Dendritically branched polymers characterization

Characterization of Dendritically Branched Polymers by Small Angle Neutron Scattering (SANS), Small Angle X-Ray Scattering (SAXS) and Transmission Electron Microscopy (TEM)... 

Bauer BJ, Amis EJ (2001) Characterization of dendritically branched polymers by small angle neutron scattering (SANS), small angle X-ray scattering (SAXS), and transmission... 

Branched macromolecules fall into three main classes star-branched polymers, characterized by multiple chains linked at one central point (Roovers, 1985), comb-branched polymers, having one linear backbone and side chains randomly distributed along it (Rempp et al., 1988), and dendritic polymers, with a multilevel branched architecture (Tomalia and Frechet, 2001). The cascade-branched structure of dendritic polymers is typically derived from polyfunctional monomers under more or less strictly controlled polymerization conditions. This class of macromolecules has a unique combination of features and, as a result, a broad spectrum of applications is being developed for these materials in areas including microencapsulation, drag delivery, nanotechnology, polymer processing additives, and catalysis. 

Hirao, A., Hayashi,M.,Loykulnant,S., and Sugiyama,K. (2005) Precise syntheses of chain-multi-functionalizedpolymers, star-branched polymers, star-linearblockpolymers, densely branched polymers, and dendritic branched polymers based on iterative approach using functionalized 1,1-diphenylethylene derivatives. Progress in Polymer Science, 30,111-182. Hogen-Esch, T.E. (2006) Synthesis and characterization of macrocyclic vinyl aromatic polymers. Journal of Polymer Science Part A-Polymer Chemistry, 44,2139—2155. 

The synthesis of well-defined LCB polymers have progressed considerably beyond the original star polymers prepared by anionic polymerization between 1970 and 1980. Characterization of these new polymers has often been limited to NMR and SEC analysis. The physical properties of these polymers in dilute solution and in the bulk merit attention, especially in the case of completely new architectures such as the dendritic polymers. Many other branched polymers have been prepared, e.g. rigid polymers like nylon [123], polyimide [124] poly(aspartite) [125] and branched poly(thiophene) [126], There seems to be ample room for further development via the use of dendrimers and hyperbran-... 

Whereas the well-characterized, perfect (or nearly so) structures of dendritic macromolecules, constructed in discrete stepwise procedures have been described in the preceding chapters, this Chapter reports on the related, less than perfect, hyperbranched polymers, which are synthesized by means of a direct, one-step polycondensation of A B monomers, where x > 2. Flory s prediction and subsequent demonstration 1,2 that A B monomers generate highly branched polymers heralded advances in the creation of idealized dendritic systems thus the desire for simpler, and in most cases more economical, (one-step) procedures to the hyperbranched relatives became more attractive. 

AF4 coupled with static and DLS detectors enables comprehensive information about structural and branching characteristics of biopolymers (e.g., starches), synthetic polymers, proteins, etc. [25, 26]. Especially in case of branched polymer stractures like dendronized glycopolymers, the separation and characterization with AF4-LS lead to comprehensive information and understanding in molecular structures and aggregation behavior [27]. Furthermore, studies of uptake studies of dendritic glycopolymers and dye molecules were performed for the first time by AF4-LS (see Fig. 4.12). Here, a good correlation was obtained between the increase of molar mass and the quantified amount of dye molecules, which were encapsulated by the glycopolymers [28]. 

Hyperbranched polymers are characterized by their degree of branching (DB). Hie DB of polymers obtained by the step-growth polymerization of AB2-type monomers is defined by Eq. (2.1) in which dendritic units have two reacted B-groups, linear units have one reacted B-group, and terminal units have two unreacted B-groups191 ... 

Dendrons and dendrimers are the most intensely investigated subset of dendritic polymers. In the past decade over 2000 literature references have appeared on this unique class of structure controlled polymers. The term dendrimer was coined by Tomalia, et al. over 15 years ago in the first reports on poly(amidoamine) (PAMAM) dendrimers [75, 76]. It is derived from the Greek words dendri-(branch tree-like) and meros - part of). Poly(amidoamine) dendrimers constitute the first dendrimer family to be commercialized and undoubtedly represent the most extensively characterized and best understood series at this time. In view of the extensive literature information in this area, much of the remaining overview will focus on PAMAM dendrimers and will... 

The core first method has been applied to prepare four-arm star PMMA. In this case selective degradation of the core allowed unambiguous proof of the star structure. However, the MWD is a little too large to claim that only four-arm star polymers are present [81], Comb PMMAs with randomly placed branches have been prepared by anionic copolymerization of MMA and monodisperse PMMA macromonomers [82], A thorough dilute solution characterization revealed monodisperse samples with 2 to 13 branches. A certain polydispersity of the number of branches has to be expected. This was not detected because the branch length was very short relative to the length of the backbone [83]. Recently, PMMA stars (with 6 and 12 arms) have been prepared from dendritic... 

A hyperbranched polymer is often characterized by the degree of branching DB [Holter et al., 1997 Jo and Lee, 2001 Kim, 1998 Lee et al., 2000]. For the hyperbranched polymer produced from AB2, there are three different types of repeat units dendritic, linear, and terminal units defined as units having two, one, and no B groups reacted, respectively. The degree (fraction) of branching (DB) is given by... 

The main feature of polymers is their MMD, which is well known and understood today. However, several other properties in which the breadth of distribution are important and influence polymer behavior (see Figure 1) include physical, the classical chain-length distribution chemical, two or more comonomers are incorporated in different fractions topological, polymer architecture may differ (e.g., linear, branched, grafted, cyclic, star or comb-like, and dendritic) structural, comonomer placement may be random, block, alternating, and so on and functional, distribution of chain functions (e.g., all chain ends or only some carry specific groups). Other properties the polymers may disperse (tacticity and crystallite dimensions) are not of the same general interest or cannot be characterized by solution methods. 

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