We report here metal-free strategies using organocatalysis based on supramolecular recognition for the ring-opening polymerization (ROP) of several cyclic phosphate monomers (CPMs) by a variety of organocatalysts such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]undec-5-ene (TBD), and a bicomponent thiourea–tertiary amine catalyst. Each of these catalysts is efficient to produce linear polyphosphoesters (PPEs) from CPMs but with different sensitivity toward transesterification side reactions. The strong basicity of DBU is sufficient to activate an alcohol initiating the polymerization in the absence of any other cocatalyst. Nevertheless, side chain transfer reactions leading to branched and/or cyclic polymeric structures are observed, especially for high monomer conversion. Unlike DBU, TBD is a dual catalyst activating both the alcohol and the monomer. This dual activation allows shorter polymerization time, but SEC analyses of polyphosphates reveal bimodal molecular weight distribution due to chains coupling. Finally, a mixture of DBU and thiourea (TU) appears by far the most efficient catalyst to carry out fast and controlled polymerization while minimizing transesterification reactions, even at near-complete conversion. Compared with polymerizations carried out with Sn(Oct)2 as a metal catalyst, the control of polymerization is much better so that it is possible to prepare polyphosphoesters (PPEs) with molecular weight close to 70 000 g mol–1 and polydispersity index below 1.10. Simultaneous activation by TU of both CPMs and the alcohol group of the initiator by DBU proves to be an effective and robust ROP catalytic system to synthesize polymers with predictable molecular weight and narrow polydispersity. The chain extension experiments through the use of hydroxy end-capped PPEs as macroinitiators confirm the controlled/living nature of the DBU/TU-catalyzed ROP of CPMs and pave the way to the synthesis of block copolymers based on polyphosphates.

SG1-based poly(d,l-lactide) (PLA) or poly(epsilon-caprolactone) (PCL) macro-alkoxyamines were synthesized and further used as macroinitiators for nitroxide-mediated polymerization (NMP) of 2-hydroxyethyl (meth)acrylate (HE(M)A) to obtain the corresponding PLA- or PCL-PHE(M)A block copolymers. First, a PLA-SG1 macro-alkoxyamine was prepared by 1,2-intermolecular radical addition (IRA) of the MAMA-SG1 (BlocBuilder) alkoxyamine onto acrylate end-capped PLA previously prepared by ring-opening polymerization. The NMP of HEA monomer from the PLA-SG1 macro-alkoxyamine appeared to be well controlled in the presence of free SG1 nitroxide, contrary to that of HEMA. In the latter case, adjustable molecular weights could be obtained by varying the HEMA to macro-alkoxyamine ratio. The versatility of our approach was then further applied to the preparation of PHEMA-b-PCL-b-PHEMA copolymers from a alpha,omega-di-SG1 functionalized PCL macro-alkoxyamine previously obtained from a PCL diacrylate by IRA. Preliminary studies of neuroblast cultures on these PCL-based copolymer films showed acceptable cyto-compatibility, demonstrating their potential for nerve repair applications.

Investigation of the micellization of degradable polyphosphoester based surfactants following a solvent-free process: the role of the pendent chain.

The properties of poly(D,L-lactide)-block-poly(2-hydroxyethyl acrylate) (PLA-b-PHEA) block copolymers by means of in vitro / in vivo (rat) degradation are investigated and compared to those of PLA homopolymer. Over 12 weeks, we observe mass loss and molecular weight decrease. In vitro and in vivo findings are very similar for each polymer tested. When a short PHEA block is used (PLA-b-PHEA 15 000-3 000 g · mol(-1) , 85/15 wt%), the degradation process is found to be very similar to that of homo-PLA, and to be typical of a bulk erosion mechanism, with no mass loss observed until week 7 and continuous decrease of molar mass within this timeframe. For a longer PHEA block length within the block copolymer (PLA-b-PHEA 15 000-7 500 g · mol(-1) , 65/35 wt%), the degradation mechanism is modified, with a significant mass loss observed at early times and only a slight decrease in molar mass. The latter finding is related to the pronounced hydrophilicity and softness of the material induced by the PHEA block, which allow easy diffusion and rapid leakage of the degradation residues from the material towards the aqueous medium. Schwann cells are found to better adhere on spin-coated films of PLA-b-PHEA (85/15 wt%) than on PLA ones. These results show the potential of such hydrophilized PLA-based copolymers for use in peripheral nerve repair.

The allyl phosphoester group is shown to be a protecting group for the synthesis of anionic polyphosphodiesters. Our strategy relies on the synthesis of a cyclic phosphate monomer bearing a pendant allyl phosphoester group, its easy purification by fractional distillation, its organocatalyzed ringopening polymerization by 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) and 1-[3,5-bis(trifluoromethyl)phenyl]-3-cyclohexyl-thiourea (TU). Finally, the deprotection of the allyl phosphoester group is carried out by reaction with sodium benzenethiolate in the absence of any detectable degradation.