Effect of Macromolecular Architecture

The polymer architecture affects the demixing behaviour of thermoresponsive polymers [562], On the basis of theoretical studies it is expected that, as a rule, branched macromolecules are more soluble than their linear analogues [563-565]. This prediction was confirmed experimentally in the case of a solution of star-like polystyrene in cyclohexane (an UCST-type phase separation) for which an increase in the degree of branching resulted in a decrease in the temperature of demixing [566, 567], On the basis of a review of water-soluble polymers of various shapes by Aoshima and Kanaoka [30], it appears that water-soluble polymers do not offer a uniform tendency in their LCST-type phase behaviour. 

Xu and Liu recently reported the syntheses of the well-defined 7-arm and 21-arm PiPAAm stars with a P-cyclodextrin core [278, 568] and presented a thorough analysis of the literature on thermoresponsive stars and polymer brushes tethered to curved surfaces, such as latex particles [279, 280, 569], gold nanoparticles [282] and microgels [570], A unique feature of these architectures is that they form a densely packed spherical core and a less-dense outer shell [159]. As a result of such a non-uniform density distribution, two temperature-induced phase transitions have been observed experimentally in several systems based on PiPAAm [279, 280, 282, 568, 569], One transition has been ascribed to the phase transition of the inner segments of PiPAAm, whereas the other transition, which is concentration dependent, was assigned to the collapse of the outer PiPAAm segments [282], 

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Teyssie and coworkers [86] studied the effect of macromolecular architecture on the lamellar structure of the poly(ethylene oxide) crystallizable arms in (poly tert-butyl styrene)(poly(ethylene oxide))2 [PtBuS(PEO)2] miktoarm stars by using SAXS and differential scanning calorimetry (DSC). The results were compared with the ones obtained on poly(tBuS-fe-EO) materials. At the same total molecular weight and composition the melting temperature, the degree of crystallinity and the number of folds of PEO chains were found to be lower for the branched samples. 

Copolymerization is the most important synthetic strategy available to tailor the physical, solution and mechanical properties of macromolecules. In this paper the synthesis of well defined random and block copolymers containing monomer units of very different polarity are described. Novel macromolecular architectures incorporating 4-hydroxystyrene, t-butylacrylate and styrene have been prepared to investigate the combined effects of macromolecular architecture and hydrophobicity on thin film aqueous base dissolution. 

Effect of Macromolecular Architecture Upon Aqueous Base Dissolution. To... 

Therefore, a fundamental understanding of solution properties of macromolecules and their assemblies is of cmdal importance for both polymer sdence and technology as well as biology and medicine. There are a number of classical books considering properties of solutions of linear-chain macromole-cules. In this chapter, we aim to make a major emphasis on the effects of macromolecular architecture, that is, topology and amphiphilic nature, on the solution properties of macromolecules. 

Protein polymers based on Lys-25 were prepared by recombinant DNA (rDNA) technology and bacterial protein expression. The main advantage of this approach is the ability to directly produce high molecular weight polypeptides of exact amino acid sequence with high fidelity as required for this investigation. In contrast to conventional polymer synthesis, protein biosynthesis proceeds with near-absolute control of macromolecular architecture, i.e., size, composition, sequence, topology, and stereochemistry. Biosynthetic polyfa-amino acids) can be considered as model uniform polymers and may possess unique structures and, hence, materials properties, as a consequence of their sequence specificity [11]. Protein biosynthesis affords an opportunity to completely specify the primary structure of the polypeptide repeat and analyze the effect of sequence and structural uniformity on the properties of the protein network. 

The dissolution behavior of copolymers in aqueous base is of primary importance in photoresist performance. As microlithography continues to decrease in exposure wavelength and the minimum feature size required from photoresist compositions decreases below 0.20 pm, control of macromolecular architecture will play an increasingly significant role. That is, how does the random, alternating or "blocky nature of the matrix polymer effect its solubility in aqueous base. It has been well documented for novolac based photoresists that the molecular weight distribution... 

As depicted in this chapter, specific structural and electronic properties of fluo-ropolymers have made them the polymers of choice to be used in SC-CO2. The study of different families of fluoropolymer demonstrated that, apart from the effect of polymer architecture and CO2 density, the lowering of polymer-polymer interactions appeared as the main critical parameter to improve polymer solubility. Moreover, the use of those polymers as building blocks to design macromolecular surfactants allows the successful formation of micelle-like structures or the formation of emulsions in the presence of additional water. Based on this knowledge, development of new fluoropolymer families will surely pave the way for the preparation of stable W/SC-CO2 emulsions with great promise for the development of environmental-friendly chemical processes in diverse fields of organic and inorganic synthesis and polymerization. 

The recent improvements in methods for [2]catenane synthesis mean that interlocked structures are now becoming readily available as building blocks and cores for novel macromolecular materials. Many new architectures and polymer systems will undoubtedly be developed over the next few years and the effects of mechanical, rather than covalent, linkages on bulk and surface properties will begin to be evaluated. 

Confinement effects in thin films of hyperbranched polyester show up at thickness much larger than those reported for linear polymers. This must be attributed to their special macromolecular architecture. 

Tests of the light stabilizing activity of monomeric HAS and the corresponding homo- and copolymers reveal mostly better properties of the monomers if physical persistence is not the decisive testing factor [8]. This was found e.g. in comparison of the functionalized urethane 182 and its copolymers with styrene or methyl methacrylate [303], The macromolecular architecture is expressed very distinctly. For example, a PP photografted HAS-functionalized acrylate was more efficient than the respective monomer or homopolymer. Another observation performed with A-(2,2,6,6-tetramethyl-4-piperidyl)methacry-lamide, piperidyl acrylate and methacrylate, their homopolymers and copolymers with dodecyl methacrylate and octadecyl acrylate revealed that the stabilizing effect in PP was in favour of copolymers [304]. Similar HAS-functionalized monomers were copolymerized with styrene. In this case, the copolymers were substantially less efficient in PS than the monomers. Masterbatches of PP-bound HAS prepared by reactive processing imparted a comparable effectivity as conventional HAS when tested at an equimolar basis [298]. 

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