Living polystyrene in THF

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. 

To ensure a reliable extrapolation to c = 0 for scarcely dissociated pairs, i.e. for 1(T7, it is imperative to extend the measurements to extremely low concentrations of the salt, at least down to 10-6 M. Hie values of the salts of living polystyrene in THF are of this order of magnitude. Since traces of moisture, alcohol, 02, etc., destroy them, a special dilution procedure is needed to avoid introduction of any impurities that could vitiate the results. Such a procedure is described in Ref. 264. 

Figure 5 Plots of the propagation constant, kp, for salts of living polystyrene in tetrahydrofuran (THF)vs. 1/[LE]. From Szwarc, M.Adv. Polym. Sc/,1983,49,1-177 reprinted with kind permission from Springer Science+Business Media B.V.

In contrast to the behaviour of living polystyrene, the slow termination of living polymethyl methacrylate is least pronounced inDME, more in THF, and is most perturbing in THP 55). It seems that in THF the termination is faster for Na+ than for Cs +. ... 

Polystyrene was prepared by the anionic polymerisation of styrene in toluene plus THF mixtures (4 1 volume ratio) using n-butyl lithium as initiator. After removing a sample for analysis at this stage, the remainder of the living polystyrene was reacted with a five molar excess of trichloromethylsilane for 15 min and then excess methanol introduced. The methoxy-terminated polystyrene was freeze-dried from dioxan. The method described here essentially follows the route proposed by Laible and Hamann (6). 

In this case some of the Sll silica was freeze-dried and degassed at 10-3 Torr and 150°C and then reacted with trichloromethylsilane in the vapour phase this replaced the surface hydroxyl groups by chloro groups. The particles were then redispersed (with the aid of ultrasonics) in a 4 1 volume ratio toluene THF solvent mixture. "Living" polystyrene (PS19), in a similar solvent mixture was then introduced and the grafting reaction allowed to proceed for 24 hr at room temperature. 

Preparation of the Living" Polystyrene. 18 g of the living polymer was prepared by standard anionic polymerization using n-butyl lithium. The reaction was carried out by the dropwise addition of 20 ml of styrene to 5 ml of the initiator solution in 150 ml of neat THF at -78°C. The styrene drip was adjusted to take approximately 30 min for completion and then the reaction was allowed to stir for two hours before the grafting reaction with mesylated lignin was carried out. The number average molecular weight of the polystyrene, as determined by HPSEC, was 9500 with polydispersity of 1.2. 

In the present communication the strontium salt of one-ended living polystyrene (SrS2) was studied In tetrahydrofuran (THF) and tetrahydropyran (THP), In order to check the validity of the triple Ion mechanism. The Ionic dissociation of SrS2 In THP was expected to be smaller than In THF and therefore It was thought that perhaps a contribution to the propagation from species, other than the free S anions, would be detectable. 

Strontium salt of one-ended living polystyrene (SrS2) in THF... 

To obtain the absolute rate constants one competes the termination with the propagation. Since the rate constant for propagation of living polystyrene-, Na+ in THF was determined in our laboratory at 25° C to... 

The first block (polybutadiene or polystyrene) is prepared by anionic polymerization, under high vacuum, in THF dilute solution (less than 5%), at low temperature (—70 °C) with cumylpotassium as initiator. Then, the living polymer is transformated into a hydroxylated polymer (PV—OH) by addition of ethylene oxide under vacuum, or into a carboxylated polymer (PV-COOH) by addition of carbon dioxide under vacuum. 

Figure 1. Linear dependence of the observed propagation constant, kD, of living polystyrene polymerization on [living polymers] 11 for Li+y Na+, K+, Rb+, and Cs+ salts in THF at 25°C.

Other multifunctional initiators include star polymers prepared from initiators via living radical or other living polymerizations. In particular, all of the star polymers via metal-catalyzed living polymerization, by definition, carry a halogen initiating site at the end of each arm, and thus they are potentially all initiators. Thus, star-block copolymers with three polyisobutylene-Mock-PMMA arms and four poly-(THF) -A/oc/F polystyrene or poly(THF)-Woc/c-polysty-rene-Wock-PMMA were synthesized via combination of living cationic and copper-catalyzed living radical polymerizations.381,388 Anionically synthesized star polymers of e-caprolactone and ethylene oxide have... 

It was shown that 2 mol of the living polymer reacts rapidly with the DPE derivatives to form the dilithium adduct in hydrocarbon solvents, whereas in THF monoaddition is reported.7>26>78 80 This reaction was monitored by UV—visible spectroscopy. The analysis revealed that the stoichiometric addition of PSLi was quantitative. However, PDDPE exhibited less tendency to form the diadduct both in polar and nonpolar solvents. This behavior can be attributed to the better delocalization of the negative charge in the para than in the meta isomer. Mainly, low molecular weight polystyrenes have been used for these studies. 

Preparation of Macromolecular Dioxolenium Salts. Living polystyrene prepared by the polymerization of styrene in THF with a-methylstyrene tetramer dianion reacted with a 2.1-molar amount of ethylene oxide for three hours at room temperature a 6.6-molar amount of adipoyl chloride was added, and the mixture was stirred for 20 horns a 20-molar amount of ethylenebromohydrin was added. This mixture was stirred for 44 hours. The bromoethylated polystyrene was precipitated in excess methanol and freeze-dried from benzene in a vacuum system. A 1-nitropropane solution of polystyrene dioxolenium salt was prepared by reaction of bromoethylated polystyrene with silver perchlorate in 1-nitropropane. Silver bromide was removed from the reaction mixture by filtration. Molecular weight of the product was measured by a vapor-pressure osmometer it was 1910 for living polystyrene and 5190 for the bromoethylated polystyrene. Bromine analysis of the bromoethylated polystyrene showed 67.9% of the calculated value. 

Blocks. The synthesis of block copolymers were attempted in the following manner. "Living" polystyrene was first prepared by conventional anionic techniques using n-BuLi as the initiator in THF at -78 C. In initial experiments, this polystyryl lithium product was treated with AICI3 to afford a polystyryl A1 species which could be capable of alkylating Ti(0Bu)4. However, we find it to... 

Blocks. The IR spectra of films cast from the soluble, colored THF fraction are consistent with the presence of both polystyrene and (CH)X segments, although do not prove the existence of a block copolymer. The required proof is derived from GPC studies (Figure 3). A sample of homopolystyrene (taken from the "living" polystyrene prior to reaction with Ti(0Bu)4) was found to have an Mjj of 27,730. Also, a sample of homopolystyrene (from the THF/acetone extraction, treated with Br2 in THF) yielded an Mjj of 27,470 indicating that the extraction does not merely fractionate the poly-... 

Figure 3. GPC traces for aliquot of "living" polystyrene (starting PS), PS extracted from acetylene/styrene block material (soluble in 10% THF/acetone), and brominated acetylene/styrene block (insoluble in 10%, THF/acetone).

A structure resembling that of the dumbbell polymers was made by Frechet et al. In this case the connector is linked with polyether dendritic groups [272, 273]. The synthetic approach involved the preparation of a difunctional polystyrene chain in THF using potassium naphthalenide as initiator. The living polymer was end-capped with 1,1-diphenylethylene (DPE) to reduce its nucle-ophilicity and avoid side reactions with benzylic halomethyl groups. Addition of the fourth generation dendrimer [G-4] -Br led to the final product (Scheme 100). 

Fig. 2. The apparatus used by Szwarc et al. to demonstrate die living nature of anionically initiated polystyrene in a homogeneous THF solution...

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