Crystallization of polycarbonates

Structure and Crystallinity. The mechanical—optical properties of polycarbonates are those common to amorphous polymers. The polymer may be crystallized to some degree by prolonged heating at elevated temperature (8 d at 180°C) (16), or by immersion ia acetone (qv). Powdered amorphous powder appears to dissolve partially ia acetone, initially becoming sticky, then hardening and becoming much less soluble as it crystallizes. Enhanced crystallization of polycarbonate can also be caused by the presence of sodium phenoxide end groups (17). 

An illustrative example for solvent polymer interactions is the solvent induced crystallization of polycarbonate. Amorphous PC was reported to crystallize when in contact with butyl acetate vapor. Figure 4.35 shows a 2D spherulite grown almost to a fully round envelope. These spherulites resemble spherulites grown from the melt. With an AFM, the growth can be in principle followed in real time down to the nanometer level. 

C02-induced crystallization has also been observed for bisphenol A polycarbonate [33], tert-butyl poly(ether ether ketone) [34], and methyl substituted poly (aryl ether ether ketone) [35]. This C02-induced enhanced crystallization rate with increasing pressure has been explained in terms of the depression of Tg being far greater than the depression of the T. However, in contrast to the aforementioned polymers, it has been shown that exposure of poly(L-lactide) [36] and isotactic polypropylene [37] to CO2 suppresses the crystallization rate. This observation was suggested to be due to the being depressed to the same extent as the Tg, which prevents the formation of critical size nuclei. It has recently been shown by Hu et al. [38] that the crystallization of polycarbonate may be initiated under scCOz conditions using nano-scale days. 

Particles of fillers, especially nanoparticles, act as nucleating agents in polycarbonates. The crystallization of polycarbonates is significantly enhanced by the addition of fillers, such as, graphite or multiwall carbon nanotubes. ... 

While normally amorphous, and generally featureless on a micron scale, crystallization of polycarbonate was solvent-induced with butyl acetate, generating a disc-like spherulitic structure of ca 10 fina in diameter surroimded by an amorphous matrix. Within the spherulite, the twisted fibrils emanating from the point of nucleation were observed in these afm images, and is consistent with known lamellar growth mechanisms (103). 

High pressure injection moulding and crystallization of polycarbonate during such a process has also been described. ... 

Tsuburaya M. Crystallization of polycarbonate induced by spinodal decomposition in polymer blends. Polymer 2004 45(3) 1027-1032. 

Solubility and Solvent Resistance. The majority of polycarbonates are prepared in methylene chloride solution. Chloroform, i7j -l,2-dichloroethylene, yy -tetrachloroethane, and methylene chloride are the preferred solvents for polycarbonates. The polymer is soluble in chlorobenzene or o-dichlorobenzene when warm, but crystallization may occur at lower temperatures. Methylene chloride is most commonly used because of the high solubiUty of the polymer (350 g/L at 25°C), and because this solvent has low flammabiUty and toxicity. Nonhalogenated solvents include tetrahydrofuran, dioxane, pyridine, and cresols. Hydrocarbons (qv) and aUphatic alcohols, esters (see Esters, organic), or ketones (qv) do not dissolve polycarbonates. Acetone (qv) promotes rapid crystallization of the normally amorphous polymer, and causes catastrophic failure of stressed polycarbonate parts. 

Yet another recent development has been the alloying of polycarbonates with liquid crystal polymers such as Vectra (see Section 25.8.1). These alloys are notable for their very good flow properties and higher strength and rigidity than conventional bisphenol A polycarbonates. 

Meldrum s acid chemistry, 21 151,152, 153 Melengesterol acetate (MGA), 10 871 Melissic acid, physical properties, 5 30t Melt behavior, of polycarbonates, 19 805 Meltblown fabrics, 17 478-479, 495 Meltblown fibers, 11 237, 240-241 Melt casting, 14 230 Melt crystallization, 3 137—141... 

The major uses of BPA are in the production of polycarbonate resins (63%) and epoxy resins (27%). Polycarbonates have major outlets in automotive parts, compact discs, eyeglasses, and sheet and glazing applications, and have caused bisphenol A consumption to more than double during the past decade. Epoxy resins are two-component adhesives for very strong bonding. Miscellaneous uses include flame retardants (mostly tetrabromobisphenol A) and other polymer manufacture. Polycarbonate grade bisphenol A is >99% p,p isomer. The epoxy grade is 95% p,p. The p,p and o,p isomers can be separated by a combination of distillation and crystallization. 

Statistical copolymerization of ethylene glycol and 1,4-butanediol with dimethyl ter-ephthalate results in products with improved crystallization and processing rates compared to poly(ethylene terephthalate). Polyarylates (trade names Ardel, Arylon, Durel), copolymers of bisphenol A with iso- and terephthalate units, combine the toughness, clarity, and proce-sibility of polycarbonate with the chemical and heat resistance of poly(ethylene terephthalate). The homopolymer containing only terephthalate units is crystalline, insoluble, sometimes infusible, and difficult to process. The more useful copolymers, containing both tere- and isophthalate units, are amorphous, clear, and easy to process. Polyarylates are used in automotive and appliance hardware and printed-circuit boards. Similar considerations in the copolymerization of iso- and terephthalates with 1,4-cyclohexanedimethanol or hexa-methylene diamine yield clear, amorphous, easy-to-process copolyesters or copolyamides,... 

In the early literature it is suggested that polycarbonates can be easily plasticized with common plasticizers. Plasticization of polycarbonate has been investigated by Kozlov et al. (12). These authors described the influence of plasticization on softening points and mechanical properties of bisphenol A polycarbonates. They conclude that the behavior of plasticized polycarbonate is similar to that encountered for most amorphous polymers. The influence of crystallization effects promoted by the plasticizer was not taken into account. 

From a practical point of view the purpose of this study was to increase the crystallizability of the polycarbonate by incorporating in it well-defined amounts of plasticizer. With this modification, crystalline polycarbonate films could be made with a higher modulus of elasticity, and these would extend the usefulness of the polymers as photographic film bases. When this study was completed an article was published by Sears and Darby (16), who made an extensive study of the plasticization of polycarbonate using 50 plasticizers of widely differing types. The crystallization tendency in the presence of plasticizers was recognized by these authors as a problem and was circumvented by quench cooling. 

The crystallization tendency of polycarbonates in the pure state is limited. Kampf (JO) found that the first spherulites appear only after heating at 180°C. for eight days more pronounced crystallization occurs only after heating at 190°C. for the same period of time. Orientation of films or fibers does not cause any crystallization, and relatively small improvement of elastic properties is noted. 

The crystallization tendency of polycarbonate is enhanced by the action of solvents. For example, crystallization may be accomplished by slow evaporation of solvent from cast film (14, 17) or by treatment with swelling agents such as ethyl acetate or acetone. 

Why is it that the maximum modulus of elasticity of crystalline film samples of polycarbonate, even when oriented, does not increase considerably over that of amorphous samples Van Kerpel (19) examined the x-ray diffraction pattern of a crystallized polycarbonate sample held under tension and showed that the crystal lattice of the polycarbonate elongates quite easily in the direction of stretch. He found that the lattice distance (d 2.670 A.) increases to d 2.691 A. and d — 2.714 A. when the polycarbonate film is elongated by 5 and 10%, respectively. 

Solubility and Solvent Resistance. The majority of polycarbonates are prepared in methylene chloride solution Chloroform, eir-1,2-dichlorocthylcnc, rym-tclrachlorocthanc. and methylene chloride arc the preferred solvents for polycarbonates. Flydrocarbons and aliphatic alcohols, esters, or ketones do not dissolve polycarbonates. Acetone promotes rapid crystallization of the normally amorphous polymer, and causes catastrophic failure of stressed polycarbonate parts. 

Komiya et al. [13] recently introduced the novel, environmentally friendly process from Asahi Chemical Industry Co. for the production of polycarbonates, which requires neither phosgene nor solvent (Scheme 1). In this process bisphenol A undergoes a prepolymerization with diphenyl carbonate in the melt. A simple crystallization of the prepolymer is fol-... 

There is a large body of patent literature and a growing amount of scientific literature on blends of polycarbonate with various crystallizable polyesters. The latter would include poly (ethylene terephthalate), poly-(butylene terephthalate), polycaprolactone, and certain copolyesters derived from mixtures of terephthalic acid and isophthalic acid co-reacted with 1,4-cyclohexanedimethanol (79, 80, 81,82). As shown recently, some of these mixtures form miscible blends although the polyester possesses the possibility of crystallizing. The number of patents on such systems indicates a degree of commercial interest. 

Thus, the employed pure solvents showed similar spreading behavior on the gold electrodes of the sensors. Similar spreading behavior on gold electrodes was also observed for dissolved copolymers that were from the same chemical family of polycarbonates. For more diverse solvents and polymers, one of possible solutions to reduce the differences in spreading of dissolved polymers may be to employ unpolished sensor crystals.35,40,41... 

The crystallization of PBT and PET in these blends is somewhat suppressed by the partial miscibifity of the PC. However, since PBT crys-talfizes intrinsically faster than PET, blends of PBT and polycarbonate after injection molding show a crystalfine PBT phase in their morphology. 

Several research investigations have been made to compatibilize PET or PBT with PPE both by reactive and non-reactive routes of compatibiliza-tion [Brown et al., 1990 and 1991 Akkapeddi and VanBuskirk, 1992]. Compatibilized binary blends of PPE/polyesters still lacked adequate toughness and invariably required the addition of rubbery impact modifiers (reactive or compatible type) and polycarbonate. The addition of polycarbonate presumably suppresses the crystallization of the thermoplastic PET or PBT phase, due to its... 

Details A solid in flake, crystal or dust form. Used in production of epoxy-phenolic resins, monomer of polycarbonates (PC), an antioxidant for PVC, and as an inhibitor used during PVC polymerisation. PC are widely used in many consumer products, from sunglasses and CD to water and food containers and shatter-resistant baby bottles. Some polymers can also contain bisphenol A, and epoxy resins containing bisphenol A are common coatings used in food cans. 

The lack of liquid crystal properties in this polymer series was not completely unexpected and inspection of molecular models allows one to observe only non-linear, highly bent conformations of the diphenyl carbonate repeating unit. Very recently, investigations by Flory and coworkers on model analogues of polycarbonates have shown that in the crystal the carbonate group is coplanar and with... 

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