Block copolymers copolyesters Poly

Aluminum isopropoxide has been used for the preparation of block copolyesters [147, 148]. Tri-block poly(e-CL-b-DXO-e-CL) was prepared by the sequential addition of different monomers to a living polymerization system initiated with aluminum isopropoxide in THF or toluene solution [95]. An alternative route for the preparation of the tri-block copolymer was to react the diblock poly(e-CL-b-DXO) containing an -OH functionality at the chain end using a difunctional coupling agent such as isocyanate or acid chloride (Scheme 18). However, the molecular weights were low and full conversion of monomers was not achieved. 

For most of the results discussed below, the following is valid concerning COP, PC and mixtures if not otherwise stated. The thermotropic copolyester derived from p-hydroxybenzoate and poly(ethylene terephthalate) [10] containing 60 mol% PHB was used exclusively as the PLC component because this composition has the best mechanical properties [10,118] of these copolymers. It was obtained from Eastman Kodak, Kingsport, TN, and had an average molar mass estimated from solvent viscosity of about 19000 g mol . The sequence distribution was calculated from C-NMR as described by Lenz et al. [119] and was nearly random the statistical parameter which describes the randomness of the copolymer is = 1 for a block copolymer and P = 0 for a completely random copolymer. The copolymer used for the experiments had P = 0.15. 

The development of fumarate-based polyesters for biomedical applications started around 20 years ago. Fumaric acid is a natural metabolite involved in Krebs cycle, and is comprised of a reactive double bond available for chemically crosslinking reactions. These characteristics make fumaric acid a candidate building block for crosslinkable polymers. The first and most comprehensively investigated fumarate-based copolymer is the biodegradable copolyester poly(propylene fumarate) (PPF) (Fig. 6.8). ... 

The next two decades saw the development of new polymers such as thermoplastic PU (1961), aromatic polyamides, polyimides (1962) polyaminimides (1965), thermoplastic elastomers (styrene-butadiene block copolymers in 1965), ethylene-vinyl acetate copolymer, ionomers (1964), polysulfone (1965), phenoxy resins, polyphenylene oxide, thermoplastic elastomers based on copolyesters, poly butyl terephthalate (1971) and polyarylates (1974). 

Copolyester Systems.— The synthesis of modified ether-type polyesters and their applications have been reviewed. Block copolymer systems based on poly-(hexamethylene sebacate)-poly(dimethylsiloxane) have been synthesized and characterized by n.m.r. and crystallization studies. Tetramethylene sebacate-tetramethylene terephthalate random copolymers have been prepared and... 

Use of monohydroxy-functionalized polymers as macroini-tiators (e.g., poly(ethylene oxide), PEO poly(styrene), PS and poly(N,N-dimethylacrylamide), PDMA) allowed the synthesis of block copolymers with PLA, P(5-VL), and P(s-CL) as second block. Interestingly, sequential ROP of cyclic esters of different reactivity employing TBD could be achieved at room temperature. Aliphatic block copolyesters could thus be obtained, by polymerizing first the slower propagating monomer to high conversion and subsequently adding the second monomer. ... 

Studies on the melt behaviour of the aromatic copolyesters of poly(ethylene terephthalate) and / -acetoxybenzoic acid have been reported previously. Baird and co-workers have examined the rheological properties of the 40/60 and 20/80 (PET/PHBA) copolyester compositions over a wide temperature range and observed that the melt viscosity of both copolyester compositions was significantly lower than that of poly(ethylene terephthalate) and dependent on the composition of the copolyester. Wissbrun has also studied the flow properties of liquid-crystalline behaving polymers and observed that the flow curves of the 40/60 (PET/PHBA) copolyester composition are very sensitive to the temperature of the melt and its thermal history. In our studies " we observed that the 20/80 (PET/PHBA) copolyester is a block copolymer in which the PHBA blocks aggregate in crystalline domains in contrast to PET/PHBA copolyesters with lower fractions of PHBA which are reported to be random copolymers. 

Many random copolyesters and polyester-polycarbonates have also been prepared by ester interchange reactions in the molten state. Thus, poly(ethylene terephthalate-co -isophthalates) can be obtained by simple melt blending of PET and poly(ethylene isophthalate) (PEI) homopolyesters at 270°C. The copolymer changes gradually from a block type at the beginning of reaction to a random-type... 

Star Copolymers A block copolyester of PLA and hydroxyl-terminated four-armed poly(8-caprolactone) was prepared by a condensation reaction using Sn(Oct)2 or Ee(OAc)2 as an initiator. The formation of a block copolyester as well as a blend was indicated, as shown in Eigure 4.13 [108]. 

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