Self-healing materials are notable for their ability to recover from physical or chemical damage. We report that commodity copolymers, such as poly(methyl methacrylate)/n-butyl acrylate [p(MMA/nBA)] and their derivatives, can self-heal upon mechanical damage. This behavior occurs in a narrow compositional range for copolymer topologies that are preferentially alternating with a random component (alternating/random) and is attributed to favorable interchain van der Waals forces forming key-and-lock interchain junctions. The use of van der Waals forces instead of supramolecular or covalent rebonding or encapsulated reactants eliminates chemical and physical alterations and enables multiple recovery upon mechanical damage without external intervention. Unlike other self-healing approaches, perturbation of ubiquitous van der Waals forces upon mechanical damage is energetically unfavorable for interdigitated alternating/random copolymer motifs that facilitate self-healing under ambient conditions.
Original perfluoropolyethers (PFPE)-based oligomeric polyesters (FOPs) of different macromolecular architecture were synthesized via polycondensation as low surface energy additives to engineering thermoplastics. The oligomers do not contain long-chain perfluoroalkyl segments, which are known to yield environmentally unsafe perfluoroalkyl carboxylic acids. To improve the compatibility of the materials with polyethylene terephthalate (PET) we introduced isophthalate segments into the polyesters and targeted the synthesis of lower molecular weight oligomeric macromolecules. The surface properties such as morphology, composition, and wettability of PET/FOP films fabricated from solution were investigated using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. It was demonstrated that FOPs, when added to PET film, readily migrate to the film surface and bring significant water and oil repellency to the thermoplastic boundary. We have established that the wettability of PET/FOP films depends on three main parameters: (i) end-groups of fluorinated polyesters, (ii) the concentration of fluorinated polyesters in the films, and (iii) equilibration via annealing. The most effective water/oil repellency FOP has two CF-PFPE-tails. The addition of this oligomeric polyester to PET allows (even at relatively low concentrations) reaching a level of oil repellency and surface energy comparable to that of polytetrafluorethylene (PTFE/Teflon). Therefore, the materials can be considered suitable replacements for additives containing long-chain perfluoroalkyl substances.
For
decades, water and oil repellency of engineering thermoplastics
has been achieved with introduction of long-chain perfluoroalkyl substances
and moieties (C
n
F2n+1, n ≥ 7). However, their bioaccumulative
and toxicological impact is now widely recognized and, consequently,
the substances have been phased out of industrial production and applications.
To this end, we have synthesized fluorinated oligomeric triblock polyesters
(FOPBs), which do not possess the long-chain perfluoroalkyl segments
and serve as effective low-surface-energy additives to engineering
thermoplastics. More specifically, we obtained original perfluoropolyether
(PFPE)-based triblock copolymers, in which two identical fluorinated
blocks were separated by a short nonfluorinated polyester block made
of poly(ethylene isophthalate) (PEI). It was found that when FOPBs
were added to poly(ethylene terephthalate), nylon-6, and poly(methyl
methacrylate) films they readily migrate to the film surface and in
doing so imparted significant water and oil repellency to the thermoplastic
boundary. The water/oil wettability of the films modified with FOPB
is considerably lower than the wettability of the films modified with
an analogous PFPE-based polyester, which differs from FOPB only by
the absence of the short nonfluorinated PEI middle block. We associate
the superiority of the triblock copolymers in terms of water and oil
repellency with their ability to form brushlike structures on polymer
film surfaces.
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