Degradable thermoplastic polyurethane (TPU) elastomers incorporating poly(D,L-lactide-co-glycolide) (PLGA) were synthesized and characterized. The soft segments consisted of a mixture of poly(butylene adipate) (PBA) and PLGA with PBA/PLGA ratios of 100/0, 75/25, and 50/50 wt %. Two PLGA polyesters were used. BD-PLGA was initiated from butanediol; whereas BHMBA-PLGA was initiated from 2,2-bis-(hydroxymethyl)butanoic acid. The hard segments consisted of dicyclohexylmethane-4,4 0 -diisocyanate (H 12 MDI) and 1,4-butanediol (BD). The hard segment content, expressed as the weight ratio of BD to polyol used in the TPU formulation, was set either at 8 or 12% (31.2 or 38.1% hard segment by weight, respectively). In all cases initial [NCO]/[OH] ratio was 1.03. The tensile modulus of the TPUs ranged from 9 to 131 MPa and ultimate strains ranged from 100 to 750%. DMA was used to probe the thermomechanical transitions of the TPUs and indicated useful application temperatures from well below zero up to 60-80 C depending on the formulation. Hydrolytic degradation of the TPUs was tested in seawater at 37 C. All of the PLGA-containing TPUs showed enhanced degradation compared to those with only PBA as the soft segment. The latter compositions remained essentially unchanged throughout the test while the PLGAcontaining TPUs lost as much as 45% of their initial mass in 153 days. Molecular weights of TPUs containing degradable polyols were lower than those derived from 100% PBA polyol.
Reactions of dicyclohexylmethane-4,4 0 -diisocyanate (H 12 MDI) with 1-or 2-butanol in N,N-dimethylformamide using dibutyltin dilaurate (DBTDL), stannous octoate (SnOct), or triethylamine (TEA) as catalyst were conducted in stirred reactors at 408C. Reactor contents were circulated through an external loop containing a temperature-controlled FTIR transmission cell; reaction progress was monitored by observing decrease in height of the isocyanate peak at 2266 cm
21. Catalyzed reactions were second order as indicated by linear 1/[NCO] plots; uncatalyzed reactions yielded nonlinear plots. In all cases, the reaction with a primary alcohol was faster than that with a secondary alcohol. DBTDL dramatically increased the reaction rate with both primary and secondary alco-25 mol/L (300 ppm Sn) the second-order rate constant, k, was 5.9 3 10 24 (primary OH) and 1.8 3 1024 L/(mol s) (secondary OH); for both alcohols, this represents an increase in initial reaction rate on the order of 2 3 10 1 when compared with the uncatalyzed reactions. The second-order rate constant was observed to increase linearly with DBTDL concentration in the range 100-700 ppm Sn. SnOct and TEA showed little to no catalytic activity with the primary alcohol and only a slight increase in reaction rate with the secondary alcohol.
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