Effect of Complexation of Monomer Units on pH- and Temperature-Sensitive Properties of Poly(N-vinylcaprolactam-co-methacrylic acid)

Abstract

Laser light scattering and differential scanning calorimetry measurements have been performed for aqueous solutions of thermosensitive linear copolymers of N-vinylcaprolactam and methacrylic acid of different composition. It was shown that the copolymers undergo a phase transition upon temperature increase in neutral and basic solutions. The enthalpy of the phase transition sharply decreases with the increase of methacrylic acid fraction, as shown by differential scanning calorimetry. The copolymers demonstrate pH-sensitive properties as well: intermacromolecular aggregation takes place in acidic media. FTIR spectroscopy measurements show that the aggregation is due to formation of insoluble macromolecular complexes. It was found that such complexes are also formed in the mixtures of homopolymers of poly(N-vinylcaprolactam) with poly(methacrylic acid). Effect of pH on thermosensitive properties of the copolymers is discussed. In weak acidic media there are narrow pH intervals close to pH of aggregation in which thermosensitive properties of the copolymers diminish considerably and the scattering intensity from the solutions at high temperatures is much less than at basic pH. Also, under these conditions the enthalpy of phase transition decreases significantly. The effect of a similarly charged surfactant (sodium dodecyl sulfate, SDS) on thermosensitive properties of the copolymer containing ∼40% of methacrylic acid is studied at pH 3 and 7. SDS solubilizes the copolymer, which is insoluble at pH 3; in the presence of SDS the copolymer is thermosensitive at both pH 3 and pH 7 at studied SDS concentrations; the transition temperature is higher than that of the copolymer in a surfactant-free solution. The enthalpy of the phase transition increases as SDS concentration in solution is increased.

Poly(N-vinylcaprolactam), a comprehensive review on a thermoresponsive polymer becoming popular

“…To further modulate the features of PNVCL aqueous solutions, PNVCL has been modified via copolymerization with a variety of monomers: 1-vinylimidazole (VIm) [51][52][53][54], 1-vinyl-2-methylimidazole (VMI) [55], N-vinylpyrrolidone (NVP) [14,20,29,[56][57][58], methacrylic acid (MAA) [19,59,60], Acrylic acid (AA) [50], 2-methacryloiloxybenzoic acid (2MBA) [19], sodium acrylate (SA) [61], N-acryloylsuccinimide (NASI) [62], nbutylacrylate (BA) [14,62], N,N-dimethylaminoethyl methacrylate (DMAEMA) [63,64], N,N-diethylaminoethyl methacrylate (DEAEMA) [19], methyl methacrylate (MMA) [47,65], vinyl acetate (VAc) [66], N-vinyl pivalate (NVPi) [66], 5-vinyltetrazole (VT) [67,68], 2-methyl-5-vinyltetrazole (MVT) [67], N-t-Boc-tryptophanamido-N'-methacryl thioureas (TrpAMT) [14], glycidyl methacrylate (GMA) [69], N-vinyl-N-acetate (VAc) [70], N-methyl-N-vinylacetamide (NVMA) [66,70], n-hexyl acrylate (HA) [19], acryloyl chloride (AC) [71], maleic acid (MA) [72], N-(t-butoxycarbonylaminopropyl)methacrylamide (t-BOCAPMA) [73], and alkyl acrylate derivations labeled with pyrene or naphthalene, as well as via grafting with PEO as an effective stabilizing agent …”

“…From the point of view of the synthetic methodology, free-radical copolymerization of NVCL in solution was performed in different solvents, such as p-dioxane [19,63,69,73], ethanol [51,54,[65][66][67][68], isopropanol [50,51,57], DMF [14,50,51,64], water [60,72], ethyl acetate [70], in mixtures of isopropanol and water [48], of DMSO and water [59], and in an emulsion of oil in water [47]. While the most widely used initiator was 2,2'-azobis(isobutyronitrile) (AIBN) [14,50,53,62,70,73], other initiators were also reported:…”

“…4,4'-azobis(4-cyanopentanol) [19], tert-butylperoxide [56], benzoylperoxide [70], azobisisobutyric acid dinitrile [67], hydrogen peroxide [48], and potassium persulfate (KPS) [60,72].…”

Functionalized Biocompatible Poly(N‐vinyl‐2‐caprolactam) With pH‐Dependent Lower Critical Solution Temperature Behaviors

“…This compositional drift is signifi cantly lower than that reported in copolymerization of VCL with MAA, where a 9:1 VCL:MAA molar feed ratio yielded a 1:1 ratio of VCL to MAA in the copolymer (50 mol% MAA). [ 29 ] It indicates that (1) the disparity of reactivity between VCL and its functional analog TBVCL is much less than that between VCL and MAA; and (2) TBVCL is more reactive than VCL, as a higher than theoretical percentage (10 mol%) of TBVCL was incorporated synthesized via nucleophilic substitution of VCL at the α -position with tert -butoxycarbonyl group (Scheme 1 ). [ 27 ] This monomer was previously reported specifi cally for applications as deep UV photoresists for lithography, [ 27 , 28 ] and to our best knowledge there is no prior study of its potential as smart biomaterials.…”

Thermosensitive graft copolymers of an amphiphilic macromonomer and N-vinylcaprolactam: synthesis and solution properties in dilute aqueous solutions below and above the LCST

“…The molecular weight distribution for all copolymers was approximately 1.7. The reactivity of VCL is known to be much lower than that of methacrylates [27]. Such a difference in reactivity usually leads to a non-random distribution of the grafts along the chain.…”