Radiation degradation of α-substituted acrylate polymers and copolymers

Radiation degradation is observed in poly(methyl α-chloroacrylate), poly(methyl α-cyanoacrylate), and poly(α-chloroacrylonitrile) homopolymers and their respective MMA copolymers when γ-irradiated in vacuo. Polymer degradation susceptibilities are quantified in terms of G(scission radicals) and G(scission) ? G(crosslinks), measured by EPR and membrane osmometry, respectively, values by these two methods are compared. Higher G(rads) values ranging from 2 to 6 and [G(s) ? G(x)] values ranging from 2 to 11 are obtained for the substituted polymers and copolymers relative to the values for PMMA (1.6; 1.9), a standard e-beam positive resist, which suggests that these modified polymers are more sensitive e-beam resists than PMMA.     

Differential dissolution and electron-beam lithographic sensitivity of poly(methyl methacrylate)

Photolithographic and electron-beam integrated circuit fabrication techniques rely heavily upon differences in polymer resist dissolution (development) rates to produce circuit patterns. We have applied the wide-line NMR, technique, augmented by dynamic nuclear polarization, to the measurement of polymer dissolution rates of poly(methyl methacrylate), (PMMA). At high gamma-ray exposures, we find PMMA to have dissolution rates from 2X to 1000X those of unirradiated material. The highest radiation-enhanced dissolution rates are obtained with carbon tetrachloride-based developer solutions, whereas generally lower enhanced rates are observed with 1:3 acetone or methylethylketone/isopropanol standard developer. E-beam line exposures are developed in PMMA and poly(ethyl methacrylate), PEMA, resists using similar developers for comparison. Using straight CCl₄ as a developer, e-beam lines 1-2 μ wide were developed in 3800 Å thick PEMA resist at 1 × 10^?5 C/cm² with ≤200 Å loss in unexposed resist thickness. The higher differential dissolution with CCl₄, a poorer solvent for unirradiated PMMA than acetone or MEK, is explained by decline in polarity of PMMA by radiationinduced decarboxylation.     

Studies of methyl methacrylate-methyl α-chloroacrylate,copolymers and poly(methyl α-chloroactylate) as electron sensitive positive resists

Poly(methyl α-chloroacrylate) (PMCA) and the copolymers of methyl methacrylate and methyl α-chloroacrylate (poly(MMA-co-MCA)) have been reported recently to be more susceptible to radiation degradation than poly(methyl methacrylate) (PMMA). In this paper we report our studies of PMCA and poly(MMA-co-MCA) as electron-sensitive positive resists. It has been found that both PMCA and the copolymers are more sensitive than PMMA. Using mixtures of dimethylformamide and 2-propanol as developers, the sensitivities of PMCA and poly(MMA-co-MCA) (38 mole percent MCA) have been found to be 1 × 10^?5 and 6 × 10^?6 coulomb/cm², respectively. It has also been found that crosslinking predominates in PMCA when the electron dose exceeds 6 × 10^?4 coulomb/cm².     

Radiation-degradation susceptibility studies of vinyl terpolymers: Search for improved electron beam resists

To develop polymer systems with improved lithographic resist properties, terpolymers of methyl methacrylate/methacrylonitrile/methyl α-chloroacryate (MMA/MCN/MCA), methyl methacrylate/methacrylonitrile/α-chloroacrylonitrile (MMA/MCN/ACAN), and methyl methacrylate/methacrylonitrile/vinylidene chloride (MMA/MCN/VDC) were prepared by emulsion polymerization. Also one methyl methacrylate/ methyl α-chloroacylate/α-chloroacrylonitrile (MMA/MCA/ ACAN) terpolymer was prepared. The radiation susceptibilities of these terpolymers were measured using the ⁶⁰Coγ-irradiation method. Molecular weights were determined both by membrane osmometry and gel permeation chromatography. All terpolymers exhibited higher radiation-degradation susceptibilities than poly(methyl methacrylate). The Gs values did not follow the general trend, previously observed with MCN/MCA copolymers, of being directly proportional to the respective terpolymer compositions. In some cases, the addition of small quantities of α-chlorine-containing monomers caused Gx to increase. This observation greatly differs from those observed for copolymer systems such as MMA/MCA, MCN/MCA, MMA/ ACAN, etc. studied previously. Terpolymerization gives highly soluble polymers especially suitable for wet development by many solvents. This is an important consideration for polymers with high mole fractions of methacrylonitrile (MCN) or vinylidene chloride (VDC) which are rendered soluble in development solvents. The electron-beam sensitivities were obtained for samples of three classes of the terpolymers and they were higher than that of PMMA. For example, at 20Kev a 62/34/4 MMA/MCN/MCA terpolymer exhibited a sensitivity of 1.3 × 10^?5 coulombs cm^?2 at l/l_o = 1. The introduction of ACAN narrows the working range for positive resist behavior. For example MMA/MCN/ACAN(41/40/19) has a sensitivity of 8.3 × 10^?6 coulombs cm^?2 at l/l₀ = 0.6 but it crosslinks at 1 ? 1.3 × 10^? coulombs cm². The MMA/MCN/VDC(21/76/3) polymer was about 25 times more sensitive than PMMA (7 × 10^?6 C cm^?2 at l/l₀=1).     

Radiation degradation behavior of chlorine-containing vinyl copolymers. Search for improved electron-beam resists

Vinyl copolymers with high radiation degradation sensitivity have been synthesized by copolymerizing vinylidene chloride (VDC), CH₂ = CCl₂, with methyl methacrylate (MMA), methacrylonitrile, methyl α-chloroacrylate, and dimethyl itaconate using emulsion techniques. In addition, copolymers of methyl α-chloroacrylate with methyl methacrylate and poly(α-chloroaerylonitrile) were studied. Introduction of vinylidene chloride into methyl methacrylate polymers caused a sharp increase in G_s even at relatively low VDC incorporation. Upon 29 percent VDC incorporation, the G_s value increased from 1.3 (homopolymer of MMA) to 3.4. G_s was found to be a linear function of copolymer content for several systems, but G_x was not. At higher VDC levels, the increase in G_s was countered by increases in G_x. At lower VDC levels, G_x was suppressed below the values predicted by a linear G_x dependence on composition for such systems as VDC/MMA, MCA/MMA, and α-chloroacrylonitrile/MMA. The VDC/MMA co-polymer(29 percent VDC) gavea sensitivity of 4.0 × 10^?5C/cm² to electron beam exposure using the 0 percent unexposed resist thickness loss criterion and is 2–3 times more sensitive than PMMA. Poly(α-chloroacrylonitrile) is a negative resist with a sensitivity of 5 × 10^?5 C/cm² using one-micron line images for testing.     

Dissolution dynamics of some polymers: Solvent-polymer boundaries

A critical angle illumination microscopy technique was used to study the in situ dissolution dynamics of polystyrene, poly (α-methylstyrene) and the two tactic forms of poly (methyl methacrylate), (PMMA), in several solvents. The dissolution characteristics; of polymers were found to be greatly influenced by several factors: type of polymer, processing condition of the sample, type of solvent, and tacticity, Polystyrene was found to exhibit extensive swelling in several solvents while atactic PMMA exhibited extensive cracking on dissolution. Isotactic PMMA, which has a glass temperature of about 70°C lower than the atactic PMMA, showed swelling behavior similar to atactic polystyrene, while the α-methylstyrene showed the cracking phenomena exhibited by atactic PMMA.     

Pultruded fiber reinforced thermoplastic poly(methyl methacrylate) composites. Part II: Mechanical and thermal properties

A novel process has been developed to manufacture poly(methyl methacrylate) (PMMA) pultruded parts. The mechanical and dynamic mechanical properties, environmental effects, postformability of pultruded composites and properties of various fiber (glass, carbon and Kevlar 49 aramid fiber) reinforced PMMA composites have been studied. Results show that the mechanical and thermal properties (i.e. tensile strength, flexural strength and modulus, impact strength and HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest impact strength and HDT, while carbon fiber/PMMA composites show the highest tensile strength, tensile and flexural modulus, and glass fiber/PMMA composites show the highest flexural strength. Experimental tensile strengths of all composites except carbon fiber/PMMA composites follow the rule of mixtures. The deviation of carbon fiber/PMMA composite is due to the fiber breakage during processing. Pultruded glass fiber reinforced PMMA composites exhibit good weather resistance. They can be postformed by thermoforming, and mechanical properties can be improved by postforming. The dynamic shear storage modulus (G′) of pultruded glass fiber reinforced PMMA composites increased with decreasing pulling rate, and G′ was higher than that of pultruded Nylon 6 and polyester composites.     

Effect of polymer microstructure on methyl group torsional vibrations

Fundamental torsional frequencies of methyl groups have been measured with neutron incoherent inelastic scattering for isotactic poly(methyl methacrylate)-COOCD₃, and heterotactic, syndiotactic and head-to-head isomers of poly(α-methylstyrene). The measurements confirm that the spectrum of isotactic PMMA differs considerably from the syndiotactic polymer in the region of the fundamental vibration, but no difference is found for the two stereoregular forms of poly(α-methylstyrene). However, the torsional frequency of the methyl group in the head-to-head configuration of α-methylstyrene lies at lower wavenumbers than that observed in the head-to-tail.     

Bulk and emulsion copolymerizations of n-butyl acrylate and poly(methyl methacrylate) macromonomer

Bulk and emulsion copolymerizations of an ω-unsaturated poly(methyl methacrylate) (PMMA) macromonomer with n-butyl acrylate (n-BA) were investigated. The reactivity of PMMA macromonomer in bulk copolymerization with n-BA was found to be lower than that of methyl methacrylate monomer with n-BA. The incorporation of PMMA macromonomer into poly(butyl acrylate) (PBA) latex particles by miniemulsion copolymerization was proved by high performance liquid chromatography-silica adsorption spectroscopy. Dynamic mechanical studies showed that PMMA macromonomer was grafted to the PBA backbone, and the degree of grafting increased as the ratio of PMMA macromonomer to n-BA increased. Microphase separation of the PMMA macromonomer grafts was observed at higher ratio of macromonomer (higher or equal to 10% weight of macromonomer based on total polymer phase). The n-BA/PMMA macromonomer copolymer behaved completely differently from the physical blend of PBA and PMMA macromonomer particles of the same composition. © 1996 John Wiley & Sons, Inc.     

Parameters,affecting the sensitivity of poly(methyl methacrylate) as a positive lithographic resist

The contribution of parameters such as molecular weight, molecular weight distribution and stereochemistry to electron beam sensitivity of poly(methyl methacrylate), PMMA, has been investigated. The sensitivity is interpreted here as the minimum radiation dose required to obtain a predetermined solubility rate ratio, S/S_o = S_R, of the exposed, S, and unexposed, S_o, material. The G-value was foam be independent of molecular weight, molecular weight distribution, and stereochemistry. Data indicate that the weight average molecular weight ratio correlates better with S_R than the number average molecular weight ratio. The tacticity of the resist and the developer solvent molecular weight or size have a large effect on solubility rate. Although the solubility rate pf isotactic PMMA is much greater than the syndiotactic and heterotactic stereoforms, the sensitivity appears to be independent of tacticity. In a homologous series of n-alkyl acetate developer solvents, the molecular size of the solvent has a greater effect on the solubility rate than the molecular weight of the resist. A developer solvent has been selected from the n-alkyl acetates which enhanced the sensitivity of PMMA.     

Self‐complementary multiple hydrogen bonding interactions increase the glass transition temperatures to supramolecular poly(methyl methacrylate) copolymers

We have prepared a series of poly(methyl methacrylate) (PMMA)‐based copolymers through free radical copolymerization of methyl methacrylate in the presence of 2‐ureido‐4[1H]‐pyrimidinone methyl methacrylate (UPyMA). The glass transition temperature was increased with the increase of UPyMA contents in PMMA copolymers due to strong self‐complementary multiple hydrogen bonding interactions of UPy moiety. The Fourier transform infrared and solid‐state NMR spectroscopic analyses provided positive evidence for the presence of multiple hydrogen bonds interaction of UPy moiety. Furthermore, the proton spin‐lattice relaxation time in the rotating frame [T_1ρ(H)] for the PMMA copolymers had a single value that was less than pure PMMA, indicating the smaller domain sizes in PMMA copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Miscibility of poly(α-methyl siyrene-co-acrylonitrile) with polyacrylates and polymethacrylates

A copolymer formed from 30 percent acrylonitrile and 70 percent α methyl styrene by weight, or αMSAN, has been examined for miscibility in blends with various polyacrylates and polymethacrylates. None of the polyacrylates or poly(vinyl acetate) were miscible with α-MSAN at room temperature or above. The methyl and ethyl esters of the polymethacrylate series (PMMA, PEMA) proved to be miscible with α MSAN, but none of the higher homologues were miscible under these conditions. Blends of both PMMA and PEMA with α MSAN exhibited lower critical solution temperatures. The observed cloud points decreased as PMMA molecular weight increased up to 10⁵ where kinetic effects caused an apparent reversal of this trend. Atactic PMMA interacts more strongly with αMSAN than does either isotactic PMMA or atactic PEMA. These structural effects are compared with similar trends found in other systems.     

Stereospecifity in radical polymerization of methyl α-(chloromethyl)acrylate

Poly(methyl α-(chloromethyl)acrylate)s (PMCMAs) obtained by homopolymerizations of methyl α-(chloromethyl)acrylate (MCMA) in benzene at different temperatures were converted to poly(methyl methacrylate)s (PMMAs) by reduction with tributyltin hydride. The reduction proceeded smoothly to yield PMMA exhibiting no ¹H NMR resonance due to the CH₂Cl group. The tacticity of the PMCMA obtained at 40 °C was determined using the ¹H NMR resonances of the α-methyl group of PMMA derived: mm/mr/rr=8/56/36. Apparently, the propagation of MCMA preferred r addition to a lower extent in comparison with that of MMA. The more polar and the bulkier α-substituent ClCH₂ (relative to CH₃) would diminish the effect of the carbomethoxy group, thus resulting in a lower level of synditacticity than in MMA polymerization. The tacticity of MMA-MCMA copolymers estimated after conversion to PMMA varied from that of PMMA to that of PMCMA; an increase in MCMA content in the feed resulted in a decrease in rr content. Coisotactic parameters for copolymerization of MCMA with MMA-d₈ were determined according to Hatada's procedure for determination of these parameters [Polym J 19 (1987) 1105].     

Segmental motion of stereoregular poly(methyl methacrylates) in a homologous series of n-alkyl acetate solvents by nmr relaxation measurements

The ¹³C spin-lattice relaxation times, T₁s, of both stereoregular poly(methyl methacrylates) (PMMA) and homologous series of n-alkyl acetate solvents in solution have been measured at 40°C. It was observed that the motion of polar side-chains was highly affected by the degree of interaction with solvent molecules. The stronger polymer-solvent interactions in predominantly syndiotactic PMMA solutions than in isotactic PMMA solutions were shown from the T₁ values for the carbonyl, methoxy, and quaternary carbons in polymer segments and also from the carbonyl T₁s of solvent molecules. By relating the solvent dependences of the T₁ data in syndiotactic polymer solutions to that of the known dissolution rate data of atactic PMMA, it was found that the solvent dependences of the T₁ values of those carbon groups in which the polymer-solvent interaction is not significant, e.g., methylene and α-methyl carbon groups, were consistent with the solvent dependence of the dissolution rate of polymer. This result suggested that the dissolution of polymer is mainly governed not by the sorption process related to the polymer-solvent interaction but by the transport process related to the local motions of polymer segments and solvent molecules.     

Synthesis of poly(vinyl acetate) containing diblock copolymer by DPE method

Diblock copolymer poly(methyl methacrylate)‐b‐poly(vinyl acetate) (PMMA‐b‐PVAc) was prepared by 1,1‐diphenylethene (DPE) method. First, free‐radical polymerization of methyl methacrylate was carried out with AIBN as initiator in the presence of DPE, giving a DPE containing PMMA precursor with controlled molecular weight. Second, vinyl acetate was polymerized in the presence of the PMMA precursor and AIBN, and PMMA‐b‐PVAc diblock copolymer with controlled molecular weight was obtained. The formation of PMMA‐b‐PVAc was confirmed by ¹H NMR spectrum. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to detect the self‐assembly behavior of the diblock polymer in methanol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Living functionalization of polymethacrylates by group transfer polymerization (GTP) using low ceiling temperature monomers

A living functionalization method for group transfer polymerization (GTP) has been developed for poly(alkyl methacrylates) using the sterically hindered monomer, methyl-2-phenylpropenoate (MPHA). The end-capping reactions of MPHA with living trimethylsilyl ketene acetal-ended poly(methyl methacrylate) (PMMA) chain ends have been systematically studied and characterized by size exclusion chromatography, vapor pressure osmometry, ultraviolet-visible, ¹H and ¹³C nuclear magnetic resonance spectroscopy. Although oligomerization of MPHA is observed at - 78° C, this is reversible and only monoaddition is observed at room temperature. In principle, various functional groups can be introduced into poly(alkyl methacrylates) via substituents on the aromatic ring of MPHA and related monomers. Amino-functionalized PMMA was prepared by end-capping reactions of living trimethylsilyl ketene acetal-ended PMMA with methyl E-3-(2-dimethylaminophenyl)-2-phenylacrylate.     

Changes in the interfacial properties of PC/SAN blends with compatibilizer

Block copolymers of polycarbonate‐b‐poly(methyl methacrylate) (PC‐b‐PMMA) and tetramethyl poly(carbonate)‐b‐poly(methyl methacrylate) (TMPC‐b‐PMMA) were examined as compatibilizers for blends of polycarbonate (PC) with styrene‐co‐acrylonitrile (SAN) copolymer. To explore the effects of block copolymers on the compatibility of PC/SAN blends, the average diameter of the dispersed particles in the blend was measured with an image analyzer, and the interfacial properties of the blends were analyzed with an imbedded fiber retraction (IFR) technique and an asymmetric double cantilever beam fracture test. The average diameter of dispersed particles and interfacial tension of the PC/SAN blends were reduced by adding compatibilizer to the PC/SAN blends. Fracture toughness of the blends was also improved by enhancing interfacial adhesion with compatibilizer. TMPC‐b‐PMMA copolymer was more effective than PC‐b‐PMMA copolymer as a compatibilizer for the PC/SAN blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2649–2656, 2003     

Effect of tacticity of poly(methyl methacrylate) on interfacial region with silica in polymer nanocomposite

The effect of tacticity on the interfacial region between poly(methyl methacrylate) (PMMA) and silica in a PMMA/silica nanocomposite was investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The glass transition temperature (T_g) values of the syndiotactic (st-) and atactic (at-) PMMA/silica nanocomposites are higher than those of the neat PMMA. Conversely, the T_g of the isotactic (it-) PMMA/silica nanocomposite is slightly higher than that of the neat it-PMMA. DSC and XRD results suggest that the restriction of the PMMA chain mobility in the silica nanoparticle interfacial region heightens as the syndiotactic content increases. FT-IR results show that this phenomenon is caused by the interaction between the carbonyl group of PMMA and the silanol group on the silicon dioxide surface. Therefore, it can be concluded that the syndiotactic-rich PMMA has a significantly different molecular mobility from that of the neat PMMA in the interfacial region with silica nanoparticle surface than isotactic-rich PMMA.     

Dissolution rates for thin films of miscible polymer blends

The dissolution rates of thin polymer films were measured and compared. Mixtures of various ratios of poly(methyl methacrylate), PMMA, and poly(p-hydroxystyrene), PPHS, were dissolved in methyl isobutyl ketone, MIBK. The polymer solutions were then spun into thin films on silicon wafers and dried. The coated wafers were immersed in an MIBK bath and the rate of dissolution was observed using laser interferometry. The results show that pure PPHS films have dissolution rates 1000 times greater than films of pure PMMA at comparable molecular weights. However, for films containing both PPHS and PMMA, a minimum dissolution rate occurs for a mixture with about 20% (by weight) PPHS. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2015–2020, 1997     

Studies on blends of LLDPE and polar polymers compatibilized by a random copolymer

Compatibilization of blends of linear low‐density polyethylene (LLDPE)–poly(methyl methacrylate) (PMMA) and LLDPE–copolymer of methyl methacrylate (MMA) and 4‐vinylpyridine (poly(MMA‐co‐4VP) with poly(ethylene‐co‐methacrylic acid) (EMAA) have been studied. Mechanical properties of the LLDPE–PMMA blends increase upon addition of EMAA. In order to further improve interfacial adhesion of LLDPE and PMMA, 4‐vinyl pyridine units are introduced into PMMA chains, or poly(MMA‐co‐4VP) is used as the polar polymer. In LLDPE–poly(MMA‐co‐4VP)–EMAA blends, interaction of MAA in EMAA with 4VP of poly(MMA‐co‐4VP) causes a band shift in the infrared (IR) spectra. Chemical shifts of N_1s binding energy in X‐ray photoelectronic spectroscopy (XPS) experiments indicate a transfer of proton from MAA to 4VP. Scanning electron microscopy (SEM) pictures show that the morphology of the blends were improved upon addition of EMAA. Nonradiative energy transfer (NRET) fluorescence results attest that there exists interdiffusion of chromophore‐labeled LLDPE chains and chromophore‐labeled poly(MMA‐co‐4VP) chains in the interface. Based on experimental results, the mechanism of compatibilization is studied in detail. Compatibilization is realized through the interaction between MAA in EMAA with 4VP in poly(MMA‐co‐4VP). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 967–973, 1999