Poly long-chain branches

Less commonly used as third monomer is dicyclopentadiene [77-73-6] or DCPD, for which, due to its symmetrical shape, the tendency of the second double bond to take part in the polymeri2ation process is more pronounced than for ENB. This is one of the reasons for the formation of long-chain branches. The resulting product is poly(ethylene- (9-prop54ene- (9-DCPD) [25034-71-3]. 

Poly(olefins), long chain branching 1980s 1990s Elastomers, plastomers ... 

Chain branching is a common occurrence during radical polymeriza ] tions and is not restricted to poiyethyiene. Polypropylene, polystyrene, andt poly(methyl methacrylate) all contain branched chains. Studies have shown that short-chain branching occurs about 50 times as often as long-chain branching. 

Rheology and crystallization of long-chain branched poly(L-lactide)s with [117] controlled branch length, Ind. Eng. Chem. Res. 51 (2012) 10731-10741. 

The long-chain branching thus produced has been shown by comparison of the radii of gyration with those of poly(methylenes) of the same molar mass, since the latter possess practically no branching. On the other hand, butyl groups are produced by intramolecular transfer reactions ... 

In analyzing polyethylene-diluent mixtures it was noted that for certain diluents and concentrations the melting temperature remained invariant with composition. This is not an isolated observation. Besides linear polyethylene, this phenomenon has also been observed in long chain branched polyethylene,(21) poly(chlorotrifluoroethylene),(22) poly(N,N -sebacoyl piperazene),(23) isotactic poly(propylene),(24) and poly (acrylonitrile) (25) when the polymers are admixed... 

Qualitatively similar melting point depressions are observed in long chain branched poly(ethylene terephthalate)(152) and poly(phenylene sulhde).(153) The extrapolated equilibrium melting temperatures of poly(phenylene sulhde) decrease by 11 °C with a modest concentration of long chain branches. Coincidentally, the extrapolated equilibrium melting temperatures of poly(ethylene terephthalate) also decrease by 11 °C for the range of branch concentrations studied. 

As well as conversion, the importance of transfer to polymer depends upon the monomer system. The reaction can be important in systems with very reactive radicals such as ethylene [30-32], vinyl acetate [33-35], and acrylate [36, 37] polymerizations, but seldom occurs in styrene and methacrylate systems. Transfer to polymer usually occurs via abstraction of a methine hydrogen as shown in Scheme 4.9, but may also involve other easily abstracted H-atoms, such as the acetate methyl hydrogens on poly(vinyl acetate). Transfer constants to polymer (C ° = k /kp) are not as readily determined as other transfer constants because the process does not decrease DP . Long-chain branching (LCB) levels are usually quite low, less than 2 per 1000 repeat units, making it difficult to employ NMR. Indirect methods such as multi-detector SEC [32, 38] are often used, leading to a significant scatter in reported values [7]. like other transfer events, the relative importance increases with temperature. 

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