Approaches to the Synthesis of Block and Graft Copolymers with Well Defined Segment Lengths (original) (raw)
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Macromolecules, 2006
Phthalimidomethyl trithiocarbonates are used as reversible addition fragmentation chain transfer (RAFT) agents to provide low polydispersity α-(phthalimidomethyl)polystyrene with number-average molecular weight in the range 1000−100000 g mol-1. The activity of the phthalimidomethyl trithiocarbonates in RAFT polymerization of styrene, which appears to be similar to that of analogous benzyl trithiocarbonates, is attributed to the electrophilic character of the phthalimidomethyl group. The trithiocarbonate functionality in the products was quantitatively transformed to inert chain ends either by radical-induced reduction with tributylstannane or by thermal elimination, allowing the phthalimido end groups to be cleanly converted to primary amine end groups by hydrazinolysis. Thermolysis experiments, in which the polymers are cleaved at the trithiocarbonate linkage, also provide information on the mechanism of RAFT polymerization. In the case of the symmetrical bis(phthalimidomethyl) trithiocarbonate the two chains grow stepwise indicating that this RAFT agent has a higher transfer constant than the phthalimidomethyl polystyrene trithiocarbonate and that polystyrene propagating radical is a better homolytic leaving group than the phthalimidomethyl radical.
Polymer, 2005
This paper provides an overview and discusses some recent developments in radical polymerization with reversible additionfragmentation chain transfer (RAFT polymerization). Guidelines for the selection of RAFT agents are presented. The utility of the RAFT process is then illustrated with several examples of the synthesis of polymers with reactive end-groups. Thus, RAFT polymerization with appropriately designed trithiocarbonate RAFT agents is successfully applied to the synthesis of narrow polydispersity carboxy-functional poly(methyl methacrylate) and primary amino-functional polystyrene. Methods for removing the thiocarbonylthio end-group by aminolysis, reduction and thermal elimination are discussed. It is shown that the thiocarbonylthio end-group can be cleanly cleaved by radical induced reduction with tri-n-butylstannane, to leave a saturated chain end, or by thermolysis, to leave an unsaturated chain end. q
Advances in RAFT polymerization: the synthesis of polymers with defined end-groups
Polymer, 2005
This paper provides an overview and discusses some recent developments in radical polymerization with reversible addition–fragmentation chain transfer (RAFT polymerization). Guidelines for the selection of RAFT agents are presented. The utility of the RAFT process is then illustrated with several examples of the synthesis of polymers with reactive end-groups. Thus, RAFT polymerization with appropriately designed trithiocarbonate RAFT agents is successfully applied to the synthesis of narrow polydispersity carboxy-functional poly(methyl methacrylate) and primary amino-functional polystyrene. Methods for removing the thiocarbonylthio end-group by aminolysis, reduction and thermal elimination are discussed. It is shown that the thiocarbonylthio end-group can be cleanly cleaved by radical induced reduction with tri-n-butylstannane, to leave a saturated chain end, or by thermolysis, to leave an unsaturated chain end.
Macromolecules, 2006
Phthalimidomethyl trithiocarbonate reversible addition−fragmentation chain transfer (RAFT) agents are effective in imparting living characteristics to radical polymerizations of butyl acrylate (BA) and N-isopropylacrylamide (NIPAM) and provide a route to end-functional polymers with predictable molecular weight and narrow molecular weight distributions (e.g., number-average molecular weight for PBA (M̄n) = 21 300 and polydispersity (M̄w/M̄n) = 1.1 at 96% conversion). End group determination suggests that bimodal molecular weight distributions and long chain branches in PBA arise by copolymerization of a PBA macromonomer formed by backbiting β-scission. The S-phthalimidomethyl xanthates provide good control over polymerizations of the less-activated monomers N-vinylpyrrolidone (NVP) and vinyl acetate (VAc). In the case of PBA with a trithiocarbonate end or PVAc with a xanthate end, the C−S bond to the thiocarbonylthio end group can be homolyzed by thermolysis at >180 °C leaving the phthalimidomethyl end group and the ester side groups intact providing macromonomers, with ω end group −CH2−C(CO2C4H9)(CH2) or −CH2−C(O2CCH3)(CH2) respectively, as the main products.
Macromolecules, 1998
The bicyclo[2.2.1]heptene and bicyclo[2.2.1]heptadiene ring systems are versatile in their polymerization behavior in that they can form polymers with very different microstructures depending upon the initiator employed. Ring-opening metathesis polymerization (ROMP) initiators yield structures with an unsaturated backbone. 1 Olefin insertion initiators yield the 2,3addition polymer (or more correctly the 5,6-addition for the substituted monomers discussed herein), 2 and 2,6addition polymerizations (via intramolecular cyclizations) are produced when cationic 3 initiators are used. Radical-initiated polymerizations of norbornadiene results in a copolymer possessing both 2,3-and 2,6addition units. 4 However, selective 2,6-addition is observed in radical polymerizations of a monoester substituted norbornadiene, presumably due to resonance stabilization of the propagating radical. 5 These structures are illustrated in Scheme 1 for norbornadiene.
Reactive and Functional Polymers, 2006
Approaches to the synthesis of amine end-functional polystyrenes through intermediary phthalimido end-functional polystyrenes have been explored. Phthalimido groups can be quantitatively converted to amine groups by hydrazinolysis according to an Ing–Manske procedure. Approaches based on α- (functional initiator) and ω-functionalisation (end-group substitution) were examined. Thus, well defined, low molecular weight, ω-bromopolystyrenes, prepared by atom transfer radical polymerisation (ATRP) with copper(I) bromide, 4,4′-di-(nonyl)-2,2′ bipyridine (dNbpy) and 1-bromoethylbenzene initiator, were transformed into ω-phthalimidopolystyrenes by substitution with potassium phthalimide. However, elimination of the terminal bromine to form an unsaturated chain end was observed as a side reaction. Various α-phthalimidopolystyrenes were successfully prepared using phthalimido-functional initiators. Phthalimido-functional bromo isobutyrate derivatives proved very effective in yielding very low polydispersity polystyrene (Mw/Mn ∼ 1.1). However, the conversion of the derived α-phthalimidopolystyrense to an α-aminopolystyrene was problematic because of concomitant hydrazinolysis of the isobutyrate ester linkage and other side reactions. N-(Bromomethyl)phthalimide was successfully used as an ATRP initiator to prepare low polydispersity α-pthalimidopolystyrene (Mw/Mn ∼ 1.3) and thence α-aminopolystyrene with a high degree of end-group purity. End-group interconversions were followed by 1H NMR.
Here we report a versatile new method for endfunctionalizing polystyrene. In order to produce polystyrene with an amino end group, 2-(3-bromo-3-phenylpropyl)isoindoline-1,3-dione was synthesized and used as a novel initiator for ATRP. After ATRP polymerization, tri-n-butyltin hydride ((n-Bu) 3 SnH) reductively replace existing halogens on polymer chains by hydrogen. Finally, the phthaloyl groups on polymer backbone were cleaved by treatment with hydrazine yielding amino terminated polystyrene. A polymer with M n ≈10,350 and M w /M n 01.17 was obtained. Therefore, this method allows the preparation of amino end functionalized polystyrene of narrow polydispersity with complete degree of functionalization.