In the last decades, many efforts have been focused on the combination of macromolecules with highly different characteristics in a single structure. Amphiphilic conetworks (APCNs) 1-3 built from hydrophilic and hydrophobic polymer chains, are exclusive representatives of this class of materials, having unique properties, such as biocompatibility, 4 mechanical strength, 5-8 amphiphilic swelling 1-3 as well as nanophase-separated structure 5-7,9 not only in short, but also in long-range order. 9(a,b) These properties make APCNs preferred for biomedical applications, as well as interesting for material and polymer science. [10][11][12] Varying the covalently interconnected hydrophilic and hydrophobic components is a great tool to change and tune the properties of these conetworks. Surprisingly, there are only a few studies in the literature on polyacid-based APCNs, 5-7,13-17 even poly(methacrylic acid) (PMAA), and poly(acrylic acid) (PAA) are substantial polymers for biological applications or metal ion binding. [18][19][20][21] Also an important feature of the negatively ionizable polymeric segments is that they could have an effect on the phase separation, particularly in the swollen state. The hydrophobic part of the conetworks can improve the physical-chemical properties of the network, compared to pure polyacidic hydrogels, such as mechanical stability and salt resistance, as it was already investigated and proved for polyisobutylene, 5,16,22 methyl methacrylate, 7 and 2-butyl-1-octyl methacrylate-based 6 PMAA-based APCNs. PAA is a wellknown pH and salt responsive, highly hydrophilic negatively ionizable polymer that can form superabsorbent gels. [18][19][20][21] In the literature, this polyacid was combined mostly with polydimethylsiloxane, polytetrahydrofuran, and polyalkylacrylate, [13][14][15]23,24 but the combination with the very apolar biocompatible polymer, polyisobutylene (PIB) was only achieved once with some contradictive results. 25 In this case, the hydrophobic part was a statistical copolymer of 3-isopropenyl-a,a-dimethylbenzyl isocyanate, and isobutylene resulting in cross-linking throughout the polymer chain. 25Besides the strength of this paper of Toman et al., there is no clear evidence in this report on the formation of conetworks in a wide composition range using PAA and the statistical PIB copolymer. One of the major problems with their materials is related to the far higher glass transition temperature (T g ) of polyacid than that of the expected T g and the temperature where anhydride formation already takes place. The compositions, determined by 13 C NMR, do not correspond to the composition and the amount of separately dissolved hydrophilic and hydrophobic extractables, what is also a controversial result of this study. 25Polyisobutylene itself is a highly hydrophobic, fully saturated, biocompatible, and rubbery polymer with good resistance against chemical and physical impacts. PIB provides increased mechanical strength to its conetworks as it was already tested on PMAAbased APCNs....
Bulk, solventless anionic ring-opening polymerization (AROP) of ε-caprolactam (CPL) with high yields, without side products and with short reaction times, initiated by caprolactamate-carbamoylcaprolactam initiating systems belong to green polymerization processes, leading to poly(ε-caprolactam) (Polyamide 6, PA6, Nylon 6). However, the effect of post-polymerization heat (i.e., slow, technically feasible cooling) on the fundamental characteristics of the resulting polymers such as yield and molecular weight distributions (MWDs) have not been revealed thus far. Significant post-polymerization effect was found by us in terms of both monomer conversions and MWDs by carrying out CPL polymerization with industrial components under conditions mimicking thermoplastic reaction transfer molding (T-RTM). Remarkably, higher monomer conversions and molecular weights (MWs) were obtained for Polyamide 6 samples prepared without quenching than that for the quenched polymers at the same reaction times. Independent of quenching or non-quenching, Mn of the resulting polymers as a function of conversion fell in the theoretical line of quasiliving AROP of CPL. At high monomer conversions, significant increase of the MW and broadening of the MWDs occurred, indicating pronounced chain–chain coupling. These findings have fundamental importance for designing processing conditions for in situ polymerization processes of ε-caprolactam by various techniques such as T-RTM, reaction injection molding (RIM), and other processing methods of Polyamide 6.
The glass transition temperature (Tg) is one of the most important properties of polymeric materials. In order to reveal whether the scissors effect, i.e., the Fox–Flory relationship between Tg and the average molecular weight between crosslinking points (Mc), reported only in one case for polymer conetworks so far, is more generally effective or valid only for a single case, a series of poly(methyl methacrylate)-l-polyisobutylene (PMMA-l-PIB) conetworks was prepared and investigated. Two Tgs were found for the conetworks by DSC. Fox–Flory type dependence between Tg and Mc of the PMMA component (Tg = Tg,∞ − K/Mc) was observed. The K constants for the PMMA homopolymer and for the PMMA in the conetworks were the same in the margin of error. AFM images indicated disordered bicontinuous, mutually nanoconfined morphology with average domain sizes of 5–20 nm, but the correlation between Tg and domain sizes was not found. These new results indicate that the macrocrosslinkers act like molecular scissors (scissors effect), and the Tg of PMMA depend exclusively on the Mc in the conetworks. Consequently, these findings mean that the scissors effect is presumably a general phenomenon in nanophase-separated polymer conetworks, and this finding could be utilized in designing, processing, and applications of these novel materials.
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