Poly polymorphism effects

Gene Role in MTX pathway Postulated effect of poly Polymorphism morphism CUnical effects Reference... 

The possibility of relating solvent effects to polymorphic crystallization at the molecular level may be realized when the individual crystal structures of the polymorphs are known. An analysis of this kind was carried out for the antiinflammatory drug piroxicam [57] which was fovmd to crystallize as the a-poly-morph from proton donor and basic solvents, but as the -polymorph from non-polar solvents. On the assumption that crystallization of the drug requires... 

Polymorphs generally dissolve more rapidly than their hydrates, but there have been reports of drug pseudopolymorphs containing, e.g., ethyl acetate or n-pentanol, which display enhanced solubilities, both in vitro and in vivo, when compared with their nonsolvated forms [25]. Figiue 12 shows powder dissolution rate curves for two polymorphs of nitrofurantoin. The significance of the curves for this system is that the retarded initial dissolution rate for the a-poly-morph may render it more favourable for pharmaceutical formulation since there is evidence that adverse side effects may be associated with rapid absorption of the -polymorph [61]. 

Di Lorenzo, M.L., Rubino, P., Luijkx, R., and Helou, M. (2014) Influence of chain structure on crystal polymorphism of poly(lactic acid). Part 1 effect of optical purity of the monomer. Colloid Polym. Sci., 292, 399 -409. 

Farmer, B. L., Hopfinger, A. J., and Lando. J. B., Polymorphism of poly(vinylidene fluoride) potential energy calculations of the effects of head-to-head units on the chain conformation and packing of poly(vinylidene fluoride), J. Appl. Phys., 43, 4293-4303 (1972). 

Poly(N-vinylpyrrohdone) (PVP) is a water-soluble and imcharged polymer. The presence of PVP has no influence on the polymorphs of CaCOs precipitation, but has a morphological effect on vaterite and calcite at high PVP concentration [101]. The precipitate obtained in the initial presence of P VA was calcite (run 2 of Table 3). The crystalline products obtained with N-vinylpyrrolidone without addition of the radical initiator were calcite with a trace amount of aragonite (run 1 of Table 3). These results indicate that both the polymer and monomer did not exert any influence on the nucleation and crystal growth of CaCOs. On the contrary, in-situ polymerization of the monomer during the precipitation of CaCOs was carried out by the doublejet method (Keiun et al, 2006, personal communication). After addition of the calcium reactants into the aqueous solution of the monomer was completed, an aqueous solution of KPS as a water-soluble radical initiator was added to the reaction mixture after incubation at 30 °C for several minutes (1, 3, or 20 min). All the products obtained by the in-situ polymerization were pre-... 

Fakirov S, Boueva D, Balta Calleja F J, Krumova M and Apostolov A A (1998) MIcto-hardness under strain. Part I. Effect of stress-induced polymorphic transition of poly(butylene terephthalate) on microhardness, J Mater Sci Lett 17 453-457. 

J. B. Laodo and W. W. Doll, The polymorphism of poly(vinylideoe fluorideX 1. The effect of head-to-head structute, 7. MaaomoL Sr Pkyi. 92 205 (1968). 

Miyamoto and co-workers [37] also studied the effect of orientation on the dielectric a, transition of the a-polymorphic crystal form of poly(vinylidcne fluoride). The relaxation strength of the transition wa.s found to be highest along the direction trf orientation and to decrease down to near zero in the perpendicular direction. With random orientation the relaxation strength b about 4, along the orientation about 22, perpendicularly to the orientation direction near zero. 

The effects of molecular orientation on the crystallization and polymorphic behavior of SPS and SPS/poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) blends were studied with wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry [37]. The oriented amorphous films of SPS and SPS/ PPO blends were crystallized under constraint at crystallization temperatures ranging from 140 to 240 °C. The degree of crystallinity was lower in the cold-crystallized oriented film than in the cold-crystallized isotropic film. It was inferred that the oriented mesophase was obtained in drawn films of SPS and that the crystallization of SPS was suppressed in that phase. The WAXD measurements showed that the crystal phase was more ordered in SPS/PPO blend than in pure SPS under the same annealing conditions. It was principally due to the decrease in the mesophase content. The crystal forms were found to be dependent on the crystallization temperature, blend composition, and... 

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