Molecular Weight Polycarbonate Research Articles

Influence of the Molecular Weight of the Polycarbonate Polyol on the Intrinsic Self-Healing at 20 °C of Polyurethanes.

Different polyurethanes (PUs) were synthesized with polycarbonate polyols of molecular weights of 500, 1000, and 2000 Da. Their self-healing abilities at 20 °C were tested, and their structural, thermal, and mechanical properties were analyzed. The PUs made with polycarbonates of molecular weights 500 (YC500) and 1000 Da (YC1000) exhibited self-healing at 20 °C, and the self-healing time of YC1000 was the shortest. The absence of crystallinity and the low degree of micro-phase separation favored self-healing at 20 °C in YC500. However, the presence of tack and the existence of allophanate species and urethane-carbonate and urea-carbonate hydrogen bonds disfavored self-healing. Consequently, the self-healing time at 20 °C of YC500 was longer than expected. On the other hand, YC1000 exhibited an "equilibrium" between urethane-carbonate and urea-carbonate hydrogen bonds and carbonate-carbonate interactions among the soft segments, so a particular structural order was produced that was associated with its fastest self-healing at 20 °C. The PU made with the polycarbonate of molecular weight 2000 Da did not exhibit self-healing at 20 °C because of its significant micro-phase separation, the presence of semi-crystalline soft domains, and the lower density of hydrogen bonds.

Ispitivanje prirodnog starenja polikarbonata srednje i visoke molekulske mase na kontinentalnoj i morskoj lokaciji za period od 96 meseci

Two thermoplastic polycarbonate bisphenol A types were exposed to the influence of natural weathering at continental location and at marine location for a period of 8 years (96 months). Every six months the specimens of medium molecular weight polycarbonate and high molecular weight polycarbonate were taken from mentioned locations and tested. Seven characteristics were chosen for determination of quality before exposition and during the process of degradation of two mentioned polycarbonate types (tensile strength, elongation to break, Shore hardness, Vicat softening point, water absorption, density and Charpy impact resistance). Changes of these seven properties at continental location are similar to the changes of mentioned characteristics at marine location during specified period of time. Data obtained by testing specimens of medium molecular weight polycarbonate pointed out that there were two important changes of quality regarding elongation to break and Charpy impact resistance (first after 36 months and second after 54 months of exposure). After 96 months of natural weathering of the above-mentioned material at both locations meaningful drop of tensile strength, moderate change of water absorption and negligible changes of Shore hardness, Vicat softening point and density were recorded. The influence of molecular weight is very apparent because high molecular weight polycarbonate exhibited higher resistance to the degradation process in natural conditions. Two very important characteristics of this polycarbonate material (tensile strength and Charpy impact resistance) practically did not change during 96 months of exposition in an open air, while drop of elongation to break is meaningful, diminution of water absorption is moderate and changes of Shore hardness, Vicat softening point and density are very small.

Pendant propargyloxy-functionalized aromatic (co)polycarbonates: synthesis, thermal crosslinking and chemical modification

A bisphenol monomer bearing pendant propargyloxy group viz, 1, 1-bis (4-hydoxyphenyl)-1-(4′-propargyloxyphenyl) ethane (BPP) was synthesized starting from commercially available 1, 1, 1-tris (4-hydroxyphenyl) ethane (THPE) by mono O-propargylation reaction using propargyl bromide. A new series of pendant propargyloxy-functionalized aromatic (co)polycarbonates was synthesized by low-temperature solution polycondensation of BPP or different molar ratios of BPP and bisphenol-A with triphosgene in dichloromethane in the presence of triethylamine. The formation of reasonably high molecular weight (co)polycarbonates was confirmed by inherent viscosity (0.52–0.83 dL/g) and gel permeation chromatography (Mn 37,000–69,800 g/mol, polystyrene standards) measurements. 13C NMR spectral studies supported formation of random copolycarbonates in copolymerization of BPP and BPA with triphosgene. The 10% weight loss temperature (T10) values of (co)polycarbonates, determined by thermogravimetric analysis under nitrogen atmosphere, were in the range 427–438 °C indicating their good thermal stability. The glass transition temperature (Tg) values of (co)polycarbonates were observed in the range 147–152 °C. The crosslinking ability of (co)polycarbonates involving pendant propargyloxy groups leading to formation of networked structure was evaluated via non-isothermal curing studies by DSC. As a proof-of-concept, the post-modification of a representative polycarbonate bearing pendant propargyloxy groups with 1-octane thiol as a model compound via thiol-yne click reaction was briefly studied.

Mechanical response of two different molecular weight polycarbonates at varying rates and temperatures

Polymers are widely used for lightweight design in industrial applications, such as helmets and car bumpers, where the most common causes of failure or damage are dynamic impact events. It is well known that the mechanical response of most polymers is highly dependent on the loading rate and temperature, and that it is not sufficient to use properties measured under static loads in the analysis of dynamic events. However, the time-temperature equivalence phenomenon offers the chance to predict high-rate performance using low-rate data. In this study, information about the constitutive behaviour of two different molecular weight polycarbonates, is obtained in low-rate experiments and then compared with the high-rate response. A master curve of storage modulus constructed from Dynamic Mechanical Analysis data is employed to understand the viscoelastic response under small-strain loading at various frequencies and temperatures. For the large-strain constitutive response, experiments at strain rates from 0.001 s-1 to 3000 s-1 are performed using a conventional crosshead device, hydraulic device, and split-Hopkinson pressure bar. Moreover, experiments at strain rates of 0.01 s-1 and temperatures from -60 to 120 °C are also performed, and the results are compared. This approach can distinguish ’constitutive’ rate dependence from the effects of specimen self-heating due to adiabatic heating under high-rate deformation. Meanwhile, the molecular weight effects on the mechanical response at varying rates and temperatures are also noted.

Theoretical study on the decomposition mechanism of bisphenol A polycarbonate induced by the combined effect of humidity and UV irradiation

Polycarbonate (PC) is a good material for covering and protecting cultural heritage sites because of its durability, mechanical properties, and transparency. When bisphenol A polycarbonate is subjected to weathering conditions this polymer shows several degradation processes depending on the irradiation wavelength, humidity and temperature. In particular, the combined effects of humidity and UV irradiation speed up the PC molecular weight reduction. In this work, the decomposition mechanisms associated to the hydrolysis process are scrutinized and the effects of UV irradiation on the hydrolysis process are evaluated throughout the Density Functional Theory (DFT) approach. It was found that under UV irradiation the hydrolysis process is speeded up because of the geometrical rearrangement due to the photo-Fries process induced by the UV light.

The effect of concentration and molecular weight of polycarbonate on the elastic constants of a nematic liquid crystal solvent

We utilized the Light Scattering from Anisotropy of Turbidity (LSAT) method and determined the three Frank’s elastic constants of; "splay" (K1), "twist" (K2) and "bend" (K3), in dilute solutions of polycarbonate (PC) in 4-pentyl-4’-cyanobiphenyl (5CB) nematic liquid crystal solvent. Within the limited solubility range of PC/5CB solutions, we determined the elastic constants of 5CB as a function of the concentration and molecular weight of PC. The results showed that K2 increases, K1 and K3 decrease, whereas K1/K3 and <K> ratio remain almost invariant by increasing the PC concentration and molecular weight.In contrast to the theoretical models and experimental data, the values and trends of K1, K2 and K3 moduli indicate that, increase of K2 at the expense of K1 and K3 moduli is due to extended chain conformation PC polymer structure and enhancment of lateral interactions between PC and 5CB moieties.

Effects of Molecular Weight of PC on Mechanical Properties of PC/ABS Blends using High-Shear Rate Processing

Each of the two polycarbonates (PC) of different molecular weights was blended with acrylonitrile-butadiene- styrene (ABS) under high-shear rate processing to afford PC/ABS. Sizes of ABS dispersed phases and mechanical properties of PC/ABS blends were investigated and high-shear rate processing of PC/ABS was carried out by changing screw speed and processing time. Prepared specimens were examined by scanning electron microscope (SEM) to observe morphology changes. Sizes of ABS dispersed phases in PC/ABS blends were observed to decrease gradually as screw speeds increased. Tensile strengths and elongations of specimens were investigated by universal testing method (UTM) to study the influence of molecular weight of PC exerting on PC/ABS blends. As a result, PC1/ABS blends (PC1: higher molecular weight PC) exhibited more strengthened properties than PC2/ABS (PC2: lower molecular weight PC). The tensile strength of PC1/ABS showed an increasing tendency when the screw speed increased, and the elongation did not show a significant decrease, but increased slightly with increasing shear time at a constant screw speed of1000 rpm.

Salcy‐Naphthalene Cobalt Complexes as Catalysts for the Synthesis of High Molecular Weight Polycarbonates

AbstractHigh molecular weight polypropylene carbonates were prepared by CO2/propylene oxide copolymerization catalyzed by salcy‐naphthalene cobalt complexes. The introduction of methyl groups in the ortho position of naphthalene‐based salcy ligands and the catalyst loading in the presence of hexane as a co‐solvent were crucial to enhance the catalytic performance for the production of polycarbonates of high molecular weight.

Ductile‐to‐brittle transition behavior of low molecular weight polycarbonate under carbon dioxide

We investigated the stress–strain behavior of low molecular weight polycarbonate for optical disc grade (OD‐PC) under carbon dioxide (CO2) at various pressures, and compared the results with that under ambient pressure at various temperatures. Elongation at break decreased sharply with increased CO2 pressure at around 2 MPa, while the elastic modulus decreased gradually up to 6 MPa. These results indicate that the tensile property changed from ductile to brittle with increased CO2 pressure, although the molecular motion is accelerated due to the plasticization effect of CO2. Such ductile‐to‐brittle transition is similar to that observed under elevated temperatures caused by chain disentanglement due to accelerated molecular motion. Although the changes of tensile properties were similar, the craze structure obtained by the brittle behavior was different, i.e., a filamented‐craze structure was obtained under high‐pressure CO2, while a lace‐like one was obtained under elevated temperatures. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Optical properties of polycarbonate/styrene-co-acrylonitrile blends: effects of molecular weight of the matrix.

In this paper, the effects of the molecular weight of a polycarbonate (PC) matrix on the phase morphology and optical properties of a PC/styrene-co-acrylonitrile (SAN) blend were investigated. A scanning electron microscope is used to analyze the phase morphology of the blends, and Mie scattering theory is used to analyze the changing laws of the optical properties of PC/SAN blends with the increasing of PC molecular weight. Results show that the average particle diameter is not strongly changed with different PC molecular weight because the values of the viscosity ratios are very close to each other. But it is obvious that the number of large particles gradually reduced while small particles (especially d<2 μm) significantly increased with the increasing of PC molecular weight. And the increase in small particles will result in an increase in backward scattering so the transmittance of PC/SAN blends decreases with the increase of PC molecular weight. However, the balance of the scattering coefficients and the number concentration of particles eventually lead to the haze of the blends being very close, despite having different PC molecular weights. Meanwhile, the photographs of scattering patterns indicate that the PC/SAN blends whose component weight ratios are fixed at 70:30 have excellent antiglare properties, despite the changes in molecular weight of the PC matrix.

Diseño de nuevos poliuretanos inspiradospor la estructura macromolecularde la seda de araña

RESUMENEn este trabajo se presentan los resultados de la síntesis en masa y caracterización de copolímeros de poliuretano (PU) formados a partir de 1,6-hexametilen diisocianato (HDI) y N-metil dietanolamina (MDEA) y 1,4-butanodiol (BD) como glicoles de las fases flexibles y rígidas, respectivamente. Se compara las propiedades mecánicas y morfológicas de este tipo de PU con las de un PU convencional formado con un policarbonato de peso molecular intermedio. Los materiales se han caracterizado mediante calorimetría diferencial de barrido, espectroscopia infrarroja de transformada de Fourier y mecánicamente mediante tracción uniaxial. Se ha observado que las unidades de MDEA que, pese a tener la capacidad de asociarse por puentes de hidrógeno, presentan características elástoméricas similares a las de glicoles de mayor peso molecular y separación entre unidades donoras-aceptoras de enlaces de hidrógeno. El comportamiento de esta nueva serie de PU con alta densidad de puentes de hidrógeno puede resultar interesante en el desarrollo de materiales resilientes y tenaces tales como las sedas.

Structure and properties of ultra‐high molecular weight bisphenol a polycarbonate synthesized by solid‐state polymerization in amorphous microlayers

ABSTRACTThe structure and properties of ultrahigh molecular weight polycarbonate synthesized by solid‐state polymerization in micro‐layers (SSPm) are reported. A low molecular weight prepolymer derived from the melt transesterification of bisphenol A and diphenyl carbonate as a starting material was polymerized to highly amorphous and transparent polycarbonate of molecular weight larger than 300,000 g mol−1 in the micro‐layers of thickness from 50 nm to 20 µm. It was observed that when the polymerization time in micro‐layers was extended beyond conventional reaction time, insoluble polymer fraction increased up to 95%. Through the analysis of both soluble and insoluble polymer fractions of the high molecular weight polycarbonate by 1H NMR spectroscopy and pyrolysis‐gas chromatography mass spectrometry (Py‐GC/MS), branches and partially crosslinked structures have been identified. The thermal, mechanical and rheological properties of the ultra‐high molecular weight nonlinear polycarbonates synthesized in this study have been measured by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and rheometry. The nonlinear chain structures of the polymer have been found to affect the polymer's thermal stability, mechanical strength, shear thinning effect, and elastic properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41609.

Novel foaming method to fabricate microcellular injection molded polycarbonate parts using sodium chloride and active carbon as nucleating agents

Microcellular injection molding can fabricate lightweight, dimensionally stable plastic parts while using less material and energy. This article investigates a new process using water vapor as the physical blowing agent and comparing two kinds of nucleating agents, namely, cubic sodium chloride (NaCl) and non‐uniform active carbon (AC). The effects of different nucleating agents on the surface roughness, mechanical properties, and microstructure of solid and foamed parts were characterized. Compared with typical microcellular injection molded parts, water vapor‐foamed polycarbonate (PC)/NaCl had a smooth surface comparable to that of solid parts, whereas foamed PC/AC had desirable specific mechanical properties as well as an attractive average weight reduction of 16.4 wt%. Low density and non‐uniform AC particles, used as a nucleating agent and reinforcement, improved the microcellular structure. Based on PC molecular weight measurement, the melt processing and water vapor‐foaming processes did induce a slight amount of thermal degradation and hydrolytic degradation, respectively. POLYM. ENG. SCI., 55:1634–1642, 2015. © 2014 Society of Plastics Engineers

Carbon dioxide as a polymer feedstock.

This review describes the progress made over the last 45 years since the seminal paper by Inoue's group in Tokyo on the utilisation of CO2 as a component of a polymerising system. This approach, rapidly taken up by others, focused initially on the copolymerisation of CO2 with an epoxide to yield a polycarbonate of high molecular weight. The initial catalysts for this process were based on organozinc compounds; these were extended to zinc phenoxides and then a series of metal-centred compounds, particularly metal porphyrins where the central metal was aluminium, cobalt, chromium, copper, manganese and various lanthanides. Later work developed in the direction of producing stereoregular polymers. The most recent advance has concerned the copolymerisation of CO2 with butadiene via a lactone intermediate; the butadiene and CO2 are initially combined with a Pd-centred catalyst to give the lactone which is then subjected to radical polymerisation. The significance of this work is that it offers a way of utilising what is normally a waste and environmentally hazardous product of many processes to synthesise a useful product.

Preparation and Characterization of Bisphenol a Polycarbonate Facilitated by Supercritical Impinging Stream

Based on the supercritical impinging stream technique, a novel synthetic process for preparing aromatic polycarbonate (PC) by transesterification between bisphenol-A (BPA) and diphenyl carbonate (DPC) was developed. Supercritical carbon dioxide (ScCO2) is an excellent plasticizing agent and a good solvent for phenol, the by-product of the reaction. Impinging stream can markedly enhance heat and mass transfer, especially mass transfer between phases. In this process, phenol formed from the reaction was dissolved and diffused into ScCO2 phase and the transfer process were accelerated through the impingement of two flows. The structure of the product was characterized by Fourier transform infrared spectrophotometry (FT-IR), 1H-nuclear magnetic resonance (NMR) and 13C-NMR measurements. Thermal analysis was measured by a differential scanning calorimeter (DSC). The PC molecular weight (MW) was determined by gel permeation chromatography (GPC) and can reach up to 4.28×104 g/mol.

Kinetics of polycarbonate distraction during laser-assisted sintering

Particularities of the selective laser sintering (SLS) on Nd+3:YAG laser and conditions of the polycarbonate (PC) destruction in the course of the manufacturing of porous three-dimensional parts made of the powdered metal–polymer compositions (MPC) were studied for their dependence on the laser influence (LI) parameters and the MPC composition. The initial powders of PC + Cu blend were prepared in the weight ratios 1:4, 1:6, and 1:10 for the micrometer-sized copper. To compare the SLS conditions, mixtures with proportions of 9:1, 7:3, 4:1 with nanosized copper additives were also provided. For the study, the scanning electron microscopy/energy dispersive X-ray spectroscopy analysis, IR spectroscopy, thermogravimetric analysis, and differential thermal analysis dates, and time-of-flight secondary ion mass spectrometry were carried out. The monitored parameter was the kinetics of a thermal destruction and thermo-oxidizing destruction of the PC evaluated by the change of the sol–gel fraction content, density, intrinsic viscosity, and molecular weight PC after the SLS process. It was shown that the activation energy of the PC destruction in nitrogen is higher than that in the air. The increase in the PC concentration in the MPC results in the decrease in the destruction processes activity. The metal inclusions have a shielding effect, thus moving the temperature range for the polymer destruction towards the region of higher temperatures, and therefore decreasing the rate of the PC decomposition under a fast temperature rise. The activation nature of the thermo-oxidizing destruction substantially goes down with the increase of the PC concentration in the MPC, and the comparison by the absolute values shows that the thermal destruction predominates over the oxidizing destruction during the SLS process.

Synthesis of biodegradable high molecular weight polycarbonates from 1,3‐trimethylene carbonate and 2,2‐dimethyltrimethylene carbonate

ABSTRACTThe possibility to obtain biodegradable high molecular weight aliphatic polycarbonates from trimethylene carbonate (TMC) and 2,2‐dimethyltrimethylene carbonate (DTC) monomers with designed composition of comonomeric units was presented. Zinc(II) acetylacetonate monohydrate was used as a catalyst. A detailed analysis of copolymer chain structure was performed by means of high resolution 13C‐NMR spectroscopy. The equations for calculation of characteristic parameters of copolymer chain such as average length of blocks, randomization and transesterification coefficients were shown. The copolymerization reactivity ratios were determined (rTMC = 1.17 ± 0.20 and rDTC= 0.42 ± 0.09). Significant differences in the reactivity of comonomers and the low transesterification result in gradient chain microstructure. The synthesized copolymer containing about 80 mol % of DTC units is a semicrystalline material with good mechanical properties, allowing for application of this material in the formation of bioresorbable flexible implants or scaffolds. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40037.

Studies on the Tensile Properties and Flow Performance of the Different Molecular-Weight Polycarbonate

Using the method of blending and two different molecular-weight polycarbonate (PC) particles, a new molecular-weight PC was prepared. Respectively analyzing the tensile property, flow performance and microstructure of three molecular-weight PC.The result shows that the molecular-weight is the main factor what influence the tensile properties and flow performance, the higher molecular-weight, the better mechanical properties, and the poorer flow properties. The tensile property of the new molecular-weight PC is Slightly worse than the original PC, and the flow performance lies somewhere in between.

The role of polycarbonate molecular weight in the poly(L-lactide) blends compatibilized with poly(butylene succinate-co-L-lactate)

Poly(butylene succinate-co-L-lactate) (PBSL)–compatibilized poly(L-lactide) (PLLA) polymer blends with two commercial grades of polycarbonate (PC) were investigated. The capillary tests showed that the steady shear viscosity of high molecular weight PC (PC-L) was 10 times higher than that of low molecular weight PC (PC-AD) throughout the shear rate range under investigation. Morphologic examination revealed that the shape of the dispersed PC-L phase in the as-extruded blends was largely spherical, but the PC-AD phase was more like a rod and elongated further during injection molding. Notched Izod impact strength (IS) of the unmodified PLLA/PC-L blend was higher than that of PC-AD blend. The IS of modified ternary blends increased with PBSL content because of enhanced phase interaction indicated from thermal and morphologic analysis. The PBSL modification also enhanced IS more significantly in PLLA/PC-L than in PLLA/PC-AD blends. On the contrary, the heat deflection temperature (HDT) of PLLA/PC-L binary system was much lower than that of PLLA/PC-AD. HDT of PBSL-modified PLLA/PC-AD blends dropped with increasing PBSL content, which is a ductile polymer. Thermal and dynamic mechanical analysis of the ternary blends showed that individual components were immiscible with distinct Tgs for PC and PLLA and distinct Tms for PBSL and PLLA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Silica supported Schiff-base cobaltIII complex-Lewis base system: a highly selective catalyst for alternating copolymerization of CO2 and propylene oxide

AbstractAn binary catalyst system of a silica supported Schiff-base cobalt complex SalenCoIII (OAC)-MCM-41 (Salen = 3-[N,N-bis-2-(3,5-di-tert-butylsalicylidenamino) ethyl] amine) was developed to generate the copolymerization of CO2 and propylene oxide in presence of (4-dimethylamino)-pyridine (DMAP). The influence of the molar ratio of catalyst components, the operating temperature, reaction time, and CO2 pressure on the yield as well as the molecular weight of polycarbonate was systematically investigated. The high selectivity of polycarbonate over cyclic carbonate at 40 °C was maintained after a longer reaction time to attain quantitative formation of the alternating copolymer. High molecular weight of 67 000 were achieved at an appropriate combination of all variables.