Polymer architectures advanced

As indicated above, conventional free-radical poljnnerization is not very well suited for the synthesis of advanced polymer architectures. Even the synthesis of di- or triblock copolymers is hardly possible using this technique. The main reason is the continuous initiation and termination of chains. This results in the early generation of dead polymer chains that no longer participate in the polymerization process. The consecutive addition of monomers as employed in living anionic polymerization for the synthesis of eg poly(styrene-6Zoc -butadiene) will only lead to the synthesis of a mixture of two homopolymers. 

Furthermore, despite still being the route able to prepare the highest Mjy, ROP inherently produces polymers with broad polydispersities (Mjy/M >2) due to its initiation mechanism, in which the formation of new chains can occur throughout. Although such polydispersity is perfectly tolerable for many medical applications, for example, as inert biomaterials, the method is less suitable for some biomedical applications, in which precise molecular size is often an essential property. Furthermore, advanced polymer architectures and macromolecular constructs cannot be readily attained via this method, due to the absence of end-group control, and hence the development of poly(dichloro)phosphazene with controlled... 

This update focuses on describing the fundamentals of controlled polymerisation techniques and methods for constructing advanced polymer architectures to be used in polymer-based nanomedicine. We review this growing field, which uses recent advances in polymer chemistry and conjugation techniques to construct advanced nanoparticles. 

Compounding, Mixing and Processing Peroxide-Cured Viton made with Advanced Polymer Architecture, DuPont Performance Elastomers Technical Bulletin (06/04 VTE-A10123-00-B0604). 

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. 

In the second chapter, we try to emphasize the possibilities of producing tailor-made polymers with predicted properties. By using different types of initiators and catalysts, ring-opening polymerization of lactones and lactides provides macromolecules with advanced molecular architecture - a careful selection of appropriate conditions is crucial. The purpose of this chapter is also to describe the mechanisms and typical kinetic features. 

Advances in the modeling of polymer systems, such as the random phase approximation (RPA) [3,4], thoroughly reviewed here, have made it possible to analyze SANS data from widely different and seemingly complicated mixtures of various polymer architectures at various concentrations and temperatures. Old modeling methods, such as the inverse Zimm formula [5] (which is the basis of the Zimm Plot), or more recent modeling methods such as the high concentration method [6-8], fall within the scope of the present overview and are... 

Complex Architectures. Perhaps the most significant recent advances in molecular understanding of polymer melts have emerged from the study of branched polymer architectures. We have noted above how a tube theory for star-polymers provided the means to treat fluctuations in entangled path length in linear polymers (see Figure lb). This is simply due to the complete suppression of reptation in star polymers without fluctuation there is no stress-relaxation at all ... 

Although the possibility of carrying out catalytic polymerizations in the presence of water had been known since the 1960s, significant advances in catalytic polymerizations in aqueous systems have only been achieved over the past decade. Today, (1) various different types of transition metal-catalyzed polymerizations can be carried out efficiently in aqueous systems. (2) A variety of polymers, ranging from hydrocarbons to water-soluble polymers, and a scope of polymer architectures are accessible. (3) Polymerization can be carried out in a controlled fashion. 

The combination of sohd phase peptide synthesis with polymer chemistry has proven to be a versatile method for the preparation of polymer-peptide hybrids. Introduction of native ligation methods even allows the synthesis of polymer modified polypeptides and proteins via an entire organic chemistry approach. In the field of polymer chemistry—besides the advances in NCA polymerization, which will be discussed by others and is therefore not part of the scope of this review—controlled radical polymerization has been shown to be a robust technique, capable of creating well-defined biofunctional polymer architectures. Through protein engineering, methods have been estabhshed that enable the construction of tailor-made proteins, which can be functionalized with synthetic polymer chains in a highly defined manner. 

A wide variety of chemical catalysts is nowadays available to polymerize monomers into well-defined polymers and polymer architectures that are applicable in advanced materials for example, as biomedical applications and nanotechnology. However, synthetic polymers rarely possess well-defined stereochemistries in their backbones. This sharply contrasts with the polymers made by nature where perfect stereocontrol is the norm. An interesting exception is poly-L-lactide, a polyester that is used in a variety of biomedical applications [1]. By simply playing with the stereochemistry of the backbone, properties ranging from a semicrystalline, high melting polymer (poly-L-lactide) to an amorphous high Tg polymer (poly-meso-lactide) have been achieved [2]. 

This book contains the descriptions and results of theoretical and experimental research in the field of efficient building material composites based on advanced polymer binders that were carried out by scientific teams from Polymate Ltd., International Nanotechnology Center (http //www.polymateltd.com, Israel) and Voronezh State University of Architecture and Civil Engineering (VGASU, Russia) with the direct participation or under the leadership of the authors. Physical and mechanical characteristics of these composites, including chemical resistance in various aggressive environments, are discussed in this book. 

This chapter will serve to highlight recent advances in polymer science that have been aided by the use of click chemistry. The copper(l)-catalyzed azide-alkyne cycloaddition (CuAAC) and thiol-ene reactions will be discussed first, after which the utilization of these chemical transformations in the construction and fimction-ahzation of a multitude of different polymeric materials will be outlined. Particular attention will be focused on the preparation of highly complex polymer architectures, such as dendrimers and star polymers, which exempHfy the essential role that chck chemistry has assumed in the polymer science community. 

In 1995, Bert joined the Eindhoven University of Technology as an assistant professor, where he was promoted to associate professor in 2002. His research is largely focused on LRP. In 1998, he came in contact with the Institute for Polymer Science at the University of Stellenbosch. From that time onwards, he was involved in the supervision of MSc and PhD students and visited Stellenbosch 2-3 times per year. In 2006, he was among the first 20 scientists who were awarded a South African Research Chair by the National Research Foundation and the Department of Science and Technology. In 2007, he received an A-rating from the NRF. In the framework of his Research Chair on Advanced Macromolecular Architectures, Bert is in the process of expanding the scope of his research toward biomedical applications. In 2008, he was elected a Fellow of the Royal Society of South Africa, and in 2009, he received the Rector s Award for Excellent Research at Stellenbosch University. From July 2009 onwards, he has been one of the editors of Elsevier s European Polymer Journal. 

The first successful ADMET polymerisation was reported by Wagener and colleagues [28]. They polymerised 1,5-hexadiene and 1,9-decadiene to 1,4-polybutadiene [with a weight average molecular weight (Mw) of 28 kDa] and polyoctenylene (Mw = 108 kDa), respectively, using a tungsten-based catalyst that required extremely dry conditions to avoid side reactions. Recent advances in the development of very active and stable catalysts now allow the synthesis of various polymer architectures with relative ease. 

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