Molecular Weight Polycarbonate Research Articles

Cationic polymerization of aliphatic cyclocarbonates

AbstractNumerous polymerizations of trimethylene carbonate (TMC) and neo‐pentylene carbonate (NPC) were conducted in solution using methyl triflate as initiator. The polymerization mechanism was elucidated and rapid backbiting degradation along with the formation of ether groups was detected. When strong Lewis acids such as BF3, SnCl4 or SnBn4 were used as initiators, much higher molecular weights were obtained, but the resulting polycarbonates still contained ether groups. BuSnCl3 was found to be the most useful initiator yielding high molecular weight polycarbonates free of ether groups. However, in this case it is not clear, if a cationic mechanism or a coordination‐insertion mechanism is involved.

Fracture behaviour of polycarbonate blends with a core-shell impact modifier

A detailed characterisation of the high speed fracture behaviour of polycarbonate/core-shell impact modifier blends using thick (6.25 mm) injection moulded bars with sharp notches via the Vu-Khanh methodology and data analysis is described. This expands on a previous report that examined the effect of polycarbonate molecular weight and melt blending conditions on the customary stress-strain and impact properties of such blends. Load-deflection curves and impact strength as a function of temperature are also reported. Morphological features near crack tips formed at high speed were examined by microscopy to gain insight about the sequence of events that occur during crack propagation. The use of thick specimens with sharp notches gives a better discrimination of how the concentration and degree of dispersion of impact modifier influence the toughness of these polycarbonate blends than does Izod testing using thin specimens with standard notches. High molecular weight of the matrix and good dispersion of the impact modifier in the matrix lead to both higher fracture energy at initiation and tearing modulus. Model calculations are presented to explain the different fracture responses under plane strain versus plane stress conditions caused by addition of impact modifier to polycarbonate.

Alternating Copolymerization of Carbon Dioxide and Propylene Oxide with a Rare-Earth-Metal Coordination Catalyst

The copolymerization of carbon dioxide and propylene oxide using rare-earth-metal catalyst systems was investigated in this study. It was found that the ternary rare-earth-metal coordination catalyst consisting of Y(CF3CO2)3 (I), diethylzinc (II), and glycerine (III) was the most effective catalyst system to generate an alternating polycarbonate. The effects of the molar ratio of catalyst components, the solvent, and the operating temperature and pressure on the yield and the molecular weight of polycarbonate were systematically studied. At an appropriate combination of all variables, the yield could be as high as 4200 (g/(mol of Y))/h and the molecular weight as high as 1.0 × 105 in a 12 h reaction period. The carbonate content in the resulting polycarbonate was found to be 95.6%.

Polycarbonate-epoxy semi-interpenetrating polymer network: 2. Phase separation and morphology

Bisphenol A-based epoxy resin (DGEBA) was modified with bisphenol A polycarbonate (PC), by either a physical or chemical process, and thermally cured with 4,4′-diaminodiphenyl sulfone, tetraethylenepentamine, and anhydride. The phase separation in the PC/epoxy blends was controlled by varying the composition, and the PC-epoxy reaction, and utilizing curing agents of different reactivity. A single phase morphology was achieved by accelerating the curing reaction, or introducing PC-epoxy reaction, or eliminating crystallization of PC. Under certain conditions, PC spherulites are able to form, in company with the formation of epoxy networks. Curing of the epoxy resin modified the crystallization mechanism, the melting behaviour and the morphology. The nuclei are likely to be pre-existing high molecular weight PC chains and are formed by the special interaction between PC molecules and the primary network. Low molecular weight epoxy resins increase the crystallization rate. The internal fractionation changes by PC chain scission during the melt blending process has an important influence on the crystallization. The spherulite morphology fixed by semi-IPN structure subjected a loss of order by annealing. It is suggested that hydrogen bonding and graft reaction in this kind of PC/epoxy semi-IPN is the key to controlling phase separation and morphology.

Thermal properties and morphology of blends of poly(ether imide) and polycarbonate

AbstractBlends of poly(ether imide) (PEI) and bisphenol‐A polycarbonate (PC) have been investigated by differential scanning calorimetry, dynamic mechanical thermal analyzer, scanning electron microscopy, and transmission electron microscopy. Three different molecular weights of polycarbonate have been used in the PEI‐PC blends. Blends were prepared by screw extrusion and solution casting with weight fractions of PEI in the blends varying from 0.90 to 0.10. From the measured glass transition temperature (Tg), the maximum decrease of Tg(PEI) is observed for 0.9 weight fraction PEI in the PEI‐PC blends. In the study of the morphology, the size of minor component domains (about 0.1 to 0.3 µm) in the 90/10 PEI‐PC blend is small compared to the size of minor component domains (about 0.2 to 2.0 µm) in the 10/90 PEI‐PC blend. This morphological behavior is attributed mainly to the difference of viscosity ratio between the dispersed phase and continuous phase. No considerable differences in the thermal behavior and morphologies have been observed among the blends of PEI and PC having different molecular weights.

Effect of polycarbonate molecular weight and processing conditions on mechanical behaviour of blends with a core-shell impact modifier

Morphology, tensile properties and impact strength behaviour of blends of three different molecular weight (or viscosity) grades of polycarbonate (PC) and a core-shell type impact modifier (3–18 wt%) were prepared in a single screw extruder with an intensive mixing head and in a co-rotating, fully intermeshing twin screw extruder at different conditions. The morphology of these blends were quantitatively analysed from transmission electron photomicrographs. Tensile properties and Izod impact strength, as a function of temperature for 3.13 mm specimens, were also measured. All mechanical properties were found to be very sensitive to the degree of dispersion of the impact modifier in the PC matrix. Blends made in the twin screw extruder consistently showed better dispersion and mechanical properties: higher tensile modulus, yield strength and elongation at break; higher notched Izod impact strength and lower ductile-brittle temperature. Blends with higher molecular PC show better impact properties reflecting the matrix properties. A subsequent paper explores a more complete analysis of the fracture toughness of such blends and the modes of deformation they undergo during fracture.

Two-component initiator systems for the ring-opening polymerization of oligomeric cyclic bisphenol-A carbonates. Studies within situ generated Wittig salts

A two-component initiator system based on the in situ generation of Wittig salts (alkytriarylphosphonium bromides) has been developed for the ring-opening polymerization of cyclic bisphenol-A (BPA) carbonate oligomers for potential use in composite applications so that the prepolymer can suitably wet the composite material before being converted to high molecular weight polymer. The Wittig salt precursors (an alkyl bromide, such as hexadecyl bromide, and a triarylphosphine, such as triphenylphosphine) did not independently initiate significant ring-opening polymerization of the oligomeric cyclic BPA carbonate mixture. However, when the two mixtures of cyclic BPA carbonate oligomers and initiator component were combined, a high molecular weight polymer (Mw = ∼ 65,000) was produced. The polymerization initiating species is thought to be hexadecyltriphenyl-phosphonium bromide. Consistent with this hypothesis is the observation that authentic Wittig salts did initiate ring-opening polymerization to provide high molecular weight polycarbonate. The effects of structure and concentration of the initiator components, reaction temperature, time, etc. on polymerization were studied; in general, the degree of polymerization ranged from 65 to 85%. © 1996 John Wiley & Sons, Inc.

Synthesis of AB and ABA block copolymers as compatibilizers in nylon 6/polycarbonate blends

Nylon 6 (Ny6) and Bisphenol A polycarbonate (PC) are immiscible and form biphasic blends. To improve the compatibility of Ny6 and PC several ABA and AB Ny6/PC block copolymers were synthesized, and their compatibilizing behavior on the blends were tested. Block copolymers were prepared by reacting monoamino- or diamino-terminated Ny6 homopolymers with high molecular weight PC at 130°C in anhydrous DMSO. The reaction of diamino- and monoamino-terminated Ny6 with polycarbonate produces block copolymers of the type PC-Ny6-PC (ABA) and PC-Ny6 (AB), respectively, plus a certain amount of unconverted PC degradated to lower molecular weights. To separate the block copolymer from the unconverted PC, a selective fractionation with tetrahydrofuran (THF) and trifluoroethanol (TFE) was carried out. Three different fractions were obtained: THF-soluble fraction, TFE-soluble fraction, and the TFE-insoluble fraction. The scanning electron microscopy (SEM) analysis of a 75/25 (wt/wt) Ny6/PC blend added with 2% of ABA or AB block copolymers, showed the presence of smaller PC particles more adherent to the polyamide matrix, with respect to the same blend nonadded, which is clearly biphasic. The size of the PC particles decreases from ABA to AB compatibilized blends and the adhesion with the matrix is increases in the same way. © 1996 John Wiley & Sons, Inc.

Phase Behavior and Transreaction Studies of Model Polyester/Bisphenol-A Polycarbonate Blends. 2. Molecular Weight, Composition, and End-Group Effects

The equilibrium phase behavior of poly(2-ethyl-2-methylpropylene terephthalate) (PEMPT)/Bisphenol-A polycarbonate (PC) blends is monitored as a function of polyester and polycarbonate molecular weight, composition ratio, and end-group type. Six polyesters, number-average molecular weights (M n s) varying from 4100 to 37 500, and two PCs, M n s of 11 000 and 21 000, are studied at PEMPT/PC composition ratios of 15/85, 30/70, 50/50, 70/30, and 85/15 (w/w). PEMPT/PC blends are found to be two phase at all but the lowest molecular weight pairs examined. Composition effects are most apparent in blends containing components with low molecular weight. Hydroxyl- and benzoate-terminated PEMPT/PC 50/50 blends exhibit similar phase behavior and qualitatively follow Flory-Huggins theory with enhancement in miscibility as molecular weight is decreased. Blends containing polyesters with heptafluorobutyrate end groups show substantially different phase behavior. Virtually no enhancement in partial miscibility of the components is observed as the molecular weight of the polyester is lowered. These results are explained in terms of a multicomponent interaction parameter that accounts for both midchain/midchain interactions and midchain/end-group interactions. The interaction parameter of the blend, as calculated from critical point data, is 0.044.

Hydrolytic aging of polycarbonate. II. Hydrolysis kinetics, effect of static stresses

AbstractPlaques of bisphenol A polycarbonate (PC) were exposed to a water‐saturated atmosphere at temperatures ranging from 40 to 90°C for up to 7 months. Certain samples were exposed under tensile load at 60 and 90°C, 100% RH with stresses ranging from 3.7 to 8.7 MPa. The PC molecular weight was determined by steric exclusion chromatography, and the kinetic parameters for hydrolytic chain scission were determined. It appears clearly that in the presence of tensile stresses, the hydrolysis rate is increased (at both temperatures under study) by a factor of about 10. The stress effect cannot be represented by the Eyring‐Zhurkov relationship because the activation volume appears as an increasing function of the temperature and a decreasing function of time. Some possible causes of the observed stress effects are discussed © 1995 John Wiley & Sons, Inc.

Miscibility studies of high Tg polyester and polycarbonate blends

Differential scanning calorimetry (d.s.c.) has been applied to characterize the miscibility of blends of a high T g polyester, synthesized by condensation polymerization from 4,4′-(2-norbornylidene)diphenol and terephthalic acid/azelaic acid in a 60 40 molar ratio (this polyester will be denoted T(40)C-GJ), with bisphenol-A polycarbonate. The theoretical development to determine the Flory-Huggins interaction parameter (χ) of phase-separated polymer blends from their phase compositions is described. The glass transition temperature ( T g) of a miscible blend of T(40)C-GJ and a low molecular weight polycarbonate (Lexan) can be accurately described by both the Gordon-Taylor equation with k = 1.7 and the Couchman equation. These equations were used to determine the phase compositions of a phase-separated blend of T(40)C-GJ and a high molecular weight polycarbonate (Makrolon) from the T g data. The χ values for these blends are in the range (8.4–9.9) × 10 −3 and are slightly composition dependent. The miscibility of these blends can be quantitatively understood in terms of the χ results from the d.s.c. measurements. The morphology observed by transmission electron microscopy for 50 50 wt% blends of T(40)C-GJ and polycarbonate is consistent with the d.s.c. results.

Effect of polycarbonate molecular weight on polymer blends of polycarbonate and ABS

AbstractThe melt viscosity of polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS) blends relative to PC is significantly lower, even lower than that of pure ABS in some compositions. Annealing above the Tg of PC coalesces and coarsens phase structure in core and skin regions. Increase in the molecular weight of PC in PC/ABS blends results in low‐temperature fracture toughness improvement but suffers from the disadvantage of higher melt viscosity. The selection of PC in PC/ABS blends must be a compromise between the toughness advantages of higher PC molecular weight and the disadvantage of higher melt viscosity. © 1993 John Wiley & Sons, Inc.

Effects of Surface Treatment on Weld Strength of Fiber-Reinforced Polycarbonate Produced by Injection Molding.

Effects of surface treatments with coupling agents and a binder on mechanical properties and processabillities were examined for fiber-reinforced polycarbonate produced by injection molding. Moldings with a weldline were used for the evaluation of the mechanical properties. Polycarbonates and glass fibers treated with a series of surface-treatment agents including three types of silane coupling agents and one type of urethane binder were compounded with a twin screw extruder into pellets for injection molding. Dumbbell test bars with or without a weldline were injection-molded and subjected to tensile test. Molecular weight of polycarbonate, average length of glass fibers and bar-flow length of the compounds in an injection mold were measured. The non-weld strengths of the materials, whose fibers were treated with a silane coupling agent and/or a urethane binder, were improved remarkably as compared with that of the untreated material. An amino silane, which was the most effective amongst three types of silanes, improved the non-weld strength up to 40% higher than that of the untreated material. This result was due to the higher strength of the fiber/resin interface and the longer fiber legth maintained during the processing. As the weld strength was not influenced by the fiber length, it depended only on the interface strength. The weld strength of the material treated with the amino silane increased to a value 25% higher than that of untreated one. The effect of the amino silane was attributed to the hydrogen bond between the amino groups and the carbonyl groups, because thermoplastics such as polycarbonate form no strong chemical bonds with the silanes. The urethane binder was not effective for the adhesion with polycarbonate, but promoted the adhesion of the silanes.

Effect of polycarbonate molecular weight on precrack hysteresis energy in determining its ductile‐brittle transition

AbstractThe distinctive ductile‐brittle transition behavior of pseudoductile polymeric materials such as polycarbonate (PC) has been discovered to be closely related to the precrack hysteresis loss energy. The higher molecular weight (MW) PC with higher ductility also results in higher precrack hysteresis energy and therefore greater precrack plastic volume under condition of constant loads. If the precrack plastic volume exceeds a critical value, crack initiation thereafter will propagate within the domain of the plastic zone and results in ductile fracture. The deformation displacement is closely related to the precrack plastic volume, and the critical displacement actually determines the critical plastic volume. The higher molecular weight polycarbonate with higher entanglement density is able to withstand earlier crack initiation more effectively. Toughening plastics, such as rubber modification, is simply the result of delaying or retarding the crack initiation and allows the precrack plastic zone to grow over its critical value. A model of crack criterion based on precrack plastic zone is proposed to interpret the ductile‐brittle transition phenomenon.

Evaluation of the interfacial tension between high molecular weight polycarbonate and PMMA resins with the imbedded fiber retraction technique

The interfacial tension between molten, high molecular weight samples of polycarbonate and poly(methyl methacrylate) was measured using the imbedded fiber retraction (IFR) technique. A value of 1.44 ± 0.16 dyn/cm was measured at 240 °C. This value was obtained on commercial resins with zero‐shear bulk viscosities and at a temperature typically encountered in the processing of blends and/or composites. Refinements to the IFR method were implemented which reduced the experimentation time. Consequently, measurements of the interfacial tension can now be routinely obtained in several hours for materials with zero‐shear bulk viscosities on the order of 104 Pa s.

Role of slow phase separation in assessing the equilibrium phase behaviour of PC-PMMA blends

It is shown that the extent of miscibility of blends of polycarbonate (PC) and poly(methyl methacrylate) (PMMA) described in recent papers has been over estimated. The solvent preparation methods used cause the two polymers to become kinetically trapped in a homogeneous, but non-equilibrium, mixture below the glass transition. The phase separation that occurs on heating above the glass transition is not a result of a lower critical solution temperature (LCST) just above T g but stems from an extremely slow rate of phase separation from the trapped non-equilibrium state. Based on this work, we believe that none of the LCST boundary may lie above the T g line when the components have molecular weights in the commercially useful range. There is some uncertainty at the extremes of the composition scale because of the excessively long times required to reach equilibrium. The effects of polycarbonate molecular weight in this situation are considered. Even though the PC-PMMA interaction is not as favourable as originally thought, it is clear that this interaction is only weakly unfavourable for mixing.

The Influence of the Molecular Weight of Polycarbonate on Chemical Compatibility

These experiments resulted from a program to reduce variability in compatibility testing of polycarbonate. This variability must be reduced to improve the level of confidence in compatibility data on which OEM's depend for application development. Our data show the chemical resistance of poly carbonate is dependent on the:

Thermal analysis of used and radiation treated polycarbonate (L-MW) biomaterial

γ-radiation treatment of radiation sterilized polycarbonate biomaterials has been carried out to ensure efficient disposal by incineration. Low molecular weight polycarbonate sterilized with 2·5 Mrad dose ofγ-radiation was further treated with different doses ofγ-radiation. The radiation-treated samples were subjected to thermogravimetry. The sterilized sample and the 7·5 Mrad-treated sample showed similar properties. These samples do not leave any residue during thermal decomposition.

Blends of polycarbonate and poly(hexamethylene sebacate): II. Effect of molecular weight on compatibility

AbstractBlends of polycarbonate (PC) and poly(hexamethylene sebacate) (HMS) with two different molecular weights were prepared and their thermal properties were studied via differential scanning calorimetry. It was found that the high molecular weight PC (HPC) and high molecular weight HMS (HHMS) were partially miscible as evidenced by the decrease in glass transition temperature of HPC in the blends. This partial miscibility is attributed to the interaction of the carbonyl dipole of the ester group and the highly polarizable aromatic carbonate structure. When the low molecular weight PC or HMS was used, the compatibility was enhanced because of the increased entropic contribution to the Gibbs free energy of mixing. In all the blends prepared, the PC crystallized as a result of the plasticizing effect of HMS. Bisphenol‐A diphenyl carbonate (dimer) was synthesized and used as the dimeric model of PC. This material was found to be an excellent diluent for HPC. A single glass transition was found in the HPC/dimer system and the temperature was dependent on the composition. The Couchman's equation was found to fit very well the glass transition temperature versus composition relationship for this system. A single glass transition was also found in the HHMS/dimer system. The melting point depression analysis was performed and resulted in a very low heat of fusion for the 100% crystalline HHMS. It may suggest that the dimer and HHMS are not completely miscible in the amorphous region.

Structure-Property Relationships of Perfectly Alternating Polycarbonate-Polydimethylsiloxane Block Copolymers, Part II

Abstract The relationships between the properties and microstructures of two series of perfectly alternating bisphenol A-polycarbonate-polydimethylsiloxane block copolymers were studied. In the first series, the polycarbonate (PC) block length was kept constant while the block length of polydimethylsiloxane (PDMS) was varied. The tensile properties of these block copolymers were found to be a function of composition. Dynamic mechanical properties measured as a function of temperature revealed the two-phase nature of these materials. Transmission electron micrographs showed that all samples had a sponge-like morphology independent of composition. The rheological maximum viscosity for the sample containing PC and PDMS blocks of equal molecular weight and extrudate swells increased with PC content. Takayamagi's mechanical coupling model was used to predict the maximum loss tangent at the glass transition temperature of PDMS using the known properties of pure components. The predictions agreed fairly well with the experimental results. In a second series of block copolymers, the block molecular weights of both PC and PDMS were varied to keep the composition constant. The tensile strength of these samples was found to increase with block molecular weights, except for the sample having the highest block molecular weights. The lower tensile strength of this material was attributed to its lamellar type morphology. Cold crystallization of PDMS blocks was found for samples having high PDMS block molecular weight (greater than 8000 g/mole). The Tg of PC blocks followed the Fox-Flory equation with a higher K value than expected. The PDMS content in PC domains was calculated to range from 11% for material of low block molecular weights to about 1.3% for high block molecular weight material.