Co-unit Content Research Articles

Melt memory in random ethylene-1-alkene copolymers.

Chain flexibility or stiffness based polymer conformation plays a crucial role in affecting the dynamics and kinetics of polymers, which is related to the hierarchical architecture of chains. A series of random copolymers of ethylene and 1-alkenes including 1-hexene, 1-octene, and 1-dodecene were synthesized with metallocene catalysts. The crystallization behavior and memory effect in random ethylene-1-alkene copolymers with different side groups were investigated via differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). Rheological tests were performed for understanding their dynamical behavior. The results show that the melting peak and the viscosity decrease but the orthorhombic crystal dimensions increase with co-unit contents increasing in the copolymers. It was found that the scaling relationship between the zero shear viscosity (η0) and molecular weight (Mn) of the copolymers containing ethylene-1-hexene and ethylene-1-octene is 3.6, which is higher than the classical scaling value of 3.4. The memory of crystals in the melt is enhanced with the increase of 1-alkene contents but is independent of the types of 1-alkenes. The enhanced melt memory effect in the copolymers was proposed due to the effect of the 1-alkene based side groups on the dynamics of polymer chains. The present work would be helpful to understand the chain stiffness based polymer dynamics and processing of polyolefins and copolymers prepared with the metallocene catalyst.

Novel biocompatible PBS-based random copolymers containing PEG-like sequences for biomedical applications: From drug delivery to tissue engineering

A series of random poly(butylene succinate)-based copolymers, (poly(butylene/triethylene succinate) (P(BSmTESn)), containing ether-oxygen atoms were successfully synthesized by melt polycondensation of succinic acid and 1,4-butanediol in the presence of triethylene glycol (TEG) (TEG content up to 40 mol%). The copolymers were characterized from the molecular, thermal, structural and mechanical point of view. Hydrolytic degradation studies were performed under physiological conditions. The biocompatibility of the samples under investigation through indirect and direct biocompatibility studies was investigated by using embryonic rat cardiac H9c2 cells. To evaluate the potential of these polymers also for controlled drug delivery systems, the diffusion profile of Dexamethasone, an anti-inflammatory drug, through nanoparticles prepared by oil-in-water miniemulsion process was investigated. Results showed that solid-state properties could be tailored nicely by simply varying copolymer composition. Crystallinity degree and hydrophobicity significantly decreased with the increase of triethylene succinate co-unit (TES) mol%. Moreover, hydrolytic degradation of PBS, depending on polymer crystallinity degree and hydrophilicity, was remarkably improved: the copolymer containing 40 mol% of triethylene succinate co-unit after 200 days lost over 22% of its initial weight. The newly developed biomaterials showed lack of cell cytotoxicity. Among them, PBS and the copolymers containing up to 20 mol% of TES co-units sustained a better cell adhesion and proliferation. In addition, such copolymers induced muscle phenotype commitment in H9c2 cells cultured onboard. Lastly, the release profile of Dexamethasone obeyed to a first order kinetic law, the copolymer richest in TES co-unit content showing the highest encapsulation capability and the fastest drug release kinetics. Anyway, PBS and the copolymers containing up to 20 mol% of TES co-unis sustained a better cell adhesion and proliferation, with the copolymers characterized by a myosin heavy chain expression, which appeared to be up to twofold increased on respect to the one of PBS homopolymer.

Counits Content and Stretching Temperature-Dependent Critical Stress for Destruction of γ Crystals in Propylene-Ethylene Random Copolymers.

Tensile deformation behavior of three random propylene–ethylene copolymers with the same molecular weight and different contents of counit was investigated at different temperatures from room temperature to close to melting point via tensile tests, step-cycle tests, and in situ wide-angle X-ray diffraction techniques. Upon stretching, the original crystalline lamellae must be destroyed, generating new highly oriented ones. A critical stress has been suggested, under which the original crystallites can be destructed. The propylene–ethylene copolymer samples in pure γ-form transformed gradually into α-form during tensile stretching. This crystalline transition proceeded via a destruction (melting) of the original γ-form crystals followed by recrystallization of the freed polymeric chain segments into α-form along stretching direction. This result provides a marker for investigating the critical stress mentioned above. Such critical stresses triggering the destruction of γ-form crystals for the propylene–ethylene copolymers of different ethylene counit contents were successfully calculated. It turned out that this critical stress depended on the ethylene counit content and stretching temperature. Samples with less ethylene counits show higher critical stress because of a lower degree of insertion of the ethylene counits into the crystalline unit cell than samples with higher ethylene counit content. The critical stresses remained constant when the samples were stretched at low-temperature region, whereas they decreased significantly at high stretching temperatures close to the melting points due to strong thermal distortion of the crystalline lattices, making the crystallites less stable.

How Stress Treatments Influence the Performance of Biodegradable Poly(Butylene Succinate)-Based Copolymers with Thioether Linkages for Food Packaging Applications.

Biodegradable poly(butylene succinate) (PBS)-based random copolymers containing thioether linkages (P(BSxTDGSy)) of various compositions have been investigated and characterized from the gas barrier, thermal, and mechanical point of view, after food contact simulants or thermal and photoaging processes. Each stress treatment was performed on thin films and the results obtained have been compared to the same untreated film, used as a standard. Barrier properties with different gases (O2 and CO2) were evaluated, showing that the polymer chemical composition strongly influenced the permeability behavior. The relationships between the diffusion coefficients (D) and solubility (S) with polymer composition were also investigated. The results highlighted a correlation between polymer chemical structure and treatment. Gas transmission rate (GTR) mainly depending on the performed treatment, as GTR increased with the increase of TDGS co-unit amount. Thermal and mechanical tests allowed for the recording of variations in the degree of crystallinity and in the tensile properties. An increase in the crystallinity degree was recorded after contact with simulant liquids and aging treatments, together with a molecular weight decrease, a slight enhancement of the elastic modulus and a decrement of the elongation at break, proportional to the TDGS co-unit content.

Synthesis and characterization of novel semiaromatic copolyamides bearing both polar hydroxyl and unsaturated allyl substituents

ABSTRACTA series of novel semiaromatic (co)polyamides, poly(octylene terephthalamide)‐ran‐poly[octylene 2,5‐bis(allyloxy)terephthalamide] (APA8T‐x, x represents the molar fraction of allyloxy containing structure unit), were prepared via the interfacial polymerization of 1,8‐diaminooctane, terephthaloyl chloride, and 2,5‐bis(allyloxy)terephthaloyl chloride. The polymerization conditions were optimized in terms of the yields and the molecular weights of the resultant polymers. These polymers were converted to the target macromolecules, poly(octylene terephthalamide)‐ran‐poly[octylene (2,5‐dihydroxy‐3,6‐diallyl)terephthalamide] (CRPA8T‐x), through solid state Claisen rearrangement reaction, as characterized by 1H NMR and FT‐IR spectroscopies. While APA8T‐x was only soluble in very limited solvents, the solubility of CRPA8T‐x in polar solvents improved remarkably, especially for those with high counit content. Due to the polarity of hydroxyl group, CRPA8T‐x showed an improved hydrophilicity than APA8T‐x. The treatment of aramid fibers with CRPA8T‐x, as sizing agents, enhanced obviously their interfacial adhesion toward epoxy resin. The fibers sized with 0.5 wt% CRPA8T‐75 solution in the mixture of 1,1,2,2‐tetrachloroethane and phenol (40:60, w/w) exhibited a maximum increase of 60% in interfacial shear strength than the naked fibers. The easy preparation and the facility for the further modification through the dual functional substituents may greatly widen the application of semiaromatic polyamides. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 690–698

Trigonal δ form as a tool for tuning mechanical behavior in poly(propylene-co-1-pentene-co-1-heptene) terpolymers

Abstract Terpolymers based on propylene with 1-pentene and 1-heptene as comonomeric units are satisfactorily synthesized containing distinct overall compositions in comonomers as well as three different 1-pentene/1-heptene ratios at a given global composition. The effect of total content in counits and ratio between comonomers on polymerization activity, intrinsic viscosity, molecular weights and microstructural details has been analyzed. In addition, their influence on the mechanical response has been preliminary checked. The results show that rigidity related parameters, like Young’s modulus and yield stress, are mainly dependent on overall composition, but comonomer ratio becomes also a primary variable for the terpolymers with a global counit content higher than 10 mol %. This fact is ascribed to the capability or inability of developing the trigonal polymorph as function of which counit (1-pentene or 1-heptene) is in majority or minority.

Novel fully biobased poly(butylene 2,5-furanoate/diglycolate) copolymers containing ether linkages: Structure-property relationships

Novel fully biobased aliphatic-aromatic poly(butylene 2,5-furanoate/diglycolate) random copolyesters were successfully synthesized from 2,5-furandicarboxylic acid, diglycolic acid and 1,4-butanediol through two-stage melt polycondensation using titanium tetrabutoxide and titanium tetraisopropoxide as catalysts. The synthesized polymers were characterized in terms of molecular and solid-state properties, among these, barrier properties to different gases. In addition, biodegradability studies in compost have been conducted.All the polymers showed a good thermal stability, even higher than that of the thermally stable homopolymer poly(butylene furanoate), and at room temperature appeared as semicrystalline materials. The main effect of copolymerization was a lowering, up to 60°C, in Tm respect to the homopolymer. The dependence of Tm on composition for copolymers was well described by Baur’s equation. Diffractometric measurements indicated that only the poly(butylene furanoate) crystalline phase is present in the copolymers under investigation. Amorphous samples showed a monotonic decrement of Tg, up to 30°C, as the content of butylene diglycolate units is increased and this can be explained on the basis of the higher flexibility induced in the polymer chain by the ether-oxygen atoms. A Wood-type equation was found to fit the Tg data of completely amorphous samples.Final properties and biodegradation rate of the materials under study were strictly dependent on the copolymer composition and the crystallinity degree. As a matter of fact, hydrophilicity regularly increased with the increasing of butylene diglycolate mol%, due to the highly electronegative ether-oxygen atoms present in the co-units (water contact angle decreased of almost 15°). The elastic modulus decreased till one order of magnitude and the elongation to break increased, up to 400%, as co-unit content was increased.Regarding the gas barrier properties, copolymerization did not imply a worsening with respect to the homopolymer. A slight increment of the gas transmission rate was recorded just for the copolymer containing the highest amount of butylene diglycolate units, as a consequence of the increasing flexibility of the macromolecular chain due to the ether-oxygen atoms. This behavior was more evident with CO2 gas test than with O2, N2 and C2H4 ones.

Synthesis and properties of poly(p-phenylene terephthalamide) bearing both polar and unsaturated substituents introduced via claisen rearrangement reaction

A series of novel wholly aromatic copolyamides, poly(p-phenylene terephthalamide)-ran-poly[p-phenylene 2,5-bis(allyloxy)terephthalamide] (APPTA-x, x (=0, 5, 25, 50, 60, 75, 90, and 100) represents the molar fraction of allyloxy containing structure unit), were prepared via low temperature solution copolycondensation of p-phenylenediamine, terephthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride. They were converted to the target copolymers, poly(p-phenylene terephthalamide)-ran-poly[p-phenylene 2,5-diallyl−3,6-dihydroxyterephthalamide] (CRPPTA-x), through Claisen rearrangement reaction, as characterized by a comprehensive analyses of NMR, FT-IR, gel permeation chromatography, and differential scanning calorimetry. Although APPTA-x had a poor solubility in common organic solvents, the rearranged products with high co-unit contents, that is, CRPPTA-60, 75, 90, and 100, were readily dissolved in m-cresol, DMF, DMAc, DMSO, and NMP. The effect of these four polymers, used as sizing agents, on the interfacial adhesion between Kevlar fiber and epoxy resin was investigated by the contact angle method, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and microbond tests. Compared with the naked fibers, the sized fibers displayed enhanced surface energy and roughness. The fibers sized with 0.5 wt % CRPPTA-60 solution in NMP exhibited a maximum increase of 19% in interfacial shear strength. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016

Time-resolved micro-indentation hardness measurement to probe the Form II/Form I crystal polymorphism in random copolymers of butene-1 with either ethylene or propylene

Time-resolved micro-indentation hardness measurements have been performed on random copolymers of butene-1 with minor amount of ethylene or propylene during the room-temperature transition of the Form II mesophase into Form I crystals. The microhardness depends on the present crystal polymorph and increases during the Form II–Form I phase transformation, which is completed faster in the random copolymers than in the butene-1 homopolymer. It is furthermore observed that the microhardness decreases with increasing concentration of ethylene and propylene co-units in the random copolymers. This experimental result is comprehensively discussed in view of the observed decreases of the crystallinity and crystal perfection in copolymers containing ethylene or propylene, respectively. Analysis of a copolymer with about 11 mol% propylene revealed that the microhardness of copolymers containing Form I’ crystals, formed directly from the melt, is higher than the initial microhardness of samples of lower co-unit content containing only Form II mesophase.

Equilibrium melting temperature and crystallization kinetics of α- and β′-PBN crystal forms

The melting behavior and the crystallization kinetics of poly(butylene/diethylene naphthalate) and poly(butylene/thiodiethylene naphthalate) random copolymers were investigated by means of DSC. By the Hoffman–Weeks’ method, the Tm° of α and β′-PBN phases were derived: the Tm° value of β′-form was higher, as expected, taking into account that it is thermodynamically favorite and more tightly packed. The presence of oxygen or sulphur atoms in PBN reduced its ability of crystallizing, the crystallization rate regularly decreasing with the co-unit content. α-PBN phase crystallized faster than β′-one, being the more kinetically favorite.

Poly(butylene terephthalate) modified with ethoxylated bisphenol S with increased glass transition temperature and improved thermal stability

Novel copolyesters have been prepared by polycondensation and by melt mixing of poly(butylene terephthalate) with an ethoxylated bisphenol S. No side reactions occur during the synthesis of the samples, as proved by NMR analysis. The polyesters were examined by TGA and DSC. The insertion of the bisphenol S (sulfonyldiphenol) group significantly improved the thermal stability of the polymer. The thermal analysis carried out using DSC technique showed that the Tm of the copolymers decreased with increasing co-unit content, differently from Tg, which on the contrary increased, exceeding in some cases 100 °C, and crystallization rate decreased. A polymer containing only terephthalate moieties and ethoxylated bisphenol S has been prepared for the first time.

Effect of comonomer type on the crystallization kinetics and crystalline structure of random isotactic propylene 1-alkene copolymers

Isothermal crystallization kinetics and properties related to the crystalline structure of four series of random propylene 1-alkene copolymers have been comparatively studied in this work. Comonomers studied include ethylene, 1-butene, 1-hexene and 1-octene in a concentration range up to 21mol%. All copolymers were synthesized with the same metallocene catalyst to provide an equivalent random distribution and a similar content of stereo and regio defects within the series. This has ensured that differences in crystallization kinetics and in crystalline properties of copolymers with matched compositions reflect the affinity of the comonomer type for co-crystallization with the propene units, and the effect of content and type of co-unit in the development of the crystalline structure. In the nucleation-driven crystallization range, that is for Tcs>Tc max, the values of the rate follow the sequence PB>PE>PH=PO for comonomer contents <13mol%, and PB>PE>PH>PO for >13mol% comonomer. These trends in overall crystallization are guided by differences in undercooling due to a similar progression of the degree of participation of the comonomer in the crystalline lattice. The variation of the rates at Tcs<Tc max follows the melt segmental dynamics driven by differences in Tg, especially at the highest co-unit contents, resulting in a reverse rate sequence for PHs and POs >15mol%, i.e., PB>PE∼PO>PH. In addition to crystallization kinetics, a comparative polymorphic analysis and unit cell expansion, crystalline morphology, and melting behavior have been instrumental in resolving the partitioning of the four types of co-units between crystalline and non-crystalline regions. 1-Butene units participate at the highest level followed by the ethylene units, as demonstrated by solid-state NMR. However, both units are defects that hinder crystallization, as given by the decreasing rates, decreased levels of crystallinity and lowered melting temperatures with increasing co-unit content. All crystalline properties of PHs and POs conform to a rejection model of the 1-octene units from the crystals in the whole compositional range, and rejection of the 1-hexene units for PH <13mol%, a conclusion also supported by NMR. The ability of PH >13mol% to pack comonomer-rich sequences into a stable trigonal lattice leads at Tcs>Tc max to an increased number of crystallizable sequences, and to faster crystallization rates than for matched PO copolymers.

Synthesis and mesophase behaviors of 2,5-disubstituted styrene-based random copolymers: Effect of difference in side-group length on liquid crystallinity

Five series of binary copolymers, poly[2,5-di(ROOC)styrene- co-2,5-di(R′OOC)styrene]s (R = n-C 3H 7–, R′ = C 2H 5–, n-C 4H 9–, and n-C 5H 11–; R = n-C 6H 13–, R′ = n-C 4H 9–, and n-C 5H 11–), were synthesized via free radical polymerization. The random nature of the copolymers was expected on the basis of the assumed similar reactivities of the analogous monomers and proved by 13C NMR analysis. It was also implied by the smoothly varying glass transition temperatures and further supported by the monotonous variation in d spacings for the liquid crystalline copolymers, where both corresponding homopolymers are liquid crystals. Subtle difference of R and R′ was found to have significant impact on the mesomorphic properties of the copolymers. When the pair of the corresponding homopolymers has the same mesogenic structure, a difference of one carbon atom in the alkyl chain can be tolerated over the whole copolymer composition range; however, the liquid crystalline structure soon disappears with the incorporation of a co-unit of an homopolymer that is not liquid crystal. For the copolymers with alkyl chain length differing by two carbon atoms, the liquid crystalline structure is lost with the incorporation of relatively low co-unit content despite the pair of corresponding homopolymers having the same mesogenic structure.

A law controlling polymer recrystallization showing up in experiments on s-polypropylene

Abstract When polymers are crystallized at large supercoolings a subsequent heating is accompanied by recrystallization processes, which proceed to a fixed final melting point. We studied these processes with small-angle X-ray scattering and DSC measurements for three s-polypropylenes with different stereoregularities and co-unit contents. As is known from previous experiments, crystal thicknesses dc depend on the crystallization temperature Tc only, being not affected by stereo defects or co-units. The new experiments, all carried out at low crystallization temperatures, again confirm this property; in plots of dc−1 versus Tc all points are located on a unique straight crystallization line. A similarly simple law controls the crystal thickness during the continuous structure reorganization on heating. Over an extended temperature range dc−1 changes linearly with temperature, guided by a unique, i.e., sample-invariant, ‘recrystallization line’. Crystallization and recrystallization lines extrapolate for dc−1 → 0 to the same limiting temperature, Tc∞, and differ only in slope. The findings indicate that both the initial crystallization at Tc and the process of recrystallization use a pathway via a transient mesomorphic phase. The DSC thermograms of the samples show a multiple peak structure which varies with the heating rate. The SAXS results enable the peaks to be assigned to different melting processes.

Novel random copoly(arylene ether-thioether ketone)s based on 2,2-bis(4-mercaptophenyl)propane and 4,4′-dihydroxybiphenyl: Synthesis and properties

A series of novel poly(arylene ether-thioether ketone) random copolymers were synthesised by copolymerisation of 4,4′-difluorobenzophenone with bis( N, N-dimethyl- S-carbamate) of 2,2-bis(4-mercaptophenyl)propane (MBTA) and 4,4′-dihydroxybiphenyl (BP). The syntheses were performed using a one pot polymerisation method starting from different mole percentages of BP with respect to MBTA, varying from 20% to 80%. The copolymers were obtained in good yields and had molecular weights in the range 10,000–17,000 as determined by GPC. The structural proof was provided by 1H-NMR spectroscopy. In order to study the effect of the copolymerisation on the thermal properties and crystal behaviour, also the poly(ether biphenyl ether ketone) homopolymer (PEBEK) has been synthesised using the same polymerisation method. The TGA analysis shows that the high stability of PEBEK is only slightly affected by the introduction of co-units in the chain. The copolymers with an amount of PEBEK variable from 80 to 50 mol% are crystalline, with percentage of crystallinity and melting temperature which decrease as the co-unit content increases. The samples with lower amount of PEBEK (40 and 20 mol%) are amorphous. The T g values tend to decrease with the reduction of the percentage of PEBEK units.

Effect of diluents on hydrophilic ethylene-acrylic acid co-polymer membrane structure via thermally induced phase separation

Abstract Hydrophilic microporous membranes were prepared via the thermally induced phase separation process using three types of hydrophilic ethylene-acrylic acid co-polymers (EAA) with different co-unit contents. The effects of diluents on the structure of membranes were also investigated. The experimental results showed that the phase diagrams of these polymer diluent systems were typical diagrams of semi-crystalline polymer diluents with weak interaction. The cloudpoint curve shifted to the lower temperature, while the crystallization temperature was not influenced so much by the type of diluents. The pore sizes of EAA membranes prepared from different diluent systems at 30 wt% polymer concentration were about 4.98 μm, 1.80 μm, 1.72 μm, 1.57 μm, and 0.59 μm for the systems of EAA3003/diphenyl ether (DPE), EAA3003/soybean oil, EAA3003/dioctyl phthalate (DOP), EAA3003/sesame oil, and EAA3003/peanut oil, respectively. The microstructure of EAA3003-soybean oil system was leafy, while other systems were cellular. Pore sizes and porosities of three EAAs with different co-unit contents decreased in the order of EAA1410/DOP, EAA3002/DOP and EAA3003/DOP.

Synthesis and thermal properties of randomly branched poly(butylene isophthalate) containing sodium sulfonate groups

Randomly branched poly(butylene isophthalate) samples containing sodium sulfonate groups were prepared from dimethyl isophthalate, 3,5-bis(carbomethoxycarbonyl) benzene sulfonate, tris(hydroxyethyl) isocyanurate, and 1,4-butanediol, according to the well-known two-stage polycondensation procedure. The polymers, containing various amounts of branching units and ionic groups, demonstrated to be soluble in the most common organic solvents, an evidence that gelation was not reached under the polymerization conditions adopted. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. The sulfonate as well as the branching units had only a limited effect on the thermal stability, which slightly decreased with respect to pure poly(butylene isophthalate). The analysis carried out using DSC technique showed that the Tm of the copolymers decreased with increasing counit content, differently from Tg, which, on the contrary, increased. Baur's equation was found to describe well the Tm-composition data. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1374–1379, 2006

Rheological, thermal and crystallisation properties of ethylene, propylene and α-olefin copolymers. II Thermal and crystallisation properties

A series of random ethylene, propylene/1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene copolymers, ethylene and propylene homopolymers were prepared and investigated. The thermal and crystallisation properties of copolymer samples with different co-unit content and molecular masses were determined and compared with the properties of homopolymers. The effects of the length of co-unit and the comonomer content were investigated. The thermodynamic melting point was determined by linear and non-linear methods. The melting points and crystallinity decrease with the length of co-unit and with the increase in comonomer content. The crystallisation kinetics was investigated with the Avrami equation.

Rheological, thermal and crystallisation properties of ethylene, propylene and α-olefin copolymers. I Rheological properties

A series of random ethylene, propylene/1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene copolymers, ethylene and propylene homopolymers were prepared and investigated. The rheological properties (steady state and dynamic shear viscosity, creep compliance and plateau modulus), of copolymer samples with different co-unit content and molecular masses were determined and compared with the properties of homopolymers. The effects of the length of counit and the comonomer content were investigated. The copolymers exhibited similar rheological properties to the homopolymer but they have a lower shear viscosity, normal viscosity, higher steady state creep compliance and smaller plateau modulus values. The effect of comonomer content was evaluated on the bases of free volume theory.

Equations describing lamellar structure parameters and melting points of polyethylene- co -(butene/octene)s

Time- and temperature-dependent SAXS-experiments were used to determine the effect of octene and butene co-units on the lamellar structure and the melting properties of polyethylene. As expected, melting points decrease with increasing co-unit content, but crystal thicknesses are not affected and depend on the crystallization temperature only. Results can be cast into some simple equations which describe the dependence: