(188ar) pH-Dependent Hydrolytic Degradation of Poly(trimethylene malonate) and Poly(trimethylene itaconate)

Two renewable copolymers, poly(trimethylene malonate) (PTM) and poly(trimethylene itaconate) (PTI), have been produced with ester bonds incorporated into the polymer backbone in order to facilitate hydrolytically and/or enzymatic degradation. PTM was synthesized from 1,3-propane diol and malonic acid to produce a linear copolymer; PTI was synthesized from 1,3-propanediol and itaconic acid to produce a branched copolymer. The synthesis and physical and chemical characterization of PTM and PTI have been described previously. A hydrolytic degradation study of these renewable polymers in aqueous solutions adjusted to pH values from ~5.5 to 11 is described. Weight change was monitored as a function of degradation time (10 to 100,000 min.) to determine if solubilization and/or degradation was ocurring. Weight loss varied from 20 to 37 wt.% for PTM and from 7 to 21 wt.% for PTI as a function of aging time and initial solution pH. Fourier transform infrared (FTIR) spectroscopy was used to monitor changes in ester bond concentration of PTM and PTI and gel-permeation chromatography was used to determine molecular weights and polydispersity index. For both PTM and PTI, a bi-modal molecular weight distribution was found and was dependent on both aging time and pH. Solutions that had high initial pH values (highest concentrations of K+ ions) resulted in the highest molecular weights over 10,000 min. aging time for both PTM and PTI. Differential scanning calorimetry and thermogravimetric analysis were used to show phase transitions shifted in response to degradation time and pH. PTI showed a slower degradation rate than PTM, which can be attributed to the crystallinity and branching found in PTI.