Weak students often continue with little guidance and feedback, and often have ongoing difficulties. Early support may stop students experiencing a cycle of failure. Key to supporting struggling students is to identify reasons for poor performance. We explored the reasons for poor performance in a cohort of fifth year students who failed their final clinical examinations. Qualitative methods (interviews and a focus group) identified several themes. Many of the students had experienced personal problems or issues. They regarded themselves as competent students although they had significantly greater problems with earlier exams than the year mean, and significantly lower scores in formative assessments during the year leading up to these exams than their peers. Factors relating to the exam itself were seen as relevant to failure. More specific support and feedback throughout the MBcHB was seen as desirable. They tended to take little personal responsibility for their performance and were reluctant to seek help. We conclude that while the onus is on Faculty to identify and support failing students, the results indicate that students would benefit from support in developing self-reflection skills in such a way to support life-long learning.
The kinetics of aminolysis between two different active ester polymer brush platforms, poly(4-pentafluorophenyl acrylate) (poly(PFPA)) and poly(N-hydroxysuccinimide-4-vinyl benzoate) (poly(NHS4VB)), are compared using primary and aromatic amines with varying reactivity toward postpolymerization modification. UV−vis was used to monitor the aminolysis of both brush platforms with 1-aminomethylpyrene (AMP), 1-aminopyrene (AP), and Ru-(bpy) 2 (phen-5-NH 2 )(PF 6 ) (Ru 2+ A). Using a pseudo-firstorder kinetics model, the pseudo-first-order rate constant (k′) was calculated for each system. The k′ of poly(PFPA) modified with AMP, AP, and Ru 2+ A were 2.46 × 10 −1 , 5.11 × 10 −3 , and 2.59 × 10 −3 s −1 , respectively, while poly(NHS4VB) can only be functionalized with the alkyl amine, albeit at a slower rate constant, k′ of 3.49 × 10 −3 s −1 , compared to that of poly(PFPA) with AMP. The kinetics of surface-initiated photopolymerization of PFPA from oxide surfaces was also investigated as an effective method to control grafting density and film thickness.
The postpolymerization functionalization of poly(N-hydroxysuccinimide 4-vinylbenzoate) brushes with reactive alkynes that differ in relative rates of activity of alkyne-azide cycloaddition reactions is described. The alkyne-derived polymer brushes undergo "click"-type cycloadditions with azido-containing compounds by two mechanisms: a strain-promoted alkyne-azide cycloaddition (SPAAC) with dibenzocyclooctyne (DIBO) and azadibenzocyclooctyne (ADIBO) or a copper-catalyzed alkyne-azide cycloaddition (CuAAC) to a propargyl group (PPG). Using a pseudo-first-order limited rate equation, rate constants for DIBO, ADIBO, and PPG-derivatized polymer brushes functionalized with an azide-functionalized dye were calculated as 7.7 × 10(-4), 4.4 × 10(-3), and 2.0 × 10(-2) s(-1), respectively. The SPAAC click reactions of the surface bound layers were determined to be slower than the equivalent reactions in solution, but the relative ratio of the reaction rates for the DIBO and ADIBO SPAAC reactions was consistent between solution and the polymer layer. The rate of functionalization was not influenced by the diffusion of azide into the polymer scaffold as long as the concentration of azide in solution was sufficiently high. The PPG functionalization by CuAAC had an extremely fast rate, which was comparable to other surface click reaction rates. Preliminary studies of dilute solution azide functionalization indicate that the diffusion-limited regime of brush functionalization impacts a 50 nm polymer brush layer and decreases the pseudo-first-order rate by a constant diffusion-limited factor of 0.233.
Advances in key 21st century technologies such as biosensors, biomedical implants, and organic light-emitting diodes rely heavily on our ability to imagine, design, and understand spatially complex interfaces. Polymer-based thin films provide many advantages in this regard, but the direct synthesis of polymers with incompatible functional groups is extremely difficult. Using postpolymerization modification in conjunction with click chemistry can circumvent this limitation and result in multicomponent surfaces that are otherwise unattainable. The two methods used to form polymer thin films include physisorption and chemisorption. Physisorbed polymers suffer from instability because of the weak intermolecular forces between the film and the substrate, which can lead to dewetting, delamination, desorption, or displacement. Covalent immobilization of polymers to surfaces through either a "grafting to" or "grafting from" approach provides thin films that are more robust and less prone to degradation. The grafting to technique consists of adsorbing a polymer containing at least one reactive group along the backbone to form a covalent bond with a complementary surface functionality. Grafting from involves polymerization directly from the surface, in which the polymer chains deviate from their native conformation in solution and stretch away from the surface because of the high density of chains. Postpolymerization modification (PPM) is a strategy used by our groups over the past several years to immobilize two or more different chemical functionalities onto substrates that contain covalently grafted polymer films. PPM exploits monomers with reactive pendant groups that are stable under the polymerization conditions but are readily modified via covalent attachment of the desired functionality. "Click-like" reactions are the most common type of reactions used for PPM because they are orthogonal, high-yielding, and rapid. Some of these reactions include thiol-based additions, activated ester coupling, azide-alkyne cycloadditions, some Diels-Alder reactions, and non-aldol carbonyl chemistry such as oxime, hydrazone, and amide formation. In this Account, we highlight our research combining PPM and click chemistry to generate complexity in polymer thin films. For the purpose of this Account, we define a complex coating as a polymer film grafted to a planar surface that acts as a template for the patterning of two or more discrete chemical functionalities using PPM. After a brief introduction to grafting, the rest of the review is arranged in terms of the sequence in which PPM is performed. First, we describe sequential functionalization using iterations of the same click-type reaction. Next, we discuss the use of two or more different click-like reactions performed consecutively, and we conclude with examples of self-sorting reactions involving orthogonal chemistries used for one-pot surface patterning.
Post-polymerization modification is a simple and effective method to add complex functionality to a polymeric interface. A wide variety of click reactions have been utilized as a means of postpolymerization functionalization on surface-bound polymers to tune interfacial properties, such as friction, wettability, and adhesion. Patterning surfaces with spatial control of chemical functionality has also been obtained through orthogonal or sequential click reactions. This review highlights the progress in post-polymerization modification of polymers covalently attached to a surface, focusing on the design of functional interfaces in terms of the various reactive functional groups.
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