The influence of thermal treatment on the morphology in differently prepared films of a oligodepsipeptide based multiblock copolymer

Abstract

Degradable multiblock copolymers prepared from equal weight amounts of poly(ε‐caprolactone)‐diol (PCL‐diol) and poly[oligo(3S‐iso‐butylmorpholine‐2,5‐dione)]‐diol (PIBMD‐diol), named PCL‐PIBMD, provide a phase‐segregated morphology. It exhibits a low melting temperature from PCL domains (Tm,PCL) of 38 ± 2 °C and a high Tm,PIBMD of 170 ± 2 °C with a glass transition temperature (Tg,PIBMD) at 42 ± 2 °C from PIBMD domains. In this study, we explored the influence of applying different thermal treatments on the resulting morphologies of solution‐cast and spin‐coated PCL‐PIBMD thin films, which showed different initial surface morphologies. Differential scanning calorimetry results and atomic force microscopy images after different thermal treatments indicated that PCL and PIBMD domains showed similar crystallization behaviors in 270 ± 30 µm thick solution‐cast films as well as in 30 ± 2 and 8 ± 1 nm thick spin‐coated PCL‐PIBMD films. Existing PIBMD crystalline domains highly restricted the generation of PCL crystalline domains during cooling when the sample was annealed at 180 °C. By annealing the sample above 120 °C, the PIBMD domains crystallized sufficiently and covered the free surface, which restricted the crystallization of PCL domains during cooling. The PCL domains can crystallize by hindering the crystallization of PIBMD domains via the fast vitrification of PIBMD domains when the sample was cooled/quenched in liquid nitrogen after annealing at 180 °C. These findings contribute to a better fundamental understanding of the crystallization mechanism of multi‐block copolymers containing two crystallizable domains whereby the Tg of the higher melting domain type is in the same temperature range as the Tm of the lower melting domain type. Copyright © 2016 John Wiley & Sons, Ltd.

Interfacial properties of morpholine-2,5-dione-based oligodepsipeptides and multiblock copolymers

“…The beta-sheet like organization did not persist over long distance. The observation of no longrange order in ultrathin films of OIBMD is also in agreement with spin-coated films of OCL-OIBMD, [44] where crystallization was only observed after mobility was increased by thermal annealing of the films. Thus, the mobility of OIBMD in thin films at room temperature is too low for the formation of ordered structures.…”

“…We note that this was also observed in the bulk materials, where OCL crystallization could only be observed after stretching, [46] and especially in thin spin coated OCL-OIBMD films, where OIBMD crystallization was only observed after annealing, and PCL crystallization was severely hindered. [44] This was attributed to the reduced mobility of OCL blocks anchored to OIBMD chains, which are glassy at room temperature. However, since the air-water interface is a reasonably good solvent for OCL-OIBMD, dynamics should be much faster than in thin films.…”

Reversible Actuation of Thermoplastic Multiblock Copolymers with Overlapping Thermal Transitions of Crystalline and Glassy Domains

“…Especially, in PIBMD38-PCL60, the glassy PIBMD chains restrict the crystallization of PCL domains during cooling. 29 In the other three samples, PCL forms the continuous matrix, where PIBMD domains have less influence on their crystallization behavior. T m corresponding to the PIBMD is not influenced, and only the intensity is changed by the composition of the copolymers.…”

“…This observation could be explained by morphological competition between the confinement/restriction from the glassy PIBMD domains and the crystallization of PCL domains. Especially, in PIBMD38-PCL60, the glassy PIBMD chains restrict the crystallization of PCL domains during cooling . In the other three samples, PCL forms the continuous matrix, where PIBMD domains have less influence on their crystallization behavior.…”

Phase Morphology of Multiblock Copolymers Differing in Sequence of Blocks

“…Here, two well separated melting temperatures ( T m s) were detected and the crystalline domains generated by PIBMD restricted the formation of crystalline PCL domains. [ 1 ] In addition, the overall molecular weight in polyurethanes with two semi‐crystalline precursors exhibited a strong influence on the melting transitions. In block copolymers based on oligo(ε‐caprolactone) (OCL) and oligotetrahydrofuran (OTHF) increase in the weight average of molecular weight ( M w ) building blocks caused a decrease of the T m .…”