Molecular weight and crystallinity

Above 100°C, most polyolefins dissolve in various aHphatic and aromatic hydrocarbons and their halogenated derivatives. For example, polybutene dissolves in benzene, toluene, decalin, tetralin, chloroform, and chlorobenzenes. As with other polyolefins, solubiHty of PB depends on temperature, molecular weight, and crystallinity. 

MIR and NIR for Simultaneous Determination of Molecular Weight and Crystallinity of Recycled HDPE... 

Turning the lactic acid into a polymer involves a chemical process called condensation, whereby two lactic acid molecules are converted into one cyclic molecule called a lactide. This lactide is purified through vacuum distillation. A solvent-free melt process causes the ring-shaped lactide polymers to open and join end-to-end to form long chain polymers. A wide range of products that vary in molecular weight and crystallinity can be produced, allowing the PLA to be modified for a variety of applications. 

The Effect of Solid-State Heat-Treatment on Molecular weight and Crystallinity. Solid-state heat-treatment had been done before on thermotropic polyester fiber to obtain advancement in tenacity (6) and on polyester-carbonate samples to get advancement in molecular weight.(H) It was understood that post polymerization and thermal annealing occurred on thermotropic polymers at solid state, as the term post-polymerization has been used interchangeably for solid-state heat-treatment. 

In table 2 are shown data relating molecular weight and crystalline content of unaged polymers. These were prepared by using an excess of OH or NCO functionality. If the functionality not in excess is used up, the theoretical (listed) is the weight charged divided by the excess number of mols. Intrinsic viscosities found show that the desired effect was achieved. 

The moduli of fluoropolymers are a function of a number of variables, most important of which is the composition of the polymer and, more specifically, the presence or absence of hydrogen in the polymer. Other variables are those affecting the other mechanical properties of these plastics. They include testing temperature, molecular weight, and crystallinity, which affect the modulus of these plastics independently of the regime/tyqie of measurements. Perfluo-ropolymiers have lower moduli than partially fluori-nated fiuoropiastics. An increase in the fluorine content of the fluoroplastic increases the modulus. 

With the R3A1— H20 system polymer molecular weight and crystallinity depend strongly on temperature, keeping the other parameters constant. Increasing the temperature from —78 °C to 0 °C leads to a decrease in the molecular weight from 5.6 105 to 104 and in the degree of crystallinity from 30 % to 0. 

The most important mechanism of stereospecific polymerization is isospecific enantiomorphic site control, which allows today the production of more than 25 million tons per year of isotactic polypropene and its copolymers, in a wide range of molecular weights and crystallinities. As already mentioned in section II, the molecular architecture of polypropenes obtained from ansa-zirconocenes is strongly dependent on the biscyclopentadienyl ligand structure. 

This approach is used in several instances to control the arms, molecular weight, and crystallinity of the resulting polymer [52], The convergent approach is illustrated elsewhere [53, 54], This subject is not reviewed here in detail because a whole chapter of this handbook (Chapter 30) is dedicated to it. 

GtabLE 12.4 Ethylene-Propylene Blend Components Differing in Molecular Weight and Crystallinity ... 

Perego, G., Celia, G.D. and Bastioli, C. (1996) Effects of molecular weight and crystallinity on poly(ltictic acid) mechtmictd properties. Journal of Applied Polymer Science, 59, 37-43. 

Chemical and Physical Properties The major physical and mechanical properties of poly(caprolactone) are summarized briefly in Table 1.5. Its physical and mechanical properties depend mainly on its molecular weight and crystallinity. In general, aromatic and some polar solvents such as benzene, toluene, cyclohexanone, dichloromethane and 2-nitropropane are good solvents for PCL. Water, alcohols, petroleum ether, diethylether are poor solvents for PCL. PCL can be slightly soluble in acetonitrile, acetone, 2-butanone, ethyl acetate and dimethylformamide. 

Figure C.8 Classification of the expected properties of materials on the basis of molecular weight and crystallinity. (Ref Billmeyer, F.W., Textbook of Polymer Science, Intersdence, New York, 1965, p. 9)...

The name chitosan covers a large collection of preparations that aU have nearly the same natural composition but are different in their characteristics and applicability due to variations in source, charge, charge density, molecular weight and crystallinity. For a specific application, this complicates the search for the most useful form of chitosan, but it presents a large range of chitosan candidates that might serve the specific purpose. Chitosans in diverse physical and chemical forms have been introduced for a variety of applications in the sector of medical... 

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