CHAIN EXTENSION OF MALEIC ANHYDRIDE END-CAPPED POLY(1,2-CYCLOHEXYLENE CARBONATE) BY BISOXAZOLINES
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Poly(1,2-cyclohexylene carbonate) (PCHC) was prepared by copolymerization of carbon dioxide and cyclohexene oxide with Y(CCl(3)OO)(3)-ZnEt(2)-glycerin rare earth metal coordination ternary catalyst. The result polymer showed number average molecular weight (M(n)) of 56.3 x 10(3) with polydispersity index of 4.9. Though PCHC showed high glass transition temperature (T(g)), PCHC was easy to degrade during melt processing, accompanied by severe deterioration of its mechanical performance, which constituted one of the main obstacles for commercialization of PCHC. In order to impove the thermal stability and mechanical properties of PCHC, the thermal decomposition reaction was compensated by the chemical chain extension reaction. At first, maleic anhydride was used as end-capper of PCHC to prevent its chain unzipping reaction, the MA and PCHC in weight ratio of 1:100 were added into dichloromethane to make a 20 wt% solution,and refluxed at 41 similar to 43 degrees C for 48 h, then the polymer was precipitated by ethanol to obtain maleic anhydride end-capped PCHC (MA-PCHC). MA-PCHC was then subjected to chain extension reaction at 180 degrees C and 60 r/min in the a Haake mixer for 5 min using 2,2'-bis (2-oxazoline) (BOZ) as chain extender. The optimal chain extension condition was found when equimolar BOZ and carboxyl group in MA-PCHC were used, the M. of MA-PCHC increased from 5. 6 x 10(4) to 12. 4 x 10(4). The thermal stability of PCHC after chain extension was greatly improved,compared with the as-polymerized PCHC, the thermal decomposition temperature at 5 wt% loss (T(d-5%)) for chain extended PCHC increased from 260 C to 317 C, the Tg increased from 114 degrees C to 133 degrees C, and most importantly, the melt viscosity increased by 30 times. It should be noted that no significant change in gelatin content was observed during chain extension reaction. Moreover, the chain extended PCHC showed tensile strength increase from 35. 8 MPa (as polymerized PCHC) to 40. 2 MPa, and the elongation at break increased from 4. 59% to 6. 22%, yielding phenomenon was observed in the stress-strain curve. Therefore, the chain extension strategy was effective to improve the mechanical performance of PCHC.Keywords:
Maleic anhydride
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Cyclohexene oxide
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High molecular weight poly (lactic acid) (PLA) was obtained by chain extending with hexamethylene diisocyanate (HDI). The influences of the amount of chain extender, reaction time, and molecular weight changes of prepolymers on the poly(lactic acid) were investigated. PLA prepolymer with a viscosity, average molecular weight (M η M w M n T g α ′ α
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The aim of this research was to modify polyamide 6 (PA6) either starting from low molecular weight end modified polymer or high molecular weight commercial grade by solution and/or solid-state polymerization (SSP) without destroying the crystalline phase. Synthetic approach consisted of first molecular mixing of all components in a common solvent preferably followed by SSP below the melting temperature of the PA6. By this way, modification of the backbone occurs in the amorphous phase which is the only mobile part of the polymer at those temperatures. By SSP reactions blocky microstructures are formed instead of random copolymers. In this study, modification of PA6 was mainly done for two purposes: for improved biodegradability and for better properties such as increased Tg. In the first part oligoesters were incorporated in the low molecular weight PA6 chain as hydrolyzable blocks which as a result provide degradability. For this aim two different synthetic routes were followed. The first one was done by making use of isocyanate and amine end groups which are highly reactive already at room temperature. Low molecular weight totally amine end-capped PA6 and totally isocyanate end-capped polycaprolactone diol were synthesized and reacted during the solution mixing in hexafluoroisopropanol (HFIP). High molecular weight multi-block copolymers of PA6-PCL were obtained which were susceptible to degradation either hydrolytically or enzymatically. The second route consisted of base-catalyzed diepoxide oligoester (DEPA)- and low molecular weight carboxyl end-capped PA6 reactions to obtain partially degradable polyesteramides by solution mixing in HFIP followed by complete removal of the solvent and finally SSP. Firstly, model reactions were performed by using polypropylene glycol diglycidyl ether to determine the optimum reaction conditions and later DEPA was used. Here, side reactions and crosslinking prevented obtaining high molecular weight multi-block copolymers as a result of very complicated nature of epoxide-carboxyl reactions. However, multi-block copolymers were achieved consisting of a few blocks of PA6 and oligoester. In the second part of the research, a commercial grade of PA6 was modified with a ‘Nylon salt’ of 1,5-diamino-2-methylpentane (Dytek A) and isophthalic acid (IPA). This modification was also done in the solid state after solution mixing of the salt and PA6. Different amounts of salt were used and melt polymerizations were also performed for comparison. Salt incorporation occurs via aminolysis and acidolysis of PA6. Therefore, in the first stages of the reaction a dramatic decrease in molecular weight is observed which later starts increasing. It was first observed that due to a loss of the volatile diamine mostly acidolysis was taking place which means chain scission by the incorporation of the diacid but not the diamine. This resulted in acid end groups and prevented further increase in molecular weight. For that reason another method was developed to keep the diamine in the mixture. Not only the reaction temperature was lowered but also the reaction was performed in a totally closed environment under Argon until all the diamine was incorporated via aminolysis. In the second stage the reaction temperature was increased and continuous Argon flow was applied to remove the condensation water produced by coupling of the broken chains. This method indeed provided higher molecular weights than before. Molecular and microstructural analysis was done in detail by SEC, 1H and 13C NMR whereas thermal analysis was done by TGA and DSC. Detailed comparison with melt-polymerized random polymer-salt copolymers was performed. It was observed that after SSP reactions the crystalline phase of the PA6 was kept intact while amorphous phase was modified. The degrees of randomness were calculated from NMR and blocky structures were confirmed. Melting points comparable to neat PA6 were achieved and higher Tg values were obtained.
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Figure melt torque of PA6 mixed with different contents of chain extender BGPPO. The addition of small molecule diepoxide (BGPPO) greatly enhanced the melt torque, rheological and mechanical properties of polyamide-6 through chain extension reaction.
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The chain extension reaction in poly(butylene terephthalate) (PBT) melt was studied in detail. A high-reactivity diepoxy, diglycidyl tetrahydrophthalate, was used as a chain extender that can react with the hydroxyl and carboxyl end groups of PBT at a very fast reaction rate and a relatively high temperature. A Haake mixer 600 was used to record the torque during the chain extension reaction. The data show that this chain extension reaction could be completed within 2 to 3 min at temperatures above 250°C, and the reaction time decreased very fast with an increase in the temperature. Shear rate also had some effects on the reaction rate. The effect of the diepoxy chain extender on the flowability, thermal stability, and mechanical properties of PBT were investigated. The melt flow index (MFI) of the chain-extended PBT dramatically decreased as the diepoxy was added to PBT. In addition, the notched Izod impact strength and elongation-at-break of the chain-extended PBT also increased. The chain-extended PBT is more stable thermally. Compared with the conventional solid post-polycondensation method, this approach is simpler and cheaper to obtain high-molecular-weight PBT resins.
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Epoxide nitrile butadiene rubber (ENBR) was prepared via in situ epoxidation from nitrile butadiene rubber (NBR) with acetic acid and hydrogen peroxide. ENBR had been selectively hydrogenated in the presence of a homogeneous Wilkinson catalyst. The hydrogenated epoxide nitrile butadiene rubber (EHNBR) and ENBR were characterized by infra-red and proton nuclear magnetic resonance. No change was noted in the epoxy content of the polymer after the reaction. The catalyst is highly selective in reducing carbon-carbon double bonds in the presence of epoxy groups. DSC analysis reveals the Tg of ENBR varied linearly with molar epoxide content and the Tg value increased by 0.82 °C per mol%. It also found that the introduction of epoxy groups can effectively reduce the extent of crystallization by impairing the regularity of the molecular chain, but crystalline structure was difficult to completely eliminate. Therefore, anhydrides were selected as ring-opening reagents to react with epoxy groups in EHNBR. The products, branched EHNBR, were characterized by infra-red and proton nuclear magnetic resonance. The conversion rate of the epoxide group was calculated by 1H NMR. The glass transition temperature of EHNBR-g-heptyl group was -34.1 °C, and its DSC curve demonstrated no crystal structure. The coefficient of cold resistance under compression of EHNBR grafted propyl ester was 0.36, which represented a superior low-temperature performance. Furthermore, residual epoxy groups and ester groups extremely enhanced the oil resistance of HNBR.
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In this study, the synthesis of poly(ethylene furanoate) (PEF), catalyzed by five different catalysts-antimony acetate (III) (Sb Ac), zirconium (IV) isopropoxide isopropanal (Zr Is Ip), antimony (III) oxide (Sb Ox), zirconium (IV) 2,4-pentanedionate (Zr Pe) and germanium (IV) oxide (Ge Ox)-via an industrially common combination of melt polymerization and subsequent solid-state polymerization (SSP) is presented. In all reactions, proper amounts of 2,5-dimethylfuran-dicarboxylate (DMFD) and ethylene glycol (EG) in a molar ratio of DMFD/EG= 1/2 and 400 ppm of catalyst were used. Polyester samples were subjected to SSP procedure, under vacuum application, at different reaction times (1, 2, 3.5, and 5 h) and temperatures of 190, 200, and 205 °C. Carboxyl end-groups concentration (⁻COOH), intrinsic viscosity (IV), and thermal properties, via differential scanning calorimetry (DSC), were measured for all resultant polymers to study the effect of the used catalysts on the molecular weight increase of PEF during SSP process. As was expected, it was found that with increasing the SSP time and temperature, the intrinsic viscosity and the average molecular weight of PEF steadily increased. In contrast, the number of carboxyl end-groups content showed the opposite trend as intrinsic viscosity, that is, gradually decreasing during SSP time and temperature increase. It is worthy to note that thanks to the SSP process an obvious and continuous enhancement in the thermal properties of the prepared PEF samples was attained, in which their melting temperatures (Tm) and degree of crystallinity (Xc) increase progressively with increasing of reaction time and temperature. To predict the time evolution of polymers IV, as well as the hydroxyl and carboxyl content of PEF polyesters during the SSP, a simple kinetic model was developed. From both the theoretical simulation results and the experimental measurements, it was demonstrated that surely the Zr Is Ip catalyst shows the best catalytic characteristics compared to all other used catalysts herein, that is, leading in reducing-in a spectacular way-the activation energy of the involved both transesterification and esterification reactions during SSP.
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Abstract The effect of prepolymer molecular weight on the solid‐state polymerization (SSP) of poly(bisphenol A carbonate) was investigated using nitrogen (N 2 ) as a sweep fluid. Prepolymers with different number–average molecular weights, 3800 and 2400 g/mol, were synthesized using melt transesterification. SSP of the two prepolymers then was carried out at reaction temperatures in the range 120–190 °C, with a prepolymer particle size in the range 20–45 μm and a N 2 flow rate of 1600 mL/min. The glass transition temperature ( T g ), number–average molecular weight ( M n ), and percent crystallinity were measured at various times during each SSP. The phenyl‐to‐phenolic end‐group ratio of the prepolymers and the solid‐state synthesized polymers was determined using 125.76 MHz 13 C and 500.13 MHz 1 H nuclear magnetic resonance (NMR) spectroscopy. At each reaction temperature, SSP of the higher‐molecular‐weight prepolymer ( M n = 3800 g/mol) always resulted in higher‐molecular‐weight polymers, compared with the polymers synthesized using the lower molecular weight prepolymer ( M n = 2400 g/mol). Both the crystallinity and the lamellar thickness of the polymers synthesized from the lower‐molecular‐weight prepolymer were significantly higher than for those synthesized from the higher‐molecular‐weight prepolymer. Higher crystallinity and lamellar thickness may lower the reaction rate by reducing chain‐end mobility, effectively reducing the rate constant for the reaction of end groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4959–4969, 2008
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Cyclic butylene terephthalate oligomers (CBT) were reacted in a ring-opening polymerization with three types of isocyanates: a bifunctional aromatic type, a bifunctional aliphatic type and a polymeric aromatic isocyanate.All reactions took place in a batch mixer.The use of 0.5 to 1 wt% isocyanate led to a dramatic increase in elongation at break of polymerized cyclic butylene terephthalate (pCBT), from 8 to above 100%.The stiffness and strength of the modified pCBT, however, were found to slightly decrease.Proton nuclear magnetic resonance (NMR) analysis shows that the formation of thermally stable amide groups is the dominant chain extension reaction mechanism.Gel content measurements suggest a linear structure for samples containing bifunctional isocyanates while pCBT modified with polyfunctional isocyanate exhibited some gel formation at higher isocyanate content.Melting and crystallization temperatures as well as degree of crystallinity were found to decrease with increasing isocyanate content.No phase separation was detected by scanning electron microscopy (SEM) analysis.Moreover, a high degree of polymerization is deduced due to the absence of CBT oligomer crystals.
Isocyanate
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