Thermal properties acetal resins

The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers. Values reported for percentage crystallinity (x ray, density) range from 60 to 77%. The lower values are typical of copolymer. Poly oxymethylene most commonly crystallizes in a hexagonal unit cell (9) with the polymer chains in a 9/5 helix (10,11). An orthorhombic unit cell has also been reported (9). The oxyethylene units in copolymers of trioxane and ethylene oxide can be incorporated in the crystal lattice (12). The nominal value of the melting point of homopolymer is 175°C, that of the copolymer is 165°C. Other thermal properties, which depend substantially on the crystallization or melting of the polymer, are Hsted in Table 1. See also reference 13. 

The chemical structure of the acetal influences the thermal properties of the resin such as glass transition temperature, decomposition temperature and thermal flow stability (32-35). This paper describes the improved thermal properties by increasing the molecular weight via a transacetalization reaction. The polymers containing such crosslinking units were evaluated in two-component positive pWoresists. 

Table 3.9 Mechanical Properties at Various Temperatures of DuPont P Type (Enhanced Thermal Stability) Delrin Acetal Resins [2]...

Engineering plastic n. (1) A broad term covering those plastics, with or without fillers and reinforcements that have mechanical, chemical, electrical, and/or thermal properties suitable for industrial applications. R. B. Seymour, an outstanding authority, defined them as polymers thermoplastic or thermosetting, that maintain their dimensional stability and major mechanical properties in the temperature range 0-100° C. He listed the big five (among neat resins) as nylons, polycarbonate, acetals, polyphenylene ether, and thermoplastic polyesters. Among many others are acrylics, fluorocarbons, phenoxy, acrylonitrile-butadiene-styrene terpolymer, polyaryl... 

POLYVINYL ALKYL ETHERS. These products have properties which range from sticky resins to elastic solids. They are obtained by the low-temperature cationic polymerization of alkyl vinyl ethers having the general formula ROCH=CH-. These monomers are prepared by the addition of die selected alkanol to acetylene in the presence of sodium alkoxide or mercury(ll) catalyst, As shown by the following equations, the latter yields an acetal which must be thermally decomposed to produce the alkyl vinyl ether. 

Epoxy Mortars Epoxies are the strongest resin mortars, have the best bond strength to other CRM materials, and resist many solvents, mild to moderate acids, non-oxidizing and alkaline media. Their useful pH range is about 2-14, and their thermal limit is approximately 230°F. Besides their excellent alkali and dilute acid resistance, epoxy mortars handle many organic chemicals and sodium hypochlorite at low temperatures. Epoxies should not be exposed to acetic acid and its esters. Epoxy mortars have the best physical and mechanical properties of all the resin mortars. 

Modification by the incorporation of metals or metalloids, styrene, vinyl acetate, poly(styrene-co-maleic anhydride), urethane linkages, and so on result in poly(ester amide) resins with good chemical properties and excellent thermal resistance. Some can also be used as effective antibacterial and biologically safe corrosion protective coating materials. Urethane-modified ethylenediamine tetraacetic add the fatty amide diol of linseed oil-based poly(ester amide) resin exhibits excellent physicomechanical properties, high thermostability up to 200°C and anticorrosive properties. ... 

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