No abstract

The nonvolatile products in thermal‐oxidized polypropylene sheet have been quantitatively identified by infrared analysis and chemical reaction. The molecular weight changes with oxidation have been studied by gel‐permeation chromatography. It was determined that there is a functional group at each end of a chain. A general oxidation mechanism scheme for polypropylene is presented. The discovery of γ‐lactone is an indication of the importance of an intramolecular backbiting process. The overall functional group distribution is found to differ from that found in a polyethylene sheet.

The self-diffusion coefficient Ds of dye-labeled polystyrene chains having Mw ) 3.90 × 10 5 g/mol and Mw/Mn < 1.10 was measured over almost 4 decades of polymer concentration in toluene solution, from 10 -4 to 0.4 g/mL, by fluorescence correlation spectroscopy. In the dilute regime up to 5 × 10 -3 g/mL, Ds remains practically constant. The transition to the semidilute regime is observed around 0.01 g/mL, and from 0.02 to 0.4 g/mL Ds decreases strongly with rising concentration. This decrease is well represented by a power law, Ds ∼ c -1.75 , as predicted by scaling and reptation theory. As an alternative, a good fit over the whole concentration range can be obtained with a stretched exponential function, Ds ) D0 exp-(-15c 0.65 ), with D0 ) 2 × 10 -7 cm 2 /s and c given in g/mL.

Coatings with vertical gradients in composition were produced by drying an aqueous polymer dispersion containing both charged and neutral particles. After drying, the neutral component was enriched at the film/air interface. The spontaneous vertical segregation between the two types of particles goes back to a difference in collective diffusivity. As the film dries, a layer enriched in polymer develops at the top. Due to their mutual repulsion, charged spheres escape from this layer more quickly than their neutral counterparts. Provided that the total time of drying is between the times of diffusion for the two types of particles (approximately H(0)(2)/D(c) with H(0) the initial film thickness and D(c) the collective diffusivity of the respective species), a concentration gradient persists after the film has turned dry. This effect can be used to create a functionally graded material (FGM) in a single coating step.

The peptide Ac‐Ser‐Ala‐Gly‐Ala‐Gly‐Glu‐Gly‐Ala‐Gly‐Ala‐Gly‐Ser‐Gly‐OH was prepared with solid‐phase peptide chemistry. Before the removal of the peptide from the solid support, the alcohol side groups of the two serines were functionalized with an α‐bromo ester moiety to create a bifunctional initiator. This peptide‐based initiator was used in solution for the atom transfer radical polymerization of methyl methacrylate to yield a well‐defined ABA triblock copolymer, in which the poly(methyl methacrylate) end blocks had a number‐average molecular weight of 1.1 kg/mol (based on 1H NMR spectroscopy) and a polydispersity of 1.17. The aggregation behavior of this amphiphilic triblock copolymer was then investigated. Upon the suspension of the polymer in a mixture of tetrahydrofuran and water, followed by the removal of tetrahydrofuran, spherical aggregates were formed. By the application of different electron microscopy techniques, it was determined that these aggregates were polymersomes, presumably coexisting with large compound micelles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6355–6366, 2005