Bert Vanhaecht

Controlled stereochemistry of polyamides derived from cis/trans-1,4-cyclohexanedicarboxylic acid

A series of copolyamides 12.y was synthesized either with y = 6, or 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) residue, or a mixture of both. The influence of the synthetic route of 1,4-CHDA containing polyamides on the obtained cis-trans ratio of the incorporated 1,4-CHDA was investigated. The use of acid chlorides provided a synthetic route with full control of the cis-trans ratio of the 1,4-CHDA residue during synthesis, whereas synthesis at elevated pressure and temperature caused isomerization. The content and cis-trans ratio of 1,4-CHDA in the copolyamides were determined by solution 13 C NMR spectroscopy. Increasing the degree of partial substitution of the adipic acid by 1,4-CHDA resulted in an increase in T m , even for low molar precentages of 1,4-CHDA. This phenomenon points to isomorphous crystallization of both the 12.6 and 12.CHDA repeating units. The mps of the synthesized polyamides were independent of the initial cis-trans ratio of 1,4-CHDA, provided that the samples were annealed at 300 °C before DSC analysis. The polyamides exhibited a different melting pattern depending on the 1,4-CHDA content. At a low a 1,4-CHDA content a net exothermic recrystallization occurred during melting, whereas at higher contents of 1,4-CHDA this recrystallization occurs to a lesser extent, and two separate melting areas are observed.

Flexibilized styrene–N‐substituted maleimide copolymers. II. Multiblock copolymers prepared from PTHF‐based iniferters

This article describes the synthesis and molecular characterization of thermal polymeric iniferters, based on hydroxy-terminated poly(tetrahydrofuran) (PTHF), bearing thiuram disulfide groups along the chain. Thermal polymerization after the addition of styrene (S) and N-methylmaleimide (MI) to these PTHF-based polymeric iniferters yielded segmented PTHF (SMI-block-PTHF) n block copolymers that proved to have a single T g . The multiblock copolymers were molecularly characterized by elemental analysis, IR, and NMR. The thermal stability, as checked by thermogravimetric analysis, proved to be good up to about 350 °C. A size exclusion chromatography/ differential viscosity (DV) analysis showed that the molecular weights of the synthesized single-phase multiblock copolymers were sufficiently high (several times the estimated molecular weight between two adjacent entanglements) to determine the entanglement density from the rubbery plateau modulus, for which the method developed by S. Wu (J Polym Sci Part B: Polym Phys 1989, 27, 723-741) was applied. The entanglement density of flexibilized SMI proved to be about 20-25% higher than that of the nonflexibilized SMI. This increase is disappointing, and more work, based on the described concept, is required to achieve the desired enhancement of the toughness.