Styrene MMA block copolymer

The additional complexity present in block copolymer synthesis is the order of monomer polymerization and/or the requirement in some cases to modify the reactivity of the propagating center during the transition from one block to the next block. This is due to the requirement that the nucleophilicity of the initiating block be equal or greater than the resulting propagating chain end of the second block. Therefore the synthesis of block copolymers by sequential polymerization generally follows the order dienes/styrenics before vinylpyridines before meth(acrylates) before oxiranes/siloxanes. As a consequence, styrene-MMA block copolymers should be prepared by initial polymerization of styrene followed by MMA, while PEO-MMA block copolymers should be prepared by... 

A different approach to obtain styrene/MMA block copolymers involves the use of bifimctional initiators containing thermal-labile azo and photo-labile benzoin moieties [139]. As a first step, prepolymers are prepared by thermal decomposition of the azo moiety in the presence of one monomer. These photoactive... 

Fig. 1 Molar mass distribution with overlaid chemical composition distribution of a styrene-MMA block copolymer with poor block formation.

Fig. 9. Simultaneous determination of molar mass and chemical composition distributions of a complex styrene/MMA block copolymer using GPC in combination with Rl and UV detection.

Figure 9 shows the molar mass distribution of a styrene/MMA block copolymer as measured using R1 and UV detection. The R1 responds to the styrene and MM A units, whereas the UV tuned to 260 nm predominantly picks up the presence of styrene in the copolymer. After detector calibration, the styrene and MMA content in each fraction can be measured. The MMA content distribution (black solid line) is superimposed on the MWD of the product in Fig. 9. It is obvious that the MMA content is not constant throughout the MWD, but continuously increases with the molar mass. The trimodal MWD itself shows only the presence of three different species. The MMA content information clearly reveals that the copolymerization process did not produce the block structure, but that the MMA was added to styrene chains of different molar mass.

The resulting poly(styrene), which is expected to have tertiary amine groups attached at each end of the polymer chain, due to the well established termination mechanism by radical-radical combination, are used, under UV irradiation, in conjunction with 9-fluorenone as a photo-redox system for the free radical polymerization of MMA to yield MMA/St/MMA block copolymers (Scheme 37) ... 

MMA and styrene grafted onto an acrylic elastomer AN-b-MMA block copolymer... 

To extend the )plications of LC-NMR, we have further examined the compositions and blockiness of various polymer mixtures, including pBA and polybutadiene, where 1,4-butadiene, 1,2-butadiene and BA were identified by their unique H chemical shifts at tqrproximately 5.35, 4.95 and 3.98 ppm, respectively. In reverse-phase HPLC with the same solvent gradient conditions as above, homopolymer pBA and polybutadiene eluted at 21.76 and 34.20 min., respectively. TTie random copolymers of p(MMA/BA) and p(MMA/Sty) both eluted between 8 and 18 minutes. Owing to their hydrophobicity, the hi er the percentage of BA and styrene in the copolymer, the longer the retention time. Figure 5 illustrates the LC separation of pMMA, pBA, p(MMA/BA) and p(BA-b-MMA) by a reverse-phase column. A comparison of p(MMA/BA) random copolymer (retention time 13.9 min.) to p(BA-b-MMA) block copolymer (retention time 18.3 min.) with similar composition shows that the block copolymer interacted more with the C-18 stationary phase and eluted at a later time. This result demonstrated that the retention of p(MMA/BA) copolymer by reverse-phase LC is predominately influenced by die pBA portion of dre copolymer. The block copolymer, which mimics the homopolymer pBA, is mote hydrophobic and retained more on die C18 colunm than the random copolymer. The excellent LC separation permits us to quantitatively determine... 

P(HB-b-I-S) Block copolymer of hydrogenated butadiene, isoprene, and styrene P(S-b-MMA) Block copolymer of styrene and methyl methacrylate PA Polyamide... 

As simple example, MALDI-tof-ms has been used to study the number of a-methyl styrene (a-MeSty) repeat units in SRM1487, a narrow MMD PMMA NIST standard reference material of about 6300 g/mol (62). Here, the major copolymer component is MMA and a-MeSty is the minor component. The a-MeSty is, in fact, part of the initiator for this polymer and the material is either a MMA styrene MMA triblock copolymer or a styrene MMA diblock copolymer, with the a-MeSty block length containing 0-6 a-MeSty. 

Recently a universal alkoxyamine initiator (16) was reported that allows LFRP of monomers other than styrene. This new alkoxyamine was discovered utilizing high speed combinatorial synthesis techniques. It has been used to make styrene-butadiene, S-BA, and S-MMA block copolymers directly without the need for tandem polymerization techniques (258). 

The TG profiles of vinyl triethoxy silane-methyl methacrylate (VTES-MMA) copolymers in N2 have been reported to be similar to that of PMMA [a.l85]. However, the initial decomposition temperature (IDT) of the copolymers decreased with increasing VTES content in the copolymer. This behaviour was attributed to the decrease in the molecular weight of these copolymers during degradation. A similar tendency for TG was also reported for styrene-siloxane block copolymers synthesised with a living anionic initiator [a.l86]. 

The oxocarbenium perchlorate C(CH20CH2CH2C0+C104 )4 was employed as a tetrafunctional initiator for the synthesis of PTHF 4-arm stars [146]. The living ends were subsequently reacted either with sodium bromoacetate or bromoisobutyryl chloride. The end-capping reaction was not efficient in the first case (lower than 45%). Therefore, the second procedure was the method of choice for the synthesis of the bromoisobutyryl star-shaped macroinitiators. In the presence of CuCl/bpy the ATRP of styrene was initiated in bulk, leading to the formation of (PTHF-fc-PS)4 star-block copolymers. Further addition of MMA provided the (PTHF-fr-PS-fc-PMMA)4 star-block terpolymers. Relatively narrow molecular weight distributions were obtained with this synthetic procedure. 

By contrast, much of the work performed using ruthenium-based catalysts has employed well-defined complexes. These have mostly been studied in the ATRP of MMA, and include complexes (158)-(165).400-405 Recent studies with (158) have shown the importance of amine additives which afford faster, more controlled polymerization.406 A fast polymerization has also been reported with a dimethylaminoindenyl analog of (161).407 The Grubbs-type metathesis initiator (165) polymerizes MMA without the need for an organic initiator, and may therefore be used to prepare block copolymers of MMA and 1,5-cyclooctadiene.405 Hydrogenation of this product yields PE-b-PMMA. N-heterocyclic carbene analogs of (164) have also been used to catalyze the free radical polymerization of both MMA and styrene.408... 

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

In this review, synthesis of block copolymer brushes will be Hmited to the grafting-from method. Hussemann and coworkers [35] were one of the first groups to report copolymer brushes. They prepared the brushes on siUcate substrates using surface-initiated TEMPO-mediated radical polymerization. However, the copolymer brushes were not diblock copolymer brushes in a strict definition. The first block was PS, while the second block was a 1 1 random copolymer of styrene/MMA. Another early report was that of Maty-jaszewski and coworkers [36] who reported the synthesis of poly(styrene-h-ferf-butyl acrylate) brushes by atom transfer radical polymerization (ATRP). 

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. 

Difunctional initiators such as sodium naphthalene are useful for producing ABA, BABAB, CAB AC, and other symmetric block copolymers more efficiently by using fewer cycles of monomer additions. Difunctional initiators can also be prepared by reacting a diene such as /n-diisoprope ny I benzene or l,3-bis(l-phenylethenyl)benzene with 2 equiv of butyl-lithium. Monomer B is polymerized by a difunctional initiator followed by monomer A. A polymerizes at both ends of the B block to form an ABA triblock. BABAB or CABAC block copolymers are syntehsized by the addition of monomer B or C to the ABA living polymer. The use of a difunctional initiator is the only way to synthesize a MMA-styrene-MMA triblock polymer since MMA carbanion does not initiate styrene polymerization (except by using a coupling reaction—Sec. 5-4c). 

Abbreviations coiX-V] = copolymers of X and Y colX-b-Yl = block copolymers of poly X and poly Y ST = styrene MA = methyl acrylate MMA = methyl methacrylate AN = acrylonitrile BD = butadiene LR (liquid rubbers) = a, cj-polybutadiene-diols and -dicarboxylic acids Cell-Ac = cellulose acetate Cell-N02 = cellulose nitrate. 

Complete thermolysis of the azo groups in polyazoesters 56,61) in the presence of monomeric styrene leads to block copolymers of an (AB) -type, whereas, when the added monomer is one that tends to terminate via disproportionation (e.g. MMA), the block copolymer products are of an ABA- or an AB-type ... 

Sheppard and Mac Leay71 73> synthesised a block copolymer from I (see below) and styrene and MM A by thermolysis of the less stable azo group adjacent to the nitrile moiety in the presence of styrene and subsequent thermolysis of the more stable azo group in the presence of monomeric MMA. 

Subsequent polymerization of styrene with these MMA prepolymers as initiators leads to block copolymers of an ABA-type due to the tendency of the growing polystyrene chains to terminate by combination ... 

In contrast to those block copolymers synthesised from styrene in bulk, those synthesised from isoprene and butyl acrylate in emulsion or solution were contaminated by only small amounts of homopolymer. Furthermore, it should be noted that Piirma et al. 74 7S) have turned to the reverse reaction order for preparing poly(styrene-b-MMA), i.e. they synthesised the prepolymer using an azo initiation and the subsequent block copolymer via a peroxide redox initiation. 

Rimmer [118] and Caffetera [119] focused their studies on the reactivity of polymers bearing double bonds in order to synthesize macroinitiators able to give block copolymers. These authors copolymerized monomers such as methyl methacrylate (MMA) or styrene (St) with 2-3 dimethyl butadiene giving copolymers presenting the structure shown in Scheme 36 with... 

It was also found that the polystyrene-b-PDMS block copolymers were not only effective at stabilizing styrene polymerizations in C02, but also in stabilizing MMA polymerizations. When using a polystyrene-b-PDMS block copolymer as the stabilizer the resulting PMMA was recovered in 94.1% yield with a Mn = 1.8 x 10 g/mol and a PDI = 2.8. The particles obtained are much smaller and more polydisperse than the particles obtained when using poly(FOA) homopolymer as the stabilizer (particle size = 1.55 - 2.86 pm vs. 0.23 pm and particle size distribution = 1.05 vs. 1.46). 

Various methacrylic-styrene copolymers were prepared in which the reactivity of methacrylate monomers used in the first step decreases in the order MM A > BuMA > benzyl methacrylate. For instance, the bulk polymerization of MMA with such an aromatic azo compound proceeds via a living radical mechanism and the sterically crowded C-C(C6H5)3 terminal bond of polymethacrylate 37 can be cleaved thermally to produce a,co-diaromatic PMMA-h-PS block copolymers in 48-72% yield. 

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