Synthesis,structural characterization,and properties of polyurethane elastomers containing various degrees of unsaturation in the chain extenders

We prepared polyurethane block copolymers with both 50 and 70% soft segment concentrations, using 4,4′‐diphenylmethane diisocyanate–poly(propylene glycol) prepolymer and 1,4‐butanediol, cis‐2‐butene‐1,4‐diol, and 2‐butyne‐1,4‐diol as chain extenders. The effects of the different chain extenders were observed during synthesis and in the final products. A comparison of spectroscopic, mechanical, and thermal data reveals that polymer properties can be significantly altered by differences in chemical bonding within the chain extender backbone. Although all data support the expected differences in phase morphology between the two series of samples, they also suggest that increasing chain extender unsaturation reduced reactivity with isocyanate, adversely affected hydrogen bonding, lowered the degree of crystallinity of the hard segments, and decreased phase separation. The tensile strength, elongation, modulus, and elastic recovery decreased and the electrical conductivity of iodine‐doped samples increased with increasing chain extender unsaturation. The thermal stability of the urethane group was also lower in samples with increased unsaturation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1316–1333, 2002     

Investigation of covalently colored polyurethane latexes based on novel anthraquinone polyurethane chain extenders

Novel red and yellow polyurethane (PU) chain extenders with one anthraquinone chromophore and two hydroxyls were synthesized, and then used to fabricate covalently colored PU latexes with pendent chromophores on the PU backbone. The chemical structures of the chain extenders were characterized by ¹H-NMR and FTIR, and the properties of PU latexes and their films were investigated by UV-Vis absorption spectra, particle size analysis, FTIR, Soxhlet's extraction and xenon arc aging testing. Results showed that the covalently colored PUs had the same UV-Vis absorption behavior as the corresponding chain extenders, and amount of the chain extenders had no obvious influence on the latex preparation process and the resulted latex colloidal properties. Compared with the corresponding non-covalently colored PU latex films, both the light fastness and the solvent fastness of the covalently colored PU latex films were significantly enhanced by the covalent incorporation of chromophores with PU matrix.     

Synthesis and thermo-mechanical characterization of high performance polyurethane elastomers based on heterocyclic and aromatic diamine chain extenders

Two series of 4,4′-diphenylmethane diisocyanate (MDI) and poly(ethylene glycol adipate) (PEGA)-based polyurethane and polyurethaneurea elastomers were synthesized via a one-shot polymerization method and characterized using FTIR, ¹H NMR and ¹³C NMR. The samples in the first series are extended by aliphatic diol chain extenders while in the second series mixtures of aliphatic diols and furanic or aromatic diamine chain extenders are used. TGA experiments revealed that with furanic or aromatic diamine chain extenders the polymer degradation temperature is shifted 90 °C upwards, irrespective of the annealing time at 100 °C according to ASTM 0573-99. The values of Young's modulus and of the tensile strength are higher and the strain at break is lower for the samples in series 2 compared to those in series 1. Increasing the annealing time at 100 °C lowers Young's modulus. Dynamic mechanical thermal analyses points to a progressive microphase separation with annealing time.     

Studies on the recycling of glycolyzed nylon 66 using novel chain extenders

Nylon 66 (NY66) polymer based products widely used in automotive applications undergo deterioration in their mechanical properties when repeatedly exposed to ethylene glycol (EG) solution. In this study, recycling of glycolyzed NY66 (g-NY66) samples was carried out through melt-compounding with novel isocyanate based chain extenders namely hexamethylene 1,6-dicarbamoyl dicaprolactam (HDC) and tolylene 2,4-dicarbamoyl dicaprolactam (TDC). The recycling efficiency of HDC and TDC on g-NY66 was compared with two commercially available chain extenders 1,1-carbonyl biscaprolactam (CBC) and 1,3-phenylene bis(2-oxazoline) (PBO), and the resultant changes in molecular weight, melt flow, and crystallization behavior in the modified NY66 samples were confirmed from intrinsic viscosity, rheology, and differential scanning calorimetry measurements, respectively. The active ingredients (isocyanate and ?-caprolactam) liberated from HDC and TDC during the melt-compounding process reacted efficiently with the end groups of g-NY66 (-OH and -NH₂) resulting in improved molecular weight compared to g-NY66 and the results are reported in detail.     

Properties and Polymerization of Biodegradable Thermoplastic Poly(Ester-urethane)

Abstract

Aliphatic polyesters, such as poly(lactic acids), need high molecular weight for acceptable mechanical properties. This can be achieved through ring-opening polymerization of lactides. The lactide route is, however, relatively complicated, and alternative polymerization routes are of interest. In this paper we report the properties of a polymer made by a two-step process: first a condensation polymerization of lactic acid and then an increase of the molecular weight with diisocyanate. The end product is then a thermoplastic poly(ester-urethane). The hydroxylterminated prepolymer was made with condensation polymerization of L–lactic acid and a small amount of 1,4-butanediol. The polymerization was performed in the melt under nitrogen and reduced pressure. The preparation of poly(ester-urethane) was done in the melt using aliphatic diisocyanates as the chain extenders reacting with the end groups of the prepolymer. The polymer samples were carefully characterized, including preliminary degradation studies. The results indicate that this route to convert lactic acid into thermoplastic biodegradable polymer has high potential. Lactic acid is converted into a mechanically attractive polymer with high yield, which could make the polymer suitable for high volume applications. The mechanical properties of the poly(ester-urethane) are comparable with those of poly(lactides). Capillary rheometer measurements indicate that the polymer is processible both by injection molding and extrusion.     

Mechanical and viscoelastic properties of confined amorphous polymers

Confinement of polymers to nanoscale dimensions can dramatically impact their physical properties. Substantial efforts have focused on the glass transition temperature (T_g) of polymers confined to thin films, but their mechanical properties are less studied despite their technological importance. In this review, challenges with mechanical measurements of polymer thin films are discussed along with novel metrologies that provide insight into their mechanical properties. A comparison of experimental measurements, simulations and theory provide several general conclusions about the mechanical properties under confinement. Confinement impacts the elastic modulus, rubbery compliance and viscosity of polystyrene, the archetypal polymer for confinement, but the confinement effect appears to depend on the measurement technique. This effect may be due to the details of averaging of gradients in properties that are dependent on the measurement details. Routes to minimize confinement effects are addressed. Despite progress in the measurements of mechanical properties of polymer thin films, there remain unresolved questions about the impact of confinement, which we highlight at the end of this review. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 9–30     

Novel Polyurethane Gels: The Effect of Structure on Gelation

Novel polyurethane gels have been reported in common solvent like dimethyl formamide (DMF). Polyurethanes have been synthesized from diisocyanates, diols and rigid chain extenders. We have illustrated the influence of chemical structure of the chain extenders on gelation rate, thermal property and morphology of the gels in DMF. Gelation rate increases significantly with the rigidity of the chain extender. Introduction of more rigid chain extender molecules in polyurethane prepolymer enhanced the thermal stability of the pure polymer. On the contrary, the solvent retention power of the gels gradually decreases with increasing rigidity of chain extender presumably because of the poor dispersion/greater aggregation of the hard segments in the soft segment matrix. Morphology and formation of gelation have been discussed.     

Mechanical properties of composite heterogeneous gels

Composites with a matrix of poly(2-hydroxyethyl methacrylate) (PHEMA) and 10% by volume of various crosslinked PHEMA polymer fillers (prepared by copolymerization with 0.1, 0.4, 1.0, and 20.0% by weight of ethylenedimethacrylate) of particle size about 1 μm were prepared. Some polymer matrixes were prepared from soluble branched PHEMA (Hydron S), and others by copolymerization, in the presence of the filler with 0.4 and 1.0% of ethylenedimethacrylate as a crosslinking agent. In the case of the uncrosslinked matrix, a linear polymer–crosslinked polymer system, resulted; in the case of the crosslinked matrix, a composite heterogeneous network was formed (in the latter case, the particles of the filler were swollen with monomer during the crosslinking polymerization). Stress–strain, equilibrium, and ultimate characteristics were measured at 3, 10, 25, 40, 60, and 80°C on samples swollen to equilibrium in water (T_g ≈ ?50°C) and at 80, 110, and 140°C on dry samples (T_g ≈ 100°C). Depending on experimental conditions, above all on the distance from the main transition region and on whether the polymer is dry or swollen, it was found that the measured hydrophilic composite systems behaves as a filled system (with the polymer filler acting mostly as solid particles, irrespective of the crosslink density) or as a system with crosslink density fluctuations (where both networks, the matrix and the filler, contribute roughly additively to the properties of the system), or finally as defect heterogeneous systems (where the properties depend primarily on the character of the polymer–filler interface).     

Liquid crystalline triblock copolymers. Mechanical behaviour and orientation under uniaxial strain

The stress‐strain and orientation behaviour of side‐chain liquid crystalline(SLCP) ABA triblock copolymers with a backbone of polystyrene‐block‐1,2‐polybutadiene‐block‐polystyrene and a cyanobiphenyl mesogen in the side chain was investigated in dependence of molecular weight. The polymer shows the behaviour of a thermoplastic liquid crystalline elastomer(TPLCE) in the nematic phase in a region between the glass transitions of the polystyrene block and the SLCP. The ultimate properties and E‐modulus is lower than for conventional thermoplastic elastomers. Under uniaxial strain liquid crystalline order perpendicular to the direction of strain is induced.     

Mechanical degradation of polypropylene solutions under large pressure drops

The degradation of polypropylene (PP), dissolved in n‐alkanes at high temperatures and pressures, during the solution discharge to ambient conditions was experimentally studied. Molecular weight distributions (MWD) of the solubilized PP were measured by gel permeation chromatography. The MWD curves of PP obtained after discharge of the polymer solution shift to the low molecular weight side of the distribution and the polydispersity is reduced. In this work, a systematic study on the discharge products was performed to elucidate the degradation mechanism and the effects of temperature and concentration on this phenomenon. Initially, pure polymers, PP and polystyrene (PS) were studied varying the solution temperature. In a second stage, the effect of polymer concentration on chain scission was assessed using experiments on physical blends of PP/PS. In all cases, thermal and oxidative degradation were previously analyzed. Mechanical degradation was found to be the main chain scission mechanism. A negative linear functionality of the chain scission was found in both temperature and polymer concentration. To analyze the relationship between polymer degradation and molecular weight, the chain scission distribution function was calculated. On this basis, a critical molecular weight for the beginning of chain scission was obtained. This value is a function of temperature but remains constant with concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 455–465, 2007     

The Mechanical Strength of a Mechanical Bond: Sonochemical Polymer Mechanochemistry of Poly(catenane) Copolymers

Topological molecular connections and structures, including physical entanglements in polymer networks, knots along polymer chains, and rotaxanes in sliding ring gels, have important consequences for the physical properties of polymeric materials. Often these topologies contribute through their ability to bear mechanical stress, but experimental measures of their relative mechanical strength are rare. Here, we use sonochemical polymer mechanochemistry to assess the relative mechanical strength of a multicatenane copolymer relative to copolymers of cyclic and linear analogs. The relative mechanical strengths are obtained by comparing the limiting molecular weights (M_lim) and contour lengths (L_lim) of the polymers under pulsed ultrasound of their dilute solutions. The values of M_lim and L_lim, and thus the inferred mechanical strengths of the polymers, are effectively identical. The mechanical bonds of the catenanes are therefore as strong, or stronger, mechanically as the covalent bonds along the polymer backbone.     

Rendering polyureas melt processible

Because of the presence of extensive H‐bonding in the hard segments, polyureas are processed by solution techniques (e.g., dry spinning) by the use of relatively costly and environmentally unfriendly solvents. Thus, the objective of this research was to render polyureas melt processible, (i.e., to reduce their flow temperature, T_flow) without compromising their excellent mechanical properties. We hypothesized and herein demonstrate that by using conventional chain extenders (CEs) in combination with small amounts of H‐bond acceptor chain extenders (HACEs), the T_flow of polyureas can be significantly reduced from ～230 to ～180 °C, and thus melt processible products with excellent mechanical properties can be obtained. We document the synthesis of conventional polytetramethylene oxide‐based and novel polyisobutylene (PIB)‐based polyureas with T_flows ～ 180 °C and excellent mechanicals by the addition of few percents of commercially available HACEs. Products were characterized by various techniques, including Instron (tensile strengths, elongations), durometer (Shore A Hardness), dynamic mechanical thermal analysis (T_flow), and thermal gravimetric analysis (TGA) (thermal weight loss). According to TGA, a polyurea with T_flow of ～180 °C did not degrade up to ～234 °C in air. A micromorphology for melt processible polyureas is proposed that emphasizes flexibilized hard segments in the presence of HACEs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Mechanical Properties of Interlocked-ring Polymers: A Molecular Dynamics Simulation Study

Interlocked-ring polymers, also known as polycatenanes, possess an interesting molecular architecture. These polymers are composed of many interlocked rings in a linear chain. The topological constrain between neighboring rings distinguishes the interlockedring polymer from its linear counterpart. Here we present extensive molecular dynamic simulations on the interlocked-ring polymers and analyze the static properties of the polymer. By applying external forces to the polymer, we also study the force-extension curves of the polymer, which provides rich information about the mechanical properties of the interlockedring polymers.     

Model hard segments from diphenyl methane diisocyanate and different chain extenders,and corresponding linear block polyurethanes

Model hard segments from MDI and different chain extenders have been studied by DSC. Among the studied α-ω alkane diol-type chain extenders, all giving crystalline hard segments, butane diol shows the highest melting temperature, while other types such as 1,4-diaminobutane, 1,4-benzene dimethanol, and 4,4′-methylene-bis(2-chloroaniline), so-called MOCA, have no melting endotherm in the range 30–260°C. In addition to DSC, dynamic mechanical properties were measured on linear block polyurethanes having both hard segments and soft ones of hydrogenated 1,2-polybutadiene. The hard segments in the polyurethane chains are of amorphous structure or low crystallinity, and their high-temperature behavior depends only on their strength of interaction in the amorphous state. Accordingly, MOCA shows the highest hard-block softening temperature.     

Investigating the Dynamic Viscoelasticity of Single Polymer Chains using Atomic Force Microscopy

In single‐molecule force spectroscopy (SMFS), many studies have focused on the elasticity and conformation of polymer chains, but little attention has been devoted to the dynamic properties of single polymer chains. In this study, we measured the energy dissipation and elastic properties of single polystyrene (PS) chains in toluene, methanol, and N,N‐dimethylformamide using a homemade piezo‐control and data acquisition system externally coupled to a commercial atomic force microscope (AFM), which provided more accurate information regarding the dynamic properties of the PS chains. We quantitatively measured the chain length‐dependent changes in the stiffness and viscosity of a single chain using a phenomenological model consistent with the theory of viscoelasticity for polymer chains in dilute solution. The effective viscosity of a polymer chain can be determined using the Kirkwood model, which is independent of the intrinsic viscosity of the solvent and dependent on the interaction between the polymer and solvent. The results indicated that the viscosity of a single PS chain is dominated by the interaction between the polymer and solvent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1736–1743     

Molecular modeling of polymers: I. Correct and efficient enumeration of intrachain conformational energetics

Polymer conformational analyses can require being able to model the intramolecular energetics of a very long (infinite) chain employing calculations carried out on a relatively short chain sequence. A method to meet this need, based upon symmetry considerations and molecular mechanics energetics, has been developed. Given N equivalent degrees of freedom in a linear polymer chain, N unique molecular groups are determined within the chain. A molecular unit is defined as a group of atoms containing backbone rotational degrees of conformational freedom on each of its ends. The interaction of these N molecular groups, each with a finite number of nearest neighbors, properly describe the intramolecular energetics of a long (infinite) polymer chain. Thus, conformational energetics arising from arbitrarily distant neighbor interactions can be included in the estimation of statistical and thermodynamic properties of a linear polymeric system. This approach is called the polymer reduced interaction matrix method (PRIMM) and the results of applying it to isotactic polystyrene (I-PS) are presented by way of example.     

Stiffness and excluded volume effects on conformation and dynamics of polymers: A simulation study

This work investigates the effects of the excluded volume and especially those of the chain stiffness on the structural and dynamical properties of a model polymer chain.The theoretical framework is the same as in the recent works by Steinhauser et al.,where a Rouse approach is adopted.Our model differs in that our chains have a finite average bending angle.As in the works by Steinhauser et al.,Langevin dynamic simulations were performed without hydrodynamic interactions.Whereas this doesn’t impact the static properties we obtain,it also allows us to compare our results on dynamic properties to those predicted by Rouse theory,where hydrodynamic interactions are also neglected.Our results show that the structural properties are very sensitive to the chain stiffness,whereas the dynamic scaling laws remain the same as those by Rouse theory,with the prefactor depending on the persistence length.     

Superstructure in segmented polyether–urethanes

The morphology of several series of segmented polyether–urethanes was studied. The “hard” segments contained urethane and urea linkages formed by 4,4′-dicyclohexylmethane diisocyanate (Hylene W) and selected aliphatic and aromatic monomeric diamines (DA). The “soft” segments were composed of oligomeric poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), or both PEO and PPO. For studying the composition–morphology relationships, the molecular weight and relative content of PEO, and the relative content of PPO were varied systematically. Different diamines were used as chain extenders. The methods of wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), polarizing microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) were employed in the investigation. The effects of PEO content on domain formation were very significant. Calculations based on a highly simplified model indicated that, for two adjacent molecules, if two hard segments are associated with each other, the probability for the association of the next two hard segments varies inversely with the third power of soft segment length. Copolymers composed of both POE and PPO displayed enhanced domain and anisotropic superstructure. The phenomenon was interpreted in terms of polymer incompatibility. The effects on morphology of different DA's as chain extenders were tentatively accounted for by the symmetry, hydrogen bonding, and rigidity of the hard segments as well as their incompatibility with the soft segments. The formation and deformation of superstructure were of particular interest. A model was proposed to account for the formation of the resultant anisotropic structure and mechanical properties.     

Mechanical and thermal properties of ternary alternating copolymers of carbon monoxide with olefins

Thermal properties and the deformational behavior of ternary alternating copolymers of carbon monoxide with ethylene and other olefins (propylene, 1-butene, styrene) with molecular masses of M _n = 1000–35000 and molar fraction of the third comonomer in the polymer chain from 0.02 to 0.70 were investigated. Temperatures of melting and glass transition are significantly affected by the composition of the products. Varying the nature of the third comonomer or the content of its units in the polymer chain and the molecular masses of terpolymers makes it possible to obtain materials with Young’s moduli of 0.003–3.090 GPa and elongations at break of 5–2000%.     

Polymer Alloys—Their Structure,Morphology, and Properties

Polymeric materials with novel properties for new technological applications are increasingly obtained by combining existing polymers, while the synthesis of new monomers has receded into the background. These polymer combinations or “alloys” (polyblends) are characterized by their chemical composition, the conformation of the chain molecules, and the morphology, i.e. the state of order at supramolecular level. Multiphase constitution is a typical characteristic of these substances, with a decisive influence on their macroscopic properties. The morphology of multiphase polymer alloys can be controlled to a limited extent via the chemical composition of their components when homopolymers are mixed in the melt or as dispersions. Graft copolymerization, on the other hand, makes it possible to achieve the desired morphology at a given chemical composition. Furthermore, transprent two-phase polymer alloys can be obtained under certain conditions. In multiphase polymers the reduction of stress without fracture, caused by mechanical loading will be treated using models. Certain combinations of properties such as hardness and toughness are connected with the coexistence of disperse and continuous phases. Equilibrium thermodynamical criteria for liquid mixtures wil be used to explain demixing phenomena in polymers. In the last few years it has become possible to determine the chain conformation experimentally using neutron scattering.