Soft, Formstable (Co)Polyester Blend Elastomers

Abstract

High crystallization rate and thermomechanical stability make polylactide stereocomplexes effective nanosized physical netpoints. Here, we address the need for soft, form-stable degradable elastomers for medical applications by designing such blends from (co)polyesters, whose mechanical properties are ruled by their nanodimensional architecture and which are applied as single components in implants. By careful controlling of the copolymer composition and sequence structure of poly[(L-lactide)-co-(ε-caprolactone)], it is possible to prepare hyperelastic polymer blends formed through stereocomplexation by adding poly(D-lactide) (PDLA). Low glass transition temperature Tg ≤ 0 °C of the mixed amorphous phase contributes to the low Young’s modulus E. The formation of stereocomplexes is shown in DSC by melting transitions Tm > 190 °C and in WAXS by distinct scattering maxima at 2θ = 12° and 21°. Tensile testing demonstrated that the blends are soft (E = 12–80 MPa) and show an excellent hyperelastic recovery Rrec = 66–85% while having high elongation at break εb up to >1000%. These properties of the blends are attained only when the copolymer has 56–62 wt% lactide content, a weight average molar mass >140 kg·mol−1, and number average lactide sequence length ≥4.8, while the blend is formed with a content of 5–10 wt% of PDLA. The devised strategy to identify a suitable copolymer for stereocomplexation and blend formation is transferable to further polymer systems and will support the development of thermoplastic elastomers suitable for medical applications.

Iron(ii) carboxylates and simple carboxamides: an inexpensive and modular catalyst system for the synthesis of PLLA and PLLA-PCL block copolymers

“…Alternative catalysts, such as Sn(Oct) 2 , produce much higher randomized structures than the Fe(OAc) 2 /DEAA catalyst via transesterification. 64 …”

“…Alternative catalysts, such as Sn(Oct) 2 , produce much higher randomized structures than the Fe(OAc) 2 / DEAA catalyst via transesterication. 64 Catalysts, which can only start block copolymerisations with one of the monomers, have been reported. 85,86 We, therefore, performed reactions starting from (L-LA) 2 (entry 3) and CL (entries 4 and 5).…”

“…Sn(Oct) 2 and other catalysts that allow rapid transesterifications between polyester chains can provide more randomized structures at long reaction times, but mostly with higher dispersities. 64 For the synthesis of block copolymers, high transesterification rates are undesirable. Fully random copolymers of ( l -LA) 2 and CL are very difficult to prepare due to the significantly different reactivities with most catalysts.…”

Synthesis of Bio-Based Polyester from Microbial Lipidic Residue Intended for Biomedical Application

“…Analyzing the polyester thermogram (Figure 5), the material showed glass transition temperature (T g ) taken at midpoint of −51.2 • C and a melting temperature (T m ) of 169.6 • C, confirming a semi-crystalline nature, and non-glassy behavior at room temperature. An amorphous phase with a low glass transition temperature (T g ) promotes the flexibility of the polymer network and physical net points that govern the form stability after elastic deformation [78].…”