Atactic poly , effect

In contrast to the case of Cp2ZrX2/MAO giving atactic poly(alkene)s, Cp MCl2/MAO, M = Zr (139) and Hf (140), are the catalyst precursors of the syndiotactic polymerization of 1-butene and propylene [176]. Triad distribution indicated that this is chain-end controlled syndiospecific polymerization. The syndiospecificity is attributed to the increase of steric encumbrance around the metal center. Thus, Cp HfX2 is the most effective syndiospecific catalyst component in this system. 

The template polymerization of methacrylic acid at 60 C in DMF was studied with atactic poly(vinyl acetate) M =66,400 used as a template. The effect of template, monomer, and initiator (AIBN) concentration on the kinetics of polymerization was studied dilatometrically. Viscometric measurements showed that complexation between poly(vinyl acetate) and poly(methacrylic acid) was maximized when the template to polymer ratio was 1 1, and for the same ratio of the monomer to the template, the rate of template polymerization also reached the maximum. The overall energy of activation was the same (115 kJ/mol) in the presence and absence of the template. The polymerization follows mechanism II ( pick up mechanism ). 

Coleman et al. 2471 reported the spectra of different proportions of poly(vinylidene fluoride) PVDF and atactic poly(methyl methacrylate) PMMA. At a level of 75/25 PVDF/PMMA the blend is incompatible and the spectra of the blend can be synthesized by addition of the spectra of the pure components in the appropriate amounts. On the other hand, a blend composition of 39 61 had an infrared spectrum which could not be approximated by absorbance addition of the two pure spectra. A carbonyl band at 1718cm-1 was observed and indicates a distinct interaction involving the carbonyl groups. The spectra of the PVDF shows that a conformational change has been induced in the compatible blend but only a fraction of the PVDF is involved in the conformational change. Allara M9 250 251) cautioned that some of these spectroscopic effects in polymer blends may arise from dispersion effects in the difference spectra rather than chemical effects. Refractive index differences between the pure component and the blend can alter the band shapes and lead to frequency shifts to lower frequencies and in general the frequency shifts are to lower frequencies. 

In Older to investigate the effect that unneutralized atactic poly(methacrylic acid) (at-PMAA) has on the rate of a neutral hydrolysis reaction, several acyl-activated esters (1) and a series of l-acyl-l,2,4-triazols (2) were chosen as subtrates [47] ... 

Kikkawa, Y Suzuki, T Kanesato, M. Doi, Y and Abe, H. Effect of phase structure on enzymatic degradation in poly(L-lactide)/atactic poly(3-hydroxybutyrate) blends with different miscibility. Biomacromole. 2009,10(4), 1013-1018. 

Tsuji, H. and Ikada, Y. (1995) Blends of isotactic tmd atactic poly(lactide)s. I. Effects of mixing ratio of isomers on crystallization of blends from melt. Journal of Applied Polymer Science, 58, 1793-1802. 

Tsuji, H. and Ikada, Y. (1996) Blends of isotactic and atactic poly(lactide) 2. Molecultir-weight effects of atactic component on crystallization and morphology of equimolar blends from the melt. Polymer, 37, 595-602. 

Li Q, Zhou J, Zhang L (2009) Stmcture and properties of the nanocomposite films of chitosan reinforced with cellulose whiskers. J Polym Sci Part B Polym Phys 47 1069-1077 Lin N, Chen G, Huang J et al (2009) Effects of polymer-grafted natural nanocrystals on the stmcture and mechanical properties of poly(lactic acid) a case of cellulose whisker-graft-polycaprolactone. J Appl Polym Sci 113 3417-3425 Ljungberg N, Bonini C, Bortolussi F et al (2005) New nanocomposite materials reinforced with cellulose whiskers in atactic polypropylene effect of surface and dispersion characteristics. Biomacromolecules 6 2732-2739... 

The simplest method to use is reversible salt formation polarimetric and spectropolari-metric studies of salts of optically inactive polyacids (such as polyacrylic, polyitaconic or poly-p-vinylbenzoic acids) with OA bases (like quinine or nicotine) as well as optically inactive bases (polyvinylpyridines) with OA acids (tartaric, mandelic, t/-camphor-/3-sulfonic or with L-menthylbromoacetate) have been reported by Schulz et al f 176, 177]. They found that the optical activity of the poly-salts affected by the microconfiguration of the polymer chain are quite different from the corresponding salts of OA low-molecular weight compounds the ORD curves of isotactic and atactic poly-2-vinylpyridine salts with D-tar-taric acid were found to be anomalous, with a higher value of rotation for the isotactic polymeric salt but in the case of methacryloylnicotine salts it seems that the observed differences can be explained by the assumption of increased specific rotation of the associated nicotine cations in the polymeric salt [178] and not by a conformational effect. 

Unlike most crystalline polymers, PVDF exhibits thermodynamic compatibiUty with other polymers (133). Blends of PVDF and poly(methyl methacrylate) (PMMA) are compatible over a wide range of blend composition (134,135). SoHd-state nmr studies showed that isotactic PMMA is more miscible with PVDF than atactic and syndiotactic PMMA (136). MiscibiUty of PVDF and poly(alkyl acrylates) depends on a specific interaction between PVDF and oxygen within the acrylate and the effect of this interaction is diminished as the hydrocarbon content of the ester is increased (137). Strong dipolar interactions are important to achieve miscibility with poly(vinyhdene fluoride) (138). PVDF blends are the object of many papers and patents specific blends of PVDF and acryflc copolymers have seen large commercial use. 

Arai, T, Sawatari, N., Yoshizaki, T., Einaga, Y. and Yamakawa, H. (1996) Excluded-volume effects on the hydrodynamic radius of atactic and isotactic oligo- and poly(methylmethacrylate)s in dilute solution. Macromolecules, 29, 2309-2314. 

The ORD and CD curves of optically active polymers containing chromo-phoric groups show that the chromophores can be asymmetrically perturbed by the chirality of the substituents and of the main chain conformation. This is the case with poly( ec-butyl vinyl ketone) (377), which presents a Cotton effect at 292 nm, its intensity being greater in the prevalently isotactic polymer than in the atactic polymer. 

The value of a for poly(propylene oxide) was obtained from the data of Moacanin 189) for polyurethanes prepared by condensation of toluene-2,4-diisocyanate with atactic polypropylene glycols of molecular weights about 1000 and 2000. The small quantity of diisocyanate present in these compositions can make only a negligible effect on the chain dimensions (less than one per cent on the freely rotating chain, as is... 

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