Microstructure of poly

The mechanism of chloroprene polymerization is summarized in Scheme 4.11. Coleman et ai9iM have applied l3C NMR in a detailed investigation of the microstructure of poly(chloroprene) also known as neoprene. They report a substantial dependence of the microstructure on temperature and perhaps on reaction conditions (Table 4.3). The polymer prepared at -150 °C essentially has a homogeneous 1,4-tra/rv-niicrostructure. The polymerization is less specific at higher temperatures. Note that different polymerization conditions were employed as well as different temperatures and the influence of these has not been considered separately. 

Finally it should be stressed that the complexation affects the microstructure of poly dienes. As was shown by Langer I56) small amounts of diamines added to hydrocarbon solutions of polymerizing lithium polydienes modify their structure from mainly 1,4 to a high percentage of vinyl unsaturation, e.g., for an equivalent amount of TMEDA at 0 °C 157) the fraction of the vinyl amounts to about 80%. Even more effective is 1,2-dipiperidinoethane, DIPIP. It produces close to 100% of vinyl units when added in equimolar amount to lithium in a polymerization of butadiene carried out at 5 °C 158 159), but it is slightly less effective in the polymerization of isoprene 160>. 

Table 20. Influence of Pressure and Initiator Concentration upon the Microstructure of Poly-2,3-dimethylbutadiene [monomer] = 3.75 molar...

Arndt, M. and Kaminsky, W., Microstructure of Poly(cycloolefin)s Produced by Metallocene/Methylaluminoxane (mao) Catalysts . Macromol. Symp., 97, 225-246 (1995). 

The microstructure of the discussed cycloaliphatic polymers concerns the cis-trans geometrical isomerism of the rings and the relative stereochemistry between the rings. A modified Bovey m-r nomenclature [507] provides a useful description of the microstructure of poly(methylene-l,3-cycloalkane)s, where capital letters (M for mesogenic, R for racemic) denote the stereochemistry of the rings and lower case letters ( m and r) denote the relative stereochemistry between the rings [503], Therefore, cA-isotactic, tram-isotactic, cA-syndiotactic and tram-syndiotactic cyclopolymers may be formed. As in many other cases, 13C NMR spectroscopy reveals information about both the tacticity of the polymer and the ratio of cis to treins rings. 

To our knowledge, there is only one study in which the influence of magnesium alkyl cocatalysts on microstructure of poly(diene)s was investigated. Duvakina et al. used the catalyst system Nd(d3/TBP/Mg( C4H9)( Q H17) for BD polymerization and investigated the influence of the molar ratio Mg/ Nd in the range of 6-60. This increase of Mg/ Nd led to a decrease in trans- 1,4-contents from 95 to 88-85% while the 1,2-content increased [135,136]. 

The molar ratio x/ Nd also influences the microstructure of poly(diene)s. Unfortunately, these studies are not consistent regarding the dependence of cis- 1,4-content on x/ Nd ratios. 

Table 26 Microstructure of poly(diene)s obtained by Nd catalysis [139], reproduced with permission of the American Chemical Society...

The mechanism is complicated by the possibility of anti-syn-isomerization and by n - a-rearrangements (it - r 3-allyl Act - r 1 -allyl). In the case of C2-unsubstituted dienes such as BD the syn-form is thermodynamically favored [646,647] whereas the anti-isomer is kinetically favored [648]. If monomer insertion is faster than the anti-syn-rearrangement the formation of the czs- 1,4-polymer is favored. A higher trans- 1,4-content is obtained if monomer insertion is slow compared to anti-syn-isomerization. Thus, the microstructure of the polymer (czs-1,4- and frazzs-1,4-structures) is a result of the ratio of the relative rates of monomer insertion and anti-syn-isomerization. As a consequence of these considerations an influence of monomer concentration on cis/trans-content of BR can be predicted as demonstrated by Sabirov et al. [649]. A reduction of monomer concentration results in a lower rate of monomer insertion and yields a higher trans-1,4-content. On the other hand the czs-1,4-content increases with increasing monomer concentration. These theoretical considerations were experimentally verified by Dolgoplosk et al. and Iovu et al. [133,650,651]. Furthermore, an increase of the polymerization temperature favors the formation of the kinetically controlled product and results in a higher cis- 1,4-content [486]. l,2-poly(butadiene) can be formed from the anti- as well as from the syn-isomer. In both cases 2,1-insertion occurs [486]. By the addition of electron donors the number of vacant coordination sites at the metal center is reduced. The reduction of coordination sites for BD results in the formation of the 1,2-polymer. In summary, the microstructure of poly(diene) depends on steric factors on the metal site, monomer concentration and temperature. 

Fig. 30. Possible microstructures of poly(methylenecyclopentane) produced by metal-locene/MAO catalysts from 1,5-hexadiene (137).

Rodriguez, C., Uddin, M.H., Watanabe, K., Furukawa, H., Harashima, A. and Kunieda, H. (2002) Self-organization, phase behavior, and microstructure of poly(oxyethylene) poly(dimethylsiloxane) surfactants in nonpolar oil. /. Phys. Chem. B, 106(1), 22-9. 

Microstructures of Poly(chlorofluoroethylene)s The carbon-13 NMR spectrum of PVCF consists of a —CH2— resonance at 54.1 ppm and a —CFC1— resonance at 108.8 ppm. There is no splitting of these lines due to tacticity, nor are there any other resonances to indicate the presence of regioirregular monomer sequences. However the polymer is stereoirregular, as shown by the fluorine-19 NMR spectrum in Figure 1. There are three principal resonances spread by 3 ppm owing to triad stereosequences, with some pentad fine structure which is barely resolved. 

King, E. and Cameron, R., Effect of hydrolytic degradation on the microstructure of poly(glycolic acid) an x-ray scattering and ultraviolet spectrophotometry study of wet samples, /. Appl. Polym. Sci, 66, 1681, 1997. 

Block copolymers can also be hydrogenated to produce unique products. Hydrogenated triblock copolymers of poly(styrene-co-butadiene-co-styrene) (SBS) are commercially available from the Shell Company under the trade name Kraton G. The middle block is usually a mixed microstructure of poly( 1,2-butadiene) and poly( 1,4-butadiene) units. The resulting product is a hydrogenated unsaturated polymer, which exhibits greater thermal and oxidative properties than the parent SBS triblock. 

Table 2 shows the microstructure of poly(methacry4ic ester)s which were prepared with radical initiators. Most methacrylates gave rather diotactic pdymers. How-... 

Faivre, A., David, L., VassoUle, R., Vigier, G., Etienne, S., and Geissler, E., Electronic density fluctuations in disordered systems 1. Effect of thermal treatments bon the dynamics and local microstructure of poly(methyl methacrylate). Macromolecules, 29, 8387-8390 (1996). 

Figure 9.5.4 Microstructure of poly (cis-1,4-isoprene) (a) for latex plants other than Hevea and (b) for Hevea.

Table 18-6. Microstructure of Poly dienes Polymerized with Alkali Metals in Hydrocarbons...

Xie, R., Chu, L.-Y., Chen, W.-M., Xiao, W., Wang, H.-D. and Qu, J.-B. 2005. Characterization of microstructure of poly(N-isopropylamide)-grafted polycarbonate track-etched membranes prepared by plasma-graft pore-filling polymerization.. 7. Memh. Sci. 258 157-166. 

WillcoxPJ, Howie DW Jr, Schimdt-Rohr K, Hoagland A, Gido SP, Pudjijanto S, Kleiner LW, Venkatraman S (1999) Microstructure of poly(vinyl alcohol) hydrogels produced by freeze/ thaw cycling. J Polym Sci Part B Polym Phys 37 3438... 

Cha WI, Hyon SH, Ikada Y (1993) Microstructure of poly(vinyl alcohol) hydrogels investigated with differential scanning calorimetry. Macromol Chem Phys 194 2433-2441... 

The microstructure of poly(2,4-hexadiene) was charactereized by IR and NMR. The H-NMR spectra (Figure 9) showed that the microstructure of pol3nner obtained is prevailingly in a 1,4-addition. Carbon-13 NMR (Figure 10) indicated that the 1,4-addition leads to a predominantly trans-structure. Carbon-13 NMR also revealed that the 1,4-trans unit might have two kinds of stereoisomers which are due to the two asymmetric carbon atoms, i.e., the... 

The microstructure of poly(methyl methacrylate) (PMMA) was studied by using NMR H spectroscopy on the spectrophotometer AM-400 fiom Bruket [10] samples of polymers synthesized in the presence of DC were obtained at the initial stage of polymerization (conversion was 5%) as described [11], was isolated by precipitation from acetone solution in the methanol, dried under vacuum to constant weight at 40°C. 

Shown [4] that not only the velocity and degree of polymerization of MMA but also the microstructure of poly (methyl methacrylate) (PMMA) can be regulated in the presence of cyclic hexamethylenetetramine. 

Kleinschmidt, R. Reffke, M. Fink, G Investigation of the microstructure of poly(propylene) in dependence of the polymerization temperature for the systems Pr[3-RCpFlu]ZrCl2/MAO, with R = H, Me, Et, Pr, Bu, and Pr[IndHu]ZrCl2/MAO. Macromol. Rapid Common. 1999, 20, 284-288. 

Babu, G. N. Newmark, R. A. Chien, J. C. W. Microstructure of poly(1-hexene) produced by ansa-zirconocenium catalysis. Macromolecules 1994, 27, 3383-3388. 

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