PMMA Block Research Articles

Surface characteristics of resin composite cores and bond strength to CAD/CAM resin matrix glass-ceramic restorations after different treatment protocols.

The purpose of this study was to evaluate the impact of various mechanical surface treatments on thesurface roughness and microtensile bond strength (µTBS) of aged composite resin cores bonded to CAD/CAM restorations. Composite resin specimens (Filtek Z350 XT, 3M-ESPE/Solventum) were thermally aged and subsequently divided into four groups (n = 36) according to surface treatments: UI-cleaning with ultrasonic diamond tip; AO-sandblasting with 50µm Al2O3; DB-cleaning with diamond burs; and CG-positive control group, without aging or surface treatment. Surface roughness was assessed using a profilometer and interferometer, with measurements taken on both sides of each specimen (n = 12). The surface characteristics were further analyzed through scanning electron microscopy (SEM) (n = 12). In addition, PMMA blocks were temporarily cemented (n = 12) onto the resin blocks, and after surface treatments, resin matrix glass-ceramic blocks were adhesively luted with dual-cure resin cement (RelyX Ultimate, 3&nbsp;M-ESPE/ Solventum, St. Paul, MN, USA) to the resin composite substrates. The CG specimens were adhesively luted to the indirect restorations without temporary restorations or surface treatment. After luting, the specimens were sectioned and tested for µTBS. The results (p = 0.05) from the profilometry and interferometry analyses indicated the highest surface roughness values for the DB group, followed by AO, UI, and CG. SEM analysis revealed marked morphological differences among the groups. Regarding µTBS, the GC specimens (25.78 ± 5.70MPa) and UI specimens (25.56 ± 11.36MPa) exhibited statisticallysimilar values, which were superior to those of the AO (12.25 ± 4.34MPa) and DB (13.16 ± 5.59MPa) groups (p < 0.001), which showed comparable results. In conclusion, the use of ultrasonic diamond tips resulted in the most favorable outcomes in terms of cleaning effectiveness, surface roughness, and bond strength among the surface treatments analyzed for resin composite cores.

Self-aggregation behavior of well-defined PEO-based amphiphilic tri-block copolymers and their application as metal detectors

PMMA-b-PEO-b-PMMA tri-block copolymers were synthesized by anionic polymerization technique usingtelechelic1,1-diphenylethylene-terminated poly (ethylene oxide)as macroinitiators and Sec-BuLi four tri-block copolymers of PMMA-b-PEO-b-PMMA with different number average molecular weight ( M ¯ n ) were synthesized, and the structure of the macroinitiators and polymers was confirmed by FTIR. and1H NMR spectroscopic methods. Through the solvent-induced association, the aqueous solutions of PMMA-b-PEO-b-PMMA were formed. After that, hydrodynamic diameter, DLS and TEM were used to study the morphology of the resulting aqueous solutions. The polymer’s self-assembled nanostructures of core-shell flower-like spherical micelles structures were observed. Also, the PMMA hydrophobic content of the tri-block increases steadily and the core size of the micelles decreases significantly, due to reverse micelle formation in which the core is hydrophobic PMMA blocks and the corona is PEO block. This micelle is an excellent detector for metal ions and acts as a reducing agent for them to convert into pure nontoxic nanoparticles.

Ferrocene-Modified Polyacrylonitrile-Containing Block Copolymers as Preceramic Materials.

In the pursuit of fabricating functional ceramic nanostructures, the design of preceramic functional polymers has garnered significant interest. With their easily adaptable chemical composition, molecular structure, and processing versatility, these polymers hold immense potential in this field. Our study succeeded in focusing on synthesizing ferrocene-containing block copolymers (BCPs) based on polyacrylonitrile (PAN). The synthesis is accomplished via different poly(acrylonitrile-block-methacrylate)s via atom transfer radical polymerization (ATRP) and activators regenerated by electron transfer ATRP (ARGET ATRP) for the PAN macroinitiators. The molecular weights of the BCPs range from 44 to 82 kDa with dispersities between 1.19 and 1.5 as determined by SEC measurements. The volume fraction of the PMMA block ranges from 0.16 to 0.75 as determined by NMR. The post-modification of the BCPs using 3-ferrocenyl propylamine has led to the creation of redox-responsive preceramic polymers. The thermal stabilization of the polymer film has resulted in stabilized morphologies based on the oxidative PAN chemistry. The final pyrolysis of the sacrificial block segment and conversion of the metallopolymer has led to the formation of a porous carbon network with an iron oxide functionalized surface, investigated by scanning electron microscopy (SEM), energy dispersive X-ray mapping (EDX), and powder X-ray diffraction (PXRD). These findings could have significant implications in various applications, demonstrating the practical value of our research in convenient ceramic material design.

Evaluation of Mechanical Properties of Self-cured, Heat-cured, and Photosensitive 3D Printing Resins After the Addition of Silica Nanoparticles

This study evaluated investigate the addition of silica nanoparticles in autopolymerizable resin and into liquid resin for 3D printing and compare them with CAD-CAM blocks and thermopolymerizable resin, regarding flexural strength and surface roughness. Eight groups (n=12) were created according to the types of materials: autopolymerizable resin (G1-G4), photosensitive resin for 3D printing (G5-G6), PMMA block (G7) and thermopolymerizable resin (G8). Functionalized silica nanoparticles (0.5-1.5 wt%) were added in groups G2-G4 and G6. Mechanical flexural strength, surface roughness and morphological analysis were carried out to evaluate the properties of the samples. One-way ANOVA, followed by Tukey's post-hoc test, was used to evaluate the data. The average surface roughness was higher in group G7 and lower in the G8 group, with a statistical difference (p &lt; 0.001). The G8 and G1-G4 showed no significant difference in surface roughness. The G5 and G6 presented surface roughness higher than that recommended by Borchers and Bollen (Ra=0.2 µm). The incorporation of nanoparticles into self-polymerizing acrylic resins negatively affected the mechanical properties of the material, reducing flexural strength. The G5 and G6 demonstrated the lowest flexural strength (p&lt;0.001), presenting values lower than those recommended by ISO (σ &gt;60 MPa) regardless of the incorporation or not of silica nanoparticles. The G7 presented the highest flexural strength value followed by the G8. Within the limits of this study, it may be concluded that the addition of silica nanoparticles did not improve the flexural strength the G6 and also affected negatively the mechanical properties of self-polymerizing acrylic resins.

Peculiar Behavior of Methyl Methacrylate Emulsion Polymerization-Induced Self-Assembly Mediated by RAFT Using Poly(Methacrylic Acid) Macromolecular Chain Transfer Agent.

Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of methyl methacrylate (MMA) is successfully performed in water in the presence of a poly(methacrylic acid) (PMAA) macromolecular chain transfer agent (macroCTA) leading to the formation of self-stabilized PMAA-b-PMMA amphiphilic block copolymer particles. At pH3.7, the reactions are well-controlled with narrow molar mass distributions. Increasing the initial pH, particularly above 5.6, results in a partial loss of reactivity of the PMAA macroCTA. The effect of the degree of polymerization (DPn) of the PMMA block, the solids content, the nature of the hydrophobic segment, and the pH on the morphology of the obtained diblock copolymer particles is then investigated. Worm-like micelles are formed for a DPn of PMMA of 20 (PMMA20), while "onion-like" particles and spherical vesicles are obtained for PMMA30 and PMMA50, respectively. In contrast, spherical particles are obtained for the DPns higher than 150. This unusual evolution of particle morphologies upon increasing the DPn of the PMMA block seems to be related to hydrogen bonds between hydrophilic MAA and hydrophobic MMA units.

Compositional asymmetry in a crystalline-amorphous block copolymer influences the phase and crystallization behaviors of its blend with an amorphous block copolymer.

This study determined the phase and crystallization behaviors of blends composed of asymmetric polystyrene-block-poly(ethylene oxide) (PS-PEO) and symmetric polystyrene-block-poly(methyl methacrylate) (PS-PMMA). The PS blocks in the various binary block copolymers exhibited nearly identical molecular weights, whereas the molecular weight ratios of PEO and PMMA varied. The compatibility of the PEO and PMMA chains aided the binary block copolymers in co-ordering in a lamellar microdomain morphology, with the PEO and PMMA blocks sharing a common microdomain. Adding short tethered PMMA chains to long tethered PEO chains led to a decrease in the common microdomain spacing and an increase in the grafting density. These behaviors increased PEO chain stretching, causing macrophase separation. The mismatch in PEO and PMMA block lengths divided the common PEO/PMMA microdomain into two sections: the coexisting PEO/PMMA section close to the microdomain interface and the neat PEO section far away from it. The high-glass-transition-temperature PMMA reduced PEO chain mobility, inhibiting PEO crystallization in the coexisting PEO/PMMA section but not in the neat PEO section. When the block length ratio of PEO to PMMA decreased, the neat PEO section narrowed. The increase in the extent of PEO confinement led to a reduction in PEO crystallizability.

Konvansiyonel, Eksiltmeli ve Eklemeli İmalat Tekniklerinde Kullanılan Geçici Kron Materyallerinin Yüzey Pürüzlülüğüne Diş Fırçalama ve Yüzey İşlemlerinin Etkisi: İn Vitro Çalışma

Background: This study aimed to compare the effect of the surface treatment and toothbrushing abrasion on the surface roughness of interim crown material specimens manufactured using conventional, subtractive, and additive processing techniques.&#x0D; Material and methods: 80 disk-shaped specimens were prepared from 4 different interim crown materials; one auto-polymerized polymethyl methacrylate resin (PMMA);(IM) and one bis-acryl composite resin;(AC) for conventional technique, one computer-aided design/computer-aided manufacturing (CAD-CAM) PMMA block;(TC) for subtractive process, one 3-dimensionally (3D) printed resin;(CB) for additive process. Specimens of each interim crown material were divided into two subgroups according to applied surface treatments; conventional polishing or surface sealant agent coupling (n=10). The surface roughness values of specimens before (Ra0) and after 10,000 cycles of toothbrushing (Ra1) were measured with a profilometer. Data were statistically analyzed.&#x0D; Results: The polished groups of all interim crown materials showed significantly higher Ra0 values compared to the sealant groups before toothbrushing (p˂0.05). While the polished IM groups exhibited the highest Ra0 value (0.44±0.08), the sealed TC groups exhibited the lowest Ra0 value (0.23±0.06). The Ra values of all material groups increased after simulated 1-year toothbrushing. While the polished IM group exhibited the highest Ra1 value (0.45±0.14), the sealed CB group had the lowest Ra1 value (0.31±0.09).&#x0D; Conclusion: It was observed that toothbrushing caused an increase in the surface roughness of all interim materials. The application of a surface sealant agent to these materials is more effective than polishing to reduce surface roughness. Sealed 3D printed resin for additive process exhibited the lowest mean roughness value after toothbrushing.&#x0D; Keywords: Additive Manufactured, Interim Crown Material, Roughness, Subtractive Manufactured, Toothbrushing Abrasion

RAFT emulsion polymerization of methyl methacrylate mediated by protonated poly(2‐(dimethylamino)ethyl methacrylate) macromolecular chain transfer agent: A mechanism study

AbstractSurfactant‐free reversible addition‐fragmentation transfer (RAFT)‐mediated emulsion polymerization has been used in the synthesis of latex particles. Although this method has been developed for some time, some detailed mechanisms are not clear. Herein, RAFT emulsion polymerization of methyl methacrylate (MMA) mediated by protonated poly(2‐(dimethylamino)ethyl methacrylate) (H+‐PDMAEMA) macromolecular chain transfer agent (macro‐CTA) is studied. The effects of the molar ratios of MMA/macro‐CTA and initiator/macro‐CTA, and the macro‐CTA chain length on the emulsion polymerizations are investigated. At the nucleation stage, H+‐PDMAEMA‐CTA is chain extended with MMA dissolved in aqueous phase; and when the length of PMMA block is above a critical length, the formed amphiphilic block copolymer (BCP) chains self‐assemble into micellar particles. The nucleation time in the emulsion polymerization is strongly dependent on the chain length of H+‐PDMAEMA‐CTA, and the molar ratio of free radical initiator/macro‐CTA. The emulsion polymerization rate is in direct proportion to the molar ratio of free radical initiator/macro‐CTA. The size and the size distribution of the latex particles can be tuned through control of the macro‐CTA chain length and MMA/macro‐CTA molar ratio. Monodispersed latex particles can be synthesized under proper conditions. It is expected that well‐defined latex particles with a variety of hydrophilic polymers (or biomacromolecules) on the surfaces can be synthesized by this approach.

Thin film and bulk morphology of PI-PS-PMMA miktoarm star terpolymers with both weakly and strongly segregated arm pairs

A series of three homologous ABC miktoarm star terpolymers having a polyisoprene (PI), a polystyrene (PS) and a poly(methyl methacrylate) (PMMA) arm, is synthesized by living anionic polymerization. While the volume fraction of the PI and the PS blocks are kept equal and constant, the volume fraction of the PMMA block is varied. The room temperature bulk structure is characterized using small-angle X-ray scattering and transmission electron microscopy, while the structure of thin films is investigated using scanning electron microscopy, atomic force microscopy and X-ray reflectometry. For both bulk and thin films, it is found that the sample with the lowest volume fraction of PMMA has a morphology distinctly different from the two samples with larger PMMA volume fraction. All data for both bulk and thin film samples are consistent with an alternating lamellar structure for the lowest PMMA volume fraction sample. The two higher PMMA volume fraction samples show standing rod structure, however the details of the packing in the PMMA matrix differ depending on sample thickness. Overall, a structure with PI domains screened from interacting with PMMA by a PS shell is seen for both samples. In bulk, core-shell cylinders pack hexagonally, while a 100 nm thin film of the sample with the largest volume fraction of PMMA shows a square-lattice packing. The structuring is driven by two factors: i) the strong segregation of the PI-PMMA arm pair together with the weak segregation of the two arm pairs with a PS block and ii) the geometrical constraints resulting from the star architecture. No wetting layers are observed for any of the thin film samples, neither at the air-polymner surface or at the polymer-substrate interface.

Shear bond strength between denture teeth and denture base using different bonding resins and tooth surface treatments

Aim of studyThe aim of the present study was to evaluate the influence of surface treatments of the ridge lap area of PMMA acrylic denture teeth on their shear bond strength with different bonding resins to denture base milled from prefabricated PMMA block, in a two-way factorial experiment. The traditional heat-curing method was included as a reference method to compare to the proposed new method that employs digital technology. Materials and methodsFifty-four cylindrical rods were prepared from two different types of PMMA based denture resin; one specially designed for the computer-aided design and computer-aided manufacturing (CAD/CAM) milling method (groups A, n = 18 and B, n = 18) and a conventional heat-curing resin (group C, n = 18). A central maxillary incisor was selected as the experimental tooth. The specimens of each group A, B, and C were divided equally into three subgroups (a, b, c; n = 6 for every subgroup) according to three surface conditionings (no treatment, sandblasting, sandblasting plus methyl-methacrylate application, respectively). A specially designed bonding resin for digital dentures was used in group A, and a common self-curing resin for repairs in group B, while in group C the specimens were prepared by the conventional heat-curing method. Shear bond strength was determined using an electro-mechanic loading frame (MTS Insight) with a cross-head speed to 1 mm/min. ResultsThere was a statistically significant interaction between the construction method (A, B, C) and tooth surface treatment (a, b, c) (p = 0.026). After eliminating one subgroup, the effect of tooth surface treatment was not significant (p = 0.42). ConclusionsSurface treatment seems not to affect the teeth-base bond. Denture teeth bonded to a CAD/CAM denture base using PMMA self-curing resin for repairs (group B) showed the highest bond strength compared to groups A and C. Clinical significanceIn terms of bond strength, the digital denture construction method can be successfully used in everyday clinical and laboratory practice and replace effectively the conventional heat curing method.

Metal‐Free Atom Transfer Radical Polymerization of PVDF‐Based Block Copolymers Catalyzed by Organic Photoredox Catalysts

AbstractPoly(vinylidene fluoride) (PVDF) and its copolymers represent a class of electroactive fluoropolymers with very attractive piezo/ferroelectric properties that can be chemically modified to achieve high‐quality composites with improved properties. Here, the synthesis of poly(methyl methacrylate)‐b‐poly(vinylidene fluoride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVDF‐b‐PMMA) triblock copolymers via metal‐free light‐catalyzed atom transfer radical polymerization (ATRP) using organic photoredox catalysts (OPRC) and light of suitable wavelength is reported. Using benzoyl peroxide bearing an ATRP active group at both ends of the molecule, telechelic PVDF is synthesized, and is used as a macroinitiator in the metal‐free, light‐catalyzed ATRP in presence of methyl methacrylate (MMA), an OPRC, and light of suitable wavelength. Kinetic studies are performed by monitoring the monomer consumed in solution and by using 1H‐NMR to calculate the formation of the new PMMA blocks. Three of the five tested OPRC, operating through an oxidative quenching pathway, guarantee a good control over the polymerization, confirmed by the constant concentration of radicals during the process and by the linear growth of the conversion versus the percentage of monomer consumed. Chain extension reactions are also performed to prove chain‐end fidelity, as well as “light ON/light OFF” reactions to test the temporal control guaranteed by the external stimuli used to catalyze the polymerization.

High‐Resolution Study of Changes in Morphology and Chemistry of Cylindrical PS‐b‐PMMA Block Copolymer Nanomasks during Mask Development

AbstractNanolithography with self‐assembled block copolymers (BCPs) is an emerging competitive alternative to conventional lithography, which is currently reaching its limits with regard to resolution and economic feasibility. For high‐resolution lithography, both the abruptness of BCP internal interfaces between self‐assembled polymer nanodomains and the processing steps used to selectively remove one of the polymers are crucial. This paper presents a detailed investigation of the chemistry, the mask wall morphology, and the line edge roughness (LER) of self‐assembled nanomasks from polystyrene‐b‐polymethylmethacrylate (PS‐b‐PMMA) before and after selective removal of the PMMA nanodomains. For the latter, either wet or plasma etching are employed and their impact on both the morphology and chemistry of resulting nanomasks is analysed using analytical (scanning) transmission electron microscopy (STEM), X‐ray photoelectron spectroscopy and polarization‐modulated infrared reflection‐absorption spectroscopy. Dedicated image analysis tools are developed to determine for the first time the LER of cylindrical openings in PS masks from STEM dark‐field images at sub‐nanometer resolution. Applying these tools prior to and after PMMA removal from the BCP films, the statistics of feature sizes, LERs, and interfacial widths are determined. In addition, the impact of wet and dry etching processes on PS‐co‐PMMA random copolymer brushes required for substrate functionalization is evaluated.

Multicolor Nitrogen-Doped Carbon Quantum Dots for Environment-Dependent Emission Tuning.

Carbon quantum dots (CQDs) have potential applications in many fields such as light-emitting devices, photocatalysis, and bioimaging due to their unique photoluminescence (PL) properties and environmental benignness. Here, we report the synthesis of nitrogen-doped carbon quantum dots (NCQDs) from citric acid and m-phenylenediamine using a one-pot hydrothermal approach. The environment-dependent emission changes of NCQDs were extensively investigated in various solvents, in the solid state, and in physically assembled PMMA–PnBA–PMMA copolymer gels in 2-ethyl-hexanol. NCQDs display bright emissions in various solvents as well as in the solid state. These NCQDs exhibit multicolor PL emission across the visible region upon changing the environment (solutions and polymer matrices). NCQDs also exhibit excitation-dependent PL and solvatochromism, which have not been frequently investigated in CQDs. Most CQDs are nonemissive in the aggregated or solid state due to the aggregation-caused quenching (ACQ) effect, limiting their solid-state applications. However, NCQDs synthesized here display a strong solid-state emission centered at 568 nm attributed to the presence of surface functional groups that restrict the π–π interaction between the NCQDs and assist in overcoming the ACQ effect in the solid state. NCQD-containing gels display significant fluorescence enhancement in comparison to the NCQDs in 2-ethyl hexanol, likely because of the interaction between the polar PMMA blocks and NCQDs. The application of NCQDs-Gel as a solid/gel state fluorescent display has been presented. This research facilitates the development of large-scale, low-cost multicolor phosphor for the fabrication of optoelectronic devices, sensing, and bioimaging applications.

Al2O3 Dot and Antidot Array Synthesis in Hexagonally Packed Poly(styrene-block-methyl methacrylate) Nanometer-Thick Films for Nanostructure Fabrication.

Nanostructured organic templates originating from self-assembled block copolymers (BCPs) can be converted into inorganic nanostructures by sequential infiltration synthesis (SIS). This capability is particularly relevant within the framework of advanced lithographic applications because of the exploitation of the BCP-based nanostructures as hard masks. In this work, Al2O3 dot and antidot arrays were synthesized by sequential infiltration of trimethylaluminum and water precursors into perpendicularly oriented cylinder-forming poly(styrene-block-methyl methacrylate) (PS-b-PMMA) BCP thin films. The mechanism governing the effective incorporation of Al2O3 into the PMMA component of the BCP thin films was investigated evaluating the evolution of the lateral and vertical dimensions of Al2O3 dot and antidot arrays as a function of the SIS cycle number. The not-reactive PS component and the PS/PMMA interface in self-assembled PS-b-PMMA thin films result in additional paths for diffusion and supplementary surfaces for sorption of precursor molecules, respectively. Thus, the mass uptake of Al2O3 into the PMMA block of self-assembled PS-b-PMMA thin films is higher than that in pure PMMA thin films.

Tuning the Glass Transition Temperature of a Core-Forming Block during Polymerization-Induced Self-Assembly: Statistical Copolymerization of Lauryl Methacrylate with Methyl Methacrylate Provides Access to Spheres, Worms, and Vesicles.

A series of poly(lauryl methacrylate)–poly(methyl methacrylate-stat-lauryl methacrylate) (PLMAx–P(MMA-stat-LMA)y) diblock copolymer nanoparticles were synthesized via RAFT dispersion copolymerization of 90 mol % methyl methacrylate (MMA) with 10 mol % lauryl methacrylate (LMA) in mineral oil by using a poly(lauryl methacrylate) (PLMA) precursor with a mean degree of polymerization (DP) of either 22 or 41. In situ1H NMR studies of the copolymerization kinetics suggested an overall comonomer conversion of 94% within 2.5 h. GPC analysis confirmed a relatively narrow molecular weight distribution (Mw/Mn ≤ 1.35) for each diblock copolymer. Recently, we reported an unexpected morphology constraint when targeting PLMA22–PMMAy nano-objects in mineral oil, with the formation of kinetically trapped spheres being attributed to the relatively high glass transition temperature (Tg) of the PMMA block. Herein we demonstrate that this limitation can be overcome by (i) incorporating 10 mol % LMA into the core-forming block and (ii) performing such syntheses at 115 °C. This new strategy produced well-defined spheres, worms, or vesicles when using the same PLMA22 precursor. Introducing the LMA comonomer not only enhances the mobility of the core-forming copolymer chains by increasing their solvent plasticization but also reduces their effective glass transition temperature to well below the reaction temperature. Copolymer morphologies were initially assigned via transmission electron microscopy (TEM) studies and subsequently confirmed via small-angle X-ray scattering analysis. The thermoresponsive behavior of PLMA22–P(0.9MMA-stat-0.1LMA)113 worms and PLMA22–P(0.9MMA-stat-0.1LMA)228 vesicles was also studied by using dynamic light scattering (DLS) and TEM. The former copolymer underwent a worm-to-sphere transition on heating from 20 to 170 °C while a vesicle-to-worm transition was observed for the latter. Such thermal transitions were irreversible at 0.1% w/w solids but proved to be reversible at 20% w/w solids.

A Supramolecular Hydrogel Enabled by the Synergy of Hydrophobic Interaction and Quadruple Hydrogen Bonding.

The increasing preference for minimally invasive surgery requires novel soft materials that are injectable, with rapid self-healing abilities, and biocompatible. Here, by utilizing the synergetic effect of hydrophobic interaction and quadruple hydrogen bonding, an injectable supramolecular hydrogel with excellent self-healing ability was synthesized. A unique ABA triblock copolymer was designed containing a central poly(ethylene oxide) block and terminal poly(methylmethacrylate) (PMMA) block, with ureido pyrimidinone (UPy) moieties randomly incorporated (termed MA-UPy-PEO-UPy-MA). The PMMA block could offer a hydrophobic microenvironment for UPy moieties in water and thus boost the corresponding quadruple hydrogen bonding interaction of Upy–Upy dimers. Owing to the synergetic effect of hydrophobicity and quadruple hydrogen bonding interaction, the obtained MA-UPy-PEO-UPy-MA hydrogel exhibited excellent self-healing properties, and injectable capability, as well as superior mechanical strength, and therefore, it holds great promise in tissue engineering applications, including in cell support and drug release.

Amphiphilic block co-polymer and silica reinforced epoxy composite with excellent toughness and delamination resistance for durable electronic packaging application

Addition of silica brings a significant improvement in flexural strength and toughness of epoxy thermoset yet; these properties suffers a huge change when an amphiphilic BCP and silica have been used together. Here, a triblock BCP, poly(methyl methacrylate)-b-poly(butyl acrylate)-b-poly(methyl methacrylate) (PMMA-b-PBuA-b-PMMA), is employed in silica-epoxy system to study its structural and mechanical properties. On copolymerization with poly(dimethyl acrylamide) (PDMA), with either PMMA block, both flexural strength and toughness enhanced manifold and found to be of 152 MPa and 0.79 J, respectively, at 83 wt% silica and 1.5 wt% PDMA copolymerized BCP loading. Moreover, it exhibits best delamination resistance index of 74 which displays its superiority in practical applications over other composites. The miscibility of PMMA-PDMA chain with epoxy, its interaction with silica particles and existence of wormlike structure of BCPs in composite simultaneously play the key role for high flexural strength, toughness and delamination resistance of the composite.

Microdomain homogeneity evaluation of perpendicular lamellar structures in block copolymer films: X-ray scattering and IR nanospectroscopy analyses

Self-assembled block copolymer (BCP) thin films necessarily require a distinct chemical contrast between the blocks (or microdomain homogeneity) for the purpose of high-resolution pattern transfer applications. Despite its importance, however, there has been difficulty in measuring the chemical distribution associated with the self-assembling processes, i.e. solvent vapor annealing (SVA) or thermal annealing (TA). Herein, we present a simple yet effective method to probe the chemical distribution over polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) films that underwent the SVA or SVA + TA processes. An IR nanospectroscopy using scattering-type scanning near-field optical microscopy (s-SNOM), in concert with X-ray scattering analyses, provides the relative chemical concentration of the perpendicular lamellar patterns. The chemical mapping for the components based on the s-SNOM reveals that the SVA process leaves a considerable portion of the intermixed zones of PS and PMMA blocks, whereas the subsequent TA process facilitates the chain segregation towards high-contrast chemical distribution. Interestingly, such a microdomain homogeneity critically affects the quality of the unidirectional Al2O3 lines that were substituted from topographically guided lamellae. Our results substantiate an important insight into understanding the chain redistribution behavior in the self-assembled BCP films using non-destructive s-SNOM technique.

Synthesis of well-defined PMMA-b-PDMS-b-PMMA triblock copolymer and study of its self-assembly behaviors in epoxy resin

PMMA- b -PDMS- b -PMMA block copolymers can mediate different reaction-induced microphase separation mechanism with different curing agents and formed ordered nanospheres. • A mild condition to conduct chain extension of Br-PDMS-Br with MMA via effective SARA ATRP was demonstrated and obtained a well-defined PMMA- b -PDMS- b -PMMA tBCP. • Then the tBCP shows its good compatibility with respect to epoxy resin, owing to the presence of compatible PMMA segments. • Through in-situ SAXS measurements, we found the tBCP underwent reaction-induced microphase separation (RIMPS) mechanism cured by 4,4′-methylenedianiline (MD) but self-assembly (SA) mechanism cured by phenol novolacs (PN). • We inspected the interesting mechanism variations, compatibility, and microphase morphology by using FT-IR, DSC, TGA, TEM, and SAXS of the obtaining MD- and PN-cured composites, mainly including nanospheres morphology in approximately 30 nm. With the evolutions of reversible deactivation radical polymerizations (RDRPs), including atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), one technique can be noted that supplemental activator and reducing agent (SARA) ATRP can conduct controlled/living radical polymerization fashion with a ppm level of catalyst. In addition, polydimethylsiloxane (PDMS) has wide ranges of applications in surfactants, sealants, and impact-relief materials. In this study, we first prepared a well-defined PDMS ended with α,ω-isobutyryl bromide (i.e., Br-PDMS-Br) macroinitiator (MI). Then chain extension of Br-PDMS-Br with methyl methacrylate (MMA) via SARA ATRP was conducted. Mild chain extension conditions were demonstrated and we successfully achieved controlled/living radical polymerization. A well-defined PMMA- b -PDMS- b -PMMA tBCP (named as ABA: M n, GPC = 49770; PDI = 1.44) comprising two external epoxy-philic blocks and a middle soft block was thus acquired. The ABA was further blended with diglycidyl ether of bisphenol-A (DGEBA) epoxy monomer and two crosslinkers of 4,4′-methylenedianiline (MD)/phenol novolacs (PN) to construct nanostructures driven by curing reactions. The cured epoxy thermoset (ET)/ABA composites showed good thermal properties and well-compatible behaviors (i.e, T g = ca. 100 °C and T (5 wt% loss) = ca. 270–335 °C) characterized by the measurements of differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). We further analyzed the two composite systems by utilizing Fourier transform infrared spectroscopy (FT-IR), (in-situ) small-angle X-ray scattering (SAXS), and transmission electron microscope (TEM). With different curing agent, interestingly, we observed a reaction-induced microphase separation (RIMPS) mechanism in MD-cured system but a self-assembly (SA) mechanism in PN-cured system. Furthermore, the PN-cured composites can create ordered nanospheres in a range of 27–41 nm.

RAFT Dispersion Polymerization of Methyl Methacrylate in Mineral Oil: High Glass Transition Temperature of the Core-Forming Block Constrains the Evolution of Copolymer Morphology

RAFT dispersion polymerization of a prototypical methacrylic monomer, methyl methacrylate (MMA), is performed in mineral oil using various poly(lauryl methacrylate) (PLMA) precursors prepared with a trithiocarbonate-based RAFT agent. GPC analysis indicated reasonably narrow molecular weight distributions (Mw/Mn ≤ 1.39) for all diblock copolymers, with 1H NMR studies indicating high MMA conversions (≥95%) for all syntheses. An efficient one-pot synthesis protocol enabled high blocking efficiencies to be achieved when targeting higher PMMA DPs. However, the relatively high glass transition temperature (Tg) of the corresponding core-forming PMMA block unexpectedly constrains the evolution in copolymer morphology during polymerization-induced self-assembly (PISA). More specifically, well-defined PLMA22–PMMAx spheres (x = 19–39) and relatively short worms (x = 69–97) can be obtained at 90 °C when using a PLMA22 precursor but targeting higher x values (x ≥ 108) invariably leads to colloidally unstable aggregates of spheres, rather than long worms or vesicles. Interestingly, similar constraints were observed when targeting higher solids, when using n-dodecane instead of mineral oil, or when employing an alternative steric stabilizer block. Raising the PISA synthesis temperature from 90 to 115 °C (i.e., from below to above the Tg of the final PMMA block) does not alleviate this unexpected problem. Moreover, only spherical nanoparticles can be obtained at 115 °C when targeting PMMA DPs between 50 and 400 with the same PLMA22 precursor. This suggests that nanoparticle formation may occur by a chain expulsion/insertion mechanism at this relatively high reaction temperature. PLMA22–PMMAx nanoparticles were characterized in terms of their particle size and morphology using dynamic light scattering (DLS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). DLS and TEM studies of a 0.1% w/w dispersion of PLMA22–PMMA69 short worms indicated an irreversible worm-to-sphere transition on heating from 20 to 150 °C. Oscillatory rheology and TEM studies indicated that this thermal transition was only partially reversible for a 20% w/w dispersion of PLMA22–PMMA69 short worms.