Narrow Results

Poly(phthalazinone ether nitrile) (PPEN) block copolymers containing polysiloxane were prepared so as to create a strongly hydrophobic polymer surface. The copolymers were synthesized from eugenol end-capped polydimethylsiloxane (PDMS) and fluoro-terminated PPEN oligomers by the aromatic nucleophilic substitution polycondensation in the presence of dimethyl sulfoxide/o-dichlorobenzene and K₂CO₃ as solvents and catalyst, respectively. The resultant copolymers were characterized by FTIR, ¹H NMR, and gel permeation chromatography. XPS analysis results indicated that the copolymer film had a very rich PDMS segment surface. Atomic force microscopy further showed that there existed a continuous PDMS phase on the copolymer surface and PPEN as the dispersive particles was dispersed at diameters between 0.1 and 0.3 nm. The enrichment of PDMS in the copolymer surface could be responsible for an increase of surface water repellency (113.4°).

By changing both the monomer composition and the polymer structure, we have varied the mechanical properties of resorbable polymers. The polymers were synthesized by ring-opening polymerization using L-lactide (LLA), ε-caprolactone (εCL), trimethylene carbonate (TMC) and 1,5-dioxepan-2-one (DXO) as monomers. Well-defined triblock copolymers, microblock copolymers and networks have been evaluated, and comparisons between them show that it is possible to tune the mechanical properties. Triblock copolymers with an amorphous middle block of poly(1,5-dioxepan-2-one) (PDXO) and semi-crystalline end-blocks of poly(ε-caprolactone) (PCL) were stronger and had a higher strain at break than triblock copolymers with poly(L-lactide) (PLLA) as end-blocks. Polymers with both DXO and TMC in the amorphous middle-block and PLLA as end-blocks showed a lower stress at break, but the material gained elasticity, a property which is very valuable in tissue engineering. Mechanical properties of networks, synthesized by a novel method, containing PDXO and PCL are also presented. Although it is difficult to compare them with the uncross-linked polymers, this is an additional way to modify and widen the properties.

In the weak segregation limit, the structure evolution of the hexagonal cylindrical phase of diblock copolymers in films was investigated. Employing the Landau-Brazovskii mean field theory, we obtained three amplitude parameters as functions of temperature, surface field strength and film thickness. By controlling confinement size and surface field strength, lamellae and undulated lamellae appear in the cylindrical bulk phase of diblock copolymers. "Phase diagrams" of confinement-induced structures are constructed at different surface field strengths. The obtained theoretical results are in agreement with relevant theoretical and experimental results.

This study demonstrates how the mechanical performance of polymeric material can be enhanced by morphology and phase orientation of block copolymers to achieve desired anisotropic mechanical properties. The material used was a new Kraton block copolymer consisting of styrene-isoprene-butadiene-styrene blocks having cylindrical morphology. We report a method of achieving long range uniaxial as well as biaxial orientation of block copolymer. Each microstructural organization results in a specific mechanical performance, which depends on the direction of the applied deformation. The method of tailoring mechanical properties by engineering microstructure may be successfully utilized to applications requiring anisotropic mechanical response, such as prosthetic heart valves.