Absorbable copolymers, block

Block/segmented absorbable copolymers of high melting crystallizable polyesters such as polyglycolide with amorphous polyether-ester such as poly-l,5-dioxepane-2-one... 

In order to achieve the desired fiber properties, the two monomers were copolymerized so the final product was a block copolymer of the ABA type, where A was pure polyglycoHde and B, a random copolymer of mostly poly (trimethylene carbonate). The selected composition was about 30—40% poly (trimethylene carbonate). This suture reportedly has exceUent flexibiHty and superior in vivo tensile strength retention compared to polyglycoHde. It has been absorbed without adverse reaction ia about seven months (43). MetaboHsm studies show that the route of excretion for the trimethylene carbonate moiety is somewhat different from the glycolate moiety. Most of the glycolate is excreted by urine whereas most of the carbonate is excreted by expired CO2 and uriae. 

Absorption is widely used as a raw material and/or product recovery technique in separation and purification of gaseous streams containing high concentrations of VOC, especially water-soluble compounds such as methanol, ethanol, isopropanol, butanol, acetone, and formaldehyde. Hydrophobic VOC can be absorbed using an amphiphilic block copolymer dissolved in water. However, as an emission control... 

Pebax, commercial block copolymer, 7 648t Pebble mills, 25 64 Pebble quicklime, 15 28 Peclet numbers (Pe), 2 63 10 763 22 746 25 686t, 687t 25 279. See also Mass transfer Peclet number (PeMT) axial dispersion in bubble tray absorbers, 2 89... 

Salt effects in polyelectrolyte block copolymer micelles are particularly pronounced because the polyelectrolyte chains are closely assembled in the micellar shell [217]. The situation is quite reminiscent of tethered polymer brushes, to which polyelectrolyte block copolymer micelles have been compared, as summarized in the review of Forster [15]. The analogy to polyelectrolyte brushes was investigated by Guenoun in the study of the behavior of a free-standing film drawn from a PtBS-PSSNa-solution [218] and by Hari-haran et al., who studied the absorbed layer thickness of PtBS-PSSNa block copolymers onto latex particles [219,220]. When the salt concentration exceeded a certain limit, a weak decrease in the layer thickness with increasing salt concentration was observed. Similar results have been obtained by Tauer et al. on electrosterically stabilized latex particles [221]. 

Short block copolymers with well defined number of units in the blocks could be applied as selective absorbents, compatibilizers for polymer blends, components for polymeric membranes, etc. 

In this chapter, the focus is largely on experimental and theoretical studies of micellization in a range of solutions of model block copolymers prepared by anionic polymerization. A discussion of both neutral and ionic block copolymers is included, and features specific to the latter type are detailed. The adsorption of block copolymers at the liquid interface is also considered in this chapter. Recent experiments on copolymer monolayers absorbed at liquid-air and liquid-liquid interfaces are summarized, and recent observations of surface micelles outlined. Thus this chapter is concerned both with bulk micellization and the surface properties of dilute copolymer solutions. 

Using the results of 12 iPP/EP blends, 4 iPP/EP block copolymers and 1 pure EP copolymer [13, 14], the Xe chemical shift of Xe absorbed in EP can be correlated to the chemical composition of EP, i.e., the ethylene fraction. Figure 12.9 shows an approximately linear relationship between the Xe chemical shift and the weight fraction ethylene in the EP copolymer. The values for the pure components PE (ethylene content = 1) and iPP (ethylene content = 0) are included. Of course, this also implies that a linear relationship exists between the Xe chemical shift and the density of the EP copolymer. 

When a block copolymer is blended with the homopolymer of one of the monomers of which it is composed, the homopolymer will enter the block polymer domain structure only when its molecular weight does not greatly exceed that of the block sequences of like composition (1,2). When it does so, the homopolymer forms its own, usually much larger, domains which may absorb some of the like-block sequences in their surface regions. 

Kimura et al. [107] made a light resistant formulation of a block E-P copolymer by extruding it at 220 °C with Mg(OH)2, and 2-hydroxy-4-octoxybenzophenone. The injection molded product (at 800 kg cm pressure) shows fire retardation also due to MgO filler and the benzophenone derivative is an efficient UV absorber. 

Practical problems associated with infrared dichroism measurements include the requirement of a band absorbance lower than 0.7 in the general case, in order to use the Beer-Lambert law in addition infrared bands should be sufficently well assigned and free of overlap with other bands. The specificity of infrared absorption bands to particular chemical functional groups makes infrared dichroism especially attractive for a detailed study of submolecular orientations of materials such as polymers. For instance, information on the orientation of both crystalline and amorphous phases in semicrystalline polymers may be obtained if absorption bands specific of each phase can be found. Polarized infrared spectroscopy can also yield detailed information on the orientational behavior of each component of a pol3mier blend or of the different chemical sequences of a copoljnner. Infrar dichroism studies do not require any chain labelling but owing to the mass dependence of the vibrational frequency, pronounced shifts result upon isotopic substitution. It is therefore possible to study binary mixtures of deuterated and normal polymers as well as isotopically-labelled block copolymers and thus obtain information simultaneously on the two t3q>es of units. 

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