Structural Investigations of Polycarbonates whose Mechanical and Erosion Behavior Can Be Controlled by Their Isomer Sequence

Abstract

One of the challenges in materials science is to design functional, synthetic polymers that match the desired properties of a specific application. Achieving high stiffness and strength under physiological conditions while maintaining the proper erosion profile is particularly difficult. This challenge is addressed here by synthesizing polymers with sequence control followed by optimal processing of the polymer. A new class of biodegradable, aromatic–aliphatic polycarbonates based on tyrosol, a naturally derived (hydroxy)alkyl phenol with an alternating (altTyPC) or scrambled (scrTyPC) sequence, is reported. AltTyPC contained strictly alternating sequences of diaryl (head-to-head, HH) and dialkyl (tail-to-tail, TT) carbonate backbone isomers; this was accomplished by using preprogrammed diaryl carbonate diol and triphosgene in polycondensation. The scrambled sequence (scrTyPC) of HH, TT, and the aryl-alkyl (head-to-tail, HT) carbonate isomers was obtained by direct polymerization of tyrosol. The isomer sequence had a large effect on the thermal behavior: altTyPC rapidly transitioned from the amorphous phase into a 1D mesophase at 90 °C and then into a 3D crystalline phase at 150 °C before melting at 204 °C; in contrast, scrTyPC remained in a 1D mesophase after extensive annealing at 100 °C for 20 h and melted at 149 °C. The modulus of the oriented, semicrystalline altTyPC films was higher than that of the similarly processed scrTyPC films (5.4 ± 0.3 vs 3.8 ± 0.2 GPa). The erosion behavior was also different: AltTyPC showed more rapid mass and thickness loss over time than scrTyPC. Thus, a combination of sequence control and processing optimization in aromatic–aliphatic polycarbonates gives rise to a new platform of tunable polymers for numerous applications.