Thermal Behavior and Photovoltaic Performance of Fullerene Grafted Dehydrochlorinated Poly(Vinyl Chloride) in Bulk Heterojunction Solar Cells

This study describes the development of an alternative conducting polymer for organic photovoltaic cell application. Chemical structure of poly(vinyl chloride) (PVC) was modified by two reactions, dehydrochlorination followed by fullerenation. The aim of this work was to explore the feasibility of using this chemically modified PVC (C₆₀-g-DHPVC) as an electron acceptor phase in ITO/PEDOT:PSS/P3HT:acceptor/TiO_x/Al bulk heterojunction (BHJ) solar cell. From the result, it was found that the power conversion efficiency of the BHJ cell employing PCBM as an electron acceptor alone increased from 0.5% to the maximum value of 1.34%, after the addition of C₆₀-g-DHPVC.     

Preparation and characterization of methanofullerenes for polymer–fullerene bulk heterojunction solar cells

A series of alkyl 4-benzoylbutyrate p-tosylhydrazones were synthesized and reacted with C₆₀ in the presence of sodium methoxide. Interestingly, n-butyl 4-benzoylbutyrate p-tosylhydrazone causes a high yield of the undesired compound-[6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM). Photovoltaic cells with these derivatives as electron acceptors were fabricated. The surface morphology of poly(3-hexylthiophene)(P3HT)/C₆₀ derivatives was characterized by atomic force microscopy. The nano-scale phase separation was observed in P3HT/PCBM film through a slow-growth process. This phenomenon is indistinguishable in P3HT/PCBiB ([6,6]-phenyl C₆₁-butyric acid iso-butyl ester) film because of the higher solubility of PCBiB in P3HT. The power conversion efficiency of the device that was made of P3HT/PCBiB blend is 2.8%, which is lower than that of P3HT/PCBM-based device (4.0%).     

Improved stability in P3HT:PCBM photovoltaics by incorporation of well‐designed polythiophene/graphene compositions

Morphological and photovoltaic stabilities of poly(3‐hexylthiophene) (P3HT):phenyl‐C₆₁‐butyric acid methyl ester (PC₇₁BM) solar cells were investigated in pristine and modified states. To this end, four types of patterned/assembled nanostructures, namely reduced graphene oxide (rGO)‐g‐poly(3‐dodecylthiophene)/P3HT patched‐like pattern, rGO–polythiophene/P3HT/PC₇₁BM nanofiber, rGO‐g‐P3HT/P3HT cake‐like pattern and supra(polyaniline (PANI)‐g‐rGO/P3HT), were designed on the basis of rGO and various conjugated polymers. Intermediately covered rGO nanosheets by P3HT crystals (supra(PANI‐g‐rGO/P3HT)) performed better than sparsely (patched‐like pattern) and fully (cake‐like pattern) covered ones in P3HT:PC₇₁BM solar cell systems. Supra(PANI‐g‐rGO/P3HT) nanohybrids largely phase‐separated in active layers (root mean square = 0.88 nm) and also led to the highest performance (power conversion efficiency of 5.74%). The photovoltaic characteristics demonstrated decreasing trends during air aging for all devices, but with distinct slopes. The steepest decreasing plots were obtained for the unmodified P3HT:PC₇₁BM devices (from 1.77% to 0.28%). The two supramolecules with the most ordered structures, that is, cake‐like pattern (10.12 mA cm^?2, 51%, 0.58 V, 2.2 × 10^?6 cm² V^?1 s^?1, 4.3 × 10^?5 cm² V^?1 s^?1, 0.69 nm and 2.99%) and supra(PANI‐g‐rGO/P3HT) (12.51 mA cm^?2, 57%, 0.63 V, 1.2 × 10^?5 cm² V^?1 s^?1, 3.4 × 10^?4 cm² V^?1 s^?1, 0.82 nm and 4.49%), strongly retained morphological and photovoltaic stabilities in P3HT:PC₇₁BM devices after 1 month of air aging. According to the morphological, optical, photovoltaic and electrochemical results, the supra(PANI‐g‐rGO/P3HT) nanohybrid was the best candidate for stabilizing P3HT:PC₇₁BM solar cells. © 2020 Society of Chemical Industry     

Efficiency above 6% in poly(3‐hexylthiophene):phenyl‐C‐butyric acid methyl ester photovoltaics via simultaneous addition of poly(3‐hexylthiophene) based grafted graphene nanosheets and hydrophobic block copolymers

A combination of reduced graphene oxide (rGO) nanosheets grafted with regioregular poly(3‐hexylthiophene) (P3HT) (rGO‐g‐P3HT) and P3HT‐b‐polystyrene (PS) block copolymers was utilized to modify the morphology of P3HT:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) active layers in photovoltaic devices. Efficiencies greater than 6% were acquired after a mild thermal annealing. To this end, the assembling of P3HT homopolymers and P3HT‐b‐PS block copolymers onto rGO‐g‐P3HT nanosheets was investigated, showing that the copolymers were assembled from the P3HT side onto the rGO‐g‐P3HT nanosheets. Assembling of P3HT‐b‐PS block copolymers onto the rGO‐g‐P3HT nanosheets developed the net hole and electron highways for charge transport, thereby in addition to photoluminescence quenching the charge mobility (μ_h and μ_e) values increased considerably. The best charge mobilities were acquired for the P3HT₅₀₀₀₀:PC71BM:rGO‐g‐P3HT₅₀₀₀₀:P3HT₇₀₀₀‐b‐PS₁₀₀₀ system (μ_h = 1.9 × 10^?5 cm² V^–1 s^–1 and μ_e = 0.8 × 10^?4 cm² V^–1 s^–1). Thermal annealing conducted at 120 °C also further increased the hole and electron mobilities to 9.8 × 10^?4 and 2.7 × 10^?3 cm² V^–1 s^–1, respectively. The thermal annealing acted as a driving force for better assembly of the P3HT‐b‐PS copolymers onto the rGO‐g‐P3HT nanosheets. This phenomenon improved the short circuit current density, fill factor, open circuit voltage and power conversion efficiency parameters from 11.13 mA cm^?2, 0.63 V, 62% and 4.35% to 12.98 mA cm^?2, 0.69 V, 68% and 6.09%, respectively. © 2019 Society of Chemical Industry     

α‐Thiophene end‐capped styrene copolymer containing fullerene pendant moieties: Synthesis,characterization, and gas sensing properties

We report the synthesis, characterization, and gas sensing properties of a styrene copolymer bearing α‐thiophene end group and fullerene (C₆₀) pendant moieties P(S‐co‐CMS‐C₆₀). First, the copolymer of styrene (S) and chloromethylstyrene (CMS) monomers was prepared in bulk via a bimolecular nitroxide‐mediated radical polymerization (NMP) technique using benzoyl peroxide (BPO) as the radical initiator and nitroxy‐functional thiophene compound (Thi‐TEMPO) as the co‐radical and this gave α‐thiophene end‐capped copolymer P(S‐co‐CMS). The chloromethylstyrene units of P(S‐co‐CMS) allowed further side‐chain functionalization onto P(S‐co‐CMS). The obtained P(S‐co‐CMS) was then reacted with sodium azide (NaN₃) and this led to the copolymer with pendant azide groups, P(S‐co‐CMS‐N₃), and then grafted with electron‐acceptor C₆₀ via the reaction between N₃ and C₆₀. The final product was characterized by using NMR, FTIR, and UV–vis methods. Electrical characterization of P(S‐co‐CMS‐C₆₀) thin film was also investigated at between 30 and 100 °C as the ramps of 10 °C. Temperature dependent electrical characterization results showed that P(S‐co‐CMS‐C₆₀) thin film behaves like a semiconductor. Furthermore, P(S‐co‐CMS‐C₆₀) was employed as the sensing layer to investigate triethylamine (TEA), hydrogen (H₂), acetone, and ethanol sensing properties at 100 °C. The results revealed that P(S‐co‐CMS‐C₆₀) thin film has a sensing ability to H₂. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43641.     

Isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

A novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) was added to binary blends of isotactic polypropylene (iPP) and atactic polystyrene (aPS) with a view to using such a copolymer as compatibilizer for iPP/aPS materials. Differential scanning calorimetry, optical microscopy, scanning electron microscopy (SEM), wide angle X-ray scattering, and small angle X-ray scattering (SAXS) techniques have been carried out to investigate the phase morphology and structure developed in solution-cast samples of iPP/aPS/uPP-g-PS ternary blends. It was found that the uPP-g-PS addition can provide iPP/aPS-compatibilized materials and that the extent of the achieved compatibilization is composition-dependent. Blends of iPP and aPS exhibited a coarse domain morphology that is characteristic of immiscible polymer systems. By adding 2% (wt/wt) of uPP-g-PS copolymer a very broad particle-size distribution was obtained, even though the particles appeared coated by a smooth interfacial layer, as expected according to a core–shell interfacial model. With increasing uPP-g-PS content (5% wt/wt), a finer dispersion degree of particles, together with morphological evidence of interfacial adhesion, was found. With further increase of uPP-g-PS amount (10% wt/wt) the material showed such a homogeneous texture that neither domains of dispersed phase nor holes could be clearly detected by SEM. The type of interface developed in such iPP/aPS/uPP-g-PS blends was accounted for by an interfacial interpenetration model. The iPP crystalline texture, size, neatness, and regularity of iPP spherulites crystallized from iPP/aPS/uPP-g-PS blends were found to decrease when the copolymer content was slightly increased. Assuming, for the iPP spherulite fibrillae, a two-phase model constituted by alternating parallel crystalline lamellae and amorphous layers, it was shown by SAXS that the phase structure generated in iPP/aPS/uPP-g-PS blends is characterized by crystalline lamellar thickness (L_c) and interlamellar amorphous layer thickness (L_a) higher than that shown by plain iPP; the higher the copolymer content, the higher the L_c and L_a. It should be remarked that considerably larger increases have been found in L_a values. Such SAXS results have been accounted for by assuming that a cocrystallization phenomenon between propylenic sequences of the uPP-g-PS copolymer and iPP occurs and that during such a process PS chains grafted into copolymer sequences remain entrapped in iPP interlamellar amorphous layers, where they form their own separate domains. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1539–1553, 1997     

Electrical and mechanical characteristics of composites consisting of fractionated poly(3‐hexylthiophene) and conducting particles

The dynamic viscoelasticity of fractionated poly(3‐ hexylthiophene)titanium carbide (P3HT/TiC) composites was examined with regard to their electrical characteristics. The elastic modulus (E′) at 0°C [i.e., near the glass‐transition temperature (T_g) of P3HT] increased with increasing TiC content of the composite. In particular, composites whose TiC content exceeded the threshold concentration showed a high E′. This was caused by the high E′ of TiC and the strong interaction between TiC and P3HT. When the sample was heated above the T_g, E′ decreased rapidly and an increase in the loss tangent appeared near the T_g of P3HT. Mechanical loss was caused by friction between TiC and P3HT. The change in mechanical characteristics affected the electrical conductivity. When the TiC content of the composite approximated to the threshold concentration, a significant change in mechanical characteristics took place, so that a large positive temperature coefficient (PTC) effect was observed near the T_g. To explain the PTC phenomenon, we propose a model of conductive pathway for P3HT/TiC. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1429– 1433, 2002     

Preparation and photoconducting property of C60Cln‐m‐bonded poly(N‐vinylcarbazole) with C60Cln/CuCl/Bpy catalyst system

C₆₀Cl_n‐m bonded poly(N‐vinylcarbazole) (C₆₀‐PVK) has been synthesized by C₆₀Cln (the average value of n is 20)/CuCl/ Bpy (2,2′‐bipyridine) catalyst system and its structure was analyzed by UV‐Vis and proton NMR. The polymerization mechanism was proposed proceeding via a atom transfer radical polymerization (ATRP). The block copolymer of poly N‐vinylcarbazole‐block‐polystyrene can also be compounded by adding styrene after N‐vinylcarbazole polymerized completely in this polymerization system. The photoconducting properties of C₆₀Cl_n‐m‐bonded poly(N‐vinylcarbazole) was better than poly(N‐vinylcarbazole) initiated by AIBN. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 606–609, 2003     

Fast scanning chip calorimetry study of P3HT/PC61BM submicron layers: structure formation and eutectic behaviour

Fast scanning chip calorimetry was used to perform an elaborate isothermal study of poly(3‐hexyl thiophene)/[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (P3HT/PC₆₁BM) submicron layers. The used scanning rates of 30 000 K s^?1 allow for a ‘true’ isothermal study, where non‐isothermal effects are avoided. Results were obtained over a wide temperature range for the 1:1 composition, used in organic solar cells, and for selected temperatures for the 3:7 composition. The results can be clearly interpreted according to the eutectic behaviour expected for this system, with the 1:1 composition being enriched in P3HT and the 3:7 composition being enriched in PC₆₁BM. In both cases, the start of the melting trajectory corresponding to the eutectic transition coincided with the T_g of PC₆₁BM. This is in agreement with earlier studies that report a vitrification effect caused by PC₆₁BM. A bell‐shaped curve of isothermal crystallization rates could be constructed for the 1:1 composition, where the T_g of the mixed amorphous phase as well as of the separate components can be seen to play a role. For the 3:7 composition, clear indications are observed that a vitrified PC₆₁BM phase can be formed in which isothermal crystallization takes place. © 2018 Society of Chemical Industry     

Morphology and thermal properties of two polymethacrylates modified by a polymer liquid crystal

We have studied blends of a polymer liquid crystal (PLC) with poly(cyclohexylethyl methacrylate) (PCHEMA) or poly(cyclohexylpropyl methacrylate) (PCHPMA). The PLC is PET/0.6PHB where PET = poly(ethylene terephthalate), PHB = p-hydroxybenzoic acid and 0.6 is the mole fraction of the latter in the copolymer. The microstructure was studied by scanning electron microscopy (SEM). PCHEMA + PLC (20 wt% of the latter, blend E) has a fine texture with LC islands evenly distributed in the matrix and good adhesion between the phases resulting from their partial miscibility. The PCHPMA + PLC (20 wt% of the latter, blend P) shows only limited compatibility. The SEM results are confirmed by values of the glass transition temperatures T_g determined via thermal mechanical analysis. The T_g value of the blend E is shifted towards the T_g of PLC; T_g of blend P is practically equal to that of PCHPMA. The linear isobaric expansivity α_L values for both blends are lower than the respective values for pure PCHPMA and PCHEMA. Thermal stabilities of the blends determined by thermogravimetry are also better than those of pure polymethacrylates. The temperature of 50% weight degradation for blend E is higher than that for pure PCHEMA by more than 60 K Copyright © 2004 Society of Chemical Industry     

A regioregular polythiophene–fullerene for polymeric solar cells

In this article, we present the synthesis and characterization of a new thiophenic copolymer bearing the C₆₀ fullerene directly linked to the end of a hexamethylenic side chain. This copolymer was prepared with good yield using a simple and straightforward post‐polymerization functionalization procedure applied on a soluble regioregular polymeric precursor obtained by regiospecific organometallic coupling. Copolymer structural and photophysical properties were investigated by gel permeation chromatography, thermal analysis (DSC and TGA), NMR, IR, UV–Vis, and atomic force spectroscopy. The double‐cable copolymer possesses good solubility in common organic solvents, high filmability, thermal stability, and low segmental aggregation tendency. It was tested as a photoactive layer in a polymeric solar cell showing a power conversion efficiency under 100 mW cm^?2 AM 1.5 illumination higher than 4%, more than that of the reference cell made with the conventionally used P3HT/PCBM blend. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42121.     

Functionalized polythiophene for corrosion inhibition and photovoltaic application

Conjugated polymers are encouraging substitute for creating clean and renewable energy for photoinduced charge generation and transport media in polymer solar cells (PSCs). Successful synthesis of a new solution processable n-type polythiophene based π-conjugated polymer (P3HT-CN) is done where polythiophene units are substituted by cyano groups through post functionalization approach of synthesized P3HT which is cheap, stable, easily prepared, and inert against ambient conditions and is expected to be a competitive candidate for the acceptor material in non fullerene acceptors (NFAs) PSCs against fullerene derivative and used as the highly efficient active layer in the bulk heterojunction (BHJ) which increase the donor-acceptor interfacial area through controlling the phase separation indicating device structure ITO/PEDOT:PSS/P3HT:P3HT-CN/Al. Photovoltaic measurement of this PSCs device based on P3HT:P3HT-CN demonstrate the PCE of 0.008% with an increased short circuit current density (J_sc) of 0.11 mA cm⁻². The thermal, optical, and electrochemical properties are examined in detail showing high thermal stability, absorbance in the visible part of the solar spectrum, higher charge carrier mobility, and also mixed type corrosion inhibitive behavior with 90 and 78% inhibitor efficiency for P3HT and P3HT-CN, respectively, built this class of material as smart which can be used for many other applications.     

Effect of [6,6]‐phenyl‐C61‐butyric acid methyl ester on the morphology of poly(3‐hexylthiophene) film

The change of morphology of poly(3‐hexylthiophene) (P3HT) film as a result of blending with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) was studied using a freeze‐dry method. A porous structure was observed as the P3HT/PCBM solution was freeze‐dried. The pore size decreased as the proportion of PCBM increased in the P3HT/PCBM blended film. Additionally, the freeze‐dried P3HT/PCBM film was more resistant to the formation of PCBM crystals than that prepared by a spin‐coating method during the thermal annealing process. Homogeneous distribution of PCBM in the freeze‐dried P3HT/PCBM film was the main reason for the reduction of large PCBM crystal formation. Copyright © 2011 Society of Chemical Industry     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

Optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering techniques were used to study the influence of crystallization conditions on the morphology and thermal behavior of samples of ternary blends constituted by isotactic polypropylene (iPP), atactic polystyrene (aPS), and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) with the purpose of assessing the uPP‐g‐PS capability to act as a compatibilizer for iPP/aPS materials. It was shown that the presence of the uPP‐g‐PS copolymer affects the interfacial tension between the iPP and aPS phases in the melt state, with the aPS particle size and the particle‐size distribution being, in fact, strongly modified. In samples of iPP/aPS/uPP‐g‐PS blends, isothermally crystallized from the melt at a relatively low undercooling in a range of the crystallization temperature of the iPP phase, the addition of the uPP‐g‐PS copolymer induced a drastic change both in the aPS mode and the state of dispersion and in the iPP spherulitic texture and inner structure of the spherulite fibrils. In particular, the phase structure developed in the iPP/aPS/uPP‐g‐PS materials was characterized by a crystalline lamellar thickness of the iPP phase comparable to that shown by the plain iPP. The extent of the induced modifications, that is, the degree of compatibilization achieved, resulted in a combined effect of composition and undercooling. Also, relevant thermodynamic parameters of the iPP phase, such as the equilibrium melting temperature (T_m) and the folding surface free energy (ς_e) of the lamellar crystals, were found to be influenced by the presence of the uPP‐g‐PS copolymer. A linear decrease of the T_m and ς_e values with increasing uPP‐g‐PS content was, in fact, observed. Such results have been accounted for by an increase of the presence of defects along the iPP crystallizable sequences and by the very irregular and perturbed surface of the crystals with increasing copolymer content. The observed decrease in T_m values revealed, moreover, that, in the iPP/aPS/uPP‐g‐PS blends, the iPP crystal growth occurs under comparatively lower undercooling, in line with higher crystalline lamellar thickness shown by SAXS investigation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1429–1442, 1999     

Enhanced open-circuit voltage of two side chain conjugated polythiophene derivatives blended with indene-C60 bisadduct

Two side chain conjugated polythiophene copolymer: poly[3-(5′-octylthienylenevinyl) thiophene]-thiophene (P1) and poly{3-[4-(2-ethyl-hexyloxy)-phenylvinyl]-thiophene}-thiophene (P2) were synthesized. Polymer photovoltaic solar cells using P1 and P2 as donor and a high LUMO energy level fullerene derivative indene-C₆₀ bisadduct (IC₆₀BA) as acceptor were demonstrated. The polymer solar cells (PSCs) based P1/IC₆₀BA and P2/IC₆₀BA showed enhanced open circuit voltage (V_oc) of 0.89 and 0.88 V respectively, in comparison with that of P1/PC₆₁BM and P2/PC₆₁BM as 0.58 and 0.56 V, respectively. The improved V_oc of IC₆₀BA as acceptor in PSCs is benefited from the higher LUMO energy levels of the C₆₀ derivatives. The power conversion efficiency of the PSCs based on P1/IC₆₀BA and P2/IC₆₀BA were 0.32% and 0.35%, respectively.     

Nano- and bulk-tack adhesive properties of stimuli-responsive, fullerene-polymer blends, containing polystyrene-block-polybutadiene-block-polystyrene and polystyrene-block-polyisoprene-block-polystyrene rubber-based adhesives

Nano-tack (measured using AFM) and bulk-tack adhesive forces of blends of C₆₀ and either polystyrene-block-polybutadiene-block-polystyrene (SBS) or polystyrene-block-polyisoprene-block-polystyrene (SIS) triblock copolymer pressure sensitive adhesives were measured after exposure to white light irradiation. The nano-tack adhesive forces in C₆₀-SIS/SBS were found to decrease with increasing C₆₀ concentration and exposure time, approaching the value for 100% polystyrene, providing an indication that significant surface hardening and crosslinking of the soft isoprene and butadiene phases occurs in the presence of C₆₀. Films produced during the study were smooth, having low RMS surface roughness, and showed nanoscale phase separation between the soft (diene) and hard (styrene) segments. This phase separation disappeared after addition of C₆₀ sensitizer and white light irradiation. Bulk adhesive measurements (tack and peel strength) showed a similar trend with C₆₀ concentration and exposure time, and in irradiated systems containing as little as 0.2 wt% C₆₀, a significant decrease in adhesion was observed. Estimated T_g (measured using DMA, shear mode) of the soft-block shifts to higher temperatures (increasing by 30-40 °C), and high gel fractions were obtained, indicating the presence of chemically crosslinked networks.     

Hydrogen adsorption on partially truncated and open cage C60 fullerene

C₆₀ buckyball molecules were partially truncated by a controlled oxidation at 400 °C and 2 bar oxygen pressure to create unique pore textures suitable for hydrogen adsorption. Pore textural analysis and density measurement confirmed the success of cage-opening and the creation of pore structures accessible to gas molecules. The specific surface area of the C₆₀ sample were increased from below detection to a measurable value (BET: 85 m²/g). Raman spectral study showed that the three main bands of C₆₀, H_g(1), A_g(1) and A_g(2) remained and significant defects were created after the C₆₀ fullerenes were partially oxidized. XRD and SEM measurements suggested that the C₆₀ fullerenes lost their crystallinity and the crystal surfaces were etched after the oxidation step. Hydrogen adsorption on the C₆₀ fullerenes were measured at three temperatures (77, 143 and 228 K) and hydrogen pressures up to 150 bar. Hydrogen adsorption capacity on C₆₀ fullerenes at 77 K at 120 bar was more than tripled (from 3.9 to 13 wt.%) after the C₆₀ fullerenes were partially oxidized. The average heat of adsorption of hydrogen on the partially oxidized C₆₀ fullerene molecules (2.38 kJ/mol) is within the range of the reported values of heat of adsorption on other porous adsorbents.     

Kinetics for copolymerization of methyl methacrylate with N‐cyclohexylmaleimide

The kinetics for the radical copolymerization of methyl methacrylate (MMA) with N‐cyclohexylmaleimide (NCMI) was investigated. The initial copolymerization rate R_p is proportional to the initiator concentration to the power of 0.54. The apparent activation energy of the overall copolymerization was measured to be 69.0 kJ/mol. The monomer reactivity ratios were determined to be r_NCMI = 0.42 and r_MMA = 1.63. R_p reduces slightly, and the molecular weight of the resultant copolymer decreases with increasing the concentration of the chain transfer agent N‐dodecanethiol (RSH). The more the transfer agent, the narrower the molecular weight distribution of the resulting copolymer. The following chain‐transfer constant of RSH for the copolymerization of MMA with NCMI in benzene at 50°C was obtained: C_s = 0.23. The glass transition temperature (T_g) of the copolymer increases with increasing f_NCMI, which indicates that adding NCMI can improve the heat resistance of Plexiglas. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1293–1297, 1999     

Enhanced Infrared Absorption of C60 on Thin Evaporated Pd Island Films

Infrared transmission spectra of C₆₀ multilayers on thin Pd films deposited onto surface-oxidized Si(100) and hydrogen-terminated Si(111) substrates are reported. In both cases, the spectra in the 1500–1100 cm⁻¹ region exhibited bands at 1444, 1429, and 1182 cm⁻¹ due, respectively, to the A_g (2), T_1u (4), and T_1u (3) modes. The appearance of the A_g (2) mode, which is originally infrared inactive (Raman active), reveals electron transfer from the metal to chemisorbed C₆₀. Indeed, increasing the thickness of C₆₀, the A_g (2) mode intensity saturated more rapidly than the T_1u (4) and T_1u (3) modes. The originally infrared active T_1u (4) and T_1u (3) modes were enhanced in intensity depending upon the Pd thickness. Actually, while both substrates gave nearly the same magnitude of enhancement, the optimum Pd thickness was smaller on the hydrogen-terminated surface than on the surface-oxidized surface. On the other hand, the A_g (2) mode was less intense on the hydrogen-terminated surface than on the oxidized surface, suggestive of a shortage of chemisorbed C₆₀ and thus pointing out the importance of the metal film morphology. Indeed, Pd films deposited on the two substrates gave rise to quite different AFM images. We also show that, regardless of the substrate, the A_g (2) mode is an order of magnitude smaller than for Ag deposition, though no remarkable intensity differences were observed with respect to the T_1u (4) and T_1u (3) modes.     

Glass transitions of styrene/α-methylstyrene statistical copolymers and of their blends with PPO® resin

The glass transition temperatures (T_g) and specific heat increments (ΔC_p) at T_g of S/AMS statistical copolymers having weight fractions AMS of 0.00, 0.09, 0.17, 0.26, 0.36, and 0.44 are (by DSC) 380.0 (0.280), 384.2 (0.275), 388.8 (0.284), 391.5 (0.275), 398.3 (0.272), and 405.9 (0.27) °K (J·g^? ·deg^?), respectively. The T_g (ΔC_p) for the PPO resin are 492.2 (0.221). The glass transitions of P(S/AMS) (1) + PPO resin (2) blends having w2 = 0.25, 0.50, and 0.75 were also measured. Examination of the copolymer and blend T_g vs. composition data indicates that a relation recently proposed by Couchman gives a somewhat better approximation than the simple Fox relation. However, the nonadjustable k = ΔC_p2/ΔC_p1 constant in the Couchman relation must be replaced by a smaller empirical k to give a true match of calculated to observed T_g.