Cyclohexane styrene polymerization solvent

Most research into the study of dispersion polymerization involves common vinyl monomers such as styrene, (meth)acrylates, and their copolymers with stabilizers like polyvinylpyrrolidone (PVP) [33-40], poly(acrylic acid) (PAA) [18,41],poly(methacrylicacid) [42],or hydroxypropylcellulose (HPC) [43,44] in polar media (usually alcohols). However, dispersion polymerization is also used widely to prepare functional microspheres in different media [45, 46]. Some recent examples of these preparations include the (co-)polymerization of 2-hydroxyethyl methacrylate (HEMA) [47,48],4-vinylpyridine (4VP) [49], glycidyl methacrylate (GMA) [50-53], acrylamide (AAm) [54, 55], chloro-methylstyrene (CMS) [56, 57], vinylpyrrolidone (VPy) [58], Boc-p-amino-styrene (Boc-AMST) [59],andAT-vinylcarbazole (NVC) [60] (Table 1). Dispersion polymerization is usually carried out in organic liquids such as alcohols and cyclohexane, or mixed solvent-nonsolvents such as 2-butanol-toluene, alcohol-toluene, DMF-toluene, DMF-methanol, and ethanol-DMSO. In addition to conventional PVP, PAA, and PHC as dispersant, poly(vinyl methyl ether) (PVME) [54], partially hydrolyzed poly(vinyl alcohol) (hydrolysis=35%) [61], and poly(2-(dimethylamino)ethyl methacrylate-fo-butyl methacrylate)... 

Recently, Kolishetti and Faust [89] reported investigations of the polymerizations of p-methylstyrene in the presence of isobutylene, styrene, p-chlorostyrene, and 1,3 butadiene at —40°C. The polymerizations were carried out in a 50/50 mixture of CH2CI2 with methyl cyclohexane as the solvent and a weak Lewis acid, SnBr2Cl2. The reactions were conducted by mono additions of each monomer that was followed by instantaneous terminations. The results showed that p-methylstyrene is roughly 3.8 times more reactive than isobutylene, 4.8 times more reactive than styrene, 7.2 times more reactive than p-chlorostyrene, and 100 times more reactive than butadiene. 

The two monomers of major interest, styrene and ethylene, are well known and details can be found on all aspects of their technology elsewhere. Poly(ethylene-co-styrene) is primarily produced via solution polymerization techniques using metallocene catalyst/co-catalyst systems, analogous to the production of copolymers of ethylene with a-olefin monomers. Solvents that can be employed include ethyl-benzene, toluene, cyclohexane, and mixed alkanes (such as ISO PAR E, available from Exxon). The thermodynamic properties of poly(ethylene-co-styrene), including solvent interactions and solubility parameter assessments, are important factors in relation to polymer manufacture and processing, and have been reported by Hamedi and co-workers (41). 

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Transfer constants for polystyrene chain radicals at 60° and 100°C, obtained from the slopes of these plots and others like them, are given in the second and third columns of Table XIII. Almost any solvent is susceptible to attack by the propagating free radical. Even cyclohexane and benzene enter into chain transfer, although to a comparatively small extent only. The specific reaction rate at 100°C for transfer with either of these solvents is less than two ten-thousandths of the rate for the addition of the chain radical to styrene monomer. A fifteenfold dilution with benzene was required to halve the molecular weight, i.e., to double l/xn from its value (l/ rjo for pure styrene (see Fig. 16). Other hydrocarbons are more effective in lowering the degree of polymerization through chain transfer. 

Free radical copolymerizations of the alkyl methacrylates were carried out in toluene at 60°C with 0.1 weight percent (based on monomer) AIBN initiator, while the styrenic systems were polymerized in cyclohexane. The solvent choices were primarily based on systems which would be homogeneous but also show low chain transfer constants. Methacrylate polymerizations were carried out at 20 weight percent solids... 

On each of the curves, the points at lowest X represent swelling in cyclohexane, the next in tetrahydrofuran and the last in benzene. In all cases, the samples were swollen in the pure solvent. The curves are reproduced from Figure 13 of Reference 19. The networks were made from anionically polymerized polyr-styrene using a bifunctional initiator crosslinked subsequently by divinyl benzene. The curves correspond to different ratios of divinyl benzene (DVB) per polystyrene living end (LE),... 

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

However, the polymerization of styrene in hydrocarbon solvents has been shown (8,10) to exhibit a 1/2 order dependency on polystyryllithium concentration. Hence, the concept that only the unassociated chain ends are reactive may be valid for this system since association studies have shown (1 2. 2 ) that the polystyryllithium chain ends are associated as dimers. (Szwarc has stated (11) that polystyryllithium is "probably tetrameric in cyclohexane." This assessment, though, failed to consider the light scattering results (J7, ) of Johnson and Worsfold). 

The second process utilizes the two stage method in which half of the styrene added at the beginning of the reaction followed by all the 1,3-hutadiene and then the remaining half of styrene is added. All these polymerization processes are done in cyclohexane since homopolystyrene with or without lithium terminated is insoluble in all straight chain or branched hydrocarbon solvents such as heptane, hexane petroleum ethers or the branched derivatives. 

From the Table IV, it also shows that the low styrene content in the copolymer may relate to the polymerization temperature. As the polymerization temperature was increased from 5° to 70°C, the styrene content of the butadiene-styrene copolymer decreased from 21.7% to 9.1%, respectively. The decreasing in styrene content at higher temperature is consistent with the paper reported by Adams and his associates (16) for thermal stability of "living" polymer-lithium system. In Adams paper, it was concluded that the formation of lithium hydride from polystyryllithium and polybutadienyllithium did occur at high temperature in hydrocarbon solvent. The thermal stability of polystyryllithium in cyclohexane is poorer than polybutadienyllithium. From these results, it appears that the decreasing in styrene content in lithium morpholinide initiated copolymerization at higher temperature is believed to be associated with the formation of lithium hydride. 

As shown In Figure 4, the rate of polymerization of styrene was retarded by good nonvlscous solvents such as benzene, cyclohexane, and octane whose solubility parameters (6) were within 1.5H of that of polystyrene at styrene to additive ratios of 3 to 1. The absolute rates were slightly Increased In poorer nonvlscous solvents such as heptane and hexane and were fastest In viscous nonsolvents such as dllsoctyl phthalate and Nujol. Rate studies Indicated a Rp dependency on [E] substantially greater than unity for the styrene emulsion systems modified with viscous poor solvents. 

Materials. Phillips polymerization grade cyclohexane and butadiene were used. Styrene was a commercial polymerization grade. Solvent was dried over activated Alcoa H151 alumina, and monomers were dried over activated Kaiser 201 alumina before they were transferred to the charge tanks. n-Butyllithium and sec-butyl lithium were purchased from Lithium Corporation of America. Chiorosilanes were vacuum distilled before use. 

Anionic polymerization was utilized again in studies of thermodynamics of styrene propagation185. The equilibrium concentration of that monomer is exceedingly low at ambient temperature, and hence the experimentation required elevated temperatures. However, living polystyrene in THF is rapidly destroyed at those temperatures. To avoid these difficulties, living polystyrene formed by BuLi initation in cyclohexane or benzene was used in the studies. The results are presented in Fig. 5 and in Table 1. The effect of the solvent s nature on Me is revealed by these data. 

As discussed elsewhere in this review, Lewis bases such as tetrahydrofuran are known to promote disaggregation of polymeric organolithium speciesThus, in the presence of excess tetrahydrofuran, both poly(styryl)lithium and poly(isopre-nyl)lithium would be expected to be unassociated (or at least much less associated). Therefore, in the presence of sufficient tetrahydrofuran, the carbonation reaction would take place with unassociated organolithium chain ends and ketone formation (Eq. (73)) would only be an intermolecular reaction (rather than an essentially intramolecular reaction as in the case with the aggregated species) competing with carbonation. In complete accord with these predictions, it was found that the carbonation of poly(styryl)lithium, poly(isoprenyl)lithium, and poly(styrene-h-isoprenyl)lithium in a 75/25 mixture (by volume) of benzene and tetrahydrofuran occurs quantitatively to produce the corresponding carboxylic add chain ends. The observation by Mansson that THF has no apparent influence was complicated by the use of methyl-cyclohexane, which is a Theta solvent for poly(styrene) (60-70 °C) furthermore. 

The above approach of using a diluent of an intermediate thermodynamic quahty during the polymerization of DVB has been intensively examined and, indeed, resulted in materials with enhanced proportions of mesopores. In order to create a rigid polymer of desired porosity, DVB (usually more than 30% in its mixture with styrenic co-monomers) must be copolymerized in the presence of a sufficient amount of a poor diluent (usually 100% or more of the volume of the co-monomers). Of crucial importance is the nature of the poor solvent. Besides cyclohexane, mixtures of a thermodynamically good solvent (ethylene dichloride, toluene, etc.) with precipitating media (hexane, octane, isooctane, higher aliphatic alcohols, etc.), taken in an appropriate proportion, can be applied. Microphase separation during the suspension copolymerization of such a mixture should take place when the major part of the co-monomers has converted into polymer. 

SBR may also be produced by anionic solution polymerization of styrene and butadiene with alky-llithium initiator (e.g., butyllithium) in a hydrocarbon solvent, usually hexane or cyclohexane. In contrast to emulsion SBR, which may have an emulsifier (soap) content of up to 5% and nonrubber materials sometimes in excess of 10%, solution SBR seldom has more than 2% nonrubber materials in its finished form. Solution SBR has a narrower molecular weight distribution, higher molecular weight, and higher cis-1,4-polybutadiene content than emulsion polymerization SBR. 

Figure 20-6. Dependence of the reciprocal number-average degree of polymerization on dilution when styrene is polymerized in diethyl benzene, ethyl benzene, toluene, benzene, or cyclohexane at 100° C S = AX, solvent M, monomer. (After G. V. Schulz, A. Dinglinger, and E. Husemann.)...

Polystyrene can be produced by dissolving the monomer styrene in the solvent cyclohexane at 25 C. During polymerization the temperature increases to 85 °C. The dependence of vapor pressure of cyclohexane on temperature is given by ... 

Styrenic block copolymers are made by anionic living polymerization using sec-butyl lithium as a preferred initiator in non polar solvents such as cyclohexane or toluene.In the normal sequential polymerization, the initiator reacts with a molecule of styrene to form a polystyryol lithium species which then propagates with transfer of the initiator anion to the active chain end. 

In this paper we describe the preparation and the properties of the title triblock with a low vinyl-1,2 (or 3,4 in the case of polyisoprene) polydiene center block. Two different solvent systems were used as the media of polymerization. In the first system, the polydiene center block was prepared in cyclohexane. Alpha-methylstyrene (AMS) and a polar solvent tetrahydrofuran (THF) were then added. This was followed by a slow and continuous styrene addition to complete the end block preparation. In the second system, AMS itself was used as the solvent with no other solvent added. The second solvent system enabled us to use several different polymerization schemes. The center block could be prepared first to form a tapered or untapered triblock. The end block copolymer also could be prepared first and then the diblock and then coupled to form a tri- or a radial block polymer. Instead of coupling, more styrene could be added to complete the triblock. All these different routes of preparation were used in this work. 

The metaUation reaction of p-MS-terminated polypropylene (PP-t-p-MS) (I in Scheme 11) was carried out under heterogeneous reaction conditions by suspending the powder form of PP in s-BuLi/TMEDA/cyclohexane solution. To examine the efficiency of the reaction, some of the metallated polymer (II) was terminated with Cl-Si(CH3)3 and examined by H NMR measurement, showing about 85% conversion. Most of the Hthiated PP-t-p-MS (II) was used to prepare diblock copolymers. By mixing polymer powder with styrene monomer in cyclohexane solvent, the living anionic polymerization took place to produce PP-6-PS diblock copolymer (III). After the reaction, the product was vigorously extracted by refluxing THF to... 

The range of solvents that can be used for the living anionic polymerization of styrene is limited due to the highly reactive anionic initiators and the propagating chain-end carbanions. The solvents of choice are mainly aliphatic and aromatic hydrocarbons and ethers. Typically, the following two polymerization conditions are used in the living anionic polymerization of styrene. In the first condition, the polymerization is carried out in nonpolar hydrocarbon media such as cyclohexane, benzene, toluene, and similar hydrocarbons at... 

---