Multi-end functionalised polymer additives synthesised by living anionic polymerisation—the impact of additive molecular structure upon surface properties

Abstract

. (2011) 'Multi-end functionalised polymer additives synthesised by living anionic polymerisation-the impact of additive molecular structure upon surface properties.', Polymer chemistry., 2 (4). pp. 851-861. Further information on publisher's website:http://dx.doi.org/10.1039/c0py00362jPublisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract Numerous applications require specific properties at polymer surfaces that differ from the bulk. Herein we describe the novel synthesis of a series of multi-end functionalised poly(styrene) and poly(isoprene) additives carrying 1 to 3 fluoroalkyl (CF) groups. The additives 10 were prepared by end capping the living chain ends of polymers prepared via living anionic polymerisation. The resulting polymers have been used as additives to render the surface of polymer films hydrophobic/lipophobic and we have characterised these polymer films using static contact angle measurements with water as the contact fluid. We have found that additive molecular weight, the number of CF groups, additive concentration and annealing conditions have a 15 significant impact upon the resulting surface properties. Increasing the additive concentration and/or number of CF groups resulted in higher contact angles whereas increasing the molecular weight of additive reduced contact angles and surface h ydrophobicity. It has been discovered that these additives undergo rapid adsorption to the surface of a thin film in the time taken to produce the film by spin coating and the result is significantly enhanced surface properties. Annealing 20 polystyrene films above the glass transition temperature revealed some interesting behaviour in so much that it demonstrated that on many occasions it is preferable to anneal films containing very small quantities of additive rather than to simply add greater quantities of additive. In addition to contact angles measurements, Rutherford backscattering analysis (RBS) has been carried out on examples of modified poly(isoprene) films to quantitatively analyse the effect of additive 25 molecular weight and number of fluoroalkyl groups on the near surface elemental composition of the modified thin films and confirming the relationship (described above) between these additive molecular parameters and surface adsorption. Finally, we have described a model which compares the behaviour of the additives in thin films to surfactants in solution.

Electrospinning Superhydrophobic Fibers Using Surface Segregating End-Functionalized Polymer Additives

“…The relationship between contact angle and molecular weight is qualitatively similar to that observed in thin films where a reduction in molecular weight also results in an increase in contact angle 17,34 . The relationship between concentration of additive and contact angle is also qualitatively similar to that observed in thin films, at least, for concentrations up to 4%.…”

“…A full discussion of the synthesis of both the end groups and the functionalized polymers has recently been described elsewhere 34 . Three end capping agents (figure 1) have been used which introduce 1, 2 or 3 fluoroalkyl groups onto the chain end of polystyrene to yield polymer additives denoted PS1CF, PS2CF and PS3CF…”

“…The relationship between concentration of additive and contact angle is also qualitatively similar to that observed in thin films, at least, for concentrations up to 4%. As discussed previously, the surface properties (contact angles) depend upon the concentration of functionalized additive at the surface of the fibre which in turn is dependent upon the molecular weight of the additive and the concentration of additive 34 . The surface composition of these polymer blends is expected to be different from the composition of the interior or bulk and the distribution of a low surface energy component between bulk and surface, and therefore the surface composition, arises as a result of a series of interrelated phenomena.…”

“…Although a small number of previous studies have shown that low molecular weight fluorinated additives do successfully migrate to the surface during the electrospinning process 29,30 , to the best of our knowledge this is the first report of low surface energy polymeric additives being used for this purpose. We have recently shown [15][16][17][18][19]34 that polymeric fluoroalkyl additives with molecular weights as high as 40,000 gmol -1 are able to successfully surface segregate in thin films, although somewhat unsurprisingly, lower molecular additives and additives with a higher fluorine contact are more effective at generating significant changes in surface properties. Spontaneous surface segregationdriven by a reduction in surface energy -was shown to be an extremely efficient process and in some cases it was possible to generate poly(tetrafluoroethylene)-like surface properties during the spin coating of a polymer film containing substantially less that 1% (by weight) of additive 17 .…”

“…The surface composition of these polymer blends is expected to be different from the composition of the interior or bulk and the distribution of a low surface energy component between bulk and surface, and therefore the surface composition, arises as a result of a series of interrelated phenomena. We have previously discussed 34,41 that there are similarities in the behavior of the fluorinated additives in thin films and that of surfactants in solution, and the formation of a maximum in contact angle at higher concentrations of fluorinated additive may be due in some part to the formation of aggregates of polymer additives in the bulk. It was argued that the fluorinated head groups are not very soluble in the matrix but at low concentrations the additives are molecularly dissolved -just as low films, the addition of further additive merely results in an increase in the number/size of aggregates 41 .…”