Low temperature cure of unsaturated polyester resins with thermoplastic additives. II. Structure formation and shrinkage control mechanism

Spontaneous, Phase-Separation Induced Surface Roughness: A New Method to Design Parahydrophobic Polymer Coatings with Rose Petal-like Morphology

While the development of polymer coatings with controlled surface topography is a growing research topic, a fabrication method that does not rely on lengthy processing times, bulk solvent solution, or secondary functionalization has yet to be identified. This study presents a facile, rapid, in situ method to develop parahydrophobic coatings based on phase separation during photopolymerization. A comonomer resin of ethylene glycol diacrylate (EGDA) and 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) is modified with a thermoplastic additive (PVDF) to induce phase separation during polymerization. If applied to a glass substrate and photopolymerized, the EGDA/PFDA copolymer forms a homogeneous network with a single glass transition temperature (T(g)) and slight hydrophobicity (θ(w) ∼ 114°). When the resin is modified with PVDF, phase separation occurs during photopolymerization producing a heterogeneous network with two T(g) values. The phase separation causes differences in composition and cross-link density within the network, which leads to local variations in polymerization shrinkage across the nonconstrained material interface. Domains with higher cross-link densities shrink and contract toward the bulk material more dramatically, permitting the formation of rough surfaces with submicron sized spheres enriched in PVDF dispersed in a continuous matrix of EGDA/PFDA copolymer. Both the surface roughness and hydrophobic components in the resin render these surfaces parahydrophobic with θ(w) ∼ 150°, high water adhesion, and a similar morphology to rose petals observed in nature.

Synthesis and characterization of vinyl ester/inorganic layered material nanocomposites

We present the osmotic swelling method for in situ free radical polymerization of well dispersed VE nanocomposites, which are expected to effectively help the development of wind blades.

The effect of carbon nanotubes/NiFe2O4 on the thermal stability, combustion behavior and mechanical properties of unsaturated polyester resin

The incorporation of MWCNT@NiFe₂O₄ into the UPR matrix exhibit significant improvements in flame retardancy and mechanical properties, compared to that of pure UPR.

Modification of linear prepolymers to tailor heterogeneous network formation through photo-initiated Polymerization-Induced Phase Separation

Polymerization-induced phase separation (PIPS) was studied in ambient photopolymerizations of triethylene glycol dimethacrylate (TEGDMA) modified by poly(methyl methacrylate) (PMMA). The molecular weight of PMMA and the rate of network formation (through incident UV-irradiation) were varied to influence both the promotion of phase separation through increases in overall free energy, as well as the extent to which phase development occurs during polymerization through diffusion prior to network gelation. The overall free energy of the polymerizing system increases with PMMA molecular weight, such that PIPS is promoted thermodynamically at low loading levels (5 wt%) of a higher molecular weight PMMA (120 kDa), while a higher loading level (20 wt%) is needed to induce PIPS with lower PMMA molecular weight (11 kDa), and phase separation was not promoted at any loading level tested of the lowest molecular weight PMMA (1 kDa). Due to these differences in overall free energy, systems modified by PMMA (11 kDa) underwent phase separation via Nucleation and Growth, and systems modified by PMMA (120 kDa), followed the Spinodal Decomposition mechanism. Despite differences in phase structure, all materials form a continuous phase rich in TEGDMA homopolymer. At high irradiation intensity (Io=20mW/cm2), the rate of network formation prohibited significant phase separation, even when thermodynamically preferred. A staged curing approach, which utilizes low intensity irradiation (Io=300µW/cm2) for the first ~50% of reaction to allow phase separation via diffusion, followed by a high intensity flood-cure to achieve a high degree of conversion, was employed to form phase-separated networks with reduced polymerization stress yet equivalent final conversion and modulus.

Do new matrix formulations improve resin composite resistance to degradation processes?

The aim of this study was to determine the degradation resistance of three new formulations-silorane-, Ormocer- and dimer-acid-based materials-and compare them to the traditional dimethacrylate-based materials. One silorane- (Filtek P90, P90), one Ormocer- (Ceram-X, CX), one dimer-acid- (N'Durance, ND) and two dimethacrylate-based (Filtek P60, P60; Tetric Ceram, TC) materials were investigated. Water sorption (Wsp) and solubility (Wsl) were determined after the materials were immersed in water for 28 days. Knoop hardness (KH) was determined before and after 24 h immersion in pure ethanol. The flexural-strength (FS) was determined by the bending test after one-week storage in a dry environment or after one-week immersion in pure ethanol. Data were submitted to analysis of variance (ANOVA) and Tukey's test (95%). The three new formulations showed lower Wsp than the dimethacrylate-based formulation. CX (0.50 ± 0.17%) and ND (0.72 ± 0.19%) exhibited the lowest Wsp, whereas P90 (0.02 ± 0.03%) and P60 (0.04 ± 0.03%) showed the lowest Wsl. All resins showed reduced Knoop hardness number (KHN) after ethanol immersion. P60 presented the lowest decrease in KH value (19 ± 5%). TC (48 ± 3%) and P90 (39 ± 9%) showed the highest KHN decrease after ethanol storage. The FS of CX, ND and TC were affected by ethanol storage. The new formulations did not improve the degradation resistance, as compared with the traditional methacrylate-based materials.

A new approach to network heterogeneity: Polymerization Induced Phase Separation in photo-initiated, free-radical methacrylic systems

Non-reactive, thermoplastic prepolymers (poly- methyl, ethyl and butyl methacrylate) were added to a model homopolymer matrix composed of triethylene glycol dimethacrylate (TEGDMA) to form heterogeneous networks via polymerization induced phase separation (PIPS). PIPS creates networks with distinct phase structure that can partially compensate for volumetric shrinkage during polymerization through localized internal volume expansion. This investigation utilizes purely photo-initiated, free-radical systems, broadening the scope of applications for PIPS since these processing conditions have not been studied previously.The introduction of prepolymer into TEGDMA monomer resulted in stable, homogeneous monomer formulations, most of which underwent PIPS upon photo-irradiation, creating heterogeneous networks. During polymerization the presence of prepolymer enhanced autoacceleration, allowing for a more extensive ambient cure of the material. Phase separation, as characterized by dynamic changes in sample turbidity, was monitored simultaneously with monomer conversion and either preceded or was coincident with network gelation. Dynamic mechanical analysis shows a broadening of the tan delta peak and secondary peak formation, characteristic of phase-separated materials, indicating one phase rich in prepolymer and another depleted form upon phase separation. In certain cases, PIPS leads to an enhanced physical reduction of volumetric shrinkage, which is attractive for many applications including dental composite materials.