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An hierarchical structure, composed of a ternary cocontinuous polymer blend, where carbon nanotubes are mostly localized in one of the phases through π–π interactions, is fabricated by direct melt mixing of polyamide 12 and polypropylene, as the two major components of the ternary blend, together with pyridine-modified poly(ethylene-co-methacrylic acid) as the minor component that can form strong interactions with the CNTs via π–π interactions and confined the percolated network at the polyamide/polypropylene interface. The hierarchical structure was designed by means of surface energies, and the obtained morphology was verified using electron microscopy. This ternary structure has lower electrical resistivity as compared to cocontinuous binary composites. Different polymer viscosities were used in this study in order to emphasize the importance of kinetics during cocontinuous morphology formation.

In this paper, we report on the production of modified pullulan derivatives that have been produced in solution by ring-opening e-caprolactone and [l]-lactide using a tin octanoate [Sn(Oct)2] catalyst system in DMSO. These derivatives designated as hexanoates (1 and 2) and dilactates (4−7) have been characterized and have varying degrees of substitution (DS). 1 and 2 were characterized by interesting thermal properties as well as crystalline morphology. From DSC analysis, 2, unlike the parent polysaccharide, appears to melt at 114 °C. The crystalline morphology of this polymer was characterized by X-ray powder diffraction and d spacings were calculated. This pullulan derivative possessed new crystallographic reflections not seen in either pullulan or poly (e-caprolactone). The pullulan-6 dilactate samples (4−7), produced had DS values ranging from 0.1 to 0.75. Depending upon the DS, these samples were soluble in a wide range of organic solvents including acetone and methanol. Although these materials did ...

This paper explores the copolymerization of l-lactide (l-LA) with 2,2-[2-pentene-1,5-diyl]trimethylene carbonate (cHTC). Since cHTC has a cyclohexene group, this provided a route for preparing poly(lactic acid), (PLA), based chains decorated with controlled quantities of CC substituents. Ring-opening copolymerizations of l-LA with cHTC were successfully conducted in bulk by using AlR3−H2O (R = ethyl, isobutyl), Al(OiPr)3, ZnEt2−H2O and Sn(Oct)2 as catalysts. Comparison of these copolymerizations showed that the Sn(Oct)2 catalyst system gave copolymers of relatively higher molecular weight. Increasing the reaction time of Sn(Oct)2 catalyzed copolymerizations from 6 to 24 h resulted in higher copolymer cHTC content and yield but lower copolymer molecular weight. Variation of the comonomer feed ratio was useful in regulating the content of cyclohexene pendant groups in the copolymer. However, regardless of the catalyst used, the mole percent of cHTC incorporated into the copolymer was lower than that used in...

[l]-Lactide ([l]-LA)/ethylene oxide (EO) ring-opening copolymerizations were successfully carried out by using various catalysts including isobutylaluminoxane (IBAO), in situ AlR3·0.5H2O systems (R = ethyl, isobutyl) and Sn−Al bimetallic catalysts. Analysis of products by 1H NMR showed that methanol insoluble copolymer fractions had multiblock structures. The multiblock segment length and molecular weight of the copolymers were regulated by a variation in the reaction temperature, reaction time, reaction medium, and the catalyst structure. An increase in the reaction temperature was used to obtain shorter segment block lengths. Bulk reactions at elevated temperatures gave shorter block lengths than those of corresponding polymerizations conducted in solution (xylene). Differential scanning calorimetry (DSC) results showed two melting transitions corresponding to poly(ethylene oxide) (PEO) and [l]-polylactide ([l]-PLA) crystalline phases. The melting temperature and enthalpy of fusion for the phase-separat...

Pentene-1,5-diyl)trimethylene carbonate (cHTC) was synthesized from cyclohexene- 4,4-dimethanol in high yield (>80%). This new carbonate monomer was successfully ring-open polymerized to form P(cHTC) in bulk at 90 °C using various organometallic catalysts including aluminoxanes (methyl and isobutyl), BunSnCl4-n (n ) 1, 2, 3), BunSn(OMe)4-n (n ) 2, 3), ZnEt2, and ZnEt2-H2O. Comparison of these systems showed that the Zn- and Al-based catalysts were preferred for the preparation of high molecular weight polymers in yields g89% and reaction times of e8 h. For the BunSnX4-n catalysts investigated, values of n ) 1w hen Xi s Cl and n )2 when X is OMe resulted in relatively greater polymerization rates and higher polymer molecular weights. The effects of reaction time and monomer/ catalyst molar ratio were investigated for the Al and Zn catalysts. An outcome of this study was determining that the ZnEt2-H2O (1/0.5) catalyst for a monomer/catalyst (M/C) molar ratio of 400 and a 2 h reaction time gave a product withMn )276 000 in 98% yield. The P( c HTC) products were characterized by FTIR, 1 H-NMR, 13 C-NMR, DSC, TGA, and GPC. NMR results showed that c HTC decarboxylation did not occur during chain propagation. P( c HTC) has a moderate glass transition temperature (Tg ) 30 °C) with high thermal stability. 13 C NMR at 62.5 MHz did not resolve chain diad sequences although the polymers are likely atactic. Epoxidation of P( c HTC) vinyl side groups was carried out to various extents by using 3-chloroperoxybenzoic acid at room temperature.

Polylactide (PLA) stereocopolymers with (l) repeat unit contents of 75%, 80%, 82%, 85%, 90%, 91%, 92%, 94%, and 95% were prepared from mixtures of (l)-/(d)-lactide and (l)-/meso-lactide. Compression molding of these products gave amorphous films which, for (l) contents ≥90%, were also annealed above Tg to crystallize. Analyses by differential scanning calorimetry and wide angle X-ray scattering gave information on the crystalline order of PLA films. For identical (l) contents, stereocopolymers of (l)-/(d)-lactide had higher crystallinities than those from (l)-/meso-lactide. PLA films were incubated with proteinase K (from Tritirachium album), and the enzyme-catalyzed film weight loss rates were measured. Film crystallinity, chain stereochemical composition, and repeat unit sequence distribution were analyzed as independent variables affecting film enzymatic hydrolysis. Amorphous films from (l)/(d)-lactide copolymerizations with (l) compositions ranging from 80% to 95% exhibited film weight loss rates that...

Chitosan films were acylated under heterogeneous conditions in methanol with acetic and hexanoic anhydrides and characterized by proton nuclear magnetic resonance, elemental analysis, and multiple internal reflective Fourier transform infrared spectroscopy. The disappearance of the NH2 vibrational band at 1590 cm-1, the appearance of the amide II band at 1555 cm-1, and the relatively low intensity of the ester band at 1735 cm-1 showed that acylation at the surface was site-selective for the amino (N) functionalities. Furthermore, N-acylation at the surface region appeared complete within 1 h. The acylated chitosan films were fractionated in aqueous acetic acid for compositional analysis. Acetylation of chitosan films for 3 h gave 52% of aqueous acetic acid insoluble chitin (outer film region) and 48% unreacted chitosan. In contrast, 3 h hexanoylation reactions resulted in 99% aqueous acetic acid soluble product. Thus, film N-acetylation was more rapid than N-hexanoylation. Moreove...

Polymerization of racemic α-methyl-β-propiolactone (MPL) was carried out using Zn-, Sn-, La-, Y-. and Al-based organometallic catalysts. It was found that Zn(C2H5)2/H2O (1/0.6), (nC4H9)2Sn(OCH3)2, Al(OiC3H7)3, and (C2H5)2AlOC2H5 produced atactic poly(α-methyl-β-propiolactone) (PMPL), whereas (nC4H9)3SnOCH3 and Y(OiC3H7)3 formed PMPL of low isotacticity with isotactic (i) diad fractions between 0.53 and 0.56. Since the Sn-based catalysts were syndioregulating for β-methyl-β-propiolactone (BL) polymerizations, placement of the lactone methyl substituent at the α- instead of the β-position alters steric interactions between the incoming monomer and the Sn catalyst−chain end so that syndioaddition is no longer preferred. Isobutylaluminoxane (IBAO) produced a PMPL sample that can be separated by acetone into two fractions: an acetone-insoluble (AI) PMPL fraction of high isotacticity (i-diad fraction 0.85) and high molecular weight (Mn = 662 000 g/mol) and an acetone-soluble (AS) PMPL fraction of low isotactic...

Polylactide (PLA) with % L repeat unit contents of 100 (PLA-100), 99, 96, 94, 92, 85, 80, 75, 70, 50, and 0 were prepared and films of these samples were prepared by solution casting and then annealing at 75°C for 36 h to crystallize. Large changes in the crystalline order for PLA with % L compositions between BS and 100% were observed by DSC and WAXS measurements. The PLA films were incubated with proteinase K (from Tritrachium album) to determine enzyme-catalyzed rates of both film weight loss and initial surface degradation. Proteinase K preferentially degraded (L)-PLZA as opposed to (D)-PLA. Optimal rates for both film weight loss and initial surface degradation were found for PLA-92

Bis(tri-n-butyltin) oxide ((n-Bu 3 Sn) 2 O), bis(triphenyltin) oxide (Ph 3 Sn) 2 O), and di-β-butyltin dimethoxide (Sn(n-Bu) 2 (OCH 3 ) 2 ) were all shown to catayze the syndiospecific polymerization of racemic butyrolactobe ((±)-BL). Of these catalysts, the Sn(n-Bu) 2 (OMe) 2 system showed dramatically decreased polymerization times for correspondingly high monomer conversion. This catalyst system was used to form syn-PHB with an M n and syndiad fraction of 8.4x10 4 and 0.62, respectively.

In this report, we havedocumented the ability of tributyltin methoxide, SnBu30CH1, to catalyze the ring-opening polymerization of 0-butyrolactone, BL, with a preference for syndiotactic (syn) placement. This has therefore resulted in the chemical synthesis of a new stereoisomeric form of poly(0-hydroxybutyrate), PHB, specifically syn-PHB, which has predominantly alternatingR and S stereocenters. The polymerization of racemic BL catalyzed by SnBu30CH3 was carried out at temperatures of 40,60,75, and 90 "C. The yields of hexane/ether (l/l) insoluble PHB ranged from 24 to 69%, with the highest yield for the polymerization temperature of 75 "C. An analysis of the stereochemical sequence distribution for the syn-PHB stereoisomers by '"C NMR allowed the degree of syndiotacticity achieved as a function of the polymerization conditions to be quantitated. Thus, it was determined that the racemic (r) diad fractions were 0.70,0.66,0.63, and 0.61 for the polymerization temperatures of 40, 60, 75, and 90 "C, respectively. Therefore, the degree of syndiotacticity decreased for higher polymerization temperatures, as was anticipated; however, the degree of change was unexpectedly small over the 50 "C temperature range investigated. The M, values of the syn-PHB samples ranged between approximately 2500 and 5300 and were determined both by lH NMR spectroscopy end group analysis (after derivatization of the products with diazomethane) and by VPO. These M,, values were approximately 72% of that calculated by the assumption that the number of polymer chains is equivalent to the number of moles of catalyst added. In addition, by analysis using 'H NMR of the number of methyl ester end groups which were present on the syn-PHB samples before and after diazomethane derivatization, it was determined that the ratio of carboxylic acid to methyl ester end groups ranged from 2.5 to 3.1. These results suggest that lactone polymerization by SnBu30CH3 is not solely initiated by an insertion mechanism between the tin-methoxide bond. The syn-PHB polymers when isolated by solution precipitation and analyzed by DSC showed three distinct endotherm component peaks with peak temperatures of approximately47,62, and 79 "C where the dominant endotherm component was, in all cases, at approximately 62 "C. Dramatic changes in the endothermic melting transitions were observed when the samples were melt annealed as opposed to solution precipitated. The X-ray diffractogram for the 70-syn-PHB sample and the calculated d-spacings were compared to those of natural-origin (R)-PHB. Specific d-spacings measured at 7.52,5.40,3.83, and 3.11 A for the 70-syn-PHB sample were not observed for (R)-PHI3 end are evidence for the existence of a different crystalline structure than that determined for an isotactic PHB stereoisomer. FTIR analysis of the 70-syn-PHB sample revealed spectral features which were unique to the conformational order and crystalline structure of this new PHB stereoisomer. Specifically, the appearance of a new band at approximately 1206 cm-I, with a notable increase in the spectral absorption band at approximately 1103 cm-I.

In this study, we have prepared poly(Beta-hydroxybutyrate), PHB, random stereocopolymers from beta-butyrolactone, BL, using a diethylzinc/water (1.0/0.6) catalyst system. (R)-and (S)-BL were synthesized in high enantiomeric purity (>98% ee(enantiomeric excess), and approximately 5% racemization occurred at the methine stereocenters upon polymerization. The PHB stereoisomers produced had R repeat unit compositions of 95, 90, 85, 81, 77, 67, and 50%. In addition, a 50% (R)-PHB stereoisomer with a predominantly syndiotactic repeat unit placement was prepared in our laboratory. The relative degradability of these PHB stereoisomers was studied with a PHB depolymerase enzyme isolated from Penicillium funiculosum. This enzyme has been shown to catalyze the hydrolysis of (R)-PHB, but does not show activity for the enantiomeric substrate (S)-PHB.