Temperature and concentration effects on polar-modified alkyllithium polymerizations and copolymerizations

Addition of polar modifiers to alkyllithium-initiated homopolymerizations of butadiene causes substantial changes in the microstructure of the polymers produced. These changes are shown to depend not only on the concentration of modifier, but also on the polymerization temperature. The combined effects of modifier concentration and reaction temperature have been considered, and a method is presented for quickly determining the proper conditions for preparation of a polybutadiene of any 1,2-microstructure within a range of 10–80%. It is also shown that in anionic polar-modified copolymerizations of butadiene–styrene, the reaction temperature is again critical. Within a certain concentration range of modifier, the temperature will influence the rate of styrene incorporation or the randomness of styrene units in the resulting copolymers.     

Copolymerization of styrene and butadiene in emulsion. II. Relative rates of crosslinking and propagation

For the styrene–butadiene emulsion copolymerization (71 parts butadiene:29 parts styrene) the ratio of the rate coefficients for crosslinking, k_x, and propagation, k_p, have been determined at 5, 15, and 25°C by using an adaption of the method of Morton and co-workers. These ratios yield a value of 4.85 kcal/mole for the difference in activation energy between crosslinking and propagation, E_x ? E_p. Since the relative frequency of crosslinking and propagation depends upon the copolymer composition, and hence upon the free monomer ratio and the temperature, the range of application of these data is more limited than in a simple homopolymerization.     

A Novel Thermotropic Elastomer based on Highly‐filled LDH‐SSB Composites

Elastomeric composites are prepared based on solution styrene butadiene elastomer and zinc‐aluminium layered double hydroxides (LDH), using a conventional sulphur cure system. Up to 100 parts per hundred rubber of LDH are incorporated into the elastomer matrix. The composites exhibit an interesting phenomenon of thermoreversible transparency, i.e. the transparent sample becomes opaque at warm condition and restores the transparency at room temperature. The transparency is found to be increased as the amount of LDH was increased. The addition of LDH gradually improved the mechanical, dynamic mechanical performance and thermal stability of the base elastomer. These developped elastomers could be utilised as smart materials in different applications.     

Dynamic mechanical relaxation behavior of block copolymers at high temperatures

We carried out dynamic mechanical measurements to investigate three different examples of block copolymers: styrene–isoprene diblock copolymers and styrene–butadiene–styrene and styrene–(styrene butadiene)–styrene triblock copolymers. Isochronal and isothermal measurements of the real and imaginary parts of the complex shear modulus were performed over wide ranges of temperature and frequency. The measurements showed the presence of an additional relaxation process appearing at temperatures higher than those of the glass relaxation of the polystyrene phase, which has been misinterpreted by some authors as an order–disorder transition. The frequency dependence revealed that this process was a relaxation process and did not belong to a first‐order transition. Moreover, the influence of crosslinking via dicumylperoxide was measured, and we constructed complete master curves to confirm the presence of two relaxation processes. The high‐temperature relaxation process was strongly suppressed by crosslinking. Therefore, it was possible to detect the glass relaxation process of the polystyrene phase in a precise manner. The results were compared with those of homopolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2198–2206, 2001     

丙烯酰氯对丁苯共聚物活性链偶联反应的研究

以n BuLi为引发剂 ,四氢呋喃 (THF)为调节剂 ,抽余油为溶剂 ,采用丙烯酰氯为偶联剂对丁二烯 苯乙烯阴离子共聚体系进行偶联反应 ,研究了影响偶联反应的各种因素 ,如偶联剂用量、相对分子质量、偶联反应时间、偶联反应温度、THF用量、末端基团、单体浓度等 ;确定了偶联剂用量与聚合物相对臂数之间的关系及其偶联效率 .     

氧对n-BuLi/THF引发丁二烯苯乙烯共聚合的影响

研究了氧分子与活性种快速失活的定量关系 ,二代杂质对活性种及聚合物微观结构的影响 .从聚合动力学及聚合物相对分子质量等方面来测定氧分子快速杀死活性种数 ,并考察了体系中氧产生的偶联反应及其对丁苯共聚物物理机械性能、动态力学性能及耐磨性能的影响 .结果表明 :氧对n BuLi THF体系丁苯共聚合有不利影响 .     

Experimental branching results for diene polymers by use of gel-permeation chromatography

Branching analyses in styrene–butadiene rubbers and polybutadiene rubbers have revealed large differences in branching between rubbers polymerized in different ways. The functionalities of several star-branched solution-polymerized styrene–butadiene rubbers were calculated and compared to their expected structures. Emulsion-polymerized polybutadiene rubber and a series of solution-polymerized polybutadienes made with different catalysts had different degrees of random branching, and evidence is presented indicating that the different available catalyst systems provide some latitude in making rubbers of different branching contents. Random branching analyses on a series of emulsion-polymerized styrene–butadiene rubbers revealed the dependency of branching on molecular weight and molecular weight distribution. The influence of polymerization temperature on the branching of emulsion-polymerized styrene–butadiene rubber was also studied.     

Dynamic mechanical and dielectric properties of epoxidized SBS triblock copolymer

The morphological and dynamic properties of epoxidized styrene–butadiene–styrene block copolymers were studied and compared with their parent styrene–butadiene–styrene block copolymer (SBS). Two peaks were observed in the mechanical loss (tan δ) curve which can be attributed to segmental motion of epoxidized polybutadiene (EPPB) and polystyrene. Analysis by DSC thermograms also showed the linear increase of glass transition temperature for EPPB domain with the epoxy group content. Phase separated structures of epoxidized SBS as observed by TEM suggests a considerable degree of mixing occurred between phases after 80 mol % of the double bonds in SBS were epoxidized. The interfacial region displays a third peak and causes much steeper drop in modulus at higher temperature than T_g of EPPB. Parallel dielectric relaxation measurements were also made in the frequency range of 30 Hz–1 KHz as a function of temperature. In each dielectric constant (?′) curve, there is a maximum near the T_g of EPPB determined from the dielectric loss tangent curve. The shift in T_g of EPPB versus epoxy group content was consistent with that measured by the thermal and dynamic mechanic analysis. These findings indicated an 8°C shift in glass transition temperature as the epoxy group content in EPPB increased 10%.     

Acrylonitrile Copolymerizations. VI. Influence of the Comonomer on the Intramolecular Cyclization Reaction

The intramolecular cyclization reaction involving the polymerization of cyano groups reported in a previous paper for the system acrylonitrile-vinyl chloride is studied for other comonomers with acrylonitrile including vinyl acetate, vinylidene chloride, butadiene, styrene, methyl acrylate, and methyl methacrylate. It is shown that the extent of the reaction is governed by the reactivity of the comonomer-unit ended radical, but the cyclization reaction cannot explain all the kinetic deviations observed.     

Effect of surface swelling on diffusion in polymers. I. Infrared spectroscopy

The effect of stress transfer-limited swelling in the surface region on the hydroxylation of styrene–butadiene–styrene block copolymers in the bulk state was investigated. Films of the copolymer were allowed to react with peracetic acid to effect epoxidation and simultaneously with acetic acid and water to cleave the epoxy rings. By infrared spectroscopy it was observed that the hydroxyl content of the films decreased with increasing film thickness and the epoxy content increased commensurately. This was attributed to the presence of a lag between the advancing diffusion fronts for the epoxide groups and for the cleavage agents. This lag increases with increasing thickness due to the presence of stress-transfer mechanisms which act to reduce the degree of swelling in the surface region and which are more effective in thicker films. The hydroxyl content increased exponentially with time, giving rise to the observation of significant induction time before there was any infrared evidence of hydroxyl formation. This resulted from the relief of part of the compressive stress in the surface region by the reaction process, which in turn increased the permeation rate of peracid.     

Simultaneous determination of the styrene unit content and assessment of molecular weight of triblock copolymers in adhesives by a size exclusion chromatography method

The content of styrene units in nonhydrogenated and hydrogenated styrene‐butadiene‐styrene and styrene‐isoprene‐styrene triblock copolymers significantly influences product performance. A size exclusion chromatography method was developed to determine the average styrene content of triblock copolymers blended with tackifier in adhesives. A complete separation of the triblock copolymer from the other additives was realized with size exclusion chromatography. The peak area ratio of the UV and refraction index signals of the copolymers at the same effective elution volume was correlated to the average styrene unit content using nuclear magnetic resonance spectroscopy with commercial copolymers as standards. The obtained calibration curves showed good linearity for both the hydrogenated and nonhydrogenated styrene‐butadiene‐styrene and styrene‐isoprene‐styrene triblock copolymers (r  = 0.974 for styrene contents of 19.3–46.3% for nonhydrogenated ones and r  = 0.970 for the styrene contents of 23–58.2% for hydrogenated ones). For copolymer blends, the developed method provided more accurate average styrene unit contents than nuclear magnetic resonance spectroscopy provided. These results were validated using two known copolymer blends consisting of either styrene‐isoprene‐styrene or hydrogenated styrene‐butadiene‐styrene and a hydrocarbon tackifying resin as well as an unknown adhesive with styrene‐butadiene‐styrene and an aromatic tackifying resin. The methodology can be readily applied to styrene‐containing polymers in blends such as poly(acrylonitrile‐butadiene styrene).     

Structure and physical properties of glow discharge polymers. I. Polymers from hydrocarbons

The polymers deposited from the vapors of pentane, ethylene, butadiene, benzene, styrene, and naphthalene subjected to glow discharge have been analyzed by infrared absorption techniques. The reaction products show unsaturation, hydrogenation, and branching in the polymer chains. Aromaticity is present only in polymers from aromatic monomers.     

高聚物两相体系相行为的流变学研究──Ⅱ．嵌段高聚物微相溶合的研究

本文从流变学角度研究了三嵌段高聚物苯乙烯－丁二烯－苯乙烯（ＳＢＳ）中的微相转变，从相转变温度前后流变行为的变化，确定了相转变温度，其结果与小角Ｘ光散射的结果一致，在此基础上，研究了嵌段高聚物的微相溶合过程，发现相溶合过程可分为四个阶段，在第二，第四阶段，Ｇ’～ｅαｔ，’～ｅβｔ，矿是相溶合时间，α，β随相溶合温度及阶段不同而改变．以Ｄｉｃｋｉｅ模型为基础，考虑到分子运动及剪切条件下的流体力学相互作用，分析了各阶段的流变行为，初步说明了微相溶合过程中，流变行为时间依赖性的本质．     

Grafting of styrene onto low molecular weight polymers and copolymers of butadiene

The grafting of styrene onto low molecular weight polybutadienes and butadiene–styrene co-polymers was studied. A mathematical method was used for the design of experiments and for the determination of the optimum grafting conditions with respect to the conversion of styrene and the efficiency of grafting. The reaction parameters were temperature (65–105°C), time (2–10 hr), concentration of the initiator, polymer to monomer ratio (10/90–90/10) and dilution by solvent (toluene). The optimum grafting conditions were chosen under which 50–60 wt-% of styrene was grafted onto backbone polymer at a high conversion of the monomer. It was found that the reactions producing graft copolymer prevailed over the styrene homopolymerization when the temperatures employed were lower (65–85°C), and the reaction time (8–10 hr), backbone polymer/monomer ratio, and the dilution by solvent were higher. The efficiency, density, and degree of grafting were found to increase with the increase in the molecular weight of the backbone polymer. The efficiencies and densities of grafting onto low molecular weight polybutedienes were higher than those of grafting onto low molecular weight butadiene–styrene copolymers. Grafting efficiencies and grafting densities were in the ranges 37.8–61.6 wt % and 0.06–0.26, respectively, in the studied range of number-average molecular weights (M?_n = 2400–6000).     

钴系催化剂催化丁二烯—苯乙烯共聚动力学研究

合成高顺-1,4-丁苯胶的催化剂主要是镍、钴、钛系3类。钴系催化剂基本上是三元体系,也有加入添加剂(含N,O,S化合物)的多元体系。该体系的特点是,共聚物顺1,4含量高(～98％),分子量大。但苯乙烯的共聚活性低,有均聚苯乙烯和凝胶形成。本文以Co(nap)_2-Al_2Et_3Cl_3进行了丁苯共聚的动力学研究。     

Alkalimetall-i minoborate,ein neuartiger typ von bor-atkomplexen

Complexes have been obtained by the reaction of iron atoms with butadiene or styrene at - 196°C followed by treatment with ligands such as CO or (MeO)₃P.     

Anionic synthesis of polystyrene and polybutadiene heteroarm star polymers

The use of living linking reactions of poly(styryl)lithium with 1,3-bis(1-phenylvinyl)benzene followed by crossover reactions with styrene or butadiene monomers has been used to prepare four-armed heteroarm, star-branched polymers. Bimodal molecular weight distributions have been observed for crossover reactions with both styrene and butadiene. Addition of THF ([THF]/[Li]=14–32) for crossover to styrene and lithium sec-butoxide for crossover to butadiene produces monomodal molecular weight distributions. Symmetrical, four-armed star polystyrenes have been synthesized; properties have been compared with a corresponding polymer prepared via a silicon tetrachloride linking reaction. Heteroarm, star-branched polymers with two polystyrene arms and two polybutadiene arms with high 1,4-microstructure have been prepared.     

Peculiarities of the Anionic Copolymerization of Styrene and Dienes in Non-Polar Solvents with Li+ as Counter-ion mvb

Summary: The anionic copolymerization of styrene and butadiene in hydrocarbon solvents initiated by lithium alkyls was first studied by Korotkov, who reported that the polymerization starts slowly and initially consumes butadiene. On exhaustion of this monomer, the reaction speeds up and then styrene polymerizes rapidly. This peculiar behaviour, which was originally explained by Korotkov by treating the monomers as solvents, butadiene being a preferential solvent for the Li⁺ cation, was later accounted for by considering the cross-over reactions. In this paper an in dept further explanation is given by admitting that the polymerization reactions occur through coordination of the Li ⁺ cation by the monomer followed by insertion of the monomer into the polymer chain. A preliminary MOPAC 93 (PM3) calculation seems to confirm this interpretation.     

Epoxidation of styrene–butadiene–styrene block copolymer and use for gas permeation

The epoxidation of styrene–butadiene–styrene triblock copolymer (SBS) by an in situ generated peracid method is discussed. The presence of an acid acting as catalyst led to side reaction. The reactivities of internal double bonds (the 1, 4-structure) were higher than those of the vinyl bonds (the 1, 2-structure). In the 1, 4-structure, the reactivities of cis-structure were higher than those of trans-structure. The oxirane weight content and total oxygen weight content were determined by titration and element analysis, respectively. The cohesive energy, solubility parameter, and the glass transition temperature of epoxidized SBS increased with increasing total oxygen weight content. But the molecular weight between crosslinking points decreased resulting in an increase of crosslinking density with increasing total oxygen weight content. The changes of properties of epoxidized SBS reduced the gas permeability of oxygen and nitrogen through epoxidized SBS membrane, but increased the gas selectivity between oxygen and nitrogen. When the operating temperature of gas permeation was increased, the permeability of oxygen and nitrogen increased but the selectivity decreased. For epoxidized SBS containing 7.35 wt % oxygen content, the activation energy was 9 and 12.2 kcal/mol for oxygen and nitrogen, respectively.     

Microphase separation in poly(acrylonitrile–butadiene–styrene) (ABS) studied with paramagnetic spin probes. II. Simulation of electron spin resonance spectra

We recently presented electron spin resonance spectra of poly(acrylonitrile–butadiene–styrene) (ABS) doped with 10‐doxylnonadecane (10DND) and 5‐doxyldecane (5DD) as spin probes. The spectra were measured in three types of ABS that differed in their butadiene contents and methods of preparation. Results for the ABS polymers were evaluated by comparison with similar studies on the homopolymers polybutadiene (PB) and polystyrene (PS) and the copolymers poly(styrene‐co‐acrylonitrile) (SAN) and poly(styrene‐co‐butadiene) (SB). Only one spectral component was detected for 10DND in PB, PS, SAN, and SB. In contrast, two spectral components differing in their dynamic properties were detected in the ABS samples and were assigned to spin probes located in butadiene‐rich domains (the fast component) and SAN‐rich domains (the slow component). The presence of two spectral components was taken as an indication of microphase separation. In this study, we present details on the dynamics and microphase separation by simulating spectra of 10DND in ABS, PB, PS, and SAN. The simulations are based on a dynamic model defined by the components of the rotational diffusion tensor and the diffusion tilt angle between the symmetry axis of the rotational diffusion tensor and the direction of the nitrogen 2p_z atomic orbital. The jump diffusion model led to good agreement with experimental spectra. In this model, the spin probe has a fixed orientation for a given time and then jumps instantaneously to a new orientation. The temperature variation of the rotational correlation time in PB and PS consisted of two dynamic regimes, with different activation energies. The transition temperature at which the change in dynamics occurs (T_tr) is 380 K for PS and 205 K for PB, essentially the same as the corresponding glass‐transition temperatures measured by differential scanning calorimetry. We suggest that T_tr is a better indicator of the glass transition than the temperature at which the total spectral width is 50 G, especially for large probes. The simulation program allowed the determination of the relative intensities of the fast and slow spectral components as a function of temperature; this information was used to clarify the redistribution of the probe above the glass transition of the SAN‐rich component in ABS systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 424–433, 2002; DOI 10.1002/polb.10110