Discussion on "Aperiodic Copolymers".

In a recent Viewpoint (ACS Macro Lett. 2014, 3, 1020), J.-F. Lutz brought to the community's attention the need for more informative nomenclature, especially with respect to macromolecules with prescribed but not repeating sequences of monomers. Lutz proposes the use of the term "aperiodic" for this situation. In this Viewpoint, we comment on the need for such nomenclature and offer some alternatives for consideration.

A Novel Method of Extraction of Blend Component Structure from SANS Measurements of Homopolymer Bimodal Blends.

A new method is presented for the extraction of single-chain form factors and interchain interference functions from a range of small-angle neutron scattering (SANS) experiments on bimodal homopolymer blends. The method requires a minimum of three blends, made up of hydrogenated and deuterated components with matched degree of polymerization at two different chain lengths, but with carefully varying deuteration levels. The method is validated through an experimental study on polystyrene homopolymer bimodal blends with [Formula: see text]. By fitting Debye functions to the structure factors, it is shown that there is good agreement between the molar mass of the components obtained from SANS and from chromatography. The extraction method also enables, for the first time, interchain scattering functions to be produced for scattering between chains of different lengths. [Formula: see text].

Surface modification of polyethylene with multi-end-functional polyethylene additives.

We have prepared and characterized a series of multifluorocarbon end-functional polyethylene additives, which when blended with polyethylene matrices increase surface hydrophobicity and lipophobicity. Water contact angles of >112° were observed on spin-cast blended film surfaces containing less than 1% fluorocarbon in the bulk, compared to ~98° in the absence of any additive. Crystallinity in these films gives rise to surface roughness that is an order of magnitude greater than is typical for amorphous spin-cast films but is too little to give rise to superhydrophobicity. X-ray photoelectron spectroscopy (XPS) confirms the enrichment of the multifluorocarbon additives at the air surface by up to 80 times the bulk concentration. Ion beam analysis was used to quantify the surface excess of the additives as a function of composition, functionality, and molecular weight of either blend component. In some cases, an excess of the additives was also found at the substrate interface, indicating phase separation into self-stratified layers. The combination of neutron reflectometry and ion beam analysis allowed the surface excess to be quantified above and below the melting point of the blended films. In these films, where the melting temperatures of the additive and matrix components are relatively similar (within 15 °C), the surface excess is almost independent of whether the blended film is semicrystalline or molten, suggesting that the additive undergoes cocrystallization with the matrix when the blended films are allowed to cool below the melting point.

In Silico Molecular Design, Synthesis, Characterization, and Rheology of Dendritically Branched Polymers: Closing the Design Loop.

It has been a long held ambition of both industry and academia to understand the relationship between the often complex molecular architecture of polymer chains and their melt flow properties, with the goal of building robust theoretical models to predict their rheology. The established key to this is the use of well-defined, model polymers, homogeneous in chain length and architecture. We describe here for the first time, the in silico design, synthesis, and characterization of an architecturally complex, branched polymer with the optimal rheological properties for such structure-property correlation studies. Moreover, we demonstrate unequivocally the need for accurate characterization using temperature gradient interaction chromatography (TGIC), which reveals the presence of heterogeneities in the molecular structure that are undetectable by size exclusion chromatography (SEC). Experimental rheology exposes the rich pattern of relaxation dynamics associated with branched polymers, but the ultimate test is, of course, did the theoretical (design) model accurately predict the rheological properties of the synthesized model branched polymer? Rarely, if ever before, has such a combination of theory, synthesis, characterization, and analysis resulted in a "yes", expressed without doubt or qualification.

Kinetic control of monomer sequence distribution in living anionic copolymerisation.

Sequence control in synthetic polymers is a subject that is sparsely reported with little research in the field of sequence control in chain growth polymerisation. We report herein preliminary investigations into anionic copolymerisation of diphenylethylene (DPE) and its derivatives with styrene. DPE is a monomer that will only copolymerise and can form alternating copolymers. However, by introducing electron donating or withdrawing substituents onto the phenyl rings of DPE it is possible to prepare new range of (alternating) copolymers and with careful choice of monomer combination and conditions, the kinetically controlled (simultaneous) copolymerisation of three or more monomers results in copolymers with a greater degree of monomer sequence control.

Nonsolvent annealing polymer films with ionic liquids.

Neutron reflectometry has been used to determine the interface structure and swelling of thin polymer films, when annealed in contact with a series of 1-alkyl-3-methylimidazolium ionic liquids (ILs). By choosing immiscible polymer/IL combinations, we have established that thin polymer films can be annealed for several hours in contact with ILs at temperatures well above the glass transition temperature and that this nonsolvent annealing environment can be exploited to direct self-assembly in polymer films. The ingress of IL into polymer films was quantified in terms of the swelling up to 10%. The polymer/IL interfacial width generally also increased from 0.9 nm up to ∼3 nm, but there was remarkably little correlation between interfacial width and swelling. For one combination of polymer and IL (deuterated PMMA and Bmim-BF(4)) the interfacial width decreased slightly with increasing temperature, consistent with LCST behavior for this system. All of the ILs tested had a profound influence the distribution of carboxy-end-functionalized deuterated polystyrene, "dPS-COOH", in blended films with polystyrene homopolymers. The ILs promoted dPS-COOH adsorption at the film/IL interface and the simultaneous rapid desorption at the film silicon-oxide interface. The rate of desorption was found to correlate with the swelling behavior of the polymer with respect to the IL anion species: PF(6)(-) < Br(-) < Cl(-) < BF(4)(-), suggesting that the polymer films are plasticized by the IL as it penetrates the film.

pH-controlled polymer surface segregation.

A new approach to promoting and controlling polymer surface functionalization with acidic or basic polar functional groups is demonstrated and evaluated. Blended polymer films were annealed under pH-buffered conditions, and polar end-functional groups were found to promote surface segregation of the functional polymers. Surface segregation of carboxylic acid (COOH)-functionalized polystyrene increases dramatically with increasing pH from 1.9 to 9.4, whereas the opposite behavior is seen for amine (NH2)-functionalized polystyrene. Neutron reflectometry and nuclear reaction analysis were used to obtain surface excess values for the functional polymers. Subsequent SCFT analysis of the composition versus depth profiles indicates that the affinity of each functional group for the polymer surface changes by about 3k(B)T over this pH range.

Aggregation, adsorption, and surface properties of multiply end-functionalized polystyrenes.

The properties of polystyrene blends containing deuteriopolystyrene, multiply end-functionalized with C8F17 fluorocarbon groups, are strikingly analogous to those of surfactants in solution. These materials, denoted FxdPSy, where x is the number of fluorocarbon groups and y is the molecular weight of the dPS chain in kg/mol, were blended with unfunctionalized polystyrene, hPS. Nuclear reaction analysis experiments show that FxdPSy polymers adsorb spontaneously to solution and blend surfaces, resulting in a reduction in surface energy inferred from contact angle analysis. Aggregation of functionalized polymers in the bulk was found to be sensitive to FxdPSy structure and closely related to surface properties. At low concentrations, the functionalized polymers are freely dispersed in the hPS matrix, and in this range, the surface excess concentration grows sharply with increasing bulk concentration. At higher concentrations, surface excess concentrations and contact angles reach a plateau, small-angle neutron scattering data indicate small micellar aggregates of six to seven F2dPS10 polymer chains and much larger aggregates of F4dPS10. Whereas F2dPS10 aggregates are miscible with the hPS matrix, F4dPS10 forms a separate phase of multilamellar vesicles. Using neutron reflectometry (NR), we found that the extent of the adsorbed layer was approximately half the lamellar spacing of the multilamellar vesicles. NR data were fitted using an error function profile to describe the concentration profile of the adsorbed layer, and reasonable agreement was found with concentration profiles predicted by the SCFT model. The thermodynamic sticking energy of the fluorocarbon-functionalized polymer chains to the blend surface increases from 5.3kBT for x = 2 to 6.6kBT for x = 4 but appears to be somewhat dependent upon the blend concentration.

Novel multi end-functionalised polymers. Additives to modify polymer properties at surfaces and interfaces.

Fréchet-type poly(arylether) dendrons with up to eight trifluoromethyl peripheral groups have been used as initiators in the copper mediated living radical polymerisation of d-styrene, the surface adsorption behaviour and resulting properties of these polymers in blends have been investigated by ion beam analysis and contact angle measurements.

Surface adsorption of polar end-functionalised polystyrenes.

Due to their inherently high surface energy, polar end-functionalised polymers do not normally adsorb to the external surfaces of blends. However, adsorption of polar functionalities can be induced rapidly by annealing in a polar environment such as glycerol prior to quenching to a glassy state. Blended films of carboxy end-functionalised deuteriopolystyrene (dPS-COOH) with hydrogenous polystyrene (hPS) were annealed at 150 °C under glycerol. Nuclear reaction analysis was used to quantify the surface excess of dPS-COOH retained at the surface after quenching the films to below the glass transition temperature. Incorporation of multiple COOH groups onto a single chain end greatly increases the affinity of these chains to the interface with glycerol. Here we have shown that even a difunctional material, dPS-2COOH, is much more surface active than either the singly functionalised dPS-COOH or the difunctional ester from which it was prepared. Self-consistent mean field theory yielded thermodynamic 'sticking energy' values per functionality at the polystyrene-glycerol surface of 1.3-1.7 for carboxy groups and 0.3 for ester groups.