A method of calculating densities of polymers

Molar volumes of substantially amorphous polymers may be calculated by using additive constants derived from constitutive atomic and structural parachor contributions. For 34 polymers, ranging in density from 0.83 to 2.03 g/cm³, the greatest error in the calculated molar volume compared with the measured value was 13.9%, while for 30 of the polymers the error was less than ±7%, with a mean error of ±3.9%.     

Primitive chain network study on uncrosslinked and crosslinked cis-polyisoprene polymers

In this paper, the polymer chain packing and primitive path (PP) network of uncrosslinked and crosslinked cis-polyisoprene (PI) polymer are analyzed upon employing coarse-grained molecular dynamics simulation. The crosslinking effect is found to enhance intra-chain packing of PI polymers, while weakening their inter-chain packing. Surprisingly, these effects cancel each other in the global packing behavior of this polymeric system. We systematically study the effects of molecular weight (MW) and crosslink density on the PP. Both the PP contour length and number of entanglements per chain, 〈Z〉, are found to increase linearly with MW for uncrosslinked cis-PI. The corresponding entanglement molecular length N_e of cis-PI is estimated to be 76 ± 1, in good agreement with experimental results. The polymer end-to-end distance, the PP contour length as well as 〈Z〉 of crosslinked PI are reduced by higher intra-chain packing density, compared with uncrosslinked PI, if the crosslinkers are ignored in the PP analysis. At the same time, the tube diameter of crosslinked PI is enlarged by the sparse inter-chain packing. By dividing the crosslinked cis-PI chain network into subchains through crosslinked or crosslinker beads, the PP networks of these partial systems are treated as well. We obtain scaling laws between MW/crosslinking density and 〈Z〉 for crosslinked PI polymers. The simulation results indicate that the random walk assumption, often encountered during the analysis of PPs, can only be applied to the entanglement-dominated (low crosslink density) polymers. For crosslink-dominated (high crosslink density) polymers, whose subchains have a molecular length below 100, this assumption would imply a greatly overestimated entanglement density; we thus avoid the assumption in our analysis. To our best knowledge, this is the first work to uncover the PP of crosslinked polymers.     

Synthesis and characterization of branched polymers by a free radical approach using a novel ‘macroiniferter’

Free radical bulk polymerization of styrene and methyl methacrylate (MMA) was carried out using a novel ‘macroiniferter’ which resulted in branched polymers with relatively narrow molecular weight distribution. This approach involving the novel macroiniferter; poly[3-(t-butylperoxy)propyl disulfide] (PBPPDS) that has side chain peroxide groups and main chain disulfide linkages was developed to prepare soluble branched polymers as well as to control the extent of branching in vinyl polymers synthesized via a free radical route. The synthesis, characterization and thermal degradation studies of PBPPDS are reported here for the first time. The resulting polystyrene (PS) and poly(methyl methacrylate) (PMMA) polymers were characterized using gel permeation chromatography (GPC), intrinsic viscosity [η] measurements and the degree of branching was studied by the determination of g′ factor.     

Wall slip of molten polymers

There is considerable experimental evidence that the classical no-slip boundary condition of fluid mechanics is not always a valid assumption for the flow of high molecular weight molten polymers. In fact, molten polymers slip macroscopically at solid surfaces when the wall shear stress exceeds a critical value. Moreover, for linear polymers there exists a second critical wall shear stress value at which a transition from a weak to a strong slip occurs. These two modes of slip (weak and strong) are due to flow-induced chain detachment/desorption at the polymer/wall interface and to chain disentanglement of the polymer chains in the bulk from a monolayer of polymer chains adsorbed at the interface. In this review, the two physical mechanisms of slip are discussed and validated on the basis of published experimental data. The slip velocity of molten polymers is a complex function and has been reported to depend on wall shear and normal stresses, temperature, and molecular characteristics of polymers (molecular weight and its distribution). Proposed slip models, static and dynamic, are also reviewed and their significance on the rheology and flow simulations of molten polymers is discussed.     

Synthesis and characterization of high molecular weight side chain liquid crystalline/photoactive polymers

Various liquid crystalline and photoactive azobenzene monomers were synthesized and attached to copoly(methyl methacrylate‐glycidyl methacrylate) [copoly (MMA‐GMA)] to get high molecular weight side chain liquid crystalline (LC)/photoactive copolymers. Further, spacers are generated in situ and reactive groups are obtained after the modification. All monomers and polymers were thoroughly characterized by FTIR, ¹H and ¹³C NMR, UV‐VIS spectrophotometry, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy. All side chain LC polymers showed higher thermal stability than that of copoly(MMA‐GMA). Three LC and one azo monomer exhibited characteristic nematic mesophase where as one LC monomer has shown nematic and sanded smectic‐A texture. The rate of trans‐cis isomerization of polymer was lower than that of the monomer and both monomers and polymers showed slow back isomerization. Present approach offers convenient way to synthesize high/desired molecular weight photoactive LC polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and radical scavenging ability of new polymers from sterically hindered phenol functionalized norbornene monomers via ROMP

Norbornene derivatives, including four novel structure compounds, bearing sterically hindered phenol (SHP) were prepared as functional monomers (1-3). The ring-opening metathesis polymerization (ROMP) of these functional monomers was carried out with typical ruthenium catalyst [bis(tricyclohexylphosphine)benzylidene ruthenium(IV) dichloride] that was so called as first-generation Grubbs catalyst to prepare hindered phenol functionalized polymers possessing radical scavenging function. The resulting polymers were characterized by means of gel permeation chromatography (GPC), ¹H and ¹³C NMR, and differential scanning calorimetry (DSC). The radical scavenging ability of polymer was evaluated by determining RSA using the α,α-diphenyl-β-picrylhydrazyl (DPPH) free radical. The results show that the resulting polymers have different radical scavenging ability with the difference in structure of side chain. Polymers bearing 3,5-di-tert-butyl-4-hydroxyphenyl-propionate (DBHP) side chain have a higher radical scavenging ability than the polymers bearing 3,5-di-tert-butyl-4-hydroxy-benzoate (DBHB) as side chain. The molecular weight of polymers is dependent on the ratio of molar concentration of monomer to catalyst ([M]/[C]); monomers bearing DBHP group have a higher activity for ROMP than the monomers bearing DBHB group comparatively.     

Cyclophane-containing polymers

In spite of the remarkable progress of cyclophane chemistry, syntheses of polymers containing cyclophane units in the main chain and side chain by utilizing the transannular π–π interaction are considerably limited. In this review, syntheses, properties, and applications of [m,n]cyclophanes-containing (m?3 and n?3) polymers prepared to date are presented. The main body of the review is classified into broadly four categories: introduction of (i) main-chain-type cyclophane-containing polymers, (ii) side-chain-type cyclophane-containing polymers, (iii) rigid-rod conjugated polymers containing pendent aromatic rings, and finally (iv) aromatic-ring-layered polymers comprising [2.2]paracyclophane.     

Study of molecular packing density in boundary layers of some polymers

Packing density of macromolecules of some amorphous polymers, poly(methyl methacrylate), polystyrene and polydimethylsiloxane, in boundary layers formed at the solid-polymer interface, was studied by a ‘molecular probe’ technique. It was shown that the boundary layers of the above polymers have a complex structure composed of regions with different densities of molecular packing: a surface region of thickness 2 to 4 μm, and a transient and loosely-packed region of thickness of the order of 30 to 60 μm. It was established that both the structure and the thickness of boundary layers for each of the polymers depends both on polymer chain flexibility, and on cohesion energy density of a polymer.     

The structure of amorphous polymers

Over the past ten years the structure of amorphous polymers has been extensively investigated. Publications on this topic were concerned with various aspects of the amorphous structure and were often based on specific molecular models. This review article attempts to discuss the interrelations between the different structural properties which were studied. The topics covered are the short range positional order, the orientational order, the chain conformation, the supermolecular structure and the relation between molecular and macroscopical properties both of the fluid and the glassy state. The basic theory of the fluid state is introduced at the beginning as well as the experimental techniques currently used to characterize the amorphous structure. Experimental results on different amorphous polymers and oligomers are then discussed and the information is pointed out which can be derived from these data. Finally models on the structure of amorphous polymers are considered briefly.     

Craze initiation in glassy polymers: Quantifying the influence of molecular orientation

A study has been made of crazing stress in oriented glassy polystyrene. The aim was to develop a methodology for prediction of crazing stress in glassy polymers with frozen-in molecular orientation. Oriented specimens of two grades of monodisperse polystyrene (PS) and one grade of polydisperse PS were produced by uniaxial melt-drawing and subsequent quenching of compression-moulded bars. Birefringence and crazing stress parallel to the draw direction (in the presence of diethylene glycol) were measured on miniature beam specimens cut from them. The crazing stress increased substantially with orientation, and the magnitude of the increase relaxed approximately on a timescale associated with the longest Rouse time. Specifically, a linear correlation was found, to within experimental scatter, between the increase in crazing stress and the orientation expressed in terms of frozen-in conformational stress, as predicted by the theory of Maestrini and Kramer [13]. The inverse gradient (constant β in the theory) was found to be 0.059 ± 0.002, when inferring the conformational stress from the measured birefringence. Crazing was found to be suppressed in favour of yielding in the most highly oriented specimens, and this could be explained in terms of the differing sensitivities of crazing and yield to molecular orientation.     

Mechanical motions in amorphous and semi-crystalline polymers

Ten areas of the field, all with some special interest to the author, were selected for predictions about the near future. In order to gain perspective, a brief review is presented of some key developments which occurred after the publication of the book ‘Anelastic, and Dielectric Effects in Polymeric Solids’ by McCrum, Read and Williams in 1967. The following predictive areas are then discussed in varying degrees of detail. (1) Apparatus: current status and the need for automation and more sophistication. (2) Extending the temperature range above T_g or T_M and the molecular weight range down to the oligomers. (3) Study of rarefied polymers (higher than normal free volume). (4) Nature of the in-chain β relaxation (T < T_g) in addition polymers. (5) Use of nitroxide probes as an auxiliary tool to study amorphous phase relaxations in highly crystalline polymers. (6) Computer simulation of molecular motion at sub-group relaxations. (7) Nature of the amorphous state and its possible effect on mechanical relaxations other than through free volume. (8) Correlation between mechanical strength of glassy polymers and secondary, glassy state relaxations. (9) The need to prepare highly crystalline polymers in the completely amorphous state. (10) The impact of new polymer types. It is concluded that mechanical spectroscopy is still a quite viable field with exciting potentialities. A synergism between automation of apparatus, new materials, new techniques (not necessarily in the field of mechanical spectroscopy) and theory is anticipated.     

Preparation of hyperbranched polymers through ATRP of in situ formed AB* monomer

The self‐condensing vinyl polymerization of an AB* monomer formed in situ by atom transfer radical addition from divinylbenzene (DVB) and (1‐bromoethyl)benzene (BEB) using atom transfer radical polymerization technique was studied. The catalyst concentration has a dramatic effect on polymerization. To study the polymerization mechanism and to achieve high molecular weight polymer, the polymerization was carried out in bulk with a catalyst to monomer ratio, 2,2′‐bipyridine to DVB, of 0.2 at 90°C. Proton nuclear magnetic resonance (¹H NMR) spectroscopy and size‐exclusion chromatography coupled with multiangle laser light scattering were used to analyze the polymerization aliquots and the obtained polymer. The intrinsic viscosities of the prepared polymers were also measured. Experimental results, from the comparison of the apparent molecular weights measured by size‐exclusion chromatography with the absolute values measured by multiangle laser light scattering as well as viscosity measurements, indicate the existence of hyperbranched structures in the prepared polymers. In sharp contrast to hyperbranched polymers from AB* monomer preprepared, hyperbranched ploy(divinylbenzene) prepared at equimolar amount of DVB and BEB has numerous residual pendant vinyl groups rather than only one double bond at its focal point. The hyperbranched polymers show relatively narrow molecular weight distribution (2.13–3.77) and exhibit excellent solubility in common organic solvents such as acetone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 850–856, 2006     

A simple method for determining protic end-groups of synthetic polymers by H NMR spectroscopy

A simple method for the determination of protic end-groups (-XH) in synthetic polymers involves in situ derivatization with trichloroacetyl isocyanate (TAI) in an NMR tube and observation of the imidic hydrogens of the derivatized products [-X-C(O)-NH-COCCl₃] by ¹H NMR spectroscopy. In this paper, we report that the method is effective for the quantitative determination of hydroxy, primary amino and carboxy end-groups of polymers with . It may also be applied to detect chain ends in higher molecular weight polymers. The signals for the imidic (and, in the case of amines, amidic) hydrogens appear in a region (δ 7.5-11) that is clear of other signals in the case of most aliphatic polymers and many aromatic polymers such as polystyrene and poly(ethylene terephthalate). The method has been applied in the characterization of polymers formed by conventional and living radical polymerization (RAFT, ATRP, NMP), to end functional poly(ethylene oxide) and to polyethylene-block-poly(ethylene oxide). The method appears less effective in the case of sulfanyl end-groups. The chemical shift of the imidic hydrogen shows remarkable sensitivity to the microenvironment of chain end. Thus, the imidic hydrogens of TAI derivatized polyethylene-block-poly(ethylene oxide) [PE-(EO)_mOC(O)NHC(O)CCl₃] are at least partially resolved for m=0, 1, 2, 3 and ≧4 in the 400 MHz ¹H NMR spectrum. It is also sensitive to the chain end tacticity of, for example, amino-end-functional polystyrenes and thus to the relative configuration of groups removed from the chain-end by two or more monomer units. TAI derivatization also facilitates analysis of amine functional polymers by gel permeation chromatography (GPC) which is often rendered difficult by specific interactions between the amine group and the GPC column packing.     

Thermal conductivity of polymers

In this review we have concentrated on the interpretation of three essential aspects of the thermal conductivity K of polymers: the temperature dependence, the crystallinity dependence and the orientation effect. K for all amorphous polymers is approximately equal in magnitude and characterized by a T² dependence below 0.5K, a plateau region between 5 and 15K and a slow increase at yet higher temperatures. While a number of models involving different phonon scattering mechanisms are capable of explaining these features, further corroborating evidence would be needed to explain the ad hoc assumptions involved. For semicrystalline polymers K shows both strong crystallinity and temperature dependence, with a distinctive cross-over point at about 10K. These marked features can now be understood as the result of the interplay between two competing factors: the intrinsically higher conductivity in the crystalline regions, and the reduction in K due to an additional phonon scattering mechanism which becomes important at low temperature. This scattering could arise from either the correlation in the spatial fluctuation of the sound velocity in the polymer or the acoustic mismatch at the interfaces between the crystallites and the amorphous matrix.Orientation produces a very large anisotropy in semicrystalline polymers, which however decreases at low temperature and becomes insignificant below 10K. This feature can again be understood in terms of the same competing mechanisms if one realizes that the molecular chains in the crystallites are essentially lined up along the direction of orientation thus offering very little thermal resistance along this direction. For polyethylene with an extrusion ratio of 25 the thermal conductivity at 100K along the extrusion direction is 91 mW/cm K, a value extremely high for polymers and close to that of stainless steel. At this temperature the anisotropy is only about 20, yet because of the different temperature dependence of the thermal conductivity along and perpendicular to the extrusion direction, we predict an anisotropy as high as 60 at room temperature.     

Allylic polymers from resin acids

An unsaturated adduct has been synthesized by the Diels-Alder reaction between resin acids and diallyl maleate. The obtained polymerizable product can be used both as monomer in the formation of allyl polymers and crosslinking agent. The monomer and its polymers were investigated by usual physical and chemical methods. The synthesized polymers present a linear structure, possibly associated with intramolecular cyclization at low molecular weights, or a three-dimensional structure at high conversions. They are fairly thermostable substances with carboxylic groups in the polymer chain.     

Mechanical relaxations and moduli of oriented semicrystalline polymers

A systematic investigation was carried out on the mechanical relaxations and moduli of four drawn semicrystalline polymers: polyoxymethylene, polypropylene, polyvinylidene fluoride and polychlorotrifluoroethylene. Low-frequency tensile and torsional measuremnts were made between-140 and 140°C, and ultrasonic measurements of all five moduli were made by the water-tank method between 0 and 60°C. The patterns of relaxations remain essentially unchanged upon orientation, but there is a marked reduction of the height of relaxation peaks associated with the amorphous phase and, correspondingly, a smaller drop of moduli in the relaxation region. This reflects a lowering of molecular mobility in the amorphous phase due to the constraining effect of taut tie-molecules. The modulus C₃₃ increases sharply with draw ratio λ while the other moduli show little variation, which result from the alignment of molecular chain axes and the production of taut tie-molecules. The λ-dependence of the moduli is consistent with the aggregate model only when the polymer is glassy, that is, when its amorphous phase is comparable in stiffness to the crystalline phase and the polymer can reasonably be regarded as a one-phase material for which the aggregate model is valid.     

Micromechanics of stress relaxation in amorphous glassy PMMA. Part I. Molecular model for anelastic behaviour

This paper describes the development of a theoretical model for the strength of mechanical relaxation in terms of micromechanics of deformation. Polymethyl methacrylate (PMMA) is used as the model amorphous polymer. The internal molecular rearrangements during relaxation are identified and accounted for by the rotation of specific atomic groups. Voronoi tessellation is used as a method to characterise the nanostructure in amorphous glassy polymer below T_g. A theoretical model is postulated and shown to provide a limited quantitative prediction capacity of the anelastic deformation and the corresponding stress relaxation based on measurable molecular parameters without adjustable factors.     

Hyperbranched polymers from divinylbenzene and 1,3-diisopropenylbenzene through anionic self-condensing vinyl polymerization

Hyperbranched polymers were synthesized using anionic self-condensing vinyl polymerization (ASCVP) by forming ‘inimer’ (initiator within a monomer) in situ from divinylbenzene (DVB) and 1,3-diisopropenylbenzene (DIPB) using anionic initiators in THF at −40 °C. The reaction of equimolar amounts of DVB and nBuLi results in the formation of hyperbranched poly(divinylbenzene) through self-condensing vinyl polymerization (SCVP). The hyperbranched polymers were invariably contaminated with small amount of gel (<15%). No gelation was observed when using DIBP with anionic initiators. The presence of monomer-polymer equilibrium in the SCVP of DIPB restricts the growth of hyperbranched poly(DIPB). The inimer synthesized from DIPB at 35 °C undergoes intermolecular self-condensation to different extent depending on the nature of anionic initiator at −40 °C. The molecular weight of the hyperbranched polymers was higher when DPHLi was used as initiator. A small amount of styrene ([styrene]/[Li⁺]=1) was used to promote the chain growth by inducing cross-over reaction with styrene, and subsequent reaction of styryl anion with isopropenyl groups of inimer/hyperbranched oligomer. The hyperbranched polymers were soluble in organic solvents and exhibited broad molecular weight distribution (2<M_w/M_n<17).     

Phase behaviour and solution properties of sulphobetaine polymers

Aqueous polyelectrolytes have been extensively studied and comprehensively described in numerous books and reviews. In contrast, systematic investigations of aqueous polyzwitterions are few. This paper describes the detailed phase behaviour and solution properties of a homopolymer based upon a recently available sulphobetaine monomer, N-(3-sulphopropyl)-N-methacrylooxyethyl-N,N-dimethyl ammonium betaine (SPE). In addition, such properties are probed at the molecular level by static and dynamic light scattering, as well as laser Raman spectroscopy. Poly[N-(3-sulphopropyl)-N-methacrylooxyethyl-N,N-dimethyl ammonium betaine], P(SPE), of 4.35 × 10⁵M_w shows remarkable phase behaviour. It exhibits both an upper critical solution temperature (UCST) and an ‘apparent inverted’ lower critical solution temperature (LCST), i.e. a 1-phase region flanked by two 2-phase regions. Moreover, the UCST occurs at an order of magnitude lower polymer concentration than predicted by theory or demonstrated by experiment with conventional polymers. The aqueous solubility of (SPE) depends upon polymer molecular weight, as well as the concentration and structure of added salts. ‘Soft’ salt anions and cations are more effective solubilizers than ‘hard’ anions and cations. Furthermore, solutions of P(SPE) display ‘antipolyelectrolyte behaviour’, i.e. viscosities which increase with increasing salt concentrations. Static light scattering experiments indicate that the solvent quality for P(SPE) increases with increasing salt concentration. Dynamic light scattering measurements show that the polymer diffusion coefficients decrease and the chain dimensions increase with increasing salt concentrations. Moreover, laser Raman spectroscopy indicates that the local environment around the zwitterion functionalities is also modified by changes in salt concentration. Based upon such molecular level probes, models have been proposed to account for the P(SPE) phase behaviour and solubility. Thus, P(SPE) is depicted as a collapsed coil in water because of intra-group and intra-chain associations. The unusual phase behaviour of P(SPE) in water is rationalized in terms of a shift from intra- to interinteractions. In turn, NaCl breaks up the intra-associations and promotes polymer solubility.