ROP Approach

HPs can also be synthesized by self-condensing ROP of AB -type cyclic monomers.Likewise, HPs can be grafted from nanosurfaces by an in situ ROP strategy. Gao and co-workers prepared hydroxy-functionalized 

Similarly, Adeli et also grafted HPG from opened MWCNTs in 

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Ring-opening Polymerization (ROP) Approach to Polymer-grafted CNTs... 

Table 5.4 Selected conditions and results of polymer-grafted CNTs via the ROP approach. ...

Figure 5.16 Synthesis of PCL-grafted CNTs by the ROP approach and degradation of PCL chains by PS lipase (top), and representative SEM images of the control experiment sample which was collected from the phosphate buffer solution of MWCNT-g-PCL (52.7 wt% of PCL) without PS lipase after 96 h (a), and the samples of MWCNT-g-PCL degraded with PS lipase for 24 h (b), 48 h (c) and 96 h (d). The scale bars in (a), (b), (c) and (d) represent 1000, 500, 500 and 500 nm, respectively. The marked tubes 1 and 2 have diameters of ca. 90.3 and 85.5 nm, respectively. After 24 h of degradation with PS lipase (b), the diameters of tubes 3 and 4 are ca. 83.3 and 75.7 nm, respectively. After 48 h of degradation (c), the diameters of tubes 5 and 6 are only ca. 54.1 and 50.5 nm, respectively. After 96 h of degradation (d), little residual polymer on the surfaces of MWCNTs can be detected, and many tubes with diameters of ca. 20-30 nm are found (tubes 7 and 8 have diameters of 22.7 and 28.2 nm, respectively). In this case, the average diameter of the degraded tubes is almost equal to that of the oxidized tubes. Reprinted with permission from Zeng et al. ...

Scheme 5.15 Grafting multihydroxyl hyperbranched polyether from CNT surfaces by ROP approach. D, L and T represent dendritic, linear and terminal units, respectively. Reprinted with permission from Xu et al ...

Ring-opening polymerization (ROP) approaches have also been reported for the formation of coordination polymers. An early report in 1960 described the formation of beryllium polymers vith / -diketonate ligation, such as 7.55, by thermal ROP (Eq. 7.15) [105]. Structural characterization of the polymers vas based on IR and elemental analysis data. Based on their intrinsic viscosities in benzene and mechanical properties, it vas inferred that the polymers vere of high molecular veight. More recently, coordination polymers based on metal-phosphine ligation have been prepared. For example, ROP of 7.56 in the solid state occurs to form the silver polymer 7.57 (Eq. 7.16) [106]. 

Polyferrocenylsilanes (PFSs) have attracted growing interest since the early 1990s. ° These materials exemplify the types of polymers accessible by the use of the novel ring-opening polymerization (ROP) approach. PFS materials can be easily fabricated and processed as films, gels, and monoliths, and have even been... 

In conclusion, the well-defined organometallic amphiphilic AB block copolymer of PFS-PDMAEMA and ABC block polymers of PFP-i-PFS- -PDMS were synthesized via anionic ROP approach. ... 

Other attempts to develop a pore pressure evaluation method from different drilling equations were made by Combs, by Bourgoyne and Young and by Bellotti and Giacca [101]. The three models follow the same general approach a drilling equation is developed assuming that all variables are independent. The ROP is then normalized to eliminate the effect of each variable but the pore pressure. These equations attempt to take more variables into account. 

By using a combination of RAFT and ring opening polymerization (ROP), (polyethylene oxide) methyl ether)(polystyrene)(poly(L-lactide) 3-miktoarm star terpolymers have been successfully synthesized [182]. The synthetic approach involved the reaction of the cw-functionalized - OH group of the poly(ethylene oxide) methyl ether with maleic anhydride under conditions where only one hydroxyl group can be esterified (MPEO). The double bond... 

By utilizing a combination of RAFT and cationic ROP, the synthesis of [poly(methyl methacrylate)][poly(l,3-dioxepane)][polystyrene] miktoarm star terpolymers was achieved [182], The approach involved the synthesis of PS functionalized with a dithiobenzoate group by RAFT polymerization and subsequent reaction with hydroxyethylene cinnamate (Scheme 98). The newly created hydroxyl group was then used for the cationic ring opening polymerization of 1,3-dioxepane (DOP). The remaining dithiobenzoate group was used for the RAFT polymerization of methyl methacrylate. 

Initiators such as (306) initiate the ROP of CL to form telechelic triblock diols.478 Molecular weights approach theoretical values with polydispersities <1.3 and no significant level of transesterification was detected at up to 95% conversions. Alternative bimetallic samarium initiators have been used to synthesize aromatic, cumulene and amine/imine link-functionalized poly(lactones).479... 

A more general strategy to approach symmetrical telechelic polyesters consists of the control of both initiation and termination steps. Indeed, combination of a functional initiator for the (di)lactones ROP with an effective coupling... 

Considerable effort has been carried out by different groups in the preparation of amphiphihc block copolymers based on polyfethylene oxide) PEO and an ahphatic polyester. A common approach relies upon the use of preformed co- hydroxy PEO as macroinitiator precursors [51, 70]. Actually, the anionic ROP of ethylene oxide is readily initiated by alcohol molecules activated by potassium hydroxide in catalytic amounts. The equimolar reaction of the PEO hydroxy end group (s) with triethyl aluminum yields a macroinitiator that, according to the coordination-insertion mechanism previously discussed (see Sect. 2.1), is highly active in the eCL and LA polymerization. This strategy allows one to prepare di- or triblock copolymers depending on the functionality of the PEO macroinitiator (Scheme 13a,b). Diblock copolymers have also been successfully prepared by sequential addition of the cyclic ether (EO) and lactone monomers using tetraphenylporphynato aluminum alkoxides or chloride as the initiator [69]. 

All these limitations were overcome by implementing a third approach based on the ROP of lactones [7, 8]. Indeed, many examples of living or/and controlled polymerization with fast initiation are reported using this technique. High molar mass aliphatic polyesters with low polydispersity indexes can be thus be synthesized. In terms of the availability of the monomers, this approach occupies... 

A less direct strategy relies on the synthesis and ROP of substituted and/or imreactive functionalized lactones [100]. Two approaches can be implemented. In the first approach, the unreactive functional group is inserted directly inside the ring. It is worth recalling that cyclic diesters such as lactide and glycolide, for which... 

To this end, a very widely used approach is ROP initiated by polyols (at least triols) in the presence of tin(II) bis-(2-ethyUiexanoate) [155,156]. By implementing this technique, alcohols are dormant species and have to be activated by reaction with tin(II) bis-(2-ethylhexanoate) into tin alkoxides to initiate or to propagate the polymerization. The alcohols are thus not activated at the same time and no side-reactions between them are observed. Besides, it is more appropriate to initiate... 

Interestingly, Hedrick and coworkers reported a metal-free approach for the synthesis of star-shaped copolymers. They synthesized star-shaped PCLs by the ROP of eCL initiated by polyols in the presence of unencumbered N-heterocyclic carbenes [87]. 

Various a-methylenemacrolides were enzymatically polymerized to polyesters having polymerizable methacrylic methylene groups in the main chain (Fig. 3, left). The free-radical polymerization of these materials produced crosslinked polymer gels [10, 12]. A different chemoenzymatic approach to crosslinked polymers was recently introduced by van der Meulen et al. for novel biomedical materials [11]. Unsaturated macrolactones like globalide and ambrettolide were polymerized by enzymatic ROP. The clear advantage of the enzymatic process is that polymerizations of macrolactones occur very fast as compared to the chemically catalyzed reactions [13]. Thermal crosslinking of the unsaturated polymers in the melt yielded insoluble and fully amorphous materials (Fig. 3, right). 

Enzymatic polymerization has been combined with various chemical polymerizations for the synthesis of block copolymers. The choice of chemical polymerization generally depends on the applied strategy for the block copolymer synthesis. These can be divided into three main approaches, as shown in Fig. 4 for the example of enzymatic ROP. It has to be noted that some of these strategies have also been applied for enzymatic polycondensations. 

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