Ethylene/propylene copolymers comonomers

As an example of the use of MIXCO.TRIAD, an analysis of comonomer triad distribution of several ethylene-propylene copolymer samples will be delineated. The theoretical triad Intensities corresponding to the 2-state B/B and 3-state B/B/B mixture models are given In Table VI. Abls, et al (19) had earlier published the HMR triad data on ethylene-propylene samples made through continuous polymerization with heterogeneous titanium catalysts. The data can be readily fitted to the two-state B/B model. The results for samples 2 and 5 are shown In Table VII. The mean deviation (R) between the observed and the calculated Intensities Is less than 1% absolute, and certainly less than the experimental error In the HMR Intensity determination. 

Since the discovery of olefin polymerization using the Ziegler-Natta eatalyst, polyolefin has become one of the most important polymers produeed industrially. In particular, polyethylene, polypropylene and ethylene-propylene copolymers have been widely used as commercial products. High resolution solution NMR has become the most powerful analytieal method used to investigate the microstructures of these polymers. It is well known that the tacticity and comonomer sequence distribution are important factors for determining the mechanical properties of these copolymers. Furthermore, information on polymer microstructures from the analysis of solution NMR has added to an understanding of the mechanism of polymerization. 

An in-reactor TPO may be defined as a reactor-produced polypropylene copolymer (PP-b-E/P), containing between 22 % and 55 % ethylene-propylene copolymer blocks. Small amounts of other comonomers, such as octene-1 or butene-1, may also be present so as to provide unique functionality. In-reactor propylene block copolymers containing less than 20 % ethylene are fairly hard and are usually classified as impact polypropylenes. Reactor-made polymers containing >50 % ethylene are soft and also have relatively poor elastomeric properties - these are classified as plastomers. 

Ethylene/Propylene Copolymers Intramolecular Distribution of THE Comonomers... 

Ethylene may be copolymerized with numerous monomers but only a few such copolymers have achieved commercial status. The more important comonomers are propylene, 1-butene, vinyl acetate, ethyl acrylate and carboxylic acids. Ethylene-propylene copolymers are particularly important and are discussed in Sections 2.7 and 2.8. 

Paxson and Randall [38] in their method use the reference chemical shift data obtained on a predominantly isotactic polypropylene and on an ethylene-propylene copolymer (97% ethylene). They concluded that the three ethylene-propylene copolymers used in their study (97-99% propylene) contained principally isolated ethylene-ethylene linkages. Knowing the structure of their three ethylene-propylene copolymers, they used the C-NMR relative intensities to determine ethylene-propylene contents and thereby establish reference copolymers for the faster IR method involving measurements at 732 cm (13.66 pm). After a detailed analysis of resonances Paxson and Randall [38] concluded that methine resonances 4 and 5 (Table 10.1) gave the best quantitative results to determine the comonomers composition. The composition of the ethylene-propylene copolymers was determined by peak heights using the methine resonances only. In no instance was there any evidence for an inclusion of consecutive ethylene units. Thus, composition data from C-NMR could now be used to establish an IR method based on a correlation with the 732 (13.66 pm) band which is attributed to a rocking mode, r, of the methylene... 

Hexafluoropropylene (CF3CF=CF2) is used as a comonomer in a number of fluoropolymers such as flu-orinated ethylene-propylene copolymer. It is also used to modify the properties of homofluoropolymers. It was first prepared by Benning, et al.,P l by pyrolysis. They identified this compound as hexafluoro-cyclopropane, erroneously. The full synthesis and identification of HFP was conducted by Henne. l A six step reaction scheme beginning with the fluorination of 1,2,3-trichloropropane (CICH2CHCICH2CI) led to 1,2-dichlorohexafluoropropane (CICF2CFCICF3). The latter was dehalogenated with zinc in boiling ethanol to yield hexafluoropropylene. 

Ray and co-workers [18] determined comonomer content in isotactic ethylene-propylene copolymers, complete diad and triad content as well as partial tetrad and... 

The chemical shift calculation (y-effect method) based on the y-effect of the chemical shift and the rotational isomeric state model (RIS model) has been developed as a reliable method for predicting chemical shift differences among pentad, hexad, and heptad sequences in various polyolefins [47-49, 14, 50, 51]. chemical shift assignments of tactic pentad and heptad sequences in polypropylene have been provided by this method [47-49]. Hayashi and co-workers [45,46] confirmed that the chemical shift due to the y-effect is also sensitive to different comonomer sequences in ethylene-propylene copolymers. Asakura and co-workers [52] have demonstrated that... 

This avoids problems associated with propylene inversion and comonomer sequence assignment. He gives methylene sequence distributions from one to six and larger consecutive methylene carbons for a range of ethylene-propylene copolymers, and uses this to distinguish copolymers which have either random, blocked or alternating comonomer sequences. 

Perez and Vanderhart [60] investigated the morphological partitioning of chain ends and methyl branches in ethylene copolymers by C-NMR in the solid state. The PE samples, which were crystallised from the melt, varied in molecular weight, polydispersity, crystallisation rate, and comonomer content. For the limited set of samples considered, the ratio of crystal to overall end concentration is independent of those variables. This ratio takes the values of 0.75 and 0.60 for the methyl and vinyl ends, respectively. When the crystalline fraction of these samples is taken into account, 50-75% of the total saturated ends and 42-63% of the total vinyls reside in the crystal. For an ethylene/propylene copolymer, 21-27% of the methyl branches were determined to be in the crystal. This level of incorporation puts methyl branches in a position intermediate between chain ends and ethyl branches. 

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