The Effect of Molecular Weight of Polycaprolactone on the Ester Interchange Reactions during Melt Blending with Poly(ethylene terephthalate)

Abstract

ABSTRACT:The molecular weight (MW) of polycaprolactone (PCL) component had a profound effect on the ester interchange reactions during melt blending with poly(ethylene terephthalate) (PET). Utilization of lower MW of PCL component gave rise to higher degree of ester interchange reactions, and it could reduce mixing time required for generating a copolyester. The thermal properties and crystalline structure of resultant copolyesters were depended on the degree of ester interchange reactions by varying MW of PCL. It converted the morphology of copolyesters to a continuous single phase, suggesting formation of more random copolyester. Further, the substitution of PCL with low MW (M w : 1250) as third component in melt blends of PET and PCL with high MW(M w : 80000) led to higher degree of ester interchange reactions as well.KEY WORDS Poly(ethylene terephthalate) / Polycaprolactone / Melt Blending / Ester Interchange Reactions / Molecular Weight / The ester interchange reactions commonly occur in melt blending of different kinds of polyesters, which produces first the block copolyesters from immiscible blends and finally microstructure becomes randomized. [1][2][3][4] The physicochemical properties of produced copolyesters are closely related to their structural characteristics such as sequence length and randomness, which influenced by the degree of ester interchange reactions. Therefore, the control of ester interchange reactions in polyester blends may be technical key for their industrial applications.On the other hand, the copolyesters consisted of amorphous aliphatic ester unit and high melting crystalline ester unit are expected to find their applications for functional materials. Among them, poly(ethylene terephthalate/caprolactone) [P(ET/CL)] copolyester has been early focused on the biodegradable polymeric materials required for desirable mechanical and thermal properties. 5-10 It has recently attracted much interest for elastomeric materials. 11, 12 Thus, the elastic fiber spun from P(ET/CL) copolyesters is used as plastic and mechanical energy-absorbing device in seat belt assembly.However, it is difficult to obtain the copolyester by melt blending of poly(ethylene terephthalate) (PET) and polycaprolactone (PCL) because of the poor thermal stability of PCL. In order to prevent the thermal degradation of PCL component during melt blending, the mixing procedure must be accomplished within a short time. However, this frequently raises the problem of immiscibility between PET and PCL because of the lack of ester interchange reactions.As well known, ester interchange reactions during melt blending includes alcoholysis, acidolysis, and direct transesterification. 4,[13][14][15] The degree of ester interchange reactions is more seriously dependent on alcoholysis than acidolysis and direct transesterification because the former reaction is kinetically faster than the latter reactions. Recently, it is reconfirmed the fact that the importance of the role of alcoholysis by hydroxyl end group via the control of mole...

Sintered electrospun poly(ɛ‐caprolactone)–poly(ethylene terephthalate) for drug delivery

“…Prior studies used 1 H NMR to demonstrate that a PCL:PET copolymer was formed during the high temperatures characteristic of hot melt extrusion. Copolymer formation was detected via the presence of multiple peaks between 4.9 and 3.9 ppm . The absence of multiple peaks in the region of 4.9–3.9 ppm in this work [Figure (a–e)] suggests that electrospinning and subsequent heat treatment likely did not form undesirable copolymers.…”

“…Note that if copolymerization reactions were sufficiently rare, it is theoretically possible that these peaks may not be detectable compared to the abundant signal from PCL and PET. However, it is clear that at a minimum, copolymerization did not occur to the extent characteristically observed as a result of melt blending . This substantial difference is attributed to the large difference in temperature between these two processes.…”

“…It is widely recognized that many of the mechanical properties of PET surpass those of PCL. Hot melt extrusion can be used to create drug delivery vehicles from a variety of biocompatible polymers or their blends. In fact, two separate studies demonstrated PCL:PET blend creation using extrusion blending .…”

“…Hot melt extrusion can be used to create drug delivery vehicles from a variety of biocompatible polymers or their blends. In fact, two separate studies demonstrated PCL:PET blend creation using extrusion blending . Advantages gained are the decreased degradation rate, increasing the potential for long‐term delivery, and the expected increase in mechanical properties.…”

“…Advantages gained are the decreased degradation rate, increasing the potential for long‐term delivery, and the expected increase in mechanical properties. However, blending low melting PCL ( T m ~60 °C) with high melting PET ( T m ~260 °C) can cause transesterification at these high extrusion temperatures, resulting in the creation of undesired copolymers having uncertain biocompatibility . An additional disadvantage is that mixing thermolabile polymers and drugs or biological products under conditions typical of hot melt extrusion would likely destroy any biological activity .…”