Polyftetramethylene oxide ,

An example of step- and chain-growth reaction mechanisms is provided by alternative pathways to polyftetramethylene oxide) (1-31), which can be made by the self-condensation of tetramethylene glycol ... 

Some polymorphic modifications can be converted from one to another by a change in temperature. Phase transitions can be also induced by an external stress field. Phase transitions under tensile stress can be observed in natural rubber when it orients and crystallizes under tension and reverts to its original amorphous state by relaxation (Mandelkem, 1964). Stress-induced transitions are also observed in some crystalline polymers, e.g. PBT (Jakeways etal., 1975 Yokouchi etal., 1976) and its block copolymers with polyftetramethylene oxide) (PTMO) (Tashiro et al, 1986), PEO (Takahashi et al., 1973 Tashiro Tadokoro, 1978), polyoxacyclobutane (Takahashi et al., 1980), PA6 (Miyasaka Ishikawa, 1968), PVF2 (Lando et al, 1966 Hasegawa et al, 1972), polypivalolactone (Prud homme Marchessault, 1974), keratin (Astbury Woods, 1933 Hearle et al, 1971), and others. These stress-induced phase transitions are either reversible, i.e. the crystal structure reverts to the original structure on relaxation, or irreversible, i.e. the newly formed structure does not revert after relaxation. Examples of the former include PBT, PEO and keratin. 

Figure 13.2 Chemical structures of (a) polyamide and (b) polyether blocks polyamide block could be PA6 (x = 5) or PA12 (x = 11) and polyether block could be polyfethylene oxide) (PEO, y = 2) or polyftetramethylene oxide) (PTMO, y = 4)...

Experimental measurements of the dipole moment and its temperature coefficient of the polyoxides poly(trimethylene oxide) polyftetramethylene oxide) and poly(decamcthylene oxide), and poly(l,3-dioxolane) are in general agreement with estimates obtained by rotational isomeric state treatments. In the latter case, an alternating copolymer of formaldehyde and ethylene oxide, the appropriate intramolecular interactions were obtained from studies of the homopolymers the matrix calculation provides the proper statistical mechanical average, in contrast to simply taking a mean. 

As has already been mentioned, the major drawback of the TPA-based route for the synthesis of PBT is that approximately double the amount of THF forms as a waste product, when TPA instead of DMT is used as a monomer. Consequently, there are two possible ways to make the TPA-based synthesis to PBT more lucrative than the DMT process - to reduce the amount of THF formed during the polymerization, or to elaborate an economical process for separation and purification of THF, which can be used further in production of, for example, polyftetramethylene oxide). Currently, DMT route is still used in most commercial plants for PBT production, with the exception of some plants in Asia, e.g. the new Zimmer AG plant in Nantong, China, which produces about 200 tones of PBT daily, starting from TPA as a raw material. Zimmer s process includes additional separation and rectification of the mixture of THF and water, and achieves THF of a purity of > 99.5 % [50]. 

Polyether Soft Segments. Polyftetramethylene oxide), polyfethylene oxide) and polyfpropylene oxide) and their random and block copolymers are most often used as soft segments. 

Pepic, D., M.S. Nikolic, and J. Djonlagic, Synthesis and characterization of biodegradable aliphatic copolyesters with polyftetramethylene oxide) soft segments. Journal of Applied Polymer Science, 106(3) p. 1777. 2007. 

The difference between the frequencies of the fundamental and hot modes is 20cm for poly(dioxolane) and 40cm" for polyftetramethylene oxide). It means that anharmonidty of torsional vibrations is much larger for the latter polymer which is consistent with the nuclear magnetic resonance measurements of potential barriers of molecular motion in these polymers [178]. In order to assign unambiguously the lower-ftequou bands considered to be hot transitions modes, temperature measurements are required. 

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