Poly , atactic

Microstructure. Interest in PVP microstmcture and the potential for tacticity has been reviewed (39,40). PVP generated by free radicals has been shown to be atactic except when polymerization is conducted in water. In this case some syndiotacticity is observed (40). In the presence of syndiotactic templates of poly(methacryhc acid) (or poly(MAA)), VP will apparentiy polymerize with syndiotactic microstmcture, although proof is lacking (41—45). The reverse, polymerization of MAA in the presence of PVP, affords, as expected, atactic poly(MAA) (46,47). 

Atactic poly(methyl methacrylate/methacrylic acid), the copolymer of methyl methacrylate (MMA) and methacrylic acid (MAA), was synthesized "directly" as a prepolymer to be esterified with bis(tri-n-butyltin) oxide (TBTO). Two formulations of poly (MMA/MAA) were synthesized, a 1 1 and a 2 1 MMA and MAA copolymer whose syntheses differ only in the proportion of monomer reacted. 

Figure 2 X-ray diffractograms recorded at room temperature, (a) Metallocene-synthesized isotactic poly(propylene), mmmm — 0.996 crystallized at 145°C. (b) Atactic poly(propylene). Reproduced with permission from Ref. [43], Copyright John Wiley Sons, Inc., 1999.

In one example, the Tics of the non-crystalline methyl, methine and methylene carbons of iPP, 70% crystalline, were compared at room temperature with those of model atactic poly(propylene), hydrogenated poly(2-methyl-l,3-pentadiene) [163]. It was found that, within the experimental error, the Tic values of each of the carbons were the same in both polymers. The conclusion can then be reached that the fast segmental motion, at or near the Larmor frequency of... 

MHz, which determine the Tics, are the same for the non-crystalline region of isotactic poly(propylene) and for atactic poly(propylene). This in turn indicates that the disordered chain structure is the same for the two cases. 

Atactic poly(methyl methacrylate) is a noncrystalline glass. 

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. 

Fig. 5.12 Molecular structure of atactic poly(propylene oxide).

Alkane dehydrogenation has been demonstrated as a suitable method for the functionalization of polyolefins such as atactic poly(l-hexene) under homogeneous conditions (Equation 12.6) [23]. 

Figure 9. 90 MHz C NMR spectnim of atactic poly(vinyl alcohol) (148). From Ovenall, D.W. Macromolecules 19 4, 17, 1458. Copyright (1984) American Chemical Society.

Fig. 2. End projection of atactic poly(vinyl fluoride) [poly(l-fluoroethane-l,2-diyl)] chains in the crystalline state. Broken circles show fluorine atoms with 50% probability [16].

FIGURE 2.5 Skeletal formulas of isotactic, syndiotactic, and atactic poly(vinyl chloride) (PVC). 

Tewari and Srivastava published the results on interaction between atactic polyCvinyl acetate) and poly(acrylonitrile), and poly(methyl methacrylate) and poly(methacrylic acid). On the basis of viscometric measurements of DMF solutions of mixtures of the pair of polymers mentioned above, the authors concluded that for all the systems examined complex formation occurs. This observation explains the results published earlier by the authors about template polymerization of acrylonitrile, methacrylic acid, and methyl methacrylate carried out in the presence of poly(vinyl acetate). It was found that polymerization of acrylonitrile in DMF in the presence of atactic poly(vinyl acetate) (mol. weight 47,900) takes place much faster than without poly(vinyl acetate), especially, when concentration of the monomer is equimolar to the concentration of template repeat units. The overall energy of activation was found to be 55.76 kJ/mol for template polymerization and 77.01 kJ/mol for polymerization in the absence of the template. 

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 ). 

Powdered amorphous polymer such as atactic poly(styrene) or poly-(methyl methacrylate)... 

Figure 2. Infrared spectra of atactic poly(a,a-dimethylbenzyl methacrylate)s unexposed (A) and exposed(B) to electron-beam, isotactic poly (a,a-dimethylbenzyl methacrylate) exposed(C) and poly(methacrylic acid)(D). Exposure charge density 1.6 x 10-4 C/cm2, film thickness 0.5 pm, prebake at 142° C. Reproduced with permission from Ref. 2. Copyright 1983, "Springer...

When the atactic poly(a,a-dimethylbenzyl methacrylate) was heated at 170°C for 30 min under vacuum, it decomposed into volatile and nonvolatile components. The former was found to be a-methylstyrene and the latter was to be very similar to polyfmethacrylic acid) as determined by H NMR spectroscopy. Figure 3 shows the infrared spectra of atactic and isotactic poly(a,a-dimethylbenzyl methacrylate)s heated at 174°C under vacuum for various times. In the spectra of the atactic polymer, the absorption of the ester carbonyl at 1729 cm-1 decreased and that of the acid carbonyl at 1700 cm-1 increased as the heating time increased. After heating for a period of 30 min... 

Figure 3. Infrared spectra of isotactic and atactic poly(a,a-dimethylbenzyl methacrylate)s heated at 174° C under vacuum for various times.

Figure 4. Infrared spectra of (A) isobutyric anhydride, (B) glutaric anyhdride, and (C) isotactic and (D) atactic poly(a,a-dimethylbenzyl methacrylate)s heated at 174° C under vacuum for 2 and 3 hr, respectively.

Spectral subtraction usually provides a sensitive method for detecting small changes in the sample. Figure 5 shows the difference spectra between the atactic poly(a,a-dimethylbenzyl methacrylate) s unexposed and exposed to electron-beam at several doses. The positive absorption at 1729 cm-1 is due to the ester carbonyl group consumed on the exposure and the negative ones at 1700 and 1760 cm-1 to the acid and acid anhydride carbonyl groups formed, respectively. The formation of methacrylic acid units was more easily detected using the difference spectrum However, these difference spectra could not be used for the quantitative determination because the absorptions overlap somewhat. 

Figure 5. Difference infrared spectra between the atactic poly(a,a-dimethylbenzyl methacrylate)s unexposed and exposed to electron-beam of several doses. (A) 4x1 ( 5, (B) 1.6x1 0 4, (C) 7 x 1 ( 4 Clem1.

The osmotic pressure of solutions of a fractionated, atactic poly(isopropylacrylate) solution was measured at 25°C with the following results ... 

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. 

An independent proof of this finding was recently obtained by Ciardelli, Benedetti, Pieroni and Pino (23, 24) who prepared an atactic poly-(S)-4-xnethyl-1-hexene having [M] >5 = +190 from a poly-(S)-4-methyl-l-hexyne having an optical purity of about 89.5% as demonstrated by the optical purity of (S)-3-methyl-pentanoic acid obtained by ozonization of the unsaturated polymer. The rotatory power of the polymer thus prepared is very near to the rotatory power of the non crystallizable poly-(S)-4-methyl-l-hexene obtained from a monomer having a 93% optical purity (see Table 8). 

Section II, 4a. Optical activity and O.K.D. of (+)-tartaric acid salts of poly-2-vinyl pyridine having different stereoregularity have been determined the optical rotation between 578 m/r and 365 mfi of the salt of atactic poly-2-vinyl-pyridine is lower than that of the salt of the isotactic poly-vinyl-pyridine [R. C. Schulz and J. Schwaab Makromol. Chem. 85, 297 (1965)]. 

Otsuka et al. (110, 112) studied the polymerization of butadiene in the presence of an aged Co2(CO)8/2 MoC15 catalyst. The product obtained was predominantly an atactic poly(l,2-butadiene), the 1,2-structure being favored by low reaction temperature (e.g., at 40° C, 97% 1,2 at 30° C, > 99% 1,2). Similar experiments with a Ni(CO)4/MoCl5 catalyst yielded a polymer with 85% cis- 1,4-structure. The results of Otsuka et al. have been confirmed by Babitski and co-workers (8), who studied the polymerization of butadiene by a large number of binary catalysts, based on transition metal halide, transition metal carbonyl combinations. These systems are of interest as further examples of alkyl-free coordination polymerization catalysts for dienes (9, 15a, 109). Little is known of the origins of stereospecificity of these reactions. 

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