Polymer , generally hyperbranched

Hyperbranched polymers generally have very low melt and indinsic viscosities. The large number of chain-end functional groups present in hyperbranched macromolecules have also been shown to dramatically affect physical properties... 

Branching in polymers generally reduces the crystallization tendency for conventional polymers. Therefore, hyperbranched polymers were first believed to behave as amorphous polymers due to the highly branched backbone. Several papers have, however, shown that both liquid crystalline and crystalline hyperbranched polymers can be made from some special A B monomers or by attachment of crystallizable end groups. 

Alditols polyols are readily renewable, inexpensive and harmless to the environment. By incorporation of polyols into aliphatic polyesters, functional linear or hyperbranched polymers can be prepared with specific biological activities and/or that respond to environmental stimuli. Polyesters with carbohydrate or polyol repeat units in chains have been prepared by chemical methods. " In some cases, the reaction conditions led to hyperbranched polymers (HBPs). The highly branched architecture of HBPs leads to unusual mechanical, rheological and compatibility properties. " These distinguishing characteristics have garnered interest for their use in numerous industrial and biomedical fields. Chemical routes to linear polyol-polyesters require elaborate protection-deprotection steps ". Furthermore, condensation routes to hyperbranched polymers generally require harsh reaction conditions such as temperatures above 150 C and highly acidic catalysts ". ... 

In general, hyperbranched polymers are obtained by the polymerization of an AB2 monomer. Thus, in the first step, the hyperbranched PES must be manufactured. For example, the synthesis of 3,5-difluoro-4 -hydroxydi-phenyl sulfone can be accomplished by the reaction of 3,5-difluorophenyl-magnesium bromide with 4-methoxyphenylsulfonyl chloride, followed by deprotection of the phenol group with HBr in acetic acid." ... 

Our review starts with the general formulation of the GGS model in Sect. 2. In the framework of the GGS approach many dynamical quantities of experimental relevance can be expressed through analytical equations. Because of this, in Sect. 3 we outline the derivation of such expressions for the dynamical shear modulus and the viscosity, for the relaxation modulus, for the dielectric susceptibility, and for the displacement of monomers under external forces. Section 4 provides a historical retrospective of the classical Rouse model, while emphasizing its successes and limitations. The next three sections are devoted to the dynamical properties of several classes of polymer networks, ranging from regular and fractal networks to network models which take into account structural heterogeneities encountered in real systems. Sections 8 and 9 discuss dendrimers, dendritic polymers, and hyperbranched polymers. 

In this subsection we will consider (distinct from the dendrimers of Sect. 8) another class of regular hyperbranched polymers. We recall that the quest for simpUcity in the study of complex systems has led to fruitful ideas. In polymers such an idea is seating, as forcefully pointed out by de Gennes [4j. Now, the price to be paid in going from linear chains to star polymers [33,194[, dendrimers [13,33,194,205] and general hyperbranched structures [216[ is that scaling (at least in its classical form) is not expected to hold anymore (at least not in a simple form, which implies power-law dependences on the frequency CO or on the time f). One of the reasons for this is that while several material classes (such as the Rouse chains) are fractal, more general structures do not necessarily behave as fractals. 

Although low-molar-mass aliphatic polyesters and unsaturated polyesters can be synthesized without added catalyst (see Sections 2.4.1.1.1 and 2.4.2.1), the presence of a catalyst is generally required for the preparation of high-molar-mass polyesters. Strong acids are very efficient polyesterification catalysts but also catalyze a number of side reactions at elevated temperature (>160°C), leading to polymers of inferior quality. Acid catalysts are, therefore, not much used. An exception is the bulk synthesis of hyperbranched polyesters reported in Section 2.4.5.1, which is carried out at moderate temperature (140°C) under vacuum in the presence of p-toluene sulfonic acid catalyst. The use of strongly acidic oil-soluble catalysts has also been reported for the low-temperature synthesis of polyester oligomers in water-in-oil emulsions.216... 

Hyperbranched polymers are generally composed of branched (dendritic), Hn-ear, and terminal units. In contrast to AB2 systems, there are two different types of linear units in SCVP one resembles a repeat unit of a polycondensate (----A -b----) and one a monomer unit of a vinyl polymer (--a(B )---). 

A challenging goal in this field, particularly from the synthetic point of view, is the development of general AB polymerization methods that achieve control over DB and narrow MWDs. Experimental results and theoretical studies mentioned above suggest that the SCV(C)P from surfaces, which are functionahzed with monolayers of initiators, permit a controlled polymerization, resulting structural characteristics (molecular weight averages, DB) of hyperbranched polymers. In particular, it is expected that the use of polyfunctional initiators with a different number of initiator functionahty, copolymerization, and slow monomer addition techniques lead to control the molecular parameters. 

Figure 23 General structure of a hyperbranched polymer synthesized by the polymerization of AB2 monomer.

Random hyperbranched polymers are generally produced by the one-pot polymerization of ABX monomers or macromonomers involving polycondensation, ring opening or polyaddition reactions hence the products usually consist of broad statistical molecular weight distributions. 

If the crosslinking reaction is interrupted before the gel point, the molecular weight and functionality distributions of such functional precursors are wider but not basically different from that of polymers of BAf monomer. It was stressed recently that they resemble hyperbranched polymers [24] in a certain respects. The pre-gel polymers are generally not stable because the crosslinking reaction can occur during storage. Stable precursors, e.g. for RAf + R Ba, can be obtained in two ways ... 

Fig. 9. Generalized description of the intrinsic viscosity as function of molar mass for linear polymers, hyperbranched polymers and dendrimers as described by Frechet [33]...

The general concept of the synthesis of hyperbranched polyesteramides allows the use of any secondary amine with at least two )5-hydroxyalkyl groups such as diisobutanolamine or di- -cyclohexanolamine for the build-up of the highly branched structure. In the case of secondary mono )5-hydroxyalkyl amines, e.g., methyl isopropanolamine, one obtains linear polymers. Primary amines cannot be used as they form imides in the polycondensation step. 

The formation of synthetic polymers is a process which occurs via chemical connection of many hundreds up to many thousands of monomer molecules. As a result, macromolecular chains are formed. They are, in general, linear, but can be branched, hyperbranched, or crosslinked as well. However, depending on the number of different monomers and how they are connected, homo- or one of the various kinds of copolymers can result. The chemical process of chain formation may be subdivided roughly into two classes, depending on whether it proceeds as a chain-growth or as a step-growth reaction. 

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