Block copolymers styrene derivatives

Styrenk Block Copolymers. Styrenic TPEs are copolymers whose molecules have the S-D-S structure, where S is a hard segment of polymerized styrene or styrene derivative, and D is a soft central segment of polymerized diene or hydrogenated diene units. Polybutadiene (B), polyisoprene (I), and polyethylenebutylene (EB) are the most commonly used rubbery segments (D). Structures for these triblock copolymers are represented as follows ... 

Polyall lene Oxide Block Copolymers. The higher alkylene oxides derived from propjiene, butylene, styrene (qv), and cyclohexene react with active oxygens in a manner analogous to the reaction of ethylene oxide. Because the hydrophilic oxygen constitutes a smaller proportion of these molecules, the net effect is that the oxides, unlike ethylene oxide, are hydrophobic. The higher oxides are not used commercially as surfactant raw materials except for minor quantities that are employed as chain terminators in polyoxyethylene surfactants to lower the foaming tendency. The hydrophobic nature of propylene oxide units, —CH(CH2)CH20—, has been utilized in several ways in the manufacture of surfactants. Manufacture, properties, and uses of poly(oxyethylene- (9-oxypropylene) have been reviewed (98). 

Thermoplastic block copolymers were used for pressure-sensitive and hot-melt rubber adhesives as from the middle sixties. These adhesives found application in packaging, disposable diapers, labels and tapes, among other industrial markets. The formulation of these adhesives generally includes an elastomer (generally containing styrene endblocks and either isoprene, butadiene or ethylene-butylene midblocks) and a tackifier (mainly a rosin derivative or hydrocarbon resin). 

Short fiber reinforcement of TPEs has recently opened up a new era in the field of polymer technology. Vajrasthira et al. [22] studied the fiber-matrix interactions in short aramid fiber-reinforced thermoplastic polyurethane (TPU) composites. Campbell and Goettler [23] reported the reinforcement of TPE matrix by Santoweb fibers, whereas Akhtar et al. [24] reported the reinforcement of a TPE matrix by short silk fiber. The reinforcement of thermoplastic co-polyester and TPU by short aramid fiber was reported by Watson and Prances [25]. Roy and coworkers [26-28] studied the rheological, hysteresis, mechanical, and dynamic mechanical behavior of short carbon fiber-filled styrene-isoprene-styrene (SIS) block copolymers and TPEs derived from NR and high-density polyethylene (HOPE) blends. 

By employing anionic techniques, alkyl methacrylate containing block copolymer systems have been synthesized with controlled compositions, predictable molecular weights and narrow molecular weight distributions. Subsequent hydrolysis of the ester functionality to the metal carboxylate or carboxylic acid can be achieved either by potassium superoxide or the acid catalyzed hydrolysis of t-butyl methacrylate blocks. The presence of acid and ion groups has a profound effect on the solution and bulk mechanical behavior of the derived systems. The synthesis and characterization of various substituted styrene and all-acrylic block copolymer precursors with alkyl methacrylates will be discussed. 

Various substituted styrene-alkyl methacrylate block copolymers and all-acrylic block copolymers have been synthesized in a controlled fashion demonstrating predictable molecular weight and narrow molecular weight distributions. Table I depicts various poly (t-butylstyrene)-b-poly(t-butyl methacrylate) (PTBS-PTBMA) and poly(methyl methacrylate)-b-poly(t-butyl methacrylate) (PMMA-PTBMA) samples. In addition, all-acrylic block copolymers based on poly(2-ethylhexyl methacrylate)-b-poly(t-butyl methacrylate) have been recently synthesized and offer many unique possibilities due to the low glass transition temperature of PEHMA. In most cases, a range of 5-25 wt.% of alkyl methacrylate was incorporated into the block copolymer. This composition not only facilitated solubility during subsequent hydrolysis but also limited the maximum level of derived ionic functionality. 

Styrene copolymer foams, 23 404 Styrene copolymers, 23 366-367 properties of, 10 206t Styrene derivative polymers, 23 367-368 Styrene derivatives, 23 348-355 Styrene-diene block copolymers, 14 251 Styrene-divinylbenzene copolymers,... 

Block copolymers such as styrene-butadiene-styrene (SBS) and its hydrogenated versions (SEBS), along with polyester-polyether block copolymers, can also be used to improve PBT impact. The SEBS and SBS copolymers [47], and especially their functionalized, grafted derivatives [48], show surprisingly good affinity for the polyester. 

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. 

It is also possible to introduce polymerizable groups at the focal point of dendritic macromolecules and a number of authors have demonstrated the synthesis of novel hybrid dendritic-linear block copolymers by this methodology [69-73]. Initial experiments in the use of the dendritic macromonomers involved the preparation of a series of polyether dendrimers, such as the third generation derivative, 37, which contains a single styrene at its focal point [74]. Copolymerization of 37 with styrene then affords a hybrid block copolymer, 38, in which... 

So far the discussion was focused on copolymers derived from a mixture of styrene and a diene. In view of the "living" nature of organolithium polymerization, it is also possible to synthesize block polymers in which the sequence and length of the blocks are controlled by incremental (or sequential) addition of monomersr This general method of preparing block polymers is readily adaptable to commercial production, and, indeed, a number of block copolymers are manufactured this way. Those that have received the most attention in recent years are the diene-styrene two-phase... 

A copolymer derived from monomers comprising a mixture of high density poly(ethylene) (HDPE), a copolymer of ethylene/methacrylic acid, and a synthetic block copolymer rubber such as styrene/butadiene, and... 

Block copolymers of e-CL with D,L-lactide, styrene, or butadiene have been synthesized using these initiators. Efficient and versatile initiators based on a,(3,y,6-derivatives of tetraphenylporphinato-aluminum for the polymerization of e-CL, (3-lactones, 6-lactones, and lactides have been reported [99,100]. 

Nearly at the same time, Johnson and Young reported a similar system for the polymerization of -butyl vinyl ether with iodine, and called the process a pseudoliving polymerization [55], Also, Pepper suggested that the active centers in polystyrene derived from perchloric acid might have a long lifetime at a very low temperature [32,50], and later obtained block copolymers of styrene with /< r/-butylazyridine by a sequential polymerization from the perchlorate-initiated polystyrene end [56]. 

Thus, how should block copolymers between styrene and a vinyl ether be prepared Starting with styrene or with a vinyl ether In the former system, the propagating styryl cation is intrinsically more reactive but present at much lower concentration. A rough estimate of the ratio of cation reactivities is = 103 but the ratio of carbocations concentrations is = I0 S. Thus, the ratio of apparent rate constants of addition is 10-2. Macromolecular species derived from styrene should add to a standard alkene one hundred times slower than those derived from vinyl ethers. Thus, one cross-over reaction St - VE will be accompanied by =100 homopropagation steps VE - VE. Therefore, in addition to a small amount of block copolymer, a mixture of two homopolymers will be formed. Blocking efficiency should be very low, accordingly. 

Block copolymerization between monomers of similar reactivities such as isobutene and various styrenes (styrene, p-chloro-, p-methyl-, and p-f-butylstyrenes, and indene) [284-288], as well as arMeSt and 2-chloroethyl vinyl ether [226], involves fewer limitations and is more successful. A detailed description of the copolymerization of ar-methylstyrene with 2-chloroethylvilnyl ether has been reported [226]. Because the reactivities of both monomers are similar, AB and BA block copolymers were prepared. However, the enhanced formation of indan derivatives was observed when vinyl ether was used as the first block. 

As the range of styrene derivatives for living cationic polymerization expands (Chapter 4, Section V.C), a variety of block copolymers with sty-renic segments have been synthesized. Most of the reported examples involve combinations of styrene derivatives with vinyl ethers or isobutene. Some examples of styrene derivative-vinyl ether block copolymers are listed in Fig. 6 [16,87-89]. Monomers that can form similar block copolymers with isobutylene are listed in Fig. 7 (Section III.B.3). 

In general, styrene and its substituted derivatives are less reactive than vinyl ethers in cationic polymerization, although the reactivity depends considerably on the nature of the substituents. This in turn requires some care in synthesizing block copolymers of styrene derivatives by sequential living cationic polymerization. For example, styrene-methyl... 

Figure 6 Block copolymers of styrene derivatives typical examples.

In block copolymerizations with vinyl ethers, as seen in this example, a styrene derivative should be polymerized after the first-stage polymerization of a vinyl ether component, and an additional dose of a Lewis acid (activator) is usually needed to accelerate the second-phase polymerization. The reverse polymerization sequence (from a styrene derivative to a vinyl ether) often results in a mixture of block copolymers and homo-... 

Considerable efforts have been directed, primarily in Kennedy s group [3], to synthesize a series of block copolymers of isobutene with isoprene [90,91], styrene derivatives [92-104], and vinyl ethers [105-107]. Figure 7 lists the monomers that have been used for the block copolymerizations with isobutene. The reported examples include not only AB- but also ABA- and triarmed block copolymers, depending on the functionality of the initiators (see Chapter 4, Section V.B, Table 3). Obviously, the copolymers with styrene derivatives, particularly ABA versions, are mostly intended to combine the rubbery polyisobutene-centered segments with glassy styrenic side segments in attempts to prepare novel thermoplastic elastomers. These styrene monomers are styrene, p-methylstyrene, p-chlorostyrene, a-methylstyrene, and indene. 

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). 

Styrenic block copolymers derive their useful properties from their ability to form distinct styrene (hard phase) and diene (rubber phase) domains, with well defined morphologies. To achieve this requires an unusual degree of control over the polymerization. The polymerization must yield discrete blocks of a uniform and controlled size, and the interface between the blocks must be sharp. This is best achieved by so-called living polymerization. For a polymerization to be classified as truly living, it is generally accepted that it must meet several criteria [3] ... 

The first commercial thermoplastic elastomers deriving their properties from an ABA block copolymer structure were poly(styrene-isoprene-styrene) and poly (styrene-butadiene-styrene) triblocks introduced in 1965 at an ACS Rubber... 

With the purpose of increasing the range of available block copolymers, comonomers other than methacrylates and acrylates can also be involved in sequential polymerization, provided that they are susceptible to anionic polymerization. Dienes, styrene derivatives, vinylpyridines , oxiranes and cyclosiloxanes are examples of such comonomers. The order of the sequential addition is, however, of critical importance for the synthesis to be successful. Indeed, the pX a of the conjugated acid of the living chain-end of the first block must be at least equal to or even larger than that of the second monomer. Translated to a nucleophilicity scale, this pK effect results in the following order of reactivity dienes styrenes > vinylpyridines > methacrylates and acrylates > oxiranes > siloxanes. 

The photoreduction of aromatic ketones by polymeric systems having tertiary amine end groups provides an ele nt way for the preparation of block copolymers with high efficiency [138]. The method consists of the synthesis of the bifimctional azo-derivative 4,4 -azobis (iV,i -dimethylaminoethyl-4-cyano pentanoate) (ADCP), successively used as fiee radical thermal initiator for the preparation of tertiary amine-terminated poly(styrene). 

Anionic polymerization of thietane and various 2-, 3- and polysubstituted thietanes has been achieved with alkali metals (Li, Na, K, Cs, Rb), naphthyl sodiumn-butyllithium, °" 1,4-dilithio-l, 1,4,4-tetraphenylbutane, and a thiolate anion.Treatment of 3-chlorothietane with aqueous sodium thiocyanate is said to give polymeric material.Polymerization of thietane has been effected with Grignard reagents.Thietane and substituted thietanes have been polymerized with dialkyl zinc reagents.A copolymer has been obtained by treating 2-methylthietane and styrene with -butyllithium a block copolymer has been derived from thietane and isoprene. " Copolymers of thietane and 3,3-dimethylthietane with pivalolactone have been reported. ... 

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