Thermally responsive segment

Xiong, X.Y., Tam, K.C. and Gan, L.H., 2005. Synthesis and thermal responsive properties of P(LA-h-EO-h-PO-6-EO-6-LA) block copolymers with short hydrophobic poly(lactic acid) (PLA) segments. Polymer, 46, 1841-1850. 

Segmented SMPUs are thermoplastic block copolymers having the unique mechanical properties, which is due to the pseudo-elasticity and thermal-responsive shape memory effect. Due to the presence of soft and hard segments, in which the former comprises the reversible phase while the latter forms the frozen phase, the material can restore its original shape upon... 

Noncrystalline domains in fibers are not stmctureless, but the stmctural organization of the polymer chains or chain segments is difficult to evaluate, just as it is difficult to evaluate the stmcture of Hquids. No direct methods are available, but various combinations of physicochemical methods such as x-ray diffraction, birefringence, density, mechanical response, and thermal behavior, have been used to deduce physical quantities that can be used to describe the stmcture of the noncrystalline domains. Among these quantities are the amorphous orientation function and the amorphous density, which can be related to some of the important physical properties of fibers. 

A quantitative model is proposed for the dynamic response, which is based on the hypothesis that the elastic part is due to thermal motions, while the viscous part is due to adsorption and desorption of chain segments and molecules. 

The PET polymer structure can also be generated from the reaction of ethylene glycol and dimethyl terephthalate, with methyl alcohol as the byproduct. A few producers still use this route. The aromatic rings coupled with short aliphatic chains are responsible for a relatively stiff polymer molecule, as compared with more aliphatic structures such as polyolefin or polyamide. The lack of segment mobility in the polymer chains results in relatively high thermal stability, as will be discussed later. 

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