Ozonolysis of polybutadienes with different microstructure in solution

The reaction of ozone with 1,4‐cis‐polybutadiene and polybutadiene having the following linking of the butadiene units: 1,4‐cis (47%), 1,4‐trans (42%), 1,2 (11%) was investigated in CCl₄ solution. It was found out by means of IR‐spectroscopy and ¹H‐NMR spectroscopy that the basic ozonolysis products of both elastomers are ozonides and aldehydes. The aldehyde:ozonide ratio was 11 : 89 and 27 : 73 for E‐BR and BR, respectively. In addition, epoxide groups were detected, only in the case of BR, and their yield was about 10% of that of the aldehydes. On the basis of BR ozonolysis it was established that the ozonide yield from 1,4‐trans units is about 50%. By using the aldehyde yields, an evaluation was made of the efficiency of ozone degradation of the two polybutadienes, according to which the respective value of BR is considerably higher than that of E‐BR. A reaction mechanism is proposed, which explains the formation of the identified functional groups and the differences in the ozone degradation of the studied elastomers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 427–433, 2007     

The determination of the addition variation and geometrical isomerism of a polybutadiene as a function of molecular weight by preparative gel permeation chromatography and infrared analysis

The addition variation, 1,2 and 1,4 units, and the geometrical isomerism, 1,4-cis and 1,4-trans units, of a fractionated polybutadiene were determined as a function of molecular weight using preparative gel permeation chromatography followed by infrared analysis of the fractions. Both the addition variation and geometrical isomerism remained essentially constant across the molecular weight distribution.     

Temperature and microstructure dependence of the Rheo-optical properties of polybutadienes

The present investigation covers the isothermal stress–strain–birefringence behavior of various polybutadienes between ?30°C and 110°C. Birefringence measurements were also made under constant stress as a function of temperature in the low temperature region between ?30°C and ?120°C. The polybutadienes studied were two high cis-1,4 (prepared by different catalysts), a linear medium cis, and an emulsion polybutadiene. At temperatures at which the photoelasticity theory could be applied, the segmental polarizability anisotropy, its temperature dependence, and other parameters associated with an elastic polymeric network were determined. The influence of the degree of crosslinking was examined. At the low temperatures, microstructure was shown to have a pronounced effect on the photoelastic properties, the crystallization phenomena, and the glass–rubber transitions.     

Effect of alkylaluminum structure on Ziegler-Natta catalyst systems based on neodymium for producing high-cis polybutadiene

Summary  In this work, a laboratory scale process for producing polybutadiene with high content of cis-1,4 repeating units was studied. A Ziegler-Natta catalyst system constituted of neodymium versatate (catalyst), an alkylaluminum compound (alkylating agent and cocatalyst) and tert-butyl chloride (chlorinating agent) was used. The solvent employed was a mixture of hexane and cyclohexane (80/20 v/v). The objective of this work was to evaluate the effect of alkylaluminum structure and the influence of Al/Nd (5 to 15) molar ratio of long chain alkylaluminium compound (tri(n-hexyl)aluminum) on catalyst activity and polybutadiene characteristics. The alkylaluminum compounds employed in this study were tri(i-butyl)aluminum, tri(n-hexyl)aluminum, tri(n-octyl)aluminum and di(i-butyl)aluminum hydride. The polybutadienes molar masses obtained were strongly influenced by the alkylaluminum structure. Polymers with the highest molar masses were obtained when tri(i-butyl)aluminum, tri(n-hexyl)aluminum and tri(n-octyl)aluminum were employed. However, polymers with the highest contents of cis-1,4 units and the lowest molar masses were produced when di(i-butyl)aluminum hydride was employed.     

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     

Polybutadiene modified by epoxidation. 1. Effect of polybutadiene microstructure on the reactivity of double bonds

The reactivity of low-molecular weight sodium polybutadiene (1,2-PB) and n-butyllithium polybutadiene (1,4-PB) has been studied during epoxidation with peracetic acid. The effect of the epoxy groups formed on the polymer solution viscosity has also been investigated. It was found that the rate constant of 1,4-PB epoxidation is ～1.9 times greater than that for 1,2-PB of a similar molecular weight. The reactivity of various structural polymer unit forms was studied by spectroscopic methods (i.r. and ¹H n.m.r.); it was found that reactivity depends on chain microstructure in the following way:for 1,2-PB: trans-1,4 >cis-1,4 ? 1,2for 1,4-PB: cis-1,4 >trans-1,4 ? 1,2An increase in the limiting viscosity number was observed with increasing epoxy content in the 1,2-PB chain, but the opposite effect was observed for 1,4-PB. The solubility parameter, δ, for both kinds of epoxy polybutadiene was found to be similar ($\text{19.8 × 10}{}^3\text{J}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{·}\text{m}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$).     

Phase equilibria in SBR/polybutadiene elastomer blends: Application of Flory–Huggins theory

Blends of anionically-polymerized polybutadiene (BR) and styrene–butadiene copolymer (SBR) must be treated as mixtures of terpolymers and tetrapolymers, due to the presence of three different BR isomers: cis-1,4, trans-1,4, and vinyl-1,2. Moreover, in the absence of specific interactions or chemical reactions that strongly influence miscibility, structural characteristics of the component polymers, such as BR isomer content, SBR styrene content, monomer sequence distribution, molecular weight, and molecular weight distribution, are expected to have an increased role in determining the blend miscibility characteristics. Small angle neutron scattering (SANS) studies of SBR/BR blends have resulted in the computation of the monomer–monomer segmental interaction energetics via a Flory–Huggins treatment. This allows quantitative prediction of miscibility behavior as a function of polymer structure. We have used the Flory–Huggins chi parameters, describing the styrene/cis-1,4, styrene/trans-1,4, and cis-1,4/trans-1,4 segmental interactions, to identify certain blend combinations expected to exhibit phase transitions in an experimentally accessible temperature range. The appropriate polymers were synthesized, solution blended, and the blends analyzed via optical microscopy and thermal analysis. Our results show that the blend behavior, observed experimentally, is consistent with the calculated cloud point curves. © 1994 John Wiley & Sons, Inc.     

Decrease in the etch rate of polymers in the oxygen afterglow with increasing gas flow rate

In this paper we report the variation of the etch rate of polymers in the afterglow of a radio frequency discharge in oxygen as a function of total flow rate in the range 2–10 cm³ (STP)/min. The measurements were made at ambient temperature with the O(³P) concentration held essentially constant. We report results on three polymers: cis-polybutadiene, a polybutadiene with 33% 1,2 double bonds, and a polybutadiene with 40% 1,2 double bonds. We have observed that the etch rate of these polymers decreases significantly with increasing flow rate, strongly suggesting that the vapor-phase products of polymer degradation contribute to the degradation process.     

Synthesis and characterization of polybutadiene with monotitanocene/methylaluminoxane catalyst

Butadiene was polymerized using a monotitanocene complex of η⁵‐pentamethylcyclopentadienyltribenzyloxy titanium [Cp*Ti(OBz)₃] in the presence of four types of modified methylaluminoxanes (mMAO), which contained different amounts of residual trimethylaluminum (TMA). The titanium oxidation states in Cp*Ti(OBz)₃/mMAO and Cp*Ti(OBz)₃/mMAO/triisobutylaluminum (TIBA) catalytic systems were determined by redox titration method. The effects of various oxidation states of titanium active species on butadiene polymerization were investigated. It was found that Ti(III) active species is more effective for preparing polybutadiene with high molecular weight. The addition of TIBA to the Cp*Ti(OBz)₃/mMAO system could reduce a greater number of Ti(IV) complexes to Ti(III) species and lead to significant increases of polymerization activity and molecular weight of polymer, whereas the polybutadiene microstructure was only slightly changed. On the basis of microstructure and property characterization by FTIR, ¹³C‐NMR, DSC, and WAXD, all resultant polymers were proved to be amorphous polybutadiene with mixed 1,2; cis‐1,4; and trans‐1,4 structures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2494–2500, 2004     

Polybutadiene modified by epoxidation: 2. The effect of epoxy groups on the crosslinking process with dicumyl peroxide

The process of crosslinking sodium and n-butyllithium polybutadienes as well as the products of their modification obtained by epoxidation has been studied. It has been found that the crosslinking efficiency of epoxy-1,2-polybutadiene is half that of the starting polybutadiene. However, the crosslinking efficiency of epoxy-1,4-polybutadiene was found to be similar to that of the starting 1,4-polybutadiene. The shift in glass transition temperature for epoxy-polybutadienes brought about by the change in the chemical composition (ΔT_g)_M was found to be 67 K for 1,4-polybutadiene, and 51 K for 1,2-polybutadiene. The effect of the epoxy groups and crosslinks on the glass transition temperatures of modified crosslinked polymers is also discussed.     

Synthesis and properties of photosensitive rubbers. III. Synthesis of chloroacetylated polybutadiene and its photosensitivity

Polymers having chloroacetate groups were prepared by addition reaction of various chloroacetic acids, such as mono-, di-, and trichloroacetic acids, to cis-1,4-polybutadiene under nitrogen atmosphere for obtaining photosensitive rubbers. The structure of products obtained was identified as a cyclized polybutadiene having pendent chloroacetate groups. The amount of the incorporated substituent increased up to the maximum of around 20 mol %, and the amount of the residual unsaturated groups in the polymer backbone decreased due to the cyclization of the double bond. Chloroacetylated polybutadiene had higher photocrosslinkability by UV irradiation than chloroacetylated polybutadiene had higher photocrosslinkability by UV irradiation than chloroacetylated chitosan or PVA owing to the high reactivity of the chloroacetate groups and the double bonds in the polymer. The photosensitivity depends both on the amount of the incorporated chloroacetate groups and the residual double bonds in the polymer and also depends on the glass transition temperature (T_g) of the polymer, and the dependence of the crosslinking reaction on T_g was interpreted to be due to diffusion controlled reaction between excited dichloroacetate groups and olefinic groups in the polymer.     

Microstructure‐thermal property relationship of high trans‐1,4‐poly(butadiene) produced by anionic polymerization of 1,3‐butadiene using an initiator composed of alkyl aluminum,n‐butyl lithium,and barium alkoxide

This article deals with the characterization of high trans‐1,4‐poly(butadiene) (TPBD) prepared by means of an anionic polymerization using an initiator composed of alkyl aluminum, n‐butyl lithium, and barium alkoxide. By controlling both initiator composition and polymerization temperature, a set of TPBD was prepared with well‐known number of 1,4‐trans units, molecular weight distribution, and average molecular weight. Analyses by differential scanning calorimetry and diffraction of wide‐angle X‐rays showed a direct relationship between the microstructure of the polymer and its thermal properties. By increasing the number of 1,4‐trans units (70–90%), the crystallinity of the polymer was increased (10–30%); polymers with less than 65% of 1,4‐trans units were amorphous, whereas TPBD with a number of 1,4‐trans units greater than 80% were polymorphous and presented two endothermic transitions. Summing up, the results presented in this article indicate that cyclohexane solutions of alkyl aluminum, n‐butyl lithium, and barium alkoxide allow produce polybutadienes with enough amount of 1,4‐trans units to display a regular microstructure that makes them susceptible to experience‐induced crystallization, likewise at a reaction rate similar to that observed for the commercial production of poly(butadiene) with n‐butyl lithium. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Influence of 1,2‐unit contents on retraction behaviors of SBR vulcanizates

Styrene‐butadiene rubber (SBR) has four different repeat units of styrene, cis‐1,4‐, trans‐1,4‐, and 1,2‐uints. Influence of the 1,2‐unit content on the retraction behaviors of SBR vulcanizates reinforced with silica or carbon black was studied. The retraction behaviors were compared in terms of the filler systems and the microstructures of SBR. The silica‐filled vulcanizates containing a coupling agent showed nearly the same retraction behaviors as the carbon black‐filled ones, but the silica‐filled vulcanizates without a coupling agent were recovered slower than the carbon black‐filled ones. The vulcanizates with lower 1,2‐unit content started to recover at lower temperature than that with higher 1,2‐unit content. The recovery rate increased with increase of the 1,2‐unit content of SBR. The experimental results were explained with the polymer‐filler interactions, filler dispersion, glass transition temperature, and modulus. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4707–4711, 2006     

On the structure of polybutadiene: 4. 13C n.m.r. spectrum of polybutadienes with cis-1,4-, trans-1,4- and 1,2-units

¹³C n.m.r. spectra of polybutadienes with different contents of cis-1,4- and 1,2-units are assigned in the resonance region of the cis and trans carbon double bond. The observed signals are assigned to configurational triads.     

Thermoplastic interpenetrating polymer networks based on a poly(styrene-b-butadiene) copolymer and an ionically-terminated polybutadiene ionomer

Thermoplastic interpenetrating polymer networks (IPN) are mixtures of two physically crosslinked polymers. Thermoplastic IPNs were prepared by blending an SBS triblock elastomer with a 1,2-polybutadiene that was ionically-terminated at both ends. The morphologies of these IPNs were studied using differential scanning calorimetry and dynamic mechanical thermal analysis. It was concluded that the ionomer was incompatible with the SBS elastomer, since the T_gs of both the 1,2-polybutadiene from the ionomer and the essentially 1,4-polybutadiene from the SBS component were observable at temperatures that were close to those of the individual components. The addition of the polybutadiene material had, however, an influence on the relaxation processes of the polystyrene blocks. The polystyrene glass transition in the pure SBS copolymer is broadened by the interfacial region between polystyrene and polybutadiene. The low temperature shoulder was much more pronounced when the ion-terminated polybutadiene was present, indicating it has a preference to be located in these interfacial regions. © 1994 John Wiley & Sons, Inc.     

Crystallization kinetics of cis‐1,4‐polybutadiene

The isothermal and nonisothermal crystallization kinetics of cis‐1,4‐polybutadiene has been investigated with respect to the content of cis units and the linearity of the main chain. The rate of spherulite growth increases with chain regularity as the presence of branches as well as segments with different configurations slows the crystallization rate. The major parameter that determines the crystallization rate is the presence in the formulation of heterogeneities that favor the formation of primary nuclei and determine an anticipated onset of crystallization. As the activity of the heterogeneous nuclei depends more on the type and number of foreign particle than on any chain parameter, no straightforward information on the influence of the chain structure on the crystallization rate can be derived by mere calorimetric analysis, at least for analyzed samples. It is only with combined analysis by optical microscopy that comprehensive information on the crystallization kinetics of cis‐1,4‐polybutadiene can be derived. The results reported in this contribution point out the importance, in polymer science, of preferring complementary instrumentation and not limiting experimental investigations to a single technique of analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymerization of 1,3-butadiene with MgCl2-supported cobalt catalysts activated by ordinary alkylaluminums

MgCl₂-supported CoBr₂ catalysts were prepared from mixture of MgCl₂ and CoBr₂L₂ (L = triphenylphosphine or pyridine) in toluene. Polymerization of 1,3-butadiene was conducted over the catalysts combined with ordinary alkylaluminums as cocatalyst. The CoBr₂(PPh₃)₂/MgCl₂ catalyst gave polybutadiene with approximately 80% of 1,2 units, whereas cis-1,4-poly-butadiene was obtained with the CoBr₂(C₅H₅N)₂/MgCl₂ catalyst. Addition of triphenylphospine to the latter catalyst caused a marked increase in the content of 1,2 units. The content of 1,2 units could be thus controlled in the range from 0 to 80% by changing the amount of triphenylphosphine. On the other hand, the CoBr₂(PPh₃)₂/MgCl₂ catalyst with very low content of CoBr₂(PPh₃)₂ hardly displayed any activity. Addition of dimethoxydiphenylsilane to the catalyst gave polybutadiene containing 90 % of 1,2 units with a fairly high activity.     

Butadiene polymerization with a rare earth compound using a magnesium alkyl cocatalyst: 1

High trans polybutadiene was obtained using a catalyst system comprising rare earth compounds plus magnesium dialkyl. The polymer appeared to contain some ‘live’ chain ends and block polymerization and coupling experiments were carried out. High cis polybutadienes formed when aluminium alkyl halides were used as a third catalyst component.     

Synthesis of high molecular weight copolymer of styrene and butadiene bearing high 1,4‐cis butadiene unit from copolymerization with CpTiCl3/methylaluminoxane catalyst

Copolymerization of styrene (St) and butadiene (Bd) with CpTiCl₃/methylaluminoxane (MAO) catalyst in the presence or absence of chloranil (CA) was investigated. The CpTiCl₃/MAO catalyst showed a high activity for the copolymerization of St with Bd. The 1,4‐cis contents in the Bd units for the copolymerization of St and Bd with the CpTiCl₃/MAO catalyst was observed, and the 1,4‐cis content was optimum at a MAO/Ti mole ratio of around 225. The effect of the polymerization temperature on the copolymerization was noted, as was the effect of the 1,4‐cis microstructure in the Bd units for the copolymerization of St and Bd. The addition of CA to the CpTiCl₃/MAO catalyst was found to influence the molecular weight of the copolymer. The high weight‐average molecular weight copolymer (M_w = ca. 50 × 10⁴) consisting of mainly a 1,4‐cis microstructure of Bd units (1,4‐cis = 80.0%) was obtained from the copolymerization with the CpTiCl₃/MAO catalyst in the presence of CA (CA/Ti mole ratio = 1) at 0°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2942–2946, 2003     

Fourier transform near‐infrared and electron spin resonance studies on the crosslinking reaction of liquid carboxylated poly(acrylonitrile‐co‐butadiene) rubber with dicumyl peroxide in dioxane

The crosslinking reaction of liquid carboxylated poly(acrylonitrile‐co‐butadiene) [or nitrile rubber (NBR); acrylonitrile = 10 wt %] with dicumyl peroxide (DCPO) was studied in dioxane by means of Fourier transform near‐infrared spectroscopy (FT‐NIR) and electron spin resonance spectroscopy (ESR). Among the three butadiene units (1,2, cis‐1,4, and trans‐1,4 units) of NBR, only the pendant vinyl group of the 1,2 unit showed an absorption at 6110 cm^?1 from the FT‐NIR examination of dioxane solutions of NBR, 1‐octene, 3,3‐dimethyl‐1‐butene, trans‐2‐octene, cis‐5‐octen‐1‐ol, poly‐cis‐1,4‐butadiene, and poly‐1,2‐butadiene. The crosslinking reaction was followed in situ in dioxane by the monitoring of the disappearance of the pendant vinyl double bond with FT‐NIR. The initial disappearance rate (R₀) of the vinyl group was expressed by R₀ = k[DCPO]^0.9[NBR]^?0.2 (120°C). The overall activation energy of the reaction was calculated to be 20.7 kcal/mol. This unusual rate equation suggests unimolecular termination due to degradative chain transfer and depressed reactivity of the vinyl group caused by crosslinking. ESR study of the reaction mixture revealed that an allyl‐type polymer radical was formed in the reaction, and its concentration increased with time and was then saturated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2095–2101, 2003