Molecular mass/weight polypropylene

Low molecular weight polypropylene with a relative molecular mass between 2500 and 6000. 

Fig. 5 Polypropylene degradation during dissolution at high temperature, (a) Shift of MMD and (b) weight-average molecular mass (M ) versus dissolution time in TCB with 300 ppm BHT, with and without nitrogen purge...

Along with many other low molecular weight organic compormds thermal degradation of PEO and polypropylene oxide (PPO) produces monomers ethylene oxide (3.9% mass) and PPO (0.1-1.16% mass). The molecular masses of oligomer fragments, being volatile at the decomposition temperature, were 400 for PEO and 330 for iPPO. 

Spaleck, W. Antberg, M. Rohrmann, J. Winter, A. Bachmann, B. Kiprof, P. Behm, J. Herrmann, W. A. High-molecular-weight polypropylene via mass-tailored zirconocene-type catalysts. Angew. Chem., Int. Ed. Engl. 1992, 31, 1347-1350. 

Polypropylene (PP) Kaplen of mark 01030 with average weight molecular mass of - (2-3) X10 and polydispersity index 4.5 was used as a matrix polymer. Nanodimensional calcium carbonate (CaCOj) in a compound form of mark Nano-Cal P-1014 (production of China) with particles size of 80 nm and mass contents of 1-7 mass % and globular nanocarbon (GNC) (production of corporations group United Systems, Moscow, Russian Federation) with particles size of 5-6 mn, speeifie surfaee of 1400 mVg and mass contents of 0.25-3.0 mass % were applied as nanofiller. 

Metal oxide semiconductor chemical sensors in combination with MDA have been shown to be useful to estimate the oxidative stability of polypropylene during processing instead of traditional melt flow index analysis (50). An array of sensors was used to receive a detailed analysis of volatiles. At quality measurements of different poly(butylene adipate)s the use of indicator products has been proven better than analyses of the decrease in molecular weight or mass loss for early degradation detection. Adipic acid, quantified using gas chromatography, was then used as the indicator product [51]. 

Low molecular weight dicarboxylic acids, keto acids and hydroxy acids have been shown to form as photooxidation products of polyethylene and polypropylene. These are almost certainly formed by intramolecular reactions of alkylperoxyl and peracyl radicals shown typically in Scheme 3.7. Back-biting along the aliphatic chain gives rise to unstable hydroperoxides and the elimination of small molecular fragments. It will be seen in Chapter 5 that these low molar mass oxidation products, which are already present in the environment from natural sources, are the first point of microbial attack in the surface of environmentally degraded polymers, leading to oxidation initiated bioerosion (Chapter 5). 

Figure 1 Effect of multiple site types and mass and heat transfer resistances on the microstructure of polypropylene made with heterogeneous Ziegler-Natta and metallocene catalysts. The overall MWD and CCD are assumed to result from the superposition of individual MWDs and CCDs for three site t)rpes (T = temperature, M = number average molecular weight, = hydrogen, CjH = propylene, C2H4 = ethylene, Fj = molar fraction of propylene in copolymer, /(F,) == copolymer composition distribution, r = chain length, wix) = weight chain length distribution).

Just for fun, calculate the mass of a sample of molecular weight 100,000 polypropylene that has just one molecule of each of the 10 possible stereoisomers. In doing so. 

Mass average molecular weight, K dalton, g/ mol, amu 1,000-5,400,000 Maier, C Calafut, T, Polypropylene. The Definitive User s Guide and Databook, William Andrew, 1998. 

During each photodegradation (in vacuum or air) small amounts of several gaseous and liquid low molecular weight compounds are formed and they can only be detected by chromatographic or mass spectrometry methods (cf. section 10.6). Table 2.1 shows, for example, products formed from polypropylene hydroperoxide photolysis. 

Figure 2.6 MALDI-FTI-CR-MS spectrum of polyethylene oxide - polypropylene oxide. For this measurement, the trapping delay was optimised to be 900 ps for the centre of the molecular weight distribution, the spectra from 250 laser shots were summed. The series of polyoxypropylene homopolymers is indicated (the first number refers to n °, the second to n °). In the expanded mass scale, the composition of all monoisotopic copolymers is indicated. Reproduced with permission from G.J. van Rooij, M.C. Duursma, C.G. de Koster, R.M.A. Heeren, J.J. Boon, RJ.W. Schuyl, E.R.E. van der Hage, Analytical Chemistry, 1998, 70,...

The previous sections of this chapter have been concerned with methods for determination of average molar masses, molar mass distributions and molecular dimensions. In many instances this information is all that is necessary to characterize a homopolymer when its method of preparation is known. However, for certain homopolymers (e.g. polypropylene, polyisoprene) knowledge of molecular microstructure is of crucial importance. Additionally, for a copolymer it is necessary to determine the chemical composition in terms of the mole or weight fractions of the different repeat units present. It is also desirable to determine the distribution of chemical composition amongst the different copolymer molecules which constitute the copolymer (Section 3.17.6), and to determine the sequence distribution of the different repeat units in these molecules. Furthermore, when characterizing a sample of an unknown polymer the first requirement is to identify the repeat unit(s) present. Thus methods for determination of chemical composition and molecular microstructure are of great intportance. 

In the case of the polyolefins, random chain scission is initially the dominant process. This is shown typically for polypropylene in Scheme 2. However some low molar mass oxidation products are formed via vicinal hydroperoxides in both PP and PE [20]. The alkoxyl radicals formed by decomposition of the hydroperoxides contain weak carbon-carbon bonds in the a positions to the hydroperoxide groups, which lead to the formation of low molecular weight aldehydes and alcohols that rapidly oxidise further to carboxylic acids. These are biodegradable species, similar to products formed by hydrolysis of aliphatic polyesters and, as in the case of cis-PI, they are rapidly bioassimilated to give cell biomass (see below). 

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