Reduction of Friction by Functionalised Viscosity Index Improvers

A range of functionalised polymethacrylate copolymers have been synthesised with different functionalities, polymer architecture and molecular weight. It is shown that appropriately functionalised block copolymers give enhanced film thickness and greatly reduced friction under low entrainment speed conditions, even with polymer concentration as low as 1% wt. This behaviour almost certainly results from the formation of an adsorbed brush-like film of thickness ca 20 nm on each polar surface. These films provide a highly viscous inlet that promotes fluid entrainment and thus maintains a separating film down to very low entrainment speed. The adsorbed polymer films are also able to maintain separation in stationary contact conditions. Randomly distributed copolymers do not show this type of behaviour. The friction reduction observed is more effective in unidirectional, mixed sliding–rolling than in reciprocating, sliding conditions. However, it is found that functionalised polymers and conventional organic and molybdenum-based friction modifiers can be combined to provide effective friction reduction over the whole range of rubbing conditions.     

Synthesis and characterization of new polymethacrylates bearing perfluorocyclobutyl and sulfonyl units

A new methacrylate monomer containing perfluorocyclobutyl and sulfonyl units, p-(2-(p-(benzenesulfonyl)phenoxy)perfluorocyclobutoxy)phenyl methacrylate, was synthesized from commercially available reagents in good yield and this kind of methacrylate can be homopolymerized by free radical polymerization using 2,2′-azobis(isobutyronitrile) as initiator or atom transfer radical polymerization using methyl 2-bromopropionate as initiator and CuBr/PMDETA as catalytic system. The reactivity ratios for BSPPFCBPMA and MMA were found to be r₁ = 1.2436 and r₂ = 0.8171 determined by Fineman-Ross method, and r₁ = 1.2279 and r₂ = 0.8023 by Kelen-Tudos method respectively. The resultant polymethacrylates bearing perfluorocyclobutyl and sulfonyl functionalities exhibit excellent thermal stability as evidenced from thermogravimetric analysis and the decomposition temperature rose dramatically with the increasing of molecular weights. Random copolymers of BSPPFCBPMA and methyl methacrylate were obtained by free radical copolymerization and their thermo-stabilities increase while raising the contents of BSPPFCBPMA.     

Comparative study of the dispersion of three oxide pigments with sodium polymethacrylate dispersants in alkaline medium

The adsorption of sodium polymethacrylate (NaPMA) dispersants onto three oxide powders (hematite, goethite and rutile) in alkaline medium has been investigated together with the resulting stabilization of the suspensions. Under basic conditions of waterborne coatings formulation, hematite and rutile are negatively charged whereas goethite is almost neutral. Adsorption isotherms, electrophoretic mobility, particle size, IR spectroscopy and rheological measurements were used to investigate the polymer–pigments interactions. It was found that adsorption of the anionic NaPMA polymer on the three pigments was still possible even at pH above the isoelectric point (IEP). Depending on the pH and the type of oxide, electrostatic interactions, chemical complexation at the surface or/and hydrogen bonding were suggested to be the predominant contributions to the adsorption process. The adsorption at high pH was enough for preventing particles aggregation and ensuring an efficient stabilization of the suspensions. The viscosity measurements performed at pH close to the IEP's also suggested that besides the electrostatic stabilization, the NaPMA polymers provided a steric stabilization. The steric effect was larger with the polymers of higher molar mass. The comparison of the three oxide showed that the affinity for the surface site came mainly from chemical interaction with acidic surface sites in the order rutile > goethite > hematite. The strong adsorption on rutile came from the aluminum treatment of its surface.     

Thermal dynamics of side-chain copolymethacrylates as studied by the dielectric spectroscopy and relaxation of second-harmonic generation

A series of copolymethacrylates with different contents of tolane-based mesogenic groups have been synthesized. The mesogenic group content was characterized with ¹H-n.m.r.. The phase behaviours were determined using a differential scanning calorimeter and optical polarizing microscopy. A smectic A phase was obtained when the mesogenic group content was increased up to 80 mol.%. Dielectric relaxation results indicated that the amplitude of the -relaxation was suppressed significantly due to the presence of the liquid crystalline phase. The reduction of the molecular motion is beneficial to the enhancement of the temporal stability of the effective second-harmonic coefficient for the polymer with a higher mesogenic group content. Moreover, the second harmonic coefficient is enhanced as the mesogenic group content increases. The self-alignment nature of the liquid crystal phase is favourable for alignment of the NLO-active mesogenic group under an applied electric field and preserving such alignment after removal of the electric field. The relationship between thermal dynamic behaviour and second-order nonlinear optical properties is also discussed.     

The Design of Boundary Film-Forming PMA Viscosity Modifiers

Previous research has shown that some viscosity modifier additives are able to adsorb from oil solution on to metal surfaces to produce thick, viscous boundary films. These films enhance lubricant film formation in slow-speed and high temperature conditions and thus produce a significant reduction in friction. This article describes a systematic study of this phenomenon, which makes use of the versatile nature of polymethacrylate (PMA) chemistry. Dispersant polymethacrylates with a range of different functionalities, molecular weights, and architectures have been synthesized using controlled radical polymerization techniques. The influence of each of these features on boundary film formation and friction has been explored using optical interferometry and friction versus speed measurement. From the results, guidelines have been developed for designing PMAs having optimal boundary lubricating and, thus, friction-reducing properties.