Macroinitiation synthesis

Scheme 4 a One-step synthesis of bis(4-methoxyphenyl)-4/-vinylphenylamine (vDMTPA) and formation of bis(4-methoxyphenyl)-4/-vinylstyrylamine. b Three-step procedure of vDMTPA. c Synthesis of Av/V/-bis(4-methoxyphenyl)-A/-phenyl-A/7-4-vinylphenyl-(l,l/biphenyl)-4,4r-diamine (vDMTPD). Macroinitiator synthesis and subsequent preparation of block copolymers via NMRP were carried out analogously to Scheme 3... 

Block Copolymers Derived from Macroinitiators Recent Advances of Synthesis, Properties, and Applications... 

The polymerization of 2-(diethylamino)ethyl methacrylate, DEAEMA, was studied under different conditions. It was shown that the best system providing narrow molecular weight distribution polymers involved the use of p-toluenesulfonyl chloride/CuCl/HMTETA as the initiator/catalyst/ligand at 60 °C in methanol [72]. Taking advantage of these results, well-defined PDEAEMA-fr-PfBuMA block copolymers were obtained. The synthesis was successful when either fBuMA or DEAEMA was polymerized first. Poor results with bimodal distributions were obtained when CuBr was used as the catalyst. This behavior was attributed to the poor blocking efficiency of PDEAEMA-Br and the incomplete functionalization of the macroinitiator. 

The direct synthesis of poly(3-sulfopropyl methacrylate)-fr-PMMA, PSP-MA-fr-PMMA (Scheme 27) without the use of protecting chemistry, by sequential monomer addition and ATRP techniques was achieved [77]. A water/DMF 40/60 mixture was used to ensure the homogeneous polymerization of both monomers. CuCl/bipy was the catalytic system used, leading to quantitative conversion and narrow molecular weight distribution. In another approach the PSPMA macroinitiator was isolated by stopping the polymerization at a conversion of 83%. Then using a 40/60 water/DMF mixture MMA was polymerized to give the desired block copolymer. In this case no residual SPMA monomer was present before the polymerization of MMA. The micellar properties of these amphiphilic copolymers were examined. 

Diblock copolymers PEO-fo-PS have been prepared using PEO macroinitiator and ATRP techniques [125]. The macroinitiator was synthesized by the reaction of monohydroxy-functionalized PEO with 2-chloro-2-phenylacetyl-chloride. MALDI-TOF revealed the successful synthesis of the macroinitiators. The ATRP of styrene was conducted in bulk at 130 °C with CuCl as the catalyst and 2,2 bipyridine, bipy, as the ligand. Yields higher than 80% and rather narrow molecular weight distributions (Mw/Mn < 1.3) were obtained. The surface morphology of these samples was investigated by atomic force microscopy, AFM. 

The triblock terpolymer polypropylene oxide)-h-poly[2-(dimethylami-no)ethyl methacrylate]-b-poly[oligo(ethylene glycol) methacrylate], PPO-fc-PDMAEMA-fc-POEGMA, was prepared using the PPO macroinitiator followed by the addition of CuCl, HMTETA, and DMAEMA for the polymerization of the second block and finally OEGMA for the synthesis of the final product (Scheme 54) [128]. 

A PEO macroinitiator with Si — H end groups was prepared through the condensation of monohydroxy-terminated PEO with CISiMePhH in the presence of pyridine [130]. The presence of the Si —Ph moiety prevents the hydrolysis of the Si — O — C bond, due to steric factors. This macroinitiator was subsequently used for the synthesis of poly(ferrocenyldimethylsilane), PFS, to afford PEO-fc-PFS block copolymers. The ROP of the ferrocenophane was conducted catalytically using the Pt(0) Karstedt s catalyst in toluene at 25 °C (Scheme 55). Rather broad molecular weight distributions (higher than 1.3) were obtained. 

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. 

More recently, the scope of using hyperbranched polymers as soluble supports in catalysis has been extended by the synthesis of amphiphilic star polymers bearing a hyperbranched core and amphiphilic diblock graft arms. This approach is based on previous work, where the authors reported the synthesis of a hyperbranched macroinitiator and its successful application in a cationic grafting-from reaction of 2-methyl-2-oxazoline to obtain water-soluble, amphiphilic star polymers [73]. Based on this approach, Nuyken et al. prepared catalyticaUy active star polymers where the transition metal catalysts are located at the core-shell interface. The synthesis is outlined in Scheme 6.10. 

Block copolymers of (R,S)-(3-butyrolactone and eCL have been synthesized by combining the anionic ROP of the first monomer with the coordinative ROP of the second one (Scheme 15) [71]. The first step consisted of the synthesis of hydroxy-terminated atactic P(3BL by anionic polymerization initiated by the alkali-metal salt of a hydroxycarboxylic acid complexed with a crown ether. The hydroxyl end group of P(3BL could then be reacted with AlEt3 to form a macroinitiator for the eCL ROP. 

In a different approach, Hedrick et al. have studied multifunctional dendritic initiators for the synthesis of multiarm star-shaped copolymers [102]. Several dendritic initiators with hydroxyl functionality ranging from 2 to 48 have been prepared according to the method developed by Hult et al. [120]. The bulk polymerization of sCL initiated by these multifunctional macroinitiators and acti-... 

Fig. 10 Synthesis of the macroinitiator precursor (I), the macroinitiator (II) and macro-molecular gradient brush copolymer (III). (Reproduced with permission from [55])...

Initial reports on chemoenzymatic block copolymer synthesis focus on the enzymatic macroinitiation from chemically obtained hydroxy-functional polymers (route A in Fig. 4). The first report on enzymatic macroinitiation was published by Kumar et ah, who used anionically synthesized hydroxy-functional polybutadiene of various molecular weights ranging from 2600 to 19,000Da (Fig. 5) [16]. In a systematic study, the authors investigated the efficiency of the macroinitiation of CL and PDF by Novozym 435 as a function of the polybutadiene macroinitiator. The reaction profile showed that polybutadiene consumption steadily increased with the reaction... 

By taking advantage of the simultaneous enzyme inhibition by nickel, the nickel-catalyzed ATRP, and the stereoselectivity of the enzyme, Peters et al. obtained chiral block copolymers by this method from 4-methyl-e-caprolactone (4-MeCL) by [27], The polymerization of racemic 4-MeCL showed good enantioselectivity and produced a chiral macroinitiator with ATRP endgroup by selectively polymerizing only the (5 )-4-MeCL. Macroinitiation was then started by adding the nickel catalyst and methyl methacrylate (MMA) to the reaction mixture, which simultaneously inhibited the enzyme and activated the ATRP process. Chiral poly[MMA-fe-(5 )-4-MeCL] was successfully obtained in this synthesis. 

Sha et al. applied the commercially available dual initiator ATRP-4 for the chemoenzymatic synthesis of block copolymers. In a first series of publications, the group reported the successful synthesis of a block copolymer comprising PCL and polystyrene (PS) blocks [31, 32]. This concept was then further applied for the chemoenzymatic synthesis of amphiphilic block copolymers by macroinitiation of glycidyl methacrylate (GMA) from the ATRP functional PCL [33]. This procedure yielded well-defined block copolymers, which formed micelles in aqueous solution. Sha et al. were also the first to apply the dual enzyme/ATRP initiator concept to an enzymatic polycondensation of 10-hydroxydecanoic acid [34]. This concept was then extended to the ATRP of GMA and the formation of vesicles from the corresponding block copolymer [35]. 

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