Sequential polymerization block copolymer formation

The first report is available from Shen et al. who studied the preparation of BR/IR block copolymers by sequential polymerization of BD and IP [92]. Shen et al. found that the polymerization of the second monomer batch resulted in an increase of solution viscosity by 100%. The viscosity increase was considered as strong evidence in favor of block copolymer formation. Further evidence came from stress strain measurements in which the respective BD/IP block copolymers were compared with blends of BR and IR (at the same molar masses). It was found that the block copolymer exhibited higher elongation at break and higher tensile strength. Unfortunately, Mn data were not provided. Therefore, these results are not fully relevant regarding requirement No. 5 for a living polymerization. 

Sequential Polymerization. The sigmoidal reaction curves, which indicate a tendency for the molecular weight to increase during the course of the reaction, and other considerations led to the suggestion that the polymerizing chains had long lifetimes (9), similar to the chains in a living polymerization. If this is the case, sequential addition of different monomers would lead to block copolymer formation. To check this hypothesis, PMDS and HMDS were polymerized sequentially with suflScient time between additions for the first monomer to be consumed. In one experiment, PMDS was the first monomer, and in another experiment, HMDS was the first. In... 

Block copolymers of /3-PL and /3-BL have been synthesized using (251), although reaction times of several weeks are required.782 Since (TPP)Al-based carboxylates are also known to polymerize epoxides (see Section 9.1.7.2), the sequential addition of /3-BL and propylene oxide (PO) results in formation of a p(/3-BL-/3-PO) diblock.782 However, reversing the order of addition fails to produce the block copolymer since the propagating alkoxide (TPP)Al(OCHMeCH2)nCl does not initiate the ROP of /3-BL. 

By also using the LASIP procedure, grafted PS-b-PI and PBd-b-PS block copolymers have been prepared (Fig. 7) [72]. Using silane and thiol-DPE initiators, polymerization was carried out on the SiOx and Au surface by sequential addition of monomers. Typically, after allowing this first reaction to reach completion, the second monomer was added to the living anion, and polymerization of the second block was allowed to proceed. The polymerization was also investigated by SPS [80], AFM, ellipsometry, FT-IR, and XPS. The schematic diagram for the reaction on Au surfaces and the formation of the block copolymers is shown in Fig. 6. The results are summarized in Table 2. 

Styrene-1,3-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) triblock copolymers are manufactured by a three-stage sequential polymerization. One possible way of the synthesis is to start with the polymerization of styrene. Since all polystyrene chains have an active anionic chain end, adding butadiene to this reaction mixture resumes polymerization, leading to the formation of a polybutadiene block. The third block is formed after the addition of styrene again. The polymer thus produced contains glassy (or crystalline) polystyrene domains dispersed in a matrix of rubbery polybutadiene.120,481,486... 

Sequential Oxidation of DMP and DPP. The usual approach to formation of block copolymers is by the sequential polymerization of two or more monomers or by linking together preformed homopolymer blocks. In view of the importance of the redistribution process in the oxidative coupling of phenols there can be no assurance that successive polymerization of two phenols will yield block copolymers under any conditions. It is certain, however, that block copolymers can be formed only if the conditions are such that polymerization of the second monomer is much faster than redistribution of the added monomer with the polymer previously formed from the first. The extent of redistribution is followed conveniently by noting the effect of added monomer on solution viscosity, as indicated by the efflux time from a calibrated pipet. 

In the formation of block copolymers by sequential addition of monomers it generally does not matter which monomer is polymerized first, and diblock or multiblock copolymers of narrow MWD and of any desired sequence length are readily prepared. Termination is usually effected by reaction of the living ends with aldehydes ketones can be used for terminating titanacyclobutane ends, while unsaturated ethers are used for terminating ruthenium carbene complexes. 

Formation of block copolymers in the sequential polymerization may be affected by chain transfer to polymer. As already discussed, in several systems the intramolecular chain transfer to polymer leads to formation of cyclic fraction. Cyclic macromolecules, being neutral, do not participate in further reaction and constitute the homopolymer fraction in resulting copolymer. Intermolecular chain transfer to polymer may lead to disproportionation, i.e., formation of fraction of macromolecules which do not carry active species ... 

Sequential polymerization of two acrylic monomers was discussed in Sections VI.E.4, VI.E.7 and VI.F. This technique was extended to three comonomers with formation of ABC-type triblock copolymers. For example, PMMA-fcZoc -PtBMA- Zoc -PMMA triblock copolymer was synthesized by the sequential DPFlLI-initiated polymerization of MMA, tBMA and MMA, respectively . Symmetrical BAB-type diblock copolymers were also prepared in two steps, polymerization of the A monomer being first initiated by a difunctional compound. The B blocks formed in the second step necessarily have the same average degree of polymerization. 

Block copolymers produced from the sequential polymerization of exo-N-bulyl-7-oxabicyclo 2.2.1 hcpl-5-ene-2,3-dicarboximide and another nor-bornene derivative carrying an adenine group were employed using a ruthe-niirm catalyst, as shown in Scheme 38 [99]. The first monomer was polymerized in CH2CI2 at room temperature followed by the addition of the second monomer and succinimide. In the presence of succinimide the conversion of the adenine-containing monomer was almost quantitative, probably due to the formation of hydrogen bonds with the adenine moiety, which prevents any undesired interaction with the catalyst. Monomodal peaks were obtained by SEC analysis with polydispersity indices ranging from 1.20 up to 1.60. 

PS-fc-poly(4-f-butylstyrene)]n, (PS-fi-PfBuS) star-block copolymers were prepared by anionic polymerization and sequential addition of monomers with DVB as the linking agent for the formation of the star structure [156]. The functionality of the stars ranged between 10 and 20. Selective sulfonation of PS blocks was subsequently performed using the sulphur trioxide and triethyl phosphate complex in 1,2-dichloroethane, followed by neutralization with sodium methoxide. For this reason DVB was used for the linking reaction instead of chlorosilanes, where a better control could be achieved. DVB stars are more robust and the sulfonation reaction proceeds without cleavage of the arms from the star structure. 

Most interesting from the standpoint of commercial development is the formation of block copolymers by the living polymer method. Sequential addition of monomers to a living anionic polymerization system is at present the most useful method of synthesizing well-defined block copolymers. Depending on whether monofunctional or difunctional initiators are used, one or both chain ends remain active after monomer A has completely reacted. Monomer B is then added, and its polymerization is initiated by the living polymeric carbanion of polymer A. This method of sequential monomer addition can be used to produce block copolymers of several different types. 

Litt claimed formation of block copolymers of 2-lauroyl-2-oxazoline and 2-methyl-2-oxazine by sequential polymerization 122). Methyl tosylate was the initiator and the polymerization was terminated by water. The proposed structure of the copolymer is ... 

We investigated the chemoenzymatic synthesis of block copolymers combining eROP and ATRP using a bifunctional initiator. A detailed analysis of the reaction conditions revealed that a high block copolymer yield can be realized under optimized reaction conditions. Side reactions, such as the formation of PCL homopolymer, in the enzymatic polymerization of CL could be minimized to < 5 % by an optimized enzyme (hying procedure. Moreover, the structure of the bifunctional initiator was foimd to play a major role in the initiation behavior and hence, the yield of PCL macroinitiator. Block copolymers were obtained in a consecutive ATRP. Detailed analysis of the obtained polymer confirmed the presence of predominantly block copolymer structures. Optimization of the one-pot procedure proved more difficult. While the eROP was compatible with the ATRP catalyst, incompatibility with MMA as an ATRP monomer led to side-reactions. A successfiil one-pot synthesis could only be achieved by sequential addition of the ATRP components or partly with inert monomers such as /-butyl methacrylate. One-pot block copolymer synthesis was successful, however, in supercritical carbon dioxide. Side reactions such as those observed in organic solvents were not apparent. 

Although polysiloxanes have superior properties compared to common organic polymers, the controlled formation of amphiphilic block copolymers consisting of a pure polysiloxane backbone remains essentially unexplored. There have been only a few reports of such polymers in the literature, for example one bearing pendant carboxyl groups on the polysiloxane chain,and another prepared by a one-pot sequential anionic ring-opening polymerization of two cyclotrisiloxanes. ... 

Polysiloxane-containing amphiphilic block copolymers have been prepared by different approaches. Coupling of an end-functionalized polydimethylsiloxane with a functionalized poly(ethylene oxide) led to the formation of PDMS- -PEO diblock copolymers. The sequential anionic ring-opening polymerization of tetramethyltetravinylcyclotetrasiloxane and hexamethylcyclotetrasiloxane resulted in the formation of a vinyl-substituted diblock copolymer, the vinyl groups of which could be modified by further reactions so as to import amphiphilic character. The phase behavior of short-chain PDMS-Z -PEO diblock copolymers revealed the preferred formation of lamellar phases by this type of amphiphile... 

The discovery of living cationic polymerization has provided methods and technology for the synthesis of useful block copolymers, especially those based on elastomeric polyisobutylene (Kennedy and Puskas, 2004). It is noteworthy that isobutylene can only be polymerized by a cationic mechanism. One of the most useful thermoplastic elastomers prepared by cationic polymerization is the polystyrene-f -polyisobutylene-(>-polystyrene (SIBS) triblock copolymer. This polymer imbibed with anti-inflammatory dmgs was one of the first polymers used to coat metal stents as a treatment for blocked arteries (Sipos et al., 2005). The SIBS polymers possess an oxidatively stable, elastomeric polyisobutylene center block and exhibit the critical enabling properties for this application including processing, vascular compatibility, and biostability (Faust, 2012). As illustrated below, SIBS polymers can be prepared by sequential monomer addition using a difunctional initiator with titanium tetrachloride in a mixed solvent (methylene chloride/methylcyclohexane) at low temperature (-70 to -90°C) in the presence of a proton trap (2,6-dt-f-butylpyridine). To prevent formation of coupled products formed by intermolecular alkylation, the polymerization is terminated prior to complete consumption of styrene. These SIBS polymers exhibit tensile properties essentially the same as those of... 

In this two-stage process, B is sequentially polymerized onto A, and then the two chains are coupled to yield an ABBA block copolymer. Triblocks of SBS have been prepared using this method, with methylene dichloride as the coupling agent. The disadvantage is the formation of radical anions, which can lead to contamination of the triblock with multiblock species. 

The wide applicability of aluminum porphyrin initiators (1) leads to a variety of tailored block copolymers such as polymethacrylate-polyether and polymethacrylate-polye-ster, as well as polymethacrylate-polymethacrylate and polymethacrylate-polyacrylate, that can be synthesized by sequential living polymerization of the corresponding monomers.- For example, when 1,2-epoxypropane (11, R = Me) is added to a polymerization mixture of methyl methacrylate (21, R = Me) with la at 100% conversion of 21, the polymerization of 11 takes place from the enolate growing end (32 ) to give a narrow MWD polymethacrylate-polyether block copolymer having an alcoholate growing terminal (Table 4). Likewise, the aluminum enolate species (32 ) can also react with lactones (14,15), thereby allowing the formation of a poly(methyl methacrylate)-polyester block copolymer with narrow MWD. 

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