Copolymer spectra

The assignments of the v (CH2) bands in terms of the assumed model are not entirely unambiguous. Two strong a bands and two weak 7t bands [re (CH2)0 is probably close to zero intensity] are predicted. In pure PVdC four bands are found, all apparently of a polarization. Two of these, however, at 2850 and 2930 cm-1, are of highly variable intensity in the copolymer spectra they become quite weak in comparison to the other two at 2948 and 2990 cm-1 [Narita, Ichinohe, and Enomoto (747) quote frequency values of 2966 and 3010 cm-1 for these two bands]. A possible explanation is that the 2850 and 2930 cm-1 bands are associated with amorphous structures, while the 2948 and 2990 cm-1 bands are associated with the Fuller structure. We would then have to assume that the vtt (CH2)0 mode is too weak to be observed. It is clear that these proposals require additional confirmation. 

C-NMR spectroscopy has also been used to investigate the composition of DADMAC copolymers [38, 45-47]. Copolymers with acrylamide (AAM) have been extensively studied. Based on the chemical shifts in the 13C-NMR spectra of the homopolymers of DADMAC [17-19] and AAM [48-50], the copolymer spectra can be analyzed. Specifically from two likely chad structures (m/r) in PAAM and six different diad structures (r/m, c/t) in PDADMAC, eight different diad structures can be expected for the copolymers. A detailed NMR analysis has therefore been carried out in order to determine the copolymer compositions. The reactivity ratios obtained were found to be in good agreement with the results from other methods, such as potentiometric titration or elementary analysis, provided that the DADMAC in the copolymer was below approximately 70% [38]. 

The range from 1.4 to 3.0S in the >ectrum is as gned to various methylene proton resonances. The indivMual assignments shown in Fig. 2 become obvious upon an examination of the ctra of the respective homopolymers. Evidently the petitions of the various methylene bands in the copolymer spectra are determined by their respective distances from the unsaturation. Thus protons a to the double bond appear at arotmd 2.0S,P protons resonate at around 1.76, and nrotons farther away appear at 1.46. 

Unfortunately, our carbon 13 and proton data (Table II) taken together with other data for the model compounds, do not allow an unambiguous assignment of the 3 stereoisomers which we have obtained. For the present, then, we must be content to leave the relative stereochemistry of the 5-membered ring model compounds in question. For now, we can only say that the fine structure in the copolymer spectra are certainly well within isomers shifts seen for the model compound. However, based on the fact that the relative stereochemistry of the tetrahydrofuran models are unknown and that we have only one pyran isomer, we are unable to make a definite assignment as to the relative stereochemistry of ring junctions in the original copolymer. 

The Infrared spectrum of the SMA copolymer labeled SMA-2, is consistent with other SMA copolymer spectra published (33). However, the absorption peaks in the range of 1700 - 1820 cm indicate that this copolymer has been partially esterified to yield a half/acid ester of maleic anhydride which should exhibit peaks in the range of 1700 - 1725 cm"l and 1735 -1750 cm (Figure 3). The small absorption bands at 1780 and 1820 cm indicate the presence of a small amount of unreacted maleic anhydride. These data appear to be consistent for those of a styrene-maleic anhydride copolymer reported by Muskat (34). The carbon, hydrogen, oxygen analyses indicate that this polymer is a half/acid ester of a 90% styrene/10% maleic anhydride copolymer wherein theoretical values of C, H and 0 are 88.89%, 7.017. and 2.58% versus values of 89.14%, 7.68% and 2.81% found for C, H and 0, respectively. The solubility parameter was found to be equal to 9.47 H. 

For syndiotactic polypropylene, the band at 11.54 ja has been very useful for the determination of the helix content and, indirectly, of the steric structure. The ratio Is between the absorbance of this band and the mean value of the two bands at 2.32 and 2.35 p has been called the index of syndiotacticity (97). The proportionality between Is and the content of crystalline form in the samples was checked by density measurements these, combined with a knowledge of the volume of the unit cell, allowed a direct, though approximate, evaluation of the crystallinity of the samples. The concept of syndiotacticity index was extended to C3— butene 1 copolymers (96) and can be applied to C2-C3 copolymers as well (98). Its value is strongly dependent upon the preliminary thermal treatment of the copolymer (spectra are recorded on samples annealed at 80° C for 12 hours) this is why standard values are not usually given. 

Figure 4.72 The Raman and FTIR spectra of a 10 p,m fiber of a nylon 6-polyethylene glycol block copolymer. Spectra were collected at exactly the same spot on the fiber with the JYHoriba LabRam-IR microscope with Same Spot technology. [Courtesy of Jobin Yvon, Horiba Group, Edison, NJ (www.jyhoriha.com).]...

The copolymer spectra recorded at 40 C showed appreciable splitting. These signals were assigned on the basis of comparison of spectra with that of homopolymers. The assignment of the various peaks was made by comparing the relative intensities of the signals for all the three copolymers. 

There are two types of styrene-butadiene copolymer a random copolymer and a block copolymer. Spectra for the block and random styrene-butadiene copolymers are provided in Reference Spectra 15 and 16, respectively. For a full characterization of SBR it is necessary to determine the composition in terms of the monomer ratios, including the three configurations of the butadiene addition reaction components, and to be able to differentiate random and block copolymerization. 

Figure 2 depicts the plasmon absorbance of gold colloids obtained by reduction of LiAuCU by hydrazine hydrate in toluene, in the presence of different block copolymers. Spectra were recorded directly after reduction and after 700 hours (29 days). It is well established that the plasmon absorbance peak is sensitive to the size of the Au-particles (7d). Right after reduction, was found to increase with increasing PEO block length of the block copolymer for PS(580)-b-PEO(45), PS(610)-b-PEO(80), and PS(540)-b-PEO(220) respectively 518, 533 and 542 nm. In the case of PS(580)-b-PEO(45), a new shoulder around 620 nm had appeared after 700 hours beside the plasmon absorbance peak which had shifted to 535 nm. For this sample, a gradual blue coloration and a dark precipitate was observed after several days. In the case of the other block copolymer/gold solutions, the shift of the plasmon absorbance was less pronounced. The absorbance band remained rather narrow and Xmxx. did not exceed 545 nm. 

H-stretching band, alkyl alcohols or water vO-H and 50-H combination reported in the literature from ethylene-vinyl alcohol copolymer spectra, probably better assigned as 2vO-H Alcohols or water 0-H CD 0 3 cb "D... 

Analysis of presented copolymer spectra shows DAAH to copolymerize with VM and SO2, both double bonds participating, with formation of cis-, trans-stereoisomeric pyrrolidine structures in cyclolinear polymer chain in the proportion 4 1. 

The influence of spin-spin interactions and of asymmetric repeating units on the quality of copolymer spectra can be seen by comparing Fig. 1 with Fig. 2,... 

When aromatic units are present in copolymers, spectra interpretation can be even more complex than in strictly aliphatic systems. This is because of the strong diamagnetic shielding that can result from aromatic units. As shown in Fig. 3, the local magnetic field in the vicinity of the face of an aromatic ring is... 

In our own laboratories, Dr. Masao Murano [52] has used Mochel s methods to study the aromatic proton resonance patterns obtained with styrene-MMA copolymers. Spectra recorded with a 100 MHz spectrometer revealed separate resonances for the o- and (m + p)-aromatic protons of isolated styrene units. Six curves were therefore used to reproduce each observed aromatic proton resonance pattern gaussian curves were used to represent the resonance of o-aromatic protons lorentzian curves were used to represent the resonance of (m + p)-aromatic protons. The o- and (m + p)-resonance areas corresponding to protons in each type of styrene centered triad were maintained in a 2 3 ratio. It proved possible to obtain an excellent fit of observed aromatic resonance patterns to calculated triad distributions for copolymers of all compositions. Fig. 14 shows how the aromatic proton resonance pattern for one copolymer could be matched by summing o- and (m + p)-curves representing the various possible... 

Table 4.1 Calibration points for the composition analysis of C2-C3 copolymers (spectra recorded at 160 °C) ...

New bands arise due to defect vibrations (local modes) the position of these bands is determined by the nature of tte defect. In copolymer spectra the new bands are generally speaking those of the second comonomer. 

A 220-MHz PMR study of ethylene-propylene copolymers is reported (122) and (132). A comparison between the spectra of polypropylene (133) and that of hydrogenated rubber (the model for the alternating copolymers) (122) enabled the authors to assign some resonances in the copolymer spectra, but the assignment of some peaks remains dubious and precludes direct comparison with statistics. 

It is well known that the usual Ziegler-Natta catalysts do not directly polymerize -olefins but that they can copolymerize them with some a-olefins. A good example of this phenomenon is the ethylene-butene-2 copolymerization, which has been thoroughly studied (13). The butene-2 content of the copolymers was measured radiochemically or by the IR method with the 1380 cm band. The absence of significant isomerization of butene-2 to butene-1 was proved by the absence from the copolymer spectra of the 773 cm band (ethyl branching). 

A new band was found in the IR spectra of these copol3mers at 1240 cm" (55) with the maximum absolute intensity in the 1 1 copolymer spectra and was considered to be characteristic for propylene-butene-1 random copolymers. 

The IR spectra demonstrate that real copolymerization of these monomers takes place when TiCl4— Al(koC4H9)3 is used as the catalyst system The 778 cm band [the helix band of poly-3-methylbutene-l, see Section II.C.2e] disappears from tte copolymer spectra, b inning from 50% vinyl cyclohexane content, and the relative intensity of the 1120cm band decreases significantly ... 

The unit distribution was estimated by IR and melting-point methods. IR data for the 4-methylpentene-l unite are based on the relative intensity of the 997 cm band in the copolymer spectra (Fig. 10) and show that these copolymers have a significant tendency to blodc formation ( i f2 3—5). This conclusion was supported by melting-point measurements 114,167). The copolymer melting points are evidently lower than those for homopolymer mixtures, thus demonstrating that a real copolymerization takes place (167), but they have an upward deviation from the theoretical curve calculated for the random copolymer model by means of the Flory equation (Section III.E) with d ff = 4710 kal/ mol (171). 

Dyad, triad and higher n-add distributions can be calculated using the above-mentioned quantities and used for interpreting copolymer spectra. The reader is referred to other articles for detailed information about the statistical calculation of copolymer... 

Ray, Johnston and Knox [75] investigated the c-spectra of ethylene-propylene copoli ers prepared with an isospecific catalyst system. The absence of propylene head-to-head or tail-to-tail inversions in these copolymers and their essentially complete isotactic enchainment enabled their spectra to be analyzed precisely. Assignments made previously for atactic ethylene-propylene copolymers, together with new assignments made possible by the simplicity of the isotactic copolymer spectra were used to obtain all n-add distributions through triads, P-P and E-E-centered tetrad distributions, and a number of pentad distributions. 

The comparison of spectra of copolymers with different norbomene content, obtained by catalysts with different symmetries, has helped to assign a number of resonances. However, use of this method alone is rather limited in the case of E-N copolymer spectra. C-NMR investigations based on a comparison between E-N copolymers of monomers with natural abundance of and those obtained with... 

The approach to interpreting the spectra of the copolymers is empirical. First, the copolymer spectra for a wide range of comonomer compositions are obtained, and then the spectra are examined by using the following steps. 

Significant differences are, however observed between the various spectra in the wavelength region from 13.0 to 13.7 pm. None of the copolymer spectra shows a clear shoulder at 13.53 pm where hydrogenated polyisoprene shows maximum absorption. 

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