Blocky Copolymers Research Articles

One-pot single-step copolymerization of aromatic trifluorovinyl ethers toward perfluorocyclobutyl (PFCB) segmented copolymers

A segmented PFCB aryl ether copolymer was synthesized directly from two aryl TFVE monomers having different reactivities and the blocky copolymer structure was confirmed by 19F NMR spectroscopic data.

Properties of PLA-co-PBSu Copolymers Rapidly Synthesized by Reactive Processing

This work describes the synthesis of poly(lactic acid) by the ring-opening polymerization of L-lactide in the presence of oligo(butylene succinate) with two different molecular weights (Mn = 6100 and 16300 g/mol) as a macroinitiator during reactive processing. The macroinitiators were added in concentrations 1 wt%, 2.5 wt%, 5 wt%, 10 wt% and 15 wt% in respect to the L-lactide mass in the premix. The properties of the received copolymers were extensively studied with spectroscopic techniques, GPC, DSC, XRD, TGA as well as nanoindentation. Blocky copolymers were received with number average molecular weights ranging from 30 to 100 kg/mol, which decreased with increasing the PBSu content in the feed. The introduction of the flexible PBSu chains decreased the single glass transition detected, while DSC and XRD gave indications that both components crystallized in the copolymers with PBSu premix content > 5 wt%. Thermal stability was maintained and depended on the composition and molecular weight. Nanoindentation showed that despite the decreasing trend of hardness and elastic modulus with increasing PBSu content, the PLA-PBSu 2.5% copolymers had simultaneously higher elasticity modulus and strength compared to the other compositions, possibly because of a complementary effect of their high molecular weight and crystallinity. These copolymers were promising for production with continuous reactive extrusion, a novel, fast and economically viable method to commercially produce PLA-based polymers.

Non‐uniform Photoinduced Unfolding of Supramolecular Polymers Leading to Topological Block Nanofibers

AbstractSynthesis of one‐dimensional nanofibers with distinct topological (higher‐order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non‐uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post‐polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene‐embedded rigid π‐conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV‐light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible‐light irradiation followed by aging to restore fully folded structures.

Non‐uniform Photoinduced Unfolding of Supramolecular Polymers Leading to Topological Block Nanofibers

Synthesis of one‐dimensional nanofibers with distinct topological (higher‐order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non‐uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post‐polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene‐embedded rigid π‐conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV‐light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible‐light irradiation followed by aging to restore fully folded structures.

Sequence-Controlled α-Methylstyrene/Styrene Copolymers: Syntheses and Sequence Distribution Resolution

The copolymerization of α-methylstyrene (MSt) and styrene (St) to form random and blocky copolymers is well-known. Strongly alternating copolymers of this type are rarely described, mainly because ...

Exploiting Addition-Fragmentation Reactions to Produce Low Dispersity Poly(isobornyl acrylate) and Blocky Copolymers by Semibatch Radical Polymerization.

Solution radical homopolymerization of isobornyl acrylate (iBoA) under starved-feed higher temperature conditions unexpectedly leads to polymer product with low dispersity (<1.3) compared to the polymerization of butyl acrylate (BA) under identical conditions. Both backbiting and β-scission reactions occur, as the poly(iBoA) product contains close to 100% terminal double bond (TDB) functionality. However, the addition of monomer to the midchain radicals formed by backbiting is sterically hindered, greatly reducing both short and long-chain branching. The poly(iBoA) macromonomer functions as an excellent addition-fragmentation agent, not only lowering dispersity but also providing a means to efficiently produce blocky acrylate copolymers through sequential monomer feeding in the starved-feed semibatch process.

Chain microstructure of two highly impact polypropylene resins with good balance between stiffness and toughness

For highly impact polypropylene (HIPP), a good balance between stiffness and toughness has attracted much attention from both industrial and academic research. Herein, two HIPP resins (A and B) with different ethylene contents and impact resistances especially at low temperatures are investigated. Their chain microstructure is studied by combining preparative temperature rising elution fractionation (P-TREF) with multiple characterization techniques such as high-temperature gel permeation chromatography (HT-GPC), Fourier transform infrared (FTIR) spectroscopy, 13C nuclear magnetic resonance (13C NMR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), rheometer, and thermal fractionation. Both samples are mainly composed of four portions: amorphous ethylene−propylene random copolymer (EPR), ethylene−propylene (EP) segmented and blocky copolymer, and isotactic polypropylene homopolymer. Sample A contains ~30 wt% EPR fractions eluted at 35 °C, ~9 wt% EP segmented and blocky copolymers eluted at 80–100 °C, and ~19 wt% highly isotactic polypropylene fractions eluted at 125–140 °C, which are higher than the contents of corresponding fractions in sample B. Moreover, most fractions of sample A have higher molecular weights than the corresponding fractions of sample B. The contribution of different components to stiffness and toughness is also discussed. The excellent impact resistance of sample A is demonstrated from the perspective of chain microstructure.

Sulfonation of blocky brominated PEEK to prepare hydrophilic-hydrophobic blocky copolymers for efficient proton conduction

Hydrophilic-hydrophobic blocky copolymers of poly(ether ether ketone) (PEEK) were prepared using a two-step post-polymerization technique. First, PEEK was brominated in the semicrystalline gel state to create a blocky BrPEEK template, which was subsequently functionalized by sulfonating the remaining runs of unfunctionalized PEEK units. The resultant degree of sulfonation of the blocky brominated, sulfonated PEEK (BrSPEEK) copolymers was inversely related to the degree of bromination, and degrees of sulfonation ranging from 26 to 71 mol% were obtained for degrees of bromination between 27 and 144 mol%. Thermal analysis using DSC and DMA revealed distinct multi-phase behavior for blocky BrSPEEK copolymers at degrees of sulfonation up to 40 mol%, suggesting phase separation between the densely brominated blocks and the sulfonated blocks into hydrophobic and hydrophilic domains, respectively. This phase separation contributed to improved dimensional stability upon swelling and enhanced proton transport at lower water content for blocky BrSPEEK membranes compared to random SPEEK membranes. Finally, morphological analysis using SAXS demonstrated that ionic aggregate size remained relatively unchanged for blocky BrSPEEK at all degrees of sulfonation, and the ionic aggregates became more closely spaced with increasing degree of sulfonation. Overall, this work demonstrates a facile, post-polymerization technique to prepare hydrophilic, hydrophobic blocky copolymers with excellent dimensional swelling and transport properties that rival those of directly polymerized block copolymers.

Effect of Copolymer Sequence on Local Viscoelastic Properties near a Nanoparticle

We simulate a simple nanocomposite consisting of a single spherical nanoparticle surrounded by coarse-grained polymer chains that are composed of two monomer types differing only in their interactions with the nanoparticle. We measure the atomic stress fluctuations and use them to estimate the local stress autocorrelation as a function of distance from the nanoparticle. This local stress autocorrelation is substituted into the well-known relationship between the bulk stress autocorrelation and the bulk (frequency-dependent) dynamic modulus, and the result is treated as an estimate of the local dynamic modulus. This allows us to examine the effect of adjusting copolymer sequence on estimations of local storage and loss modulus as a function of distance from the nanoparticle. Notably, we find certain blocky copolymer sequences can lead to a higher tan(δ) (hysteresis) in the interphase than either homopolymer system, suggesting that tuning the copolymer sequence could allow for significant control over nanoc...

Organocatalytic Ring-Opening Copolymerization of Trimethylene Carbonate and Dithiolane Trimethylene Carbonate: Impact of Organocatalysts on Copolymerization Kinetics and Copolymer Microstructures.

The ring opening copolymerization of trimethylene carbonate (TMC) and dithiolane trimethylene carbonate (DTC) using acidic and basic organocatalysts, i.e., diphenyl phosphate (DPP) and triazabicyclo[4.4.0]dec-5-ene (TBD), was systemically investigated. Interestingly, DPP and TBD gave rise to completely different polymerization kinetics and copolymer sequences. The copolymerization of TMC and DTC using methoxy poly(ethylene glycol) (mPEG-OH) as an initiator and DPP as a catalyst proceeded in a first-order manner and to near completion in 72 h for both monomers, yielding well-controlled copolymers with random sequences, predictable molar mass, and low dispersity ( Mw/ Mn = 1.09-1.19). By contrast, TBD brought about much faster copolymerization of TMC and DTC under similar conditions (high monomer conversion achieved in 2-4 h), to furnish copolymers with controlled molar mass and moderate dispersity ( Mw/ Mn = 1.27-1.80). Moreover, polymerization kinetics revealed that DTC was preferentially polymerized followed by first-order polymerization of TMC, leading to blocky copolymers. These results signify that type of organocatalysts has a critical influence on polymerization kinetics of cyclic carbonates, copolymer sequence, and molar mass control.

Multivariate analysis of 13C NMR spectra to extract information about monomer sequences in poly(methyl methacrylate-co-benzyl methacrylate)s prepared by various polymer reactions

The 13C NMR spectra of atactic copolymers of methyl methacrylate (MMA) and benzyl methacrylate (BnMA) show complicated resonance patterns due to variations in their configurational sequences and monomer sequences in the macromolecular chains. Principal component analysis (PCA) was found to be useful for extracting information regarding the chemical composition and monomer sequence from the complicated resonances of the copolymers. To assess the feasibility for monomer sequence analysis, a PCA approach was applied to the spectra of MMA-BnMA copolymers prepared by partial modification of atactic poly(benzyl methacrylate) through catalytic hydrogenolysis, acidic debenzylation, saponification, and transesterification and by two-step esterification of atactic poly(methacrylic acid) (PMAa). The analysis clearly showed the formation of highly blocky copolymers via hydrogenolysis, as well as the formation of copolymers with a somewhat alternating tendency via acidic debenzylation, saponification, and transesterification in the late processes of the reactions. The copolymers formed in early processes of these reactions were essentially random sequences. The analysis also revealed that the copolymer prepared through partial methylation of PMAa with diazomethane was a random copolymer, while the copolymer prepared through partial benzylation of PMAa with benzyl bromide was a blocky copolymer. MMA-BnMA copolymers with various monomer sequences (blocky, random, alternating tendency) were prepared by partial modifications of atactic poly(BnMA) or by direct copolymerization of MMA and BnMA. 13C NMR spectra of the copolymers were subjected to principal component analysis, one of the standard procedures of multivariate analysis. The analysis showed clearly the formation of highly blocky copolymers by hydrogenolysis as well as the formation of copolymers with somewhat alternating tendency by the acidic debenzylation, saponification, and transesterification at late processes of the reactions.

Effect of copolymer sequence on structure and relaxation times near a nanoparticle surface.

We simulate a simple nanocomposite consisting of a single spherical nanoparticle surrounded by coarse-grained polymer chains. The polymers are composed of two different monomer types that differ only in their interaction strengths with the nanoparticle. We examine the effect of adjusting copolymer sequence on the structure as well as the end-to-end vector autocorrelation, bond vector autocorrelation, and self-intermediate scattering function relaxation times as a function of distance from the nanoparticle surface. We show how the range and magnitude of the interphase of slowed dynamics surrounding the nanoparticle depend strongly on sequence blockiness. We find that, depending on block length, blocky copolymers can have faster or slower dynamics than a random copolymer. Certain blocky copolymer sequences lead to relaxation times near the nanoparticle surface that are slower than those of either homopolymer system. Thus, tuning copolymer sequence could allow for significant control over the nanocomposite behavior.

Blocky Sulfonation of Syndiotactic Polystyrene: A Facile Route toward Tailored Ionomer Architecture via Postpolymerization Functionalization in the Gel State

Blocky sulfonated syndiotactic polystyrene (SsPS) copolymers were produced using a recently developed postpolymerization functionalization procedure conducted in the gel state. The thermal properties and crystallization behavior of a matched set of blocky and random SsPS copolymers containing 3 and 10 mol % sulfonate groups were compared using differential scanning calorimetry (DSC), which shows that the blocky functionalization architecture displays a much faster rate of crystallization even at low sulfonate contents and a higher crystallizability at high sulfonate contents. The glass transition temperature for gel-state-functionalized copolymers was found to be independent of sulfonic acid content above 4% sulfonation, consistent with behavior observed in previous studies of sodium styrenesulfonate block copolymers. Small-angle X-ray scattering (SAXS) from the blocky copolymer indicates that the sulfonated units are distributed within the amorphous interlamellar domains. Wide-angle X-ray diffraction (WA...

Catalytic Ring-Opening (Co)polymerization of Semiaromatic and Aliphatic (Macro)lactones

The ring-opening polymerization (ROP) of cyclic butylene terephthalate oligomers (cBT) using an aluminum salen catalyst was investigated. The kinetic analysis of the ROP of cBT in tetrachloroethane (TCE) revealed a first-order dependence of the rate constant in catalyst as well as monomer concentration. Comparison with the ROP in other solvents showed that TCE significantly retards the reaction by short-term reversible catalyst deactivation and by long-term permanent deactivation. The apparent activation energy for the ROP of cBT and e-caprolactone (CL) were determined independently, and the difference in reactivity was used to investigate the possibility to synthesize blocky copolymers. Sequence distribution analysis of the copolymers obtained over a period of time from a single feed copolymerization revealed that over the full reaction range the degree of randomness was high. A sequential feed approach, in which CL was added after the polymerization of cBT was completed, showed that the propagation reac...

Homopolymerization and copolymerization kinetics of trimethylene carbonate bearing a methoxyethoxy side group

The polymerization kinetics of 5-[2-{2-(2-methoxyethoxy)ethyoxy}-ethoxymethyl]-5-methyl-trimethylene carbonate (TMCM-MOE3OM) synthesized using the organocatalyst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were studied and compared to those with the commonly used catalyst/initiator for ring-opening polymerization of cyclic carbonates and esters, stannous 2-ethylhexanoate. Further, the utility of each of these catalysts in the copolymerization of TMCM-MOE3OM with trimethylene carbonate (TMC) and l-lactide (LLA) was examined. Regardless of conditions with either catalyst, homopolymerization of TMCM-MOE3OM yielded oligomers, having number average molecular weight less than 4000 Da. The resultant molecular weight was limited by ring-chain equilibrium as well as through monomer autopolymerization. Interestingly, autopolymerization of TMC was also achieved with DBU as the catalyst. Copolymerization with TMC using stannous 2-ethylhexanoate as the catalyst yielded random copolymers, while diblock copolymers were formed by copolymerization with LLA. With DBU as the catalyst, copolymers with LLA could not be formed, while blocky copolymers were formed with TMC. These findings should be useful in the incorporation of this monomer in the design of polymer biomaterials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 544–552

Self‐nucleation behaviors of olefinic blocky copolymer/montmorillonite nanocomposites with collapsed and intercalated clay layers

ABSTRACTThe self‐nucleation behavior of olefinic blocky copolymer (OBC) / organically modified montmorillonite (OMMT) nanocomposites with a novel collapsed clay structure (c‐OMMT) was studied and compared with that of the nanocomposites with an intercalated clay structure (OBC/i‐OMMT). Their behaviors appear different in three temperature domains, Domain I (DI) in which the polymer is completely melted and only the heterogeneous nuclei are present, Domain II (DII) in which only self‐nucleation occurs and Domain III (DIII) where both self‐nucleation and annealing take place. As the OMMT loading increases, the boundary temperature of DI and DII (TI→II) shifts to lower temperature and DII becomes narrower. For the OBC/c‐OMMT nanocomposites, the TI→II or TI→III (the boundary temperature of DI and DIII) can be lower than the end melting temperature ( ) and leads to appearance of a subdomain of DI, DI′, in which the self‐nuclei of un‐melted fragmental crystals exist but the following crystallization is still initiated by c‐OMMT. DII may even disappear at high c‐OMMT loadings. By contrast, the TI→II of the OBC/i‐OMMT nanocomposites is always approximate to or higher than the . DII does not disappear and no DI′ is observed for the OBC/i‐OMMT nanocomposites. The nucleation efficiency of c‐OMMT is also evidently higher than that of i‐OMMT. These results verify that the c‐OMMT has stronger nucleation ability than i‐OMMT at the same OMMT loading. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41771.

The Influence of Ziegler-Natta and Metallocene Catalysts on Polyolefin Structure, Properties, and Processing Ability.

50 years ago, Karl Ziegler and Giulio Natta were awarded the Nobel Prize for their discovery of the catalytic polymerization of ethylene and propylene using titanium compounds and aluminum-alkyls as co-catalysts. Polyolefins have grown to become one of the biggest of all produced polymers. New metallocene/methylaluminoxane (MAO) catalysts open the possibility to synthesize polymers with highly defined microstructure, tacticity, and steroregularity, as well as long-chain branched, or blocky copolymers with excellent properties. This improvement in polymerization is possible due to the single active sites available on the metallocene catalysts in contrast to their traditional counterparts. Moreover, these catalysts, half titanocenes/MAO, zirconocenes, and other single site catalysts can control various important parameters, such as co-monomer distribution, molecular weight, molecular weight distribution, molecular architecture, stereo-specificity, degree of linearity, and branching of the polymer. However, in most cases research in this area has reduced academia as olefin polymerization has seen significant advancements in the industries. Therefore, this paper aims to further motivate interest in polyolefin research in academia by highlighting promising and open areas for the future.

Thermotropic Polyesters from 2,5-Furandicarboxylic Acid and Vanillic Acid: Synthesis, Thermal Properties, Melt Behavior, and Mechanical Performance

In this work, we address the synthesis of novel aromatic–aliphatic biobased polyesters showing thermotropic behavior in the melt. Successful incorporation of different biobased monomers such as 2,5-furandicarboxylic acid (2,5-FDCA), suberic acid (SuA), and vanillic acid (VA) in thermotropic liquid crystalline polymers (TLCPs) is made possible by performing synthesis at low temperatures. The chemical structures, molecular weights, phase transitions, thermal behavior, and mechanical performance of the synthesized polymers are studied using polarization optical microscopy, WAXD, DSC, TGA, DMTA, solid-state NMR spectroscopy, rheology, and tensile tests. It is shown that the incorporation of the rigid, aromatic 2,5-FDCA moiety enhances the formation of blocky copolymers, whereas the VA moiety tends to decrease the block formation. However, when combined, nonblocky TLCPs containing 2,5-FDCA and VA with high aromatic content can be obtained. These materials show a low temperature transition from the crystalline ...

Regulation of Crystallization Kinetics, Morphology, and Mechanical Properties of Olefinic Blocky Copolymers

Two olefinic blocky copolymers (OBCs) were quenched from different mixing states in the melt, and crystallization kinetics and morphology at various crystallization temperatures (Tcs) and corresponding mechanical properties were studied. It is observed that, at lower Tcs, premesophase separation in the melt accelerates crystallization of OBC-A with a weak segregation strength and a larger fraction of the crystalline hard blocks due to enrichment of the hard blocks in the hard-block-rich domains. By contrast, premesophase separation retards crystallization of OBC-B with a stronger segregation strength and lower fraction of the hard blocks because of the prevailing confinement effect at lower Tcs. Moreover, since the hard blocks dissolved in the soft-block-rich domains can crystallize at lower Tcs, which can bridge the crystals formed in different hard-block-rich domains, the crystal growth is not restricted. At higher Tcs, OBC-A crystallizes more slowly from the premesophase-separated melt than that from the homogeneous melt, which is attributed to the weaker crystallizability of the hard blocks dissolved in the soft-block-rich domains and thus the restricted crystal growth. Nevertheless, mesophase separation always takes place prior to crystallization at higher Tcs for OBC-B because of the faster rate of mesophase separation. Therefore, the mixing state in the melt has little effect on crystallization and morphology of OBC-B at higher Tcs. It is found that the mechanical properties of OBCs can be regulated in a wide range by alteration of crystallization conditions. Better mechanical properties can be achieved when OBCs crystallize from the homogeneous melt and at a lower Tc.

Olefinic blocky copolymer/montmorillonite nanocomposites with collapsed clay layers

Abstract In the present work, the nanocomposite of olefinic blocky copolymer with collapsed organically modified montmorillonite (OBC/c-OMMT) was prepared by co-precipitation of OBC and OMMT with excess ethanol. The dispersion state of clay in the nanocomposites was identified by WAXD and further confirmed by FT-IR. It is found that ethanol can extract parts of the organic modifier and OBC can further squeeze the resultant OMMT layers, yielding collapsed OMMT. Crystallization and morphology of OBC/c-OMMT were compared with those of the nanocomposites containing intercalated organically modified montmorillonite (i-OMMT) and aggregated un-modified montmorillonite (a-MMT). The collapsed OMMT has a stronger nucleation effect on crystallization of OBC than i-OMMT and a-MMT, as revealed by the higher crystallization temperature, smaller crystallite size and larger number of crystallite. Rheology test reveals that the complex viscosity of OBC/c-OMMT at low frequencies is smaller, possibly due to the lower volume fraction of c-OMMT in OBC.