Effects of the o‐aromatic ring in the molecular chain on the properties of polyester polyols

A series of liquid polyester polyols from adipic acid (AA), phthalic anhydride (PA), ethylene glycol, propanediol‐1,2, and trihydroxymethylpropane, varying in the molar ratio of PA to AA, were prepared. The effects of the o‐aromatic ring in the molecular chain, which came from PA, on the viscosity, glass‐transition temperature, and thermal degradation temperature of the polyester polyols were studied with viscometry, differential scanning calorimetry, and thermogravimetry. The intrinsic viscosity and glass‐transition temperature increased with the concentration of the o‐aromatic ring increasing. The temperature of the maximum thermal degradation rate for aliphatic polyester polyols was 434.20°C. Two steps of thermal degradation were found when there were o‐aromatic rings in the molecular chain. One thermal degradation temperature was 358.36–360.48°C, and the other was 412.85–427.18°C. Polyester polyols with o‐aromatic rings had higher stability at lower temperatures (<240.00°C). However, aliphatic polyester polyols had higher stability at higher temperatures (300.00–480.00°C). The activation energy and order of degradation were calculated from thermogravimetric curves. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1617–1624, 2002     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

Influence of polymerization conditions on the viscosity and yield of poly(phenylene sulfide ether)

High molecular weight poly(phenylene sulfide ether) (PPSE) was successfully synthesized by reaction of 4,4′‐dihydroxy diphenyl sulfide with 4,4′‐dichloro diphenyl sulfide in N‐methyl‐2‐pyrrolidone (NMP). The influence of polymerization conditions on the intrinsic viscosity and yield of PPSE was investigated and the optimized reaction condition was concluded. Reactions at about 180°C for 6 h along with sodium benzoate as an additive and monomer concentration of 0.588 mol/L NMP were found to produce the highest intrinsic viscosity (0.55 dL/g). Longer reaction time and/or higher temperature reduced the intrinsic viscosity and yield of the resulting product, probably due to side reactions, such as reductive dehalogenation and chemical degradation. X‐ray diffraction indicated that the polymer possessed of orthorhombic cell and had a high crystallinity of 65.8%. The high molecular weight PPSE is a crystalline polymer with T_m of 252°C and T_mc of 224°C. The polymer shows good chemical resistance, but is soluble in organic amide, halo‐hydrocarbon and oxohydrocarbon solvent at a temperature over 150°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

In vitro degradation of dry‐jet‐wet spun poly(lactic acid) monofilament and knitted scaffold

In vitro degradation behavior of dry‐jet‐wet spun poly(lactic acid) (PLA) monofilament and knitted scaffold were studied at three different pH i.e., at 4.6, 7.4, and 8.0 at 37°C for 20 weeks. Characterization of PLA by intrinsic viscosity, thermal properties, and scanning electron microscopy (SEM) was carried out. It is observed that the pH of the medium has significant role on degradation behavior of PLA. The degradation at pH 4.6 is observed to be maximum, which is confirmed by the drop of 52% in intrinsic viscosity. The degradation process has effect on the hydrophobicity of the PLA. The decrease in contact angle from 73° to 48° indicates that the PLA surface tends to become more hydrophilic as the degradation proceeds. The SEM analysis showed that with the degradation, surface deterioration takes place. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2006–2012, 2007     

CaCl2对聚间二苯砜对苯二甲酰胺/DMF溶液特性的影响

为了研究CaCl₂对聚间二苯砜对苯二甲酰胺(mt-PSA)在DMF中分子构象和形态的影响,采用流变仪测定了mt-PSA/DMF/CaCl₂浓溶液的流变行为,并通过乌氏黏度计和激光光散射研究其稀溶液的溶液黏度和高分子形态尺寸。结果表明:CaCl₂的加入增大了大分子与溶剂在mt-PSA/DMF/CaCl₂浓溶液和其稀溶液中的相互作用,同时CaCl₂使大分子链段得到舒展。但大分子的重均分子量没有发生明显的变化,说明CaCl₂未使mt-PSA高分子链段发生聚集或者坍塌。     

Thiol–ene addition enables tailored synthesis of poly(2‐oxazoline)‐graft‐poly(vinyl pyrrolidone) copolymers for binder jetting 3D printing

The continued interest in graft copolymer architectures arises from their unique solution properties and potential for a myriad of applications ranging from drug delivery to adhesives. Poly(vinyl pyrrolidone) (PVP) represents a popular amorphous, water‐soluble polymer used as a polymeric binder in binder jetting additive manufacturing, as fillers in cosmetic products, and for subcutaneous drug delivery systems. This report describes the synthesis of poly(2‐oxazoline) and PVP graft copolymers using a ‘grafting to’ methodology with an efficient thiol–ene ‘click’ reaction. Copolymerization of 2‐methyl‐2‐oxazoline and 2‐(3‐butenyl)‐2‐oxazoline introduced pendent vinyl grafting sites with a predictable absolute number‐average molecular weight. In parallel, reversible addition‐fragmentation chain‐transfer polymerization and subsequent aminolysis yielded well‐defined, oligomeric, thiol‐terminated PVP. Thiol–ene click chemistry enabled the formation of poly(2‐oxazoline)‐graft‐poly(vinyl pyrrolidone) (PMeOx‐g‐PVP) copolymers with varying mole percent grafting sites and PVP graft length. ¹H NMR spectroscopy, aqueous SEC with multiangle light scattering (SEC‐MALS), and bromine titrations confirmed chemical structure, and DSC with TGA elucidated thermal transitions. Aqueous SEC‐MALS and ¹H NMR spectroscopy also determined absolute number‐ and weight‐average molecular weights and average grafting levels, which revealed optimal reaction conditions. Zero‐shear viscosities of 5 and 10 wt% solutions in deionized water for each graft copolymer compared to their linear analogs demonstrated a significant (ca 31%) decrease in viscosity at the same number‐average molecular weight. This decrease in solution viscosity suggested PMeOx‐g‐PVP copolymers as exceptional alternatives to linear analogs for aqueous‐based, binder jetting additive manufacturing.     

Chain extension of polybutylene adipate and polybutylene succinate with adipoyl‐ and terephthaloyl‐biscaprolactamate

HO‐terminated polybutylene adipate (HO‐PBA‐OH) with molecular weight from 1040 to 3540 and HO‐terminated polybutylene succinate (HO‐PBS‐OH) with intrinsic viscosity of 0.37 dL/g were synthesized through melt condensation polymerization from adipic acid or succinic acid with excess of butanediol. Chain extension of HO‐PBA‐OH or HO‐PBS‐OH with adipoyl biscaprolactamate and terephthaloyl biscaprolactamate was carried out at 200–240°C under reduced pressure. At the optimal conditions, chain‐extended PBA with M_n up to 50,700, and M_w up to 125,700 was synthesized, and the chain‐extended PBS with intrinsic viscosity of 1.25 dL/g was obtained. Meanwhile, p‐toluenesulfonic acid, SnCl₄ and zinc acetylacetonate catalyzed chain‐extending reaction of HO‐PBA‐OH and HO‐PBS‐OH was also studied. The chain‐extended polyesters were characterized by IR spectra, ¹H‐NMR spectra, and differential scanning calorimetry (DSC). The chain extension proceeds through the elimination of caprolactam rings in the chain‐extenders, the adipoyl groups or the terephthaloyl groups couple the hydroxyl‐terminated polyesters together and make the molecular weight of PBA or PBS increased, whether the acid catalyst such as p‐toluenesulfonic acid was present or not. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Viscosities of moderately concentrated solutions of polyethylene in ethane,propane, and ethylene

The viscosities of moderately concentrated solutions of low-density polyethylenes in ethane, propane, and ethylene have been measured at low shear rate in the temperature range of 150–250°C and in the pressure range of about 15000–30000 psi. Within the precision of the measurements, the relative viscosity is independent of pressure over the range investigated but increases as the solvent is changed from propane through ethane to ethylene. The activation energy for the relative viscosity in ethane varies from about 0.5 to 2.5 kcal/mole as the concentration changes from 5 to 15 g/dl. Effects of polymer concentration and molecular weight on solution viscosity in ethane at 150°C have been determined, and all of the data can be represented by a single straight-line plot of the logarithm of relative viscosity versus the intrinsic viscosity (in p-xylene at 105°C) times concentration. This simple relation is valid over wide ranges of polymer concentration and molecular weight and over more than two orders of magnitude of relative viscosity. The solution viscosities of the polyethylenes in the three supercritical fluid solvents used appear surprisingly low at first sight. This behavior is partly a result of the low solvent viscosities but also might mean that the polymer has an abnormally low segmental friction factor compared to that in solutions under more familiar conditions.     

Measurement of Porosity in a Composite High Explosive as a Function of Pressing Conditions by Ultra‐Small‐Angle Neutron Scattering with Contrast Variation

We have used ultra‐small‐angle neutron scattering (USANS) with contrast variation to measure the porosity over length scales 0.1–20 μm in a composite high explosive, PBX 9501, formulated with a deuterated binder. Here, we explore the effect of varying the pressing intensity on the PBX 9501 microstructure. Samples of PBX 9501 were die‐pressed with applied pressures ranging between 69 and 200 MPa at 90 °C. Five samples were prepared at each pressure that differed in the fraction of binder that was deuterated, resulting in a change in the neutron scattering length density contrast (Δρ) of the binder relative to that of the high explosive crystallites and voids. By using this approach to discriminate scattering from voids from that due to the binder, we determined microstructure and composition that otherwise would not have been apparent. The sample composition was determined by calculating the Porod Invariant as a function of Δρ and comparing it with compositional estimates obtained from the bulk sample density. Structural modeling of the USANS data, assuming both spherical and cylindrical morphologies, allowed the mean size and size distribution of voids and binder‐filled regions to be determined.     

Chain‐extended polyurethanes—Synthesis and characterization

Chain‐extended polyurethanes (PUs) were prepared using castor oil and different diisocyanates such as toluene‐2,4‐diisocyanate and 4,4′‐methylene bis(phenylisocyanate) as a crosslinker and different aromatic diamines like 4,4′‐diaminodiphenyl methane and 4,4′‐diaminodiphenyl sulphone as chain extenders. The effect of aromatic diamines on the swelling and thermal degradation behavior of PU have been discussed. A thermogravimetric analyzer (TGA) curve shows that all the chain‐extended PUs are stable up to 194°C and that maximum weight loss occurs at 490°C. The TGA thermograms show that the thermal degradation of the PUs was found to proceed in two steps. The average molecular weight between crosslinks (M?_c) was determined by swelling studies. The properties imparted by the aromatic chain extenders are explained on the basis of groups present in the diamines. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 359–369, 2002; DOI 10.1002/app.10347     

Modeling of poly(L‐lactide) thermal degradation: Theoretical prediction of molecular weight and polydispersity index

A mathematical model to describe the molecular weight and polydispersity index (Q) in poly(L ‐lactide) (PLLA) thermal degradation has been developed. Based on the random chain scission mechanism, effects of temperature and time on the molecular weight and polydispersity index are included in this model. It incorporates the degradation and recombination reaction of PLLA thermal degradation, while taking into account the equal probability assumption. The developments of molecular weight and polydispersity index of PLLA polymer in the thermal degradation process were investigated at temperature ranging from 180–220°C, the experimental data show PLLA reaches its thermal degradation equilibrium in 2 h. The simulated results of this model are compared with the measured molecular weight and polydispersity index of the PLLA polymer. The changes of the molecular weight and polydispersity index in the PLLA thermal degradation can be predicted by this model. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2557–2562, 2003     

Effect of gamma irradiation and irradiation temperature on hydrolytic degradation of synthetic absorbable sutures

The purpose of this study is to examine the effects of γ irradiation and the relative magnitude of T_irr to T_g on the physical, mechanical, thermal, morphological, and hydrolytic properties of two types of synthetic absorbable polymers. Polyglycolic acid (PGA) and glycolide-trimethylene carbonate block copolymer fibers in the form of 2/0 size Dexon and Maxon sutures from Davis/Geck were used in this study. In addition, injection-molded PGA disks were also used for determining how different polymer morphology affected the outcomes of γ irradiation and irradiation temperature. These two types of biomaterials were ⁶⁰Co γ irradiated at two irradiation temperatures (55 and ?78°C in dry ice). Both γ-irradiated and control speciments were immersed in a phosphate buffer solution of pH 7.44 at 37°C for various durations of hydrolysis. After each predetermined duration, the specimens were removed for subsequent testing which included determinations of tensile strength, weight loss, level of crystallinity, melting temperature, intrinsic viscosity, surface morphology, and infrared spectroscopic characteristics. γ irradiation at both irradiation temperature resulted in a faster hydrolytic degradation of these two biodegradable polymers. There was no apparent irradiation temperature effect in terms of mass loss, intrinsic viscosity, level of crystallinity, and melting temperature. However, irradiation temperature effect was evident in those properties that depended on the tie-chain segments located in the noncrystalline domains, such as tensile strength. The observed seffect of irradiation temperature was attributed to chain mobility which could facilitate cage recombination of macromolecular radical pairs at the irradiation temperature lower than the glass transition temperature of the irradiated polymers. © 1995 John Wiley & Sons, Inc.     

Understanding the Compatibility of the Energetic Binder PolyNIMMO with Energetic Plasticizers: Experimental and DFT Studies

The development of energetic binders with suitable energetic plasticizers is required to enhance the mechanical properties and to reduce the glass transition temperature of propellant and explosive formulations. The compatibility of the energetic binder poly(3‐nitratomethyl‐3‐methyloxetane) (polyNIMMO) with five different energetic plasticizers viz. bis(2,2‐dinitro propyl)acetal (BDNPA), dinitro‐diaza‐alkanes (DNDA‐57), 1,2,4‐butanetriol trinitrate (BTTN), N‐N‐butyl‐N ‘(2‐nitroxy‐ethyl) nitramine (BuNENA) and diethyleneglycoldinitrate (DEGDN) was studied by differential scanning calorimetry (DSC), rheology, and DFT methods. The results obtained for the pure binder were compared with the results obtained for the binder/plasticizer blend in regard of the decomposition temperature and the format of the peak indicated the compatibility of polyNIMMO with the plasticizers. The glass transition temperatures of the blends were determined by low temperature DSC and showed desirable lowering of glass transition temperature with single peak. The rheological evaluation revealed that the viscosity of the binder is considerably lowered by means of flow behavior upon addition of 20 % (w/w) plasticizer. The addition of BuNENA and DEGDN has maximum effect on the lowering of viscosity of polyNIMMO. The predicted relative trend of interaction energies between plasticizer and binder is well correlated with the corresponding trend of viscosity of binder/plasticizer blends. These experimental studies verified by theoretical methods are valuable to design practical blends of new plasticizers and binders.     

Properties and Application of a Novel Type of Glycidyl Azide Polymer (GAP)‐Modified Nitrocellulose Powders

GAP‐modified nitrocellulose powders were prepared by an internal solution method and applied in cross‐linked modified double base (XLDB) propellants. It was found that GAP‐modified nitrocellulose powders exhibit high round, no bonding between the particles and excellent fluidity. When the amount of GAP increased from 10.0 % to 30.0 %, the median diameter (d₅₀) of powders decreased from 134.53 μm to 94.54 μm. The thermal decomposition process of GAP appeared also in the GAP‐modified nitrocellulose powders, but the thermal decomposition peak temperatures of  N₃ and the GAP main chain were found to be lower for the 10.0 % and 20.0 % GAP‐modified samples than the corresponding peak temperatures for pure GAP, respectively. The plasticizing properties of GAP‐modified nitrocellulose powders are better than that of pure nitrocellulose powders, and the drop weight impact sensitivity of the modified powders is reduced as the mass ratio of GAP increases. It was experimentally shown that GAP‐modified nitrocellulose powders can improve the mechanical characteristics of the propellant with a maximum tensile strength (σ_m) between 0.36 MPa<σ_m< 1.10 MPa and an elongation at maximum tensile strength (ε_m) between 28.8 %<ε_m<51.8 % at temperatures of −40, +20 and +50 °C.     

Evaluating the thermal stability of high performance fibers by TGA

The thermal degradation of eight types of high performance fibers (HPFs) was measured under nitrogen and air atmosphere. The degree of degradation, as measured by weight loss using thermogravimetric analysis (TGA), and the characteristic degradation temperatures were obtained. The kinetics of the thermal degradation has also been analyzed according to the Freeman–carroll method and the activation energies of the HPFs were estimated. The experimental results show that para‐aramids (Kevlar® 29, 49, 129, and Twaron®2000) have similar thermal stability, but their thermal degradation temperatures and activation energies in air are different from those in nitrogen, which means that the thermostability of the fiber depends not only on its intrinsic structure but also on the atmosphere and temperature of testing environment. Terlon® fiber shows higher degradation temperature as a copolymer of para‐aramid, and its initial degradation temperature is 476.4°C in air. It can also be found that the PBO (poly(p‐phenylene benzobisoxazole)) fiber has the highest thermal degradation temperature among the samples tested, but its activation energy is not the highest in both air and nitrogen atmosphere. And the UHMW‐PE (ultra high molecular weight polyethylene) fiber has the lowest thermal degradation temperature, and it begins to degrade when the temperature reaches 321.8°C under air atmosphere. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 937–944, 2006     

Long‐term investigation on hydrolytic degradation and morphology of poly(ethylene glycol terephthalate)‐b‐poly(butylene terephthalate) copolymer films

Poly(ethylene glycol terephthalate)‐b‐Poly(butylene terephthalate) copolymer (PEGT‐b‐PBT) films with different copolymer compositions were incubated in phosphate buffered saline under pH 7.4 at 37°C to study hydrolytic degradation and morphology up to 300 days. With the fall of intrinsic viscosity and mass of degraded films, SEM micrographs show that a set of particular and highly interconnected porous morphologies closely related to the content of PBT hard segments in copolymer is developed. Moreover, the variation in PBT crystallinity for copolymer films with weight ratio of 70/30 fluctuates with the development of degradation profiles, and PEGT content for copolymer films with weight ratio of 80/20 and 70/30 gradually decreases. The hydrolytic experiments demonstrate that the degradation of PEGT‐b‐PBT copolymer results from the cleavage of ester bonds between hydrophilic PEG and terephthalate. At the beginning period of degradation, PEGT‐b‐PBT copolymer films follow a typical mechanism of bulk degradation, and then undergo both bulk degradation and surface erosion, all of which finally generate the particular porous morphologies for copolymer films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and thermal properties of poly(urethane‐imide)

The synthesis and thermal properties of thermoplastic poly(urethane‐imide) (PUI) resins were studied. Model reaction studies on the reactions of 4,4′‐diphenylcarbamatodiphenylmethane and 4,4′‐diisocyanatodiphenylmethane with phthalic anhydride were performed. We found that the reaction of anhydrides with urethane groups could take place under certain reaction conditions. According to the model reaction studies, N‐2‐methyl‐pyrrolidone was employed as a solvent, and no catalyst was used in the polymerization. To restrain the side reaction of anhydrides with urethane groups, we adopted a two‐step chain‐extending procedure in a chain‐extending reaction. The inherent viscosity of PUI was 0.83–0.99 dL/g. The prepared polymers not only exhibited improved solubility in organic solvents but also formed flexible films. Thermogravimetric analysis showed that PUI exhibited a two‐step thermal weight‐loss pattern. The first step of the thermal degradation of PUI was attributed to the thermooxidizing cleavage of weak and labile linkage, such as urethane groups, isopropylidene, and methylene, except for imide rings. The polymer inherent viscosity decreased sharply during the first step of thermal degradation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 773–781, 2001     

Low temperature solid‐state extrusion of recycled poly(ethylene terephthalate) bottle scraps

The processing of poly(ethylene terephthalate) (PET) involves thermal and hydrolytic degradation of the polymer chain, which reduces not only the intrinsic viscosity and molecular weight, but also the mechanical properties of recycled materials. A novel PET/bisphenol A polycarbonate/styrene–ethylene–butylene–styrene alloy based on recycled PET scraps is prepared by low temperature solid‐state extrusion. Hydrolysis and thermal degradation of PET can be greatly reduced by low temperature solid‐state extrusion because the extrusion temperature is between the glass‐transition temperature and cold‐crystallization temperature of PET. Modification of recycled PET by low temperature solid‐state extrusion is an interesting method; it not only provides an easy method to recycle PET scraps by blend processing, but it can also form novel structures such as orientation, crystallization, and networks in the alloy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2692–2699, 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     

Thermal degradation kinetics of para‐substituted poly (styrene peroxide)s in solution

The thermal degradation of three polymeric peroxides of styrene monomers with substituents in the para position was studied at various temperatures (65, 75, 85, and 95°C). A continuous distribution model was used to evaluate the rate coefficients for the random‐chain and chain‐end scission degradation from the evolution of molecular weight distributions with time. The activation energy determined from the temperature dependence of the rate coefficients was in the range 18–22 kcal mol^?1. This result suggests that the thermal degradation of polyperoxide is controlled by the dissociation of the O—O bonds in the polymer backbone. The thermal stability for poly(p‐methylstyrene peroxide) lies in between that of poly(p‐tert‐butylstyrene peroxide) (highest) and poly(p‐bromostyrene peroxide) (lowest). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 957–961, 2002