Intermediate segregation type chain length dependence of the long period of lamellar microdomain structures of supramolecular comb-coil diblocks

A characteristic intermediate segregation type chain length dependence of the long period D of the lamellar microdomain structure of a class of comb-coil supramolecules is reported. The supramolecular comb-coil diblock copolymers studied consist of a polystyrene (PS) “coil” block and a “comb” block of poly(4-vinylpyridine) (P4VP) either hydrogen bonded to pentadecyl phenol (PDP) (i.e., P4VP(PDP)-b-PS) or first protonated with methanesulfonic acid (MSA) and then hydrogen bonded to PDP (i.e., P4VP(MSA)(PDP)-b-PS). In both cases we find a scaling D ~ Ntotδ, δ ≈ 0.8, where Ntot denotes the total number of monomers of the P4VP-b-PS backbone. In the case of diblock copolymers this would correspond to a characteristic intermediate segregation regime behavior. Pure PS-b-P4VP, on the other hand, shows the expected strong segregation behavior D ~ Ntotδ, δ ≈ 0.7.

Self-Assembly of Supramolecular Triblock Copolymer Complexes

Four different poly(tert-butoxystyrene)-b-polystyrene-b-poly(4-vinylpyridine) (PtBOS-b-PS-b-P4VP) linear triblock copolymers, with the P4VP weight fraction varying from 0.08 to 0.39, were synthesized via sequential anionic polymerization. The values of the unknown interaction parameters between styrene and tert-butoxystyrene and between tert-butoxystyrene and 4-vinylpyridine were determined from random copolymer blend miscibility studies and found to satisfy 0.031<χS,tBOS<0.034 and 0.39<χ4VP,tBOS<0.43, the latter being slightly larger than the known 0.30<χS,4VP≤0.35 value range. All triblock copolymers synthesized adopted a P4VP/PS core/shell cylindrical self-assembled morphology. From these four triblock copolymers supramolecular complexes were prepared by hydrogen bonding a stoichiometric amount of pentadecylphenol (PDP) to the P4VP blocks. Three of these complexes formed a triple lamellar ordered state with additional short length scale ordering inside the P4VP(PDP) layers. The self-assembled state of the supramolecular complex based on the triblock copolymer with the largest fraction of P4VP consisted of alternating layers of PtBOS and P4VP(PDP) layers with PS cylinders inside the latter layers. The difference in morphology between the triblock copolymers and the supramolecular complexes is due to two effects: (i) a change in effective composition and, (ii) a reduction in interfacial tension between the PS and P4VP containing domains. The small angle X-ray scattering patterns of the supramolecules systems are very temperature sensitive. A striking feature is the disappearance of the first order scattering peak of the triple lamellar state in certain temperature intervals, while the higher order peaks (including the third order) remain. This is argued to be due to the thermal sensitivity of the hydrogen bonding and thus directly related to the very nature of these systems.

Enzyme-Catalyzed Synthesis of Aliphatic-Aromatic Oligoamides

<p>Enzymatically catalyzed polycondensation of p-xylylenediamine and diethyl sebacate resulted in oligo(p-xylylene sebacamide) with high melting temperatures (223-230 degrees C) and the enzymatic polycondensation of dimethyl terephthalate and 1,8-diaminooctane leads to oligo-(octamethylene terephthalamide) with two melting temperatures at 186 and 218 degrees C. No oligoamides, but products 1 and 2, were formed from the enzymatic reaction of dimethyl terephthalate and p-xylylenediamine. All reactions were catalyzed by CAL-B, icutinase, or CLEA cutinase. All reactions catalyzed by CAL-B show higher conversion than reactions catalyzed by icutinase or CLEA cutinase. The highest DPmax of 15 was achieved in a one-step and two-step synthesis of oligo(p-xylylene sebacamide) catalyzed by CLEA cutinase.</p>

On the dissolution behaviour of extended chain polyethylene fibres

The influence of stress on the dissolution behaviour of extended-chain high molecular weight polyethylene fibres in p-xylene was investigated. Freely suspended in the solvent, the fibres dissolved at 119.5°, a temperature close to the equilibrium solubility temperature of 118.6° for perfect polyethylene crystals. However, when a stress of 0.4 GPa was exerted by straining the fibre 0.7%, it could withstand a temperature as high as 130° for at least three days. At still higher temperatures the induced stress relaxed completely, and dissolution immediately followed. These phenomena indicate that the fibre has a network structure. The cross-links are of a physical nature. Molecules are connected by topological defects such as entanglements, intertwinings and twist disclinations. These defects are trapped in crystallites; therefore the theory of Gee and Flory is applicable predicting that in such a system dissolution temperature of extended chain crystallites increases with stress. The required stress is transduced by tie molecules bridging the amorphous regions between crystallites. A study of dissolution under stress seems to be a direct method for the detection of topological defects such as entanglements

Enzyme-Catalyzed Synthesis of Aliphatic–Aromatic Oligoamides

Enzymatically catalyzed polycondensation of <i>p</i>-xylylenediamine and diethyl sebacate resulted in oligo­(<i>p</i>-xylylene sebacamide) with high melting temperatures (223–230 °C) and the enzymatic polycondensation of dimethyl terephthalate and 1,8-diaminooctane leads to oligo­(octamethylene terephthalamide) with two melting temperatures at 186 and 218 °C. No oligoamides, but products 1 and 2, were formed from the enzymatic reaction of dimethyl terephthalate and <i>p</i>-xylylenediamine. All reactions were catalyzed by CAL-B, icutinase, or CLEA cutinase. All reactions catalyzed by CAL-B show higher conversion than reactions catalyzed by icutinase or CLEA cutinase. The highest DP_max of 15 was achieved in a one-step and two-step synthesis of oligo­(<i>p</i>-xylylene sebacamide) catalyzed by CLEA cutinase