Facile conversion of RAFT polymers into hydroxyl functional polymers: a detailed investigation of variable monomer and RAFT agent combinations

Abstract

We report the systematic investigation of a recently introduced one-pot radical transformation of methacrylate and acrylate-type polymers prepared via reversible addition fragmentation chain transfer (RAFT) polymerization into hydroxyl functional polymers. The simple reaction procedure involves stirring a solution of the RAFT functional polymer and an azo-initiator in tetrahydrofuran at elevated temperatures (T ¼ 60 C) in the presence of ambient air. Subsequent reduction of the formed hydroperoxide functional polymers to hydroxyl functional polymers is achieved in a one-pot procedure using triphenylphosphine. Polymers investigated in the current study are poly(methyl acrylate) (pMA), poly(butyl acrylate) (pBA), poly(isobornyl acrylate) (piBoA) and poly(tert-butyl acrylate) (ptBA) carrying a dithiobenzoate or phenyldithioacetate end terminius as well as a symmetrical trithiocarbonate mid chain function. Quantitative conversion into the hydroperoxyl and hydroxyl terminated product is observed when trithiocarbonate functional polymers are employed. In the case of dithiobenzoate and phenyldithioacetate functional acrylic polymers, some minor side products due to the oxidation of the RAFT end-group are generated. Size exclusion chromatography (SEC) and size exclusion chromatography-electrospray mass spectrometry (SEC-ESI-MS) were employed to monitor the progress of the reaction and to investigate the proposed reaction mechanism for the model polymers. When trithiocarbonate functional polymers are employed in the transformation reaction, the SEC analysis shows a bisection of the initial M n . Collision induced dissociation (CID) MS experiments of the intermediate reaction products were conducted to gain in-depth information about the chemical structure. The new backbone linked hydroxyl group provides a versatile anchor for chemical end-group conversions and conjugation reactions with RAFT prepared polymers, alleviating problems with the rather limited ability of the dithioester end-group to undergo non-radical transformations.

Living Radical Polymerization by the RAFT Process – A Third Update

“…[182,605] The process was demonstrated for polymers with dithiobenzoate or dithiophenylacetate end-groups and for polymers with trithiocarbonate mid-groups (synthesized with dibenzyl trithiocarbonate) ( Table 19).…”

“…[44] The first reports involved the use of N,N-dialkyl dithiocarbamate derivatives as ATRP initiators. Dithiocarbamates do not provide effective control over the polymerization [241] MMA, St 456 Propylamine Network cleavage [603] BA, St 441 Butylamine/TCEP/BA In situ thiol-ene multiblock cleavage [604] PEGA 47 Butylamine/TCEP/divinyl sulfone In situ thiol-ene [281] MA, DMAm, NIPAm, St, C 2 H 5 S (121) Hydrazine - [375] St, PEGMA Ph (54, 18) Hydrazine - [375] St Ph (18) Hydrazine Used in thiol-epoxide [193] St Ph (18) DEAm (18) Hydrazine In situ thiol-epoxide [193] St/AcS Ph (11) Hydrazine Au nanoparticles [176] EGDMA, 421, 420 Ph (18) Hexylamine Used in thiol-ene or other reaction [588] St PhCH 2 S 1) KOH, 2) Zn/AcOH Au nanoparticles [338] St PhCH 2 S (89) Ethylene diamine Initiator for ROP C [339] HPMAm Ph (11) NaBH 4 /PBu 3 In situ thiol-ene (AA) [161] HPMAm Ph (68) Butylamine MeOH/degassed used in thiol-ene [307] NIPAm Ph (18) NaBH 4 Used in thiol-ene [247] MMA Ph (18) Hexylamine In situ thiol-ene [220] HPMAm Ph (18) Hexylamine In situ thiol-ene [220] NIPAm CH 2 (CO 2 H)CH 2 S (179) Hexylamine In situ thiol-ene [220] NIPAm C 4 H 9 S (159) Hexylamine/DMPP Used in thiol-ene [446] NIPAm C 12 H 25 S (123) Hexylamine/Bu 3 Ph Used in thiol-ene [398] Am Ph (18) NaBH 4 Used in thiol ene [244] DEAm Ph ( StMe OEt Ozone --(C¼O)SOEt [606] BA OEt Ozone --(C¼O)SOEt [607] iBoA 2-pyridyl Air AIBN, THF/Ph 3 P -OH [605] MMA, acrylates Ph Air AIBN, THF/Ph 3 P -OH [182,605] St, acrylates P n S Air AIBN, THF/Ph 3 P -OH [182] MA, BA CH 2 Ph Air AIBN, THF/Ph 3 P -OH [182] St CH 2 Ph Air AIBN, THF/Ph 3 P -OH …”

“…S S * BzMA [161] MMA [162] PEGMA [163] 302 [164] 301 [165] 312 [166] 396 [167] MA [168] PFPVB [169] PVS [169] St [132,162] 359 [170] St [171] BA [122] MMA/BDSMA [172] (MAA/TPMMA) [173] (MAA/293) [173] DEGMA/PEGMA [174] tBMA/DMAEMA/290 [175] MMA/LMA [163] 396-b-PEGMA [167] St/AcS [176] 4VP/EGDMA [177] (St-b-DMAEMA) [171] BzMA-b-HPMAm [161] DEGMA/PEGMA-b-DMAPMAm [174] PEGMA-b-MMA [163] LMA/MMA-b-PEGMA [163] 12 S S CN D* [178] MMA [178][179][180][181][182][183][184] PEGMA [111,185] GMA [186] 289 [186,187] 297 [188] 324 [189] 453 [190] iPOx [191] St [132,…”

“…[529] Further details of RAFT polymerization using 'switchable' RAFT agents that can be switched to offer good control over polymerization of both MAMs and LAMs and a route to poly-MAM-b-polyLAM has been reported. [530][531][532] [310] MA [182] BA [182] 348 [311] B/AN [312] 73 S S * St [313,314] BD [315] NIPAm [316] St/MAH [313] St [315] St-b-(St/BD) [314,315] St-b-(St/MAH) [313] ((St/MAH)-b-St) [313] 74 S S * MAA/EGDMA [291] 75 poly(3-hexylthiophene) macro-RAFT agent…”

“…S S S A* [331,335] CMS [336] St [182,[337][338][339] tBS [337] AN [331] BA [182,274] DMAEA [221] MA [182] iBoA [182] tBA [182] ODA [337] 2EHA [337] PEGA [340] NVP [248] (VAc) [274] B/AN [312] DVE/MAH [341,342] PEGA-b-CIPEA [340] ODA-b-NIPAm [337] 2EHA-b-NIPAm [337] St-bNIPAm [337] tBS-b-NIPAm [337] (BA-b-VAc) [274] DVE/MAH-bSt [341,342] …”