Concentration semi-crystalline

The polymerization of dimethyl maleate and 1,6-hexanediol proceeded using lipase CA catalyst in toluene to give the polymer exhibiting exclusively cis structure [55]. During the polymerization, cyclic oligomers were formed. The cycles were semi-crystalline, whereas the linear polymer was amorphous. In the lipase CA-catalyzed copolymerization of dimethyl maleate and dimethyl fumarate with 1,6-hexanediol, the content of the cyclization was found to depend mainly on the configuration and concentration of the monomers [56]. 

The concept Tie molecules" was introduced by Peterlin (1973), see Chap. 2. Tie molecules are part of chains or bundles of chains extending from one crystallite (or plate or lamella) to another in fibres they even constitute the core of the stretched filament. They concentrate and distribute stresses throughout the material and are therefore particularly important for the mechanical properties of semi-crystalline polymers. Small amounts of taut tie molecules may give a tremendous increase in strength and a decrease in brittleness of polymeric materials. 

This equation is not particularly useful in practice, since it is difficult to quantify the relationship between concentration and activity. The Flory-Huggins theory does not work well with the cross-linked semi-crystalline polymers that comprise an important class of pervaporation membranes. Neel (in Noble and Stern, op. cit., pp. 169-176) reviews modifications of the Stefan-Maxwell approach and other equations of state appropriate for the process. 

Conversely, nodules can significantly increase the amount of energy dissipated during deformation of notched specimens (Fig, 5., 6.). They contribute to decrease brittle to ductile transition temperature. Non-reactive nodule can toughen amorphous PET to a certain extend, being nevertheless always less efficient than reactive one. On the contrary, only the reactive nodules exhibit a certain level of efficiency in semi-crystalline PET, provided that concentration is at least 21 %. 

This chapter has concentrated on crystalline materials. X-ray diffraction can also furnish structural information about amorphous and semi-amorphous solids, even though the structure is much more diffuse. 

In order to inhibit the oxidation of polymers, the antioxidant has to be present in sufficient concentration at the various oxidation sites. In this respect, both the distribution of antioxidants and the morphology of the host polymer assume greater significance. Examination of the distribution of photo-antioxidants in typical commercial semi-crystalline polymers, such as polyolefins, has shown " " " that they are rejected into the amorphous region on the boundaries of spherulites. Such nonuniform distribution of antioxidants leads to an increase in their concentration in the amorphous region, which is most susceptible to oxidation (the crystalline phase is normally impermeable to oxygen). However, in the case of polymer blends, a nonuniform distribution of antioxidants can undermine the overall stability of the blend, especially when the more oxidizable component of the polymer blend is left unprotected. 

The potential advantage of crystalline polymers for barrier applications was recognized by Morgan (1) although, previous investigators had reported reduced permeabilities in semi-crystalline polymers (2,2) As will be discussed, the equilibrium concentration of sorbed penetrant and the diffusion process are affected by crystallinity in uniquely different ways. 

The Vistalon 404 and 4608 are amorphous C2C3 rubbers, while Vistalon 5600 contains a crystalline fraction of 4 %wt. The Nordel 1500 and 3391 are typical semi-crystalline C2C3 rubbers with crystalline fractions of respectively 15 %wt. and 12 %wt. Bach of these rubbers was added to the PP in three different concentrations i.e. 10, 15 and 20 %wt. Only the amorphous fraction of these C2C3 rubbers is assumed to contribute to the measured low temperature rubber loss maximum. 

Unmodified PBT is a fairly ductile material exhibiting high elongation at break, even after crystallization. However, as to be expected of all rigid semi-crystalline polymers, molded parts of PBT show low notched Izod impact strength indicating that under conditions of stress concentration, the... 

This chapter describes the microstructures of the main types of polymer, concentrating on features used later to explain physical properties. The order of magnitude of elastic moduli for rubbers, glassy polymers and polymer crystals will be related to their molecular mobility and inter-molecular forces. These values will be used in Chapter 4 to predict the moduli of semi-crystalline polymers. 

The crack-tip environment with its stress and plastic-strain concentration furnishes the means and driving forces for local fracturing of material, making the crack propagate to final fracture. The material separation in crack extension can occur by a variety of mechanisms in which a number of factors can play important roles, such as the structural constitution of the polymer, i.e., whether it is in unoriented or oriented glassy form or in semi-crystalline form, with a variety of morphologies. We consider first a selection of prominent forms of fracture in polymers and end with a short section on the fracture toughnesses of some prominent polymers. 

Figure 10.58 indicates that temperature is an essential factor in creation of a crystalline stiucture. Figure 10.59 shows the importance of the crystalhzation time on the stiuc-ture of plasticized material. Three major parameters are involved here concentration of plasticizer, temperature, and time. On the one hand these parameters influence materials stracture, on the other the time-temperature regime is one of the factors complicating the determination of the degree of crystallinity. In spite of matty methods used for crystallinity determination (IR, WAXS, DSC) or perhaps because of many methods and variability in conditions of sample preparation and treatment, only rough estimates of crystallinity may be obtained for semi-crystalline materials. " ... 

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