In Situ X‐Ray Scattering Studies of Poly(ε‐caprolactone) Networks with Grafted Poly(ethylene glycol) Chains to Investigate Structural Changes during Dual‐ and Triple‐Shape Effect

Abstract

The dual- and triple-shape effects of multiphase polymer networks that contain two crystallizable chain segments have been assessed in situ by combining X-ray measurements with thermomechanical investigations. The studied polymer, named CLEG, is a multiphase polymer network of crystallizable poly(ε-caprolactone) (PCL) with grafted poly(ethylene glycol) (PEG) side chains. Wide-angle (WAXS) and small-angle X-ray scattering (SAXS) measurements were combined with temperature-controlled in situ tensile testing experiments. This integrated approach enables systematic investigation and interpretation of relevant structural features during the programming procedures and the thermally-induced recovery process. Main results concern the combined effect of PCL and PEG crystals on shape fixation, the specific role of low-melting PCL crystallites in the fixation of the low temperature temporary shape, and the different orientation behavior of PCL and PEG crystals during certain stages of the programming procedure. These results demonstrate that crystal orientation effects are dominant for the PCL crystals. The effects of the low temperature PCL crystals could only be investigated when synchrotron radiation was applied. These findings indicate the great potential of in situ X-ray investigations for the creation of design-relevant knowledge about the microscopic foundations of dual- and triple-shape effects in appropriate polymer systems.

Shape-memory properties of magnetically active triple-shape nanocomposites based on a grafted polymer network with two crystallizable switching segments

“…This difference in H sw,1 (A(B) can be related to the difference in the two programming procedures. In SMCP-2s-I shape (A) was fixed by PEG crystallites and 'low' melting PCL crystallites resulting in higher values for H sw,1 (A(B), whereas during SMCP-2s-II only PEG crystallites are responsible for fixation of shape (A), as previously reported for photocrosslinked CLEG polymer networks [8,43,44]. For samples programmed by SMCP-2s-I H sw,2 (B(C) $ 25 kA·m -1 could be determined, while slightly lower values for H sw,2 (B(C) were obtained when SMCP-2s-II was applied.…”

“…Here, the lower values observed for SMCP-2s-II programmed samples can be related to the contribution of 'low' melting PCL crystallites to the fixation of shape (B) at T low = 0°C. When one-step programming SMCP-1s was used for programming, a single transition, which is characteristic for a dual-shape effect, was achieved for all nanocomposites in the "% rec -H curves with H sw $ 23 kA·m -1 , because the temporary shape is predominantly fixed by PCL crystallites during SMCP-1s, while crystallization of the grafted PEG chains did contribute to the fixation of shape (A) [43,44].…”

“…[41]. The matrix material is a grafted polymer network structure based on covalently crosslinked PCL chains with grafted PEG side chains as previously reported [8,42,43]. Silica coated nanoparticles were chosen showing improved compatibility with the polymer matrix in comparison to uncoated fillers.…”

Thermal Properties and Crystallinity of Grafted Copolymer Networks containing a Crystallizable Poly(ε-caprolactone) Crosslinker in an aqueous environment

“…The copolymer networks were synthesized according to the method described in [3,9]. Here the synthesis is exemplarily described for CLEG050 containing 50 wt% of poly(ε-caprolactone) diisocyanatoethyl dimethacrylate (PCLDIMA; M n = 8300 g·mol -1 ) relative to the starting reaction mixture.…”

“…the crosslinking density or the chemical composition [1][2][3][4][5]. Such copolymer materials can be designed as AB-polymer networks [4,6,7], where all segments contribute to the overall mechanical properties or as polymer networks with grafted side chains [3,8,9], where the mechanical properties were dominated by the switching segments acting as crosslinker. However, the variation of the overall mechanical properties of such copolymer networks is typically limited to mechanical properties in the MPa range [4,10], and therefore novel approaches or concepts are required to achieve a material elasticity in the kPa range for biomedical applications [11,12].…”