Macromonomers diblock

In order to prepare various kinds of Seesaw-type macromonomers, we firstly synthesized two kinds of functional Seesaw-type initiators. Figure 3.3 shows how the functional initiators 1 and II are prepared. Their high purities were further confirmed by H NMR characterization (Fig. 3.4). Initiator I was used to construct macromonomer homopolymers and tiiblock copolymers, and initiator II was used to consbuct macromonomer diblock copolymers, respectively. Using these two initiators, we have prepared a number of Seesaw-type macromonomer homopolymers and copolymers with different block components and lengths. 

Preparation of Seesaw-Type Macromonomer Diblock Comopolymers... 

Fig. 3.12 Schematic of synthesis of Seesaw-type macromonomer diblock Ns-PS-h-PCL-Ns...

PS-fr-PBd) star-block copolymers were synthesized by the macromonomer technique in combination with anionic polymerization and ROMP [ 158], following the procedure outlined in Scheme 83. The macromonomers were prepared with two different methods. In the first the living diblock copolymer was reacted with ethylene oxide to reduce the nucleophihcity of the living end followed by termination with 5-carbonyl chloride bicycle (2.2.1) hept-2-ene, while in the second method the functional initiator 5-lithiomethyl bicycle... 

A series of amphiphilic diblock macromonomers were successfully used as steric stabilizers in the emulsion polymerization styrene [98]. Copolymerization led to the formation of polymer latexes of high colloidal stability. These... 

Capek described the use of a macromonomer in miniemulsion polymerization [54]. Lim and Chen used polyfmethyl methacrylate-fr-(diethylamino)ethyl methacrylate) diblock copolymer as surfactant and hexadecane as hydrophobe for the stabilization of miniemulsions [55]. Particles with sizes between about 150 and 400 nm were produced. It is possible to create stable vinyl acetate miniemulsions employing nonionic polyvinyl alcohol (PVA) as surfactant and hexadecane as hydrophobe [56]. 

This is similar to the synthesis of macromonomers of vinyl chloride [109]. Furthermore, the following photocrosslinkable diblock cooligomers were... 

Attempts to prepare star-block copolymers via the macromonomer technique have also appeared in the Hterature [26-28]. The method involves the preparation of diblock arms and subsequent end functionalization with p-chloromethyl-... 

Diblock polyoxyethylene-polyoxypropylene styrenic macromonomers, with the polymerizable group at the end of the hydrophobic part have been prepared and used in styrene emulsion polymerization [34]. Latexes of high stability towards added electrolyte have been obtained. However the HLB was not well-optimized so that a high amount of coagulum was formed (Surfmer XI). 

One of the significant developments in living cationic polymerization has been the synthesis of telechelics and production of diblock copolymers. PIB based macromonomers are another class of functional precursors. Copolymerization of these... 

ISH Ishizu, K., Tsubaki, K.-I., and Ono, T., Synthesis and dilute solution properties of poly(diblock macromonomer)s. Polymer, 39, 2935, 1998. 

Oligomeric surfactants have been prepared for use as stalnlizers in emulsion polymerization. Functionalized co-oligomars of acrylonitrile and acrylic acid have been used as surfactants in the emulsion polymoization of butadiene, styrene and itaconic acid [169], Diblock copolymers (oxazoline based) with narrow MMD appeax to be excellmt emulsifiers for the inverse emulsion polymerization of styraie [170], and amphiphilic oligomeric diblock macromonomers (PEO-PPO type) have been relied as steric stabilize in regular styrene emulsion polymraizarion [171]. 

Frechet et al. described the first synthesis of such a linear dendronized block copolymer 10 (Figure 37.6) [23]. For this purpose, a setof G2 and G3 aryl ether-based dendrons equipped with a norbornene unit was synthesized. Unfortunately, only the G3-exo-isomer could be polymerized, using a Grubbs third-generation catalyst the endo-isomer failed to polymerize, possibly due to a shielding effect of the G3 dendron. The obtained polydispersity index (PDI) of 1.03 indicated a good control over the polymerization process. However, when this G3 polymer was used as a macroinitiator for polymerization of the G2 monomer, the system failed to produce any diblock copolymer. Gonsequently, the order of monomer addition was reversed, such that the G2 macromonomer was polymerized first to complete conversion. 

Block Synthesis. Water-soluble block copolymers are formed from the copolymerization of macromonomers of methacrylates with acrylic and methacrylic acid monomers and their solution properties compared with random copolymers of similar composition (224). Diblock and triblock copolymers may be prepared by a number of techniques and are also used on ink-jet inks (225) and scale inhibition in water boilers (226), respectively. Associative properties of block polymers to form micellar structures are well established (227,228). Triblock polyampholyte polymers are also known (229). 

An alternative procedure has been utilized to prepare 1,1-diphenylethy-lene-functionalized poly(ethylene oxide) macromonomers as shown in Scheme27 [210, 211]. This macromonomer (81) reacted quantitatively with poly(styryl)lithium to form the corresponding living diblock copolymer adduct. After cooling to 5 °C, ferf-butyl methacrylate was added and polymerized for ca. 2h. After quenching with acidic methanol, the hetero, threearmed, star-branched, ABC-type block copolymer was isolated. The molecular weight determined by SEC (universal calibration M = 19,500 M /M =1.14) and by H NMR (M =17,300) were somewhat higher than the calculated value (M = 15,500) [211]. 

Cycloolefin macromonomers have been recently used in ring-opening metathesis polymerization reactions to manufacture block and graft copolymers of novel macromolecular architectures [84]. For this purpose, a- and co-norbornenyl-polybutadiene macromonomers, a-NBPB (R = CH2) and co-NBPB (R = COO), were reacted in the presence of molybdenum alkylidene complex, Mo(NAr)(CHtBu)(OtBu)2, to form polynor-bornene-polybutadiene diblock copolymers (117), with comb-like structure [85] [Eq. (49)]. 

Polymerization of a-norbornenyl-polystyrene macromonomer, a-NBPS, with the Schrock-type catalyst Mo(NAr)(CHtBu)(OC(CH3)(CF3)2)2 in toluene at room temperature gave polynorbornene-polystyrene diblock copolymer (118) in a quantitative yield [86] [Eq. (50)]. 

It should be mentioned that the type of Seesaw-type macromonomer is not only limited to homopolymer chains, but also can expand to copolymer chains if it is possible from the perspective of polymer chemistry, namely, the macromonomer can be homopolymer, triblock copolymer and diblock copolymer, as shown in Fig. 3.2. 

Fig. 3.2 Schematic illustration of three types of Seesaw-type macromonomers homopolymer, triblock copolymer and diblock copolymer...

Therefore, we further developed an approach to solve such a challenging problem. Namely, we intentionally prepared a B—A—B Seesaw-type diblock macromonomer precursor, where — and -— respectively represent polystyrene (PS) and poly(E-caprolactone) (PCL) blocks. Using such a special diblock macromonomer, we have successfully prepared hetero-subchain hyperbranched copolymers with two kinds of controllable uniform long subchains. 

II) with one alkyne (-=-), one hydroxyl (-OH) and one bromine groups (-Br) to first initiate the polymerization of the e-caprolactone and then the polymerization of styrene by successive ROP and ATRP processes, resulting in two diblock macromonomers (Br-PS-=-PCL-OH) with an identical PCL block but two PS blocks with different lengths. Further bromination and azidation led to two N3-PS-S-PCL-N3 precursors. The schematic synthesis is shown in Fig. 3.12. 

In order to find how the PS subchain length and the overall chain molar mass affect the properties of such prepared hyperbranched copolymers HB-(PS-fc-PCL)n, we further made a diblock copolymer presursor (N3-PSi8-=-PCL28-N3) with an identical PCL block but a shorter PS block, and its characterization result is shown in Fig. 3.14. In the next chapter, we will further discuss the preparation of hypCTbranched hetero-subchain copolymers by using such kind of macromonomers as precursors. 

In conclusion, by overcoming the disadvantage of the previous synthetic methods for the preparation of hyperbranched polymers, we designed an all-new Seesaw-type macromonomer strategy to construct perfect hyperbranched model samples with uniform subchains. In onr stndy, we successfully prepared various kinds of Seesaw-type macromonomers, snch as homopolymers, triblock copolymers and diblock copolymers. Using these maCTomonomers as precursors, we have further prepared a series of perfect hyperbranched homopolymers, block copolymers, graft copolymers and hetero-snbchain copolymers by a combination of controlled/ living polymerization and click chemistry. Various solution properties of these novel hyperbranched (co) polymers in dilnte and semidilute solntions have been studied in detail. More specifically, the main achievements of this work are as follows ... 

Successfully prepared Seesaw-type diblock macromonomer (Na-PS- -PCL-N3) and model hyperbranched hetero-subchain copolymer [HB-(PS-f>-PCL)n] with controllable and uniform PS and PCL subchains, and found that such prepared hyperbranched copolymer chains still have a fractal-like structure, and the PCL subchains inside HB-(PS-f>-PCL)n crystallize less as the branching degree increases and the PS subchain becomes longer. This work demonstrates that we can use the chain topology to control the crystallization of PCL subchains inside hyperbranched copolymers to regulate their biodegradation for biomedical applications. 

Eigure 7.6 shows a schematic synthesis of diblock macromonomer N3-PS- -PQ.-N3 and its resultant hyperbranched chain HB-(PS-fc-PCL)n. 

Fig. 7.6 Schematic of synthesis of seesaw-type diblock macromonomer N3-PS-1)-PCL-N3 and an resultant hyperbranched chain HB-(PS-i>-PCL)n...

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