Showing papers in "Journal of Polymer Science Part A in 1995"

Synthesis and barrier properties of poly(ε‐caprolactone)‐layered silicate nanocomposites

Abstract: A new polymer-ceramic nanocomposite has been synthesized consisting of well-dispersed, two-dimensional layers of an organically modified mica-type silicate (MTS) within a degradable poly(e-caprolactone) matrix. A protonated amino acid derivative of MTS was used to promote delamination/dispersion of the host layers and initiate ring-opening polymerization of e-caprolactone monomer, resulting in poly(e-caprolactone) chains that are ionically bound to the silicate layers. The polymer chains can be released from the silicate surface by a reverse ion-exchange reaction and were shown to be spectroscopically similar to pure poly(e-caprolactone). Thick films of the polymer nanocomposite exhibit a significant reduction in water vapor permeability that shows a linear dependence on silicate content. The permeability of nanocomposite containing as low as 4.8% silicate by volume was reduced by nearly an order of magnitude compared to pure poly(e-caprolactone)

Molecular characterization of maleic anhydride-functionalized polypropylene

Abstract: This work deals with the molecular characterization of maleic anhydride melt-functionalized polypropylene (PP-g-MA). The functionalization mechanism, the nature, the concentration, and the location of grafted anhydride species onto the polypropylene chain are discussed. The polypropylene functionalization was performed using a pre-heated Brabender Plastograph (190 degrees C, 4 min of mixing time). Several concentrations of maleic anhydride and organic peroxide were used for this study. In those experimental conditions, the organic peroxide undergoes an homolytic rupture and carries out a polypropylene tertiary hydrogen abstraction. The resulting macroradical undergoes a beta-scission leading to a radical chain end which reacts with maleic anhydride. When a termination reaction occurs at this first step a succinic type anhydride chain end is obtained. However, oligomerization of maleic anhydride is found to occur more frequently leading to poly( maleic anhydride) chain end. Concentration of both anhydride types and minimal length of the grafted poly(maleic anhydride) were determined. A fraction of maleic anhydride does not react with polypropylene or homopolymerize leading to nongrafted poly(maleic anhydride). (C) 1995 John Wiley and Sons, Inc.

Studies on the Chemical Syntheses and on the Characteristics of Polyaniline Derivatives

Abstract: SYNOPSIS Syntheses of parent polyaniline and methyl, methoxy, and ethoxy ortho-substituted polyanilines were performed using the conventional chemical methodology and monitored using the new open-circuit-potential ( V,) profile technique. The intermediate pernigraniline oxidation state was identified and isolated at the V,,, maximum (A) during the conventional chemical synthesis of poly(o-methoxyaniline) in the emeraldine oxidation state. The introduction of the substituent on the aniline ring leads to longer polymerization times and lower V,, values. Syntheses in the presence of two different monomers in solution were also investigated and showed preferential polymerization of the monomer with the lowest V, potential. All polymers produced were characterized by elemental analysis, gel permeation chromatography, UV-VIS spectroscopy, and cyclic voltammetry. The influence of the substituent on the V,, profile and on the polymer characteristics are rationalized in terms of steric and electronic effects. 0 1995 John Wiley & Sons, Inc.

Chemical treatment of membranes of a polymer blend: Mechanism of the reaction of hypochlorite with poly(vinyl pyrrolidone)

Abstract: Sodium hypochlorite solutions are used to treat membranes prepared from a polymeric blend containing poly(vinyl pyrrolidone) (PVP) to increase their water permeability. Sodium hypochlorite affects the membrane material in such a way that PVP is selectively removed from the membrane matrix. The mechanism of the reaction between hypochlorite and PVP is investigated by several chemical analysis techniques of the reaction products. Strong indications are found that the reaction involves chain scission of PVP according to a radical mechanism.

Close loop mechanistic schemes for hydrocarbon polymer oxidation

Abstract: Mechanistic schemes of radical oxidation of hydrocarbon polymers in which initiation is only due to unimolecular or bimolecular hydroperoxide decomposition have been studied. The results of their kinetic analysis have been compared with literature data relative to the thermal oxidation of polypropylene in solid state (60-160 o C). These data are in remarkably good agreement with the «unimolecular» scheme whose main characteristics are: (1) the quasi-independence of the kinetic behavior with initial conditions (for low initial content of thermolabile structures), and (2) the fact that an arbitrarily defined induction period depends only on the rate constant of unimolecular hydroperoxide decomposition

Factors affecting propagating fronts of addition polymerization: Velocity, front curvature, temperatue profile, conversion, and molecular weight distribution

Abstract: Several properties of propagating fronts of addition polymerization were studied. A power function could be fit to the velocity dependence on initiator concentration, but not with the exponents predicted by current models or in agreement with other published work. Bubbles from the volatile by-products of initiator decomposition were found to affect the front velocity and curvature. The front velocity for triethylene glycol dimethacrylate polymerization was found to depend linearly on temperature over a moderate range. The conversion of methacrylic acid in fronts varied greatly with initiator type and concentration. Benzoyl peroxide produced much lower conversion than t-butyl peroxide, but fronts with tBPO propagated slower. A dual initiator system of BPO and tBPO produced rapidly propagating fronts with good conversion but the contribution of each initiator to the velocity was not additive. The possibility of chain branching was considered. The apparent molecular weight distributions were very broad, often trimodal, and found to depend on initiator type and concentration as well as the tube diameter. The temperature profiles were measured and found to be very sharp for BPO and broader for tBPO but both had front temperatures in excess of 200°C, indicating a high ceiling temperature. © 1995 John Wiley & Sons, Inc.

Molecular weight distributions of linear polymers: Detailed analysis from GPC data

Abstract: The GPC method is used widely to measure molecular weights of linear polymers. High-quality GPC data contains detailed information on many aspects of the polymer's molecular weight distribution (MWD). This information can be extracted from the data using computer analysis. Equations have been derived for the two simplest MWD functions in the GPC coordinates: the Flory function (one growing polymer chain produces one polymer molecule), and for the case when two polymer radicals combine into one polymer molecule. The equations were used to analyze MWD of two classes of polymers. The first class includes polymers with narrow MWD: polyethylene, ethylene-propylene and ethylene-hexene copolymers, syndiotactic polystyrene, and radical polystyrene. The second class includes polymers with broad MWD: ethylene copolymers and polypropylene produced with heterogeneous, Ti-based catalysts. The examples demonstrate that the resolution of complex GPC curves into their constitutents serve as an important source of information about kinetics of polymerization reactions. © 1995 John Wiley & Sons, Inc.

Propene polymerization using homogeneous MAO‐activated metallocene catalysts: Me2Si(Benz[e]Indenyl)2ZrCl2/MAO vs. Me2Si(2‐Me‐Benz[e]Indenyl)2ZrCl2/MAO

Abstract: SYNOPSIS Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me2Si(Benz[elIndenyl)2ZrCI2 (BI) and rac-Me2Si(2-Me­ Benz[elIndenyl)2ZrCl2 (MBI). Catalyst BI/MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI/MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI/MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both me­ tallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H 2-addition, which affords active metallocene hydrides. This effect of H 2addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1. 7 with respect to propene. MBI/MAO shows a much higher dependence of the activity on temperature than BI/MAO. At elevated temperatures, MBI/MAO polymerizes propene faster than BI/ MAO.

Vacuum‐ultraviolet induced oxidation of the polymers polyethylene and polypropylene

Abstract: The emission from low-pressure microwave plasmas in the vacuum-ultraviolet (VUV) region (X < 200 nm) was investigated in order to use these plasmas as light sources for the study of the VUV photochemistry of polyethylene (PE) and polypropylene (PP) as part of the study of plasma-polymer interaction. These polymers, immersed in low-pressure oxygen, were exposed to radiation with wavelengths down to 112 nm, the cutoff of magnesium fluoride used as a window to separate the polymer specimen from the plasma light source. Total oxygen incorporation in the surface [O], and the formation of hydroxyl, carbonyl, and carboxyl groups were measured using XPS in combination with chemical derivatizations, particularly their dependence upon the radiation spectrum and the oxygen pressure around the sample. In most experiments the surface oxygen concentration [O] attained a constant value that appears to be related to the initial oxidation rate ; this suggests a competition between oxygen incorporation and chain scission reactions, followed by the removal of volatile oxidation products. PE is usually oxidized to a higher level than PP, the latter appearing to be more susceptible to reaction with atomic oxygen than PE. A general initiation mechanism for the VUV experiments is proposed that allows us to explain the observed differences in behavior between PE and PP, and the results obtained under different irradiation conditions. The nature of oxidation products is in both cases very similar to what is observed after direct plasma treatment of the polymers. We conclude that short wavelength radiation contributes very appreciably to the observed surface modification effects during plasma treatment of PE and PP.

Propylene polymerization through supported metallocene/ MAO catalysts: Kinetic analysis and modelling

Abstract: Several propylene polymerizations are carried out with supported metallocene catalyst, prepared by reaction of silica gel with methylaluminoxane and then with rac-dimethylsilanediylbis(indenyl)zirconiumdichloride. The rate-time curves obtained are analyzed to understand the influence of support and triisobutylaluminium on the reaction. As a first attempt to model this system we developed a partially new particle growth model, based on a shell by shell fragmentation hypothesis (gradual break-up from the outside to the inside of the particle), and a final multigrain structure of the particle. A kinetic scheme including the TIBA interaction with the supported catalyst is also presented. The model prediction and the experimental data are compared for the rate-time curves and polymer properties.

Synthesis and degradabilities of polyesters from 1,4:3,6‐dianhydrohexitols and aliphatic dicarboxylic acids

Abstract: Six different polyesters (6a–6c and 7a–7c) were prepared by the bulk polycondensations of the respective combinations of 1,4:3,6-dianhydro-D-glucitol (3) and 1,4:3,6-dianhydro-D-mannitol (4) with succinyl dichloride (5a), glutaryl dichloride (5b), and adipoyl dichloride (5c) at 140–180°C. Polyesters having number average molecular weights up to 2.6 ×104 were obtained in high yields. Only polyester 7a based on 4 and 5a was partially crystalline, whereas all the other polyesters were amorphous. Thin films of these polyesters except that of 7a were spontancously hydrolyzed in a neutral phosphate buffer solution at 50°C, whereas they were reluctant to be hydrolyzed at 27°C. The polyesters were more or less degraded at 27°C by treatment with an activated sludge or by prolonged burial in soil. © 1995 John Wiley & Sons, Inc.

Synthesis, structure, and thermal properties of epoxy‐imide resin cured by phosphorylated diamine

Abstract: New phosphorylated epoxy-imide polymer was obtained using diimide-diepoxide (DIDE) cured with bis(3-aminophenyl)methylphosphine oxide (BAMP). In addition, composition of the synthesized diimide-diepoxide (DIDE) with common curing agents, e.g., 4,4′-diaminodiphenylether (DDE) and 4,4′-diaminodiphenylsulfone (DDS), were used for making a comparison of its curing reactivity, heat and flame retardation with that of bis(3-aminophenyl)methylphosphine oxide. The reactivity of those curing agents toward epoxy-imide, as measured by differential scanning calorimetry (DSC), was of the order DDE > BAMP > DDS. Through the evaluation of thermal gravimetric analysis (TGA), the new phosphorylated epoxy-imide polymer demonstrated excellent thermal properties as well as a high char yield. © 1995 John Wiley & Sons, Inc.

Fundamental studies of grafting reactions in free radical copolymerization. II. Grafting of styrene, acrylate, and methacrylate monomers onto cis-polybutadiene using AIBN initiator in solution polymerization

Abstract: Grafting can be initiated by primary and/ or polymer radical attack on the backbone polymer and it is well known that AIBN does not readily promote grafting, even when using poly-butadiene. We have studied the grafting of several different monomers onto cis-polybuta-diene using AIBN initiator and find dramatically different results among the monomers. As expected, styrene grafts at very low levels due to the inactivity of the initiator radicals and the polystyryl radicals. Methacrylate monomer grafts at a slightly higher level due to its more reactive polymer radical, while acrylate monomer readily grafts onto the poly-butadiene because polyacrylate radicals are quite reactive. The use of a kinetic model allowed the evaluation of rate coefficients for graft site initiation to be in the relative order of 0.1 : 1.0 : 10.0 (L/mol/s) for styrene:methacrylate:acrylate monomers. The model also pro-vided successful interpretations of the grafting data and its dependence upon the concen-trations of monomer, initiator, and backbone polymer. Due to the relatively higher reactivity of the polyacrylate radicals, the benzene solvent acted as a chain transfer agent in this system. This affected the molecular weight of both free and grafted acrylate polymer and also surpressed the graft level. Polyacrylate radicals attack the cis-polybutadiene backbone by abstracting an allylic hydrogen and also adding across the residual double bond. The latter mechanism is responsible for the majority of the grafting; the hydrogen abstraction leads to relatively inactive radicals which cause a retardation in the overall reaction rate. © 1995 John Wiley & Sons, Inc.

Electrochemical and structural studies on soluble and conducting polymer from o‐phenylenediamine

Abstract: A conducting polymer, poly(o-phenylenediamine) (PoPD), has been obtained as stable film onto an electrode surface by the electropolymerization of o-phenylenediamine in 0.1 mol dm -3 H 2 SO 4 . The film thickness did not exceed 0.85 μm because of its low electrical conductivity. The virgin doped polymer film was soluble in dimethylsulfoxide, N,N-dimethylformamide, acetone, and tetrahydrofuran without any pretreatment. The highest solubility obtained was 17 g dm -3 in dimethylsulfoxide. A cast film of PoPD on a substrate was prepared from its dimethylsulfoxide solution. The mean molecular weight of PoPD was found to be 11,000 with the gel permeation chromatography. The STM observation exhibited that the cast film was considerably uniform compared to the electrodeposited film. The cyclic voltammogram of such film showed a reversible redox property accompanied with excellent electrochromism between transparent yellow and brown. It was suggested from the 1 H-FTNMR and FTIR spectra and the elemental analysis that the polymeric backbone has 1,4-substituted benzenoid-quinoid structure. ® 1995 John Wiley & Sons, Inc.

Dispersion copolymerization of styrene and divinylbenzene: Synthesis of monodisperse, uniformly crosslinked particles

Abstract: Monodisperse, crosslinked polystyrene latexes were prepared by the dispersion technique. Some general observations regarding the effect of initial reagent concentrations on final particle size and size distribution are offered, in addition to a detailed discussion concerning the problems encountered with the use of the crosslinker divinylbenzene (DVB) in latex preparation. Particles synthesized in very polar media were found to reach their growth plateau sooner than those made in less polar surroundings. This trend was proposed to be the result of more effective nucleation in polar environments, which increases available surface area, thereby allowing the rapid replacement of monomer consumed within the particle phase during the polymerization. Attempts to favorably influence the growth rate and size distribution of particles during the reaction were unsuccessful, underlining the importance of the nucleation period in defining particle size characteristics. Up to 1% DVB was successfully incorporated in the synthesis of coagulum-free, monodisperse, 5 μm beads, by controlling the entry of the crosslinker into the particle phase during the major particle growth period. Latex stability is proposed to be largely dependent on the mobility of the adsorbed steric stabilizer. © 1995 John Wiley & Sons, Inc.

Miniemulsion polymerization of styrene: Evolution of the particle size distribution

Abstract: The mechanism of the miniemulsion polymerization of styrene was investigated through a combination of calorimetry to monitor the polymerization rate and transmission electron microscopy (TEM) to follow the evolution of the particle size distribution. These techniques proved to be a powerful combination for gaining detailed mechanistic information regarding these polymerizations. Particle size analysis of the latexes withdrawn during the course of the reaction revealed that most of the polymer particles were formed by a relatively low conversion (i.e., 10% conversion). However, nucleation continued well past this point (to 40-60% conversion). In fact, it was observed that nucleation in miniemulsion polymerizations using cetyl alcohol continued past the maximum in the rate of polymerization. As a result of these long nucleation periods, the latex particle size distributions produced from these miniemulsion polymerizations were broader than their conventional emulsion polymerization counterparts, and were negatively skewed with a tail of small particles. The amount of negative skewing of the particle size distributions was found to decrease with increasing initiator (potassium persulfate) concentration. Finally, a correlation was observed between the length of time to the maximum polymerization rate and the breadth of the particle size distribution as reflected in the standard deviation

Fundamental studies of grafting reactions in free radical copolymerization. I. A detailed kinetic model for solution polymerization

Abstract: Graft site initiation occurs by primary radical and/ or polymeric radical attack on the back-bone polymer. The controlling mechanism is determined by the structure of the backbone and the activity of the free radicals. The efficiency of incorporating monomer into the graft chains depends upon the graft site initiation mechanism and the mode of polymer chain termination (recombination or disproportionation). A kinetic analysis results a series of uniquely different expressions describing the graft efficiency, ϕ corresponding to different combinations of graft site initiation and chain termination mechanisms. The dependency of ϕ upon monomer, initiator, and backbone concentrations is different from case to case. The complete kinetic model is capable of predicting reaction rate, graft efficiency, graft frequency, graft ratio, and molecular weight averages and distributions. Simulations are provided to compare predicted results with experimental data for two different systems which show contrasting mechanisms of graft site initiation and mode of termination. © 1995 John Wiley & Sons, Inc.

Poly-3-Hydroxyalkanoates containing unsaturated repeating units produced by pseudomonas oleovorans

Abstract: Poly-3-hydroxyalkanoates (PHAs) containing repeating units with terminal alkene substituents at the 3-position were produced by Pseudomonas oleovorans grown with either 7-octeneoic acid [OA()] alone, or 10-undeceneoic acid [UND()] alone, or mixtures of UND() and either nonanoic acid (NA) or octanoic acid (OA). For the latter, the biomass and PHA yields decreased as the fraction of UND() increased in the mixed carbon substrates. Essentially all of the repeating units in the PHA obtained from cells grown with UND() alone contained terminal alkene groups, including 3-hydroxy-10-undeceneoate, 3-hydroxy-8-noneneoate, and 3-hydroxy-6-hepteneoate units, but less than half of the units in the PHA from OA() had alkene substituents. The PHAs obtained from cells grown with various mixtures of UND() and either OA or NA were random copolymers, and the fraction of units with alkene substituents in these polymers increased in proportion to the fraction of UND() in the mixed carbon substrates. © 1995 John Wiley & Sons, Inc.

Mechanistic study of the reactivity of 3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexancarboxylate in photoinitiated cationic polymerizations

Abstract: An investigation of the reactivity of the cycloaliphatic diepoxide, 3,4-epoxycyclohexyl 3′, 4′-epoxycycloexane carboxylate (I) in photoinitiated cationic polymerization was carried out with the aid of model compounds. It was shown that the presence of the ester group greatly retards the rate of polymerization of this bisepoxide. Molecular modeling studies indicate that the ester carbonyl group can interact in a number of ways with the initially formed protonated or alkylated oxiranium cation to give bicylic dialkoxycarbenium ions. These latter species are both more sterically hindered and less reactive than the oxiranium cation precursors and undergo propagation at a considerably reduced rate. Reactivity studies em-ploying model compounds also showed that epoxy monomers that contain ester groups undergo polymerization at much slower rates than those in which the ester group is absent. © 1995 John Wiley & Sons, Inc.

Dispersion polymerization in polar solvents

Abstract: The effect of the nitrogen purge, monomer purification, type of agitation, and presence of costabilizer on the particle size distribution (PSD) was investigated in the dispersion po-lymerization of styrene in ethanol and in the dispersion copolymerization of styrene and butyl acrylate in a water–ethanol mixture. Purging with nitrogen and, to a lesser extent, monomer purification, were of paramount importance to achieve monodispersity. The type of agitation had a week effect on the PSD, whereas the presence of costabilizer had no effect on the PSD. © 1995 John Wiley & Sons, Inc.

Polymers of carbonic acid. XIV. High molecular weight poly(trimethylene carbonate) by ring‐opening polymerization with butyltin chlorides as initiators

Abstract: Numerous BuSnCl 3 - , Bu 2 SnCl 2 - , and Bu 3 SnCl-initiated polymerizations of cyclo(trimethylene carbonate) (TMC) were conducted in bulk. In addition to the initiator, reaction time, temperature, and monomer/initiator (M/I) ratio were varied. Yields above 90% were obtained with all three initiators, but their reactivities decrease in the order BuSnCl 3 > Bu 2 SnCl 2 > Bu 3 SnCl. The maximum molecular weights decrease in the same order. With BuSnCl 3 M w s up to 250,000 were obtained. These molecular weights were determined by GPC on the basis of the universal calibration method. In this connection Mark-Houwink equations for two solvents, tetrahydrofuran (THF) and CH 2 Cl 2 were determined and compared with literature data. Furthermore, mechanistic aspects were studied. 1 H- and 13 C-NMR spectra revealed that BuSnCl 3 forms complexes with the CO-group of TMC, whereas Bu 2 SnCl 3 and Bu 3 SnCl do not cause NMR spectroscopic effects. Kinetic studies in chloroform and nitrobenzene and a comparison with Bu 3 SnOMe suggest that at least BuSnCl 3 initiates a cationic mechanism. However, in contrast to SnCl 4 (or SnBr 4 ), BuSnCl 3 does not cause decarboxylation. Regardless of the initiator 1 H-NMR spectroscopy revealed CH 2 OH and CH 2 Cl endgroups in all cases.

The synthesis and study of the photoinitiated cationic polymerization of novel cycloaliphatic epoxides

Abstract: The synthesis of a series of difunctional epoxides bearing two epoxycyclohexyl groups linked together by an alkylene ether group has been carried out. Subsequently, the reactivities of these novel monomers was investigated and compared to the reactivity of the cycloaliphatic epoxide, 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate (I) in photoinitiated cationic polymerization. It was observed that alkylene oxide linking the two epoxycyclohexyl groups was short and the monomers are more reactive than I. The effects of the photoinitiator structure and the experimental conditions of the cationic photopolymerization on the rates was also studied using real-time infrared spectroscopy. 1995 John Wiley & Sons, Inc.

Phosphoric acid diesters protonated polyaniline: Preparation, spectroscopic properties, and processability

Abstract: Aliphatic and aromatic diesters of phosphoric acid were tested as dopants improving pro-cessability of polyaniline (PANI) in its doped (conducting) state. It has been found that both aromatic and aliphatic diesters effectively protonate polyaniline, inducing at the same time its solubility. The protonated state has been confirmed by three independent spec-troscopic methods (FTIR, Raman, and UV-vis-NIR). Both aromatic and aliphatic diesters of phosphoric acid plasticize polyaniline which, in turn, allows for the preparation of highly conducting films of PANI or highly conducting blends of PANI with classical nonconducting polymers by thermal processing. © 1995 John Wiley & Sons, Inc.

Chain extension of polyesters PET and PBT with N,N′‐bis (glycidyl ester) pyromellitimides. I

Abstract: Three N,N'-bis(glycidyl ester imide)s of pyromellitic acid (diepoxides) were prepared and were used as chain extenders for poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT). The typical reaction conditions for the coupling of the polyester macromolecules were heating with the chain extender under argon atmosphere above the melting temperature (280°C for PET and 250°C for PBT) for several minutes. The characterization of the samples, obtained at variable residence times in the reactor, was based on solution viscosity measurements and carboxyl and hydroxyl end-group determinations. Two of the diepoxides used gave satisfactory results. Starting from a PET having intrinsic viscosity [η] = 0.60 dL/g, and carboxyl content CC = 42 eq/10 6 g, one could obtain PET with [η] = 1.15 dL/g and CC = 16 eq/10 6 g within 30 min at 280°C. Analogous results were observed for PBT. The hydroxyl content of polyester in all cases was increased. When the quantity of the chain extender used was higher than that theoretically required for its reaction with all carboxyl end groups of the polyester, this resulted in some gel formation indicative of crosslinking. © 1995 John Wiley & Sons, Inc.

Reversible photodimerization of coumarin derivatives dispersed in poly(vinyl acetate)

Abstract: Four photoreactive coumarin derivatives were successfully synthesized from 7-hydroxy-coumarin and 7-hydroxy-4-methylcoumarin, i.e., 7-propionyloxy-4-methylcoumarin (M1), 7-palmitoyloxy-4-methylcoumarin (M2), 7-propionyloxycoumarin (M3), and 7-palmitoy-loxycoumarin (M4). Reversible photodimerization (350 or 300 nm) and photocleavage (254 nm) of these coumarin derivatives dispersed in poly(vinyl acetate) (PVAc) were investigated by tracing their UV absorbance variations at 310 nm. The M2 and M4 with long palmitoyl chain show much better photoreaction reversibility than M1 and M3 with short propionyl chain. Moreover, photodimerization rate (under 350 nm) of M2 is greater than 200 times of that of M1. This has been explained by the formation of suitable conformation for revers-ible photodimerization due to the hydrophobic interactions. Photodimerization of M2 is ca. 3 times quicker than that of M4, indicating 4-methyl substitution enhances pho-todimerization. The influence of photodimerization wavelength (350 and 300 nm) and photosensitizer (benzophenone) have also been investigated in detail. © 1995 John Wiley & Sons. Inc.

Surface graft polymerization of glycidyl methacrylate onto polyethylene and the adhesion with epoxy resin

Abstract: Surface graft polymerization of glycidyl methacrylate (GMA) was carried out onto a high- density polyethylene (PE) sheet pretreated with corona to introduce peroxides onto the PE surface. Graft polymerization of GMA was effected by UV irradiation of the coronatreated PE in the presence of monomer solution without the use of any photosensitizer. The graft layer was found by staining the PE cross section to localize in the surface region of PE. The physical change in the PE surface was characterized by scanning electron microscopy, while the chemical changes due to the GMA graft polymerization were assessed by the dynamic contact angle, FT-IR, and x-ray photoelectron spectroscopy (XPS) measurement. The peroxide formation by corona exposure was confirmed by the XPS measurement after derivatization with SO2. The epoxy groups introduced onto the PE surface by the GMA graft polymerization were reactive with water (in the presence of HCI) and amines. The adhesion between the GMA-grafted PE and an epoxy resin was studied by means of a shear strength test method. The GMA-grafted PE exhibited strong interfacial adhesion with the epoxy resin, compared to the original and corona-treated PE. The adhesion strength of the GMA-grafted PE was nearly two times higher than that of the corona-treated PE. This strongly suggests that the enhanced adhesion between the surface-grafted PE and the epoxy resin is ascribed to covalent bonding of the epoxy groups on the GMA-grafted surface to the amines in the epoxy resin. © 1995 John Wiley & Sons, Inc.

Perfluorocyclobutane aromatic ether polymers. II. Thermal/ oxidative stability and decomposition of a thermoset polymer

Abstract: The results of thermal and oxidative stability studies are reported for one perfluorocyclo-butane aromatic ether thermoset polymer. The polymer was prepared from 1,1,1-tris (4-trifluorovinyloxyphenyl)ethane by the thermal cyclodimerization of the trifluorovinyl either functionality, resulting in a network polymer comprising alternating perfluorocy-clobutane and aromatic either groups. The results of isothermal and dynamic thermal gravimetric analysis (TGA) studies are reported with kinetic approximations for de-composition in nitrogen, along with FTIR studies of the oxidative process in air and TGA/mass spec determination of the gasses evolved from decomposition in air. Based on these results, thermal and oxidative decomposition mechanisms are proposed. © 1995 John Wiley & Sons, Inc.

Biodegradable polymers derived from natural fatty acids

Abstract: A new class of polyanhydrides synthesized from nonlinear hydrophobic fatty acid esters, based on ricinoleic, maleic acid, and sebacic acid, possessed desired physico-chemical and mechanical properties for use as drug carriers. The polymers were synthesized by melt condensation to yield film-forming polymers with molecular weights exceeding 100,000. Their rate of elimination from rats in the course of about 2 months was faster than that found for similar polyanhydrides previously tested. In vitro studies showed that these polymers underwent rapid degradation in the first 10 days. The drug release followed first-order kinetics, showing a rapid drug release rate in the first 10 days which correlated with the degradation of the polymers. The fatty acid ester monomers underwent in vitro enzymatic degradation to the natural starting acids. Tests in rats demonstrated their toxicological inertness and biodegradability. © 1995 John Wiley & Sons, Inc.