Polymers ring/star

Another important feature controlling the properties of polymeric systems is polymer architecture. Types of polymer architectures include linear, ring, star-branched, H-branched, comb, ladder, dendrimer, or randomly branched as sketched in Fig. 1.5. Random branching that leads to structures like Fig. 1.5(h) has particular industrial importance, for example in bottles and film for packaging. A high degree of crosslinking can lead to a macroscopic molecule, called a polymer network, sketched in Fig. 1.6. Randomly branched polymers and th formation of network polymers will be discussed in Chapter 6. The properties of networks that make them useful as soft solids (erasers, tires) will be discussed in Chapter 7. 

Fig. 4 Polymer architectures (a) linear polymers, (b) ring polymers, (c-f) branched polymers (c) graft polymers, (d) star-shaped polymers, (e) hyperbranched polymers, and (1) dendrimers...

INTRODUCTTON Polymer molecules may have a variety of architectural structures such as linear, ring, star, branched, and ladder chains as well as three-dimensional network structures. The first synthetic cychc jxjlymers to be prepared and characterized were the poly(dimethylsiloxanes) (PDMS), which were reported in 1977. Since that time a number of other cychc pwlymers have been synthesized including cyclic polystyrene, cyclic poly(phenyhnethylsiloxane), cyclic poly(2-vinylpyridine), cyclic polybutadiene, and cychc poly(vinyhnethylsiloxane). ... 

Figure 1 (a) Linear PE chain, (b) Polymer ring, (-CH2-)48- (c) PE chain with one branching point, (d) Comb-like polymer, (e) Star-like polymer, (f) Ladder polymer, (g) Randomly branched polymer. 

First-order perturbation calculations of the mixed second virial coefficients A have been carried out for chains differing in molecular weight but having the same architecture and chemical structure (so that the segment-segment excluded volume parameter is the same for all polymer species), and for some combinations of topologically different chains, e,g. linear chains with rings, stars or combs, stars with stars of different functionality, stars with combs, The simplest result is that for... 

Using all six positions on the cyclotriphosphazene ring, star polymers can be formed. An example is the formation of a star polymer with poly(caprolactone) and poly(2-(diethylamino)ethyl methacrylate) linkages. 

A three-armed star polymer in which polystyrene blocks are linked to a benzene ring at specified positions ... 

The main topic of interest is the properties of molecules of finite size, having no large rings, and in general having trifunctional branch-points. These are typically produced by chain-transfer with polymer in free-radical polymerizations, though they can of course be made in other ways. Molecules with branch-points of higher functionality are also of interest, especially star-shaped molecules with several arms, as these are both easy to synthesize and relatively easy to discuss theoretically. 

Chompff,A.J. Normal modes of branched polymers. I. Simple ring and star-shaped molecules. J. Chem. Phys. 53,1566-1576 (1970). 

Prepared by bulk polymerization, an MIP for the detection of dicrotophos based on the Eu3+ complex has recently been presented [58]. The authors used reversible addition fragmentation chain transfer (RAFT) polymerization followed by ring closing methathesis (RCM) to obtain the star MIP with arms made out of block copolymer. The star MIP containing Eu3+ exhibited strong fluorescence when excited at 338 nm with a very narrow emission peak (half width -10 nm) at 614 nm. This MIP was sensitive to dicrotophos in the range of 0-200 ppb, but showed saturation above this limit. Cross-reactivity of this MIP was evaluated with respect to structurally similar compounds dichlorvos, diazinon and dimethyl methylphosphonate. In these tests no optical response of the polymer was detected even at concentrations much higher than the initial concentration of dicrotophos (>1000 ppb). 

The exterior of carbosilane dendrimers can also serve as initiator sites for polymerization, in which case the dendrimers serve as cores for star polymers. Vasilenko and coworkers95 synthesized a multilithiated carbosilane dendrimer which they then used as an initiator for the ring-opening polymerization of hexamethylcyclotrisiloxane to yield star polymers of narrow weight distribution (Scheme 7). The researchers later extended this work to polymerize styrene, isoprene and ethylene oxide96,97. Star poly(ethylene oxides) were also prepared using hydroxy-terminated carbosilane dendrimers as the core98,99. 

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