The Oxidative Coupling of 2,6-Xylenol Catalyzed by Polymeric Complexes of Copper, 2. Physicochemical Study on Copper(II) Complexes of Partially Dimethylaminomethylated Polystyrene

The polymeric catalyst formed by complexation of copper(II) chloride and partially dimethylaminomethylated polystyrene was investigated to explain its behaviour in the oxidative coupling of 2,6-xylenol. Viscometric studies indicated that at low polymer concentrations coordination of tertiary amine groups to copper(II) causes an intramolecular crosslinking. UV measurements and preliminary results of ESR point to a dimeric structure of these complexes with two amine groups per copper. A mechanism for the action of this polymeric catalyst is suggested, based on these results and on those described in Part 1. It appeared that some "free" copper(II) is essential for the catalytic activity, without which the reoxidation of copper(I) cannot take place.

Changes in articular cartilage after meniscectomy and meniscus replacement using a biodegradable porous polymer implant

Purpose: To evaluate the long-term effects of implantation of a biodegradable polymer meniscus implant on articular cartilage degeneration and compare this to articular cartilage degeneration after meniscectomy. Methods: Porous polymer polycaprolacton-based polyurethane meniscus implants were implanted for 6 or 24 months in the lateral compartment of Beagle dog knees. Contralateral knees were meniscectomized, or left intact and served as controls. Articular cartilage degeneration was evaluated in detail using India ink staining, routine histology, immunochemistry for denatured (Col2-¾M) and cleaved (Col2-¾Cshort) type II collagen, Mankin’s grading system, and cartilage thickness measurements. Results: Histologically, fibrillation and substantial immunohistochemical staining for both denatured and cleaved type II collagen were found in all three treatment groups. The cartilage of the three groups showed identical degradation patterns. In the 24 months implant group, degradation appeared to be more severe when compared to the 6 months implant group and meniscectomy group. Significantly more cartilage damage (India ink staining, Mankin’s grading system, and cartilage thickness measurements) was found in the 24 months implant group compared to the 6 months implant group and meniscectomy group. Conclusion: Degradation of the cartilage matrix was the result of both mechanical overloading as well as localized cell-mediated degradation. The degeneration patterns were highly variable between animals. Clinical application of a porous polymer implant for total meniscus replacement is not supported by this study.

Has the Rate of CD4 Cell Count Decline before Initiation of Antiretroviral Therapy Changed over the Course of the Dutch HIV Epidemic among MSM?

Introduction:Studies suggest that the HIV-1 epidemic in the Netherlands may have become more virulent, leading to faster disease progression if untreated. Analysis of CD4 cell count decline before antiretroviral therapy (ART) initiation, a surrogate marker for disease progression, may be hampered by informative censoring as ART initiation is more likely with a steeper CD4 cell count decline.Methods:Development of CD4 cell count from 9 to 48 months after seroconversion was analyzed using a mixed-effects model and 2 models that jointly modeled CD4 cell counts and time to censoring event (start ART

Langmuir-Blodgett mono- and multilayers of preformed poly(octadecyl methacrylate)s, 1. Surface-area isotherms of atactic and isotactic poly(octadecyl methacrylate)s and transfer into multilayers

In order to elucidate some of the parameters controlling the transfer of compressed monomolecular layers of preformed poly(octadecyl methacrylate)s (PODMA) onto substrates by the so-called Langmuir-Blodgett technique, an investigation was undertaken of PODMA's of different tacticity and different molecular weights. For the preparation of multilayered structures it was necessary to decrease the interaction between the side chains. This could be accomplished by introducing side chain inhomogeneities especially in the form of comonomers with shorter alkyl side chains. The transferability of a monolayer could be correlated with features in the pressure-area diagrams, as there is a liquid-analogous state formed when shorter alkyl chains are introduced; moreover a partial "melting" with lowering of the collaps pressure of the layer is seen. It appeared that with isotactic PODMA regular Y-type transfer took place, whereas with the atactic polymers at the beginning a Z-type transfer occurred, gradually changing into a Y-type transfer. Applying the concept of decreasing interaction of the side chains it was possible to prepare multilayers of isotactic and atactic PODMA's.

Oriented Thin Film Formation by Surface Graft Polymerization of γ-Methyl L-Glutamate N-Carboxyanhydride in the Melt

A new and versatile method to produce grafted layers of poly(γ-methyl L-glutamate) (PMLG) on silicon wafers by the ring-opening polymerization of γ-methyl L-glutamate N-carboxyanhydride (MLG-NCA) is described. Compared with the polymerizations in solution, this approach provides grafted synthetic polypeptide layers very easily and reproducibly.

The Oxidative Coupling of 2,6-Xylenol Catalyzed by Polymeric Complexes of Copper, 1. Kinetic Study of the Catalysis by Copper(II)-Complexes of Partially Aminated Polystyrene

The oxidative coupling reaction of 2,6-xylenol catalyzed by copper(II) complexes of chemically modified polystyrene was investigated. Under the applied reaction conditions the main reaction product was 2,6,2',6'-tetramethyl-1,1'-dioxo-4,4'-bicyclohexa-2,5-dienylidene. It was found that the polymeric complexes behave quite different from the low molecular analogue and that these differences can mainly be ascribed to a better complexation of copper within polymer coils. It appeared that a Michaelis-Menten description of the kinetics fits rather well when the concentration of the phenol was not too high.

End-Grafting of (co)polyglutamates and (co)polyaspartates onto Si-OH containing Surfaces

(Co)polyglutamates and (co)polyaspartates were grafted onto microparticulate silica and flat Si-OH containing surfaces, by initiating the N-carboxyl anhydrides of the corresponding α-amino acids with an immobilized primary amine. The copolymers were prepared by polymerization of mixtures of N-carboxy anhydrides. In the case of microparticulate silica, all the available monomer was converted into grafted polymer, whereas in the case of flat surfaces, non-grafted material was formed as well. The grafted products were identified with infra-red spectroscopy and X-ray photoelectron spectroscopy.

Conformation and orientation of end-grafted (co)polyglutamates and (co)polyaspartates

The conformation and orientation of end-grafted (co)polyglutamates and (co)polyaspartates were investigated using several infra-red spectroscopy techniques. The grafted polymers took on the same conformations as the corresponding free polymers; however, the change in conformation at higher temperatures did not take place. The orientation of the polymers grafted onto flat surfaces turned out to be bent towards the surface, but became more perpendicular after interdiffusion of trans-ethyl-β-apo-8’-carotenoate.

Anionic grafting of polystyrene and poly(styrene-block-isoprene) onto microparticulate silica and glass slides

Polystyrene and poly(styrene-block-isoprene) were grafted onto microparticulate silica by initiating immobilized double bonds at the silica surface with t-butyllithium, and subsequently adding monomer to the reaction suspension. Grafted block copolymers could be synthesized by adding a second monomer after the first monomer had reacted completely. The obtained molecular-weight distributions were somewhat broader than those for comparable anionic homopolymerizations.