Polyester chain length formation

While catalysts are also used in the production of other types of polymers, the properties of most of these materials are not particularly dependent on the type of catalyst employed. Many poly condensation reactions, e. g. the formation of polyesters, polyamides or urea-formaldehyde resins, are speeded up by addition of some Bronsted or Lewis acids. Since relevant properties of these polymer products, such as their average chain lengths, are controlled by equilibrium parameters, primarily by the reaction temperatures and molar ratios of the monomers employed, and since their linkage patterns are dictated by the functional groups involved, addition of a catalyst has little leverage on the properties of the resulting polymer materials. 

More evidence In favor of polymer chain growth on both sides of a metalloporphyrln plane was obtained In the copolymerization of propylene oxide and phthallc anhydride. The catalyst was the combination of EtPh3PBr and TPPAl-(-0-CHMe-CH2-)-Cl (TPPAlPPO), which can be obtained by the polymerization of propylene oxide with TPPAICI (Equation 1). If the copolymerization proceeds on both sides of a metalloporphyrln plane, a block copolymer, polyetherpolyester. Is expected to be formed on one side, and a polyester Is expected on the other side. In fact, GPC of the reaction product (Figure 8) showed two narrow peaks and clearly Indicated the formation of polymers with different chain lengths. Thus, this reaction provides the first example of a catalytic reaction occurring on both sides of a metalloporphyrln pleme. 

Timm, A. and Steinbuchel, A., 1990, Formation of polyester consisting of medium chain length 3-hydroxyalkanoic acid from gluconate by Pseudomonas aeruginosa and other fluorescent pseudomonads. Appl. Environ. Microbiol. 56 3360-3367... 

Timm A, Steinbtichel A (1990) Formation of polyesters consisting of medium-chain-length... 

Let us emphasize the main facts for alkyl-substituted stiff macromolecules. The conformation of the main chain is affected by side groups and depends critically on the chain length. For relatively short side chains hexagonal packing of macromolecules is possible, whereas for longer chains the boardlike shape of the molecules leads to formation of a highly ordered layered structure. In the crystal state the coplanar arrangement of the fully extended aromatic backbone for polyesters is possible. In the liquid crystalline state both a well-ordered layered structure and a nematic structure are observed. Because of the boardlike shape of the molecules, the nematic phase is biaxial. 

This phenomenon is attributed to the melting point of the material - a correlation already demonstrated by Tokiwa and co-workers for different aliphatic polyesters [79]. In aliphatic-aromatic copolyesters, the melting behaviour is mainly determined by the length of the aromatic sequences in the polymer chains, which depends both on the composition and structure [86, 87]. For many aliphatic polyesters, a correlation of the degradability with the melting point was observed [2]. Marten [86] interpreted it as a decrease in the mobility of the polyester chains at lower temperatures in this situation the polymer chains are highly fixed in the polymer crystals and cannot adjust easily into the active sites of the extracellular enzymes. A random insertion of some aromatic monomers in aliphatic polymer chains disturbs the formation of crystals. 

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