Molecular Weight Of PMMA Research Articles

Unravelling the role of poly(methyl methacrylate) (PMMA) molecular weight in poly(vinylidene fluoride) (PVDF)/PMMA/expanded graphite (ExGr) blend nanocomposites: Insights into morphology, thermal behavior, electrical conductivity, and wetting property

Poly(vinylidene fluoride) (PVDF) based conducting polymer composites with carbon nanomaterials can be used for mechanical energy harvesting through piezoelectric or triboelectric effect. This study aims to investigate the influence of PMMA molecular weight on the electrical, thermal, and wetting properties of PVDF/40 wt.% PMMA blend nanocomposites reinforced with expanded graphite (ExGr). The blend nanocomposites with 40 wt.% PMMA have been prepared by solution blending method by using two different molecular weights of PMMA whose melt flow indices are 2 g/10 min and 2.3 g/10 min. The coexistence of the electroactive gamma and non-polar alpha phases of PVDF in the blend nanocomposites has been confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry analyses. While overall crystallinity (%) of low molecular weight PMMA employed blend nanocomposites is lower than that of high molecular weight PMMA blended nanocomposites, the electroactive gamma phase has been found to increase in the former blend nanocomposites. The dispersion of graphite nanosheets has been observed to be better in high molecular weight PMMA employed blend nanocomposites which results in higher electrical conductivity. Impedance analysis of PVDF-40 wt.% PMMA-2 wt.% ExGr blend nanocomposite with high molecular weight PMMA results in enhanced interjunction capacitance (74.5 pF) in comparison to low molecular weight PMMA mixed blend nanocomposites (68 pF). Water contact angle (WCA) increases with molecular weight of PMMA and ExGr loading level. Thermogravimetric analysis has shown that the char content (above 500°C) is slightly higher for the blend with low molecular weight PMMA than with high molecular weight PMMA.

Effects of the PMMA Molecular Weight on the Thermal and Thermo-Oxidative Decomposition as the First Chemical Stage of Flaming Ignition

The piloted and the spontaneous ignition of low and high molecular weight (LMW and HMW) polymethyl methacrylate are simulated using a one-dimensional condensed-gas phase model for constant heat fluxes in the range of 25–150 kW/m2. Purely thermal (nitrogen) and thermo-oxidative (air) decomposition is considered, described by a single and four-step kinetics for the low and high molecular weight polymer, respectively. Different optical properties are also examined. The same trends of the ignition time and other ignition parameters are always observed. Due to a more significant role of the chemical kinetics, the effects of the sample molecular weight and reaction atmosphere are higher at low heat fluxes. Times are shorter for the black HMW samples and thermo-oxidative kinetics. For piloted ignition, factors are around 2.8–1.6, whereas for thermal decomposition, they are 1.3–1.2. The corresponding figures are 1.8–1.3 and 1.3–1.1, in the same order, for the spontaneous ignition. Overall, the effects of the molecular weight are more important than those related to the reaction kinetics environment. These differences are confirmed by the comparison between predictions and measurements.

Enhanced Polarization Properties of Holographic Storage Materials Based on RGO Size Effect.

Polarized holographic properties play an important role in the holographic data storage of traditional organic recording materials. In this study, reduced graphene oxide (RGO) was introduced into a phenanthraquinone-doped polymethylmethacrylate (PQ/PMMA) photopolymer to effectively improve the orthogonal polarization holographic properties of the material. Importantly, the lateral size of RGO nanosheets has an important influence on the polymerization of MMA monomers. To some extent, a larger RGO diameter is more conducive to promoting the polymerization of MMA monomers and can induce more PMMA polymers to be grafted on its surface, thus obtaining a higher PMMA molecular weight. However, too large of a RGO will lead to too much grafting of the PMMA chain to shorten the length of a single PMMA chain, which will lead to the degradation of PQ/PMMA holographic performance. Compared with the original PQ/PMMA, the diffraction efficiency of the RGO-doped PQ/PMMA photopolymer can reach more than 11.4% (more than 3.5 times higher than the original PQ/PMMA), and its photosensitivity is significantly improved by 4.6 times. This study successfully synthesized RGO-doped PQ/PMMA high-performance photopolymer functional materials for multi-dimensional holographic storage by introducing RGO nanoparticles. Furthermore, the polarization holographic properties of PQ/PMMA photopolymer materials can be further accurately improved to a new level.

The implication of PMMA molecular weight on compatibility of SAN/PMMA blends containing GO-g-PMMA hybrid compatibilizers

The molecular weight of a polymer is one of the most important factors defining material properties and performance. Within the current study, poly(styrene-co-acrylonitrile)/poly(methyl methacrylate) (SAN/PMMA) blends containing hybrid particles of graphene oxide-g-poly(methyl methacrylate) (GO-g-PMMA) were designed so that the molecular weight of the PMMA chains tethered on the GO particles was correlated with the molecular weight of the PMMA matrix. Hybrid particles were prepared using surface-initiated atom transfer radical polymerization (ATRP). The number average molecular weight of the matrix PMMA was Mn = 20,100 or 130,900 g/mol, while in the case of hybrids it was Mn = 5600, 27,300 or 191,600 g/mol. Two blend compositions were investigated: SAN/PMMA= 70/30 and 90/10 wt/wt, and the content of GO-g-PMMA was 1 wt%. Based on rheological studies it was demonstrated that higher molecular weights of the matrix PMMA promoted the compatibility of SAN/PMMA due to the similar viscosity of both blend components. Furthermore, the length of the PMMA chains grafted to the GO influenced the viscoelastic response of the material, resulting in different relaxation behavior as confirmed by mean relaxation times calculated from Cole-Cole plots. In addition, the effect of neat GO and GO-g-PMMA particles on the blend morphology and size distribution of PMMA droplets was discussed based on rheology and TEM analyses.

Synthesis of Ultrahigh Molecular Weight Poly(methyl Methacrylate) via the Polymerization of MMA Initiated by the Combination of Palladium Carboxylates with Thiols.

A novel synthesis of ultrahigh molecular weight poly(methyl methacrylate) (PMMA) using organosulfur compounds combined with a catalytical amount of transition metal carboxylates as an initiator has been developed. The combination of 1-octanethiol with palladium trifluoroacetate (Pd(CF3COO)2) was found to be a very efficient initiator for the polymerization of methyl methacrylate (MMA). An ultrahigh molecular weight PMMA with a number-average molecular weight of 1.68 × 106 Da and a weight-average molecular weight of 5.38 × 106 Da has been synthesized at the optimal formulation of [MMA]:[Pd(CF3COO)2]:[1-octanethiol] = 94,300:8:23 at 70 °C. A kinetic study showed that the reaction orders with respect to Pd(CF3COO)2, 1-octanethiol, and MMA are 0.64, 1.26, and 1.46, respectively. A variety of techniques such as proton nuclear magnetic resonance spectroscopy (1H NMR), electrospray ionization mass spectroscopy (ESI-MS), size exclusion chromatography (SEC), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron paramagnetic resonance spectroscopy (EPR) were employed to characterize the produced PMMA and palladium nanoparticles (Pd NPs). The results revealed that Pd(CF3COO)2 was firstly reduced by the excess of 1-octanethiol to form Pd NPs at the early stage of the polymerization, followed by the adsorption of 1-octanethiol on the surface of nanoparticles and subsequent generation of corresponding thiyl radicals to initiate the polymerization of MMA.

Effect of molecular weight on polymer solution facilitated transfer of non-Brownian particles

Solution driven particle transfer on solid substrates has many industrial applications but can be difficult to control and characterize. In this study, poly(methyl methacrylate) (PMMA) is considered as the binder polymer, and the effect of the molecular weight (MW) on particle transfer through entrainment is investigated. The transfer phenomenon of polydisperse spherical rigid micro-particles from the PMMA solution has been analyzed and two hypotheses are tested here: (i) there exists a threshold polymer content below which only the smallest particles will be transferred from the bulk; (ii) at the same viscosity of different molecular weight PMMA solution, the solid transfer phenomenon will be similar. By changing the mass and viscosity using three PMMA samples with different MWs in the 1,3-dioxolane solvent, we observe low, intermediate, and high viscous regimes of the PMMA-dioxolane solution system. The low, intermediate, and high viscous regimes can be controlled with the MW and can entrain distinct particle size distributions onto surfaces. This behavior is thoroughly analyzed and relates to the film formation. These results confirmed our first hypothesis that we could use polymer content to control the particle size distribution and that a threshold polymer content exists. However, at similar viscosities, higher molecular weight polymers yielded lower average particle sizes and narrower distributions, which is counter to our second hypothesis. These findings can provide a better understanding of the binder behavior and its influence on the particle transfer process which opens-up the possibility of particle sorting process from a polydisperse suspension mixture and high-yield material transfer for porous structure coating and joining processes. Understanding the particle transfer process can also enable reverse engineering of the liquid carrier system in a complex mixture, which can be beneficial for industrial applications.

Study of the radical polymerization mechanism and its application in the preparation of high-performance PMMA by reactive extrusion.

In this study, the mechanism of radical polymerization was further explored by pre-dissolving different polymers and studying the kinetics of the bulk polymerization of methyl methacrylate (MMA) under shear-free conditions. Based on the analysis of the conversion and absolute molecular weight, it was found that, contrary to the shearing effect, the inert polymer with viscosity was the key factor to preventing the mutual termination of radical active species and reducing the termination rate constant k t. Therefore, pre-dissolving the polymer could increase the polymerization rate and molecular weight of the system simultaneously, making the polymerization system enter the automatic acceleration zone faster and greatly reducing the generation of small molecular weight polymers, leading to a narrower molecular weight distribution. When the system entered the auto-acceleration zone, k t decreased rapidly and greatly and entered the second steady-state polymerization stage. Then, with the increase in the polymerization conversion, the molecular weight gradually increased, while the polymerization rate gradually decreased. In shear-free bulk polymerization systems, k t can be minimized and radical lifetimes maximized, but the polymerization system is at best a long-lived polymerization rather than a living polymerization. On this basis, by using MMA to pre-dissolve ultrahigh molecular weight PMMA and core-shell particles (CSR), the mechanical properties and heat resistance of the PMMA with pre-dissolved polymer obtained by reactive extrusion polymerization were better than for pure PMMA obtained under the same conditions. Compared with pure PMMA, the flexural strength and impact strength of PMMA with pre-dissolved CSR were up to 166.2% and 230.5%. With the same quality of CSR, the same two mechanical properties of the samples obtained by the blending method were just improved by 29.0% and 20.4%. This was closely related to the distribution of CSR in the pre-dissolved PMMA-CSR matrix with a distribution of spherical single particles 200-300 nm in diameter, which enabled PMMA-CSR to exhibit a high degree of transparency. This one-step process for realizing PMMA polymerization and high performance shows extremely high industrial application prospects.

Preparation of graded materials for miscible polycarbonate/poly(methyl methacrylate) blends by segregation under shear flow

AbstractExposure to shear flow produced by a pressure‐driven capillary rheometer provides a concentration gradient without phase separation in miscible polymer blends of bisphenol‐A polycarbonate containing low‐molecular‐weight poly(methyl methacrylate) (PMMA). The strand surface extruded from the rheometer contains a large amount of PMMA. However, the strand is transparent because there is no light scattering due to phase separation. The segregation behavior, that is, enrichment of the PMMA content at the strand surface, is enhanced when the molecular weight of PMMA is low. Furthermore, the segregation is also enhanced at high temperatures and at high shear rates. By contrast, the die length barely affects the degree of segregation. The segregation phenomenon should be noted because it may facilitate the modification of the surface properties of various products.

Development of Synthesis and Application of High Molecular Weight Poly(Methyl Methacrylate).

Poly(methyl methacrylate) (PMMA) is widely used in aviation, architecture, medical treatment, optical instruments and other fields because of its good transparency, chemical stability and electrical insulation. However, the application of PMMA largely depends on its physical properties. Mechanical properties such as tensile strength, fracture surface energy, shear modulus and Young’s modulus are increased with the increase in molecular weight. Consequently, it is of great significance to synthesize high molecular weight PMMA. In this article, we review the application of conventional free radical polymerization, atom transfer radical polymerization (ATRP) and coordination polymerization for preparing high molecular weight PMMA. The mechanisms of these polymerizations are discussed. In addition, applications of PMMA are also summarized.

Glass transition behavior of poly(methyl methacrylate) in compressed carbon dioxide revisited – New perspectives

Glass transition behavior of poly(methyl methacrylate) (PMMA) in compressed carbon dioxide has been investigated with a relatively new technique, High-Pressure Torsional Braid Analysis (HP-TBA), using two polymer samples of widely differing molecular weights, with Mw = 89,700 and 457,000 g/mol. For each sample, the glass transition temperature was determined along constant-temperature and constant-pressure pathways at 35, 70, and 90 °C and 30, 50, 75, 100, and 200 bar, respectively. The results show that the observed Tg behavior depends not only on the molecular weight but also on the rate of pressurization. Based on the present observations new interpretations are provided for the differences in the data reported in the literature along with new insights regarding the presence or absence of the retrograde Tg behavior. This study suggest that high molecular weight PMMA samples may not display classic retrograde Tg behavior.

Norbornene and methyl methacrylate polymerizations catalyzed by palladium(II) complexes bearing aminomethylpyridine and aminomethylquinoline derivatives

A series of Pd(II) complexes, 1–4 bearing N,N-bidentate aminomethylpyridine and aminomethylquinoline derivatives were synthesized and characterized. Single crystal X-ray diffraction analysis demonstrated that tetra-coordinated Pd(II) complexes adopted distorted square planar geometries around the metal center. In the presence of modified methylaluminoxane (MMAO) as a co-catalyst, Pd(II) complexes 1–4 exhibited significant activities (up to 43.2×105 gPNB mol Pd−1 h−1) towards the addition polymerization of norbornene (NB) at 25 ℃. Insoluble poly(norbornene) (PNB) was obtained by all the tested catalytic systems, i.e., 1–4/MMAO. The catalytic capabilities of synthesized Pd(II) complexes were also tested towards methyl methacrylate (MMA) in the presence of modified methyl aluminoxane MMAO. Complex 3 with quinoline/piperidine functionalities showed the highest catalytic activity of 8.83×104 gPMMA mol Pd−1 h−1 at 60°C and resulted in high molecular weight PMMA (Mw = 2.16×106 g mol−1). All the complexes yielded syndiotactic poly(methyl methacrylate) (PMMA) (rr = 0.70). Notably, the steric bulk and electronic properties of the ligand framework affect their activities towards NB and MMA polymerizations, whereas, for PMMA, the stereoselectivities remained unaffected.

Direct Photolysis RAFT Polymerization of (Metha)acrylate with 2‐Cyano‐2‐propyldodecyl Trithiocarbonate as Mediator

AbstractA direct photolysis reversible addition‐fragmentation chain transfer (RAFT) polymerization of (meth)acrylates is developed with 2‐cyano‐2‐propyldodecyl trithiocarbonate (TTP), which plays the dual role as photoinitiator and chain transfer agent. The polymerizations can be efficiently activated by blue light while maintaining a linear increase in Mn versus conversion. With poly(methyl methacrylate)‐TTP (PMMA‐TTP, Mn = 6700 g mol–1, Ð = 1.29) as precursor, a higher molecular weight PMMA (Mn = 14 600 g mol–1, Ð = 1.67) by chain extension, and a series of block copolymers, including poly(methyl methacryalte)‐b‐poly(glycidyl methacrylate), poly(methyl methacrylate)‐b‐poly(tert‐butyl methacrylate), and poly(methyl methacrylate)‐b‐poly(benzyl meacrylate)(PMMA‐b‐PBnMA), are prepared. The Mn,NMR = 14 900 g mol–1 of PMMA‐b‐PBnMA measured by NMR is very close to Mn,GPC = 14 200 g mol–1 determined by gel permeation chromatography. Furthermore, the polymerization of acrylates exhibits higher controllability in regarding to dispersity (Ð < 1.20) compared to those of polymethacrylates (Ð = 1.10–1.80). With poly(methyl acrylate) (PMA‐TTP, Mn = 11 900 g mol–1, Ð = 1.09) as macro‐RAFT agent, a higher molecular weight PMA (Mn = 23 500 g mol–1, Ð = 1.28) by chain extension, and PMA‐b‐PBnA (Mn = 26 500 g mol–1, Ð = 1.19) are also prepared. A positive synergic effect is demonstrated by enhanced apparent polymerization rates at elevated temperature. For example, the apparent polymerization rates of MA increases from 0.0860 to 0.115 h–1 with temperature rising from 32 to 50 °C.

Fabrication of cylindrical microlens array using rotatable multi-arrayed needle coating module for light out-coupling of OLEDs

We have performed coatings of poly(methyl methacrylate) (PMMA) using a rotatable multi-arrayed needle coating module to achieve high-density and high-aspect-ratio cylindrical microlens arrays (C-MLAs) for potential applications in organic light-emitting diodes (OLEDs). It is shown that high-density C-MLAs can be fabricated by rotating the coating module in such a way that the spacing between microlenses can be reduced (tuned). To enhance the aspect ratio of C-MLAs, we have analyzed the coating behaviors by varying the material parameters such as the molecular weight of PMMA, solute concentration, and wettability of the PMMA solution. It is demonstrated that high-aspect-ratio C-MLAs can be achieved using a coating solution with a small amount of a hydrophobic solvent, in which a high concentration of low-molecular-weight PMMA is dissolved. To further enhance the aspect ratio, we have come up with a new process method; repetitive coating and pre-drying treatment in ambient air. Such a repetitive coating method is shown to boost the microlens thickness without a much compromise on the microlens width. With this scheme, we have fabricated the C-MLA with the average thickness of 22.6 μm and width of 125 μm (aspect ratio as high as 0.18) at a coating velocity of 3 mm/s. The light out-coupling efficiency of OLED with the C-MLA increases by 20%, which is in good agreement with the result by ray tracing simulations.

Effect of PMMA Molecular Weight on Its Localization during Crystallization of PVDF in Their Blends.

In miscible crystalline/amorphous polymer blends, the exclusion behaviors of the latter with various molecular weights during the crystallization of the former were investigated by the combination of SAXS and DSC by taking a PVDF/PMMA blend as an example. The ratio between internal crystallinity from SAXS and overall crystallinity of the entire blend from DSC was employed to characterize the exclusion of PMMA. Our results indicate that the molecular weight of the amorphous component produces a remarkable influence on the diffusion coefficient (D) and the crystal growth rate (G) of the crystalline component. There are both inter-lamellar and inter-fibrillar structures when PVDF blended with lower-molecular-weight PMMA. With increasing molecular weight of PMMA, the decrease in crystal growth rate (G) dominates the enhanced exclusion behaviors of PMMA, resulting in bigger pores after extraction. Our results are significant not only for the basic understanding of crystallization in polymer blends, but also for the fabrication and structure control of porous structures based on crystallization templates.

Effect of the molecular weight on the depth profiling of PMMA thin films using low‐energy Cs+ sputtering

In this work, we investigate the influence of the molecular weight of poly(methyl methacrylate) (PMMA) thin films coated on silicon wafer on the time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) sputtering mechanisms and kinetics during depth profiling using low‐energy monoatomic caesium ions. The sputtering yield volumes are determined as function of molecular weight, film thickness and beam energy. The results show that the sputtering yield volume decreases with increasing molecular weight Mw down to a threshold value below which it becomes nearly constant, as previously observed with argon cluster ions. The relevance of physical parameters such as the glass transition temperature Tg—determined here from ellipsometry measurements—and the entanglement of the polymer chains to account for this behaviour is discussed. The variation of the sputtering yield was also found to vary logarithmically with the primary beam energy. In addition, preliminary experiments carried out using a low molecular weight PMMA (4 kg/mol) evidenced a nanoconfinement effect similar to that observed with argon cluster sputtering but of lower magnitude.

Dual Microcapsulation of an Environmentally‐Friendly‐Based Reactive Multifunctional Acrylated Epoxy Resin and Thiol by Internal Phase Separation Technique for Self‐healing Applications

In this research, the microcapsules were individually prepared via internal phase separation technique using reactive bio-based acrylated epoxidized soybean oil, AESO, and trimethylolpropane tris(3-mercaptopropionate), TMPMP as healing and curing agents respectively in PMMA shell for self-healing intentions. The desired variables used were the ratio of the shell/core, the type of surfactant (ionic and polymeric) and PMMA molecular weights. FTIR confirmed very fast crosslinking reaction between reactive epoxy and acrylate functional groups in AESO and thiol groups in TMPMP, which is very important for self-healing purposes. Furthermore, FTIR and thermal characterization results confirmed the encapsulation of both the resin and the curing agent components in two different core–shell microcapsules. The surface morphology of microcapsules obtained changed from dimpled and holed to plain for AESO and TMPMP respectively suggesting that it depends strongly on the nature of the core, type of surfactant and the ratio of shell/core. The produced core–shell microcapsules had a mean diameter of 7.9–169.7 µm and 9.9–64.1 µm for AESO/PMMA and TMPMP/PMMA, respectively. With changing the percentage of shell revealed that increasing the PMMA dosage in both surfactants causes a decrease in the size of TMPMP-filled microcapsules.

Influence of structure and solubility of chain transfer agents on the RAFT control of dispersion polymerisation in scCO2.

Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerisation of methyl methacrylate (MMA) is performed in supercritical carbon dioxide (scCO2) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. Kinetic studies of the polymerisation in scCO2 also confirm these data. By contrast, only poor control of MMA polymerisation is obtained in toluene solution, as would be expected for this CTA which is better suited for acrylates. In this regard, we select a range of CTAs and use them to determine the parameters that must be considered for good control in dispersion polymerisation in scCO2. A thorough investigation of the nucleation stage during the dispersion polymerisation reveals an unexpected “in situ two-stage” mechanism that strongly determines how the CTA works. Finally, using a novel computational solvation model, we identify a correlation between polymerisation control and degree of solubility of the CTAs. All of this ultimately gives rise to a simple, elegant and counterintuitive guideline to select the best CTA for RAFT dispersion polymerisation in scCO2.

Facile Synthesis of Ultrahigh Molecular Weight Poly(Methyl Methacrylate) by Organic Halides in the Presence of Palladium Nanoparticles.

A facile and versatile approach for the synthesis of ultrahigh molecular weight poly(methyl methacrylate) (PMMA) at mild conditions was developed. Certain organic halides combined with a catalytical amount of palladium nanoparticles (Pd NPs) were found to be very effective in initiating polymerizations of methyl methacrylate (MMA), methyl acrylate, vinyl acetate and other vinyl monomers. An ultrahigh molecular weight PMMA with a number-average molecular weight of 4.65 × 106 Da and a weight-average molecular weight of 8.08 × 106 Da was synthesized at 70 °C using 2-bromoisobutyric acid ethyl ester (EBiB) as an initiator in the presence of catalytical amount (10.1 ppm) of Pd NPs. A kinetic investigation found that the orders of polymerization with respect to EBiB, Pd NP and MMA were 0.23, 0.50, and 0.58, respectively. Proton nuclear magnetic resonance (1H NMR) combined with matrix-assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF) and gel permeation chromatography (GPC) were used to prove that the macromolecular chain had an end-group of EBiB residue. The electron spin resonance (ESR), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) results reveal that the reaction of EBiB with Pd NPs caused a bromo atom (Br) transfer from EBiB to Pd NPs and resulted in the generation of EBiB residue radical to initiate the polymerization of MMA and the formation of PdIIBr2 on the surface of Pd nanoparticles.

Blending modification to porous polyvinylidene fluoride (PVDF) membranes prepared via combined crystallisation and diffusion (CCD) technique

PVDF membranes prepared by the combined crystallisation and diffusion (CCD) technique, a variation of ice templating, have shown permeation rates far superior to those made via conventional methods such as nonsolvent induced phase separation (NIPS) or thermally induced phase separation (TIPS). However, so far the smallest pore size achieved for PVDF membranes prepared by CCD is about 30 nm. In this study, the pore size of CCD PVDF membranes is reduced to 15 nm by blending poly(methyl methacrylate) (PMMA) into PVDF-dimethyl sulfoxide (DMSO) dope solutions without altering the operational conditions. Systemic study shows the pore size reduces when increasing PMMA concentration in the membranes; but after an initial drop compared to the pure PVDF membrane, the pure water flux doesn't decline with PMMA concentration. The effect of different molecular weights of PMMA (120 kDa and 35 kDa) was also investigated, where the results showed a smaller pore size for membranes prepared using the higher molecular weight PMMA. Scanning electron microscopy (SEM), cloud-point temperature measurement and Fourier transform infrared spectroscopy (FTIR) was used to characterise the membranes and help understand how PMMA affects membrane formation. From the evidence gathered, we attribute the effects of PMMA to the change in the number of nucleation centres, diffusional rates, as well as the gelation point based on a previously proposed CCD mechanism.

Direct Monte-Carlo simulation of dry e-beam etching of resist

Novel model of e-beam interaction with PMMA, based on Direct Monte-Carlo simulation algorithm, is presented. It takes into account valence bond structure in PMMA monomers and could be easily applied for the study of e-beam-induced PMMA at higher temperatures due to various PMMA degradation pathways. The model was verified by the simulation of changes in PMMA molecular weight distribution and comparison of simulated and experimental G(S) values for e-beam irradiation of PMMA. Simulation algorithm of dry e-beam etching of resist (DEBER) is provided, including simulation of most significant processes: e-beam-induced PMMA degradation above glass transition, PMMA chain depropagation with subsequent released monomer diffusion and structure profile melting due to low PMMA viscosity at higher temperatures. Only 70% of DEBER profile depth is expected to be caused by monomer evacuation from the specimen, while the remaining 30% are supposed to be a result of PMMA swelling. Simulation of DEBER profile obtained by PMMA exposure at 160 °C in series of parallel lines was carried out. PMMA chain scissions are suggested to originate from ionization events on C–С backbone atoms and hydrogen abstraction. PMMA zip length at 160 °C was determined from the comparison of simulated and experimental profiles and comprised 3400. Experimental DEBER profiles were reproduced basing on the assumption of gaussian profile nature.