Properties of random and block copolymers of butadiene and styrene. II. Melt flow

Flow curves, log (rate of shear) versus log (shear stress), as functions of temperature were obtained for several butadiene-styrene copolymers of fixed (25%) styrene content, differing in monomer sequence distribution. A random copolymer of constant composition along the polymer chain and narrow molecular weight distribution (MWD) exhibited behavior similar to linear, narrow MWD polybutadienes; the flow was Newtonian at low shear stresses, and the flow curves for various temperatures were accurately superimposable by a shift along the log (shear rate) axis. In a random copolymer varying in composition along the polymer chain, non-Newtonian behavior was more pronounced, and temperature-shear rate superposition did not succeed, a trend further perpetuated in copolymer of a single long styrene block sequence. The latter resemble branched polymers, as would be expected from association of the styrene blocks. With two styrene blocks, association produces network structures below the glass transition of polystyrene with consequent loss of flow. Disruption of these associations above T_g (styrene) imparts the greatest thermoplasticity to these elastomers. There is evidence, however, that some of the associations persist at temperatures well in excess of T_g (styrene).     

Some effects of monomer sequence on the viscoelastic behavior of random copolymers of butadiene and styrene

The copolymerization of butadiene and styrene by lithium alkyls can be regulated to give either random or block copolymers. The block copolymers exhibit characteristic mechanical behavior which is attributable to their two-phase domain structure. In random copolymers free of long sequences of styrene there exists, nevertheless, the possibility of varying the sequence distribution by changing the manner in which composition varies along the polymer chain. Since copolymers of butadiene and styrene differing sufficiently in composition are likewise incompatible and will form multi-phase systems, it is likely that microheterogeneity can exist in certain “random” copolymers. Five copolymers of monomer ratio 70 : 30 butadiene/styrene, varying from a uniformly randomized sample, in which composition was very nearly independent of conversion, to a block polymer containing 22% block styrene chemical analysis, were prepared for the present investigation. Composition vs. conversion data indicated that all but the last polymer were free of long styrene sequences, with the composition distribution (along the chain) broadening systematically throughout the remainder of the series. The melt viscosity of the unvulcanized copolymers was distinctly affected by sequence distribution effects. Thus, the temperature coefficient of the apparent viscosity was independent of shear stress only for the uniformly randomized copolymer. In all others temperature superposition of the non-NEWTON ian flow curves was impossible, the discrepancies becoming larger the broader the composition distribution. The results can be explained qualitatively by association effects attributable to a domain structure similar to that found in block polymers. When these copolymers were cross-linked with dicumyl peroxide at 153 °C and the dynamic properties of the networks examined, no clear evidence of a domain structure was found except in the block polymer. Only the latter exhibited more than a single loss maximum. Temperature-frequency reduction of the dynamic measurements was successful with all but the block polymer. Whereas the parameters C₁ and C₂ in the WILLIAMS -LANDEL -FERRY equation appear to change systematically with the degree of randomness, there is evidence that this is attributable to a slight systematic drift toward higher vinyl unsaturation with increasing randomization of the monomer sequence. Relaxation spectra calculated for 25 °C were very nearly the same for all four random copolymers. When the polymers were cross-linked by gamma radiation at room temperature, the resulting networks did show properties indicative of a domain structure in the compositionally more heterogeneous copolymers. It is proposed that compatibility of chain segments of varying composition at the temperature of cross-linking leads to a suppression of the domain structure in the peroxide-cured rubbers, as segments of different composition are joined together. Independent evidence from stress-optical measurements supports this interpretation. The present investigation permits the conclusion that differences in sequence distribution of butadiene-styrene copolymers have, at best, only very minor effects on the visco-elastic properties of conventional vulcanizates, provided the polymers contain no long sequences of styrene units, i.e., polystyrene blocks detectable by classical methods. This is not true of the low shear melt viscosity, which senses relatively small differences in the composition and/or sequence distributions of the uncured rubbers.     

Thermoplastic urethane elastomers IV. Effects of cycloaliphatic chain extender on dynamic mechanical properties

The dynamic mechanical properties of a series of thermoplastic urethane elastomers have been studied as a function of molecular composition and temperature. Polymers based on polycaprolactone diol, an isomeric mixture of tolylene diisocyanate and hydrogenated Bisphenol-A as the chain extender were prepared at various relative concentrations of hard and soft segments. The glass transition temperatures of these polymers progressively shifted to higher temperatures as the relative hard segment content was increased. This variation was accurately described by the Fox relationship for amorphous copolymers. These results can be interpreted in terms of the relative degree of segregation between the segment of the block copolymers.     

Synthesis and characterization of well‐defined random and block copolymers of ε‐caprolactone with l‐lactide as an additive for toughening polylactide: Influence of the molecular architecture

Well‐defined multiarmed star random and block copolymers of ε‐caprolactone with l ‐lactide with controlled molecular weights, low polydispersities, and precise numbers of arms were synthesized by the ring‐opening polymerization of respective cyclic ester monomers. The polymers were characterized by ¹H‐NMR and ¹³C‐NMR to determine their chemical composition, molecular structure, degree of randomness, and proof of block copolymer formation. Gel permeation chromatography was used to establish the degree of branching. Star‐branched random copolymers exhibited lower glass‐transition temperatures (T_g's) compared to a linear random copolymer. When the star random copolymers were melt‐blended with poly(l ‐lactic acid) (PLA), we observed that the elongation of the blend increased with the number of arms of the copolymer. Six‐armed block copolymers, which exhibited higher T_g's, caused the maximum improvement in elongation. In all cases, improvements in the elongation were achieved with no loss of stiffness in the PLA blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43267.     

Thermoplastic urethane elastomers. I. Effects of soft-segment variations

A series of thermoplastic urethane elastomers with soft segments of varying sequence length was prepared and their dynamic mechanical properties were characterized over a wide temperature range. The polymers were prepared using various molecular weight polycaprolactone diols as the soft segment and 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segment. The urethane elastomer exhibited soft-segment crystallization when a polycaprolactone diol greater than 3000 M?_n was used. The glass transition temperature of these materials progressively shifted to lower temperatures as the chain length of the soft segment was increased. This dependence was interpreted in terms of a molecular weight relationship similar to that associated with amorphous homopolymers. The dynamic mechanical properties of these polyurethanes appear to be consistent with responses observed for compatible copolymers.     

New soybean oil–styrene–divinylbenzene thermosetting copolymers. I. Synthesis and characterization

The cationic copolymerization of regular soybean oil, low‐saturation soybean oil (LoSatSoy oil), or conjugated LoSatSoy oil with styrene and divinylbenzene initiated by boron trifluoride diethyl etherate (BF₃·OEt₂) or related modified initiators provides viable polymers ranging from soft rubbers to hard, tough, or brittle plastics. The gelation time of the reaction varies from 1 × 10² to 2 × 10⁵ s at room temperature. The yields of bulk polymers are essentially quantitative. The amount of crosslinked polymer remaining after Soxhlet extraction ranges from 80 to 92%, depending on the stoichiometry and the type of oil used. Proton nuclear magnetic resonance spectroscopy and Soxhlet extraction data indicate that the structure of the resulting bulk polymer is a crosslinked polymer network interpenetrated with some linear or less‐crosslinked triglyceride oil–styrene–divinylbenzene copolymers, a small amount of low molecular weight free oil, and minor amounts of initiator fragments. The bulk polymers possess glass‐transition temperatures ranging from approximately 0 to 105°C, which are comparable to those of commercially available rubbery materials and conventional plastics. Thermogravimetric analysis (TGA) indicates that these copolymers are thermally stable under 200°C, with temperatures at 10% weight loss in air (T₁₀) ranging from 312 to 434°C, and temperatures at 50% weight loss in air (T₅₀) ranging from 445 to 480°C. Of the various polymeric materials, the conjugated LoSatSoy oil polymers have the highest glass‐transition temperatures (T_g) and thermal stabilities (T₁₀). The preceding properties that suggest that these soybean oil polymers may prove useful where petroleum‐based polymeric materials have found widespread utility. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 658–670, 2001     

Structure and thermal behavior of nylon‐6/polytetrahydrofuran triblock copolymers obtained via anionic polymerization

The structure, crystallization, and phase behavior of nylon6‐b‐polytetrahydrofuran‐b‐nylon6 triblock copolymers synthesized via activated anionic polymerization have been studied. The composition, molecular weight of polytetrahydrofuran (PTHF) soft block, and type of polymeric activators (PACs) have been varied. Differential Scanning Calorimetry (DSC), Wide‐Angle X‐ray Diffraction (WAXD), Transmission Electron Microscopy (TEM), and Polarized Light Microscopy (PLM) experiments have revealed that in triblock copolymers only the nylon‐6 component crystallizes while PTHF segments are amorphous. The soft blocks do not alter the spherulitic crystalline structure of nylon‐6 and hard blocks crystallize in the α‐modification. The degree of crystallinity decreases with increasing PTHF concentration. The phase behavior has been investigated by Dynamic Mechanical Thermal Analysis (DMTA). Two different glass transition temperatures (T_g) for all samples have been observed. This indicates that nylon‐6 and PTHF segments are not molecularly miscible and the copolymers are microphase separated. The mechanical properties of the copolymers synthesized have been evaluated. Nylon‐6 copolymers with soft block concentrations up to 10 w/w %, exhibit improved notched impact strength in comparison to the nylon‐6 homopolymer, retaining relatively high hardness and tensile strength. All copolymers possess low water absorption and good thermal stability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1448–1456, 2002; DOI 10.1002/app.10448     

Improved mechanical properties of shape‐memory polyurethane block copolymers through the control of the soft‐segment arrangement

High‐performance shape‐memory polyurethane block copolymers, prepared with two types of poly(tetramethylene glycol) (PTMG) used as soft segments, were investigated for their mechanical properties. Copolymers with a random or block soft‐segment arrangement had higher stresses at break and elongations at break than those with only one kind of PTMG. Random copolymers with fewer interchain interactions showed higher elongation than block copolymers. All the copolymers had shape‐recovery ratios higher than 80%. In dynamic mechanical testing, the glass‐transition behavior clearly depended on the soft‐segment arrangement: random copolymers had only one glass‐transition peak, whereas block copolymers showed two separate glass‐transition peaks. Overall, the control of the soft‐segment arrangement plays a vital role in the development of high‐performance shape‐memory polyurethane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2410–2415, 2004     

Block copolyetheresters. V. Low-temperature properties of thermotropic block copolyetheresters

The low-temperature properties of block copolyetheresters with hard segments of poly(alkylene p,p′-bibenzoate) and soft segments of poly(tetramethylene ether) were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). In the temperature range of −100 to 60°C, two transition temperatures, a glass transition temperature (T_g) and a melting temperature (T_m), were found by DSC and are attributed to the polyether segments. The T_g monitored by DSC of the polyether segments of the block copolyetheresters is around −68°C and independent of the composition and the type of polyester segment. Thus, the amorphous parts of the polyether segments should be immiscible with the amorphous parts of the polyester segments. The polyether segments of the block copolyetheresters exhibit a lower T_m and a lower crystallinity than those of the poly(tetramethylene ether)glycol due to the presence of the polyester segments. The crystallizability of the polyether segments is dependent on the composition to some extent. The DMA data show that the dynamic modulus drops more abruptly around −10 to 15°C, indicating that the mechanical properties may change significantly due to the melting of the polyether segments. © 1996 John Wiley & Sons, Inc.     

Novel ternary block copolymerization of carbon dioxide with cyclohexene oxide and propylene oxide using zinc complex catalyst

Block copolymers of poly (propylene carbonate—cyclohexyl carbonate) (PPC-PCHC) were successfully synthesized by a one-pot method with the zinc complex catalyst (Zn2G). The IR and ¹H-NMR and ¹³C-NMR spectra verified the introducing of PCHC segments in the copolymers. The GPC curves of the copolymers appeared only one peak and the DSC results showed three glass transition temperatures at 40 °C, 66 °C and 115 °C, indicating the three-block copolymer structure. TGA tests revealed that the thermal decomposition temperature of the synthesized block copolymers increased up to about 300 °C. The mechanical properties proved to be also enhanced greatly as evidenced by static and dynamic mechanical tests. The thermal and mechanical properties of the resultant block copolymers lay between those of PPC and PCHC, demonstrating the desired properties of a polymer can be achieved via block copolymerization.     

Morphology and Viscoelastic Behavior of Styrene-Diene Block Copolymers in Pressure Sensitive Adhesives

Linear (SDS) and radial (SD)_x block copolymers of styrene (S) and dienes (D=butadiene or isoprene), varying in composition and molecular weight, were formulated as pressure sensitive adhesives. The morphology of these compositions was determined by electron microscopy of ultra-thin sections and dynamic viscoelastic measurements were made at 35 Hz between -90° and + 140°C or higher. Pressure sensitive tack and holding power were determined and interpreted in terms of morphological and rheological properties.

A high degree of tack resulted only when the tackifying resin was compatible with the polydiene segments of the block polymer and incompatible with the polystyrene segments, provided also that the polydiene-tackifier phase was the continuum with the polystyrene phase forming spherical domains. All effective tackifying resins raised the glass transition temperature (T_g) of the rubbery phase, but plasticized the polymer at temperatures well above T_g Polystyrene domain connectivity was found to lead to diminished tack in block polymers containing more than 30% styrene, a result of decreased creep compliance on the time scale of the bonding process and failure to achieve full contact with the substrate. For adhesives not limited by contact, tack increased with the loss modulus of the adhesive on the time scale of the debonding process. Holding power (shear resistance) increased with polymer styrene content and molecular weight, the polystyrene domain structure effectively inhibiting viscous flow at temperatures sufficiently below T_g of the styrene blocks.     

Blends of bitumen with polymers having a styrene component

The properties of a 100 penetration grade bitumen are modified considerably, and in a number of ways by the addition of 10 to 40 parts per hundred (pph) of a homopolystyrene and graft, block and random copolymers of styrene with butadiene and acrylonitrile. At low temperatures some blends have a similar stiffness to or even lower stiffness than the bitumen, but generally the blends are more than one order of magnitude stiffer, even when a rubber is added. The contrasting behavior is displayed by a polystyrene and a high impact polystyrene, ～3% to 4% of grafted rubber on the latter being sufficient to cause the enhancement, even at the 10 pph level, by two different random styrene‐butadiene copolymers, and also by blends consisting of different amounts of SBS block copolymer. Some polymers apparently trigger a Hartley inversion of the micellar structure of the asphaltene micelles. High low temperature stiffness correlates roughly with a lower Tg' as measured by the peak maximum in the E″ plots of the dynamic mechanical thermal analysis (DMTA) and by the steps in the differential scanning calorimetry (DSC) curves at temperatures below O°C. Tan δ maxima and DSC traces detected the glass transition in the continuous phase and in the dispersed phases, but none of these amorphous polymers formed a crystalline phase, though the DSC traces of the polystyrene and the SBS blends suggested that the polymer‐rich phases underwent an aging/ordering process on cooling. Our SBS blends differ in phase inversion behavior and the pattern of loss processes from others that had a smaller asphaltene component.     

Synthesis and properties of novel random and block copolymers composed of phthalimidine‐ and perfluoroisopropylidene‐polyarylether‐sulfones

A series of novel polyarylethersulfone (AB) _n block copolymers with different segment lengths have been synthesized by nucleophilic solution polycondensation of phenoxide‐terminated and fluorine‐terminated oligomers; random copolymers have been prepared over the whole composition ranges. The structures of the resultant copolymers have been confirmed by FTIR, ¹³C NMR spectra and differential scanning calorimetry (DSC). Compared with two homopolymers and random copolymers, the block copolymers of this study possess excellent thermal stability (5% thermal decomposition under nitrogen atmosphere above 500 °C) and high glass transition temperatures, and have a wide melt‐processing temperature range. They may become a new class of mouldable high performance thermoplastics. © 2001 Society of Chemical Industry     

Thermal and structural analysis of heparin–PEO–PDMS–PEO–heparin pentablock copolymers

ABCBA-type amphiphilic block copolymers comprising polydimethylsiloxane (PDMS), poly(ethylene oxide) (PEO), and heparin segments were synthesized by coupling reactions between end-functionalized oligomers. These multiblock copolymers were characterized to examine bulk properties using ¹H-NMR, FTIR, end-group analysis, and sulfur elemental analysis. Block copolymers were further characterized in bulk using differential scanning calorimetry and X-ray diffraction measurements. The PDMS glass transition remains unchanged with increasing PEO content, indicating coexistence of pure PDMS with mixed phases. Furthermore, endothermic melting of the block copolymers shifts to higher temperatures and becomes more intense with increasing PEO molecular weight. Additionally, the crystallinity of the PEO segment in the block copolymers increases with increasing PEO molecular weight. The PEO melting endotherm peak shifts from near 318 to 323 K with annealing. In the cooling thermogram, the block copolymers exhibit two crystallization exotherms, one near 303 K and the other near 193 K, attributed to PEO and PDMS recrystallization and nucleation, respectively. © 1994 John Wiley & Sons, Inc.     

Dynamic mechanical and thermomechanical properties of silicone-polycarbonate block copolymers

Representative random, alternating block copolymers of polydimethylsiloxane (PDMS) and bisphenol-A-polycarbonate (BPAPC) were studied by thermomechanical and dynamic mechanical techniques. Data on glass transition temperatures (T_g), heat-deflection temperatures (T_d), Vicat softening temperatures (T_s), coefficients of linear expansion (α), stress-strain, and stress relaxation for four PDMS-BPAPC block co-polymers are presented. The effect of casting films from mixed n-hexane-methylene chloride solution on the thermomechanical and dynamic mechanical properties was also studied.     

Morphology and thermal properties of liquid crystal p‐PAEB/n‐propyl methacrylate copolymers

The copolymers of p‐phenylene di{4‐[2‐(allyloxy) ethoxy]benzoate} (p‐PAEB) with n‐propyl methacrylate (PMA) were synthesized. The liquid crystalline behavior and thermal properties of copolymers were studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X‐ray diffractometer (XRD), and torsional braid analysis (TBA). The results of XRD, POM, and DSC demonstrate that the phase texture of copolymers is affected by the composition of liquid crystal units in copolymers. The POM and XRD reveal that liquid crystal monomer (p‐PAEB) and copolymers of p‐PAEB with PMA are all smectic phase texture. The dynamic mechanical properties of copolymers are investigated with TBA. The results indicate that the phase transition temperatures and dynamic mechanical loss peak temperature T_p of copolymers are affected by the composition of copolymers and liquid crystal cross networks. The maximal mechanical loss T_p is 114°C and is decreased with added PMA. The behaviors of phase transition are affected by the crosslinking density, and it is revisable for lightly crosslinking LC polymer networks, but it is nonreversible for the densely crosslinking of LC polymer networks. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Correlation of chemical composition and microstructure with properties of poly(ɛ‐caprolactone‐co‐p‐dioxanone) random copolymers

With the aim to develop novel biodegradable materials with good flexibility and fast degradation rate, random copolymers of ?‐caprolactone (CL) and p‐dioxanone (PDO) with a full range of compositions were synthesized in bulk using stannous octoate as the ring‐opening catalyst. The chemical composition and number average sequence lengths of CL and PDO units determined by ¹H‐NMR were used to correlate with various properties of the copolymers. Although both CL and PDO are crystalline components, only one crystalline phase could be present for each copolymer. The low limit of average block length for the copolymers that could crystallize is 3.22 for L_CL and 3.43 for L_PDO, respectively. The crystallinity and crystalline morphology of the copolymers are dependent on the crystalline component as well as its number average sequence length. Irrespective of composition, all the copolymers have good solubility in chloroform with glass transition temperature much below room temperature, implying good flexibility of the materials. The incorporation of PDO component could significantly increase the water wettability of the copolymer surfaces and thereby accelerate the degradation rate of the materials. In conclusion, flexible biodegradable polymers with adjustable degradation and crystalline properties were acquired by random copolymerization of CL and PDO, which are expected to use in tissue engineering and drug delivery fields. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2978–2986, 2013     

High vinyl high styrene solution SBR

Objective: the objective of this study is to prepare high vinyl copolymers containing various levels of styrene and butadiene, and also to prepare random butadiene in high styrene content styrene-butadiene copolymers (SBR) while controlling the styrene block length. These materials could be used in race tread applications. Summary: This reports presents the synthesis and characterization of random, high vinyl copolymers containing styrene and butadiene (SBR's). The styrene content of these SBR's ranged from 10 to 80%. These SBR's were synthesized via anionic polymerization initiated by a catalyst system with a ratio of 1/0.4/5 of n-butyllithium (n-BuLi) to sodium dodecylbenzene sulfonate (SDBS) to N,N,N′,N′-tetramethylethylenediamine (TMEDA). Kinetic data as well as NMR and ozonolysis techniques confirm that random SBR copolymers are being produced for low styrene content polymers. The glass transition temperature (T_g), increased dramatically as the styrene content was increased. The amount of vinyl based upon the polymer's total composition within the copolymer was found to decrease linearly as you increase the amount of styrene in the polymer. TGA results show that high styrene content polymers degrade at lower temperatures. The RPA confirms that as the styrene content increases, the elastic modulus decreases. As the frequency increased, the tan delta decreased for each polymer. Tan delta does not appear to be a function of styrene content. TEM results helped to describe polymer microstructure.     

Compatibility of the Polystyrene/Polyolefin Blends Containing Block Copolymers I. Processing Behaviour and Characterization

Abstract

The processing behaviour and mechanical and thermal properties of the polystyrene/polyethylene or polystyrene/polypropylene blends containing block copolymers of KRATON type as compatibilizing agents have been studied. It has been established that the compounding on a twin screw extruder followed by γ-irradiation assures satisfactory homogeneity of the blends and also good mechanical properties.

A thermomechanical method was developed to characterize the blends. The variation of the α-relaxation or glass transition temperatures with blend composition as well as the variation of the other thermal characteristics such as melt flow rate, melting and crystallization temperatures, Vicat temperatures, etc. exhibit the important differences in respect to the average values indicating a good compatibilization of the components.     

Differences in enthalpy recovery of gradient and random copolymers of similar overall composition: styrene/4-methylstyrene copolymers made by nitroxide-mediated controlled radical polymerization

Styrene/4-methylstyrene (S/MS) random and gradient copolymers were synthesized by nitroxide-mediated controlled radical polymerization (NM-CRP) and compared to random copolymers made by conventional free radical polymerization (ConvFRP). The gradient copolymers have molecular weight (MW) values approaching 85,000 g/mol, making these some of the higher MW gradient copolymers reported to date. Due to the proximity of the glass transition temperatures (T_g) of polystyrene (PS) and poly(4-methylstyrene) (PMS), there is no significant difference in T_g between the gradient and random copolymers, with both copolymer types yielding single T_gs that typically increase slightly with increasing MS content. While enthalpy relaxation studies demonstrate similarity in random copolymers made by NM-CRP and ConvFRP, they reveal significant differences between random and gradient copolymers. Gradient copolymers exhibit broad enthalpy recovery peaks, whereas random copolymers exhibit narrower enthalpy recovery peaks. The maxima in the enthalpy recovery peaks are at substantially lower temperature, as much as 17 °C, in the gradient copolymers as compared to random copolymers of equal overall composition. While random and gradient copolymers of a given overall composition exhibit similar enthalpy recovery values at a common physical aging time and quench depth relative to T_g, the major differences in the enthalpy recovery peaks indicate that differences in sequence distribution along the chain length can lead to unusual behavior in gradient copolymers relative to random copolymers.