Multibranched polymers

An unsubstituted hexose, such as D-glucopyranose (1), contains four alcoholic hydroxyl groups and one hemiacetal hydroxyl group. Such a polyfunctional1 monomer can polymerise to give a multibranched polymer, such as (2). A trisubstituted hexose, such as 2,3,6-tri-0-(JV-phenyl-carbamoyl)-D-glucopyranose (3),1W contains only one alcoholic hydroxyl... 

Use of polyfunctional linking agents, instead of bifunctional ones, for termination of living polymers can lead to the formation of multibranch polymers. For example, using methyltrichlorosilane and silicon tetrachloride, tribranch and... 

The tube modd has been refined also for consistent description of the linear and nonlinear rheological behavior of star-branched and multibranched polymers. For the star-branched polymers, the equilibrium relaxation mechanisms (arm retraction and CR/DTD) can be combined with the nonequilibrium mechanisms (chain stretch and CCR) in a way similar to that for the linear polymers. 

For the multibranched polymers, an additional mechanism not considered for the linear/star-branched polymers needs to be introduced. For the simplest multibranched polymer, the pom-pom polymer schematically illustrated in Figure 16, McLdsh and Larson combined the equilibrium mechanisms (arm retraction/trunk reptation in the dynamically dilated tube) and the nonequilibrium mechanisms (arm/trunk stretch, CCR, and the arm withdrawal) to formulate a constitutive equation. The arm withdrawal mechanism, leading to partial contraction of the trunk up to a point of tension balance with the arms, is the mechanism not considered for the linear/ star-branched chains. The resulting constitutive equation for the pom-pom chains cannot be cast in a Bemstein-Zapas-Kearsley (BKZ)-type convolution form. This pom-pom con-stimtive equation reproduces the hierarchical relaxation (from... 

Considering this lack of the general constitutive equation having a robust molecular basis, we may focus on the MSF model extended to the dendritic, multibranched polymers. Rolon-Garrido et al7 adopted eqn [65] as the basic constitutive equation of this extended model but modified the time evolution equation of MSF/, through analysis of the free energy and CR, as... 

Fig. 14.26 Diameter (SD, thickness (S7), and weight (Sw) swell of a parison extrudate from a commercial blow-molding machine equipped with CCD camera equipment and parison pinch-off mold based on the design of Shepak and Beyer (69). (a) A chain extended multibranched polyamide-6 resin (b) the former with 12% glass fiber of 10 pm diameter 60 1 L/D and (c) polyolefin modified polyamide-6 with some carbon black. [Reprinted by permission from A. H. Wagner and D. Kalyon, Parison Formation and Inflation Behavior pf Polyamide-6 During Extrusion Blow Molding, Polym. Eng. Sci., 36, 1897-1906 (1996).]...

In addition to the repeat unit sequence, another area of current interest in polymer structural control (Fig. 1) may be the spatial or three-dimensional shapes of macromolecules. In fact, the recent development of star [181-184] and graft [185] polymers, as well as starburst dendrimers [126], arborols [186,187], and related multibranched or multiarmed polymers of unique and controlled topology, has been eliciting active interest among polymer scientists. In this section, let us consider the following macromolecules of unique topology for which living cationic polymerizations offers convenient synthetic methods that differ from the stepwise syntheses (polycondensation and polyaddition) [126,186,187]. 

The proportionality between N and y has been observed at low deformation rates for concentrated LCP solutions in cresol [Kiss and Porter, 1980 Moldenaers and Mewis, 1992], for colloidal and noncolloidal suspensions, and fiber suspensions in a Newtonian matrix [Zirnsak et al., 1994], as well as for block copolymers and multibranched star polymers [Brady and Bossis, 1985 Kotaka and Watanabe, 1987 Masuda et al., 1987 English et al., 1997]. For LCP this behavior was considered originating in polydomain flow [Larson and Doi, 1991], while for rigid fiber suspensions in interparticle interactions [Zirnsak et al., 1994]. It is tempting to postulate that the clay platelet orientation is the origin of the difference. Evidently, the scan direction and the pre-shearing time between data points affect the orientation, but the proportionality Ni =ay and complexity of the ) = f(y) dependence remain. The Larson-Doi [1991] theory of polydomain flow leads to... 

Masuda, T., Ohta, Y., and Onogi, S., Viscoelastic properties of multibranch polystyrenes, in Current Topics in Polymer Science, Vol. II, Ottenbrite, R. M., Utracki, L. A., and Inoue, S.,Eds., Hanser-Verleg, Munich, 1987. 

Dendrimers are multibranched macromolecules with nanometer-scale dimensions. They are considered to be ideal candidates for biological applications. Such macromolecules are monodisperse or closely monodisperse and they give reliable drug or gene deliveries compared to other polymers. Dendrimers are then used for the formation of labelled-ligand bioconjugates [225]. 

The proteoglycans are macromolecules of a more complex multibranched structure. Present evidence indicates that they consist of a primary glycosaminoglycan core, to which is attached, by link proteins, secondary protein cores at spaced intervals, to which are attached tertiary glycosaminoglycan polymers. It should be noted that the proteoglycans of the matrix are not a single molecular species but comprise a polydisperse family of rather similar macromolecules which differ in complexity, molecular weight, hydro-dynamic size, chemical composition, and reactivity (132). 

The precursor polymer blend can be made out of (1) linear block copolymers, (2) AB block copolymers, (3) ABA block copolymers, (4) ABC block copolymers, (5) multiblock copolymers, (6) symmetrical and asymmetrical star block copolymers, (7) blends of polymers, (8) graft copolymers, (9) multibranched copolymers, (10) hyperbranched or dendritic block copolymers, and (11) novel brush copolymers. 

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