Melting Points Of Copolymers Research Articles

The Investigation of Copolymer Composition Sequence on Non-Isothermal Crystallization Kinetics of Bio-Based Polyamide 56/512.

A new bio-based polyamide 56/512 (PA56/512) has been synthesized with a higher bio-based composition compared to industrialized bio-based PA56, which is considered a lower carbon emission bio-based nylon. In this paper, the one-step approach of copolymerizing PA56 units with PA512 units using melt polymerization has been investigated. The structure of the copolymer PA56/512 was characterized using Fourier-transform infrared spectroscopy (FTIR) and Proton nuclear magnetic resonance (1H NMR). Other measurement methods, including relative viscosity tests, amine end group measurement, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), were used to analyze the physical and thermal properties of the PA56/512. Furthermore, the non-isothermal crystallization behaviors of PA56/512 have been investigated with the analytical model of Mo's method and the Kissinger method. The melting point of copolymer PA56/512 exhibited a eutectic point at 60 mol% of 512 corresponding to the typical isodimorphism behavior, and the crystallization ability of PA56/512 also displayed a similar tendency.

Monte Carlo Simulations of Strong Memory Effect of Crystallization in Random Copolymers

Recently, experiments reported a strong memory effect of crystallization in model ethylene-based homogeneous random copolymers after being annealed at temperatures higher than the equilibrium melting point of copolymers. By means of dynamic Monte Carlo simulations of random copolymers, we reproduced this phenomenon in the similar model copolymer systems. We attributed this phenomenon to the sequence-length segregation upon first-time crystallization. The resulting heterogeneous melt of copolymers survives upon annealing below the critical demixing point that could be much higher than the equilibrium melting point of copolymers. Therefore, the local high concentration of long sequences raises the local melting point to accelerate primary crystal nucleation upon second-time crystallization. This source of memory effects demonstrates how crystallization can be influenced by the substantial trend of demixing between different sequences in homogeneous random copolymers.

Graft copolymers of poly(methyl methacrylate) and polyamide-6 via in situ anionic polymerization of ε-caprolactam and their properties

Graft copolymers of poly(methyl methacrylate) and polyamide-6 (PMMA-g–PA6) were investigated via in situ anionic polymerization of e-caprolactam, using PMMA precursors with N-carbamated caprolactam pendants (PMMA–CCL) as macroactivators and sodium caprolactamate as catalyst. Three grades of PMMA–CCLs obtained by free radical copolymerization were used for synthesizing the PMMA-g–PA6 copolymers with different PMMA content. The resulting graft copolymer was characterized by Fourier-transform infrared spectroscopy and selective extraction. Scanning electron microscopy is used to clarify the phase morphology of obtained polymer by fracture surface. The thermal property, crystallinity and dimensional stability of graft copolymer were studied using differential scanning calorimetry, X-ray diffraction and water absorption measurement. The results show the Tg of graft copolymer is higher than that of neat PA6, but the onset and peak points of graft copolymer melting point are shifted to lower temperature. The percentage crystallinity and water absorption of PMMA-g–PA6 copolymer decrease with increasing PMMA content, but the crystal structure of PA6 is scarcely affected by the presence of PMMA. Graft copolymers have improved dimensional stabilities relative to neat PA6. Upon the incorporation of 19.9 wt% PMMA into PA6, the water absorption of PMMA-g–PA6 copolymer has been reduced from 4.8 for neat PA6 to 2.1%.

Thermal degradation of ethylene-carbon monoxide alternating copolymer under inert atmosphere

This work aims to understand the mechanism of the thermal degradation of the ethylene–carbon monoxide (E-CO) alternating copolymer under mild conditions. The copolymer was subjected to accelerated ageing in an oven at different temperatures below the copolymer melting point, under argon atmosphere, and in the absence of light. The properties of the aged samples were compared with the properties of the untreated copolymer. Untreated and aged samples were analysed by mass spectroscopy (MS) with the direct introduction probe (DIP) and pyrolysis (Py) techniques. The accelerated ageing experiments showed that the thermal degradation of the E-CO alternating copolymer under inert atmosphere is characterized by chain cross-linking, loss of water, and changes in the UV absorption spectrum. The IR spectrum shows modifications only for highly degraded samples in which O−H and C=C groups are present. The experiments performed with the DIP-MS technique have confirmed that the E-CO alternating copolymer loses water during its thermal ageing. The pyrolysis products of the copolymer are linear molecules with 1,4-diketonic structure, 2-cyclopentenone derivatives, alkyl furans, and aromatic compounds. These results suggest that during the thermal degradation of the E-CO alternating copolymer under inert atmosphere, and at low temperatures, aldol condensations and/or dehydration to furan rings probably occur. © 1998 SCI.

Functionalized polyacetals, 1. Copolymerization of trioxane with 1,3‐dioxep‐5‐ene and properties of the resulting copolymer

Abstract1,3,5‐Trioxane (1) and 1,3‐dioxep‐5‐ene (2) were copolymerized with BF3OEt2 at 65°C. The products, after base hydrolysis, were characterized by 13C and 1H NMR and were found to assume the chemical structure 4 of a copolymer containing oxymethylene and oxy‐2‐butenylene units with 4‐hydroxy‐2‐butenyl and methoxy end groups, with the ratio of hydroxy‐2‐butenylene to methoxy end groups varying with experimental conditions. The copolymer demonstrates crystallinity and thermal stability comparable to poly(trioxane‐co‐ethylene oxide)s. Copolymer melting point was observed to decrease with increasing comonomer incorporation. The upper limit for incorporation of the comonomer 2 was found to be ca. 4 mol per cent. Viscosity and end group analysis (by 1H NMR) indicate molecular weights in the range of 104 to 105. The comonomeric unit demonstrates the ability to act as both a stopper against unzipping and as a trap for certain degrading agents.

Melting behavior of polyacrylonitrile copolymers

The melting behavior of acrylonitrile copolymers, ter- and tetrapolymers was studied in the dry state and in the presence of water. The melting point depression caused by the incorporation of a specific comonomer into the polyacrylonitrile chain was shown to be dependent on the molecular structure of the comonomer. Not all comonomers gave equivalent melting point depressions on a molar basis. The Eby theory of comonomer melting was used to model the melting behavior. This theory assumes that the non-crystallizing (non-AN) comonomers enter the crystal lattice as point defects rather than being relegated to the amorphous phase. An equation was developed for predicting the melting point of copolymers, terpolymers and higher order polymers as a function of the polymer composition and the specific melting point depression constant for each comonomer. The latter constants are derived from the copolymer melting point curves. The equation is applicable to both dry and wet polymers and excellent agreement between the observed and calculated melting points for wet terpolymers and tetrapolymers was observed.

Melting of ethylene oxide - propylene oxide type P(EP) n block copolymers

Multiblock copolymers of poly(ethylene oxide) and poly(propylene oxide), type P(EP) n , have been prepared by condensation of hydroxy- and chlorocarboxy-ended polymers. Small-angle X-ray scattering and dilatometry have been used to determine lamella spacings and melting points of the copolymers. The melting points of the multiblock copolymers can be predicted from the melting points of corresponding triblock (PEP) copolymers.

Poly(chloroaldehydes). I. Polychloral stabilization

AbstractPolychloral diol, unlike polyoxymethylene diol, is not readily capped in the presence of alkali catalysts. Polychloral is capped under acid conditions by acid anhydrides and chlorides and does not appear to undergo degradation during the process. Evidence for end‐capping is provided by infrared analysis in the case of the low DP polychloral, metachloral. End‐capped polychlorals possess good stability towards hot dimethylformamide and good stability at elevated temperatures (255°C.). From the melting points of copolymers, polychloral itself is estimated to have a melting point of about 460°C. The high melting point is consistent with the rigidity of the polymer chain. A means of estimating the DP of the polymer is proposed, based on a form of endgroup analysis. By this technique, metachloral is estimated to have a DP of about 50.

The melting of defect polymer crystals

Melting of imperfect crystals is treated, using the methods of irreversible thermodynamics. A reproducible limiting heating path of zero entropy production from the metastable solid to the supercooled molten state is described. Experimental evidence shows that this ‘equilibrium’ heating path can often be approximated by heating fast enough so that reorganization and recrystallization in the crystalline aggregates are minimized, but not so fast that superheating is experienced. Expressions for the melting of perfect homopolymer lamellae, defect copolymer lamellae, and for the experimental maximum melting point of copolymers are discussed. For polyethylene a self-consistent set of data based on melting experiments carried out under zero entropy production heating is given. By this method the equilibrium maximum melting point for polyethylene homopolymer is found to be 142°C, while the surface free energy of a (001)-surface of polymer lamellae is about 75 erg/cm 2.

Transition metal catalysts. IX. Random ethylene‐propylene copolymers with a low pressure polymerization catalyst

AbstractEthylene–propylene copolymers were prepared at atmospheric pressure with the VCl4–(C6H5)4Sn–AlBr3, hydrocarbon‐soluble, polymerization catalyst. A controlled rate of initiation and thus a constant comonomer composition were obtained by the introduction of a constant amount of oxygen into the monomer stream. Four copolymers, containing 2.6, 3.8, 10, and 27 mole‐% propylene, were found to have uniform comonomer compositions when fractionated by successive extraction with boiling solvents, in contrast to copolymers prepared with other reported Zieglertype catalysts. An elution fractionation of the 10 mole‐% propylene copolymer was conducted with cellosolve‐xylene mixtures above the copolymer melting point. The molecular weight distribution was shown to approximate the “most probable” distribution. This is in agreement with a previously proposed polymerization mechanism. The propylene contents of each of the fractions from the 10% copolymer were within ±1% propylene of the value of the whole copolymer. This narrow composition distribution is in accord with the statistical distribution predicated theoretically for random copolymers and is in accord with the previous finding that r1r2 ≅ 1. These data suggest that Ziegler‐type catalysts containing a single active species are amendable to the same statistical and kinetic treatment that has been used for the classic polymerization catalysts.1Phillips, G. W., and W. L. Carrick, J. Am. Chem. Soc., 84, 920 (1962).

Transition Metal Catalysts. IX. Random Ethylene-Propylene Copolymers with a Low Pressure Polymerization Catalyst

Ethylene–propylene copolymers were prepared at atmospheric pressure with the VCl4–(C6H5)4Sn–AlBr3, hydrocarbon-soluble, polymerization catalyst. A controlled rate of initiation and thus a constant comonomer composition were obtained by the introduction of a constant amount of oxygen into the monomer stream. Four copolymers, containing 2.6, 3.8, 10, and 27 mole-% propylene, were found to have uniform comonomer compositions when fractionated by successive extraction with boiling solvents, in contrast to copolymers prepared with other reported Zieglertype catalysts. An elution fractionation of the 10 mole-% propylene copolymer was conducted with cellosolve-xylene mixtures above the copolymer melting point. The molecular weight distribution was shown to approximate the “most probable” distribution. This is in agreement with a previously proposed polymerization mechanism. The propylene contents of each of the fractions from the 10% copolymer were within ±1% propylene of the value of the whole copolymer. This narrow composition distribution is in accord with the statistical distribution predicated theoretically for random copolymers and is in accord with the previous finding that r1r2 ≅ 1. These data suggest that Ziegler-type catalysts containing a single active species are amendable to the same statistical and kinetic treatment that has been used for the classic polymerization catalysts.11

Melting points and heats of fusion of polymers and copolymers

AbstractTheoretical calculations indicate that the melting point of a linear polyethylene should be experimentally determinable within 0.1°C., that of a low density polyethylene within 1°C., that of a 80/20 copolyester within 2°C. copolyester within 2°C. and that of a 60/40 copolyester within 5°C. Heats of fusion of polyethylene and polyesters as estimated by diffeerent methods are in good agreement, but uncertainties still exist in the case of polyamides. It is shown that correlation of melting points with molar cohesion energies is misleading and without theoretical foundation. Eastimation of the absolute entropies of polyethylene, polyethylene sebacate and several polyamides gives results indicating that the high melting point of the polyamides is due to a low entropy of the liquid phase rather than to a high entropy of the solid phase as has hitherto been proposed. On the other hand the low melting point of the aliphatic polyesters results chiefly from a low heat of fusion, and not from a high entropy of fusion as has also been previously suggested.Two melting regions which can be observed in certain copolyesters result from melting of crystals formed under two conditions; namely, small crystals produced by random crystallization of nearest neighbours, “cold crystallization”, and crystals of equilibrium size produced under ideal thermodynamic conditions. Because of restrications to crystallization due to the decreasing numbers of long sequences of crystallizable units with decreasing mole fraction, it is doubtful if melting points of copolymers hitherto measured have any thermodynamic significance. Much more precise measurements of carefully annealed samples at high mole fractions will be required before heats of fusion of activity coefficients of crystallizable units can be calculated from melting point data.

On the properties of polymers with random stereo‐sequences

AbstractIt is proposed that in most free radical polymerizations of polymers containing asymmetric carbon atoms in the principal chain, the relationships between the stereo‐positions of the substituents on adjacent units are governed by independent Bernoulli trials. An event in which a given substituent has the same stereo‐position as its immediate predecessor is called an “isotactic placement.” The probability, α, of this event may be a function of the temperature of polymerization. The methods of Flory's theory of the melting point of copolymers are used to derive an upper bound for the melting point of a homopolymer with “tacticity,” α. The notation and calculations are then extended to include polymers whose stereo‐sequences are governed by statistics of a more general type than Bernoulli trials. It can happen that the calculated upper bound for the melting point may lie near (or even below) the glass point for the amorphous polymer; when such is the case, the polymer cannot be crystallized by annealing.