Crystallization Of Isotactic Polystyrene Research Articles

Diffusion Aspects in the Crystallization of Isotactic Polystyrene from Solutions

Isothermal crystallization rates of isotactic polystyrene from tripropionin (TP), dimethyl sulfoxide (DMSO), and dimethyl phthalate (DMP) solutions were investigated by differential calorimetric measurements. The overall crystallization rate in the DMP solution exhibited a maximum at ca. 70 °C, which indicates that the diffusion factor plays an important role in the solution crystallization. The observed temperature dependence of the isothermal crystallization rate was analyzed on the basis of the Fokker-Planck type formula for the diffusion factor. The frictional interaction between the polymer and solvent was estimated, and the result showed that the diffusion processes (molecular motions) in the solution crystallization do not belong to the diffusion limit of Kramers. This fact has been expected for the solution crystallization, in which the frictional interaction between the polymer and solvent is weak. It has also been shown that the above tendency is remarkably dependent on the solvent. The frictional interaction was qualitatively evaluated to be DMP > DMSO > TP.

FT-IR Study of Concentration Dependence for Crystallization of Isotactic Polystyrene Arising from Freeze-Drying Dilute Solutions

FT-IR Study of Concentration Dependence for Crystallization of Isotactic Polystyrene Arising from Freeze-Drying Dilute Solutions

Rapid Crystallization of Isotactic Polystyrene by Shock-Cooling and Subsequent Freeze-Drying of Its Very Dilute Solution

Rapid Crystallization of Isotactic Polystyrene by Shock-Cooling and Subsequent Freeze-Drying of Its Very Dilute Solution

On morphology and polymer blends: polystyrene and polyethylene

This paper compares the morphologies observed in two blend systems, namely blends of isotactic and atactic polystyrene, and blends of linear and branched polyethylene. Crystallization of isotactic polystyrene at high temperatures ( ≳ 200°C) produces immature sheaf-like aggregates of lamellae. Addition of atactic polymer results in modified morphologies that are based upon bundles of lamellae, separated from one another by non-crystalline regions. At high atactic contents sheaf-like objects are no longer observed, crystallization occurring to give structures that are better described as multilayered crystals. At temperatures below ∼ 200°C, mature spherulites develop. Addition of atactic polystyrene again results in morphologies in which lamellae are grouped into stacks separated from one another by non-crystalline regions. Again, at high atactic contents a less complex (sheaf-like) overall morphology is observed. In all the above microstructures, lamellae exhibit an inherently hexagonal habit. However, at lower crystallization temperatures observations suggest that lateral lamellar growth may be restricted. Isothermal crystallization of linear polyethylene at temperatures above ∼ 125°C results in morphologies in which a complex lamellar hierarchy exists, as a consequence of molecular fractionation during crystallization. Addition of branched polyethylene, which is unable to crystallize at these temperatures, suppresses fractionation such that the resulting morphologies may be described in terms of only one dominant and one subsidiary lamellar population. When viewed along the crystallographic b axis, dominant lamellae appear planar or mildly S-shaped in profile, whilst subsidiary lamellae are planar and inclined at an angle of ∼25° to the local dominant population. In blends with a high branched content, apparently non-crystalline regions can be seen between individual lamellae. Thus, in polyethylene blends, the non-crystallizing component is located between individual lamellae rather than between bundles of lamellae, as is the case in polystyrene. This difference arises from the parallel growth of dominant and subsidiary lamellae in polystyrene as opposed to the inclined development of subsidiaries with respect to the dominant lamellae in the polyethylene blends. In all the samples studied, spherulite growth occurs via a dominant/ subsidiary mechanism.

Growth rate of isotactic polystyrene crystals in concentrated solutions and in the melt

The growth rate of isotactic polystyrene (iPS) crystals has been investigated for crystallization in concentrated dimethyl phthalate solutions and in the melt over a wide range of supercooling from 20 to 170 K. For most of the supercoolings studied, the growth faces are rough; nucleation is not present. However, the growth rate G for each concentration shows approximately the same dependence on supercooling ΔT as growth controlled by secondary nucleation: log( G β ) depends linearly on K TΔT , where β is a transport factor and K is a constant. The value of K increases with decreasing concentration. Possible mechanisms for crystal growth are discussed, taking account of the deposition of one stem on growth faces; the side surface free energy increases with decreasing concentration.

Growth rate and morphology of isotactic polystyrene crystals in solution at high supercoolings

The morphology and temperature dependence of the lateral growth rate G are reported for isotactic polystyrene crystallized from 0.1% dimethyl phthalate solution at high supercoolings. The outline of a lamella is a rounded hexagon for the highest temperature and a ragged circle for lower temperatures. The edges of the lamellae become ragged and overgrowth is pronounced with decreasing temperature. A linear relationship is found between log( G η ) and 1 TΔT over a wide range of supercooling ( ΔT = T o d − T) from 70 to 170 K, where η is a retardation factor of Arrhenius form with an activation energy of 8400 K, and T o d is the equilibrium dissolution temperature. The value of T o d is determined to be 200°C by differential scanning calorimetry. In these high supercoolings, the nucleation theory of polymer crystallization loses its validity; in fact, the slope of the plot of log( G η ) versus 1 TΔT is four times as large as the value predicted by nucleation theory. Possible growth mechanisms at high supercoolings are discussed on the basis of the morphology.

Solution-grown crystals of isotactic polystyrene: neutron scattering investigation of the variation of chain trajectory with crystallization temperature

Previous neutron scattering investigations carried out on isotactic polystyrene single crystals grown at 130°C from dilute solutions have revealed a sheet-like conformation and hence very regular chain folding. Here we report the same type of experiments performed on samples crystallized at T c = 75, 85, 105 and 115°C. From the results in both the Guinier and the intermediate ranges, we come to the following conclusions: (i) At 115°C, we reproduce the results obtained at 130°C (regular folding in a single sheet). (ii) Decreasing T c leads to a change of conformation for relatively high molecular weights (7 × 10 5 and 5 × 10 5). While crystallization still occurs along an hk0 plane, the regular folding is interrupted, leading both to superfolding and to crystallization in at least two different lamellae. (iii) For lower molecular weights (3 × 10 5 and 1.5 × 10 5) significant deviations from the sheet-like model appear only at T c = 85°C. We conclude that above a critical molecular weight, which is temperature-dependent, irregularities in the folding habit take place. In this respect, polystyrene resembles polyethylene.

Retardation of spherulitic growth rate in the crystallization of isotactic polystyrene due to the presence of nucleant

AbstractAlthough the rate of heterogeneous nucleation of crystallization in isotactic polystyrene, as studied by photomicroscopy, is markedly increased by addition of fine‐particle silica, the rate of subsequent radial growth of spherulites formed is diminished. The latter observation is rationalized on the basis of a modified Hoffman–Lauritzen treatment wherein the nucleant is depicted as a quasicrosslink which impedes the transport of polymer segments.

Bulk crystallization of isotactic polystyrene near its melting point: a neutron scattering study of the chain trajectory

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBulk crystallization of isotactic polystyrene near its melting point: a neutron scattering study of the chain trajectoryJean Michel Guenet and Claude PicotCite this: Macromolecules 1983, 16, 2, 205–210Publication Date (Print):February 1, 1983Publication History Published online1 May 2002Published inissue 1 February 1983https://doi.org/10.1021/ma00236a010RIGHTS & PERMISSIONSArticle Views339Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Diffusion‐controlled growth of lamellar crystals in an isotactic polystyrene–polyphenylene oxide blend

AbstractThe growth rates of lamellar crystals grown onto preseeded fibrillar crystals (“shishes”) in isotactic polystyrene and blends of isotactic polystyrene (iPS) with polyphenylene oxide are followed by using transmission electron microscopy. The preseeded fibrillar crystals avoid the problem of timedependent primary nucleation. The time dependence of lamellar growth is investigated. At a concentration of 50% PPO in iPS, the lateral lamellar growth rate of the precipitating isotactic polystyrene crystals conforms to a time law characteristic of diffusion‐controlled growth (R ∝ t1/2). Diffusion coefficients are estimated from the growth kinetics. The method could prove a simple means of measuring diffusion coefficients in polymer blends in which one component is crystallizable.

Ultradrawing and crystallization of isotactic polystyrene and blends with atactic polystyrene

AbstractPure isotactic polystyrene (iPS, Mw = 8.89 × 104, Mw/Mn = 4.89) and its blends with an atactic polystyrene (aPS, Mw = 3.9 × 105, Mw/Mn < 1.13) were subjected to draw by solid state coextrusion at 127°C within polyethylene. The content of amorphous iPS in these blends was varied from 100 to 24.4 wt %. The extent of draw‐induced crystallization was found to depend on the draw ratio and on iPS concentration. The blend with 24.4% iPS was coextruded in two stages. The highest effective draw ratio (EDR) was 7.6 and 13.7 for one‐ and two‐stage draw, respectively. The highest crystallinity of 33.2% was obtained for pure iPS at the maximum EDR of 7.6. Considerable crystallinity was induced in blends, requiring successively higher draw ratio to reach similar crystallinity with increased aPS content. The tensile modulus increased from 1.5 to 3.2 GPa, independent of iPS concentration. Thermal shrinkage results indicate that the elastic recovery of draw in the blends is near quantitative for an EDR < 8. For pure iPS, extrudate elastic recovery was dramatically altered by the draw‐induced crystallinity.

On the size of core crystals of isotactic polystyrene grown from polystyrene blends

On the size of core crystals of isotactic polystyrene grown from polystyrene blends

Electron microscopic investigation of the molecular mechanism of plastic deformation of polyethylene and isotactic polystyrene crystals

AbstractThe molecular process involved in the plastic deformation of crystals of linear polyethylene and isotactic polystyrene by necking was investigated by transmission electron microscopy (TEM). The results for the draw ratio, the height, and the shape of the neck and the molecular structure of the deformed material suggest that plastic deformation occurs basically by the unfolding and bending of the molecules in a deformation region only a few nm wide. The observations are at variance with deformation models involving complete unfolding of the molecules or the breaking off of folded‐chain blocks and the incorporation of these blocks into the deformed material.

Lamellar changes during heat treatment in isotactic polystyrene crystals

Abstract In the present investigation, the melting and thickening processes in lamellar crystals of isotactic polystyrene have been studied by transmission electron microscopy. It is shown that under properly chosen experimental conditions for the polymer, one can continuously follow the physical changes involved during the thickening as well as melting of lamellar crystals on heat treatment. The study of crystals grown at different temperatures reveals that melting of a single lamella starts at various areas. A commonly observed feature is the preferential melting of elastically bent parts of a lamella. It is indicated that the occurrence of melting in the various parts is due to a structural variation along the surface of lamellae resulting in a hindrance of the lamellar thickening process. At particular temperatures, melting of lamellar crystals is followed by recrystallization. The occurrence of a solid-stage thickening process is the major process so far observed during slow heat treatments. Considerable change in surface structure of the crystals grown at different temperatures is clearly reflected during the heat treatment. The rates of heating have marked influence on the resulting morphology of the crystalline superstructures.

Observation of screw dislocations in lamellar stacks of polyethylene and isotactic polystyrene

Lamellar stacks of polyethylene and isotactic polystyrene crystals are investigated by dark-field electron microscopy and electron diffraction. The observed effects suggest the presence of screw dislocations, the Burgers vector of which is parallel to the chain direction. The dislocation density in lamellar stacks is greater than 10 11 cm −2. The occurrence of the dislocations is attributed primarily to shear forces arising from thermal stresses.

The heterogeneous nucleation of crystallization in isotactic polystyrene

Isothermal crystallization of isotactic polystyrene was studied by differential scanning calorimetry. From the bell-shaped rate versus temperature diagram, a crystallization maximum is observed in the region of 175°C and the results are interpreted in terms of the Turnbull-Fisher equation for nucleation. The effectiveness of virgin silica and chemically treated silica filler, both having similar physical characteristics, as nucleating agents for isotactic polystyrene (i-PS), was examined. Incorporation of silica powder into i-PS increased the rate of crystallization of the polymer. It was also found that varying the polymer-silica interfacial energy by treating a silica surface with trimethylchlorosilane caused a change in its nucleating ability; the greater the interfacial energy the more efficiently the silica nucleates. The treated silica, which has no net interfacial energy with the polymer, appears to act as an inhibitor to the crystallization of isotactic polystyrene.

Solution grown isotactic polystyrene crystals. I. Degree and distribution of crystallinity; thermal stability

AbstractThe subject of this paper is the degree of crystallinity and annealing behavior of solution grown single crystals of isotactic polystyrene (IPS) in relation to the fold length, an enquiry which acquires special significance in view of the fact that previously the fold length had been found to be identical over a wide range of crystallization temperatures (Tc). It was found that both crystallinity and thermal stability increase with Tc even over the range of constant fold length thus invalidating the usual assumption that the fold length and crystal properties are uniquely correlated. Further, the crystallinity figures as measured by conventional calorimetry are very low (<50% throughout) which by conventional ideas would require an unrealistically thick amorphous surface layer. However, the “linear crystallinity” (crystal core thickness as determined from x‐ray linewidths) is much larger, commensurate with crystallinities in single crystals from other materials. It is suggested that this is the more relevant figure for the subdivision of the lamellas into crystal core and surface layer. The additional amorphous content being otherwise accommodated. Further, this “linear crystallinity” is broadly unaffected by fold length changes induced by heat annealing. The thermal stability (including annealing ability) of the crystals differs markedly whether Tc is above or below ∼60°C, a Tc value which is in the range where the fold length is constant, but corresponds to a maximum in the crystallization rate. Possible connections between crystallization conditions and the stability of the resulting crystals (fold length considerations apart) are pointed out.

Solution grown isotactic polystyrene crystals. II. Kinetics of thermal changes by x‐ray diffraction

AbstractThe present paper is a study of the annealing, melting, and recrystallization behavior of solution grown isotactic polystyrene crystals in order to elucidate changes both in total lamellar thickness and in the thickness of the crystalline “core” as a function of temperature. The lamellar thickness was obtained from x‐ray long spacings and the core thickness from the broadening of appropriate reflections, both assessed by a high sensitivity x‐ray detector system able to produce records within a few minutes during time dependent processes. The x‐ray results were correlated with differential scanning calorimetry (DSC) measurements. On heating, first the usual annealing effects with little net melting were observed, but on increasing the temperature large changes in long spacing, which were reversible with temperature, were seen accompanied by only small changes in crystal core thickness. The second effect was found to be associated with a substantial degree of melting. Even after heating above the temperature where complete melting was indicated by DSC, the recrystallization rate was found to decrease as the melt temperature was increased and to be much faster than on cooling from the usual melts. Strikingly, this recrystallization was accompanied by a decrease in long period with time even under isothermal conditions. It is inferred that the memory of the preceding crystalline stack is preserved throughout the melting range and even beyond this, far into the molten state. This “seeding” effect is intrinsic to the polymer even if its nature cannot be specified. The principal effects in question can then be explained by envisaging that randomly placed lamellas gradually disappear within the stack on melting and successively reappear on crystallization during cooling. These ideas agree well with previous work on reversible long spacing changes in polyethylene (see ref. 9) and are likely to be of wider generality for melting and recrystallization phenomena in systems having stacked lamellar morphologies.

Crystallization of isotactic polystyrene induced by organic vapours

The crystallization of isotactic polystyrene induced by dichloromethane and acetone was studied. From equilibrium absorption data, the critical concentration for crystallization was deduced. The crystallization kinetics were followed and diffusion coefficients were calculated. It was found that the crystallization was diffusion controlled. The increase in the rate of crystallization is explained by the high rate of diffusion and nucleation in the presence of the organic solvents. Evidence for the high nucleation probability was found in morphological observations (SAXS and electron microscope observations). The melting behaviour of the solvent crystallized samples suggests formation of a very unstable crystalline structure which re-organizes rapidly on heating.

Crystallization of isotactic polystyrene from dilute solutions

AbstractThe overall rate of crystallization of isotactic polystyrene from dilute solutions, 1% by weight, in trans‐decalin and benzyl alcohol was studied as a function of temperature using dilatometry. These solvents were chosen because the dissolution temperatures of crystalline isotactic polystyrene are practically the same in both solvents. The overall rate of crystallization as a function of crystallization temperature showed a maximum in both solvents at about 50°C. At lower crystallization temperatures the rate of crystallization is much lower. The overall rate of crystallization of isotactic polystyrene in benzyl alcohol is far larger than in trans‐decalin at the same undercooling throughout the temperature range, which is in apparent contradiction to present crystallization theories. At very large undercooling (Tc lower than about 0°C) the solutions of isotactic polystyrene in both solvents quickly become “rigid” gels. Surface replicas of freeze‐etched gels indicate that a fringed micelle type of crystallization takes place at these low temperatures. The transition from folded chain crystallization to fringed micelle crystallization may be due to a stiffening of the polymer chain below about 50°C, with a reduced rotational mobility of the phenyl groups on the chain. If very dilute solutions, below 0.5% by weight, are crystallized at these low temperatures no gels were formed but fibrous crystals are produced which could be observed under the polarizing microscope.