Partially deuterated polymers

This model had been proposed by Fowells et al. (17) on the basis of NMR measurements of partially deuterated polymers prepared in the system THF/Li, and it was applied by Fisher and Szwarc (3o) and Sigwalt and coworkers (31,32)to the polymerization of 2-vinyl pyridine. 

While it cannot be said that all of the assignments in the spectrum of PVdC are satisfactorily established, it would seem that the majority are. The important ones from the standpoint of the chain structure are the v (CC12) modes, and the present evidence on their assignment supports the correctness of the Fuller structure. A study of a partially deuterated polymer might be of further assistance in this respect. What is also clearly needed is a more detailed study of the skeletal modes to be expected from the proposed chain structure, since these clearly contribute significantly to the spectrum. Finally, knowledge of the crystal structure might permit more to be said on the nature of interchain interactions and their effect on the spectrum. 

Since its introduction in the early 1970s, the small angle neutron scattering (SANS) method has had a substantial impact on polymer research. When used with partially deuterated polymers, SANS permits a close monitoring of macro-molecular conformations in polymer solutions, melts, and blend mixtures. This advantage has made it a unique tool for the understanding of the morphology of polymer materials and of the relationship between their structures and physical properties. 

In a similar maimer, thermal degradation mechanisms of fully aromatic polyesters were investigated in detail by Py-GC/MS using a partially deuterated polymer sample. Moreover, the mechanisms of reactive pyrolysis of the same aromatic polyester in the presence of tetramethylammonium hydroxide (TMAH) was also studied by Py-GC/MS. In this case, the contribution of solvent (methanol) to the reaction was confirmed by use of a deuterated methanol solution of TMAH. 

Notes The values of A, B, and C and thus of y are based on a reference volume Vre/ = 0.1 nm Polymer notation A d- label preceding the polymer acronym indicates a per-deuterated polymer partially deuterated polymers are labeled as dy, df, etc., for selective deuteration of 3, 4, etc., hydrogens. Numbers in subscripted parentheses after the polymer name indicate the primary comonomer fraction, e.g., SPB(6s) is a saturated polybutadiene with 66 mol% butadiene Polymer acronyms P2VP poly(2-vinyl pyridine), P4MS poly(4-methylstyrene), PBMA poly(n-butyl methacrylate), PCHA poly(cyclohexyl acrylate), PEB poly(ethyl butylene), PIB polyisobutylene, PI polyisoprene, PMMA poly(methyl methacrylate), PPMA poly(n-pentyl methacrylate), PP polypropylene, HHPP head-to-head polypropylene, PS polystyrene, PVME poly(vinyl methyl ether), PXE poly(2,6-dimethyl-l,4-phenylene oxide), SPB saturated polybutadiene, SPI saturated polyisoprene... 

Small-angle neutron scattering may be used to measure the size of the molecular envelope, which is usually expressed as the radius of gyration of the molecule. This is achieved by dissolving partially deuterated polymers in undeuterated material. Experiments of this type have been reported by Kirste and Ohm and by Keller et Both studied methacrylate-based side-chain liquid crystal polymers in which only the backbone was deuterated. Kirste and Ohm used the... 

The effects of spin-spin coupling on the spectra of polymers can be eliminated by decoupling experiments or by investigating partially deuterated polymers. 

These are usually badly overlapped and deuterated polymers must be studied if stereosequences are to be evaluated. Although the chemical shifts of protons in various stereosequences in polymers are very similar dyad and triad distributions are generally measurable and studies on partially deuterated polymers often enable tetrad and pentad sequence distributions to be measured [41-47]. In a few instances, shift reagents have been helpful in separating resonances of various stereosequences in polymers [48-50], but they are much more valuable for studies on copolymers than for homopolymers. ... 

We have learned from neutron scattering on partially deuterated polymers that the molecules exhibit a random configuration, at least on a nonlocal scale, provided, of course, that we restrict... 

The use of an electric field is not the only effective way to influence the LC polymer structure, magnetic fields displays a closely similar effect167 168). It is interesting as a method allowing to orient LC polymers, as well as from the viewpoint of determining some parameters, such as the order parameter, values of magnetic susceptibility, rotational viscosity and others. Some relationships established for LC polymer 1 (Table 15), its blends with low-molecular liquid crystals and partially deuterated polyacrylate (polymer 4, Table 15) specially synthesized for NMR studies can be summarized as follows ... 

The above study is noteworthy for a few reasons. Firstly, the data were obtained using only one partially deuterated form of the amphiphilic molecules of interest. Secondly, while SANS studies of polymers at a contrast-matched interface are common, the work of Riley et al. is unique owing to the small size of the core particle and the fact that it was the off-contrast match data that provided the more detailed structural information via solvent contrast variation. 

In a series of experiments on //-containing materials, starting with an experiment on partially deuterated water [Chatzidimitriou-Dreismann 1997 (a)] and later continued with polymers [Chatzidimitriou-Dreismann 2000 (b)], metal hydrides [Chatzidimitriou-Dreismann 2001] etc., it was found that the normalized area ratios Ah /Ad, Ah/A0, and, 4 n/AMetai, did not agree with the expected ratios Ah/Ad = uh/o d, etc., where the an s are the tabulated neutron total scattering CS, but were reduced by up to 30%. This loss of intensity was interpreted as a short-time effect, mainly involving the 77-nuclei (since heavier atoms are observed on a longer time scale and are supposed to be less sensitive to quantum effects). 

The peak at 0.97 ppm in the spectrum in Fig. 7 should be due to the proton of this partially deuterated methyl group. As mentioned above, the Tx for this peak was much longer than those for other two peaks. The longer should be due to the loss of dipolar relaxation from the two protons in the methyl group. The amount of CHD2 group was determined to be 0.71 per polymer molecule. On the other hand, some coinitiator is usually necessary for the cationic polymerization of styrene by metal halide.52 In this work the coinitiator was a small amount of water which was admitted incidentally into the reaction mixture. 

This means that the partially deuterated methyl group was introduced into the polymer chain by the initiation reaction as well as the chain transfer reaction. The difference between the number of terminal CHD2 groups and the number of toluene fragments corresponds to the amount of water which... 

High molecular weight samples of the polyformal were kindly supplied by General Electric. The structure of the repeat unit is shown in Figure 1 as well as the structure of a partially deuter-ated form which was synthesized (9) to reduce proton crossrelaxation. A 10 weight percent solution of the polymer in deu-terated tetrachloroethane was prepared in an NMR tube, subjected to five freeze, pump, thaw cycles and sealed. 

In the case of H-Ti the mechanism of relaxation is rather complicated and the observed Tj cannot be directly related to the segmental mobility of pdymer. However, the H-T s of pdy(alkyl methaciylate)s were found to be parallel with C-Ti s namely, the T of the protons in isotactic pdymer was alw s longer than that of the comparable protons in syndiotactic polymer. The study of the H-T in partially deuterated and undeuterated poly(methj4 methacrylate)s indicated that the T s of the protons in the side chain groups were mainly controlled by the segmental motion of the polymer chain and that the longer Tj s of side chain protons in isotactic polymer were due to the greater mobility of the pdymer chain compared with the syndiotactic one. ... 

As already mentioned, SANS on partially deuterated networks allows a direct measurement of polymer chain deformation (stretching or swelling). This makes SANS a unique tool for assessing the validity of theoretical models of polymer... 

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