Methyl block copolymers with styrene

Preparation and Reactions of S-b-MM. As mentioned in the introduction, we were interested in block copolymers of styrene and alkali metal methacrylates with overall molecular weights of about 20,000 and methacrylate contents on the order of 10 mol%. The preparation of such copolymers by the usual anionic techniques is not feasible. An alternative is to prepare block copolymers of styrene and methacrylic esters by sequential anionic polymerization, followed by a post-polymerization reaction to produce the desired block copolymers. The obvious first choice of methacrylic esters is methyl methacrylate. It is inexpensive, readily available, and its block copolymers with styrene are well-known. In fact, Brown and White have reported the preparation and hydrolyses of a series of S-b-MM copolymers of varying MM content using p-toluenesulfonic acid (TsOH) (6). The resulting methacrylic acid copolymers were easily converted to their sodium carboxylates by neutralization with sodium hydroxide. 

Some of block copolymers with styrene derivatives are also amphiphilic, such as methyl vinyl ether-p-alkoxystyrene [88] and alkyl vinyl ether-p-hydroxystyrene (from p-r-butoxystyrene) [89] (Fig. 6). 

The first method of transformation of living ROMP into controlled/ living ATRP was reported by Matyjaszewski for the preparation of diblock copolymers. Thus, macroinitiators were prepared by ROMP of norbomene (Scheme 5) or dicyclopentadiene and subsequent Wittig-like reactions with /7-(bromomethyl)benzaldehyde. In these cases, the ROMP of norbomene was terminated with a terminating reagent that could also function as an ATRP initiator. Thus, these compounds were used as efficient macroinitiators for homogeneous controlled/ living ATRP to prepare block copolymers with styrene and methyl acrylate (Scheme 6) [21]. 

Thus, performing the activation in the presence of radically polymerizable alkenes leads to the first examples of well-defined AB or ABA-type PVDF-block copolymers with styrene (e, e ), butadiene (f, f, vinyl chloride (g, g ), vinyl acetate (h, h ), methyl acrylate (i, i, i"). and acrylonitrile (j, j ), initiated from both the PVDF halide chain ends. While here Mn2(CO)io simply performs irreversible halide activation, and there is no IDT, control of the block copolymerization can be envisioned by other CRP methods. 

Very well defined block copolymers of styrene, p-methyl styrene, p-tert-butyl styrene and PSX were prepared, as judged by GPC, with molecular weights of over 100,000 g/mole. 

Brown and White employed this approach to prepare block copolymers of styrene and mcthacrylic acid (6). They were able to hydrolyze poly(styrene-b-methyl methacrylate) (S-b-MM) with p-toluenesulfonic acid (TsOH). Allen, et al., have recently reported acidic hydrolysis of poly(styrene-b-t-butyl methacrylate) (S-b-tBM) (7-10). These same workers have also prepared potassium methacrylate blocks directly by treating blocks of alkyl methacrylates with potassium superoxide (7-10). 

Our requirements for certain applications called for the preparation of block copolymers of styrene and alkali metal methacrylates with molecular weights of about 20,000 and methacrylate contents of about 10 mol%. In this report we describe the preparation and reactions of S-b-MM and S-b-tBM. In the course of our investigation, we have found several new methods for the conversion of alkyl methacrylate blocks into methacrylic acid and/or metal methacrylate blocks. Of particular interest is the reaction with trimethylsilyl iodide. Under the same mild conditions, MM blocks are completely unreactive, while tBM blocks are cleanly converted to either methacrylic acid or metal methacrylate blocks. As a consequence of this unexpected selectivity, we also report the preparation of the new block copolymers, poly(methyl methacrylate-b-potassium methacrylate) (MM-b-MA.K) and poly(methyl methacrvlate-b-methacrylic acid) (MM-b-MA). 

Preparation of Block Copolymers. Poly(styrene-b-methyl methacrylate) and poly(styrene-b-t-butyl methacrylate) were prepared by procedures similar to those reported for poly(styrene-b-methyl methacrylate (12,13). Poly(methyl methacrylate-b-t-butyl methacrylate) was synthesized by adaptation of the method published (14) for syndiotactic poly(methyl methacrylate) polymerization of methyl methacrylate was initiated with fluorenyllithium, and prior to termination, t-butyl methacrylate was added to give the block copolymer. Pertinent analytical data are as follows. 

Thus, the synthesis of a styrene-methyl methacrylate block polymer requires that styrene be the first monomer. Further, it is useful to decrease the nucleophilicity of polystyryl carbanions by adding a small amount of 1,1-diphenylethene to minimize attack at the ester function of MMA [Quirk et al., 2000]. Block copolymers of styrene with isoprene or 1,3-butadiene require no specific sequencing since crossover occurs either way. Block copolymers of MMA with isoprene or 1,3-butadiene require that the diene be the first monomer. The length of each segment in a block copolymer is controlled by the ratio of each monomer to initiator. The properties of the block copolymer vary with the block lengths of the different monomers. 

The range of monomers that can be incorporated into block copolymers by the living anionic route includes not only the carbon-carbon double-bond monomers susceptible to anionic polymerization but also certain cyclic monomers, such as ethylene oxide, propylene sulfide, lactams, lactones, and cyclic siloxanes (Chap. 7). Thus one can synthesize block copolymers involving each of the two types of monomers. Some of these combinations require an appropriate adjustment of the propagating center prior to the addition of the cyclic monomer. For example, carbanions from monomers such as styrene or methyl methacrylate are not sufficiently nucleophilic to polymerize lactones. The block copolymer with a lactone can be synthesized if one adds a small amount of ethylene oxide to the living polystyryl system to convert propagating centers to alkoxide ions prior to adding the lactone monomer. 

Macroradicals obtained by the copolymerization of equimolar quantities of styrene and maleic anhydride in benzene or in cumene were also used as initiators to produce block copolymers with methyl methacrylate, ethyl methacrylate, and methyl acrylate. The yields of these block copolymers were less than those obtained with styrene, but as much as 38% of methyl methacrylate present in the benzene solution added to the macroradical to produce a block copolymer. The amount of ethyl methacrylate and methyl acrylate that was abstracted from the solution to form block copolymers was 35 and 20%. 

The formation of block copolymers from styrene-maleic anhydride and acrylic monomers was also indicated by pyrolytic gas chromatography and infrared spectroscopy. A comparison of the pyrograms of the block copolymers in Figure 7 shows peaks comparable with those obtained when mixtures of the acrylate polymers and poly(styrene-co-maleic anhydride) were pyrolyzed. A characteristic infrared spectrum was observed for the product obtained when macroradicals were added to a solution of methyl methacrylate in benzene. The characteristic bands for methyl methacrylate (MM) are noted on this spectogram in Figure 8. 

Among copolymers containing isoprene, AB and ABA block copolymers of styrene and isoprene have been the most studied, but interesting results have also been obtained with copolymers of isoprene and vinylpyridine and of isoprene and methyl methacrylate. 

New macroradicals have been obtained by proper solvent selection for the homopolymerization of styrene, methyl methacrylate, ethyl acrylate, acrylonitrile, and vinyl acetate, and by the copolymerization of maleic anhydride with vinyl acetate, vinyl isobutyl ether, or methyl methacrylate. These macroradicals and those prepared by the addition to them of other monomers were stable provided they were insoluble in the solvent. Since it does not add to maleic anhydride chain ends, acrylonitrile formed a block copolymer with only half of the styrene-maleic anhydride macroradicals. However, this monomer gave excellent yields of block polymer when it was added to a macroradical obtained by the addition of limited quantities of styrene to the original macroradical. Because of poor diffusion, styrene did not add to acrylonitrile macroradicals, but block copolymers formed when an equimolar mixture of styrene and maleic anhydride was added. 

Polyparaphenylenevinylene based macro-initiator 2 was used for NMRP of various monomers (styrene, methyl aciylate, butyl acrylate). From this compound various well defined rod-coil blocks copolymers with polystyrene and polyaciylate based coil blocks have been obtained. Furthermore, in each case, it is possible to random copolymeiize a second monomer for instance chloromethylstiyrene. The first monomer determines mechanical properties and phase transitions of the coil block, for example, bytulacrylate based coils have low Tg and can provide easy processabihty towards thin films. The second monomer (between 5% and 10% in molar ratio) provides the introduction of functional moieties which are necessary for a further modification in order to tune the electronic properties of the copolymer. NMRP from DEH-PPV macroinitiator 2 is schematically presented in Figure 2. 

Effects of addition of a compatibilizing block copolymer, poly(styrene-b-methyl methacrylate), P(S-b-MMA) on the rheological behavior of an immiscible blend of PS with SAN were studied by dynamic mechanical spectroscopy [Gleisner et al., 1994]. Upon addition of the compatibilizer, the average diameter of PS particles decreased from d = 400 to 120 nm. The data were analyzed using weighted relaxation-time spectra. A modified emulsion model, originally proposed by Choi and Schowalter [1975], made it possible to correlate the particle size and the interfacial tension coefficient with the compatibilizer concentration. It was reported that the particle size reduction and the reduction of occur at different block-copolymer concentrations. 

In the subsequent step, a radical polymerization of styrene was carried out with an alkoxyamine-terminated PTHF. Although an increase in conversion with polymerization time was observed, and block copolymers with polydispersities dose to those of the prepolymers were readily formed, the initiation effidency of )-aIkoxyamine PTHF was rather poor. This was attributed to the relativdy slow decomposition and initiation of alkoxyamine attached to unsubstituted methylene groups. Recently, it was reprorted that aUroxyamines containing an unsubstituted carbon atom are very slow to decompose, and that the o -methyl group is essential for the conventional radical polymerization to proceed with a truly Hving character [76]. 

Polyfunctional polybutadienyldilithium anions have been used to prepare ABA block copolymers of butadiene-styreneCl jl5) and butadiene-a-me thy 1 styrene(l )containing rubbery center blocks. Comparable block copolymers of butadiene-a-methyl styrene with a-methyl styrene center blocks have also been reported(19,20). In a similar preparation, Worsfold has capped an isoprene-a-methyl styrene block copolymer with p-divinyl benzene(21). This polymer is capable of further copol3nnerization. 

The preparations by anionic mechanism of A——A type block copolymers of styrene and butadiene can be carried out with the styrene being polymerized first. Use of alkyl lithium initiators in hydrocarbon solvents is usually a good choice, if one seeks to form the greatest amount of c/s-1,4 microstructure [346]. This is discussed in Chap. 4. It is more difficult, however, to form block copolymers from methyl methacrylate and styrene, because living methyl methacrylate polymers fail to initiate polymerizations of styrene [347]. The poly(methyl methacrylate) anions may not be sufficiently basic to initiate styrene polymerizations [345]. 

A bromine-terminated monofunctional poly(rerr-butyl acrylate) resulting from ATRP of rBA catalyzed by the CuBr/At, At,At, iV, lV"-pentamethyldiethylenetriamine (PMDETA) system (initial mole concentration ratios tBA methyl bromopropionate (MBrP) CuBr PMDETA CuBr2 = 50 1 0.5 0.525 0.025, 25% acetone, 60°C conversion = 96% after 6.5 h) was used as macroinitiator for block copolymerization with styrene (St) with the initial mole concentration ratios of St P(rBA) CuBr PMDETA = 100 1 1 1 at 100°C (conversion 94%). The monofunctional bromo-terminated copolymer P(rBA)-A-P(St) formed was subsequently used as a macroinitiator for a further copolymerization with methyl acrylate (MA). The polymerization was also catalyzed by CuBr/PMDETA (initial concentration ratios MA P(rBA-i>-P(St) CuBr PMDETA = 392 1 1 1), under high dilution in toluene and reached 23% monomer conversion after 3.5 h at 70°C. The experimental molecular weight (M ) of the resulting triblock copolymer P(tBA)-fo-P(St)-fr-P(MA) was 24,800 with a PDI = 1.10. Calculate the theoretical M to compare with the experimental value. 

---