Ketone polymers crystallinity effects

As is for low mass liquid crystals, incorporation of kinked moieties will result in destructive effects on the liquid crystallinity of polymers (Figure 3.4). 2,2-diphenylpropane, diphenylmethane, diphenyl ether, diphenyl ketone, 1,2-phenylene, 1,3-phenylene, and 1,2-naphthalene are examples of kinked moieties used in the modification of liquid crystalline polymers. They are very effective in destroying the linearity of rigid rods. Polymers with kinked units have less crystallinity and lower phase transition temperatures. Appropriate use of kinked units is thus of help from case to case. However, the type and amount of kinked units should be carefully determined so as to maintain desirable liquid crystallinity. 

Other engineering thermoplastics have also been examined and found to be effective e.g., polyetherimide [121-124], poly(ether ketones) (PEK) [125,126], poly(phenylene oxide) [127-129], and liquid crystalline polymers [130, 131]. 

When small amounts of water were deliberately added to butylhthiiun in hydrocarbon solution, it was possible to prepare polystjrrene with as much as 85% polymer that was insoluble in refluxing methyl ethyl ketone and identified as isotactic polystyrene by x-ray crystallography (164). Isotactic polystyrene (10-22% crystalline) can be prepared when lithium f-butoxide is added to w-C4H9Li initiator and the polymerization in hexane (styrene/hexane = 1) is effected at —30°C (165). This polymerization becomes heterogeneous and is quite slow (after 2-5 days, 50% monomer conversion 20-30% conversion to isotactic polymer). 

A series of copolymers comprised of repeat units I and III were prepared by altering the proportions of bls-chlorophenyl ketone and bls-chlorophenyl sulphone In reaction (8) and the crystallisation characteristics of the copolymers obtained were determined (Table II) [10]. It was found that to obtain adequate crystallinity in melt fabricated samples the copolymers should not contain more than 10 mol% of PES repeat units, III. Unfortunately, reducing the proportion of bls-chlorophenyl sulphone employed reduced the average halogen reactivity In the system and increased the temperature required to keep the more crystalline copolymers in solution. The effect of both these factors was to make the preparation of linear, high molecular weight polymers more... 

R. A. Chivers and D. R. Moore. "The effect of molecular weight and crystallinity on the mechanical properties of injection moulded poIy(aryI-ether-ether ketone) resin." Polymer, pp. 110-116,1994. 

The radiation-initiated polymerization of vinylidene fiuoride is used on a laboratory scale only. The effect of polymerization conditions on the chain defects, content, and changes in the crystalline phases have been studied [528,536,537,544]. Doll and Lando [544] used a °Co source with an average dose rate of 0.33 Mrad/h. The polymerization was carried out between 0 and 400 °C at a pressure equal to the vapor pressure of the solvent-vinylidene fluoride mixture. Esters and ketones (acetone, methyl ethyl ketone, ethyl acetate, acetophenone), DMF, DMSO, and y-butyrolactone were used as solvents. All these solvents are good chain-transfer agents for vinylidene fluoride. The molding characteristics of the resulting polymers were very poor and the intrinsic viscosity of the sample polymerized in acetone solution was low (0.183 dL/g) compared to that of a suspension-polymerized polymer (1.68 dL/g) [544]. 

It is therefore a highly crystalline material and has a crystalline melting point of about 220°C. At this temperature the polymer has a high rate of decomposition. Copolymerization reduces the molecular regularity and thus lowers the softening point, which for 85% vinylidene chloride — 15% vinyl chloride copolymer is about 140°C. Since crystallization is thermodynamically favoured even in the presence of liquids of similar solubility parameter and since there is little interaction between the polymer and any liquid, there are no effective solvents at room temperature for the homopolymer. The copolymers, however, are soluble in ethers and ketones and the solutions may be used for coating applications. The copolymers are resistant to most other organic solvents and to acids there is some attack by alkalis. 

As mentioned earlier, polymers of formaldehyde are described in the next section. Polymers of higher aliphatic aldehydes and ketones have been extensively investigated but, in general, they do not have the stability necessary for commercial development. For example, acetaldehyde may be polymerized using organometallic initiators at low temperatures, e.g., triethylaluminium at —78 C in this case crystalline isotactic polymer is obtained. Also, the polymerization of acetaldehyde may be effected with cationic initiators at low temperatures (e.g., aluminium chloride at —65°C) or with metal oxides at low temperatures (e.g., alumina at —70°C) in these cases amorphous atactic polymer is obtained. The tacticity of polyacetaldehyde arises because the polymer comprises structural units which contain an asymmetric carbon atom ... 

Poly(ethylene terephthalate) is most usually encountered in the crystalline form and, as such, it is soluble at normal temperatures only in proton donors which are capable of interaction with the ester group. Effective solvents of this kind are chlorinated and fluorinated acetic acids, phenols and anhydrous hydrofluoric acid. The polymer is soluble at elevated temperatures in various organic liquids, which include anisole, aromatic ketones, dibutyl phthalate and dimethyl sulphone. Chloroform has the peculiar property of dissolving amorphous poly(ethylene terephthalate) at temperatures below 0°C,but on warming such solutions the polymer separates in crystalline form. Chloroform is without effect on polymer which has already been crystallized. 

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