Amorphous poly

Amorph. LC Amorph/LC Copolymer Poly(amorph) Poly(LC) i.homo... 

In principle, amorphous solids can change their (short-range) atomic structure in the same manner as crystalline solids do. So far, all cases of this so-called polyamorphism have been observed at non-ambient pressures. Thus, the N in amorphous (a-Si) and liquid silicon was found to increase monotonically with pressure [36] and later, a poly amorphous transition was observed [37]. Between the pressures of 3... 

Our process demonstrated several advantages over the known proeess assoeiated with catalytic growth plasma process such as better uniformity, purer, lower, poly amorphous struetures. 

Polyester sheet products may be produced from amorphous poly(ethylene terephalate) (PET) or partiaHy crystallized PET. Acid-modified (PETA) and glycol modified (PETG) resins are used to make ultraclear sheet for packaging. Poly(butylene terephthalate) (PBT) has also been used in sheet form. Liquid-crystal polyester resins are recent entries into the market for specialty sheet. They exhibit great strength, dimensional stabHity, and inertness at temperatures above 250°C (see Polyesters,thermoplastic). 

Quenched sheet is pulled horizontally from the stack and is then either wound on roUs or sheared into sheets of the required dimension. Among the polymers made into sheet this way are the polyolefins, poly(vinyl chloride), amorphous polyester, polycarbonate, and polyarjiate. 

Sodium Poly(4-styrene sulfonate). The sol—gel processing of TMOS in the presence of sodium poly-4-styrene sulfonate (NaPSS) has been used to synthesize inorganic—organic amorphous complexes (61). These sodium siUcate materials were then isotherm ally crystallized. The processing pH, with respect to the isoelectric point of amorphous siUca, was shown to influence the morphology of the initial gel stmctures. Using x-ray diffraction, the crystallization temperatures were monitored and were found to depend on these initial microstmctures. This was explained in terms of the electrostatic interaction between the evolving siUcate stmctures and the NaPSS prior to heat treatment at elevated temperatures. 

Polylactide is the generaUy accepted term for highly polymeric poly(lactic acid)s. Such polymers are usuaUy produced by polymerization of dilactide the polymerization of lactic acid as such does not produce high molecular weight polymers. The polymers produced from the enantiomeric lactides are highly crystalline, whereas those from the meso lactide are generaUy amorphous. UsuaUy dilactide from L-lactic acid is preferred as a polymerization feedstock because of the avaUabUity of L-lactic acid by fermentation and for the desirable properties of the polymers for various appUcations (1,25). 

Applications. Among the P—O- and P—N-substituted polymers, the fluoroalkoxy- and aryloxy-substituted polymers have so far shown the greatest commercial promise (14—16). Both poly[bis(2,2,2-trifluoroethoxy)phosphazene] [27290-40-0] and poly(diphenoxyphosphazene) [28212-48-8] are microcrystalline, thermoplastic polymers. However, when the substituent symmetry is dismpted with a randomly placed second substituent of different length, the polymers become amorphous and serve as good elastomers. Following initial development of the fluorophosphazene elastomers by the Firestone Tire and Rubber Co., both the fluoroalkoxy (EYPEL-F) and aryloxy (EYPEL-A) elastomers were manufactured by the Ethyl Corp. in the United States from the mid-1980s until 1993 (see ELASTOLffiRS,SYNTHETic-PHOSPHAZENEs). 

Similarly, the random introduction by copolymerization of stericaHy incompatible repeating unit B into chains of crystalline A reduces the crystalline melting point and degree of crystallinity. If is reduced to T, crystals cannot form. Isotactic polypropylene and linear polyethylene homopolymers are each highly crystalline plastics. However, a random 65% ethylene—35% propylene copolymer of the two, poly(ethylene- (9-prop5lene) is a completely amorphous ethylene—propylene mbber (EPR). On the other hand, block copolymers of the two, poly(ethylene- -prop5iene) of the same overall composition, are highly crystalline. X-ray studies of these materials reveal both the polyethylene lattice and the isotactic polypropylene lattice, as the different blocks crystallize in thek own lattices. 

Cycloahphatic diamines react with dicarboxyUc acids or their chlorides, dianhydrides, diisocyanates and di- (or poly-)epoxides as comonomers to form high molecular weight polyamides, polyimides, polyureas, and epoxies. Polymer property dependence on diamine stmcture is greater in the linear amorphous thermoplastic polyamides and elastomeric polyureas than in the highly crosslinked thermo set epoxies (2—4). 

The crystallinity of poly(lactide- (9-glycoHde) samples has been studied (36). These copolymers are amorphous between the compositional range of 25—70 mol % glycoHde. Pure polyglycoHde was found to be about 50% crystalline whereas pure poly-L-lactide was about 37% crystalline. An amorphous poly(L-lactide-i (9-glycoHde) copolymer is used in surgical cHps and staples (37). The preferred composition chosen for manufacture of cHps and staples is the 70/30 L-lactide/glycoHde copolymer. 

The maximum rates of crystallisation of the more common crystalline copolymers occur at 80—120°C. In many cases, these copolymers have broad composition distributions containing both fractions of high VDC content that crystallise rapidly and other fractions that do not crystallise at all. Poly(vinyhdene chloride) probably crystallises at a maximum rate at 140—150°C, but the process is difficult to foUow because of severe polymer degradation. The copolymers may remain amorphous for a considerable period of time if quenched to room temperature. The induction time before the onset of crystallisation depends on both the type and amount of comonomer PVDC crystallises within minutes at 25°C. 

As shown in Table 3, the glass-transition temperatures of the amorphous straight-chain alkyl vinyl ether homopolymers decrease with increasing length of the side chain. Also, the melting points of the semicrystalline poly(alkyl vinyl ether)s increase with increasing side-chain branching. 

Table 3. Glass-Transition Temperature of Amorphous Poly(Vinyl Ether)s and Melting Points of Crystalline Poly(Vinyl Ether)s ...

Fig. 1. Chemical stmctures of barrier polymers, (a) Vlaylidene chloride copolymers (b) hydroly2ed ethylene—vinyl acetate (EVOH) (c) acrylonitrile barrier polymers (d) nylon-6 (e) nylon-6,6 (f) amorphous nylon (Selar PA 3426), y = x - - z-, (g) nylon-MXlD6 (h) poly(ethylene terephthalate) and (i) poly(vinyl...

Silver [7440-22-4]—The coloi additive silvei (EEC No. E 174) is a crystaUine powdei of high purity silver prepared by die reaction of silver nitrate with ferrous sulfate in the presence of nitric, phosphoric, and sulfuric acids. Poly(vinyl alcohol) is used to prevent the agglomeration of crystals and the formation of amorphous silver. 

Epichlorohydrin Elastomers without AGE. ECH homopolymer, polyepichlorohydrin [24969-06-0] (1), and ECH—EO copolymer, poly(epichlorohydrin- (9-ethylene oxide) [24969-10-6] (2), are linear and amorphous. Because it is unsymmetrical, ECH monomer can polymerize in the head-to-head, tail-to-tail, or head-to-tail fashion. The commercial polymer is 97—99% head-to-tail, and has been shown to be stereorandom and atactic (15—17). Only low degrees of crystallinity are present in commercial ECH homopolymers the amorphous product is preferred. 

AGE-Gontaining Elastomers. ECH—AGE, poly(epichlorohydrin-fo-allyl glycidyl ether) [24969-09-3] (3), ECH—EO—AGE, poly(epichlorohydrin- (9-ethylene oxide-i (9-allyl glycidyl ether) [26587-37-1] (4), ECH—PO—AGE, and PO—AGE are also amorphous polymers. 

Crystallinity is low the pendent allyl group contributes to the amorphous state of these polymers. Propylene oxide homopolymer itself has not been developed commercially because it cannot be cross-baked by current methods (18). The copolymerization of PO with unsaturated epoxide monomers gives vulcanizable products (19,20). In ECH—PO—AGE, poly(ptopylene oxide- o-epichlorohydrin- o-abyl glycidyl ether) [25213-15-4] (5), and PO—AGE, poly(propylene oxide-i o-abyl glycidyl ether) [25104-27-2] (6), the molar composition of PO ranges from approximately 65 to 90%. 

Fig. 1. Engineering resins cost vs annual volume (11) (HDT, °C) A, polyetheretherketone (288) B, polyamideimide (>270) C, polyarylether sulfone (170- >200) D, polyimide (190) E, amorphous nylons (124) F, poly(phenylene sulfide) (>260) G, polyarylates (170) H, crystalline nylons (90—220) I, polycarbonate (130) J, midrange poly(phenylene oxide) alloy (107—150) K, polyphthalate esters (180—260) and L, acetal resins (110—140).

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