Polymer/polymeric architectures

Some 17 years later, many of these predictions are turning into experimental reality as many of these questions are being answered in each new publication or patent that appears on dendritic architecture. Presently, dendritic polymers are recognized as the fourth major class of polymeric architecture consisting of three subsets that are based on degree of structural control, namely (a) random hyperbranched polymers, (b) dendrigraft polymers and (c) dendrimers (Figure 6). 

While in most of the reports on SIP free radical polymerization is utihzed, the restricted synthetic possibihties and lack of control of the polymerization in terms of the achievable variation of the polymer brush architecture limited its use. The alternatives for the preparation of weU-defined brush systems were hving ionic polymerizations. Recently, controlled radical polymerization techniques has been developed and almost immediately apphed in SIP to prepare stracturally weU-de-fined brush systems. This includes living radical polymerization using nitroxide species such as 2,2,6,6-tetramethyl-4-piperidin-l-oxyl (TEMPO) [285], reversible addition fragmentation chain transfer (RAFT) polymerization mainly utilizing dithio-carbamates as iniferters (iniferter describes a molecule that functions as an initiator, chain transfer agent and terminator during polymerization) [286], as well as atom transfer radical polymerization (ATRP) were the free radical is formed by a reversible reduction-oxidation process of added metal complexes [287]. All techniques rely on the principle to drastically reduce the number of free radicals by the formation of a dormant species in equilibrium to an active free radical. By this the characteristic side reactions of free radicals are effectively suppressed. 

Mori H, Muller AHE (2003) New polymeric architectures with (meth)acrylic acid segments. Prog Polym Sci 28 1403-1439... 

Hyperbranched polymers represent a compromise between the perfect structures of dendrimers and the partially degraded architecture of activated PAMAMs. In this way such polymeric architectures are the structural prerequisites implicated in the design of an efficient gene vector. Hyperbranched polymers are highly branched molecules, composed of dendritic (D), linear (L), and terminal units (T) (Fig. 5). 

Twenty years have passed since DuPont announced a startling new process for polymerization of methacrylate monomers [1]. The method uses a trimethylsilyl ketene acetal initiator catalyzed by nucleophilic anions. It operates at 80 °C and gives unprecedented control over polymer chain architecture (Scheme 1). 

ATRP gives excellent control of polymer chain architecture. For industrial use, however, two problems need to be overcome residual halides and metals in the product would be a problem for electronic device uses. The rate of polymerization may be too slow. This is because the chain end concentrations must be low so that typical radical chain termination is kept to a minimum. Chain termination is a second order reaction and will be minimized by low concentrations of chain end radicals. The low rate of polymerization may increase the cost of the process since the optimum time for a polymerization run is about 6 h. 

A wide variety of polymeric membranes with different barrier properties is already available, many of them in various formats and with various dedicated specifications. The ongoing development in the field is very dynamic and focused on further increasing barrier selectivities (if possible at maximum transmembrane fluxes) and/ or improving membrane stability in order to broaden the applicability. This tailoring of membrane performance is done via various routes controlled macro-molecular synthesis (with a focus on functional polymeric architectures), development of advanced polymer blends or mixed-matrix materials, preparation of novel composite membranes and selective surface modification are the most important trends. Advanced functional polymer membranes such as stimuli-responsive [54] or molecularly imprinted polymer (MIP) membranes [55] are examples of the development of another dimension in that field. On that basis, it is expected that polymeric membranes will play a major role in process intensification in many different fields. 

Polymer-based systems offer numerous advantages, such as biocompatibility, biodegradability, and ability to incorporate functional groups for attachment of drugs. Drugs can be incorporated into the polymer matrix or in the cavity created by the polymeric architecture, from which the drug molecule can be released with an element of temporal control, and controlled pharmacokinetic profile with almost zero-order release achievable. 

Modem applications of polymeric materials desire and in certain instances require various functions in one family of polymeric architectures. To achieve such a goal most of the time one needs to devise new functional monomers with desired functionalities and study their polymerization to generate new polymeric materials. This approach is time tested and finally leads to desired materials. Though, one drawback to this approach is that for each new polymer a new functional monomer has to be synthesized and in certain instances new processes have to be developed to convert them to useful polymeric materials. In order to expedite the discovery of new functional polymers, one strategy could be to use a template polymer and investigate strategies to modify the property profile of such templates to achieve desired polymeric materials with required functionalities. This strategy allows a fast and efficient way to obtain functional polymeric materials in an economical fashion (Scheme 1). 

Kakwere, H. Perrier, S. Design of complex polymeric architectures and nanostructured materials/ hybrids by living radical polymerization of hydroxylated monomers. Polym. Chem. 2011,2 (2), 270-288. 

In conclusion, we seek in this article to clarify the terminology used to describe supramolecuiar isomerism observed in coordination polymer frameworks. The terminology used has wider implications and can readily be applied to hydrogen-bonded arrays and also to non-polymeric architectures. 

Since the development of soft ionization mass spectrometry [9], which allows to analyze large organic molecules without fragmentation, various polymer architectures were characterized by mass spectrometry. In principle, different parameters tailoring polymeric material properties such as molar mass (MJ, architecture (linear, branched, cyclic, star, etc.), monomer composition, degree of functionalization, end groups, and the presence of impurities or additives can be evaluated by mass spectrometry, however, with some limitations. The determination of molar masses of polymers by mass spectrometry is only possible for reasonable low dispersity polymeric architectures, which can be achieved by using controllable polymerization techniques such as anionic or... 

Dendrimer chemistry is constantly maturing to deliver advanced maaomolecules with increased stmctural control. A prime example is the full integration of the click concept for the constmction of a variety of polymeric architectures including dendrimers, dendronized polymers, and hyperbranched polymers. The concept of click reactions was introduced in 2001 by Kolb et alP and includes extremely versatile organic reactions that exhibit a high thermodynamic driving force (>20 kcal mor ). A reaction must satisfy the following requirements to be characterized as a click reaction ... 

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