Amorphous copolymer

Styrene-Acrylonitrile (SAN) Copolymers. SAN resins are random, amorphous copolymers whose properties vary with molecular weight and copolymer composition. An increase in molecular weight or in acrylonitrile content generally enhances the physical properties of the copolymer but at some loss in ease of processing and with a slight increase in polymer color. 

The effect of copolymer composition on gas permeability is shown in Table 9. The inherent barrier in VDC copolymers can best be exploited by using films containing Htde or no plasticizers and as much VDC as possible. However, the permeabiUty of even completely amorphous copolymers, for example, 60% VDC—40% AN or 50% VDC—50% VC, is low compared to that of other polymers. The primary reason is that diffusion coefficients of molecules in VDC copolymers are very low. This factor, together with the low solubiUty of many gases in VDC copolymers and the high crystallinity, results in very low permeabiUty. PermeabiUty is affected by the kind and amounts of comonomer as well as crystallinity. A change from PVDC to 50 wt °/ VC or 40 wt % AN increases permeabiUty 10-fold, but has Httle effect on the solubiUty coefficient. 

Polyamides (nylons) The main types of nylon are oil and petrol resistant, but on the other hand susceptible to high water absorption and to hydrolysis. There are a few solvents such as phenol, cresol and formic acid. Special grades include a water-soluble nylon, amorphous copolymers and low molecular weight grades used in conjunction with epoxide resins. Transparent amorphous polyamides are also now available. 

The Zr-FI catalyst selectively forms PE even in the presence of ethylene and 1-octene, while the Hf complex affords amorphous copolymers, resulting in the catalytic generation of PE- and poly(ethylene-c6>-l-octene)-based multiblock copolymers through a reversible chain transfer reaction mediated by R2Zn. The development of an FI catalyst with extremely high ethylene selectivity as well as a reversible chain transfer nature has made it possible to produce these unique polymers. Therefore, both Ti- and Zr-FI catalysts are at the forefront of the commercial production of polyolefinic block copolymers. 

In theory, almost any comonomer diacid or dialcohol could lead to amorphous copolymers of PET. For example, incorporation of 20-80% of 2,6-naphthalate, or greater than 30% of isophthalate, will generate amorphous materials [9], Amorphous copolymers of PET, produced by the wholesale substitution of other monomers into the polymeric backbone, rarely possess desirable thermomechanical properties, unlike the Eastman PETG compositions. 

Figure 6.1 Some examples of modifiers used to produce amorphous copolymers of PET...

The presence of the large cyclic olefin units randomly distributed in the backbone leads to an amorphous copolymer combining high transparency, low birefringence, stiffness, barrier properties and the general characteristics of olefins. 

Copolymers of vinylidenc chloride and acrylonitrile are also transparent. These amorphous copolymers are also resistant to permeation by gases. 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

EP ethylene-propulene amorphous copolymer blend RACO ethyl-ene-co-propylene random copolymer. 

Since the discovery of Teflon by Roy Plunkett in 1937 a number of fluorinated plastics have reached commercial status. These plastics, exemplified by polytetrafluoroethylene (PIPE), have outstanding electrical, chemical, and thermal properties. AU these commercial materials are either crystaUine or semicrystalline. Teflon AF is a family of amorphous copolymers that retain the desirable electrical, chemical, and thermal properties of semicrystalline fluorinated plastics and also have such properties associated with amorphous materials as optical clarity, improved physical properties, and solubility in selected fluorinated solvents. 

The Teflon AF family consists of copolymers of tetrafluoroethylene, (TFE) and 2,2-bis-trifluoromethyl-4,5-difluoro-l,3-dioxole, (PDD), whose structure is shown in Figure 2.1. The properties of these amorphous copolymers vary with the relative amounts of the comonomers. At present the two commercial grades of Teflon AF are AF-1600 and AF-2400 with glass transition temperatures of 160 and 240°C respectively. The variation of glass transition temperature with composition is shown in Figure 2.2. Thus AF-1600 and AF-2400 contain 64 and 83 mol % PDD, respectively. 

Elvax. DuPont Co trademark for a series of high.molecular weight vinyl resins. They are translucent white, amorphous copolymers, wax-compatible but in sol in aqueous mixts and in most polar solvents. Used as a wax additive to improve its toughness, its heat-seal bond strength.and to reduce flaking. 

Another graft copolymer having the same composition, but presumably a somewhat greater density of PEO side chains, had the same transparent appearance and low Tg. Modulus as well as dilatometric data exhibited a hysteresis loop between — 20° and 60°C. These results along with x-ray measurements indicate presence of some crystallinity in contrast to the first completely amorphous copolymer. For given composition the relation between the size and distribution of the side chains, and their ability to crystallize is not yet clear. 

COC cyclic olefin copolymer amorphous copolymer of 2-norbomene and ethylene (Zeonor)... 

It should be added that alternating ethylene/2-butene copolymers can exhibit stereoregularity namely the ethylene/cA-2-butene copolymer, which possesses an erythro-diisotactic structure and is a crystalline polymer. It may be interesting to note that from the formal point of view the alternating eryt/zro-diisotactic ethylene/cA-2-butene copolymer, i.e. erythro-diisotactic poly[ethylene- //-(c/.v-2-butene)], can be treated as isotactic head-to-head and tail-to-tail polypropylene. Isomeric trans-2-bu. ene gives atactic amorphous copolymers with ethylene [2,82]. 

Only cycloolefins with rings containing an odd number of carbon atoms, such as cyclopentene (x = 3) and cycloheptene (x = 5), yield crystalline copolymers with an erythro-diisotactic configuration. Cycloolefins with an even number of carbon atoms in the ring, such as cyclobutene (x = 2) and cyclooctene (x = 6), give amorphous copolymers [241]. 

We shall only describe here the structure of the LC and LCC phases, because the structures found at temperatures higher than the melting temperature of the crystallizable chains are similar to that of amorphous copolymers. 

Discussion Point DP7i While ethylene and norbornene give essentially alternating, amorphous copolymers, attempts to copolymerize ethylene and cyclohexene give only crystalline polyethylene. Which factors might contribute to these observations Unsaturated norbornenyl chain ends cannot arise by ji-H transfer... 

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