Synthesis, Morphology, and Properties of Segmented Poly(ether amide)s with Uniform Oxalamide-Based Hard Segments

Abstract

The synthesis, morphology, and properties of segmented poly(ether amide)s based on flexible PTHF segments (M n = 1.1 × 103 g mol–1) and uniform rigid oxalamide segments were investigated. The amount of oxalamide groups in the hard segment and the spacer length of bisoxalamide-based hydrogen bonded arrays were varied systematically. The segmented poly(ether amide) with single oxalamide groups connecting the polyether blocks was a sticky solid with a melting temperature of ∼25 °C. Incorporation of uniform hard segments consisting of two interconnected oxalamide units provided highly phase-separated thermoplastic elastomers with a broad temperature-independent rubber plateau. By decreasing the aliphatic spacer length separating two oxalamide units from 10 to 2 methylene groups, the melting transitions increased from 140 to 200 °C. FT-IR evidenced strongly hydrogen bonded and highly ordered bisoxalamide hard segments with degrees of ordering between 66 and 90%. AFM revealed the presence of fiber-like nanocrystals with lengths up to several hundreds of nanometers randomly dispersed in the soft PTHF matrix. The long dimension of the crystals was found parallel to the direction of the hydrogen bonds. One of the other small dimensions of the crystal approximately equals the length of the oxalamide segment, whereas the other one may correspond to the height of a stack containing ca. 10–20 hydrogen-bonded sheets. Upon heating, the crystalline phase melts over a broad temperature range to give a homogeneous melt according to temperature-dependent FT-IR, SAXS, and rheology data. Increasing the number of oxalamide groups in the hard segment to three afforded a highly phase-separated material with a melting transition above 200 °C. The segmented copolymers with two or three oxalamide groups in the hard segment show a distinct yield point and have an elastic modulus between 121 and 210 MPa, a stress at break ranging from 15 to 27 MPa, and strain at break of 150 up to 900%. The results demonstrate that alternating block copolymers with soft PTHF segments and uniform hard segments containing two or three oxalamide groups are TPEs with good thermal and mechanical properties.

Effects of Copolymer Structure on the Mechanical Properties of Poly(dimethyl siloxane) Poly(oxamide) Segmented Copolymers

“…At 30 °C, N–H stretching vibrations in the ordered, hydrogen bonding state resided at 3297 cm −1 and at higher temperatures, the free N–H band appeared at 3398 cm −1 (Figure S1, Supporting Information). Wave numbers for each state of hydrogen bonding and the thermal dissociation profile agreed well with earlier reports …”

“…Currently, detailed reports of the structure–property relationships for PDMS polyoxamide segmented copolymers do not exist in the literature. Recently, Sijbrandi et al published a report on the structure–property relationships of poly(tetramethylene oxide) (PTMO)‐based polyoxamide copolymers. Their study focused on the effects of HS composition through varying the number of oxamide groups and the HS spacing.…”

Amide-containing segmented copolymers

“…As oxamide spacing increased, the T m and onset of flow decreased due to a reduction in the cooperative effects of neighboring hydrogen bonds. [111,114] This effect was clearly illustrated by variable temperature FTIR spectroscopy, which revealed the order-to-disorder transition for hydrogen bonding occurred at lower temperatures as the oxamide spacing increased (Figure 18). …”

“…[111] Spacing between oxamide groups also proved important, and the most significant effects were observed in PDMS-based copolymers. As oxamide spacing increased, the T m and onset of flow decreased due to a reduction in the cooperative effects of neighboring hydrogen bonds.…”

“…PTMObased poly(oxamide)s also showed a high moduli >120 MPa with stress and strain at break up to , copolymer composition and level of crystallinity greatly affected the mechanical properties [114]. DMA revealed long, temperature-insensitive, service windows up to 180 ˚C for PDMS poly(oxamide) copolymers, and the rubbery plateau length and storage moduli varied with copolymer composition(Figure 17) [111,113,114] [111]. Recent reports include the structure-property relationships of poly(oxamide) copolymers for both PTMO and PDMS based copolymers.…”