A one-step method of plant oil direct transesterification was used to synthesize new vinyl monomers from sunflower (SFM), linseed (LSM), soybean (SBM), and olive (OVM) oils. The degree of unsaturation in plant oil fatty acids was used as a criterion to compare the free radical polymerization behavior of new monomers. The number-average molecular weight of plant oil-based homopolymers synthesized in toluene in the presence of AIBN at 75 °C varies at 11 000–25 000 and decreases as follows: poly(OVM) > poly(SFM) > poly(SBM) > poly(LSM), corresponding to increasing degree of unsaturation in the monomers. Rate of polymerization depends noticeably on the degree of unsaturation in monomers. Due to the allylic termination, chain propagation coexists with effective chain transfer during polymerization. The obtained values of C M (ratio of chain transfer and propagation rate constants) depends on monomer structure as follows: C M(LSM) > C M(SBM) > C M(SFM) > C M(OVM). 1H NMR spectroscopy shows that the fraction of the reacting allylic atoms does not vary significantly for the synthesized monomers (7–12%) and is determined entirely by plant oil degree of unsaturation. The glass transition temperature of homopolymers [T g = 4.2 °C for poly(SFM), T g = −6 °C for poly(SBM)] from new monomers indicates that varying biobased fragments in copolymers might considerably change the intermolecular interactions of macromolecules and their physicochemical properties.
Strategically designed amphiphilic invertible polymers (AIPs) are capable of (i) self-assembling into invertible micellar assemblies (IMAs) in response to changes in polarity of environment, polymer concentration, and structure, (ii) accommodating (solubilizing) substances that are otherwise insoluble in water, and (iii) inverting their molecular conformation in response to changes in the polarity of the local environment. The unique ability of AIPs to invert the molecular conformation depending on the polarity of the environment can be a decisive factor in establishing the novel stimuli-responsive mechanism of solubilized drug release that is induced just in response to a change in the polarity of the environment. The IMA capability to solubilize lipophilic drugs and deliver and release the cargo molecules by conformational inversion of polymer macromolecules in response to a change of the polarity of the environment was demonstrated by loading IMA with a phytochemical drug, curcumin. It was demonstrated that four sets of micellar vehicles based on different AIPs were capable of delivering the curcumin from water to an organic medium (1-octanol) by means of unique mechanism: AIP conformational inversion in response to changing polarity from polar to nonpolar. The IMAs are shown to be nontoxic against human cells up to a concentration of 10 mg/L. On the other hand, the curcumin-loaded IMAs are cytotoxic to breast carcinoma cells at this concentration, which confirms the potential of IMA-based vehicles in controlled delivery of poorly water-soluble drug candidates and release by means of this novel stimuli-responsive mechanism.
A one-step method that converts soybean oil into (acryloylamino)ethyl soyate, a new vinyl monomer of free radical polymerization, was developed. The synthesized monomer combines vinyl double bond (acryloyl functional group) and non-conjugated (isolated) double bonds of fatty acids. The double bond of the acryloyl group is reactive in a free radical chain polymerization that yields linear macromolecules containing isolated double bonds in side chains. Monomer reactivity ratios (r 1 , r 2 ) in copolymerization of the new soybean oil-based acrylic monomer (SBA) with styrene, methyl methacrylate, and vinyl acetate, as well as the Q-e parameters of the SBA, were determined. The obtained results indicate that copolymerization can be described with the classical Mayo-Lewis equation. In terms of polymerizability, the SBA can be classified as an acrylic monomer. The double bonds of the fatty acid chains remain mainly unaffected during the free radical polymerization. The remaining unsaturated fragments in the side chains make the resulting macromolecules capable of further oxidative cross-linking and the development of cross-linked polymer coatings.
The enzymogel nanoparticle made of a magnetic core and polymer brush shell demonstrates a novel type of remote controlled phase-boundary biocatalysis that involves remotely directed binding to and engulfing insoluble substrates, high mobility, and stability of the catalytic centers. The mobile enzymes reside in the polymer brush scaffold and shuttle between the enzymogel interior and surface of the engulfed substrate in the bioconversion process. Biocatalytic activity of the mobile enzymes is preserved in the enzymogel while the brush-like architecture favors the efficient interfacial interaction when the enzymogel spreads over the substrate and extends substantially the reaction area as compared with rigid particles.
Polystyrene films have been grafted by radical polymerization in situ on the surface of glass slides. The morphology of these films resulting from different grafting temperatures has been investigated by both the contact angle method and scanning probe microscopy with respect to the grafting time. At a grafting density regime where the theory proposes the existence of a homogeneous layer, the formation of island structures of grafted polymer with a size substantially higher than expected by the theory has been observed. Overshot polymer structures of large sizes are created. The amount of grafted polymer is substantially higher than that predicted from the conception of monolayer covering. The grafting layer becomes impermeable for water only at a high amount of grafted polymer, which corresponds to the multilayer structure of the coating. We suggested a mechanism for the grafting process that included at least three stages: (a) first, a brushlike polymer layer is formed; (b) subsequently, a second layer of ungrafted chains is created in the regime when excess chains are forced out from the first layer; (c) big polymer clusters, with an average size of 100−200 nm due to gel polymerization in the clusters, formed in the force out regime.
Vinyl monomers from soybean, sunflower, linseed, and olive oils were copolymerized with styrene (St), methyl methacrylate (MMA), and vinyl acetate (VAc) to determine the reactivity of biobased monomers in radical copolymerization, as well as their feasibility in emulsion processes for the synthesis of biobased latexes. Radical copolymerization of plant-oil-based monomers is described with the classical Mayo–Lewis equation. Using emulsion (or miniemulsion) polymerization with MMA or VAc, stable aqueous polymer dispersions with latex particles measuring 80–160 nm and containing 3–35 wt % of biobased monomer units were successfully synthesized. The number-average molecular weight of the latex copolymers (20 000–150 000) decreases by increasing the degree of unsaturation in monomers and their content in the reaction feed. The presence of plant-oil-based fragments changes the T g of resulting copolymers from 105 to 79 °C in copolymerization with MMA and from 30 to 11 °C in copolymerization with Vac. As a result, biobased units provide considerable flexibility (elongation at break of about 250%) and improve the toughness of the normally rigid and brittle poly(MMA). Even a small amount (2–5%) of biobased fragments incorporated into the structure of poly(VAc) significantly improves water resistance and provides hydrophobicity to the resulting polymer latex films. The obtained results clearly indicate that the vinyl monomers from plant oils can be considered as good candidates for internal plasticization of polymeric materials through reducing intermolecular interactions in copolymers.
The environment-dependent behavior of invertible polyesters has been studied by 1H NMR spectroscopy. In dilute toluene solutions, the micelle exterior is made up of the lipophilic fragments, and the interior consists of the hydrophilic constituents. The polyester inverts the structure in an aqueous medium to form micelles with a hydrophobic inner part and a hydrophilic outer part. Increasing polyester concentration leads to the formation of hierarchical structures both in toluene and in an aqueous medium as a result of the aggregation of unimolecular micelles and the formation of hydrophilic and lipophilic domains. On the contrary, no unimolecular micelles or micellar aggregation has been observed in acetone or chloroform.
End-grafted polystyrene "brushes" of various thickness and grafting density on silica surfaces were synthesized by surface-initiated polymerization. The "brushes" were studied by contact angle measurements, ellipsometry, and scanning force microscopy (SFM). Wetting behavior of thin polystyrene film on the top of the grafted layers was investigated using optical microscopy and SFM. The film stability was strongly dependent on the grafting amount. We identified three grafting density regimes with respect to stability of the top polystyrene films: at small and very large grafting density the top film dewets "brushes", while at moderate grafting density the polystyrene film was stable after 80 h of annealing time at 155°C.
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