Hyper-Branched Polyesters

Hyper-branched aliphatic polyesters are different from linear polyesters because of their unique mechanical and rheological properties, which can easily be tailored by changing the nature of the end group [156-159]. Both dendrimers and hyper-branched macromolecules are prepared from AB2 monomers, using dif- 

Hyper-branched polymers are prepared in a single-step polymerization from ABX monomers. Thus, a perfectly branched structure is present in dendrimers, whereas irregular branching is present in hyper-branched polymers. Aluminum alkoxide-based initiators or tin-based catalysts have been successfully used for the preparation of, hyper-branched [160-162, 166-168], dendrimer-like star polymers [160], and star-shaped polymers. The first and second generations of the benzyl ester of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) are effective initiators for the ROP of lactones (e-CL) in the presence of Sn(Oct)2. The 

A commercially available hyper-branched polyester derived from bis-MPA was used as the multifunctional initiating core for the ROP of e-CL and this led to the synthesis of hybrid dendritic linear star polymers. The reactivities of the chain-end hydroxymethyl groups in the dendrimer were significantly greater than in the isomeric hyper-branched case. 

Lipase catalysis has been used for the synthesis of a poly(e-CL)-monosubsti-tuted first generation dendrimer [169]. 

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In our first chapter, we summarize the synthesis of aliphatic polyesters. This includes homopolyesters, random, block, graft, and star- and hyper-branched polyesters. Mainly materials such as PLA and PCL homopolymers have so far been used in most applications. There are, however, many others monomers which one can use as homopolymers or in copolymerization with lactide and caprolactone. Different molecular stuctures give a wider range of physical properties as well as the possibility of regulating the degradation rate. 

The reproducibility of the sample preparation has been carefully checked. An example is given in Fig. 6 measuring two different samples (thin films of hyper-branched polyesters) prepared under identical experimental conditions revealed coincident dielectric spectra. 

Fig. 6 Dielectric loss vs. temperature at different frequencies, as indicated, for two thin films of hyper-branched polyesters of 27 nm and 28 nm...

Fig. 8 Time dependence of the dielectric loss at 200 °C and 0.3 Hz in a pure nitrogen atmosphere for a thin film of hyper-branched polyesters of 17nm...

The AB2 monomer, 3,5-bis-(3-hydroxypropyl-l-yl)benzoic acid is converted to a hyper-branched polyester using a carbodiimide to affect the polymerization. In this manner, soluble polyesters with molecular weights ranging from 500 to 11 000 and branching from... 

Chu, F. K., Hawker, C. J. (1993). Different syntheses of isomeric hyper branched polyester ketones Polym. Bull, 30(3), 265-272. 

Voit, B, Beyerlein, D. Eichhom, K. Grundke, K. Schmaljohann, D. and Loontjens, T. Functional hyper-branched polyesters for application in blends, coations, and thin films. Chem. Eng. Technol, 25, 704-707 (2002). 

MuUcem, T. J., Tan, N. C. Processing and characterization of reactive polystyrene/hyper-branched polyester blends. Polymer (2000)... 

Figure 10.13 Argand plot showing two dielectric relaxation processes a and P for a hyper-branched polyester measured at 260 K. Experimental data are indicated by the points and the lines are obtained by fitting the Havrilak-Negami equation to experimental data. After data from Malmstrom et al. (1994).

Figure 7 100 MHz 1h NMR spectrum of the star-shaped, hyper-branched polyester 15 (in CDCI3).

Recently a great deal of research work has been carried out on new hyperbranched polyethers synthesized from HMO or HEO by CROP Compared with the hyper-branched polyesters as mentioned previously, these hyperbranched polyethers were synthesized in a one-pot protocol. Motivated by this novel synthetic strategy, a new oxetane-derived 3-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxymethyl)-3 -methyloxetane (HEMO) monomer was prepared in our laboratory. Subsequently, a novel hyperbranched polyether, referred as PHEMO (Fig. 14.10), was synthesized... 

Sauer et al. described several miscible blends of PAEK with thermoplastic polyimide (TPI). Thus, PEK, PEEK and PEKK were melt-blended at T > 400°C with three TPIs. The blends had lower viscosities and so were easier to process. More recently miscible HTPB are mentioned below. New hyper-branched polyesters of the AB2 and A2B3 type (the subscripts indicate the number of reactive groups), with Tg = 199-268°C and TGA 10 % weight loss at 400-427°C, were found miscible with semi-aromatic PA6T/6.15... 

In order to compare general properties of hyperbranched polymers and dendrimers, Wooley et al. examined a model hyperbranched polyester and corresponding dendrimer. Pol)miers prepared from 3-hydroxy-5-( eri-butyldi-methylsiloxy)benzoic acid, as branching point, showed that thermal properties, such as Tg and those shown by thermogravimetic analysis (TGA), were independent of pol)mier architecture. However, the dendritic and hyperbranched materials demonstrated comparative solubilities that were much greater than that found for the linear polymer [99]. Their conclusions on the thermal properties may contradict some other findings. For examples, the of hyper-... 

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