Segmented polyurethane multiblock polymers containing polydimethylsiloxane and polyether soft segments form tough and easily processed thermoplastic elastomers. Two commercially available examples, Elast-Eon E2A (denoted as E2A) and PurSil 35 (denoted as P35), were evaluated for molecular and mechanical stability after immersion in buffered water for up to 52 weeks at temperatures ranging from 37 to 85 °C. Dynamic mechanical spectroscopy experiments, performed in tension and shear, were used to characterize the linear viscoelastic properties of compression-molded (dry) specimens. Small-angle X-ray scattering measurements indicated a disorganized microphase-separated morphology for all test conditions. Upon aging in phosphate buffered saline, samples of E2A and P35 were analyzed by size exclusion chromatography (SEC) and tensile testing as a function of time and temperature. The absolute molar mass of each material prior to aging in water was determined by SEC using a multiangle light scattering detector. Aging at 85 °C and 52 weeks lead to a 67% and 50% reduction in molar mass from the original values for E2A and P35, respectively. We attribute the reduction in molar mass to hydrolysis of the polymer backbone and have evaluated the data using a pseudo-zero-order kinetics analysis. The temperature dependence of the extracted rate data is consistent with an activated (i.e., Arrhenius) process, and thus all the molar mass reduction data can be reduced to a single master curve. Concomitant with the reduction in molar mass, E2A and P35 transformed with aging from strain-hardening to strain-softening materials, characterized by substantially reduced tensile strength (stress at failure) and ultimate elongation (strain at failure) relative to the original properties.

Segmented polyurethane multiblock polymers containing polydimethylsiloxane and polyether soft segments form tough and easily processed thermoplastic elastomers (PDMS-urethanes). Two commercially available examples, PurSil 35 (denoted as P35) and Elast-Eon E2A (denoted as E2A), were evaluated for abrasion and fatigue resistance after immersion in 85 °C buffered water for up to 80 weeks. We previously reported that water exposure in these experiments resulted in a molar mass reduction, where the kinetics of the hydrolysis reaction is supported by a straight forward Arrhenius analysis over a range of accelerated temperatures (37-85 °C). We also showed that the ultimate tensile properties of P35 and E2A were significantly compromised when the molar mass was reduced. Here, we show that the reduction in molar mass also correlated with a reduction in both the abrasion and fatigue resistance. The instantaneous wear rate of both P35 and E2A, when exposed to the reciprocating motion of an ethylene tetrafluoroethylene (ETFE) jacketed cable, increased with the inverse of the number averaged molar mass (1/Mn). Both materials showed a change in the wear surface when the number-averaged molar mass was reduced to ≈ 16 kg/mole, where a smooth wear surface transitioned to a 'spalling-like' pattern, leaving the wear surface with ≈ 0.3 mm cracks that propagated beyond the contact surface. The fatigue crack growth rate for P35 and E2A also increased in proportion to 1/Mn, after the molar mass was reduced below a critical value of ≈30 kg/mole. Interestingly, this critical molar mass coincided with that at which the single cycle stress-strain response changed from strain hardening to strain softening. The changes in both abrasion and fatigue resistance, key predictors for long term reliability of cardiac leads, after exposure of this class of PDMS-urethanes to water suggests that these materials are susceptible to mechanical compromise in vivo.

Poly(lactide) (PLA) and its copolymers can be made from naturally occurring materials. They are ideal candidates as sustainable materials to replace the petroleum based polymers. However, these polymers often are brittle so toughening is needed. One of the most effective toughening methods is to reactive blend brittle polymers with materials having very different rigidity. This approach requires that the two materials chemically bond with each other at the interface to compatibilize the blends. Thus, to design and make reactive systems is a key to the success of reactive blending. In this article, we studied toughening poly(lactide‐co‐glycolide) (PLGA) with a rubbery material poly(trimethylene carbonate) (PTMC). We observed that PTMC spontaneously reacted with PLGA during melt blending. The reaction produced PLGA‐co‐PTMC copolymers that stayed at the PLGA/PTMC interface. Those copolymers not only helped to create a stable blend microstructure at a length scale of 100 nm but also promoted the bonding between the PLGA and PTMC domains. It is interesting that the reaction did not need a catalyst or initiator. We speculated that this reaction between PLGA and PTMC was a transesterification reaction. This reaction is easy to achieve and is expected to broaden the property range of the PLGA and other degradable polyesters, enabling them to replace certain types of petroleum based polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Poly(lactide) (PLA) and its copolymers degrade through hydrolysis into non-toxic and water soluble metabolic products in vivo. They are ideal materials for resorbable biomedical applications such as drug delivery and tissue engineering. However, these polymers are brittle and often need to be toughened. One of the most effective toughening methods is reactive blending, in which additives are dispersed into polymer matrices as small particles with strong bonding between the two materials. In this paper, we studied toughening poly(lactide-co-glycolide) (PLGA) through reactive blending with poly(trimethylene carbonate) (PTMC). We observed warm-like micelle or swollen warm-like micelle structures created during the reactive blending process with a twin screw extruder at high temperature. The micelle structures were orientated along the extrusion direction with their length ranging from 50 to 1000 nm and diameters about 50 nm. This structure could be produced only with a twin screw extruder. When a batch mixer was used, the PTMC additive (10 to 30 wt%) formed spheres with diameters on the order of 100-500 nm. The PLGA/PTMC copolymers formed in situ were responsible to this microstructure. The mechanical properties of this blend were significantly improved over the pure PLGA.