Star-polymers

Star polymers are used as additives to improve optical density and waterfastness of the image printed with the ink (32). Quasi-spherical structures that can be used as the core of a star pol5maer are  

Branched polymers derived from molecules that contain difunctional C=C polymerizable groups, 

A condensation polymer. Star polymers with condensation polymers as the core are also referred to as hybrid star polymers. 

Specific examples are acrylates, methacrylates, styrene, a methyl styrene, dienes, and mono-olefins. Useful acrylic star pol mers and hybrid acrylic star pol mers have been described (33,34) 

Several basic approaches to star polymer synthesis leading to architectures as 

The generic features of these approaches are known from experience in anionic polymerization. However, radical polymerization brings some issues and some advantages. Combinations of strategies (a-d) are also known. Following star formation and with appropriate experimental design to ensure dormant chain end functionality is retained, the arms may be chain extended to give star block copolymers (321). In other cases the dormant functionality can be retained in the core in a manner that allows synthesis of mikto-arm stars (324). 

A comment should be made on the dispersity of star polymers. If the arms each have a most probable distribution 2), dispersity of the star 

A comment should be made on the dispersity of star polymers. If the arms each have a most probable distribution (M ./M,-2), dispersity of the star polymers is expected to be l + l/ 3, where a is the number of arms of the star polymer, simply as a consequence of statistical averaging. This explains why polymers formed by conventional radical polymerization with termination by combination i.e. 2 arms) have =1.5. When wc additionally take into 

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Stark spectra Star polymers Star sapphires Startch [9005-25-8]... 

The anionic polymerization of methacrylates using a silyl ketene acetal initiator has been termed group-transfer polymerization (GTP). First reported by Du Pont researchers in 1983 (100), group-transfer polymerization allows the control of methacrylate molecular stmcture typical of living polymers, but can be conveniendy mn at room temperature and above. The use of GTP to prepare block polymers, comb-graft polymers, loop polymers, star polymers, and functional polymers has been reported (100,101). 

Block (Star) Arrangement. The known star polymers, like their linear counterparts, exhibit microphase separation. In general, they exhibit higher viscosities in the melt than their analogous linear materials. Their rheological behavior is reminiscent of network materials rather than linear block copolymers (58). Although they have been used as compatibiUzers in polymer blends, they are not as effective at property enhancements as linear diblocks... 

In this example, X is difunctional and the product is linear. If the fiinctionahty of X is higher, the product is branched, ie, it is a star polymer. 

Block copolymer chemistry and architecture is well described in polymer textbooks and monographs [40]. The block copolymers of PSA interest consist of anionically polymerized styrene-isoprene or styrene-butadiene diblocks usually terminating with a second styrene block to form an SIS or SBS triblock, or terminating at a central nucleus to form a radial or star polymer (SI) . Representative structures are shown in Fig. 5. For most PSA formulations the softer SIS is preferred over SBS. In many respects, SIS may be treated as a thermoplastic, thermoprocessible natural rubber with a somewhat higher modulus due to filler effect of the polystyrene fraction. Two longer reviews [41,42] of styrenic block copolymer PSAs have been published. 

M. Watzlawek, H. Lowen, C. N, Likos. Phase diagram of star polymer solutions (submitted for pubhcation, 1999). 

The use of mono-, di- and multifunctional initiators provides scope for designing polymer architectures. The use of 14, 18 and 19 in the production of block or star polymers has been demonstrated.41 4445 Homopolymers of 20 or copolymers of 20 with S or MMA have been successfully used in photoinitiated... 

The use of dendritic cores in star polymer synthesis by NMP, ATRP and RAFT polymerization was mentioned in Section 9.9.1, In this section wc describe the synthesis of multi-generation dendritic polymers by an iterative approach. 

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

The distinctive properties of densely tethered chains were first noted by Alexander [7] in 1977. His theoretical analysis concerned the end-adsorption of terminally functionalized polymers on a flat surface. Further elaboration by de Gennes [8] and by Cantor [9] stressed the utility of tethered chains to the description of self-assembled block copolymers. The next important step was taken by Daoud and Cotton [10] in 1982 in a model for star polymers. This model generalizes the... 

It is interesting, for comparison, to apply the Flory approximation, parallel to Eq. 2, to a curved geometry. As an example, consider a star polymer with f arms and radius R. The segment volume fraction within the star can be written, tp ss fNa3/R3, so that FjtU/kT per arm can be written as v(fN)2 a3/fR3, giving rise to a total free energy per arm ... 

The second method is the most efficient way to synthesize well defined star polymers. It involves preparation of a living monocarbanionic precursor, which can be accurately characterized. In a second step, this polymer is reacted with a pluri-... 

Some multifunctional electrophilic deactivators for star polymer synthesis... 

Blood compatibility see Biocompatibility Born-Oppenheimer separation 180, 182 Branch points, labeled 164 Branches, in star polymers 162... 

Jacob S. and Kennedy J.P., Synthesis, characterization and properties of octa-arm polyisobytylene-based star polymers, Adv. Polym. Set, 146, 1, 1999. 

Wunsch J. and Geprags M., Star polymers and their preparation, US Patent 6303806, 2001. 

Pryke, A. et al. Synthesis, hydrogenation, and rheology of 1,2-polybutadiene star polymers. Macromolecules, 35, 467, 2002. 

As the synthetic approach to polydichlorophosphazene put forward by R. De Jaeger has been already described in several recent review articles [10,38,57, 172], in this paper we will illustrate only the polycondensation approach proposed by I. Manners and H. R. Allcock, together with the consequences of this reaction on the preparation of chain phosphazene copolymers (block copolymers) [220,223,224,232-234,240], and star polymers [222]. 

Star polymers are a class of polymers with interesting rheological and physical properties. The tetra-functionalized adamantane cores (adamantyls) have been employed as initiators in the atom transfer radical polymerization (ATRP) method applied to styrene and various acrylate monomers (see Fig. 21). 

Figure 21. Atom transfer radical polymerization (ATRP) synthetic route to tetrafunctional initiators of a star polymer with adamantyl (adamantane core). Taken from Ref. [91] with permission.

For star polymers a value of e = 0.5 has been obtained (1, V7) and studies (18) of model comb polymers indicate a value of 1.5. Other work (191 has suggested that e is near 0.5 at low LCB frequencies. For a random LCB conformation of higher branching frequency an e value between 0.7 and 1.3 might be expected, i.e. somewhere between a star and a comb configuration. 

Hadjichristidis, N, Pispas, S.t Pitsikalis, MIatrou, H Vlahos, C. Asymmetric Star Polymers Synthesis and Properties, VoL 142, pp, 71428. 

Jacob, S, and Kenned /. Synthesis, Characterization and Properties of OCTA-ARM Poly-isobutylene-Based Star Polymers. Vol 146, pp. 1-38. 

In order to illustrate the potential applications of rheo-NMR five examples have been chosen. The first example deals with wormlike micelles [22] in which NMR velocim-etry is used to profile anomalous deformational flow and deuterium NMR spectroscopy is used to determine micellar ordering in the flow. The second example concerns flow in a soft glassy material comprising a solution of intermittently jammed star polymers [23], a system in which flow fluctuations are apparent. The third... 

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