Dichlorocarbene Modified Natural Rubber

Natural rubber dissolved in chloroform was reacted with aqueous NaOH using a phase transfer reagent or with solid NaOH to produce dichlorocarbene modified natural rubber. The ¹³C n.m.r. spectrum of the 100% modified natural rubber showed the presence of diastereoisomers due to two modes of addition of dichlorocarbene units as previously observed in epoxidation. There was no evidence of cis-trans iso-merisation, occurrence of other side reactions or of chain scission (shown by measurements of intrinsic viscosity). Partially dichlorocarbene modified natural rubber gave rise to a complex ¹³C n.m.r. spectrum that was assigned in terms of triad structures (for methylene carbon atoms)and pentad structures (for olefinic carbon atoms). Using ¹³C n.m.r. and measurements of glass transition temperature, it was found that reaction with aqueous NaOH and with solid NaOH both gave a random distribution of dichlorocarbene units, as compared with a block copolymer structure observed by previous workers with dichlorocarbene modified polybutadiene. The thermal stability of natural rubber is intermediate between that of the more stable 100% dichlorocarbene modified rubber and the less stable partially modified rubber.     

Styrene–butadiene block copolymer with high cis‐1,4 microstructure

The sequential block copolymerization of styrene (St) and butadiene (Bd) was carried out with an activated rare earth catalyst composed of catalyst neodymium tricarboxylate (Nd), cocatalyst Al(i‐Bu)₃ (Al), and chlorinating agent (Cl). The microstructure, composition, and morphology of the copolymer were characterized by FTIR, ¹H NMR, ¹³C NMR, and TEM. The results show that styrene–butadiene diblock copolymer with high cis‐1,4 microstructure of butadiene units (～ 97 mol %) was synthesized. The cis‐selectivity for Bd units was almost independent on the content of styrene units in the copolymer ranging from 18.1 mol % to 29.8 mol %. The phase‐separated morphology of polystyrene (PS) domains of about 40 nm tethered by the elastomeric polybutadiene (PB) segments is observed. The PS‐b‐cis‐PB copolymer could be used as an effective compatilizer for noncompatilized binary PS/cis‐PB blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

N.m.r. studies of butadiene - styrene copolymers

An analysis of the ¹³C nuclear magnetic resonance spectra of copolymers of butadiene—styrene, both block or random type, shows the possibility of observing the microstructure of the copolymers themselves. The microstructure of the copolymers was analysed in terms of triads of monomeric sequences. The units present in the copolymers are of the type: trans-1,4-butadiene, cis-1,4-butadiene, 1,2-butadiene and styrene. An assignment for all the experimental bands observed is proposed on the basis of correlation with homopolymers as well as on the basis of the frequencies for the single triads, calculated by additivity rules.     

Evolution of interphase in styrene-butadiene block copolymers as revealed by H solid-state NMR: Effect of temperature and molecular architecture

¹H spin-diffusion solid-state NMR, in combination with other techniques, was utilized to investigate the effect of molecular architecture and temperature on the interphase thickness and domain size in poly(styrene)-block-poly(butadiene) and poly(styrene)-block-poly(butadiene)-block-poly(styrene) copolymers (SB and SBS) over the temperature range from 25 to 80 °C. These two block copolymers contain equal PS weight fraction of 32 wt%, and especially, polystyrene (PS) and polybutadiene (PB) blocks are in glass and melt state, respectively, within the experimental temperature range. It was found that the domain sizes of the dispersed phase and interphase thicknesses in these two block copolymers increased with increasing temperature. Surprisingly we found that the interphase thicknesses in these two block copolymers were obviously different, which was inconsistent with the theoretical predictions about the evolution of interphase in block copolymer melts by self-consistent mean-field theory (SCFT). This implies that the interphase thickness not only depends strongly on the binary thermodynamic interaction (χ) between the PS and PB blocks, but also is influenced by their molecular architectures in the experimental temperature range.     

Kinetic investigations of the electrochemical bromination of peracetylated d-glucal in organic solvents

Cyclic voltammetry and ultramicroelectrodes were used to investigate the kinetic aspects of the electrochemical bromination of 3,4,6-tri-O-acetyl-d-glucal (1) in acetonitrile (AN), dichloromethane (DCM), and dimethylsulfoxide (DMSO). Qualitative and quantitative results, determined notably from the kinetic parameter [glucal]/v representing the competition between glucal concentration and time, clearly showed that glucal bromination depended on the nature of both the solvent and the in situ electrogenerated reactive brominated species (Br₂ or Br₃⁻) obtained from the oxidation of a bromide salt. It was especially shown that Br₂ reacted more rapidly than Br₃⁻ towards (1). On the other hand, the reactivity of both brominated species appeared to follow the solvent polarity order since the highest reactivity was obtained in DMSO whereas the lowest one was found in DCM.     

Graded block and randomized copolymers of butadiene-styrene

Graded block and randomized copolymers of butadiene-styrene were prepared anionically by polymerizing a mixture of butadiene and styrene with n-BuLi, in the absence and in the presence of t-BuOK respectively. Determination of the monomer composition and microstructure of the poly-butadiene sequence was achieved by 300 MHz ¹H n.m.r. and infra-red spectroscopy. ¹H n.m.r. equations developed previously for butadiene-styrene copolymers were modified and extended. In this way, cis, trans butadiene contents were determined from the aliphatic region of the n.m.r. spectra. The monomer sequence distribution of the copolymers has been investigated by examination of the morphology and their dynamic mechanical properties. The experimental conditions have been established for the preparation of random copolymers with inter- and intramolecular composition distribution.     

Co-aggregation process of poly(ethylene oxide)-b-polybutadiene/poly(acrylic acid) based on evolution of interpolymer hydrogen bonding in solutions

The co-aggregation process of a diblock copolymer poly(ethylene oxide)-block-polybutadiene (PEO-b-PB) and a homopolymer poly(acrylic acid) (PAA) in solutions was studied. The number-average molecular weights of both the PEO and PB blocks are 5100 g/mol; the weight-average molecular weight of PAA is ∼2000 g/mol. The co-aggregation was induced by adding a PB selective solvent (i.e., alkane or cycloalkane) into the THF solution of the two polymers, with the processes characterized by turbidity, ¹H NMR, dynamic light scattering, and microscopy experiments. During the selective solvent titration, the solution underwent a macro-phase separation that was mainly related to PAA, followed by a micro-phase separation that corresponded to the formation of vesicles with the shell of PB block and the core of PAA/PEO complex. The experimental results indicated that the evolution of interpolymer hydrogen bonding complexation between the PAA and PEO blocks determined the co-aggregation process. The loose and soluble interpolymer complex could be formed at rather low selective solvent content (f). The complexation was enhanced with increasing f, resulting in “redissolving” the PAA-rich domains in the blend solutions. Afterwards, the more compact PAA/PEO complex chemically linked with a soluble PB block acted as the building blocks to form the vesicles at higher f.     

Mechanical properties of SBS block copolymers. II. Effect of structure and selective solvent casting on stress–strain properties and mechanical hysteresis

Near-equilibrium stress–strain properties were obtained for poly(styrene–b–butadiene) copolymer films cast from different solvents at 35°C. The solvents used were methyl ethyl ketone and cyclohexane, selective for PS and PB, respectively, and toluene, a common solvent for both copolymer components. Tensile properties were studied at two successive loading cycles up to a maximum elongation ratio of λ_max = 7.0. At constant composition, the results were interpreted on the basis of the available morphology for these systems. The effect of hard block content (35% to 45% styrene) and at constant composition (39% styrene) of block length was also examined on such properties as elasticity and mechanical hysteresis. The results indicate that at constant composition the PB block length influences elasticity and mechanical hysteresis, also that films cast from a common solvent have higher tensile strength and increased mechanical hysteresis presumably because of a more effective load transfer between phases.     

Temperature-composition phase diagrams of binary blends of block copolymer and homopolymer

The temperature-composition phase diagrams for six pairs of diblock copolymer and homopolymer are presented, putting emphasis on the effects of block copolymer composition and the molecular weight of added homopolymers. For the study, two polystyrene-block-polyisoprene (SI diblock) copolymers having lamellar or spherical microdomains, a polystyrene-block-polybutadiene (SB diblock) copolymer having lamellar microdomains, and a series of polystyrene (PS), polyisoprene (PI), and polybutadiene (PB) were used to prepare SI/PS, SI/PI, SB/PS, and SB/PB binary blends, via solvent casting, over a wide range of compositions. The shape of temperature-composition phase diagram of block copolymer/homopolymer blend is greatly affected by a small change in the ratio of the molecular weight of added homopolymer to the molecular weight of corresponding block (M_H,A/M_C,A or M_H,B/M_C,B) when the block copolymer is highly asymmetric in composition but only moderately even for a large change in M_H,A/M_C,A ratio when the block copolymer is symmetric or nearly symmetric in composition. The boundary between the mesophase (M₁) of block copolymer and the homogeneous phase (H) of block copolymer/homopolymer blend was determined using oscillatory shear rheometry, and the boundary between the homogeneous phase (H) and two-phase liquid mixture (L₁+L₂) with L₁ being disordered block copolymer and L₂ being macrophase-separated homopolymer was determined using cloud point measurement. It is found that the addition of PI to a lamella-forming SI diblock copolymer or the addition of PB to a lamella-forming SB diblock copolymer gives rise to disordered micelles (DM) having no long-range order, while the addition of PS to a lamella-forming SB diblock copolymer retains lamellar microdomain structure until microdomains disappear completely. Thus, the phase diagram of SI/PI or SB/PB blends looks more complicated than that of SI/PS or SB/PS blends.     

Microstructure analysis of brominated styrene–butadiene rubber

The bromine addition to the SBR double bonds in chloroform at 0°C has been investigated by FTIR, ¹H NMR and DSC techniques. In this case, bromine molecules react exclusively with the polydiene double bonds and the polystyrene units are unaffected. The bromine reacts preferentially with 1,4‐trans double bonds of the polybutadiene segment of SBR. At low bromination level (below 15%) the bromine reacts mainly with the 1,4‐trans double bonds of SBR, while at higher bromination level (up to 30%) the bromine shows the most reactivity toward the vinylic double bond. Above 30%, the addition reaction occurs on 1,4‐trans double bonds. The microstructure of modified and unmodified styrene–butadiene copolymers were fully characterized by ¹H NMR technique. Expanded regions have been utilized to resolve the complex ¹H NMR spectrum and establish the compositional and configurational sequences of styrene–butadiene copolymers. POLYM. ENG. SCI., 47:87–94, 2007. © 2007 Society of Plastics Engineers     

Controlled radical polymerization with polyolefin macroinitiator: a convenient and versatile approach to polyolefin-based block and graft copolymers

This paper introduces the new synthetic methodology of polyolefin-based block and graft copolymers with polar segments [e.g., polystyrene and poly(meth)acrylates]. Various brominated polyolefins were prepared by bromination of polyolefins with N-bromosuccinimide. The resulting brominated polyolefins were able to initiate the controlled radical polymerization of polar monomers, such as methyl methacrylate, ethyl acrylate, t-butyl acrylate, styrene and 2-(dimethylamino)ethyl acrylate, using a CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyst system, leading to a variety of polyolefin-based copolymers with a different content of the corresponding polar segment. Because of the accessible synthesis of polyolefin macroinitiators, this synthetic methodology is expected to result in the preparation of a wide range of polyolefin-based block and graft copolymers.     

天然胶乳小分子模型物的溴化反应历程研究

选择与天然橡胶（ NR）分子链节具有相似结构的小分子2－甲基－2－丁烯作为天然橡胶溴化反应的参照模型,通过乳液法使小分子发生溴化反应,应用傅立叶红外光谱和气相色谱－质谱联用等测试手段对小分子溴化反应产物结构进行表征,并探讨小分子溴化反应历程。结果表明,小分子2－甲基－2－丁烯的C＝C双键在溴化过程中被还原为C－C单键,同时发生甲基氢原子的溴化取代,但溴化产物中并没有醛类物质生成。乳液法小分子溴化反应可能是自由基反应历程,且没有出现次溴酸参与反应历程的现象。     

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.     

Nuclear magnetic resonance studies on sequence distributions in vinyl alcohol-vinyl acetate copolymers

The microstructure of vinyl alcohol-vinyl acetate copolymers was studied using both ¹³C n.m.r. and ¹H n.m.r. techniques. The sequence lengths of vinyl acetate units calculated respectively from the compositional dyads, from the methylene absorptions and feom the triple carbonyl absorptions in the ¹³C n.m.r. spectrum were not identical, and moreover the dyad-triad relationship showed a large discrepancy. ¹H and ¹³C n.m.r. spectra of a 5 mol% re-acetylated random sample, containing mainly isolated acetate units, indicate that configurational splitting complicates the assignment of the triple carbonyl absorption, which originally was interpreted as a compositional triad. After correcting for tacticities the results could be brought in line and the C=O resonances proved to be useful in obtaining information on the percentage of isolated vinyl acetate units and the sequence length n^A₂₊ (the average length of vinyl acetate units ≥2).     

Synthesis of a high‐trans 1,4‐butadiene/isoprene copolymers with supported titanium catalysts

The copolymerization of butadiene (Bd) and isoprene (Ip) with a supported titanium‐triisobutyl aluminum catalyst system was studied. An analysis using differential scanning calorimetry, X‐ray diffraction, and ¹³C‐NMR spectra indicated that products with 25–60 mol % Bd units were random copolymers and that the melting temperatures and glass‐transition temperatures (Tg) were 30–40 and ?74°C (or thereabout), respectively, which were very similar to those of natural rubber. The chemical structure of these copolymers was characterized by a high‐trans 1,4‐configuration: the trans 1,4‐content of Ip units was greater than 98%, and the trans 1,4‐content of Bd units was greater than 90%. The reactivity ratio of Bd was greater than that of Ip (r_Bd = 5.7 and r_Ip = 0.17). The sequence distribution of the monomer units of the copolymers followed a first‐order Markov statistical model. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1800–1807, 2003     

Conformational behaviour of (styrene-p-chlorostyrene) triblock copolymers in dilute solutions. 2. Temperature dependence of conformational behaviour in a selective solvent

Intrinsic viscosity, osmotic second virial coefficient and light scattering of the B_mA_nB_m and A_mB_nA_m copolymers (A, styrene monomeric unit; B, p-chlorostyrene monomeric unit, m and n denote the number of units) in cumene which is a good solvent for polystyrene but a θ solvent for poly(p-chlorostyrene) at 59.0°C, were studied over the temperature range 65° to 15°C. The results suggested that conformational transition from a random coil form to a segregated form occurs at a critical temperature which appears to be in the range 40° to 30°C, depending on the composition, molecular weight and structure of the block copolymers; the θ condition could not be attained by cooling the block copolymer solutions, and micelle formations due to intermolecular associations were found in some cases below the transition temperature.     

Synthesis and kinetic behavior of stereotriblock polybutadiene using dilithium as initiator

Anionic polymerization of butadiene was conducted in cyclohexane using 1,1,4,4‐tetraphenyl‐1,4‐dilithium butane (TPB–DiLi) as initiator and dipiperidinoethane (DPE) as modifier. The polymer design effects of DPE/TPB–DiLi (simplified as DPE/Li) and polymerization temperature on the 1,2 content of polybutadiene (PB) were examined and 1,2‐polybutadiene (1,2‐PB) with a nearly 100% 1,2 content was obtained. 1,2–1,4–1,2‐Stereotriblock polybutadiene (STPB) can be synthesized easily by means of one feed reaction. DSC and DMA analyses showed that STPB with the designed molecular structure (molecular weight, block ratio, and 1,2 content in 1,2 blocks) has two T_g's and two loss moduli and exhibits microphase separation. Studies on reaction kinetics established the polymerization kinetics equation of 1,4‐PB as ?d[M]/dt = 0.356[C]^0.5[M], indicating the first‐order relationship between polymerization rate and monomer concentration. At 50°C, the addition of the strong polar modifier DPE into the system increased the reaction rate. The apparent propagating activating energies before and after DPE addition were also determined in this study. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1049–1054, 2003     

立构三嵌段聚丁二烯

考察了以１，１，４，４－四苯－１，４－二锂丁烷为引发剂，二哌啶乙烷为结构调节剂，环己烷为溶剂的丁二烯负离子聚合。研究了ＤＰＥ用量和聚合温度对聚丁二烯微观结构的影响。     

Development of silk-like materials based on Bombyx mori and Nephila clavipes dragline silk fibroins

In order to develop new silk-like materials in the form of fiber and non-woven nano-fiber, this study synthesized a new silk-like protein by selecting the sequence from the crystalline region of Bombyx mori silk fibroin, (GAGSGA)₆, to imitate the processing condition of the silk fibroin with the combination of the sequence YGGLGSQGAGRG, the hydrophilic motif of spider dragline silk which was considered as the origin of supercontraction of spider dragline silk (Yang Z, et al. J Am Chem Soc 2000;122: 9019-25). The CD pattern of the silk-like protein in hexafluoroacetone (HFA) indicates that it takes helical structure. The solid-state structures of the silk-like protein before and after methanol treatment were determined to be random coil and Silk II structure (mainly β-sheet structure), respectively, using ¹³C CP/MAS NMR. The ¹³C CP/MAS NMR spectra of the protein after methanol treatment in hydrated state showed that the random coil peaks from Ala Cβ and Ser Cβ carbons become sharper compared with the corresponding peaks in the dry state. The 2D-WISE spectra in the hydrated state also showed increase of the narrow components for these carbons. Thus, water molecules are relatively easy to access at the random coil regions of the protein. The fiber formation of the silk-like protein was possible with wet-spinning or electrospinning methods using HFA as dope solvent and methanol as coagulation solvent.     

Novel strategies for the synthesis of hydroxylated and carboxylated polystyrenes

Hydroxylated and carboxylated polystyrenes (PHMSt and PCSt, respectively) were synthesized using facile strategies. For this purpose, PSt was synthesized through atom transfer radical polymerization (ATRP) approach and then brominated at the para-position of the aromatic rings to produce PBrSt. The bromination efficiency was calculated to be 37 and 68%, even though there was a degradation of the polymer chains, using 60 or 100 mol% of bromine relative to the PSt, respectively. The brominated polymer was converted into Grignard reagent (PSt-magnesium-Br), and then reacted with anhydrous formaldehyde and solid carbon dioxide (Dry Ice) to afford PHMSt and PCSt, respectively. The chemical structures of all synthesized polymers were characterized using Fourier transform infrared (FTIR) as well as proton nuclear magnetic resonance (¹H NMR) spectroscopies. Furthermore, the thermal behavior of the synthesized PHMSt and PCSt were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).