Ce Cor Koning

The plastic deformation of ultra-high molecular weight polyethylene

Gel-spun filaments of different initial morphologies have been subjected to controlled drawing at elevated temperatures. The drawn samples have been examined by high-resolution scanning electron microscopy. The deformation mechanism at temperatures up to 120° C is very similar to crazing, especially in the case of unoriented gel-spun filaments. Filaments exhibiting a shish-kebab morphology offer the opportunity of examining the deformation of elementary fibrils in a quantitative way. The transformation of individual lamellae into fibrils is the initial deformation mode, which is followed by slip of fibrils at a later stage. This is concluded from a comparison of experimental data and model calculations of the maximum draw ratio. Drawing at 144° C results in the formation of globular aggregates of lamellae, with a characteristic long period of 40 nm. This long period persists until all the globules have been converted, by micronecking, into aggregate fibrils of extended-chain character. On a molecular scale, the various processes can be described as the temperature-dependent flow behaviour of an entanglement network.

ANCHORED MACROMOLECULAR COPPER-CATALYSTS FOR OXIDATIVE COUPLING

Abstract Immobilized macromolecular copper catalysts were prepared by radical graft copolymerization of styrene and 4-vinylpyridine on nonporous silica spheres and by subsequent complexation with copper(II) chloride. The activities of the catalysts were measured in the oxidative coupling of 2,6-di-t-butylphenol (DTBP) with oxygen. Variations of shaking speed and oxygen pressure showed that no oxygen diffusion limitation occurs. Neither the molar mass of unbound macromolecular analogs nor the size of the silica spheres influenced the catalytic activity. The intrinsic activity was not affected by immobilization as was shown by the equal redox rate constants (k2) for bound and unbound catalysts. An increasing degree of loading, θ, of the silica spheres with macromolecular ligands led to higher values of the substrate complexation constant K1, approaching the value of unbound macromolecular catalysts. Application of the anchored catalysts in a stirred flow reactor appeared to be possible.

Polyamides 4.10 and 4.12 and their Isomers

A series of aliphatic 1, 4-diaminobutane based polyamides 4.y with y = 8, 9, 10 and 12 was synthesized and characterized. For comparison, some 1, 6-diaminohexane based counterparts were also studied. PA 4.12, and in particular PA 4.10, proved to have a very beneficial combination of Tm , crystallization rate and physical properties. First indications were obtained, that for a series of aliphatic polyamide isomers, containing 16 carbon atoms in the repeating unit, the melting points are related to the number of ways to make an energetically favourable chain fold upon crystallization: isomers having two possible ways of chain folding have Tm s which are 13–15 °C lower than isomers having only one possible way of chain folding upon crystallization.

STRUCTURE OF COPPER 4-(N,N-DIMETHYLAMINO)PYRIDINE COMPLEXES AND THEIR CATALYTIC ACTIVITY IN THE OXIDATIVE COUPLING OF 2,6-DIMETHYLPHENOL

Abstract The oxidative coupling of 2,6-dimethylphenol (DMP) by copper complexes of 4-(N,N)-dimethylamino)pyridine (DMAP) has been studied. Catalytic experiments were carried out in which the DMAP-to-copper ratio and the amount and nature of the copper counter ions were varied. Supporting UV and EPR experiments were performed, and it was concluded that both dinuclear and mononuclear complexes are catalytically active, the mononuclear species being the more active. In solution both species are in equilibrium with one another. The mono/di ratio can be increased by addition of extra DMAP ligands. An excess of coordinating counter-ions increases the amount of dinuclear species. However, a few coordinating counterions are inevitable, and the catalytically most active species was found to be ‘Cu(DMAP)4Cl(OH)’, the role of Cl− probably being that of a bridging counter-ion promoting the formation of dinuclear Cu(I) complexes for the reoxidation step. The DMAP ligands are coordinated to Cu(II) through the pyridine N-atoms, as was determined by X-ray analysis. The Cu(II)DMAP complexes are catalytically active even without initial hydroxide addition. It is believed that the strongly basic DMAP ligands produce some hydroxide from traces of water present in the reaction medium. The species ‘Cu(DMAP)4Cl(OH)’ proved to be able to produce relatively high molecular weight polyphenylene oxide (PPO) in short time and with good specificity ( >95%).

Catalytic activity of copper(II)complexes of immobilized polystyrene-bound 4-(N,N-dimethylamino)pyridine for the oxidative coupling of 2,6-disubstituted phenols

Abstract ‘Polystyrene-bound 4-( N , N -dimethylamino)pyridine’-copper (PS-DMAP-Cu( ii )) catalysts for the oxidation of 2,6-disubstituted phenols were immobilized by grafting or by partial adsorption on silica and by crosslinking with 2% divinylbenzene. The most active immobilized catalyst is the most flexible, i.e. the grafted one, which however is still six times less active than unbound linear PS-DMAP-Cu(II). The less extended conformation of the adsorbed polymeric catalyst exhibits a significantly lower activity. For the crosslinked catalyst, indications were obtained that diffusional limitations occur. Application of all three types of immobilized PS-DMAP based catalysts in a continuous stirred tank (CST) reactor was unsuccessful. The phenol conversion drastically decreased in time. This loss of activity could be explained by the destructive effect of water: interaction of reaction water with the very basic DMAP ligands may result in the production of an excess of hydroxide which, according to our earlier work, deactivates the catalyst. A catalyst based on the less basic poly(styrene- co -4-vinylpyridine) adsorbed onto silica exhibited an invariable phenol conversion in the CST reactor for at least 230 h.

A mechanistic study on the oxidation of 2,6-dimethyl-phenol by DMAP- and polystyrene-bound DMAP-based copper catalysts

Abstract A possible mechanism for the oxidation of 2,6-dimethylphenol by soluble- and polystyrene-bound Cu(II)-DMAP catalysts is described. From our earlier work it is known that, under our standard reaction conditions, the only Cu(II)-DMAP complexes that are initially present in significant amounts in the catalyst solution are mononuclear. From the difference in reaction order in copper for the phenol oxidation and the Cu(I) reoxidation, viz . 1 and 2 respectively, it had been concluded that dimerization of Cu(I) complexes is needed to allow the reoxidation step. For this dimerization, a small amount of copper-coordinating counter-ions proved to be required. The present study shows that under standard conditions for the low molar mass catalyst the dimerization reaction is rate-limiting. For the polymeric catalyst, however, the local copper concentration within the polymer coils is relatively high, the dimerization is accelerated and now the phenol oxidation becomes rate-limiting. The present work further shows that the phenol oxidation obeys Michaelis-Menten kinetics. For the Cu(I) reoxidation, an equilibrium is suggested in which molecular O 2 is reversibly bound to mononuclear Cu(I)-DMAP complexes, prior to Cu(I) dimerization and electron transfers. Combination of the present results with generally accepted steps in the oxidation of phenols allowed the construction of a possible reaction mechanism for our particular system.

The influence of chain and surface polarity on the activity of anchored macromolecular copper catalysts for the oxidative coupling of 2,6-di-t-butylphenol

Abstract Copolymers of styrene and 4-vinylpyridine have been utilized as macromolecular ligands for copper. The intrinsic activities of unbound and anchored macromolecular copper catalysts were identical in the oxidative coupling reaction of 2,6-di-t-butylphenol. Anchorage to silica resulted in a decrease of the equilibrium constant for substrate complexation because of water enrichment around the non-porous silica spheres. This effect could be suppressed by silanization of the silica support, and after such treatment higher substrate complexation equilibrium constants were observed than for unbound macromolecular catalysts. However, partial adsorption of the macromolecular ligands on to the silanized silica support occurred, leading to deactivation of catalytically active sites. This adsorption was strongly influenced by the nature of the silica surface and by the polarity of the comonomer, e.g. styrene or methyl methacrylate, in the macromolecular amine.

Copper(II) complexes of "polystyrene-bound DMAP" : synthesis, structure and catalytic activity in the oxidative coupling of 2,6-dimethylphenol

Abstract The oxidative coupling of 2,6-dimethylphenol by Cu(II) complexes of “polystyrene-bound DMAP” was studied. The polymer was prepared by radical copolymerization of styrene and 4-(N-methyl-N-p-vinylbenzylamino)pyridine (1). Monomer (1) was prepared as described by Tomoi et al. [7]. By purifying the monomer by column chromatography instead of distillation, however, we succeeded in raising its yield by some 20%. Catalytic experiments supported by UV and EPR experiments revealed that in the catalytically active solution an equilibrium exists between dinuclear and mononuclear Cu(II) complexes. The concentration of the catalytically most active, mononuclear species Cu(II)(ligand)4(OH)Cl increases on enhancing the ligand/Cu ratio and decreases on addition of an excess of copper-coordinating hydroxide ions. From this structural point of view the polymeric catalyst proved to behave just like low molar mass Cu(II)-DMAP complexes, although the mononuclear polymeric catalyst is more stable because of a polydentate effect. From the difference in reaction order in copper for unbound and polystyrene-bound DMAP catalysts, it was concluded that for the reoxidation step dimerization of Cu(I) complexes is needed, whereas mononuclear Cu(II) complexes are the most active species for the oxidation of DMP. The mentioned dimerization is promoted by the polymer chain. The specificity of the polystyrene-bound DMAP catalyst for formation of polyphenyleneoxide exceeds 95%.

Preface to the special edition of High Performance Polymers on Polycondensation 2010

Polycondensation or step-growth polymerization is one of the three dominating polymerization mechanisms applied for the industrial manufacturing of polymers. Step-growth polymers form the basis for many commodity polymers, engineering plastics, coatings, (hot melt) adhesives, films and fibers, and almost all high performance polymers are manufactured using this polymerization mechanism. With this in mind, the first meeting of the series of Polycondensation conferences was organized in Paris in 1996. Ever since, this specialized meeting has been organized every 2 years, and from 5–8 September 2010, the 8th Polycondensation Conference in the well-known series was held at the Rolduc Abbey in Kerkrade, The Netherlands. The organization of this event was in the hands of the local (Dutch) organizing committee, consisting of representatives of academia and industry, located in the Netherlands, for which step-growth polymers form a significant part of the current product portfolio and/or research program. The organization was performed in close collaboration with the Dutch Polymer Institute (DPI), and would not have been possible without the financial support received from the DPI, DSM, Sabic Innovative Plastics, Tata, TeijinAramid, BASF AG, Dow, CRODA, Rhodia and the Royal Dutch Academy of Sciences. The organizing committee wanted the conference to cover a wide range of topics, and the final program was based on the following themes:

Copper(II) complexes of "polystyrene-bound DMAP" : effect of chain loading on the catalytic activity in the oxidative coupling of 2,6-dimethylphenol

Abstract The effect of the degree of loading, α, of polystyrene with DMAP ligands on the catalytic activity of “polystyrene-bound DMAP”-copper catalysts in the oxidative coupling of 2,6-dimethylphenol was studied. The intrinsic activity increases upon enhancing α from 0.096 to 0.23. This increase proved to be mainly brought about by an increasing “strain” in the polymeric catalyst. An additional accelerating effect is the increase of the amount of catalytically active mononuclear complexes CuL4(OH)Cl with increasing α up to α = 0.134. This is due to a stronger polydentate effect for higher α because of the higher local ligand concentration within the polymer coils, which can be regarded as separate micro-reactors. For α > 0.23 the interligand distance becomes too short to link adjacent ligands to the same copper ion. Consequently, some ligands have to be skipped in favour of next ones, the strain is somewhat released and the intrinsic activity slightly decreases. For α⩾ 0.096 the phenol oxidation step proved to be rate limiting. However, for very low chain loadings, e.g. α = 0.044, the local concentration of mononuclear copper complexes within the coils becomes too low and the dimerization which is needed for the Cu(I) reoxidation becomes rate determining. The catalytic specificity proved to be independent of α under our reaction conditions.