Morphology nascent

Since the publication by the discoverers (3) of chromium oxide catalysts a considerable number of papers devoted to this subject have appeared. Most of them (20-72) deal either with the study of the chromium species on the catalyst surface or with the problem of which of this species is responsible for polymerization. Fewer results have been published on the study of processes determining the polymer molecular weight (78-77) and kinetics of polymerization (78-99). A few papers describe nascent morphology of the polymer formed (100-103). 

For the analysis of the role of monomer diffusion during ethylene polymerization while forming a solid polymer a model of the polymer grain (see Fig. 2) has been suggested (95). This model is consistent with the results of the study of nascent morphology of the polymer and its porosity (95, 100, 103). According to this model three levels are considered in the analysis of transport phenomena. 

Future challenges for polymerization model catalysts are to study the structure of polymers below their melting point in what is called the nascent morphology. Such work can be undertaken on silica-supported chromium catalysts as discussed above, or on so-called single-site catalysts, such as metallocenes, applied on flat silica supports. 

The polymers were characterized by their compositions, intrinsic viscosities, crystallinities and nascent morphologies. Copolymer compositions were measured by IR spectroscopy. Samples were prepared by hot pressing about SOmg.of polymer between aluminium foil at 170 C and 100 kg x cm pressure during 60 s. After removal from the press, they were water-cooled to ambient temperature for about 5 min. Films of approximately lOOp thickness were annealed at 106 C under N2 for 168 h. in sealed tubes. The hexene contents (C ) in mol % were determined by calculation of the 3<> bion ratio and with... 

The nascent morphology of the produced pol5oner was examined in a scanning electron microscope (SEM) Philips model SEM 500 using an acceleration voltage of 20 KV. The samples were coated with a layer... 

This material is a reserve substance in bacteria and in the natural state is a 0.5 ym diameter crystalline granule. The polyester biosynthesis is coupled with the dynamics of the "log phase" growth of bacterial systems (41). With the onset of sporulation, a rapid depolymization to monomer and turnover occurs. A full understanding of the nascent morphology of native granules PHB has been achieved (42). 

Han, J. J., Yoon, W. J., Lee, H. W., Choi, K. Y. Nascent morphology of syndiotactic polystyrene synthesized over silica-supported metallocene catalyst. Polymer, 49, 4141 149 (2008). 

Marchessault R H, Monasterios C J, Lepoutre P (1990), Properties of poly(/3-hydroxyalkanoate) latex nascent morphology, film formation and surface chemistry , in Dawes E A, Novel Biodegradable Microbial Polymers, Dordrecht, Kluwer, 97-112. 

The nascent morphology of polyethylene granules made in a reactor can be investigated by scanning electron microscopy. Competent analysis of such images can yield information regarding catalyst activity and polymerization conditions. Such analyses may be combined with energy-dispersive spectroscopy to aid in the identification of the class of catalyst used. 

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