Polydispersity, control

Macromonomers generally exhibit low molecular weights (up to 20,000) which allows accurate control of functionalization yield. Careful sample characterization and polydispersity control are necessary to check the efficiency of the synthesis. 

Thus, preparation of well-defined polymers by controlled polymerization should not be confused with living polymerization. Herein we define a controlled polymerization to be a synthetic method to make polymers with predetermined molecular weights, low polydispersity, controlled functionality, block copolymers, etc. Transfer and termination can happen in controlled polymerization but their contribution is sufficiently reduced by the proper choice of the reaction conditions. 

Well-characterized systems. This depends on the appropriate chemistry and subsequent characterization (typical issues here are the polydispersity, control of grafting density, reproducibility of procedure to obtain identical particles). One frequent problem here is that the price one pays for such systems is tlie availability of small amounts (sometimes only fractions of 1 g) of material. For example, multiarm star polymers are in many ways unique, clean, soft colloids [ 19,23], but their nontrivial synthesis makes them not readily available. On the other hand, recent developments witli block copolymer micelles from anionically synthesized polymers [54-58] and arborescent graft copolymer synthesis [40] appear to have adequately addressed this issue for making available different alternative star-like systems. 

As a conventional radical initiator, the use of BPB, which decomposes faster than VRllO, led to a faster polymerization (Figure 2 (filled square) and Table 1 (entry 2)). In the examined case, the conversion reached 76 % for 7 h, keeping a good polydispersity control. 

The polymerization of MMA was also examined with the alcohols (precursors). To ensure a fast initiation from the alkyl iodide, we used a tertiary alkyl iodide, CP-I (Figure 1), irrstead of the secondary one, PE-1. All of the mentioned five alcohols and BHA (Figrtre 1) well controlled the MMA polymerization at 80 °C, as the examples in Table 2 illustrate. We are now systematically studying the relatiorrship between the stmctrrre of alcohol and the polydispersity control, which will be reported elsewhere. 

The benefit of microfluidic reaction for N CA polymerization is not just confined to Lys-NCA. For example, in glutamate-based NCA, a similar result was obtained, that is, lower PDI of polyglutamate synthesized by the microreactor compared with batchwise reaction. Furthermore, the similar polydispersity control of NCA copolymerizations, which is known to be more uncontrollable due to the difference in the reactivities of individual NCAs [29], was achieved successfully [22]. 

Ahmed, S.R., Bullock, S.E., Cresce, A.V., and Kofinas, P. (2003) Polydispersity control in ring opening metathesis polymerization of amphiphilic nrabomene diblock copolymers. Polymer, 44,4943. 

Narain R, Armes SP (2002) Synthesis of low polydispersity, controlled-structure sugar methacrylate polymers under mild conditions without protecting group chemistry. Chem... 

For MMA polymerization with X=TeMe, Yamago a al. synthesized low-polydispersity polymers (Mw/M 1.15) by the addition of a small amount of dimethyl ditelluride (MeTe)2, without which Mw/Mn exceeded 1.35 due to a small Cex (e.g., 3.6 at 60° C ). This suggests an inaease of k a in the presence of (MeTe)2. A kinetic study on the role of (MeTe)2 demonstrated that (MeTe)2 worked as an efficient deactivator of P to in situ generate MeTe (and P-TeMe), and MeTe" then worked as a highly reactive activator of the dormant species P-TeMe. Namely, there is a rapid reversible activation-deactivation process mediated by (MeTe)2, that is, P-TeMe+MeTe" P" + (MeTe)2 as another activation mechanism besides E)T, accounting for the observed dramatic improvement of the polydispersity controllability. 

One should note that the polymerization rate (4.10) and livingness (4.13) depend on the ratio A d,dcAc,ac on the equihbrium constant K. On the other hand, the polydispersity (control) of the polymer (4.14) depends on the product of A d,dc and A c,ac- Thus, Kvingness and control are not necessarily mutually inclusive. 

We studied the polymerizations of MMA with amine catalysts at 60-90 The polydispersity control was essentially the same at these... 

Mechanistically, RCMP includes DT as well as RC. However, as mentioned above, the rate constant of DT is too small, and the good polydispersity control observed in RCMP is mainly due to the work of the catalyst (RC) with a small contribution of DT. 

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