Norman C. Billingham

Synthesis and aqueous solution properties of near-monodisperse tertiary amine methacrylate homopolymers and diblock copolymers

Group transfer polymerisation (GTP) of four tertiary amine methacrylates, 2-(dimethylamino)ethyl methacrylate (DMA), 2-(diethylamino)ethyl methacrylate (DEA), 2-(diisopropylamino)ethyl methacrylate (DPA) and 2-(N-morpholino)ethyl methacrylate (MEMA) produced a series of near-monodisperse homopolymers (Mw/Mn<1.15). Molecular weights were controlled by varying the monomer/initiator ratio. The DMA and MEMA homopolymers were both water-soluble at 20°C in acidic or neutral media. Inverse temperature solubility behaviour was observed at higher temperatures, with cloud-points ranging from 32 to 53°C at pH 8. The Cloud-points decreased monotonically with increasing degrees of polymerisation, as expected. The MEMA homopolymers were particularly sensitive to the added electrolyte, with ‘salting out’ occurring at 20°C on addition of 0.2–0.3 M Na2SO4. The more hydrophobic DEA and DPA homopolymers were both insoluble at 20°C and neutral pH but readily dissolved as cationic polyelectrolytes in acidic media due to protonation of the tertiary amine residues. In addition, DMA was block copolymerized in turn with each of the other three tertiary amine methacrylate comonomers. These diblock copolymers could be dissolved molecularly without co-solvents in aqueous media at 20°C, with micellization occurring reversibly on judicious adjustment of the solution pH, temperature or electrolyte concentration. In all three cases, stable block copolymer micelles were formed with DMA coronas and hydrodynamic diameters of 20–60 nm.

A Schizophrenic Water-Soluble Diblock Copolymer

Two micellar states are possible for a novel PPO-PDEA diblock copolymer synthesized by atom-transfer radical polymerization. Subtle variation of the solution pH value and temperature is all that is needed to form both conventional micelles (with the PDEA block in the core) and reverse micelles (with the PPO block in the core) in aqueous media (shown schematically). DEA=2-(diethylamino)ethyl methacrylate, PO=propylene oxide.

Carbon nanotubes as polymer antioxidants

The oxidation of polystyrene, polyethylene, polypropylene and poly(vinylidene fluoride) is retarded by carbon nanotubes. Incorporation of boron into the nanotubes enhances the electron affinity of the tubes and leads to a small increase in antioxidant efficiency.

Chemiluminescence from peroxides in polypropylene. Part I: Relation of luminescence to peroxide content

Abstract The weak chemiluminescence observed when partially oxidised samples of polypropylene are heated in an inert atmosphere has been studied as a function of oxidation. The integrated luminescence is shown to be proportional to titratable peroxides in the early stages of oxidation but the relation is curved at higher oxidation levels. Measurements during peroxide decomposition in an inert atmosphere show luminescence decaying faster than the drop in peroxide concentration. Both observations suggest that the luminescence originates in a small fraction of reactive peroxides. Experiments with antioxidants confirm that the luminescent step is a radical recombination.

Influence of testing conditions on the performance and durability of polymer stabilisers in thermal oxidation

Information on the efficiency of stabilisers in protecting polymers against thermal oxidation under service conditions is essential for selection and development of appropriate stabilizing systems. Accelerated tests are necessary to get data in an acceptable time and need carefully selected failure criteria. Appropriate testing severity, avoiding misuse of accelerated methods and understanding of the limitations of the methods are essential if reliable data are to be obtained. The potential and limitations of oven ageing tests, oxygen uptake measurements, differential scanning calorimetry (DSC) and chemiluminescence (CL) in stabiliser testing are reviewed.

Physical spreading of oxidation in solid polypropylene as studied by chemiluminescence

Abstract Highly sensitive chemiluminescence equipment was applied to study the oxidative behaviour at 125–150°C of individual polypropylene powder particles (10–500 μm) and film sections pressed from the powder. The chemiluminescence curves from the oxidation of single isolated powder particles revealed a range of induction periods equivalent to different intrinsic stabilities of the individual particles. Physical contact of the particles, however, resulted in a relatively early oxidation of the combined sample, i.e. a single induction period, as a result of the apparent initiation by the weakest particle and a subsequent spreading of the oxidation through the ensemble of particles. Evidence of this oxidative spreading was also found in polypropylene film samples. The physical spreading of the oxidation from an initial highly reactive centre has therefore been established as being the predominant step in the oxidation of a larger sample, and thus the weakest centre can control the overall oxidation of a sample. This mechanism was found to be consistent with the sigmoidal curve shape of the chemiluminescence curve obtained from the oxidation of both powder and film. The observed spreading is believed to be a highly efficient process, as the oxidation can ‘jump’ from particle to particle over distances of approximately 100 μm. In stabilized film the oxidation at the end of the induction period shows features different from that of an unstabilized film, and it is proposed that the spreading of the oxidation is limited by residual stabilizer in zones of lower reactivity.

Localization of oxidation in polypropylene

Abstract The distribution of oxidative degradation in isotactic polypropylene has been monitored using ultra-violet microscopy. Reaction of carbonyl groups in the oxidized polymer with 2,4-dinitrophenylhydrazine allows the oxidation to be seen with illumination at 350 nm. There is much extraction of oxidized material during the staining process. It is shown that oxidation initially favours the atactic fraction of the polymer. With increasing oxidation prior to crystallization rejection of oxidized material to the spherulite boundaries leads to increasing weakness in these regions although there is no evidence that their subsequent oxidation rate is enhanced. Localized oxidation in diluent-phase polymer is shown to correlate strongly with the distribution of catalyst residues in the polymer. Similar localization can be observed in polymer formed on a high efficiency, gas phase, catalyst although catalyst residues are not directly visible in this polymer.

Chemiluminescence from oxidation of polypropylene: Correlation with peroxide concentration

Abstract The Chemiluminescence (CL) on heating in an inert atmosphere has been measured for samples taken at various times during oxidation of polypropylene (PP). Proportional relationships were obtained when the integrated emission (TLI) was plotted against peroxide concentration for all studied sets of parameters. Changes in melting temperature and molecular weight with ageing time were found to correlate with changes in the TLI. Oxidised PP was exposed to dimethylsulfide (DMS) for different periods with subsequent measurements of the CL and the peroxide concentration. The peroxide concentration has earlier been found to exhibit a two-step decay with DMS exposure time, indicating two fractions of peroxides with different reactivity. The CL was found to follow the same two-step decay, indicating that both peroxide fractions contribute to CL. The oxidative stability of PP, measured by CL induction times in oxygen, increases when the polymer is exposed to DMS.

Chemiluminescence imaging of the oxidation of polypropylene

A commercial high-sensitivity CCD camera has been applied to image the weak chemiluminescence from the oxidative degradation of polypropylene. Images of powder and film samples were obtained after various oxidation times and showed the heterogeneous characteristics of oxidation. The results are consistent with a model for oxidative spreading from zones with a high local rate of oxidation.

Durham poly acetylene: preparation and properties of the unoriented material

Abstract Polyacetylene prepared by the Shirakawa route is a mat of crystalline fibrills, which are capable of being oxidized or reduced to a highly conducting state. Polyacetylene can also be produced from a soluble precursor polymer by a thermally driven transformation reaction (the ‘Durham’ route) as a solid, coherent film. This transformation consists of the elimination of a substituted benzene unit followed by the isomerization of the largely cis polyacetylene produced to a disordered trans isomer. We have studied the effect of different transformation conditions and from these studies it is possible to gain an insight into these processes. Techniques such as caloremetry, infrared, resonance Raman and optical spectroscopy, e.s.r., X-ray diffraction and electrical conductivity have all been used to probe the transformation and the product. The resultant information gives a consistent picture of the overall transformation processes detailed above but also shows an ordering associated with higher transformation temperatures. A thorough knowledge of these processes enables the orientation of the precursor to produce highly crystalline material.