Short branches

Locust bean (carob) is derived from the endosperm portion of seeds of a tree widely cultivated in the Mediterranean area. It is a polysaccharide built of mannose units with short branches of single galactose units, with an average molecular weight of 310,000. 

The short side chain branching frequency is inversely proportional to polymer crystallinity. Short branches occur at frequencies of 2—50 per 1000 carbons in chain length their corresponding crystallinity varies from 35 to 75%. Directiy proportional to the polymer density, crystallinity can be calculated by the following formula,... 

Cosurfactant requirements can be minimized usiag a surfactant having a short-branched hydrophobe or a branched-alkyl substituent on an aromatic group (232,234) and a long ethoxy group chain (234). Blends of surfactants optimized for seawater or reservoir brine salinity include linear alkyl xylene sulfonate—alcohol ether sulfate mixtures (235). 

Branching can to some extent reduce the ability to crystallise. The frequent, but irregular, presence of side groups will interfere with the ability to pack. Branched polyethylenes, such as are made by high-pressure processes, are less crystalline and of lower density than less branched structures prepared using metal oxide catalysts. In extreme cases crystallisation could be almost completely inhibited. (Crystallisation in high-pressure polyethylenes is restricted more by the frequent short branches rather than by the occasional long branch.)... 

Branches in PVC can be formed by transfer to polymer during polymerization. Short branches in PVC have usu-... 

Intermolecular chain transfer reactions may occur between two propagating polymer chains and result in the termination of one of the chains. Alternatively, these reactions take place by an intramolecular reaction by the coiling of a long chain. Intramolecular chain transfer normally results in short branches ... 

From these approaches, DBnmr=0.42 and DBtheo=0-49 can be obtained at y=l.l (h=0.62), respectively. Note that these values represent a rough estimate, as they are calculated based on the assumption of equal rate constants for copolymerization. For low y values (y=0.5),the DB (DBnmr=0-48) even exceeds the value for poly(inimer 1) (DBnmr=0-43) obtained by a homo-SCVP. This is an accordance with theoretical prediction that a maximum of DB=0.5 is reached at y=0.6 [73]. The effect can be explained by the addition of monomer molecules to in-chain active centers (i.e., in linear segments), leading to very short branches. For 2.5>y>0.5, DBnmr decreases with y, as predicted by calculations. 

C. bantianum grows at 42 to 43°C and forms long, sparsely branching chains of conidia from hyphalike conidiophores, with conidia ca. 6.4 pm long. C. carrionii grows up to 36°C and forms short, branching chains of conidia from distinct conidiophores, with conidia ca. 5 pm long. 

The polyethylene obtained (the already cited HDPE) is more highly crystalline and more rigid and dense and has a much more regular structure than the one previously known and obtainable at very high temperature and pressure and which had been industrially produced in the previous 15 years (now called low-density polyethylene, LDPE). The latter shows macromolecules with both long and short branches and is consequently less crystalline than the almost completely linear HDPE. It is obvious that polyethylene does not present tertiary carbon atoms in its constitutional unit, hence it does not show problems of stereoisomerism. 

The reaction temperature is above the critical temperature of ethylene so that the ethylene is in gas phase. High pressures are needed for propagation reaction. Only about 6-25 per cent of ethylene is polymerised. Rest of monomer is recycled. Extensive chain transfer reactions takes place during polymerisation to yield a branched chain polyethylene. In addition to long branches, it also contains a large number of short branches of upto 5 carbon atoms produced by intra-molecular chain transfer reactions. A typical molecule of Low density polyethylene contains a short branch for about every 50 carbon atoms and one or two long branches per molecule. 

PS has discrete pores with no branches, with short branches, or with dendritic... 

Free radical vinyl polymerization, the oldest process, leads to branched low density polyethylene (LDPE). Macromolecules have numerous short branches, which reduce the melting point, tensile strength and crystallinity. Polymers are relatively flexible because of the high volume of the branched molecule and the low crystallinity. 

Unlike cellulose, hemicelluloses consist of different monosaccharide units. In addition, the polymer chains of hemicelluloses have short branches and are amorphous. Because of the amorphous morphology, hemicelluloses are partially soluble... 

The acyl-Co A dehydrogenases are a family of mitochondrial flavoenzymes involved in fatty acid and branched chain amino-acid metabolism. In addition to long chain acyl-Co A dehydrogenases (LCADs), there are short/ branched chain acyl-CoA dehydrogenase (SBCAD) that act on 2-methyl branched chain acyl-CoA substrates of varying chain lengths. 

Make sketches or diagrams showing (a) a linear polymer, (b) a polymer with pendant groups, (c) a polymer with short branches, (d) a polymer with long branches, and cross-linked polymers with (e) low and (f) high cross-linked density. 

LDPE has a combination of short-to-long branches, with long branches occurring at a rate of about 10 short branches to every long branch. 

Short branching has also been verified in poly(vinyl acetate), poly(vinyl chloride), and various polyacrylates. Branching in poly(vinyl acetate) and polyacrylates involve the intramolecular backbiting mechanism as in polyethylene [Adelman and Ferguson, 1975 Heatley... 

Short branches, specifically ethyl branches up to about 2 mol%, are formed in the polymerization of ethylene by meso-ansa zirconocenes containing unsubstituted cyclo-pentadienyl and indenyl ligands [Melillo et al., 2002]. Ethyl branches form by an isomerization process in which the usual P-hydride transfer to monomer is immediately followed by reinsertion of the vinyl-terminated polymer into the formed ethyl-zirconium bond. 

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