Copolymers comparative physical properties

Table 6.10 Some comparative physical properties of copolymers ...

The commercial copolymers have physical properties similar to those of polytetrafluoroethylene but with somewhat greater impact strength. Comparative values for some properties are given in Table 7.1. The copolymers also have similar excellent electrical insulation properties and chemical resistance. The maximum service temperature for the copolymers is about 60 deg C lower than that for the homopolymer under equivalent conditions. The temperature range of useful performance is from about —80°C to 200°C. Tetrafluoro-ethylene-hexafluoropropylene copolymers are used for various electrical and corrosion resistant mouldings, coatings and wire covering. 

Mech nic lProperties. Extensive Hsts of the physical properties of FEP copolymers are given in References 58—63. Mechanical properties are shown in Table 3. Most of the important properties of FEP are similar to those of PTFE the main difference is the lower continuous service temperature of 204°C of FEP compared to that of 260°C of PTFE. The flexibiUty at low temperatures and the low coefficients of friction and stabiUty at high temperatures are relatively independent of fabrication conditions. Unlike PTFE, FEP resins do not exhibit a marked change in volume at room temperature, because they do not have a first-order transition at 19°C. They ate usehil above —267°C and are highly flexible above —79°C (64). 

Among the techniques employed to estimate the average molecular weight distribution of polymers are end-group analysis, dilute solution viscosity, reduction in vapor pressure, ebuUiometry, cryoscopy, vapor pressure osmometry, fractionation, hplc, phase distribution chromatography, field flow fractionation, and gel-permeation chromatography (gpc). For routine analysis of SBR polymers, gpc is widely accepted. Table 1 lists a number of physical properties of SBR (random) compared to natural mbber, solution polybutadiene, and SB block copolymer. 

The physical properties of block copolymer TPE also depend on the type and arrangement of the blocks. Table 5 compares the property advantages of various block copolymer thermoplastic elastomers. 

An IPN has different properties from either a copolymer or a polymer blend. It may swell in solvents, but will not dissolve it will resist creep or flow to a greater extent than copolymers or blends. Some differences in the physical properties of IPNs compared with polymer blends can be seen in Table 10.3. The major reason for the differences in properties between polymer blends and IPNs is that the latter have greater adhesion and better mixing. 

This block copolymer has substantially different physical properties as compared to a random styrene-butadiene copolymer. 

Linear low-density polyethylene (LLDPE)440-442 is a copolymer of ethylene and a terminal alkene with improved physical properties as compared to LDPE. The practically most important copolymer is made with propylene, but 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are also employed.440 LLDPE is characterized by linear chains without long-chain branches. Short-chain branches result from the terminal alkene comonomer. Copolymer content and distribution as well as branch length introduced permit to control the properties of the copolymer formed. Improvement of certain physical properties (toughness, tensile strength, melt index, elongation characteristics) directly connected to the type of terminal alkene used can be achieved with copolymerization.442... 

Graft and block copolymers of cotton cellulose, in fiber, yam, and fabric forms, were prepared by free-radical initiated copolymerization reactions of vinyl monomers with cellulose. The properties of the fibrous cellulose-polyvinyl copolymers were evaluated by solubility, ESR, and infrared spectroscopy, light, electron, and scanning electron microscopy, fractional separation, thermal analysis, and physical properties, including textile properties. Generally, the textile properties of the fibrous copolymers were improved as compared with the properties of cotton products. 

Alicagenes eutropha produces a copolymer of hydroxyvalerate and hydroxybutyrate when deprived of key nutrients, such as amino acids and minerals. The product, biopol, represents up to 90 percent of the dry weight of the bacterium. It is comparable to polypropene in physical properties, has better flexibility at low temperatures, and is biodegradable to CO2 and water within months. However, the polymer (trade name Biopol) is not currently cost-competitive with synthetic polymers because of the high costs of the fermentation substrates and the fermentation plants. 

Commerically available samples of biaxially oriented polystyrene and SMA copolymer sheet material, having a thickness of 0.0381cm, were used in this investigation. It is generally recognized that crystallization under stress can enhance the tensile properties of a semi-crystalline polymer through a special arrangement of the crystalline portion ( 23). Therefore, the physical properties of the styrene-maleic anhydride copolymers chosen were compared to those of polystyrene produced in the same manner and are shown in Table I (24). 

T he type of counterion used in an ion-containing polymer can have a substantial effect on the physical properties of the material. Many studies have been made in the past comparing the properties of metal- or ammonium-neutralized ionomers two recent books on ion-containing polymers present a comprehensive review of the literature (1,2). There is a wealth of information comparing different metal counterions in neutralized or partially neutralized ethylene-carboxylic acid copolymers. Rees and Vaughan studied the melt flow and tensile properties of... 

It Is known that most radiation Initiated polymerization processes are Initiated by Che free radicals created by radlolysls of Che monomers. If a monomer or a mixture of monomers Is Irradiated In Che presence of a polymer, a graft copolymer Is formed which has different physical properties. For example. If a second polymer like polyacrylonitrile or polyvlnylldlne chloride, which possess superior barrier properties against permeation by oxygen, carbon dioxide, water vapor etc.. Is grafted to a polyolefin film like polyethylene, polypropylene, etc., the barrier properties of the composite film are greatly enhanced compared with Che polyolefin film. 

As far back as in the late 1940s to the early 1950s, it was noticed that if the suspension copolymerization of mono- and divinyl monomers is carried out in the presence of an inert solvent, it wiU yield beads that are opaque in appearance and much more resistant to osmotic shock compared with the known gel-type copolymers. It soon became evident that the improved physical properties of the new resins are caused by their special internal structure, which, in its turn, results from the phase separation of the initially homogeneous comonomer—diluent solution. This finding opened the door to a new generation of polymeric adsorbents, the so-called macroporous resins that exhibit stable porosity in both the dry and the solvated states. 

In a random copolymer, the monomers are randomly distributed along the chain, so there is no pattern to their arrangement (Fig. 3.4). For example, random polypropylene copolymers are a type of polypropylene in which the basic structure of the polymer chain is modified by the incorporation of ethylene comonomer during the polymerization process. This results in changes in the physical properties compared to homopolymer PP such as increased clarity, improved impact resistance, increased flexibility, and a decrease in the melting point and heat sealing temperature. 

Some physical properties of polyethylene ionomers are compared with those of polyethylene and the acid copolymer, poly(ethylene-co-methacrylic acid) in Table 5.15. lonomer is generally tougher and, as shown in Table 5.15, relative to the acid copolymer, its tensile strength is increased by 27—53% and its stiffness is nearly tripled. 

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