RESUMEN
Surface-tethered polymers have been shown to be an efficient lubrication strategy for boundary and mixed lubrication by providing a solvated film between solid surfaces. We have assessed the performance of various graft copolymers as friction modifier additives in oil and revealed important structure-property relationships for this application. The polymers consisted of an oil-soluble, grafted poly(lauryl acrylate) segment and a polar, linear poly(4-acryloylmorpholine) anchor group. Reversible addition-fragmentation chain transfer polymerization was used to access various architectures with control of the grafting density and position of the anchor group. Macrotribological studies displayed promising results with ≈50% reduction in friction coefficient at low polymer treatment rates. QCM-D experiments, neutron reflectometry, small-angle neutron scattering, and atomic force microscopy were used to gather detailed information on these polymers' surface adsorption characteristics, film structure, and solution behavior.
RESUMEN
We report the polymerisation-induced self-assembly of poly(lauryl methacrylate)-graft-poly(benzyl methacrylate) copolymers during reversible addition-fragmentation chain transfer (RAFT) grafting from polymerisation in a backbone-selective solvent. Electron microscopy images suggest the phase separation of grafts to result in a network of spherical particles, due to the ability of the branched architecture to freeze chain entanglements and to bridge core domains. Small-angle X-ray scattering data suggest the architecture promotes the formation of multicore micelles, the core morphology of which transitions from spheres to worms, vesicles, and inverted micelles with increasing volume fraction of the grafts. A time-resolved SAXS study is presented to illustrate the formation of the inverted phase during a polymerisation. The grafted architecture gives access to unusual morphologies and provides exciting new handles for controlling the polymer structure and material properties.
RESUMEN
We present a robust manganese-catalyzed cationic reversible addition-fragmentation chain transfer (RAFT) polymerization induced by visible light. Well-defined poly(vinyl ether)s with controlled molecular weight and molecular weight distributions (MWDs) can be conveniently prepared at room temperature without monomer purification. The commercially available manganese carbonyl bromide is used as the photocatalyst for cationic RAFT polymerization. Moreover, this method has been further applied in both batch and continuous flow systems, providing a visible light induced flow cationic polymerization under mild conditions.
Asunto(s)
Manganeso , Polímeros , Catálisis , Cationes , Luz , PolimerizacionRESUMEN
This study aimed to describe concept of social competence as a theoretical background for social skills group intervention for children with autism spectrum disorder (ASD). A model of social competence comprised of three components: social skills, social performance, and social adjustment. We also examined the feasibility and preliminary efficacy of the manualized Social Competence group intervention for children with autism spectrum disorder (SOCO) using a variety of outcome measures. The nine-month intervention included children groups, parental support groups and co-operation with teachers. A pilot study involved 23 children aged 7 to 12 years (n = 16 intervention, n = 7 control) and intervention outcomes were measured with questionnaires for parents and teachers, neuropsychological tests, and observations. The parents of the intervention group reported improvements in social skills and social adjustment, whereas the teachers reported increases in social performance. Findings also indicated that affect recognition skills, social overtures, and reactions to peers were improved in the intervention group. Although the evidence of the pilot study should be considered as preliminary, it gives some indication of the feasibility of the SOCO group intervention and supports the usability of the theoretical background and approach for multiple outcome measures.
Asunto(s)
Trastorno del Espectro Autista/terapia , Psicoterapia de Grupo , Habilidades Sociales , Niño , Femenino , Humanos , Masculino , Proyectos PilotoRESUMEN
An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side-chain polymers to be grafted from the pendant RAFT agent by a radical-mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one-pot tandem without intermediate purification.