C), can be prepared by I Jllmann coupling of bromo- [344-04-7] chloro- [344-07-0] or iodopentafluorobenzene [827-15-6] with copper. This product shows good thermal stabiHty decafluorobiphenyl was recovered unchanged after 1 h below 575°C (270). Decafluorobiphenyl-based derivatives exhibit greater oxidative stabiHty than similar hydrocarbon compounds (271). Therm ally stable poly(fluorinated aryl ether) oligomers prepared from decafluorobiphenyl and bisphenols show low dielectric constant and moisture absorption which are attractive for electronic appHcations (272). 

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

Six novel fluorinated poly(aryl ether)s containing 1,4-naphthalene moieties were synthesized in high yield using 2,2-bis[4-( 1 -naphthoxy)phenyl]hexafluoro-propane (1). Oxidative coupling ofl yielded a polymer with high 7, low moisture absorption, and low dielectric constant that could be cast into flexible films. The low dielectric constant and low moisture absorption of 6FNE may make it useful as a dielectric insulator in microelectronics applications. 

In a comparison of 5 and 6 (see Table 1 1.1), the existence of a perfluoroalkyl ether linkage seems to play an important role in further reducing the DE values. Teflon AF and 6 both have low dielectric constants and contain ether linkages. Since the dielectric constant of Teflon AF is lower than that of Teflon, which has a higher fluorine content, it appears that the ether linkage has an effect in lowering the DE. The Teflon AF has been reported by Resnick7 as the lowest dielectric constant (189-1.93) of any polymer thus far. 

In this work we have demonstrated that a new class of heavily fluorinated acrylic and methacrylic resins can be efficiently synthesized and then cured to solid form with radical initiator at elevated temperatures. These cured resins were found to have low dielectric constants, which are close to the minimum known values for Teflon and Teflon AF. In contrast to tetrafluoroethylene, our monomers are processable owing to the fact that they are liquids or low-melting solids, and moreover are soluble in common organic solvents. Lower dielectric constants are obtained as fluorine contents on the polymer backbone or side chain increase, when acrylate is replaced by methacrylate, when ether linkages are present in the fluorocarbon, and when aromatic structure is symmetrically meta-substituted. 

Using a fluorinated benzocyclobutene-based monomer (Figure 18.4) should provide at least one advantage over the already promising properties of fluorinated poly(j9-xylylene). All the desirable properties such as low dielectric constant and low affinity for water should remain but the thermal stability should be enhanced because of the cross-linking that would accompany the generation of these films. The synthesis and polymerization paths for poly(octafluorobisbenzocyclobutene) are depicted in Scheme 5. 

A new method for the syntheses of fluorocarbon polyarylate polymers has been demonstrated. The chemistry utilizes the [2jt+2rr] cyclodimerization of fluorinated olefins and generates polymers of novel composition. The first generation of polymers prepared by this method are polyarylate homopolymers. Theremoplastic polymers of high molecular weight can be achieved via neat or solution polymerization. One example of a thermoset polymer prepared by this method has a high Tg, low dielectric constant and dissipation factor, low moisture... 

However, since it can be shown that fluoride ion also can participate in the addition-oxidation mechanism (p. 130), at least in media of low dielectric constant (Eberson, 1994), the latter possibility also cannot be excluded on the basis of existing information. Thus, the fluorine dogma makes fluoride ion a key species for mechanistic study (Eberson and Persson, 1997). 

It was indeed found necessary to have excess antimony pentafluoride present in order to obtain stable alkylcarbonium hexafluoroantimonate complexes. Antimony pentafluoride is a liquid Lewis acid fluoride (b.p. 148-150°) of low dielectric constant (e 3), which has been shown by fluorine N.M.R. studies in the pure liquid state and in solution to exist in both cyclic and acyclic polymeric forms involving fluorine bridges. The antimony is in approximately octahedral co-ordination with predominant bridging by coordinating fluorines (Gillespie and Rothenbury, 1963). As fluorine generally does not show bridging properties, the structure of antimony pentafluoride itself indicates the very... 

The role of excess antimony pentafluoride can best be explained by assuming that it is capable of solvating the alkylcarbonium ion salt through interaction of the unshared electron pairs of fluorine with the vacant p-orbital of the sp -hybridized planar central carbon atom of the carbonium ion. In the system of low dielectric constant the alkylcarbonium ion is present not in the free form, but as a tightly bound ion-pair solvation affects this species rather than the free ion. 

Fluorinated poly(imide-ether-amide)s are readily soluble in organic solvents like dimethylformamide (DMF), N-methylpyrrolidone (NMP), pyridine or tetrahydrofu-ran (THF) and give flexible films by casting of such solutions. These polymers exhibit decomposition temperatures above 360°C, and glass transition temperatures in the 221-246° C range. The polymer films have a low dielectric constant and tough mechanical properties. 

Recently the synthesis and characterization of novel fluorinated poly(aryl ether)s containing perfluorophenylene moieties " " was also reported. These fluorinated polyethers were prepared by reaction of decafluorobiphenyl with bisphenols. These polymers exhibit low dielectric constants, low moisture absorption, and excellent thermal and mechanical properties. Tough, transparent films of the polymers were prepared by solution-casting or compression-molding. The fluorinated poly(aryl ether)s containing perfluorophenylene moieties are good candidates for use as coatings in microelectronics applications. 

An alternative means of reducing the dielectric constant of polyimides is to have a low dielectric constant component dispersed as a second phase within the rigid polyimide matrix. Two key approaches have been pursued to this end. The first involves the preparation of polyimide block copolymers with highly fluorinated coblocks and the second involves the generation of a polyimide foam. The main drawback to the first approach is the solubility of highly fluorinated blocks in organic media which will permit copolymerization with polyimides. This led to the investigation of new semi-fluorinated polymers derived from polyfaryl ethers). 

The most important application for bismaleimide resin is multilayer boards. The development in this area requires resins with low dielectric constants. It is well documented in the literature that fluorine containing linear polyimides show lower dielectric constants vis a vis their non-fluorinated counterparts. Recently, Hitachi Research Laboratory, Japan, reported the thermal and dielectric behaviour of fluorine-containing bismaleimides (29). The chemical structures of the fluorinated BMIs investigated are provided in Fig. 6. The non-fluorinated four aromatic rings containing BMI, 4,4 -bis(p-maleimidophenoxyphenyl) propane, was tested in comparison. 

Carbon-fluorine bonds also have unusual electrooptical properties. Fluoropolymers are often used to provide favorable electrical properties such as low dielectric constants. The low dielectric constants are another consequence of the relatively low polarizability of C—F bonds. Polarizability a is related to index of refraction n through the following equation ... 

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