Polymer properties moisture absorption

PCTFE exhibits very good electrical properties ia terms of high iasulation resistance, minimal trackiag, corona formation, and surface flashover due to the polymer s nonwettable surface and ultralow moisture absorption (Table 3). 

A number of high melting poiat semiaromatic nylons, iatroduced ia the 1990s, have lower moisture absorption and iacreased stiffness and strength. Apart from nylon-6 /6,T (copolymer of 6 and 6,T), the exact stmcture of these is usually proprietary and they are identified by trade names. Examples iaclude Zytel HTN (Du Pont) Amodel, referred to as polyphthalamide or PPA (Amoco) and Aden (Mitsui Petrochemical). Properties for polyphthalamide are given ia Table 2. A polyphthalamide has been defined by ASTM as "a polyamide ia which the residues of terephthaUc acid or isophthahc acid or a combination of the two comprise at least 60 molar percent of the dicarboxyhc acid portion of the repeating stmctural units ia the polymer chain" (18). 

Certain copolymers of this type have been found to have excellent gas barrier properties, with the dry polymer having an oxygen permeability only about 1/lOth that of polyvinylidene chloride. Unsurprisingly, the copolymer has a high moisture absorption and a high moisture vapour transmission rate. Where the material is swollen by water, gas permeability is also higher. 

In addition, PEN has better resistance to moisture absorption than PET and polyurethane [44], All of these properties endow PEN film with better electrical resistant properties than any other polymer. 

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. 

Moisture absorption. Directly related to the atoms making up the polymer. The more moisture-absorbing the molecule, the less dimensional stability strength, stiffness, electrical properties are also adversely affected. 

Interest in cyclic olefin (co)polymers has increased dramatically over the past decade. This is because this class of polymers displays many attractive properties such as high thermal stability, high optical transparency, low dielectric constants, and low moisture absorption. Thus, these polymers can potentially be utilized in many electronic and optical applications. Although cyclic olefin (co)polymers typically include ring-opening metathesis polymers, vinyl-addition homopolymers, and vinyl-addition co-polymers with acyclic co-monomers such as ethylene, we will mainly deal with vinyl-addition homo- and co-polymers in this section. 

Long-chain a,o)-dicarboxylic acids have been condensed with diamino-isohexides, forming linear polyamides suitable for producing fibers having a silklike texture and higher moisture-absorption properties than nylon-like polymers.206... 

Moisture has, in itself, usually not much effect on polymer properties, though the amount of moisture which can be absorbed by polymers varies within wide limits (between zero and a few %). Logically, the electric properties such as resistivity and dielectric losses are the most sensitive to water. As to mechanical properties, nylons show the strongest dependence on water absorption. PA-6 is able to take up a... 

Only recently, there has been a tremendous surge of interest in these coatings, particularly in the microelectronic industry, although the deposition of polymers by CVP dates back to 1947. The key to the growing interest can be attributed to both the material properties of the films such as low dielectric constant, low moisture absorption, excellent corrosion resistance as well as the unique capabilities of the CVP process. These polymers and their polymerization mechanisms along with the properties of the films obtained are the focus of this section. The following polymers are discussed in detail separately. 

Studies of the moisture absorption (hygroscopicity) and water absorption (hydro-scopicity) of gas-filled plastics are of considerable practical importance, since foamed polymers always contain moisture (with the exception of their use in space or under extremely rare conditions on Earth) n4iich noticeably affects all physico-mechanical characteristic of materials, in particular electrical and heat insulation properties. 

Since the electroconductivity of pure water is by several orders of m itude hi er than those of polymers, even smaU amounts of moisture markedly reduce electrical insulation properties of foams. For this reason, measuren nt of dielectric properties is a precise, rapid and non-destructive method of monitoring the kinetics and level of moisture absorption. Thus, the establishment of correlations between dielectric properties and the hygroscopicity of plastic foams makes it possible to solve two practical problems how moisture affects dielectric properties and how to determine non-electrical properties by electrical measurements ... 

These differences in physical structure are responsible for the different properties of foamed polymers containing varying proportions of open cells. In contrast to closed-cell foamed polymers, open-cell foamed plastics have a higher water and moisture absorptive capacity, a higher gas and vapor permeability, less pronounced electric and heat insulation characteristics but a stronger sound absorptive and damping power... 

Since 1991, Nippon Zeon Co. has been producing the polymer Zeonex, obtained by ROMP of norbomene and related (multi-ring) monomers, followed by hydrogenation. The product is an amorphous, colorless, transparent polymer with a high Tg (140 °C) and low moisture absorption. These properties make it very suitable for optical applications (e. g., disks, lenses, and prisms). 

Components of switches, relays, and connectors use glass fiber reinforced semicrystalline polymers, such as PA, PPS, PBT, and PET. The following requirements are important in these applications dimensional stability and precision, low moisture absorption, strength, resistance to creep, electrical insulating properties, and resistance to high working temperatures ( 85°C). 

The nature of the interaction between water and the polymers is important because absorbed water can adversely affect thermal, electrical and mechanical properties of the polymer. Moisture absorption increases the dielectric constant, (5.6) and dielectric loss, (7) and has been related to device reliability problems. (8) Water-induced plasticization causes hygroscopic expansion, lowering of Tg, and degradation of mechanical properties. (9)... 

The 6FDA/BDAF polyimide was modified using PPD in an effort to "stiffen" the polymer backbone and improve thermal performance (Tg). A better overall property balance was achieved in several of these 6FDA/BDAF/PPD copolyimides. A series of random copolymers was prepared in which the level of PPD was varied from 0% to 100% based on the total moles of diamine. The incorporation of PPD had little effect on the dielectric constant but did result in improved thermal performance and was accompanied by increased moisture uptake (Figures 1,2, and 3). This behavior is consistent with the overall reduction in the amount of bound fluorine in the polymer backbone however, additional work is required to establish a direct correlation. A reasonable property balance was realized over a range of 40 to 60 mole% PPD which displayed dielectric constants from 2.85 to 2.90, moisture absorption from 1.5% to 2.0%, and Tg from 280°C to 290°C. In addition, the 6FDA/BDAF/PPD copolyimides displayed somewhat less solvent sensitivity than the 6FDA/BDAF homopolymer as described above. 

Aromatic polyimides with dielectric constants < 3.0 and reduced levels of moisture absorption can be obtained by the incorporation of fluorine into the polymer backbone. However, this approach can also lead to a reduction in the thermal properties (Tg), and/or solvent resistance of the polymer. It has been found that the incorporation of paraphenylene diamine (PPD) into the 6FDA/BDAF polyimide affords copolymers having improved thermal performance and solvent resistance as compared with the parent homopolymer while maintaining a dielectric constant of 2.9 and moisture uptake < 2.0%. This approach can be considered as a possible alternative to the use of... 

Ordered polymer films made from poly benzthiazole (PBZT) and poly benzoxazole (PBO) can be used as substrates for multilayer printed circuit boards and advanced interconnects to fill the current need for high speed, high density packaging. Foster-Miller, Inc. has made thin substrates (0.002 in.) using biaxially oriented liquid crystal polymer films processed from nematic solutions. PBZT films were processed and laminated to make a substrate with dielectric constant of 2.8 at 1 MHz, and a controllable CTE of 3 to 7 ppm/°C. The films were evaluated for use in multilayer boards (MLBs) which require thin interconnect substrates with uniform controllable coefficient of thermal expansion (CTE), excellent dielectric properties, low moisture absorption, high temperature capability, and simple reliable processing methods. We found that ordered polymer films surpass the limitations of fiber reinforced resins and meet the requirements of future chip-to-chip interconnection. 

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