A new proposal for polymer dynamics in steady shearing flows

Beginning with a recently proposed expression for the drag force on a single macromolecule pulled with constant velocity through a fluid of long‐entangled molecules (V. R. Mhetar and L. A. Archer, Macromolecules 1998, 31, 6639), we investigate the effect of entanglement loss on polymer dynamics in steady shearing flows. At steady‐state, a balance between the elastic restoring force and viscous drag acting on entangled polymer segments reveals a critical molecular strain γ_m,c beyond which the drag force exerted on polymer molecules by their neighbors is insufficient to support arbitrarily small orientation angles. Specifically, we find that in fast steady shear flows τ < γ˙ < τ, polymer orientation in the shear plane approaches a limiting angle χ_c ≈ atau(1/(1 + γ_m,c)) beyond which flow becomes incapable of producing further molecular alignment. Shear flow experiments using a series of concentrated polystyrene/diethyl phthalate solutions with fixed entanglement spacing, but variable polymer molecular weight 0.94 × 10⁶ ≤ M_w ≤ 5.48 × 10⁶, reveal a limiting steady‐state orientation angle between 6° and 9° over a range of shear rates; confirming the theoretical result. Orientation angle undershoots observed during start‐up of fast steady shearing flows are also explained in terms of a transient imbalance of elastic restoring force and viscous drag on oriented polymer molecules. Our findings suggest that the Doi–Edwards affine orientation tensor (Q) is not universal, but rather depends on deformation type and deformation history through a balance of elastic force and viscous drag on polymer molecules. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 222–233, 2000     

Postgel properties in the statistical crosslinking of heterochains. I. Systems with N types of chains

The heterochain crosslinking model describes nonrandom crosslinking of polymer chains and is an extension of the classical Flory/Stockmayer gelation theory. We consider the postgelation relationship for the system consisting of N types of polymer chains, in which the probability that a crosslink point on an i‐type chain is connected to a j‐type chain is explicitly given by p_ij. The analytical solutions for the weight fraction of the sol, the number‐average and weight‐average molecular weights within the sol fraction, and the crosslinking density within the sol and gel fractions are derived for the systems, with each type of chain conforming to the Schulz–Zimm distribution. Illustrative calculations are shown for the systems consisting of two and three types of chains, and the obtained results agree with those from the Monte Carlo method. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2333–2341, 2000     

Naphthodithiophene‐Diketopyrrolopyrrole‐Based donor–Acceptor alternating π‐Conjugated polymers for Organic thin‐Film transistors

Novel naphtho[1,2‐b:5,6‐b′]dithiophene (NDT) and diketopyrrolopyrrole (DPP)‐containing donor‐acceptor conjugated polymers (PNDTDPPs) with different branched side chains were synthesized via Pd(0)‐catalyzed Stille coupling reaction. Octyldodecyl (OD) and dodecylhexadecyl (DH) groups were tethered to the DPP units as the side chains. The soluble fraction of PNDTDPP‐OD polymer in chloroform has much lower molecular weight than that of PNDTDPP‐DH polymer. PNDTDPP‐DH polymer bearing relatively longer DH side chains exhibited much better charge‐transport behavior than PNDTDPP‐OD polymer with shorter OD side chains. The thermally annealed PNDTDPP‐DH polymer thin films exhibited an outstanding charge carrier mobility of ～1.32 cm² V^?1 s^?1 (I_on/I_off ～ 10⁸) measured under ambient conditions, which is almost six times higher than that of thermally annealed PNDTDPP‐OD polymer thin films. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5280–5290     

Morphological study of an intrinsically stretchable photovoltaic bulk heterojunction

Thin‐film polymer solar cell consisting of [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) and poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) demonstrates elastic stretchability with the aid of a high boiling point additive, 1,8‐diiodooctane (DIO). The usage of DIO not only helps to form uniformly distributed nanocrystalline grains, but may also create free volumes between the nano‐grains that allow for relative sliding between the nano‐grains. The relative sliding can accommodate large external deformation. Large dichroic ratios of the optical absorption of both PC₇₁BM and PTB7 were observed under large‐strain deformation, indicating reorientation of the nanocrystalline PC₇₁BM and PTB7 polymer chains along stretching direction. The dichroic ratio decreases to nearly 1.0 as the blend was relaxed to 0% strain. Therefore, the nanometer‐size grain blending morphology provides an approach to impart stretchability to organic semiconductors that are otherwise un‐stretchable. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 814–820     

Continuous phase viscosity influence on maximum diameters of poly(styrene‐divinylbenzene) beads prepared by suspension polymerization

The influence of the continuous phase viscosity (μ_c) on the diameter of styrene‐divinylbenzene polymer beads was studied over a large range of viscosities at constant dissipated power. This study was based on the inertial breakup and viscous shear breakup theories for a stirred dispersion. These two theoretical models were compared with an experiment for the two highly viscous agents sucrose and acacia gum [dispersed and continuous phase viscosities (μ_d, μ_c) = 10⁻³ < μ_d/μ_c < 1]. We found that the maximum diameters of the polymer beads could not be described by an inertial breakup. The maximum diameters were in good agreement with a viscous shear breakup model for the two viscous agents in turbulent and semilaminar flows. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 201–210, 2001     

Molecular mobility of poly(methyl methacrylate) glass during uniaxial tensile creep deformation

An optical photobleaching method has been used to measure the segmental dynamics of a poly(methyl methacrylate) (PMMA) glass during uniaxial creep deformation at temperatures between T_g ? 9 K and T_g ? 20 K. Up to 1000‐fold increases in mobility are observed during deformation, supporting the view that enhanced segmental mobility allows flow in polymer glasses. Although the Eyring model describes this mobility enhancement well at low stress, it fails to capture the dramatic mobility enhancement after flow onset, where in addition the shape of the relaxation time distribution narrows significantly. Regions of lower mobility accelerate their dynamics more in response to an external stress than do regions of high mobility. Thus, local environments in the sample become more dynamically homogeneous during flow. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1713–1727, 2009     

In situ bubble‐stretching dispersion mechanism for additives in polymers

An in situ bubble‐stretching (ISBS) model has been proposed on the basis of an analysis of the dispersion process of inorganic additives in polymers. The ISBS model is applicable to a dispersion of solid granular aggregates in polymer melts because the dispersed phase itself serves as a nucleation agent, giving rise to bubbles that expand at the surface of the microgranules and their aggregates. In terms of bidirectional stretching, the ISBS process can increase the degrees of freedom of granule dispersion, which favors more homogeneous dispersion. According to theoretical predictions and indirect experimental estimations of the dispersion of nanoscale CaCO₃ and nanoscale hydrotalcite in high‐density polyethylene (HDPE), when the bubble expands, the stretching rate of the polymer melt on the bubble wall can reach 10⁵–10⁶ s^?1. The field emission scanning electron microscopic images indicated that the granular size of dispersed CaCO₃ and hydrotalcite in HDPE with the ISBS method is about 60–80 nm, two orders of magnitude smaller than that attained with a shearing rate of 10³ s^?1 in a capillary rheometer. It is also predicted that elastic bubble oscillations may be generated through suitable control of process parameters and that their oscillatory frequency can be in the ultrasound range. This type of bubble oscillation can also promote dispersion. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1051–1058, 2003     

Small‐angle neutron scattering analysis of bottlebrush backbone and side chain flexibility

Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are determined through small‐angle neutron scattering analysis of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a “grafting‐through” ring‐opening polymerization. Scattering profiles are modeled with the empirical Guinier–Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end‐to‐end distance proportional to N^0.55, while the overall bottlebrush increases in size proportional to N^0.77. These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in solution. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 104–111     

Synthetic polyhydroxypolyamides from galactaric,xylaric, D‐glucaric,and D‐mannaric acids and alkylenediamine monomers—some comparisons

The condensation polymerization in a methanol solution of four different esterified aldaric acids (D ‐glucaric, meso‐xylaric, meso‐galactaric, and D ‐mannaric) with even‐numbered alkylenediamines (C₂–C₁₂) gave polyhydroxypolyamides whose water solubilities and melting points were compared. In general, an increase in the alkylenediamine monomer length resulted in decreased polyamide water solubility. Differences in the polymer melting points and water solubilities were linked primarily to conformational differences of the monomer aldaryl units; for example, polyamides from meso‐galactaric acid with an extended zigzag conformation aldaryl monomer unit had higher melting points and lower water solubilities than those from D ‐glucaric and meso‐xylaric acids. The latter acid monomer units tended toward bent conformations that served to diminish intermolecular attractive forces between polymer chains, affecting polymer solubility and melting characteristics. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 594–603, 2000     

Dynamics of entangled polymer chains with nanoparticle attachment under large amplitude oscillatory shear

This paper presents a nonlinear viscoelastic model for polymer nanocomposites and the computed model response to large amplitude oscillatory shear flow. The model predicts the stress in a mixture of entangled polymer chains, with different convective constraint release (CCR) rates for free chains and nanoparticle‐attached chains, through an averaging scheme which is consistent with double reptation in the Marrucci–Ianniruberto constitutive equation. The nonlinear response of the mixture is evaluated both numerically in terms of Q and by an asymptotic analysis in terms of four frequency dependent parameters of medium amplitude oscillatory shear (MAOS) as well as the intrinsic nonlinearity parameter Q₀ . In the case of free polymer chains alone, the MAOS signatures are comparable to those of the Giesekus model with the notable difference of a minimum in the elastic parameter [e₁] at De >1. The viscous nonlinear parameters of the mixture model depart significantly from those of the free chains, especially in mixtures where the CCR parameter for attached chains is larger than that for the free chains: [v₁] has a prominent minimum and [v₃] has a prominent maximum near De = 2/c, the low frequency plateau region, along with a higher Q₀ compared to the matrix at all Deborah numbers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 62–76     

Synthesis and properties of poly‐(2‐ethynylpyridinium bromide) having propargyl side chains

Poly‐(2‐ethynylpyridinum bromide) (PEPBP) having propargyl side chains was prepared by the direct polymerization of 2‐ethynylpyridine and propargyl bromide under mild reaction conditions without any initiator and catalysts. The polymerization proceeded well to give PEPBP with propargyl side chains in relatively high yields. Various spectral data for the polymer structure indicated that the conjugated polymer system having N‐propargylpyridinum substituent was formed. This ionic polymer was completely soluble in water, methanol, dimethylformamide, dimethyl sulfoxide, and N,N‐dimethylacetamide and well processable into thin homogeneous film. The photoluminescence intensity (λ_max = 760 nm) of this polymer increased as the temperature was increased. At 1 KHz and room temperature, this polymer has k′ = 2.9 and σ = 7.3 × 10^?10 (S/cm). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3151–3158, 2001     

Mixed solvent effect on lithium-coordination to poly(ethylene oxide)

This article presents a comparative study of the structure formation of poly (ethylene oxide) PEO/Li complexes in aqueous and acetonitrile solutions using small-angle neutron scattering (SANS). We demonstrate that in acetonitrile solutions, Li-cations coordinate to the ether–oxygen of the monomeric unit, and this results in charging and stretching of the polymer chains. This is found to be in contrast to aqueous solutions, where the ions remain free in solution. In particular, we demonstrate that the “binding” and “screening” regimes that were observed in case of PEO/K⁺ solutions in acetonitrile are also found in the respective PEO/Li⁺ solutions. The addition of water to solutions in acetonitrile increasingly diminishes the ion-coordination to the polymer, eventually resulting in neutral polymer chains at water contents above ϕ*_water = 30% (w/v). The preferential adsorption of water on PEO in mixtures of acetonitrile and water is evidenced by the pronounced stretching of polymer chains, in particular, at a water content of ϕ_water = 25% and 33.33% (w/v) where complete stretching of the chains is observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3642–3650, 2006     

Ethynylene‐containing donor–acceptor alternating conjugated polymers: Synthesis and photovoltaic properties

Four ethynylene‐containing donor‐acceptor alternating conjugated polymers P1 – P4 with 2,5‐bis(dodecyloxy) substituted phenylene or carbazole as the donor unit and benzothiadiazole (BTZ) as the acceptor unit were synthesized and used as donor polymers in bulk heterojunction polymer solar cells. The optical, electrochemical, and photovoltaic properties of these four polymers with the ethylene unit located at different positions of the polymer chains were systematically investigated. Our results demonstrated that absorption spectra and the HOMO and LUMO energy levels of polymers could be tuned by varying the position of the ethynylene unit in the polymer chains. Photovoltaic devices based on polymer/PC₇₁BM blend films spin coated from chloroform and dichlorobenzene solutions were investigated. For all four polymers, open circuit voltages (V_oc) higher than 0.8 V were obtained. P4 , with ethynylene unit between BTZ and thiophene, shows the best performance among these four polymers, with a V_oc of 0.94 V, a J_sc of 4.2 mA/cm², an FF of 0.40, and a PCE of 1.6%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Effect of solvent–matrix interactions on structures and mechanical properties of micelle‐crosslinked gels

Previous studies on hydrogels crosslinked by acrylated PEO₉₉–PPO₆₅–PEO₉₉ triblock copolymer (F127DA) micelles demonstrate outstanding strength and toughness, which is attributed to the efficient energy dissipation through the hydrophobic association in the micelles. The current study further focuses on how the solvent property affects the structures and the mechanical properties of F127DA micelle crosslinked polyacrylamide gels. Binary solvents comprised of dimethyl sulfoxide (DMSO) and water are used to adjust the polymer/solvent interactions, which consequently tune the conformations of the polymer chains in the network. The presence of DMSO significantly decreases the strength but increased the stretchability of the gels, whereas the overall tensile toughness remained unchanged. In situ small‐angle X‐ray scattering measurements reveal the deformation of micelles along with the stretching direction. A structure evolution mechanism upon solvent change is proposed, according to the experimental observations, to explain influence of solvent quality on the mechanical properties of the micelle‐crosslinked gels. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 473–483     

High molecular weight atactic polypropene synthesized with (η5‐pentamethylcyclopentadienyl)tribenzyl titanium activated with MAO

The half‐titanocene (η⁵‐pentamethylcyclopentadienyl)tribenzyl titanium (Cp*TiBz₃) with methylaluminoxane (MAO) as the cocatalyst was employed to catalyze propene polymerization at ambient pressure. A novel atactic polypropene elastomer with a high molecular weight (M̄_w = 2 − 8 × 10⁵) was produced. The effects of the polymerization conditions on the catalytic activity and polymer molecular weight are discussed. ¹³C NMR analysis confirmed that the catalyst system Cp*TiBz₃/MAO produced atactic polypropenes, and the polymerization mechanism was in agreement with the Bernoullian process. The triad sequence distribution of the polymer was measured and found to be as follows: mm = 6.15%, mr = 40.87%, and rr = 52.98% (Bernoullian factor B = 1.03); this indicated that the insertion of propene with the catalyst system followed a chain‐end control model. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 411–415, 2000     

Predicting chain dimensions from an artificial neural network model

Artificial neural network models are used to investigate polymer chain dimensions. In our model, the input nodes are glass transition temperature (T_g), entanglement molecular weight (M_e), and melt density (ρ). The number of nodes in the hidden layer is eight. We found that the relative error for prediction of the characteristic ratio ranges from 0.77 to 7.5% and that the overall average error is 3.57%. Artificial neural network models may provide a new method for studying statistics properties of polymer chains. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3163–3167, 2000     

Mechanism of generation of photoelastic birefringence in methacrylate polymers for optical devices

We clarified the birefringence properties of poly(methyl methacrylate), poly(ethyl methacrylate), poly(isobutyl methacrylate), poly(cyclohexyl methacrylate), poly(isopropyl methacrylate), and poly(tert‐butyl methacrylate). We demonstrated that the conformational change in polymer molecules that causes orientational birefringence differs from that causing photoelastic birefringence. Orientational birefringence depends mainly on the orientation of the main chains of the methacrylate polymers above T_g. On the other hand, photoelastic birefringence in elastic deformation below T_g depends mainly on the orientation of the side chains while the main chains are scarcely oriented. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2029–2037, 2010     

Synthesis of conjugated polymers with azobenzene moieties in the main chain

Poly(phenylenevinylene)‐based conjugated polymers with azobenzene groups in the main chains were prepared by the Pd‐catalyzed coupling polymerization of divinylarenes with dihaloarenes. The Pd‐catalyzed coupling polymerization of 4,4′‐divinylazobenzene with dihaloarenes such as 1,3‐dibromobenzene, 1,4‐dibromo‐2,5‐dihexylbenzene, 4,4′‐dibromoazobenzene, and 4,4′‐diiodoazobenzene resulted in polymers with poor solubility. In contrast, soluble polymers containing azobenzene moieties in the main chains were attainable from divinylbenzenes with 4,4′‐dihaloazobenzenes if either or both of the monomers possessed hexyl groups on the aromatic rings. The number‐average molecular weight of the polymer exceeded 10,000 under optimized conditions, and the polymer showed a remarkably redshifted absorption in the visible region (456 nm). ¹H NMR and IR spectra supported that the polymers having only trans‐geometry for the double bonds. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1057–1063, 2000     

Double‐helical network in amylose as seen by slow calorimetry and FTIR

The phase content and crystallinity of initially amorphous amylose–water mixtures (70/30 W/W) have been changed by slow cycles of dissolution and recrystallization from T_max with 50 °C < T_max < 120 °C. Analysis of the treatment‐induced changes is made by X‐ray diffraction, FTIR, fast T‐ramp DSC and slow calorimetry. Our interest was to follow the relaxation of the network phase and its consequence on the growth of crystallinity. The DSC technique, which gives the temperature of disappearance of long‐range order, is unable to quantitatively follow the growth of crystallinity achieved by treating the samples. In highly interactive polymer–solvent systems, order is unmeltable in a fast T‐ramp due to strain developed during the ramp. In a 6 K/h T‐ramp, the order becomes meltable and grows from 21 J/g to 147 J/g when T_max increases. The other conclusion is that strain‐melting and the network phase, characterized first in polyolefins has a more prominent role in the characterization of H‐bonded polysaccharide–water mixtures. Correlation is achieved between the concentration of bands in the C O stretching region, the fraction of single and double helices, and the three endotherms found on the slow T‐ramp dissolution traces. FTIR spectra show that chains in the network cannot be disentangled by quenching but can be organized during a slow cooling. The B and V crystalline modifications are observed in the treated samples. Quenched treated amylose and enzyme‐resistant amylose seem to contain a comparable amount of double‐helical/strainable fraction. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1662–1677, 2000     

Energy transfer along a sequence controlled hybrid polymer

The present work provides an ideal model for intra‐chain energy transfer study in conjugated polymer through shielding the polymer backbone by using bulky polyhedral oligomeric silsesquioxanes (POSS). POSS provides a circumference shielding of the polymer backbone to prevent closed packing of the polymer chains, allowing the intra‐chain energy transfer dominating in large concentration range. Bi‐functional POSS (B‐POSS) is specially designed to separate donor (fluorene) and acceptor (benzothiadiazole) within the polymer chain. The dynamics of energy transfer in poly(fluorene‐POSS‐alt‐POSS‐benzothiodiazole) (PTBtTbOFl₃) is studied by steady state as well as time resolved fluorescence spectroscopy at different donor/acceptor ratios. Results reveal that POSS can effectively shield inter‐chains energy transfer of the polymers, suggesting it is an effective model for energy transfer study with less inter‐chains effects. PTBtTbOFl₃ works as a chemosensors is also reported in the detection of explosive derivatives. These results provide insights for optimizing nanostructured materials for use in optoelectronic devices. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1225–1233