Crystallizability

C3H6O4, HO OCHCOHj-CH OH. An un-crystallizable syrup it occurs in optically active forms. Prepared by oxidation of glycerin with nitric acid. 

Williams R C and Smith K M 1957 A crystallizable insect virus Nature 179 119-20... 

The cyclic carbonate of benzoin (4,5-diphenyl-l,3-dioxol-2-one, prepared from benzoin and phosgene) blocks both hydrogen atoms of primary amines after dehydration acid stable, easily crystallizable Sheehan oxazolinones are formed, which are also called Ox derivatives. The amine is quantitatively deblocked by catalytic hydrogenation in the presence of 1 equiv. of aqueous acid (J.C Sheehan, 1972, 1973 M.J. Miller, 1983). An intelligent application to syntheses of acid labile -lactams is given in the previous section (p. 161). 

Variations of all the above points-all the way to the complete failure of a crystallizable polymer to actually crystallize-are possible, depending on experimental conditions. 

The attitude we adopt in this discussion is that only those chain segments in the middle of the chain possess sufficient regularity to crystallize. Hence we picture crystallization occurring from a mixture in which the concentration of crystallizable units is Xj and the concentration of solute or diluent is Xg. The effect of solute on the freezing (melting) point of a solvent is a well-known result T j, is lowered. Standard thermodynamic analysis yields the relationship... 

In Chap. 4 we discussed the crystallizability of polymers and the importance of this property on the mechanical behavior of the bulk sample. Following the logic that leads to Eq. (4.17), the presence of a comonomer lowers T for a polymer. Carrying this further, we can compare a copolymer to an alloy in which each component lowers the melting point of the other until a minimummelting eutectic is produced. Similar trends exist in copolymers. 

Amorphous (most likely atactic) 3,4-polyisoprene of 94—100% 3,4-microstmcture was prepared with a (C2H 3A1—Ti(0—/ -C Hy) catalyst (11). Crystalline 3,4-polyisoprene containing about 70% 3,4-units and about 30% i7j -l,4-microstmcture was prepared using a catalyst derived from iron acetyl acetonate, trialkyl aluminum, and an amine in benzene (37). However, this polyisoprene contained gel and was obtained in poor yield. Essentially gel-free crystallizable 3,4-polyisoprene of 70—85% 3,4-microstmcture with the remainder being cis-1,4 microstmcture was prepared in conversions of greater than 95% with a water-modified tri alkyl aluminum, ferric acetyl acetonate, and 1,10-phenanthroline catalyst (38). The 3,4-polyisoprene is stereoregular and beheved to be syndiotactic or isotactic. 

Ferre-D Amare, A.R., Burley, S.K. Use of dynamic light scattering to assess crystallizability of macromolecules and macromolecular assemblies. Structure 2 357-359,... 

The saline residue on the filter is extracted once again with 50 ml. of boiling absolute ethanol. On concentrating the filtrate from the second extraction and the mother liquor from the first crystallizate to a small volume, a second crop (4-6 g.) of product is obtained. The yield of the hydroxyurea is 10-14 g. (53-73%) of white crystals, m.p. 137-141° (dec.). 

Crystalline polyesters are highly important as adhesive raw materials. They are normally crystalline waxes and are highly symmetrical in nature, which can aid the crystallization process [26]. Poly(hexamethylene adipate) and poly(caprolactone), shown in Table 2, are only two of the many crystallizable backbones. Poly(ethylene adipate) and poly(letramethylene adipate) are also commonly used in urethane adhesives. The crystalline polyesters are used in curing hot melts, waterborne polyurethanes, thermoplastic polyurethanes, and solvent-borne urethane adhesives. The adipates are available mostly as diols. The poly(caprolactones) are available as diols and triols. 

The role of crystallizable soft segments in urethane adhesives... 

Most moisture-curing hot-melt adhesives utilize a crystallizable backbone and are based almost exclusively on monomeric MDI at NCO/OH ratios of 1.5 to 2.2. Poly(hexamethylene adipate) polyol is the workhorse of the curing hot-melt adhesives. 

After separation of the catalyst the product was concentrated until dry, the residue was triturated with acetone, the resulting crystallizate was removed by suction and washed with acetone. The yield of N,N -bis-(2-(3, 4 -dihydroxyphenyl)-2-hydroxyethyl]-hexamethylene-diamine-dichlorohydrate was 3.3 grams, i.e., 92% of the theoretical value. A quantity of 2.8 grams having a melting point of 197,5° to 198°C was obtained by precipitation from a mixture of methanol-ether. 

A solution of 44 grams of 2-bromo-4 -benzyloxypropiophenone and 44 grams of 2-(4-meth-oxyphenyDethylamine in 270 ml of ethanol was refluxed for 3 hours. Then the ethanol was distilled off in vacuo and the concentrate mixed with ether. The resulting crystallizate was Sucked off after which the filtrate was mixed with an excess of 2 N hydrochloric acid. As a result of this the hydrochloride of 4 -benzyloxy-2-[2-(4-methoxyphenyl)ethylamino]-propiophenone slowly crystallized. This substance was also Sucked off, washed with water and alcohol, and dried in vacuo. After recrystallization from dilute alcohol the yield was 25.5 grams of a product with a melting point of 217 to 218°C. 

Solomko VP (1980) Filled Crystallizable Polymers Naukova Dumka, Kiev... 

Introduction Fundamental Aspects of Orientational Processes in Crystallizable... 

For rigid-chain crystallizable polymers, spontaneous transition into the nematic phase is accompanied by crystallization intermolecular interactions should lead to the formation of a three-dimensional ordered crystalline phase. 

Fig. 1. Schematic representation of the structure of a crystallizable rigid-chain polymer point defects are located at end joints...

At present, it is known that the structures of the ECC type (Figs 3 and 21) can be obtained in principle for all linear crystallizable polymers. However, in practice, ECC does not occur although, as follows from the preceding considerations, the formation of linear single crystals of macroscopic size (100% ECC) is not forbidden for any fundamental thermodynamic or thermokinetic reasons60,65). It should be noted that the attained tenacities of rigid- and flexible-chain polymer fibers are almost identical. The reasons for a relatively low tenacity of fibers from rigid-chain polymers and for the adequacy of the model in Fig. 21 a have been analyzed in detail in Ref. 65. 

A very recent application of the two-dimensional model has been to the crystallization of a random copolymer [171]. The units trying to attach to the growth face are either crystallizable A s or non-crystallizable B s with a Poisson probability based on the comonomer concentration in the melt. This means that the on rate becomes thickness dependent with the effect of a depletion of crystallizable material with increasing thickness. This leads to a maximum lamellar thickness and further to a melting point depression much larger than that obtained by the Flory [172] equilibrium treatment. 

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