Poly(macrolactones) (PMLs) can be considered as biodegradable alternatives of polyethylene; however, controlling the ring-opening polymerization (ROP) of macrolactone (ML) monomers remains a challenge due to their low ring strain. To overcome this problem, phosphazene (t-BuP 4), a strong superbase, has to be used as catalyst. Unfortunately, the one-pot sequential block copolymerization of MLs with small lactones (SLs) is impossible since the high basicity of t-BuP 4 promotes both intra-and intermolecular transesterification reactions, thus leading to random copolymers. By using ROP and the "catalyst-switch" strategy [benzyl alcohol, t-BuP 4 /neutralization with diphenyl phosphate/(t-BuP 2)], we were able to synthesize different well-defined PML-b-PSL block copolymers (MLs: dodecalactone, ω-pentadecalactone, and ωhexadecalactone; SLs: δ-valerolactone and ε-caprolactone). The thermal properties and the phase behavior of these block copolymers were studied by differential scanning calorimetry and X-ray diffraction spectroscopy. This study shows that the thermal properties and phase behavior of PMLs-b-PSLs are largely influenced by the PMLs block if PMLs components constitute the majority of the block copolymers.
Substrate surface energy/chemistry gradients provide a means for high-throughput exploration of the surface interactions that are important in many chemical and biological processes. We describe the implementation of a controlled vapor deposition approach to surface modification that enables the facile production of substrate surface energy/chemistry gradients while maintaining versatility in both the gradient profile and the surface chemistry. In our system, gradient formation relies on the cross-deposition of functionalized chlorosilanes onto the substrate surface via vaporization of the deposition materials from liquid reservoirs under dynamic vacuum. The effects of liquid reservoir size (reservoir surface area), reservoir position relative to the substrate, vacuum application, and volatility of the deposition materials are examined in detail and demonstrate the level of gradient tunability afforded by this vapor deposition approach.
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