Solid‐state polymerization of poly(ethylene terephthalate). III. Thermal stabilities in terms of the vinyl ester end group and acetaldehyde

Poly(ethylene terephthalate) (PET), precursors, and solid‐stated samples were evaluated in terms of changing vinyl ester (VE) concentrations. The results obtained through the application of reaction kinetics gave VE contents ranging from 0.7 to 5.5 mmol/kg of PET. As the initial intrinsic viscosity (IV) of the precursor increased, the VE content also increased, representing the different thermal histories of the samples during melt‐phase polymerization. The VE contents decreased as the solid‐state polymerization (SSP) time increased from 0 to 12 h and as the temperature of SSP increased up to 220°C. A series of acetaldehyde (AA) generation experiments were conducted from 270 to 300°C with samples solid‐stated from three precursors with different initial IVs. The rate of AA generation decreased as the final IV of the solid‐stated PET increased, and this showed that the SSP process improved the thermal stability of PET. The AA generation rates of samples that had similar final IVs but were solid‐stated from different IV precursors were also compared. When the heating temperature was low, the amount and rate of AA generation were higher for samples with higher initial precursor IVs. This tendency, however, became less clear as the generation temperatures increased, probably because interference from the dissociation reactions (occurring between the polymer chains to produce VE) increased with increasing temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 228–237, 2003     

Continuous production of polyester‐poly(ethylene terephthalate) resins in melt‐phase and solid‐state reactors

A simple reaction model has applied net polycondensation rates to predict the steady‐state performance of three distinct continuous processes for manufacturing polyester‐PET resins. A net melt‐phase polycondensation rate was described by the simple second‐order kinetics. A net solid‐state polycondensation rate was assumed to follow the modified second‐order kinetics with respect to active end group concentration. A moving‐packed bed requires a longer residence time to deal with the diffusion‐limited SSP of standard pellets or challenging pastilles. The calculations and data showed low IV pastilles to have much slower diffusion‐controlled SSP rates than medium IV pellets. The tanks‐in‐series model demonstrated a narrow RTD in a gas fluidization bed with five mixing stages. Higher reaction temperatures may significantly increase the low diffusion resistance SSP rates of smaller beads or micro‐pellets in a gas‐fluidized reactor. The reaction‐controlled SSP of micro‐beads becomes apparent at 230°C. The high IV melt resins may challenge the slow reaction rates of Ti or Al‐catalyzed SSP resins. The efficacy of catalyst promoters on Ti activity enhancement may depend upon various ligands in Ti glycolate, Ti citrate, or titanic acid. The thermo‐oxidative stability of Ti or Al‐catalyzed resins may decrease at higher hot air drying temperatures (188°C or above). POLYM. ENG. SCI., 57:505–519, 2017. © 2016 Society of Plastics Engineers     

Post‐extrusion solid‐state polymerization of fully drawn polyester yarns

Post‐extrusion solid‐state polymerization (SSP) of a commercial fully drawn filament yarn (FDY) of poly(ethylene terephthalate) was carried out at 220°C, 230°C, and 240°C for a duration of 30 min to 2 h under inert atmosphere. Molecular weight of the solid‐state polymerized polyester filaments was increased from 1.67 × 10⁴ gm/mol to a maximum of 2.61 × 10⁴ gm/mole for the sample subjected to 240°C for 2 h. The kinetics of the SSP in the highly oriented crystalline FDY polyester filaments was investigated using an empirical relation between initial molecular weight and time of SSP and was found to be greatly enhanced, compared to amorphous unoriented polyester chips. Though the free annealing (i.e., under no tension) of samples at high temperature during solid‐state polymerization had a detrimental effect on the orientation of the FDY yarn, the simultaneous increase in the molecular weight compensated the loss in mechanical properties to a great extent. Application of tension during SSP was found to improve the mechanical properties of the SSP yarn by a small value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5113–5122, 2006     

A physicochemical route for compensation of molecular weight loss during recycling of poly(ethylene terephthalate)

This work is aimed to undertake the simultaneous effect of chain extension (chemical modification) and solid‐state polymerization (SSP) on the structural properties of recycled poly(ethylene terephthalate) to compensate the molecular weight (MW) losses caused by thermal degradation. This hybrid technique was qualified by tracking changes in the MW, intrinsic viscosity (IV), and concentrations of hydroxyl and carboxylic groups of various samples containing different concentrations of chain extender that experienced different residence times (2, 4, 6, 8, and 10 h) and different SSP process temperatures (190, 200, and 210°C). It was found that at high concentrations of chain extender, thermal degradation is facilitated owing to the lack of functional groups, as witnessed by a sharp drop in the MW and IV. The re‐recycled poly(ethylene terephthalates) experienced chemical modification followed by SSP physical treatment and revealed a rise in MW and IV. Accordingly, the synergistic effect of hybrid modification in comparison with the individual chemical modification was highlighted. J. VINYL ADDIT. TECHNOL., 22:387–395, 2016. © 2015 Society of Plastics Engineers     

Chain extension reaction in solid‐state polymerization of recycled PET: The influence of 2,2′‐bis‐2‐oxazoline and pyromellitic anhydride

Conventional and chain extended‐modified solid‐state polymerization (SSP) of postconsumer poly(ethylene terephthalate) (PET) from beverage bottles was investigated. SSP was carried out at several temperatures, reaction times, and 2,2′‐bis‐2‐oxazoline (OXZ) or pyromellitic anhydride (ANP) concentrations. The OXZ was added by impregnation with chloroform or acetone solution. Higher molecular weights were reached when the reaction was carried out with OXZ, resulting in bimodal distribution. The molecular weights of the flakes reacted at 230°C for 4 h were 85,000, 95,000, and 100,000 for samples impregnated with 0, 0.5, and 1.25 wt % OXZ solution, respectively. In the case of reactions with ANP, branched chains were obtained. The thermal and thermal‐mechanical‐dynamic properties of these high‐molecular‐weight recycled PET were determined. For OXZ‐reacted samples, the reduction of crystallinity was observed as the reaction time was increased, becoming evident the destruction of the crystalline phase. The chain extended samples did not show changes in thermal relaxations or thermal degradation behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of PTT/clay nanocomposites with solid‐state polymerized polytrimethylene terephthalate

To enhance the effectiveness of polytrimethylene terephthalate (PTT) for the preparation of clay‐based nanocomposites by melt intercalation and to upgrade the mechanical performance of these materials, solid‐state‐polymerization (SSP) experiments with neat PTT were carried out at 190, 200, and 210°C prior compounding to increase the average molecular weight and, based on this, the melt viscosity of this polymer. The progress of SSP was registered by time dependent sampling of intrinsic viscosity data. From this, activation energy of 180.6 kJ mol^?1 was calculated. A characteristic sublimate formed during these SSP‐reactions was identified by mass‐spectroscopy to be a mixture of cyclic oligomers containing 2, 3, 4, and 5 monomeric units. The melt viscosity of neat PTT(SSP) could be increased from ～ 460 to 15,000 Pa s^?1. Therefore, tensile strength and Young's modulus were improved by 3.5 and 9%, respectively. Manufacturing of PTT(SSP) and the modified nanoclay was carried out with a corotating twin‐screw‐extruder at 230°C. A concentration of 3% of the inorganic filler component in the composites was aimed at. Compared with the data of virgin PTT, tensile strength, and modulus of the PTT(SSP)‐based nanocomposites could be enhanced by ～ 9 and 40%, respectively. Additionally, a SSP‐reaction of the nanocomposite prepared with non‐pretreated PTT and nanoclay was performed at 210°C to test the robustness of the matrix polymer PTT against the influences of the nanofiller. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of high‐molecular weight aliphatic polyesters from monomers derived from renewable resources

A series of high‐molecular weight aliphatic polyesters have been synthesized, at temperatures of < 200°C, through a polycondensation reaction between 1,4‐butanediol and three diacids of different chain length (succinic acid, azelaic acid, and sebacic acid). All the polyesters obtained have a bio‐based content of 100% and number average molecular weight in the range of 28,000–116,000 Da. These average molecular weights are about 5–10 times higher than those of most reported aliphatic polyesters synthesized through similar reaction routes but at temperatures > 230°C. The over‐heating phenomenon, i.e., the observation of thermal degradation behavior of these polyesters at 230°C is reported. The crystallization behavior, mechanical properties, and enzymatic hydrolysis rate of the polyesters obtained are characterized. Poly(butylene succinate) (PBSu) shows the highest crystallinity and melting temperature, but the lowest thermal stability and slowest potential rate of enzymatic biodegradation rate compared with poly(butylene azelate) and poly(butylene sebacate). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40579.     

Thermal polymerization of styrene

An experimental investigation of the kinetics of bulk thermal polymerization of styrene in the temperature range of 200°–230°C is reported. Conversions and molecular weight averages were measured by gel permeation chromatography. At elevated temperatures, oxygen in the polymerization mixture appears to have negligible effect on the rate of polymerization and the molecular weights of the polymer. Experimental evidence suggests that the molecular weight development of the polymer is strongly influenced by transfer reactions.     

Polyamide solid state polymerization: Evaluation of pertinent kinetic models

Nylon 6,6 resins, in the form of pellets, were solid state polymerized in the temperature range of 160–200°C in a fixed‐bed reactor under flowing nitrogen for times of 0–4 h. The kinetics of the solid state polymerization (SSP) of nylon 6,6 were examined by the evaluation of pertinent rate expressions and the selection of the most suitable one for describing the apparent overall process. The Flory‐theory‐based kinetic models were the most effective both for this study's data and for data previously published on SSP of different polyamides. Accordingly, SSP rate constants and activation energies were derived, and process parameters, such as the temperature and time, were investigated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 671–681, 2005     

Response Surface Analysis for Competition between Thermooxidation and Polycondensation Reactions of PET Flakes. Part 1: Low Vacuum Atmosphere

This work was accomplished employing solid-state polymerization (SSP) under less severe vacuum intensity (30 mmHg) in static mode at different times and temperatures. The influence of these parameters on intrinsic viscosity measurements was performed using Response Surface Methodology. The effect of temperature on intrinsic viscosity gains showed to be less pronounced than expected due to SSP being surface diffusion-controlled. The SSP efficiency for temperature as high as 230°C and dwell times higher than approximately 330 min showed lower increment on intrinsic viscosity than at immediately lower temperatures, although above approximately 215°C. This effect is a consequence of higher conversion rates of side reactions with increasing temperatures, their cumulative effect with increasing dwell time, and lower increment of polycondensation convertion rate with temperature under less severe vacuum intensity. The process temperatures and intervals determined, which allow PET recycling into new injected bottles, were moderates.     

Morphological changes of poly(ethylene terephthalate‐co‐isophthalate) during solid state polymerization

Poly(ethylene terephthalate‐co‐isophthalate) (PETI) prepolymer was submitted to solid state polymerization (SSP) at 184–230°C in a fixed bed reactor, to study the evolution of morphological changes during the process. Short reaction times were selected to investigate crystallization phenomena during nonisothermal (heating) and isothermal SSP phases. More specifically, multiple PETI melting behavior was observed and attributed to secondary crystallization, the rate of which increased significantly with SSP temperature. Reaction time was also found to exert a positive effect on solid‐phase perfection of secondary crystals, leading at each temperature to melting points close to the value of bottle‐grade poly(ethylene terephthalate). Finally, the mass fraction crystallinity of the SSP grades was found to comply with the crystal morphology encountered. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photopolymerized low‐surface‐energy coatings based on a novel fluorinated ether acrylate

The synthesis, characterization, and polymerization of a perfluoroalkyl ether substituted methacrylic acid (C8F7) were investigated. C8F7 was photopolymerized at different temperatures, higher double‐bond conversions being achieved at higher polymerization temperatures. The polymerization rates were fast in comparison with those of typical methacrylate esters. Thermogravimetric analysis of the obtained polymers showed thermal stabilities up to 270–290°C. The initial degradation at 200°C involved the loss of water and the partial loss of the perfluoroalcohol via the intramolecular formation of anhydride and lactone groups. The surface properties of coatings obtained with C8F7 coatings on various substrates were evaluated with water and hexadecane contact‐angle measurements, which confirmed that low‐surface‐energy polymeric coatings were obtained. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3301–3314, 2004     

Solid‐state polymerization of poly(ethylene terephthalate). II. Modeling study of the reaction kinetics and properties

Comprehensive modeling studies were used to describe the kinetics of the solid‐state polymerization (SSP) of poly(ethylene terephthalate). The validity of the model was confirmed by the successful fitting of the experimental results for molecular weight increases, at temperatures ranging from 180 to 230°C and for times up to 12 h, with one fitting parameter. The changes in the concentrations for hydroxyl end groups ([? OH]), carboxyl end groups ([? COOH]), vinyl end groups, and terephthalic acid (TPA) were simulated with the model. During SSP, the contents of not only hydroxyl and carboxyl end groups but also vinyl ester end groups and TPA monomer were predicted to decrease as a function of the SSP time and temperature. The effects of the pellet size and the molar ratio of carboxyl end groups to hydroxyl end groups were also calculated. At an end‐group molar ratio ([? COOH]/[? OH]) of around 0.7, a maximum SSP rate was obtained. As the [? COOH]/[? OH] ratio increased, the contents of the vinyl end groups and TPA monomer were predicted to increase. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 213–227, 2003     

Supercritical fluid extraction of cyclic oligomers from depolymerizing PBT

Cyclic oligomers of polyester show great potential for a reaction‐injection‐molding process, because of their initial low viscosity and rapid ring‐opening polymerization at low temperatures (180°C) without exothermic reaction or condensates. In this work, we report the synthesis of cyclic oligo(butylene terephthalate) (COBT) from linear poly(butylene terephthalate) by a formation–extraction process employing supercritical fluids (SCF) CO₂ and pentane at T = 230°C and P = 250 bar. Following this, depressurization of SCF leads to easy recovery of the COBTs. When compared with SCF CO₂, SCF pentane is found to be an attractive solvent because of its higher solubilizing capacity (0.8 mg COBT dimer/g pentane) for the COBTs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4487–4492, 2006     

Mathematical model for the bulk polymerization of styrene chemically initiated by sequential and total decomposition of the trifunctional initiator diethyl ketone triperoxide

This work experimentally and theoretically investigates the use of the symmetrical cyclic trifunctional initiator diethyl ketone triperoxide (DEKTP) in the bulk polymerization of styrene (St). The study focused on temperatures of 150 to 200°C, considering chemical initiation by both sequential and total decomposition reactions. The experimental work consisted of a series of isothermal batch polymerizations at higher temperatures, 150 and 200°C, with an initiator concentration of 0.01 mol/L. The mathematical model is based on a kinetic mechanism that includes thermal and chemical initiation (both sequential and total decomposition reactions), propagation, transfer to monomer, termination by combination and re‐initiation reactions. Experimental and theoretical results show that the decomposition mechanism of the initiator is modified by the reaction temperature and can be modeled as a set of two parallel reactions with different temperature dependences. The developed mathematical model simulates the bulk polymerization of St in the presence of DEKTP for a wide temperature range (120–200°C). It was found that due to these two decomposition mechanisms, the system may behave as a “dead‐end” polymerization system above a certain temperature, yielding low molecular weights and a limiting conversion value. Simulation results indicate the value of this temperature to be about 185°C. POLYM. ENG. SCI., 55:145–155, 2015. © 2014 Society of Plastics Engineers     

Solid‐state polymerization of poly(trimethylene terephthalate)

The solid‐state polymerization (SSP) of poly(trimethylene terephthalate) (PTT) has been studied and compared with that of poly(ethylene terephthalate) (PET). Because PTT and PET share the same SSP mechanism, the modified second‐order kinetic model, which has successfully been used to describe the SSP behaviors of PET, also fits the SSP data of PTT prepolymers with intrinsic viscosities (IVs) ranging from 0.445 to 0.660 dL/g. According to this model, the overall SSP rate is ?dC/dt = 2k_a(C ? C_ai)², where C is the total end group concentration, t is the SSP time, k_a is the apparent reaction rate constant, and C_ai is the apparent inactive end group concentration. With this equation, the effects of all factors that influence the SSP rate are implicitly and conveniently incorporated into two parameters, k_a and C_ai. k_a increases, whereas C_ai decreases, with increasing SSP temperature, increasing prepolymer IV, and decreasing pellet size, just as for the SSP of PET. Therefore, the SSP rate increases with increasing prepolymer IV and increasing SSP temperature. The apparent activation energy is about 26 kcal/mol, and the average SSP rate about doubles with each 10°C increase in temperature within the temperature range of 200–225°C. The SSP rate increases by about 30% when the pellet size is decreased from 0.025 to 0.015 g/pellet. Compared with PET, PTT has a much lower sticking tendency and a much higher SSP rate (more than twice as high). Therefore, the SSP process for PTT can be made much simpler and more efficient than that for PET. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3188–3200, 2003     

Preparation of high‐molecular‐weight poly(N‐vinylcarbazole) by the photoinduced low‐temperature solution polymerization of N‐vinylcarbazole in 1,1,2,2‐tetrachloroethane

For the preparation of high‐molecular‐weight (HMW) poly(N‐vinylcarbazole) (PVCZ) with a narrow molecular weight distribution, N‐vinylcarbazole (VCZ) was solution‐polymerized in 1,1,2,2‐tetrachloroethane (TCE) at ?20, 0, and 20°C with photoinitiation. The effects of the polymerization temperature and the concentrations of the polymerization solvent and photoinitiator on the polymerization behavior and molecular parameters of PVCZ were investigated. A low polymerization temperature with photoirradiation was successful in obtaining HMW PVCZ with a smaller temperature rise during polymerization than that for thermal free‐radical polymerization by azobisisobutyronitrile (AIBN). The photo‐solution‐polymerization rate of VCZ in TCE was proportional to [AIBN]^0.45. The molecular weight was higher and the molecular weight distribution was narrower for PVCZ made at lower temperatures. For PVCZ prepared in TCE at ?20°C with a photoinitiator concentration of 0.00003 mol/mol of VCZ, a weight‐average molecular weight of 920,000 was obtained, with a polydispersity index of 1.46, and the degree of transparency converged to about 99%. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2391–2396, 2003     

Gas‐phase ethylene polymerization using zirconocene supported on mesoporous molecular sieves

Mesoporous molecular sieves, with pore diameters of 2.6–25 nm, were impregnated with methylaluminoxane and bis(butylcyclopentadienyl)zirconium dichloride and tested as catalysts for the gas‐phase homopolymerization of ethylene at ethylene pressures of 200 psi and temperatures of 50–100°C and for 1‐hexene/ethylene copolymerization at 70°C. The activities and activity profiles, at constant Zr and Al contents, depended on the pore size of the supports and the polymerization temperature. Maximum activities for both the homopolymerizations and copolymerizations were observed for catalysts made with supports having pore diameters of 2.6 and 5.8 nm. Homopolymerization activities were highest at temperatures of 70–80°C; average homopolymerization and copolymerization activities up to 9000 kg of polyethylene/(mol of Zr h) were obtained. The weight‐average molecular weights (M_w's) were not a function of the support pore size but decreased with increasing reaction temperatures, from about 260,000 at 50°C to about 165,000 at 100°C. The polydispersities were essentially constant at 2.5 ± 0.2 for the homopolymers. M_w's for the 1‐hexene/ethylene copolymers had an average value of 117,000 with an average polydispersity of 2.8. The amount of triisobutyl aluminum added to the reactor significantly affected the activity and activity profiles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1161–1177, 2003     

Effect of high polymerization temperature on the microstructure of isotactic polypropylene prepared using heterogeneous ticl4/mgcl2 catalysts

The effects of alkylaluminum and polymerization temperature on propylene polymerization without an external donor in the use of a TiCl₄–MgCl₂–diether(BMMF) catalyst were investigated. The results indicated that with increasing polymerization temperature the concentrations of [mmmm] of heptane‐insoluble poly(propylene) (PP) fraction increased. Crystallization analysis fractionation (CRYSTAF) results showed the fractions of different crystallization temperatures were changed according to various polymerization temperatures. The activity with Et₃Al as cocatalyst at 100°C was much lower than that at 70°C. However, the activity with i‐Bu₃Al at 100°C was as high as that at 70°C. The fraction of high‐crystallization temperature of PPs obtained with i‐Bu₃Al increased with increasing polymerization temperature, which was opposite to that with Et₃Al, thus implying that the copolymerization of propylene with the monomer arising from Et₃Al led to the lower crystallization ability of PPs obtained with Et₃Al. The terminal groups of PP suggested that the chain‐transfer reaction by β‐H abstraction was the main chain‐transfer reaction at 120°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3980–3986, 2003     

Synthesis and kinetic behavior of stereotriblock polybutadiene using dilithium as initiator

Anionic polymerization of butadiene was conducted in cyclohexane using 1,1,4,4‐tetraphenyl‐1,4‐dilithium butane (TPB–DiLi) as initiator and dipiperidinoethane (DPE) as modifier. The polymer design effects of DPE/TPB–DiLi (simplified as DPE/Li) and polymerization temperature on the 1,2 content of polybutadiene (PB) were examined and 1,2‐polybutadiene (1,2‐PB) with a nearly 100% 1,2 content was obtained. 1,2–1,4–1,2‐Stereotriblock polybutadiene (STPB) can be synthesized easily by means of one feed reaction. DSC and DMA analyses showed that STPB with the designed molecular structure (molecular weight, block ratio, and 1,2 content in 1,2 blocks) has two T_g's and two loss moduli and exhibits microphase separation. Studies on reaction kinetics established the polymerization kinetics equation of 1,4‐PB as ?d[M]/dt = 0.356[C]^0.5[M], indicating the first‐order relationship between polymerization rate and monomer concentration. At 50°C, the addition of the strong polar modifier DPE into the system increased the reaction rate. The apparent propagating activating energies before and after DPE addition were also determined in this study. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1049–1054, 2003