Poly , water absorption

Polyimide. Polyimide is a biaxiaHy oriented high performance film that is tough, flexible, and temperature- and combustion-resistant. Its room temperature properties compare to poly(ethylene terephthalate), but it retains these good characteristics at temperatures above 400°C. Its electrical resistance is good and it is dimensionally stable. The principal detriment is fairly high moisture absorbance. The main uses are for electrical insulation, particularly where high temperatures are prevalent or ionizing radiation is a problem. The films may be coated to reduce water absorption and enhance... 

Poly(methyl methacrylate). PMMA offers distinct advantages over BPA-PC with respect to significandy lower birefringence, higher modulus, and lower costs, but has not been successhil as a material for audio CDs and CD-ROM as well as a substrate material for WORM and EOD disks because of its high water absorption (which makes it prone to warp) and its unsuitabiUty for metallising, and less so because of its low resistance to... 

Fig. 26. Qualitative compatison of substrate materials for optical disks (187) An = birefringence IS = impact strength BM = bending modulus HDT = heat distortion temperature Met = metallizability WA = water absorption Proc = processibility. The materials are bisphenol A—polycarbonate (BPA-PC), copolymer (20 80) of BPA-PC and trimethylcyclohexane—polycarbonate (TMC-PC), poly(methyl methacrylate) (PMMA), uv-curable cross-linked polymer (uv-DM), cycHc polyolefins (CPO), and, for comparison, glass.

Although poly(vinyl fluoride) resembles PVC in its low water absorption, resistance to hydrolysis, insolubility in common solvents at room temperature and a tendency to split off hydrogen halides at elevated temperatures, it has a much greater tendency to crystallise. This is because the fluorine atom (c.f. the chlorine atom) is sufficiently small to allow molecules to pack in the same way as polythene. 

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. 

Poly(styrene) is a polymer which finds widespread use in the developed world on account of its desirable properties, combined with its relative cheapness. Among its features are excellent colour range, transparency, rigidity, and low water absorption. 

ISO 8361-2 1991 Thermoplastics pipes and fittings - Water absorption - Part 2 Test conditions for unplasticized poly(vinyl chloride) (PVC-U) pipes and fittings ISO 9393-2 1997 Thermoplastics valves - Pressure test methods and requirements - Part 2 Test conditions and basic requirements for PE, PP, PVC-U and PVDF valves ISO 9852 1995 Unplasticized poly(vinyl chloride) (PVC-U) pipes - Dichloromethane resistance at specified temperature (DCMT) - Test method ISO 9853 1991 Injection-moulded unplasticized poly(vinyl chloride) (PVC-U) fittings for pressure pipe systems - Crushing test... 

The deflection temperature of poly(vinyl formal) is about 90°C. Because of the presence of residual hydroxyl groups, commercial poly(vinyl formal) has a water absorption of about 1%. Poly(vinyl formal) (Equation 6.67) has a Tg of about 105°C and is soluble in moderately polar solvents, such as acetone. 

Poly((3-PL) has been hydrolytically degraded in a buffered salt solution (pH 7.2) at 37 °C [125,175], Oriented fibers and unoriented fibers showed different mechanical properties on degradation. The changes in tensile strength were slower for the oriented material. The molecular weight decreases rapidly during the first 50 days while the crystalline phase increases, probably due to an anneal-ing-like effect caused by the temperature at which the degradation was performed and rapid water absorption [175]. 

It is known that papers, cotton, and cellulose are natural hydrophilic polymers, which can absorb water, but are insoluble in water. Therefore, they have been used as disposable diapers, feminine napkins, etc. They absorb water by capillary action. Therefore, they absorb only a small amount of water and the water absorbed is easily removed by applying low pressure. Synthetic crosslinked poly(vinyl alcohol) and crosslinked poly(oxyethylene) are also hydrophilic polymers and they have almost the same water-absorption capacity of about 1-20 g water per gram of polymer as natural polymers. Those natural polymers and synthetic polymers do not essentially have ionic groups. 

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