Generating Triple Crystalline Superstructures in Melt Miscible PEO‐b‐PCL‐b‐PLLA Triblock Terpolymers by Controlling Thermal History and Sequential Crystallization

Abstract

The morphology, crystallization behavior, and properties of multi‐crystalline polymer systems based on triple crystalline biodegradable PEO‐b‐PCL‐b‐PLLA triblock terpolymers are reviewed. The triblock terpolymers, with increasing poly(l‐lactide) (PLLA) content, exhibit a triple crystalline nature. Upon cooling from melt, the PLLA block crystallizes first and templates the spherulitic morphology of the terpolymer. Then, the poly(ε‐caprolactone) (PCL) block crystalizes and, finally, the poly(ethylene oxide) (PEO) block. These triblock terpolymers are melt miscible according to small angle X‐ray scattering (SAXS) results. Thus, the crystallization of PCL and PEO blocks takes place within the interlamellar zones of the PLLA spherulites that are formed previously. Therefore, the lamellae of PLLA, PCL, and PEO exist side‐by‐side within a unique spherulite, constituting a novel triple crystalline superstructure. The theoretical analysis of SAXS curves implies that only one lamella of either PCL or PEO can occupy the interlamellar space in between two contiguous lamellae of PLLA. Several complex competitive effects such as plasticizing, nucleation, anti‐plasticizing, and confinement take place during the isothermal crystallization of each block in the terpolymers. New results on how successive self‐nucleation and annealing thermal treatment can be used as an additional suitable technique to properly separate the three crystalline phases in these triple crystalline triblock terpolymers are also included.

Direct identification of three crystalline phases in PEO-b-PCL-b-PLLA triblock terpolymer by In situ hot-stage atomic force microscopy

“…To that purpose, model triblock terpolymers of PLLA, PCL, and PEO blocks (PEOb-PCL-b-PLLA) have been exhaustively studied. 4,[33][34][35][36] Particularly, the morphology of these melt miscible and triple crystalline triblock terpolymers have been reported by Chiang et al 37 and Palacios et al 33,35,36 Wide-angle X-Ray scattering (WAXS) measurements, carried out during cooling, confirmed that the PLLA block is the one that crystallizes first, followed by the PCL and lastly, the PEO. PLOM observations indicated that the microscale structure is templated by the PLLA block as a result of its crystallization.…”

“…The PEO-b-PCL-b-PLLA is a triblock terpolymer with an alternating superstructure of three crystalline phases, as we had reported in previous publications. 4,[33][34][35][36] The PLLA block ) was employed as a single catalyst. For more details on the synthesis procedure and characterization, refer to 60,61 , and the references in them.…”

“…The samples under study are listed in Table 1, with composition of the blocks as subscript numbers and molecular weights of the entire diblock copolymer and terpolymer as superscript numbers. The melting points of each component determined by DSC previously [33][34][35][36] are also given in Table 1. *The melting point values reported here are a range because they depend on previous thermal history (controlled cooling or isothermal crystallization) and scanning rates employed during their determination (1, 5 or 20 ºC/min) [33][34][35][36] Films Preparation.…”

Crystallization and Morphology of Triple Crystalline Polyethylene-b-poly(ethylene oxide)-b-poly(ε-caprolactone) PE-b-PEO-b-PCL Triblock Terpolymers

“…The addition of a third potentially crystallizable block to diblock copolymers results in a more complex analysis of the crystallization behavior. Few studies have been published about tricrystalline triblock terpolymers, such as ABC-type triblock terpolymers and ABCBA pentablock terpolymers, including the apolar PE block, and the polar PEO, PCL, and PLLA blocks [ 17 , 24 , 37 , 42 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 ].…”

“…Palacios et al studied the crystallization and morphology of ABC triblock terpolymers with three crystallizable blocks: PEO, PCL, and PLLA [ 92 , 93 , 94 , 95 ]. They [ 92 ] highlighted the triple crystalline nature of the PEO- b -PCL- b -PLLA triblock terpolymer, with the three different blocks crystallizing independently upon cooling from the melt.…”