Polyimide bonded magnets: Processing and properties

We report a new method of polyimide synthesis based on the interaction of dianhydrides with acylated diamines for preparing a melt processable mixture of prepolymer and rare earth magnetic alloy particles in the form of 75–100 μm particles. This mixture can be easily converted to useful thermoplastic polyimide bonded magnets by heating at 300°C. It is shown that the prepolymer based on 1,3‐bis(3,4‐dicarboxyphenoxy)benzene dianhydride and the diacetyl derivative of 2,2‐bis(4‐(4‐aminophenoxy)phenyl)sulfone diamine after removing less than 5% by weight of the volatile components can be melted at 220–240°C to give a fluid with a viscosity of 10–20 Pas. This low viscosity of the prepolymer facilitates blending it with magnetic particles at relatively high volume fractions (up to 85 vol %) that are not possible using conventional methods. The resulting polyimide‐bonded magnets exhibit excellent thermal stability and a high storage modulus of 10 GPa at 400°C. Magnetic property measurements showed a ≥10% increase in energy products over that of typical commercial bonded magnet materials such as the ones containing thermoplastic poly(phenylene sulfide) or polyamide matrices. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3151–3158, 2003     

Thermally stable polyimide binders from aromatic dianhydrides and acetyl derivatives of aromatic diamines: Formation mechanism

Polyimide resins based on dianhydrides of aromatic tetracarboxylic acids and acetyl derivatives of aromatic diamines have been developed for impregnating carbon fibers and glass cloth. Binder prepolymers are soluble in amide solvents and acetone and also form melts with a viscosity of 0.1–0.3 Pa · s at 250–300°C. The melt lifetime is 20–30 min. An increase in temperature leads to the formation of a crosslinked insoluble system of high thermal stability. The formation of polyimide binders was studied with the aid of IR and NMR spectroscopy. A mechanism of the reaction of aromatic dianhydrides with acylated amines is proposed. On the basis of polyimide binders from dianhydride of 3,3′,4,4′-benzophenonetetracarboxylic acid and bis-[4-acetaminophenyl]-sulfone, bis-[4-acetaminophenyl]-ether, and N,N-diacetyl-p-phenylene diamine, carbon fiber composites with good physico-mechanical properties were obtained.     

Novel phenylethynyl‐endcapped polyimide oligomers: Synthesis and characterization

A series of novel phenylethynyl‐endcapped polyimide oligomers were prepared by polycondensation of an aromatic diamine mixture of 1,3‐bis(4‐aminophenoxy) benzene (1,3,4‐APB) and 3,4′‐oxydianiline (3,4′‐ODA) with different aromatic dianhydrides including 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐(hexafluoro isopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA), and 4,4′‐[2,2,2‐trifluoro‐1‐(3′,5′‐bis‐(trifluoro‐methyl)phenyl)ethylidene]diphthalic anhydride (9FDA) in the presence of 4‐phenyl‐ethynylaniline (PEA) as endcapping agent in aprotic solvent at elevated temperature. The chemical structures, thermal behavior, and melt rheological properties of the synthesized polyimide oligomers were investigated. Experimental results indicated that the fluorinated polyimide oligomers derived from 6FDA (PI‐2) and 9FDA (PI‐4) are amorphous solid resins and exhibited lower melt viscosities than those prepared from the unfluorinated aromatic dianhydrides such as BPDA and ODPA. The BPDA‐based polyimide oligomers with a molar ratio of 1,3,4‐APB/3,4′‐ODA = 50:50 (PI‐5) showed lower melt viscosity than those derived from a mixture of 1,3,4‐APB and 3,4′‐ODA with molar ratios of 75:25 and 100:0, respectively. In addition, the melt viscosity of the polyimide oligomers increased obviously with increasing of the polymer calculated molecular weights. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Polymer bonded magnets. II. Effect of liquid crystal polymer and surface modification on magneto‐mechanical properties

We studied the effect of liquid crystal polymer (LCP) and surface modification of neodymium‐iron‐boron (Nd‐Fe‐B) magnetic alloy on the magneto‐mechanical behavior of poly (phenylene sulfide) (PPS) bonded Nd‐Fe‐B magnets to accelerate efforts to develop useful thermoplastic magnets with optimal performance. The results indicate that blending the LCP with PPS provides the required balance of properties for the targeted applications. These properties include superior magneto‐mechanical performance at elevated temperatures, minimal melt viscosity at optimal LCP volume fraction, high stiffness, and improved dimensional stability, making the thermoplastic magnets suitable for use at elevated temperatures and in chemically corrosive environments where commercial rare earth alloy magnets are not useable. Enhanced wetting of the magnetic Nd‐Fe‐B powders by the polymers, formation of reinforcing LCP domains, and interactions between the polymers and the magnetic powders are thought to be responsible for the beneficial function of the LCP and Nd‐Fe‐B surface modifier in the PPS bonded Nd‐Fe‐B magnets.     

Fully aliphatic polyimides from adamantane‐based diamines for enhanced thermal stability,solubility, transparency,and low dielectric constant

We have synthesized a series of fully aliphatic polyimides (APIs) from bicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BOCA) and various aliphatic diamines, including linear aliphatic, flexible alicyclic, and rigid adamantyl diamines. We performed the polymerization reactions using one‐step syntheses in m‐cresol at elevated temperatures without the isolation of poly(amic) acid. The chemical composition and structure of the polymers were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectrometry. The characterization data are reported from analyses using gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and wide‐angle X‐ray diffraction (WXAD) measurements. The polyimides are also subjected to solubility, solution viscosity, tensile strength, transparency, and dielectric constant measurements. The resultant polyimides possess well‐controlled molecular weight, reasonable intrinsic viscosity, good transparency, enhanced solubility, low dielectric constants, and high glass transition temperature, together with marginal thermal and mechanical stability. These properties were enhanced in copolyimides containing equimolar amounts of rigid and flexible moieties. These rigid‐rod APIs derived from the alicyclic dianhydride and aliphatic diamines are promising candidates as advanced materials for future applications in micro‐ and photoelectronic devices. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3316–3326, 2006     

Eco-Friendly Ether and Ester-Urethane Prepolymer: Structure,Processing and Properties

This study concerns bio-based urethane prepolymers. The relationship between the chemical structure and the thermal and processing parameters of bio-based isocyanate-terminated ether and ester-urethane prepolymers was investigated. Bio-based prepolymers were obtained with the use of bio-monomers such as bio-based diisocyanate, bio-based polyether polyol or polyester polyols. In addition to their composition, the bio-based prepolymers were different in the content of iso-cyanate groups content (ca. 6 and 8%). The process of pre-polymerization and the obtained bio-based prepolymers were analyzed by determining the content of unreacted NCO groups, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, thermogravimetry, and rheological measurements. The research conducted facilitated the evaluation of the properties and processability of urethane prepolymers based on natural components. The results indicate that a significant impact on the processability has the origin the polyol ingredient as well as the NCO content. The thermal stability of all of the prepolymers is similar. A prepolymer based on a poly-ether polyol is characterized by a lower viscosity at a lower temperature than the prepolymer based on a polyester polyol. The viscosity value depends on the NCO content.     

Preparation and properties of melt‐processable polyimides based on fluorinated aromatic diamines and aromatic dianhydrides

Two series of melt‐processable polyimides were prepared from 4,4′‐bis(3‐amino‐5‐trifluoromethylphenoxy)biphenyl (m‐6FBAB) and 4,4′‐bis(4‐amino‐5‐trifluoromethylphenoxy) biphenyl (p‐6FBAB) with various aromatic dianhydrides. The effects of the chemical structures of the polyimides on their properties, especially the melt processability and organic solubility, were investigated. The experimental results demonstrate that some of the fluorinated aromatic polyimides showed good melt processability at elevated temperatures (250–360°C) with relatively low melt viscosities and could be melt‐molded to produce strong and tough polyimide sheets. Meanwhile, the polyimides showed excellent organic solubility in both polar aprotic solvents and common solvents to give stable polyimide solutions with high polymer concentrations and relatively low viscosities. Thus, we prepared high‐quality polyimide films by casting the polyimide solutions on glass plates followed by baking at relatively low temperatures. The polyimides derived from m‐6FBAB showed better melt processability and solubility than the p‐6FBAB based polymers. The melt‐processable polyimides showed a good combination of thermal stability and mechanical properties, with decomposition temperatures of 547–597°C, glass‐transition temperatures in the range 205–264°C, tensile strengths of 81.3–104.9 MPa, and elongations at break as high as 19.6%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization behavior of poly(p‐dioxanone)‐PU/montmorillonite nanocomposites prepared by chain‐extending reaction

Organo‐modified montmorillonites and poly(p‐dioxanone) (PPDO) diol prepolymers were used to prepare Poly(p‐dioxanone)‐PU/organic montmorillonite (PPDO‐PU/OMMT) nanocomposites by chain‐extending reaction. The crystallization behavior and spherulitic morphology of PPDO‐PU/OMMT nanocomposites were investigated by WXRD, differential scanning calorimetry, and polarized optical microscopy. The results show that the regularity of the chain structure plays a dominant role during the crystallization process rather than that of OMMT content and its dispersion status in PPDO matrix. With similar molecular weight and same OMMT content, PPDO‐PU/OMMT nanocomposite, which derived from lower molecular weight PPDO prepolymer, exhibits lower crystallization rate, melting point, and crystallinity. The influence of the clay content on the crystallization behavior highly depends on its dispersing state. The nucleating effect of OMMT can be only observed at high loading percentage. For the nanocomposites with low clay loading percentage, the retarding effect of exfoliated platelets on the chain‐ordering into crystal lamellae became the key factor. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigation of readily processable thermoplastic-toughened thermosets. III. Toughening BMIs and epoxy with a comb-shaped imide oligomer

This is the third in a five-part series describing the preparation of tough, high-performance thermosets from low viscosity, autoclave-processable prepolymers. The first 2 articles described toughening of bismaleimides (BMI) and epoxy with linear imide thermoplastics of ∼ 1000 g/mol. Highly processable prepolymers were obtained, which resulted in increases in fracture toughness for BMI of ∼ 75–100%, while the fracture toughness of epoxy was increased by up to 220%. This article describes the preparation of a low-molecular-weight comb-shaped imide oligomer (∼ 4100 g/mol) and the effect of the oligomer architecture and end-group on BMI and epoxy prepolymer viscosity and fracture toughness. When an unreactive comb-shaped oligomer was incorporated in a BMI prepolymer (10% thermoplastic loading in the thermoset), the fracture toughness increased by 67% over that of an untoughed control, while a reactive oligomer increased the fracture toughness by 150% over an untoughened control. At 55°C, the viscosity of the solution of the reactive comb-shaped imide in B was only 6.2 Pa · S. When the oligomer was dissolved in epoxy resin, the viscosity was less than 0.2 Pa · S at 90°C, and the fracture toughness increased by 110 and 133% (at ∼ 13% loading in the thermoset), relative to an untoughened control, depending on the reactivity of the end group. The T_g and high-temperature modulus of BMI and epoxy remained approximately the same relative to the untoughened controls. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 943–951, 1998     

Oligomeric poly(ether‐imide)s bearing ortho trifluoromethyl groups: Solubility,thermal studies,and optical properties

In the development of processable high‐temperature materials, six new aromatic poly(imide)s based on diamines containing ortho trifluoromethyl groups, ether linkages and R,R‐methylenes moieties (R = Me or Ph) and previously reported dianhydrides have been synthesized vía polycondensation reactions. All polymers were obtained with good yields, were soluble in a variety of polar aprotic solvents, and exhibited inherent viscosity (η_inh) values between 0.15 and 0.20 dL g^?1, which is indicative of low molecular‐weight species. Preliminary studies of their physical properties were carried out. The new materials were transparent in the visible region and they exhibited thermal decomposition temperatures ranging from 475 to 545 °C and glass‐transition temperatures varying from 288 to 304 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46613.     

Effect of coupling agent and filler particle size on melt rheology of polymer-bonded Nd-Fe-B magnets

The effect of coupling agents and filler particle size on melt rheology of poly(phenylene sulfide)-bonded neodymium-iron-boron (Nd-Fe-B) alloy magnets was studied with oscillatory flow experiments to accelerate efforts to optimize their processing. The minimum viscosity of the polymer-bonded magnets near 290°C was obtained with Nd Fe B fillers (106–150 particle size range) that were coupled with a silane coupling agent. All the samples tested followed power-law fluid flow behavior. Morphological and dynamic mechanical analysis of the samples showed that the beneficial function of the coupling agent may be ascribed to enhanced wetting of the magnetic Nd Fe B powders by the polymer, improving the processability of the polymer bonded magnets.     

Organosoluble polyimides derived from asymmetric 2‐substituted‐and 2,2′,6‐trisubstituted‐4,4′‐oxydianilines

We report a new method for the preparation of asymmetric diamines using 4,4′‐oxydianiline (4,4′‐ODA) as the starting material. By controlling the equivalents of bromination agent, N‐bromosuccinimide, we were able to attach bromide and phenyl substituents at the 2‐ or 2,2′,6‐positions of 4,4′‐ODA. Thus, four new asymmetric aromatic diamines, 2‐bromo‐4,4′‐oxydianiline (6), 2,2′,6‐tribromo‐4,4′‐oxydianiline (7), 2‐phenyl‐4,4′‐oxydianiline (8) and 2,2′,6‐triphenyl‐4,4′‐oxydianiline (9), were synthesized by this method. Their structural asymmetry was confirmed using ¹H NMR spectroscopy. Asymmetric polyimides (PI10–PI13) were prepared from these diamines and three different dianhydrides (pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride) in refluxing m‐cresol. The formed polyimides, except PI10a derived from 6 and PMDA, were all soluble in m‐cresol without premature precipitation during polymerization. These polyimides with inherent viscosity of 0.41–0.96 dL g^?1, measured at a concentration of 0.5 g dL^?1 in N‐methyl‐2‐pyrrolidone at 30 °C, can form tough and flexible films. Because of the structural asymmetry, they also exhibited enhanced solubility in organic solvents. Especially, polyimides PI11a and PI13a derived from 7 and 9 with rigid PMDA were soluble in various organic solvents at room temperature. The structural asymmetry of the prepared polyimides was also evidenced from ¹H NMR spectroscopy. In the ¹H NMR spectrum of PI11a, the protons of pyromellitic moiety appeared in an area ratio of 1:2:1 at three different chemical shifts, which were assigned to head‐to‐head, head‐to‐tail and tail‐to‐tail configurations, respectively. These polyimides also exhibited good thermal stability. Their glass transition temperatures ranged from 297 to 344 °C measured using thermal mechanical analysis. © 2013 Society of Chemical Industry     

Viscosities of unsaturated polyester resins: Combining effects of prepolymer structure,resin composition,and temperature

The effects of temperatures, styrene concentration, and molecular composition of unsat-urated polyester (UP) prepolymers on the viscosity of UP-styrene systems are studied. The viscosity of UP resins follows the Arrhenius-type expression with resin temperature as well as with the styrene molar fraction of the resin. The two Arrhenius correlations can be combined into a simple dual-Arrhenius equation by combination rule. This dual-Arrhenius equation comprises pseudo viscosity parameters of styrene monomer and UP prepolymer, respectively. The pseudo viscosity parameters of styrene monomer are experimentally found constant; while those of UP prepolymer seem to be number-average molecular weight correlated rather than weight-average molecular weight correlated. The UP prepolymers having different molecular structures show different pseudo viscosity parameters due to their own molecular interaction parameters. The pseudo viscosity parameters of UP'prepolymers should be determined experimentally for the time being. © 1996 John Wiley & Sons, Inc.     

The synthesis of lactic-acid-based telechelic prepolymers

We have studied how different catalysts and diols affect the properties of low-molecular-weight (M_w (GPC) < 49800 g/mol) lactic-acid-based telechelic prepolymers. The catalysts and diols were tested separately in our previous studies. In this study, we used the best previously tested diols and catalysts together in order to prepare different types of telechelic prepolymers (for example, crystalline or amorphous). All condensation polymerizations were carried out in the melt, using different diols and different catalysts. The prepolymers were characterized by differential scanning calorimetry, gel permeation chromatography, titrimetric methods, and ¹³C nuclear magnetic resonance (¹³C-NMR). According to NMR, the resulting polymers contained less than 1 mol % of lactic acid monomer and less than 5.1 mol % of lactide. Dibutyltindilaurate, like tin(II)octoate, produced quite good molecular weights, but the resulting prepolymers contained exceptionally high amounts of D-lactic acid structures, and, therefore, these prepolymers were totally amorphous. Antimony(III)oxide produced a high-molecular-weight prepolymer when the diol used was aliphatic. Like DBTL, Sb₂O₃ produced amorphous prepolymers, which contained a lower amount of D-lactic acid structures than DBTL prepolymers. 1,8-dihydroxyanthraquinone produced a different kind of chain structure with Ti(IV)bu and Ti(IV)iso because one prepolymer had high crystallinity, and the other showed only a slight crystallinity. Sulphuric acid produced a very high-molecular-weight prepolymer with aliphatic 2-ethyl-1,3-hexanediol; and with aromatic diols, it produced quite good molecular weights, except with 1,8-dihydroxyanthraquinone. High-molecular-weight prepolymers produced with H₂SO₄ also showed high crystallinity; and, according to ¹³C-NMR, they did not contain lactide and D-lactic acid structures. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1011–1016, 1998     

Solid-state polymerization of poly(ethylene terephthalate)

Solid -state polymerization of poly(ethylene terephthalate) (PET) is carried out by heating the low molecular weight prepolymer at temperatures below its melting point but above its glass transition temperature. Postcondensation occurs and the condensation byproducts can be removed by applying vacuum or inert gas. Polymers obtained usually have high molecular weight, low carboxyl and acetaldehyde content, and can be used for beverage bottle or industrial yarns. Polyesters for textile purposes are manufactured by a melt process. Chemical reactions involved in the solid state polymerization are transesterification, esterification, as well as the diffusion of byproducts. Overall reaction rate was governed by the molecular weight, carboxyl content of prepolymer, crystallinity, particle size, reaction temperature, and time. Prepolymer for solid state polymerization should have intrinsic viscosity 0.4 dL/g or more, density 1.38 g/mL, and minimum dimension 3 mm or less. The reaction temperature could be 200–250°C. When textile grade PET is used as prepolymer, crystallization at 180–190°C for 1–2 h increases the density to 1.38 g/mL. Polymerization at 240–245°C for 3–5 h can raise the intrinsic viscosity to 0.72 dL/g and carboxyl content less than 20 meq/kg. Appropriate reaction conditions are subject to the properties of prepolymers and the design of reactors. Reactor used for solid state polymerization could be vacuum dryer type or stationary bed. The former is suitable for a small capacity and is run batchwise. The latter is a continuous process and is economically feasible for large -scale production.     

Self‐reinforcing isotactic polypropylene prepared using crystallizable solvents

A new approach to reinforce and toughen isotactic polypropylene (iPP) with improved processability is evaluated. The concept involves using a crystallizable solvent that, at process temperatures melts, is miscible with the polymer thereby reducing its process viscosity. As the polymer cools, the solvent undergoes thermally induced phase separation (TIPS) to produce crystallites that increase the modulus of the solid through reinforcement and promote an increase in impact resistance by mechanisms similar to rubber‐toughened materials. Tetrabromobisphenol‐A (TBBPA) is introduced to iPP that forms a homogeneous mixture at elevated temperature and acts as a processing aid, but undergoes phase separation and subsequent crystallization upon cooling to form rigid particles which, in turn, acts as a toughening agent at room temperature. A phase diagram constructed with Flory‐Huggins solution thermodynamics shows good agreement with the experimental results. The steady state shear viscosity decreases as TBBPA content increases for the mixtures in melt state, indicating improved processability. The decrease in viscosity enhances crystallization rate of iPP significantly, most likely due to increased diffusivity, while the structure of iPP crystals remain unchanged. Tensile tests show that as TBBPA content increases (up to 15 wt %), the yield stress decreases while elongation at break increases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Solid state polymerization of bisphenol A polycarbonate: Effect of the crystallization method and polymerization conditions

A study on the effect of the crystallization method on the solid state polymerization (SSP) process of bisphenol A polycarbonate has been performed. Prepolymer samples were crystallized via four different techniques (solvent induced, shear induced, organic salt induced, and thermal crystallization) and SSP progress was checked by measuring the molecular weight increase. The fastest polymerization rate was obtained with prepolymers crystallized with acetone. The reaction rates were correlated with the crystallinity and plasticization of solvents, which both affected the chain mobility. The experiments conducted using different sweep gas flow rates and different particle sizes showed that, for the acetone‐crystallized prepolymers, the reaction rate was limited by the by‐product diffusion inside the polymer particles and from the surface of the particles into the sweep gas. ¹H‐nuclear magnetic resonance analysis proved that polymers prepared through a solid state process had a consistently lower content of Fries rearrangement by‐products with respect to commercial samples obtained by standard melt polycondensation methods. POLYM. ENG. SCI., 55:1024–1029, 2015. © 2014 Society of Plastics Engineers     

Catalyzed chain extension of poly(butylene adipate) and poly(butylene succinate) with 2,2′‐(1,4‐phenylene)‐bis(2‐oxazoline)

Low‐molecular‐weight HOOC‐terminated poly(butylene adipate) prepolymer (PrePBA) and poly(butylene succinate) prepolymer (PrePBS) were synthesized through melt‐condensation polymerization from adipic acid or succinic acid with butanediol. The catalyzed chain extension of these prepolymers was carried out at 180–220°C with 2,2′‐(1,4‐phenylene)‐bis(2‐oxazoline) as a chain extender and p‐toluenesulfonic acid (p‐TSA) as a catalyst. Higher molecular weight polyesters were obtained from the catalyzed chain extension than from the noncatalyzed one. However, an improperly high amount of p‐TSA and a high temperature caused branching or a crosslinking reaction. Under optimal conditions, chain‐extended poly(butylene adipate) (PBA) with a number‐average molecular weight up to 29,600 and poly(butylene succinate) (PBS) with an intrinsic viscosity of 0.82 dL/g were synthesized. The chain‐extended polyesters were characterized by IR spectroscopy, ¹H‐NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, wide‐angle X‐ray scattering, and tensile testing. DSC, wide‐angle X‐ray scattering, and thermogravimetric analysis characterization showed that the chain‐extended PBA and PBS had lower melting temperatures and crystallinities and slower crystallization rates and were less thermally stable than PrePBA and PrePBS. This deterioration of their properties was not harmful enough to impair their thermal processing properties and should not prevent them from being used as biodegradable thermoplastics. The tensile strength of the chain‐extended PBS was about 31.05 MPa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis,characterization and crosslinking of functional star‐shaped poly(ε‐caprolactone)

Star‐shaped low molecular weight poly(ε‐caprolactone)s (PCLs) were synthesized and functionalized with crosslinkable terminal groups for subsequent crosslinking. The ε‐caprolactone (CL) prepolymers were polymerized by ring‐opening in the presence of polyglycerine (PGL) as an initiator (1, 3 and 5 mol%) and Sn(II)2‐ethylhexanoate as a catalyst. Characterization of the prepolymer by ¹³C/¹H nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) revealed a six‐armed star‐shaped structure for the prepolymer with the molecular weight controlled by the ratio of PGL and CL. Functionalization of the hydroxyl‐terminated prepolymer was carried out with maleic or itaconic anhydride. In both cases, the characterization of the functionalized prepolymer showed that the hydroxyl groups were completely substituted. The functionalized PCLs were successfully crosslinked through the reaction of double bonds. The crosslinking was induced either thermally with organic peroxide or photochemically with a photosensitive initiator. Characterization of the crosslinked PCLs by Soxhlet extraction, DSC and FTIR showed that the itaconic double bond was much more reactive in thermal crosslinking than the maleic double bond. Thus, the crosslinked prepolymers that were functionalized with itaconic double bonds achieved a gel content of about 90%. A gel content of 100% was achieved with several compositions where crosslinking agents were employed. © 2002 Society of Chemical Industry     

Hydrophilic drug release from bioerodible polyanhydride microspheres

The present investigation was carried out to develop bioerodible drug delivery systems. Copolymers of fumaric anhydride and isophthalic anhydride were synthesized by melt polycondensation. To synthesize a copolymer with known composition, soluble in common organic solvents, a prepolymer of each monomer was first prepared. Copolymers were synthesized by mixing two prepolymers followed by melt polycondensation of the resulting mixture with a specific ratio of each prepolymer. Microspheres loaded with theophylline and diltiazem hydrochloride (DHC) were obtained using the solvent removal method in an oil‐in ‐oil (O/O) emulsion system. The size of the drug loaded microspheres was less than 75 μm, which is suitable for subcutaneous or intramuscular injection. DHC was incorporated in a polymeric carrier better than theophylline because of its solubility in chloroform and dichloromethane. In vitro release of two drugs in the phosphate buffer solution indicated that the release profile of DHC was closer to a zero‐order kinetic profile compared with theophylline. Finally, drug release data was compared with three semiempirical models. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1457–1464, 2002