Side-chain branching crystallinity

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,... 

Side-chain liquid-crystalline polymers with controlled molecular weights have been obtained by the polymerization of FM-25 with 1-22 (X = Br)/CuBr/ L-3 in the bulk at 100 °C, to examine the thermotropic transition as a function of the MWD.324 Second-order nonlinear optical materials with branched structure were prepared by the copper-catalyzed radical polymerization of FM-26 and FM-27 using hyperbranched poly[4-(chloromethyl)styrene] as a multifunctional initiator.325... 

LDPE typically has long side-chain branching off the main molecular chain and therefore is a more amorphons polymer. As a resnlt, it shows lower shrinkage compared to a more crystalline HDPE, in which many of the polymer molecules are packed closely together. 

Polyethylene is a major commodity plastic, with more than 33 billion pounds of the resin produced in the United States in 2000 [1]. Polyethylene encompasses a family of semi crystalline polymers with ethylene as the major building block [6]. The resins are loosely grouped into three classes low-density polyethylene (LDPE), high-density polyethylene (HD.PE), and linear-low-density polyethylene (LLDPE). LDPE is a homopoiymer of ethylene with side-chain branching at a frequency... 

Linear polyethylenes are produced in solution, slurry, and increasingly, gas-phase low-pressure processes. The Phillips process developed during the mid 1950s used supported chromium trioxide catalysts in a continuous slurry process (or particle-form process) carried out in loop reactors. Earlier, Standard Oil of Indiana patented a process using a supported molybdenum oxide catalyst. The polyethylenes made by both these processes are HDPE with densities of 0.950-0.965 g/cm and they are linear with very few side-chain branches and have a high degree of crystallinity. 

MW, MW distribution and side-chain branches in PE influence its material properties, including melting point and crystallinity. Linear low-density PE is more easily processed than high-density PE due to the presence of side-chain branches. The combination of stiffness and stress-crack resistance of the material are improved by the presence of these side chains [6, 7]. To improve processing, polymers with different MW can be melt-blended, but with the resultant problems and cost. 

Copolymerization e.g., of 1-butene or 1-hexene with ethylene, gives short-chain branching-, e.g., the branches contain three or five carbon atoms. The random location of the side-chains lowers the crystallinity and density. Long-chain branching refers to branches that are similar in length to the polymer backbone and this type occurs in polyethylene manufactured using the... 

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