Polymer Nanocomposites for Emulsion‐Based Coatings and Adhesives

Emulsion‐based coatings and adhesives are in growing demand due to an increased awareness of health and safety issues arising from solvent‐based polymer manufacturing processes. However, emulsion‐based techniques often require additional development to achieve equal or better application performance compared to solvent‐based processes. The inclusion of nanoparticles in emulsion‐based coatings and adhesives can be considered as a promising means to enhance performance. This paper reviews the current progress on the synthesis of emulsion‐based nanocomposites for coating and adhesive applications and addresses the principles and techniques for nanoparticle dispersions and their inclusion into polymer latexes. The effects of nanoparticle shape and size on the enhancement of nanocomposite properties are also highlighted. Among the reinforcing nanoparticles such as nanoclays, carbon nanotubes, and cellulose nanocrystals (CNCs), CNCs are promising due to their abundance, nontoxicity, and accessible surface hydroxyl groups, which facilitate their compatibility with polymer latexes via physical and chemical treatments.     

Hierarchical Functionalized Polymeric‐Ceramic Coatings on Mg‐Ca Alloys for Biodegradable Implant Applications

Magnesium‐based implants present several advantages for clinical applications, in particular due to their biocompatibility and degradability. However, degradation products can affect negatively the cell activity. In this work, a combined coating strategy to control the implant degradation and cell regulation processes is evaluated, including plasma electrolytic oxidation (PEO) that produces a 13 µm‐thick Ca, P, and Si containing ceramic coating with surface porosity, and breath figures (BF) approach that produces a porous polymeric poly(ε‐caprolactone) surface. The degradation of PCL‐PEO‐coated Mg hierarchical scaffold can be tailored to promote cell adhesion and proliferation into the porous structure. As a result, cell culture can colonize the inner PEO‐ceramic coating structure where higher amount of bioelements are present. The Mg/PEO/PCL/BF scaffolds exhibit equally good or better premyoblast cell adhesion and proliferation compared with Ti CP control. The biological behavior of this new hierarchical functionalized scaffold can improve the implantation success in bone and cardiovascular clinical applications.     

Nanocomposites based on crosslinked polyacrylic latex/silver nanoparticles for waterborne high‐performance antibacterial coatings

Functional polymer/AgNPs nanocomposites have been prepared. Silver nanoparticles (NPs) were synthesized to which polyacrylamide, PAAm, was covalently bound. PAAm was synthesized via a RAFT reaction and carried thiol and carboxylic acid end groups. Thiol was used to bind the polymer to the metal surface and carboxyl for further reactions. The AgNPs were used in a post‐crosslinking reaction with a separately synthesized poly(butyl acrylate‐co‐methyl methacrylate)/polyglycidyl methacrylate core/shell latex bearing epoxy functional groups. Dynamic mechanical analysis showed that the functional AgNPs effectively crosslinked the latex polymer, and that the final product had excellent mechanical strength. Antibacterial tests revealed that the nanocomposite films had strong antibacterial activity against all types of the bacteria and the immobilization of silver NPs by crosslinking retarded the release of silver in comparison to the uncrosslinked ones. With the presented method, it is possible to obtain ductile antibacterial nanocomposites to be used as waterborne functional coatings. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1435–1447     

Biodegradable Polylactide and Its Nanocomposites: Opening a New Dimension for Plastics and Composites

The academic and industrial aspects of the preparation, characterization, mechanical and materials properties, crystallization behavior, melt rheology, and foam processing of pure polylactide (PLA) and PLA/layered silicate nanocomposites are described in this feature article. Recently, these materials have attracted considerable interest in polymer science research. PLA is linear aliphatic thermoplastic polyester and is made from agricultural products. Hectorite and montmorillonite are among the most commonly used smectite‐type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity, and transparency in solution. In their pristine form, they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to overcome this difficulty is to replace interlayer cations with quaternized ammonium or phosphonium cations, preferably with long alkyl chains. In general, polymer/layered silicate nanocomposites are of three different types: (1) intercalated nanocomposites, in which insertion of polymer chains into the layered silicate structure occurs in a crystallographically regular fashion, regardless of polymer to layered silicate ratio, with a repeat distance of few nanometer; (2) flocculated nanocomposites, in which intercalated and stacked silicate layers are sometimes flocculated due to the hydroxylated edge–edge interactions between the silicate layers; (3) exfoliated nanocomposites, in which individual silicate layers are uniformly distributed in the polymer matrix by average distances that totally depend on the layered silicate loading. This new family of composite materials frequently exhibits remarkable improvements in its material properties when compared with those of virgin PLA. Improved properties can include a high storage modulus both in the solid and melt states, increased flexural properties, a decrease in gas permeability, increased heat distortion temperature, an increase in the rate of biodegradability of pure PLA, and so forth.

Illustration of the biodegradability of PLA and various nanocomposites.     

Epoxy/Silica Nanocomposites: Nanoparticle‐Induced Cure Kinetics and Microstructure

This study reveals the influence of silica nanoparticles on the cure reactions of a diglycidyl ether of bisphenol A epoxy resin. As soon as the silica nanoparticles are added to the neat resin (1, 3, and 5 vol.‐%), the total degree of conversion increases with an increasing amount of nanoparticles, and the cure reaction shows a more complex autocatalytic behaviour, which can not be described by a traditional kinetic model. Results from subsequent thermo‐mechanical analyses confirm an alteration in the microstructure attributable only to the presence of the nanoparticles in the curing stage. An amino‐rich interphase around the reactive treated particles is formed, which shifts the resin/hardener ratio, and benefits the homopolymerization of the epoxy and leads to a more highly crosslinked epoxy network. At the same time, the nanophase consists of a core‐shell structure with the rigid particle inside and a rubber‐like shell because of the excess hardener in this region.

TEM image of two neighboring silica nanoparticles in the epoxy matrix showing a 2–3 nm altered interphase region.     

Hybrid Nanocomposite Films from Mono‐ and Multi‐Functional POSS Copolyacrylates in Miniemulsion

Summary: The synthesis of aqueous dispersions of hybrid acrylic copolymer particles with either a monofunctional or a multifunctional polyhedral oligomeric silsesquioxane methacrylate comonomer has been performed by free radical heterophase polymerization. The miniemulsion process gives stable latexes, whereas the less controlled emulsion route results in colloidal instability of the products. The thermal and mechanical properties of the nanocomposite latex films have been preliminarily investigated.

The nanocomposite latex particles based on hybrid copolyacrylates with highly dispersed POSS cages.     

Synthesis and Characterization of Photocrosslinkable Biodegradable Polymers Derived from 4‐Hydroxycinnamic Acid

A novel series of photocrosslinkable biodegradable polymers was prepared by a high‐temperature solution polycondensation from a dichloride of 4,4′‐(adipoyldioxy)dicinnamic acid (CAC) and alkane diols of various methylene lengths (HO(CH₂)_nOH; n = 6–10) or poly(ethylene glycol)s (PEG) of various molecular weights . The CAC was synthesized by the condensation of adipoyl chloride and 4‐hydroxycinnamic acid. The chemical structures and properties of these polymers were characterized by elemental analysis, ultraviolet‐visible spectroscopy (UV‐VIS), Fourier transform infrared spectroscopy (FT‐IR), ¹H NMR spectroscopy, differential scanning calorimertry (DSC), and thermogravimetry (TG). All polymers had a high molecular weight and good solubility in organic solvents. DSC showed that T_m values of CACn (134–180 °C) were much higher than those of CACEm (25–56 °C). The CACE200 degraded very rapidly in the buffer solutions (pH 7.2) of Ps. Cepacia or Rh. delemar lipase at 37 °C, while CACn resisted the hydrolysis by these lipases during the test period. The ultraviolet light irradiation (λ ≥ 280 nm) caused the photocrosslinking reaction by an intermolecular dimerization at ambient temperature without a photosensitizer, as examined by UV‐VIS, FT‐IR spectroscopy, and gel formation. The gels prepared from CACEm (m ≈ 1 000) were swollen in water and showed characteristic properties of a hydrogel. The irradiation time and the molecular weight of PEGs controlled the degree of swelling of these hydrogels. The CACE8 300 gel irradiated for 20 min showed the largest degree of swelling of 10.5.

Weight loss of a CACE200 film as a function of time in a phosphate buffer solution containing no lipase (□), Ps. cepacia lipase (?), or Rh. delemar lipase (○) at 37 °C.     

Porous Biodegradable Scaffold: Predetermined Porosity by Dissolution of Poly(ester‐anhydride) Fibers from Polyester Matrix

A novel selective leaching method for the porogenization of the biodegradable scaffolds was developed. Continuous, predetermined pore structure was prepared by dissolving fast eroding poly(ε‐caprolactone)‐based poly(ester‐anhydride) fibers from the photo‐crosslinked poly(ε‐caprolactone) matrix. The porogen fibers dissolved in the phosphate buffer (pH 7.4, 37 °C) within a week, resulting in the porosity that replicated exactly the single fiber dimensions and the overall arrangement of the fibers. The amount of the porosity, estimated with micro‐CT, corresponded with the initial amount of the fibers. The potential to include bioactive agents in the porogen fibers was demonstrated with the bioactive glass.

     

Polymer Nanocomposites Using Urchin‐Shaped Carbon Nanotube‐Silica Hybrids as Reinforcing Fillers

Summary: Carbon nanotubes (CNTs) have been grown on MCM‐41 supported Fe nanoparticles and the as‐prepared (no further purification) CNT‐silica hybrid was directly incorporated into nylon‐6 (PA6) by simple melt‐compounding. The urchin‐shaped CNT‐silica hybrid filler was observed to be homogeneously dispersed throughout the matrix by scanning electron and transmission electron microscopy. Compared with neat PA6, the tensile modulus and strength of the composite are greatly improved by about 110%, with incorporation of only 1 wt.‐% CNT‐silica filler.

SEM image and schematic representation showing polymer chains wrapping around the urchin‐shaped CNT‐silica hybrid filler.     

Acrylic,Elastomeric, Particle‐Dispersed Epoxy‐Clay Hybrid Nanocomposites: Mechanical Properties

Summary: Nanocomposites were formulated by curing a sonicated mixture of epoxy resin, C18 clay, and acrylic rubber dispersants. At 5.5 phr (parts per hundred) organoclay loading and a rubber concentration of 15 phr, the tensile‐failure strain of the nanocomposite was found to be higher than that of epoxy nanocomposite, rubber‐dispersed epoxy, and pristine epoxy. A plausible mechanism for improvement of the failure strain of nanocomposites is proposed.

Stress strain curves of filled and unfilled epoxy specimen.     

Mitochondria‐Targeting,Intracellular Delivery of Native Proteins Using Biodegradable Silica Nanoparticles

Mitochondria are key organelles in mammalian cells whose dysfunction is linked to various diseases. Drugs targeting mitochondrial proteins provide a highly promising strategy for potential therapeutics. Methods for the delivery of small‐molecule drugs to the mitochondria are available, but these are not suitable for macromolecules, such as proteins. Herein, we report the delivery of native proteins and antibodies to the mitochondria using biodegradable silica nanoparticles (BS–NPs). The modification of the nanoparticle surface with triphenylphosphonium (TPP) and cell‐penetrating poly(disulfide)s (CPD) facilitated their rapid intracellular uptake with minimal endolysosomal trapping, providing sufficient time for effective mitochondrial localization followed by glutathione‐triggered biodegradation and of native, functional proteins into the mitochondria.     

Development of novel phosphorus‐containing epoxy resins from renewable resources

Novel biobased epoxy resins were prepared from two fatty acid derivatives; epoxidized 10‐undecenoyl triglyceride and epoxidized methyl 3,4,5‐tris(10‐undecenoyloxy)benzoate, with 4,4′‐diaminodiphenylmethane as a crosslinking agent. The flame retardancy of these epoxy resins was improved by the addition of 10‐[2′, 5′‐bis(9‐oxiranyl‐nonayloxy)phenyl]‐9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and by crosslinking with a phosphorus‐containing curing agent, bis(m‐aminophenyl)methylphosphine oxide. The thermal, thermomechanical, and flame‐retardant properties of the cured materials were measured with differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and the limiting oxygen index. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6717–6727, 2006     

Long‐Chain Polyacetals From Plant Oils

Plant oil‐derived α,ω‐diacetals are polycondensated to the novel polyacetals [OCH₂O(CH₂)_y]_n (y = 19 and 23) with molecular weight of ca. M _n = 2 × 10⁴ g mol⁻¹. The long methylene sequences provide substantial melt and crystallization temperatures (T_m = 88 °C and T_c = 68 °C for y = 23), and rates of hydrolytic degradation are dramatically lower for the long‐chain polyacetals versus a shorter chain analogue (y = 12) studied for comparison.     

Effect of Drawing Induced Dispersion of Nano‐Silica on Performance Improvement of Poly(propylene)‐Based Nanocomposites

Summary: A new route that combines graft pre‐treatment and drawing techniques with melt mixing to prepare nanoparticle‐filled thermoplastic polymer composites is reported. Nano‐SiO₂ particles are first modified by graft polymerization and then the grafted nanoparticles are melt‐compounded with poly(propylene) (PP) to produce composite filaments via drawing. Finally, the filaments are injection molded into bulk materials. Because the proposed manufacturing method is able to induce separation of the nanoparticles and the formation of beta‐crystals in the PP matrix, the resultant PP‐based nanocomposites are much tougher than the unfilled polymers, as characterized by either static or dynamic tests, in addition to showing a simultaneous increase in strength and stiffness.

Force–time curves of PP and its nanocomposites recorded during notch impact tests.     

Cinnamate‐functionalized poly(ester‐carbonate): Synthesis and its UV irradiation‐induced photo‐crosslinking

A functionalized cyclic carbonate monomer containing a cinnamate moiety, 5‐methyl‐5‐cinnamoyloxymethyl‐1,3‐dioxan‐2‐one (MC), was prepared for the first time with 1,1,1‐tri(hydroxymethyl) ethane as a starting material. Subsequent polymerization of the new cyclic carbonate and its copolymerization with L ‐lactide (LA) were successfully performed with diethyl zinc (ZnEt₂) as initiator/catalyst. NMR was used for microstructure identification of the obtained monomer and copolymers. Differential scanning calorimetry (DSC) was used to characterize the functionalized poly(ester‐carbonate). The results indicated that the copolymers displayed a single glass transition temperature (T_g) and the T_g decreased with increasing carbonate content and followed the Fox equation, indicative of a random microstructure of the copolymer. The photo‐crosslinking of the cinnamate‐carrying copolymer was also demonstrated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 161–169, 2009     

Microwave‐Assisted Synthesis of Crosslinked Poly(vinyl alcohol) Nanocomposites Comprising Single‐Walled Carbon Nanotubes,Multi‐Walled Carbon Nanotubes,and Buckminsterfullerene

We report a facile method to accomplish the crosslinking reaction of PVA with SWNTs, MWNTs, and C‐60 using MW irradiation. Nanocomposites of PVA crosslinked with SWNT, MWNT and C‐60 were prepared expeditiously by reacting the respective carbon nanotubes with 3 wt.‐% PVA under MW irradiation, maintaining a temperature of 100 °C, representing a radical improvement over literature methods to prepare such crosslinked PVA composites. This general preparative procedure is versatile and provides a simple route to manufacture useful SWNT, MWNT and C‐60 nanocomposites.

     

A pH‐Responsive Hydrogel Based on a Tumor‐Targeting Mesoporous Silica Nanocomposite for Sustained Cancer Labeling and Therapy

A facile strategy is presented to synthesize hyaluronic acid (HA) and a fluorescein isothiocyanate (FITC)‐conjugated mesoporous silica nanocomposite (MSN) with multiple functions of fluorescence, tumor‐cell targeting, pH‐triggered gelation, and enzyme‐responsive drug release. This injectable nanocomposite is able to indicate the entire tumor location and provides a microenvironment with rich anticancer drugs in and around tumor tissue for a long time, to avoid recrudescence. In this design, the mesoporous silica serves as the drug container, the FITC serves as a fluorescent probe, and the anchored HA plays multiple roles as drug‐release cap, tumor‐targeting points, and responsive gel matrix. Owing to the specific affinity between the HA on MSNs and the CD44 antigen over‐expressed on tumor cells, the MSNs can selectively attach to tumor cells. The nanocomposites then exploit the pH‐responsive interactions (hydrogen bonds) among the HA to self‐assemble in situ into a hydrogel around the tumor tissue. The resulting hydrogel gradually releases its payload (doxorubicin, anticancer drugs)‐loaded MSNs upon HA degradation in the presence of hyaluronidase‐1 (Hyal‐1), followed by endocytosis and intracellular drug release. All these properties have distinct benefits for tumor treatment, demonstrating that this device is a promising candidate for oncotherapy applications.

     

Biodegradable hyperbranched polyesters derived from 1,1,1‐tris(hydroxymethyl)ethane

Low molar mass hyperbranched polyesters were prepared by polycondensation of 1,1,1‐tris(hydroxymethyl)ethane and various dimethyl esters of aliphatic dicarboxylic acids in bulk. The usefulness of nontoxic bismuth salts as transesterification catalysts for these polycondensations was studied. The maximum conversion increased, and the reaction time decreased in the following sequence of increasing reactivity: dimethyl sebacate < adipate < glutarate < succinate. Regardless of the monomer combination, gelation occurred at conversions > 91.5%. The hyperbranched structure was proven by ¹H NMR spectroscopy and the absence of cyclic elements by MALDI‐TOF mass spectrometry. Quantitative acylation of all CH₂OH groups was achieved with an excess of acetic anhydride or methycrylic anhydride. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 231–238, 2009     

Novel siloxane‐carrying dithiol derived from 5‐membered cyclic dithiocarbonate and its curing reactions for coating application

A new efficient and straightforward method to convert amines into siloxane‐thiol hybrid molecules was developed. The method relies on the nucleophilic addition of amines to a cyclic dithiocarbonate having siloxane moiety (DTC‐Si), and the successive ring‐opening reaction of the dithiocarbonate moiety to give the corresponding acyclic thiourethane having a thiol moiety. Based on this method, amine‐terminated poly(propylene glycol) was successfully transformed into the corresponding polyether having thiol‐terminals and siloxane groups. In the presence of moisture, the alkoxysilyl moiety underwent condensation reaction to make the polyether cured into a transparent resin having solvent‐resistance. Addition of bisphenol A diglycidyl ether (Bis A‐DGE) to the curing process resulted in two simultaneous reactions, i.e., (1) condensation of siloxane part and (2) addition reaction of the thiol terminal and the epoxide group. When this curing process was carried out on a glass surface, the siloxane part reacted with silanol group on the surface, forming a coating layer having excellent mechanical toughness graded as maximum 7H by pencil toughness test (JIS‐K5400). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5119–5126, 2005