Elastomers Physically Cross-Linked by Oligo (Beta-Alanine)

In this research, the focus is the synthesis and characterization of a class of novel A-B-A triblock copolymers and their properties as thermoplastic elastomers.

Several A-B=A block copolymers have been made where the B block is poly(isobutylene), and the A blocks are oligo(b-alanine) (nylon 3). Nylon 3 is unique to the nylon family because its only observed secondary structure is flat (non-pleated), anti-parallel beta sheets [1, 2]. It is hypothesized that the system will microphase separate and the oligo(beta-alanine) will form a hard domain with the same structures observed for nylon 3. These hard domains will physically cross-link and reinforce the TPE.

It has been observed that with the weight percents of oligo(b-alanine) as low as 2%, the system is a physically cross-linked network, as demonstrated by rheological measurements. Micro-phase separation is demonstrated by the observation of a T_m and T_g corresponding to the hard and soft blocks respectively. Further evidence for micro-phase separation is the observation of discrete domains shown in TEM images. Infrared spectroscopy and wide angle X-ray diffraction data support the formation of an antiparallel b-sheet secondary structure by the oligo(b-alanine) block. The physical properties of the material, such as modulus and T_m can be controlled by changing the length of the oligo(b-alanine) block by a single repeat unit. Melting temperatures have been observed in excess of 225°C.

 References

1. Masamoto, J.; Sasaguri, K.; Ohizumi, C.;  J. Polymer Sci. Part A-2 1970, 8, 1703-1711
2. Lin, S.; Yu, X.; Tu, Y.; Xu, H.; Cheng, S. Z. D.; Jia, L. Chem Commun 2010, 46, 4273-4275