Conetworks

Tiller JC, Sprich C, Hartmann L (2005) Amphiphilic conetworks as regenerative controlled releasing antimicrobial coatings. J Control Release 103 355-367... 

Physical and mechanical properties of amphiphilic and adaptative polymer conetworks produced by Atom Transfer Radical Polymerization... 

The overall synthesis of both PCL cross-linkers and poly[2-(N,N-dimethylamino)ethyl methaciylate-/mA eJ-poly(8-caprolactone)] model amphiphilic conetworks PDMAEMA-/-PCL have been already reported in a separate contribution with all experimental conditions described in details (33). 

Scheme 1 Three-step synthesis ofpoly[2-(N,N-dimethylamino)ethyl methacrylate-l-poly(s-caprolactone)] conetworks (PDMAEMA-l-PCL)...

Table I. Molecular parameters of PDMAEMA-/-PCL conetwork samples as obtained by ATsi in THF at 60°C, initiated by E BBr and catalyzed by CuBr.2HMTETA for an initial comonomer concentration of 4.8 moLL and various degrees of cross-linking.

Figure 2 Swelling behavior of a representative PDMAEMA-l-PCL polymer conetwork (Entry 1, Table 1) in toluene at r.t.

Table I (entries 2-4) presents molar and weight compositions as well as the gel fraction (Fq) of the polymer conetworks as recovered after 24h of reaction. Note also that Fq was determined from the following relationship Fq = Wg / Wp (after extraction of the remaining soluble fraction) where Wg and Wp represent the weight of the final insoluble part and the initial weight of all introduced...

Scheme 2 Synthesis ofP(DMAEMA-co-PCLMA)-l-PCL conetworks with different degrees of cross-linking and constant PCL content by ATRP copolymerization between DMAEMA, PCLDMA cross-linker and PCLMA...

Figure 3 Swelling behavior ofP(DMAEMA-co-PCLMA)-l-PCL polymer conetworks in Millipore water atr.t. in function of the cross-linking degree 0) 2 mol%, d) 3 mol% and A) 4 mol% in dimacromonomer (see Table I, entries 2-4).

Figure 7 Temperature dependence of the swelling degree at equilibrium as recorded in water for a representative conetwork (Entry I, Table 1).

Figure 8 Reversibility of swelling-deswelling behavior as a function of time by varying the temperature between 20 and 60°C in Millipore water at r.t. [PDMAEMA-l-PCL conetwork sample from Table I, Entry 1]...

Detenuination of the state of water molecules in PDMAEMA-/-PCL conetworks... 

Table II. Fraction of non freezable (bound) water and freezable (intermediate + bulk-like) water in PDMAEMA-/-PCL conetwork (from Entry 1, Table 1) at three different swelling degrees.

In a first series of experiments, the positive impact of the incorporation of PCL segments on the mechanical properties of the PDMAEMA-/-PCL conetworks have been highlighted by comparing the resulting true strain-strain curve with that displayed by a PDMAEMA homopolymer network ([DMAEMA]o/[I]o = 100, Fuegdma = 3%, Fq = 95.4%), both produced by ATRP in the same conditions. The PCLDMA cross-linker employed for this study was characterized by an average molecular weight of 4300 g.mof and a Mw/M of... 

Young modulus, ultimate strength and percent elongation at break have been also determined experimentally for PDMAEMA-/-PCL conetworks with different contents in cross-linker ranging from 2 to 4 mol% but with a constant PCL weight fraction fixed at 31.1% (see Table I, entries 2-4). As a reminder, these APCNs were synthesized by ATRP copolymerization of DMAEMA with the suited amount of PCLDMA cross-linker (Mn = 1700 g.mof, M, /Mn = 1.2) and PCLMA macromonomer (Mn = 1700 g.mof, M /Mn = 1.07) as illustrated by Scheme 2. As expected, an increase of the Young Modulus with the crosslinker content was observed (Figure 12). 

Figure 12 Evolution of the Young modulus ofPDMAEMA-l-PCL conetworks (Table /, Entries 2-4) with increasing cross-linker concentration from 2 to 4% (at constant hydrophobic PCL content 31.1 wt%).

According to the aforementioned adaptative properties displayed by the PDMAEMA-/-PCL APCNs, the Young modulus has been also recorded as a function of the solution pH. For this purpose, specimens of a polymer conetwork (Entry 2, Table III) were allowed to swell until equilibrium in aqueous solution buffered at pH 4, 7 and 9, respectively, prior mechanical testing. It is worth mentioning that the ionic strength was maintained constant and fixed to 0.05... 

Figure 14 Effect ofpH on the Young modulus for a swollen representative PDMAEMA-l-PCL conetwork (Entry 2, Table 3) at r.t.

Figure 16 Evolution of the swelling degree of a representative PDMAEMA-l-PCL conetwork in SBF at 37°C (inset evolution over the first two days).

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