Synthesis and characterization of “Living” star‐shaped poly(N‐vinylcaprolactam) with four arms and carboxylic acid end groups

Abstract

Poly(N-vinylcaprolactam) (PNVCL) star-shaped polymers with four arms and carboxyl end groups were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylcaprolactam (NVCL) employing a tetrafunctional trithiocarbonate as an R-RAFT agent. The resulting star polymers were characterized using 1 H NMR, FT-IR, gel permeation chromatography (GPC), and UV-vis. Molecular weight of star polymers were analyzed by GPC and UV-vis being observed that the values obtained were very similar. Furthermore, the thermosensitive behavior of the star polymers was studied in aqueous solution by measuring the lower critical solution temperature by dynamic light scattering. Starshaped PNVCL were chain extended with ethyl-hexyl acrylate (EHA) to yield star PNVCL-b-PEHA copolymers with an EHA molar content between 4% and 6% proving the living character of the star-shaped macroCTA. These star block copolymers form aggregates in aqueous solutions with a hydrodynamic diameter ranged from 170 to 225 nm.

Preparation of a Mini-Library of Thermo-Responsive Star (NVCL/NVP-VAc) Polymers with Tailored Properties Using a Hexafunctional Xanthate RAFT Agent

“…This behavior is different from that previously reported for other PNVCL star polymers [33]. Generally, the D h above the LCST (maximum value) of the aggregates is related to the molecular weight: lower M n , yield aggregates with smaller size [33]. To evaluate the influence of the xanthate end group on the LCST, four samples of (PNVCL)6 were subjected to removal of this group by using the method of radical-induced reduction [18].…”

“…This is because the hydrophobic PVAc segment is concentrated in the core of the flower-like micelle; consequently, its molecular mobility is reduced. The preparation of star-like architectures in which the hydrophobic segment is located at the end of the polymeric chain is rare in the literature [33,34,66,67]. It can be expected that in aqueous solution these kinds of polymers would tend to form flower-like micellar aggregates of the star block copolymers, or large associations between these segments leading to the formation of physical networks [66,67].…”

“…Poly( N -vinylcaprolactam)- b -poly(vinyl acetate) (PNVCL- b -PVAc) is an interesting amphiphilic combination that has emerged in the last years. PNVCL is biocompatible, thermoresponsive and water-soluble below its lower critical solution temperature (LCST) [ 31 , 32 , 33 , 34 , 35 , 36 ]. For its part, PVAc is a hydrophobic, biocompatible and biodegradable polymer used in pharmaceutical applications [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ].…”

Dendritic poly(benzyl ether)‐b‐poly(N‐vinylcaprolactam) block copolymers: Self‐organization in aqueous media, thermoresponsiveness and biocompatibility

“…The linearly PNVCL‐based block copolymers have gained much impetus in recent years due to the enhanced boost of the so‐called controlled free radical polymerization methods, such as atom transfer free radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT) polymerization, or organometallic‐mediated radical polymerization . However, only six recent articles were concerned on nonlinear block copolymers containing the PNVCL moiety . Recently, star‐shaped copolymers with four and six poly(ε‐caprolactone)‐block‐poly( N ‐vinylcaprolactam) S(PCL‐ b ‐PNVCL) arms were successfully synthesized by combining ring opening polymerization of ε‐caprolactone (CL) and RAFT polymerization of N ‐vinylcaprolactam (NVCL) .…”

“…[35][36][37] However, only six recent articles were concerned on nonlinear block copolymers containing the PNVCL moiety. [38][39][40][41][42][43] Recently, star-shaped copolymers with four and six poly(e-caprolactone)-block-poly(N-vinylcaprolactam) S(PCL-b-PNVCL) arms were successfully synthesized by combining ring opening polymerization of e-caprolactone (CL) and RAFT polymerization of N-vinylcaprolactam (NVCL). 39 Hyperbranched polycaprolactone-click-poly(N-vinylcaprolactam) amphiphilic copolymers was synthesized.…”