Methylene Sequences Research Articles

Ultralong-Chain-Spaced Crystalline Poly(H-phosphonate)s and Poly(phenylphosphonate)s

Aliphatic poly(H-phosphonate)s were obtained by polyesterification of dimethyl H-phosphonate with bio-based long-chain diols. Nonadecane-1,19-diol, tricosane-1,23-diol, and octatetracontane-1,48-diol with dimethyl H-phosphonate yield the corresponding polyphosphoesters (PPE19H, PPE23H, and PPE48H) with molecular weights (Mn) up to 4.3 × 104 g mol–1. Postfunctionalization of these polymers via Hirao cross-coupling yields the selectively functionalized poly(H-phosphonate)s PPE19Ph, PPE23Ph, and PPE48Ph. DSC analysis revealed significantly enhanced crystallinities and melting points (up to Tm = 110 °C) with increasing methylene sequence lengths. Hydrolytic degradation of polymer powder of poly-(H-phosphonate) occurred up to 95% in 2 days. The degradation rates decreased with increasing methylene sequence length. After postfunctionalization, degradation occurred only to a minimal extent over 3 months in basic and in acidic media.

Semicrystalline Long-Chain Polyphosphoesters from Polyesterification

Semicrystalline aliphatic polyphosphoesters can be obtained in a one-step approach by polyesterification of readily available bio-based long-chain diols with dichlorophosphorus compounds. Nonadecane-1,19-diol and tricosane-1,23-diol with respectively methylphosphonic dichloride or phenyl dichlorophosphate yield polymers (PPE19Me, PPE23Me, PPE19(OPh), and PPE23(OPh)) with molecular weights Mn up to 3 × 104 g mol–1. DSC analysis of these polymers and a C12 analogue reveal significantly enhanced crystallinities and melting points (up to Tm = 87 °C) with increasing methylene sequence length. DMA on injection-molded samples shows glass transitions at −19 °C (PPE19Me) and −12 °C (PPE23Me). Single crystals of PPE19Me accommodate a single C19 repeat unit, as concluded from a lamella thickness of only 3 nm thick determined by AFM. Hydrolytic degradation of solid polymer samples under ambient conditions occurred only to a minimal extent over three months by hydrolysis of very small amounts of in-chain anhydride def...

Sharp and strong “Brill transition” of poly(hexamethylene dithiocarbonate)

In this paper, the reversible crystal-crystal transition of poly(hexamethylene dithiocarbonate) (PHMDC) has been systematically studied. According to various experimental results, we confirm that the transition shares the common features with Brill transition that is widely observed in nylons. This transition is clearly associated with the reversible trans-gauche conformational transformation of the methylene sequences in the crystal lattice. Therefore, in addition to its analogue poly(octamethylene carbonate) POMC (ACS Macro Lett. 2015, 4, 317–321), PHMDC can be considered as a new example of the polymers exhibiting Brill transition outside the nylon family. Careful examination of the experimental data reveals that for PHMDC the enthalpy ratio of the Brill transition to the melting is a constant of ∼2/3, independent of the crystallization condition applied. Furthermore, the difference between the Brill transition temperatures determined from heating and cooling is also a constant, which is of ∼4 °C. These new observations are obtained because the Brill transition of PHMDC is sharp and possesses a large transition enthalpy. Such a transition is associated with that the methylene segments in PHMDC can change their conformation between trans and gauche rapidly and completely in a narrow temperature interval.

Relaxation behavior of polyurethane networks with different composition and crosslinking density

The relaxation behavior of a series of solvent free polyurethane model networks with variable cross-link density prepared based on different commercial diols and a diisocyanate containing component are studied by differential scanning calorimetry (DSC), dynamic-mechanical analysis (DMA) and dielectric relaxation spectroscopy (DRS). A systematic decrease of the calorimetric glass temperature Tg as well as of the softening temperatures TαDMA and TαDRS from relaxation methods is observed with increasing length of the diol sequences between neighbored diisocyanate units acting as cross-linker. This trend is explained based on an internal plasticization of the polymeric network by long, highly mobile diol units containing an increasing fraction of methylene sequences. Cold crystallization effects are only indicated for the longest diol sequence under investigation. This is understood as a consequence of a large fraction of methylene sequences in combination with weaker geometrical constraints. Two secondary relaxations, β and γ, are observed in the glassy state for all amorphous samples at low temperatures by dielectric spectroscopy indicating the existence of localized motions in the polyurethane networks. Below Tg these relaxation processes are practically unaffected by changes in the length of the diol units and the softening behavior of the polymeric model networks. Interrelations between secondary β relaxation and cooperative α dynamics are indicated. An onset of the dielectric α relaxation strength Δεα is observed for all amorphous polyurethane networks. A linear extrapolation of Δεα vs. 1/T gives onset temperatures Ton which are in good agreement with αβ crossover temperatures Tαβ being the temperature where the difference between α and β relaxation times τα−τβ approaches a minimum. This finding supports an onset of the cooperative α motions in the αβ crossover region as reported in the previous literature for many other glass forming materials.

Single-Step Access to Long-Chain α,ω-Dicarboxylic Acids by Isomerizing Hydroxycarbonylation of Unsaturated Fatty Acids

Dicarboxylic acids are compounds of high value, but to date long-chain α,ω-dicarboxylic acids have been difficult to access in a direct way. Unsaturated fatty acids are ideal starting materials with their molecular structure of long methylene sequences and a carboxylate functionality, in addition to a double bond that offers itself for functionalization. Within this paper, we established a direct access to α,ω-dicarboxylic acids by combining isomerization and selective terminal carbonylation of the internal double bond with water as a nucleophile on unsaturated fatty acids. We identified the key elements of this reaction: a homogeneous reaction mixture ensuring sufficient contact between all reactants and a catalyst system allowing for activation of the Pd precursor under aqueous conditions. Experiments under pressure reactor conditions with [(dtbpx)Pd(OTf)2] as catalyst precursor revealed the importance of nucleophile and reactant concentrations and the addition of the diprotonated diphosphine ligand (dt...

Anionic Nylon 612/TiO2 Composite Materials: Synthesis, Characterization and Properties

Two novel series of composites have synthesized in situ by simultaneous anionic ring-opening copolymerization-rotational molding fast environment-friendly process using e-caprolactam (CL) with laurolactam (LL) as starting comonomers and TiO2 as filler. The type of filler (with surface treated or not) differentiates the two series. Aminopropyl triethoxysilane (APTES) coupling agent was used. By adjusting the TiO2 in the range 0.0–8.0 wt.% in the feed monomers mixture, various composites were obtained. The characterization of samples was performed, in the context of filler type and content variation by combined use of ATR–FTIR spectroscopy, X-ray spectroscopy, DSC, TGA/DTG, SEM and mechanical measurements. In addition, degree of conversion, intrinsic viscosity and water absorption were evaluated. Introduction of the long methylene sequences through the second monomer into the nylon 6 chains improved especially the water uptake of the composites. The melting temperature (Tm), crystallization temperature (Tc), degree of crystallinity (αDSC) and the interface interactions between filler and nylon 612 matrix prove to be improved by treatment of filler surface. The same trend was recorded for tensile strength, tensile modulus, elongation at break and impact strength. The results related to composites were compared with those obtained for neat nylon 612 copolymer synthesized in the same conditions.

Isomerization‐hydroboration‐oxidation strategy: Access to long chain AB‐ and AA‐type oleyl based monomers and polymers thereof

A strategy to convert by isomerization‐hydroboration‐oxidation reaction the internal double bond of oleic acid to a terminal alcohol function, leading to linear long‐chain α,ω‐difunctional substrates has been investigated. Using this strategy, oleic acid‐based AB‐ and AA‐monomers were prepared and characterized by FTIR‐ATR and NMR spectroscopy. Thermoplastic aliphatic linear polyesters, polycarbonates, and polyurethanes were then synthesized by reacting the so‐formed bio‐based monomers via polycondensation in bulk, using 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) as an organocatalyst. Thus, starting from easily available bio‐based starting compound, the synthesis of linear long methylene chain aliphatic polyesters, polycarbonates, and polyurethanes (by isocyanate free route) is reported. The structural and thermal characterizations of the synthesized polymers were performed by means of NMR, SEC, DSC, and TGA experiments.Practical applications: The objective of the work is to obtain long methylene sequence alpha, omega difunctional fatty acid‐based substrates that can be used as original monomers.A strategy to convert by isomerization‐hydroboration‐oxidation reaction the internal double bond of oleic acid to a terminal alcohol function, leading to linear long‐chain α,ω‐difunctional substrates is described.

Long-Chain Aliphatic Polymers To Bridge the Gap between Semicrystalline Polyolefins and Traditional Polycondensates.

Other than their established short-chain congeners, polycondensates based on long-chain difunctional monomers are often dominated by the long methylene sequences of the repeat units in their solid-state structures and properties. This places them between traditional polycondensates and polyethylenes. The availability of long-chain monomers as a key prerequisite has benefited much from advances in the catalytic conversion of plant oils, via biotechnological and purely chemical approaches, likewise. This has promoted studies of, among others, applications-relevant properties. A comprehensive account is given of long-chain monomer syntheses and the preparation and physical properties, morphologies, mechanical behavior, and degradability of long-chain polyester, polyamides, polyurethanes, polyureas, polyacetals, and polycarbonates.

The aliphatic counterpart of PET, PPT and PBT aromatic polyesters: effect of the molecular structure on thermo-mechanical properties

The aliphatic counterparts of the most used aromatic polyesters (PET, PPT, and PBT) have been synthesized by a two-stage polycondensation process, starting from dimethyl 1,4-cyclohexane dicarboxylate and different diols. The fully aliphatic polyesters are characterized by two cis/trans isomeric ratios (50 and 90 mol%) of the 1,4-cycloaliphatic rings. According to the cis/trans content, the properties of the materials notably change. Indeed, polymers rich in trans isomer are semicrystalline, whereas polymers with low trans content are fully amorphous, due to the presence of kinks along the chain. Trans isomer is characterized by higher rigidity than the cis one and the corresponding polymers have high glass transition temperatures. Moreover, the length of the methylene sequences in the diol has a notable influence on the final thermal and mechanical properties. Therefore, tunable properties can be easily obtained. This characteristic, in association with good mechanical performances, potential sustainability of the monomers and biodegradability, makes these aliphatic polyesters an interesting class of polyesters for some specific applications.

Structure and thermal properties of ethylene/4-methyl-1-pentene copolymers: Effect of comonomer and monomer sequence distribution

A series of ethylene/4-methyl-1-pentene (E/4M1P) copolymers is synthesized, using the Ti(IV) diisopropoxy complex bearing a dianionic [O−,S,O−] bis(phenolato) ligand, in combination with methylalumoxane, as catalyst system. The semicrystalline copolymers are characterized by NMR, DSC, WAXD and SAXS. The structure and the thermal behavior of the copolymers are strongly influenced by composition and monomer sequence distribution. The copolymer crystallinity decreases as a function of 4M1P content, while an increase of the periodicity due to the enhancement of the amorphous interlamellar thickness is registered. The non-homogeneous distribution of the 4M1P units along the polymer chains is evidenced by the multimodal crystallization and melting behavior. The chain heterogeneity of the copolymers is investigated by successive self-nucleation and annealing thermal fractionation evaluating the methylene sequence length, the short chain branching and the lamellar thickness. In order to get more information on the comonomer distribution in the copolymers, solvent extraction is performed and all the fractions are characterized by thermal and X-ray techniques.

Molecular chain heterogeneity of a branched polyethylene resin using cross-fractionation techniques

The typical standard long chain branching (LCB) polyethylene (PE) SRM1476 is issued by the American National Bureau of Standards, which is widely used as a standard reference material in chromatographic experiments. Although some works have been reported in literatures, they are not consistent, such as the data about its molecular weight and molecular weight distribution. Therefore, it is necessary to further investigate the microstructure features of SRM1476 in order to better serve as a reference object in comparison with other unknown resins. In this study, the molecular chain heterogeneity of SRM1476 is investigated extensively and compared with the linear PE SRM1475. Based on the characterization of the original sample, SRM1476 actually has both LCB and short chain branching (SCB) structures, as well as the SCB content is more than LCB content in 13C-NMR results. After successive self-nucleation and annealing (SSA) thermal fractionation, SRM1476 shows a broad-range endotherm with multiple melting peaks (more than eight peaks), which proves the molecular chain heterogeneity in SRM1476. SRM1476 is fractionated into nine fractions by preparative temperature rising elution fractionation (TREF). At the high elution temperature region, the amounts of fractions are more than 90 %, and their molecular weights are higher. At the low elution temperature region below 50 °C, molecular weights of fractions are lower and their amounts are less than 5 %. Differential scanning calorimetry (DSC) melting curves of TREF fractions with higher elution temperatures shift toward higher temperature with sharper melting peaks. In the results of TREF-SSA cross-fractionation, each fraction shows a broad-range endotherm with multiple melting peaks that shift toward the high elution temperature region with the elution temperature. The arithmetic mean methylene sequence lengths of TREF fractions gradually increase from 33 to 105 as elution temperature increases. Results from TREF-DSC and TREF-SSA cross-fractionations indicate that SRM1476 and its TREF fractions have both intramolecular and intermolecular heterogeneity.

The interrelationships between microstructure and melting, crystallization and thermal degradation behaviors of fractionated ethylene/1-butene copolymer

The interrelationships between microstructure and melting, crystallization and thermal degradation behaviors of a commercial Ziegler–Natta (Z–N)-based ethylene/1-butene copolymer were investigated. The copolymer was fractionated based on short chain branch (SCB) content by preparative temperature-rising elution fractionation (P-TREF) method. A broad multipeak chemical composition distribution was obtained for both molecular weight distribution and short chain branch distribution. A difference of about 48 °C in melting temperature (Tm) has been observed for fractions with 50 branches of different SCB contents. A logarithmic relationship was obtained between the methylene sequence length calculated based on proton-1 nuclear magnetic resonance results and the P-TREF elution temperature (ET). A relationship between the SCB content and the inverse of lamellae thickness (Lc) was established. Two linear functionalities were found for Tm versus ET and crystallization temperature (Tc) versus the SCB content. To the best of our knowledge, as a first effort, surprisingly a linear relationship between the temperature at the maximum rate of degradation (Tmax) and the SCB content was acquired, which showed less sensitivity to the SCB content than Tm. Also, it was found that the degradation initiation temperature (T5%) and activation energy (Ea) are increased by the decreasing SCB content. Moreover, it was demonstrated that Hosoda equation is not applicable for different ethylene/α-olefin copolymers based on different catalyst types with dissimilar fractionations and experimental conditions.

"Brill Transition" Shown by Green Material Poly(octamethylene carbonate).

Poly(octamethylene carbonate) (POMC), as the eighth member of the newly developed biodegradable aliphatic polycarbonate family, demonstrates a reversible crystal-crystal transition, which is highly similar to Brill transition extensively studied in the nylon family. With the dipole-dipole interaction in POMC much weaker than the hydrogen bonding, POMC exhibits its "Brill transition" temperature at around 42 °C, much lower than nylons. The two crystalline structures of POMC at below and above the transition temperature can be identified. The transition of POMC is largely associated with the reversible conformation change of methylene sequences from trans-dominated at low temperatures to trans/gauche coexistence at high temperatures.

Ligand-Directed Regioselectivity in Amine–Imine Nickel-Catalyzed 1-Hexene Polymerization

1-Hexene polymerizations were carried out with amine–imine nickel complexes [(ArN═C(R1)–(R2R3)CNHAr)NiBr2, 1a, R1 = R2 = R3 = Me, Ar = 2,6-(iPr)2C6H3; 1b, R1 = R2 = R3 = Me, Ar = 2,6-(Me)2C6H3; 2a, R1 = Me, R2 = R3 = H, Ar = 2,6-(iPr)2C6H3; 3a, R1 = Me, R2 = tBu, R3 = H, Ar = 2,6-(iPr)2C6H3] in the presence of MMAO or Et2AlCl. The ligand-directed regioselectivity involving insertion fashion and chain walking in amine–imine nickel-catalyzed 1-hexene polymerization is clearly observed. Catalyst 1a with two methyl substituents on the bridging carbon can polymerize 1-hexene to afford semicrystalline “polyethylene” with long methylene sequence (−(CH2)n–, n = 40–74) via a combination of 90% selectivity of 2,1-insertion fashion and precise chain walking, whereas catalyst 3a with a tert-butyl on the bridging carbon can polymerize 1-hexene in 80% selectivity of 1,2-insertion to produce amorphous polyolefin with predominant methyl branches through 2,6-enchainment.

Microstructure characterization of short-chain branching polyethylene with differential scanning calorimetry and successive selfnucleation/annealing thermal fractionation

A series of the copolymers of ethylene with 1-hexene (M1-M9) synthesized by metallocene catalyst Et[Ind]2ZrCl2/MAO was studied by differential scanning calorimetry and successive self-nucleation and annealing (SSA) thermal fractionation. The distribution of methylene sequence length (MSL) in the different copolymers was determined using the SSA method. The comonomer contents of samples M4 and M5 are 2.04 mol% and 2.78 mol%, respectively. Both M4 and M5 have low comonomer content and their MSL distribution profiles exhibit a monotonous increase trend with their MSL. The longest MSL of M5 is 167, and its corresponding molar percent is 43.95%, which is higher than that of M4. Moreover, the melting temperature (T m) of M5 is also higher than that of M4. The comonomer contents of samples M7, M8, and M9 are 8.73 mol%, 14.18 mol% and 15.05 mol%, respectively. M7, M8, and M9 have high comonomer contents, and their MSL distribution profiles display unimodality. M7 has a lower peak value of 33 and a narrow MSL distribution, resulting in a T m lower than that of M8 and M9. The MSL and its distribution are also key points that influence the melting behavior of copolymers. Sometimes, MSL and its distribution of copolymers have a greater impact on it than the total comonomer contents, which is different from traditional views.

Crystal structure analyses of arylate polyesters with long methylene segments and their model compounds on the basis of 2-D X-ray diffractions and infrared progression bands

Crystal structures have been determined by the X-ray diffraction analyses for a series of aromatic polyesters –[–O(CH2)mO–COC6H4CO–]n– (mGT) with the long methylene sequence (m = 9–20) and their model compounds. The X-ray diffraction spots of these polyesters were observed more or less to shift upward and downward slightly from the averaged horizontal layer lines, indicating the tilting phenomenon of the molecular chains from the draw direction, the analysis of which was helpful for the definite determination of the unit cell parameters. For example, the c axis of 10 GT was found to be tilted by about 1° from the drawn axis in the 2¯10 tilt plane. The unit cell parameters obtained by the quantitative analysis of the tilting phenomenon were a = 4.77 ± 0.01 Å, b = 5.66 ± 0.01 Å, c (f.a.) = 20.7 ± 0.1 Å, α = 108.2 ± 0.1°, β = 122.7 ± 0.2°, and γ = 97.1 ± 0.1°. In the case of 20 GT, the tilting phenomenon was not observed in the X-ray fiber diagram. The triclinic unit cell parameters were determined for 20 GT: a = 4.59 ± 0.02 Å, b = 5.75 ± 0.02 Å, c (f.a.) = 33.3 ± 0.1 Å, α = 113.2 ± 0.2°, β = 116.6 ± 0.2°, and γ = 98.1 ± 0.2°. The space group was P1¯ for both of 10 GT and 20 GT. One chain is included in the unit cell. The chain conformation is of the all-trans-zigzag type. The reliability factor or the measure of the agreement between the observed and calculated X-ray diffraction intensity was 18.8% for 10 GT (90 reflections in total) and 18.5% for 20 GT (67 reflections). The crystal structures of 12 GT and 16 GT were found to be essentially the same as those of 10 GT and 20 GT. As for the odd-numbered mGT or 9 GT, 11 GT and 15 GT, the most plausible structure models were built up, which gave the good correspondence to the observed diffraction patterns semi-quantitatively. As the total number of methylene monomeric units was increased, the chain conformation was found to change from the trans-gauche combined form (3 GT and 5 GT) to the all-trans form (15 GT). The single crystal structure analysis of the low-molecular-weight model compounds confirmed the reasonableness of the crystal structures of the corresponding polymers.

Nanocomposites of Poly(1,4‐cis‐Isoprene) with Graphite Oxide Intercalation Compounds

AbstractInnovative nanocomposites are obtained by melt blending poly(1,4‐cis‐isoprene) (PI) and graphite oxide intercalation compounds (GOICs) with dimethyl di(hydrogenated tallow) ammonium (2HT) cations ionically bonded to the graphite oxide layers. GOIC samples with different contents of 2HT are prepared and homogeneously dispersed in the PI matrix. The X‐ray diffraction pattern of the GOIC shows an intense 100 reflection due to the hexagonal rotator order of the methylene sequences of long alkyl chains. Said rotator order is present in the nanocomposites, in the absence of any evidence of stacked layers, suggesting the prevailing exfoliation of the GOICs. The cross‐linking reaction promoted by sulfur is remarkably accelerated by the GOICs and the maximum modulus is enhanced. GOICs increase stresses at given elongations and the reinforcement under strain. magnified image

Which Polyesters Can Mimic Polyethylene?

Self-metathesis of erucic acid by [(PCy(3))(η-C-C(3)H(4)N(2)Mes(2))Cl(2)Ru = CHPh] (Grubbs second- generation catalyst) followed by catalytic hydrogenation and purification via the ester yields 1,26-hexacosanedioate (>99% purity). Polyesterification with 1,26-hexacosanediol, generated from the diester, affords polyester-26,26, which features a T(m) of 114 °C (T(c) = 92 °C, ΔH(m) = 160 J g(-1)). Ultralong-chain model polyesters-38,23 (T(m) = 109 °C) and -44,23 (T(m) = 111 °C), generated via multistep procedures including acyclic diene metathesis polymerization, underline that melting points of such aliphatic polyesters do not gradually increase with methylene sequence chain length. Available data suggest that to mimic linear polyethylenes thermal properties, even longer sequences, amounting to at least four times a fatty acid chain, fully incorporated in a linear fashion are required.

Correlation between chain microstructural changes and embrittlement of LLDPE-based films during photo- and thermo-oxidative degradation

The changes to the polymer microstructure during thermo- and photo-oxidative aging of LLDPE-based films have been investigated by thermal fractionation. During thermo-oxidative aging there was an exponential increase in the rate of the reduction in the fraction of polymer segments with a methylene sequence length (MSL) of approximately 249. All films embrittled only after the fraction of these segments decreased to below 7.5%, suggesting that the thermal fractionation data can be correlated to embrittlement time. In contrast, during photo-oxidative aging there was an initial rapid reduction followed by a gradual increase in the relative fraction of segments with an average MSL of 249. The initial decrease in the fraction of segments with an average MSL of 249 was similar to what was observed during thermo-oxidative aging and was consequently attributed to chain scission and/or oxidation of chains including tie-molecules. The latter increase in the fraction of chains with this average MSL was attributed to alkyl radical recombination which would result in an overall loss of branches and the formation of chain segments with high MSLs.

Poly(1‐hexene) with long methylene sequences and controlled branches obtained by a thermostable α‐diimine nickel catalyst with bulky camphyl backbone

Abstract1‐Hexene polymerizations catalyzed by α‐diimine nickel complexes after activation with modified methylaluminoxane were performed at various reaction temperatures. Effects of catalyst structure and polymerization temperature on activity and polymer microstructure were evaluated in detail. Bulky catalyst 1b with camphyl backbone exhibited good control ability and greatly enhanced thermal stability to be capable of polymerizing 1‐hexene at 80°C. The poly(1‐hexene)s with long methylene sequences and dominate branches (methyl and butyl) were synthesized using catalyst 1b. Differential scanning calorimetry analysis further confirmed that long polymethylene block ((CH2)n, n > 20) was formed in the poly(1‐hexene)s with melting point of 64°C obtained by catalyst 1b on the basis of initial branched model polyethylene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012