13C NMR spectra, of the polymers

Many of the older bis-indenyl catalysts are less selective at higher temperatures, which was ascribed initially to a lower selectivity of the insertion reaction itself. More recent work by Busico, based on deuteration studies and again based on very detailed and elegant analysis of 13C NMR spectra of the polymers, has shown that in fact epimerisation of the growing alkyl chain occurs via a series of (3-hydride eliminations and re-insertion reactions [36] involving even tertiary alkyl zirconium species. 

NMR Spectra. 13C NMR spectra of the polymers and depolymerization residues were obtained on two instruments an IBM Instruments WP-200 (operating at a 13C resonance frequency of 50.33 MHz, equipped with high-power amplifiers and a Doty Scientific probe for MAS at 5.0 kHz) and a homebuilt solid-state NMR spectrometer operating at 31.94 MHz and a spinning speed of 3.0 kHz. 

Polymers of 208 can be made with cis contents ranging from 97% (OSCI3 catalyst) to 20% (MoCl5/Me4Sn/Et20 catalyst) a somewhat narrower range (80-33%) is observed for polymers of 209. The 13C NMR spectra of the polymers of 208, containing mainly... 

Miscellaneous. NMR spectra of 1,3-dioxolanes were obtained with a Varian A-60 spectrometer. 1H- and 13C-NMR spectra of the polymers were obtained with a JEOL FX-100 spectrometer. The molecular weight was determined by gel permeation chromatography (Toyo Soda HLC-802UR) using monodisperse polystyrene as reference. 

Figure 5 compares 13C-NMR spectra of the polymers prepared at different temperatures. The main structure A becomes predominant at a low polymerization temperature as shown in Figure 5a, but the content of the other structures, particularly the branched cis ring B, increases at a higher temperature(Figure 5b). The fraction of structure A Increased from 66 to 89 X by lowering the polymerization temperature from 70 to 10°C at a fixed monomer concentration of 2.5 mol/1.

NMR Measurements - 1H- and 13C- NMR spectra of the polymers in CDCI3 solution at ambient temperature were recorded at 300 and 20 MHz, respectively, using Varian HR-300 (CW mode) and CFT-20 (FT mode) spectrometers. The 13C-NMR spectra were the result of over 100 K accumulations using a pulse width of lOy sec. Tetramethylsilane was used as an internal standard. 

Figure 2. 13C NMR spectra of the TrMPTrA liquid monomer (lower) and solid polymer (upper).

C and H NMR spectra of the polymer isolated after irradiation show the formation of essentially pure p-hydroxystyrene polymer but provide no... 

The 300 MHz H NMR and 20 MHz 13C NMR spectra of poly(4-methyl-l-pentene) have been found to be more complex than the corresponding spectra of poly(3-methyl-l-butene) due to the presence of an additional isomer structure in the polymer. Investigation of the 20 MHz 13C NMR spectrum of the polymer has indicated that placement of units in different triad sequences is die cause of multiple methyl proton resonances which have been observed in the H NMR spectra of poly(3-methyl-l-butene) and poly(4-methyl-l-pentene). The use of a computer program for simulating and plotting spectra has enabled measurements of polymer composition to be made of poly(4-methyl-l-pentene) s prepared under a variety of synthesis conditions. 

As illustrated in Fig. 24, the addition of ethylene during the living polymerization of propylene resulted in rapid increases in both yield and Mn of the polymers. After the rapid increases which required several minutes, yield and lVln increased by a slower rate, identical with that of the propylene homopolymerization. The propylene content in the resulting polymers attained a minimum value several minutes after the addition of ethylene. These results indicate that the second stage of the polymerization with ethylene was complete within several minutes to afford a diblock copolymer, followed by the third stage of propylene homopolymerization leading to the formation of a triblock copolymer. The 13C NMR spectra of the diblock copolymers showed that the second block was composed of an ethylene-propylene random copolymer sequence. 

Transfer to A1 was reported to be operative with several non-metallocene catalysts. It is the only chain-release mechanism operative with the diamido complexes MCl2 ArN(CH2) NAr catalysts, as well as with the mono-and tris(benzamidinate) catalysts, since no olefinic resonances were observed in the H or 13C NMR spectra of these polymers.275 276 This chain-release reaction is also dominant with bis(phenoxy-imine)zirconium cat-... 

Of all the catalyst types, the sterically fluxional bis(2-arylindenyl) complexes749,752-768 produce elastomeric PP with the best combination of properties, that is, relatively high melting points and very low crystallinity, due to their stereoblock nature,769-772 but unfortunately their activity and molecular mass capability are too low at industrial polymerization temperatures (60-80 °C). The mechanism of stereoblock formation originally proposed by the inventors74 has recently been questioned and an active role of the counterion has been proposed to better account for the heptad distribution in the 13C NMR spectra of the elastomeric, stereoblock pp 773>773a These polymers are PP reactor blends, since they can be fractionated with solvents into low- and high-tacticity components.162,767,769,770,774,775... 

Polymer Properties. Preliminary studies are being carried out with the various cross-linked polymers using 13C NMR spectroscopy to determine the changes in structure that occur with different pH changes and with different metal ions present. Of particular interest have been samples of cross-linked resins XIII and XIV that have been hydrolyzed to the amino acid polypyrrolidines XVII and XVIII, respectively. In these cases there are extensive changes in the 13C NMR spectra of the water-swollen polymers depending on whether the conditions are acidic, basic, or neutral (Figure 5). 

C 1-NMR spectroscopy is the method of choice for determining the molecular structure of polymers in solution [230]. Polyolefin 13C NMR is mainly quantitative ID 1-NMR multiple pulse techniques are used for spectral interpretation. The resolution obtained in 13C NMR spectra of LDPE is an order of magnitude larger than in the corresponding 1H-NMR spectra... 

The nucleophilic substitution on poly(vinyl chloroformate) with phenol under phase transfer catalysis conditions has been studied. The 13c-NMR spectra of partly modified polymers have been examined in detail in the region of the tertiary carbon atoms of the main chain. The results have shown that the substitution reaction proceeds without degradation of the polymer and selectively with the chloroformate functions belonging to the different triads, isotactic sequences being the most reactive ones. 

Moreover it has been shown that PV0CC1 prepared by free-radical polymerization of vinyl chloroformate (V0CC1) is an atactic polymer having a Bernouillian statistical distribution as expected (J[9). In order to extend our studies on the chemical modification of PV0CC1, the stereoselective character of the nucleophilic substitution of the chloroformate units with phenol has been examined by the study of the 13c-NMR spectra of partly modified polymers in the region of the aliphatic methine carbon atoms. The results obtained in this field are presented here. 

For NMR spectroscopic experiments, a thin film of pTrMPTrA was prepared by reacting a quantity of monomer and photoinitiator confined between glass plates with 1 mm separation. The polymerization conditions were the same as those for the photocalorimetry experiments. After 1 hour of UV exposure, the film was removed from the plates and ground to a fine powder using a mortar and pestle. A solid-state 13C NMR spectrum of the powder was obtained immediately, as described below. The remaining polymer powder was divided into two portions, one of which was stored under atmospheric conditions. The other portion was stored under N2. After one week, 13c spectra were again obtained for each of these polymer samples. Both samples were then heated to 280 °C in a vacuum oven and analyzed once more by 13C NMR spectroscopy. 

Figure 9 exhibits the 13C NMR spectra of 50 and 52. The monomer has acetylenic carbon peaks at 70 and 82 ppm, but 52 does not show these peaks. Instead, the olefinic carbon peaks of the 52 backbone appear at 123 and 141 ppm, although the value for the quaternary carbon is very weak. The peak of the methylene carbon adjacent to the polymer backbone is shifted from 20 to 43 ppm on polymerization. 

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