Crystallization and enzymatic degradation of novel poly(ε-caprolactone-co-propylene succinate) copolymers

A series of novel poly(ε-caprolactone-co-propylene succinate) P(CL-co-PSu) copolymers having low propylene succinate content and high molecular weight were synthesized following a combinatory scheme of ring opening and polycondensation reactions, in an attempt to obtain copolymers of sufficient performance and increased biodegradation rates. Enzymatic hydrolysis of the copolymers was studied in the presence of mixture of Rhizopus delemar and Pseudomonas cepacia lipases. Much higher hydrolysis rates, comparing to neat PCL, were proved by both mass loss measurements and scanning electron microscopy (SEM) observations of the degraded film surfaces. Thermodynamics of cocrystallization and wide-angle X-ray diffraction (WAXD) patterns were investigated to estimate the extent of comonomer cocrystallization. Results of the study showed that comonomer inclusion may hold, though the molar fraction of the comonomer in the PCL crystals is lower than in the bulk. This means that not only the observed decrease of the degree of crystallinity from about 48% for PCL to about 29% for the P(CL-co-PSu) 75/25 favours enzymatic hydrolysis, but also the enrichment of the amorphous phase in the fast degrading propylene succinate units plays its role. The non-isothermal crystallization rates of the copolymers, like the melting points, decreased substantially when the propylene succinate content exceeded 8 mol%. The activation energy of crystallization was calculated using the isoconversional method of Friedman, over the whole range of crystallization temperatures. An increase was found in the activation energy with increasing the comonomer content in the copolymers also proving the reduced symmetry along the copolymer chains due to the presence of comonomer units.     

Cocrystallization in blends of random tetrafluoroethylene fluorinated copolymers: The effect of the chain structure and crystallization conditions

The possibility of the cocrystallization of random fluorinated tetrafluoroethylene copolymers was investigated with differential scanning calorimetry and wide‐angle X‐ray scattering. In particular, mixtures composed of poly(tetrafluoroethylene)‐co‐(hexafluoropropylene) containing 8 or 1 mol % comonomer or poly(tetrafluoroethylene)‐co‐perfluoromethylvinylether (2–10 mol % comonomer) were examined. The extent of cocrystallization was determined by the difference in the comonomer content, being higher when the difference was lower, and it was favored when quenching from the melt state was adopted. Nevertheless, a key to determining the extent of cocrystallization was the behavior of counits with respect to inclusion or exclusion from the crystal lattice: when the components were different with respect to this behavior, they were not likely to be miscible in the crystal state even if the difference in the comonomer content was low. Moreover, the similarity in the crystallization rates between the components played an important role: the cocrystallization decreased as the difference in the crystallization rate increased until, when the difference became high enough, the blend became immiscible. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1477–1489, 2002     

A Raman-spectroscopic study of solution-crystallized polyethylenes

An analysis of the Raman internal modes of dilute-solution-crystallized homopolymers and co-polymers of ethylene has been made, similar to the work previously reported for the bulk-crystallized polymers. The crystallite structure can be described in terms of the relative amounts of the crystalline orthorhombic phase, the liquidlike amorphous phase, and the interfacial region. These quantities change with the molecular constitution of the chains and the crystallization conditions. The level of crystallinity decreases significantly with increasing counit content as would be expected. In addition, an appreciable interfacial structure develops in copolymers as compared with the homopolymers. A possible relationship between the interfacial content and the relaxation transitions in polyethylene is discussed.     

Cocrystallization of ethylene/1‐octene copolymer blends during crystallization analysis fractionation and crystallization elution fractionation

Blending of ethylene/1‐octene copolymers can be used to achieve a well‐controlled broad chemical composition distribution (CCD) required in several polyolefin applications. The CCD of copolymer blends can be estimated using crystallization analysis fractionation (CRYSTAF) or crystallization elution fractionation (CEF). Unfortunately, both techniques may be affected by the cocrystallization of chains with different compositions, leading to profiles that do not truly reflect the actual CCD of the polymer. Therefore, understanding how the polymer microstructure and the analytical conditions influence copolymer cocrystallization is critical for the proper interpretation of CRYSTAF and CEF curves. In this investigation, we studied the effect of chain crystallizabilities, blend compositions, and cooling rates on cocrystallization during CEF and CRYSTAF analysis. Cocrystallization is more prevalent when the copolymer blend has components with similar crystallizabilities, one of the components is present in much higher amount, and fast cooling rates are used. CEF was found to provide better CCD estimates than CRYSTAF in a much shorter analysis time. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Transferability of cocrystallization propensities between aromatic and heteroaromatic amides

New virtual cocrystal screening was proposed taking advantage of the similarities between cocrystallization landscapes of different compounds. Assuming that cocrystallization propensities can be modeled by miscibility affinities of liquid components under supercooled conditions, the quantitative rules of likeness were formulated and validated for 45 aromatic and heteroaromatic amides interacting with a variety of coformers. The most important finding comes from the observed linear trends between the values of mixing enthalpies of amides with respect to a reference molecule. Particularly isonicotinamide was found as a very convenient comparative system since it constitutes 97 binary cocrystals. Many experimentally observed cocrystals were used for supporting the analogy hypothesis, which states that a properly selected reference molecule, for which cocrystals were experimentally documented, can provide practical information about cocrystallization propensities of another compound provided that two criterions are met, namely sufficiently high similarities and high enough affinities. Hence, it is not necessary to perform experimental cocrystallization of every pair of coformers since miscibility in the solid state of one compound can be transferred to another one at least in the case of aromatic or hetero-aromatic amides.     

Synthesis and non‐isothermal crystallization kinetics of poly(ethylene terephthalate)‐co‐poly(propylene glycol) copolymers

Poly(ethylene terephthalate)‐co‐poly(propylene glycol) (PET‐co‐PPG) copolymers with PPG ratio ranging from 0 to 0.90 mol% were synthesized by the melt copolycondensation. The intrinsic viscosity, structure, non‐isothermal crystallization behavior, nucleation and spherulitic growth of the copolymers were investigated by Ubbelohde viscometer, Proton Nuclear Magnetic Resonance (¹H‐NMR), differential scanning calorimetry, and polarized optical microscopy, respectively. The non‐isothermal crystallization process of the copolymers was analyzed by Avrami, Ozawa, Mo's, Kissinger, and Dobreva methods, respectively. The results showed that the crystallizability of PET was apparently enhanced with incorporating a small amount of PPG, which first rose and then reduced with increasing amount of PPG in the copolymers at a given cooling rate. The crystallization mechanism was a three‐dimensional growth with both instantaneous and sporadic nucleation. Particularly, PET‐co‐PPG containing 0.60 mol% PPG exhibited the highest crystallizability among all the copolymers. Copyright © 2015 John Wiley & Sons, Ltd.     

Morphological Changes of Linear,Branched Polyethylenes and their Blends during Crystallization and Subsequent Melting by Synchrotron SAXS and DSC

Summary: The crystalline structure and phase morphology of linear, branched polyethylenes and their blends during crystallization and subsequent melting were investigated, using a combination of differential scanning calorimetry (DSC), and synchrotron small angle X-ray scattering (SAXS). A linear polyethylene (PE1) with weight-average molecular weight (M_w) of 114 000 g/mol, and two branched polyethylene copolymers, containing 4.8 mol% (PE4) and 15.3 mol% (PE10) hexane, with molecular weights of 93 000 g/mol and 46 000 g/mol were used as pure samples. Two blends, PE1-4 and PE1-10, each with a weight ratio of 50/50, were prepared by solution blending. Our results indicate that in PE4 a phase separation within the branched component itself occurred, forming a broad distribution of lamellar thicknesses during the crystallization process. PE10 on the other hand did hardly crystallize because of the high degree of branching. Co-crystallization of both components took place in blend PE1-4 and liquid-liquid phase separation occurred in the melt of PE1-10. Morphological parameters were determined by using Bragg's law and the correlation function, respectively. The detected semicrystalline morphology can be well described by the lamellar insertion mode where thin lamellae develop between thicker primary lamellae. During subsequent heating, lamellae melted in the reversed sequence of their formation. The evolution of the structural parameters as a function of temperature revealed that surface melting began at first, and then the complete melting of stacks occurred until the final melting temperature was reached.     

Wide‐angle X‐ray diffraction and differential scanning calorimetry study of the crystallization of poly(ethylene naphthalate), poly(butylene naphthalate), and their copolymers

The crystallization behavior of a series of poly(ethylene‐co‐butylene naphthalate) (PEBN) random copolymers was studied. Wide‐angle X‐ray diffraction (WAXD) patterns showed that the crystallization of these copolymers could occur over the entire range of compositions. This resulted in the formation of poly(ethylene naphthalate) or poly(butylene naphthalate) crystals, depending on the composition of the copolymers. Sharp diffraction peaks were observed, except for 50/50 PEBN. Eutectic behavior was also observed. This showed isodimorphic cocrystallization of the PEBN copolymers. The variation of the enthalpy of fusion of the copolymers with the composition was estimated. The isothermal and nonisothermal crystallization kinetics were studied. The crystallization rates were found to decrease as the comonomer unit content increased. The tensile properties were also measured and were found to decrease as the butylene naphthalate content of the copolymers increased. For initially amorphous specimens, orientation was proved by WAXD patterns after drawing, but no crystalline reflections were observed. However, the fast crystallization of drawn specimens occurred when they were heated above the glass‐transition temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 843–860, 2004     

Effect of operation parameters on temperature rising elution fractionation and crystallization analysis fractionation

Crystallization analysis fractionation and temperature rising elution fractionation are two techniques used to estimate the chemical composition distributions of semicrystalline copolymers. This study investigates the cooling rate and cocrystallization effects for both techniques with a series of ethylene/1‐olefin copolymers and their blends. Ideally, both techniques should operate in the vicinity of thermodynamic equilibrium so that crystallization kinetic effects are avoided. The results show that, in fact, crystallization kinetic effects play an important role at the typical cooling rate used with both techniques. Cocrystallization is significant when fast cooling rates are used. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1762–1778, 2003     

Advanced Characterization of Propylene-Based Copolymers and Olefin Block Copolymers

Summary: The newly developed interactive separation of polyolefins by high temperature liquid chromatography (HTLC) provides new information about the chemical composition distribution of polyolefin elastomers. The technique has the advantage of being quantitative in its separation, and has high resolution for the separation of polyolefins by their chemical composition without influence by cocrystallization. Chemical composition distributions can be determined for individual polymers and blends which contain the full range of comonomer typically present in polyethylene and poylypropylene homopolymers, semi-crystalline copolymers, and amorphous copolymers. HTLC analysis in combination with the other fractionation techniques, such as DSC, TREF, NMR, and xylene fractionation, can be used to estimate the amount of olefin block copolymer present in a block composite produced by chain shuttling catalysis.     

Phase behavior of crystalline blends of poly(tetrafluoroethylene) and of random fluorinated copolymers of tetrafluoroethylene

In the present article, we investigate by differential scanning calorimetry (DSC) the thermal behavior (melting, crystallization, and crystal–crystal transitions) far from equilibrium of blends constituted of two crystalline polymers. In particular, the following blends are examined: PTFE–PFMVE, PTFE–FEP, and FEP–PFMVE where PTFE is poly(tetrafluoroethylene), PFMVE is poly(tetrafluoroethylene‐co‐perfluoromethylvinylether), and FEP is poly(tetrafluoroethylene‐co‐hexafluoropropylene). The two last ones are random tetrafluoroethylene copolymers with small amounts of comonomer. Our results indicate that, under the experimental investigated conditions, the blends containing PTFE do not give cocrystallization on cooling from the melt, although under very rapid crystallization conditions, quenching, the presence of the copolymer would seem to slightly influence PTFE crystallization (lower peak temperatures are observed for the crystalline transitions and the melting with respect to those of the neat homopolymer). The behavior of the FEP–PFMVE blend is completely different; in fact, our results indicate the occurrence of cocrystallization, then miscibility in the crystalline phase, for almost all compositions and all investigated experimental conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 679–689, 1999     

Isomorphic interactions of ethylenic polymers and paraffin wax

The high degree of flexibility of blends containing minor amounts of partly crystalline copolymers of ethylene and vinyl acetate in paraffin wax seems to be a manifestation of some type of interaction. Low-angle x-ray diffraction of such blends showed a new long spacing intermediate in length between the polymer long spacing and the c axis length of the wax unit cell. This new long spacing appears to be a consequence of isomorphism involving cocrystallization of polymeric ethylene sequences and wax molecules. A lesser type of isomorphic interaction, epitaxy, occurs in polyethylene–wax blends: wax overgrows crystals of already crystallized polyethylene in the same orientation without a change in its c axial dimension.     

Structural study of the influence of partially crystalline poly(ethylene butene) random copolymers on paraffin crystallization in dilute solutions

Random crystalline–amorphous copolymers containing ethylene and butene segments, yielded from dilute-solution, and self-assembled to one-dimensional, needle-shaped aggregates, can modify wax crystal structures through the cocrystallization of the copolymer and wax molecules into hairy platelets. These copolymers show selectivity in their wax crystal modification capacities that depends on the ethylene content of the backbone. Thus, it has been qualitatively established that a copolymer containing larger crystallizable polyethylene sections [poly(ethylene butene) with 7.5 ethyl branches per 100 backbone carbons (PEB-7.5)] is very efficient for longer wax molecules (C₃₆), whereas for shorter waxes (C₂₄), its efficacy diminishes. Here we present a quantitative evaluation of the small-angle neutron scattering results obtained in a complex study of the self-assembling behavior of PEB-7.5 and paraffin waxes (C₂₄ and C₃₆) in decane and of cocrystallization for different polymer–paraffin combinations and solution conditions. The richness of the morphologies was evaluated with a contrast variation technique and the application of structural models. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3113–3132, 2004     

磺化间规聚苯乙烯和间规聚苯乙烯的非等温结晶动力学

对磺化度分别为 1 6 0mol% ,3 0 5mol% ,4 41mol%的磺化间规聚苯乙烯和间规聚苯乙烯的非等温结晶动力学进行了研究 ,用DSC测试了四种样品的非等温结晶过程 ,对所得数据分别用Mandelkern方法和莫志深方法进行了处理 ,发现磺化间规聚苯乙烯和间规聚苯乙烯的非等温结晶动力学参数差别较大 ,说明磺酸基团的引入对sPS结晶行为有较大的影响 ,磺酸基团之间的氢键相互作用使SsPS的结晶速率降低 ,结晶度减小 .此外 ,SsPS和sPS的Avrami指数n值均在 2～ 3之间 ,且为非整数 ,说明它们主要是以混合成核的方式结晶 .SsPS的成核与生长活化能ΔE值高于sPS的 ,并且随磺化度的增加而递增 ,sPS的ΔE值为 2 40 5 0kJ/mol,磺化度为 1 6 0mol% ,3 0 5mol%和 4 41mol%的SsPS的ΔE值分别为 2 5 1 70kJ/mol,2 72 33kJ/mol和2 90 79kJ/mol.     

Isothermal crystallization of propylene-1-decene copolymers

The isothermal crystallization and subsequent melting behavior of one propylene homopolymer and three propylene-1-decene copolymers with different comonomer contents prepared by metallocene catalyst were studied using differential scanning calorimetry (DSC). It is found that the Avrami exponent of the propylene copolymers decreases gradually with the increase of comonomer content, from 3.0 for the propylene homopolymer to 1.4 for the copolymer with 7.83 mol% 1-decene units. Higher comonomer content also weakens the dependence of crystallization rate constant and crystallization halftime on temperature. Double melting peaks, which correspond to α and γ crystal phases, respectively, are observed for all copolymers under isothermal crystallization. The result shows that higher crystallization temperature is favorable to the segregation of α and γ crystal phases, resulting in higher proportion of γ crystal phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

High norbornene incorporation in ethylene-norbornene copolymerization with a bis(α-alkyloxoimine) titanium-MAO catalyst

A novel bis(α-alkyloxoimine) titanium(IV) complex was synthesized and used as a catalyst precursor to catalyze homo- and copolymerization of ethylene and norbornene. The titanium complex activated with methylalumoxane exhibits good activities for the homopolymerizations of ethylene and norbornene under high temperature to produce high-molecular-weight linear polyethylene and vinyl-type polynorbornene, respectively. Ethylene-norbornene copolymers with high molecular weight can also be produced by this catalyst. The incorporation of norbornene from 0 to 76 mol% in the copolymers can be controlled by varying the charged norbornene. ¹³C NMR analyses show that the microstructures of the ethylene-norbornene copolymers with low norbornene incorporation are predominantly alternated and isolated norbornene units, while those with high norbornene incorporation are random polymers containing long norbornene sequences.     

Thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers at the curie transition

The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers near the ferroelectric-to-paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 mol% trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 mol% TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intemediate supplementary phase. Both hypotheses are discussed.     

On the fractionation of homopolymers during crystallization from the pure melt

The question as to whether fractionation occurs during the crystallization of homopolymers from the pure melt has been addressed by studying linear polyethylene mixtures. Two methods were used. In one procedure, mixtures of well-defined fractions were crystallized under controlled conditions and the subsequent fusion process was analyzed. In the other procedure, a selective extraction was carried out on an isothermally crystallized polydisperse whole polymer, and the residue was analyzed by gel permeation chromatography. Both methods lead to the same conclusion, namely that during isothermal crystallization only the very low molecular weight species crystallize separately. An extreme upper limit to fractionation corresponds to M = 7000. More likely, fractionation in linear polyethylene during bulk crystallization is restricted to molecular weights of 5000 or less.     

Dielectric and thermal characterization of low density ethylene/10‐undecen‐1‐ol copolymers prepared with nickel catalysts

Ethylene and 10‐undecen‐1‐ol copolymers, prepared using a nickel complex as catalyst, were studied using differential scanning calorimetry (DSC), X‐ray diffraction, and dielectric relaxation spectroscopy. The behavior exhibited by copolymers containing incorporated 10‐undecen‐1‐ol amounts within 0.5 and 4.6 mol % was compared with neat polyethylene. DSC revealed that a new crystalline region with lower thickness lamellae emerges in copolymers due to the side‐chains crystallization. Nevertheless, the global crystallization degree decreases due to the loss of crystallinity that occurs in a greater extent in PE‐like regions. Dielectric relaxation spectroscopy detected two processes, a low activation energy process below ?20 °C related with localized mobility increasing in intensity and deviating to higher temperatures with the increase in 10‐undecen‐1‐ol amount, and a high activation energy process ascribed to the glass transition, located at higher temperatures for the different copolymers relatively to neat polyethylene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2802–2812, 2007