Asymmetric Copolymers Research Articles

Nonlinear optical properties of polymeric materials

AbstractIn this paper we discuss the molecular and macroscopic requirements for large second order nonlinear optical effects in polymeric systems. A new enhancement mechanism attributable to cooperative interactions between dipoles in polar polymer chains is proposed and tested by the synthesis and characterization of asymmetric condensation copolymers derived from p‐oxy‐α‐cyanocinnimate derivatives. An enhancement of a factor of 20 in electric field induced second harmonic generation relative to an equivalent concentration of chemically identical nonpolymerized chromophores in solution is obtained. Conformational and perhaps alignment restrictions in the rubbery state result in a reduction in alignment relative to what would be expected for an equivalent concentration of the polymerized chromophores in a moderately viscous medium. A model is proposed to account for the enhancement factors.

Structure‐property relationships in thermoplastic elastomers III. Segmented polyacetal‐polyurethanes

AbstractDihydroxy‐terminated polyacetals had been synthesized from aldehydes and glycols and used as soft segments to obtain segmented polyurethane block copolymers. For soft segment ≥ 1700Mn, the Tg ranges from–48 to −58°C and is insensitive to the structures of diisocyanate and chain extender. The Tg of PacPU with 1350 Mn polyacetals is raised to −38°C, and none was observed for shorter polyacetal chains. The copolymers can be synthesized to have a broad range of mechanical properties, such as modulus from 0.5 to 130 MPa, stress at break from 0.7 to 21 MPa, and elongation at break from 66 to 1300% through the variation of the constituents and composition. The rheologic properties are only slightly dependent on temperature for symmetrical diisocyanates but quite temperature sensitive with asymmetric diisocyanate copolymers. The polyacetals are selected to build in acid‐catalyzed thermal decomposition of the thermoplastic elastomers. The extreme acid sensitivity of the polyacetal block is buffered in the coplymers.