Thermal Properties of Aliphatic Polypeptoids

Abstract

A series of polypeptoid homopolymers bearing short (C 1 -C 5 ) side chains of degrees of polymerization of 10-100 are studied with respect to thermal stability, glass transition and melting points. Thermogravimetric analysis of polypeptoids suggests stability to >200 °C. The study of the glass transition temperatures by differential scanning calorimetry revealed two dependencies. On the one hand an extension of the side chain by constant degree of polymerization decrease the glass transition temperatures (T g ) and on the other hand a raise of the degree of polymerization by constant side chain length leads to an increase of the T g to a constant value. Melting points were observed for polypeptoids with a side chain comprising not less than three methyl carbon atoms. X-ray diffraction of polysarcosine and poly(N-ethylglycine) corroborates the observed lack of melting points and thus, their amorphous nature. Diffractograms of the other investigated polypeptoids imply that crystalline domains exist in the polymer powder.

Polypeptoid polymers: Synthesis, characterization, and properties

“…In recent years, the substrate scope for polymerization studies was further expanded to include a variety of R-NCA monomers bearing various N-substituents ( Figure 2). [5,6,[15][16][17][18][19][20][21][22] Luxenhofer et al demonstrated that the polymerizations of Me-NCAs using benzyl amine initiators were shown to proceed in a controlled manner without chain transfer or termination events, producing polysarcosines with narrow Poisson distribution (PDI < 1.1-1.3) and M n s that can be controlled by the initial monomer to initiator feed ratios. [56] The molecular distribution remains narrow (PDI 5 1.01-1.07) even after ten sequential polymerizations of Me-NCA monomers (DP < 100), attesting to the robustness of the living polymerization and suggesting the potential uses of the methods towards the synthesis of well-defined block copolypeptoids via sequential monomer addition.…”

“…[20][21][22]24] Polypeptoids with linear aliphatic N-substituents shorter than 2 carbons are amorphous, whereas polymers with longer linear aliphatic N-substituents (n 5 3, 4, 5, 6, 8, 10, 12, and 14) tend to be highly crystalline and pack into SCHEME 9 Postpolymerization functionalization of polypeptoids SCHEME 10 Synthesis of a library of cationic polypeptoids bearing different cationic amino groups (P1-P4), backbone chain lengths (DPs) (P4-P7), hydrophobic linker lengths (P4, P8, P9, and P10) and incorporation of hydrophobic N-substituents (P11). [78] Adapted with permission from the American Chemical Society lamellar structure in the solid state ( Figure 9A).…”

“…[78] Adapted with permission from the American Chemical Society lamellar structure in the solid state ( Figure 9A). [21,22] Asymmetric branching of the aliphatic N-substituents (eg, 2-ethylhexyl) suppresses the degree of crystallization. [21] A comparative study of cyclic and linear polypeptoids bearing linear aliphatic N-substituents with more than 4 carbons (n 5 4, 6, 8, 10, 12, and 14) revealed that all polymers exhibited two melting points (T m1 and T m2 ) due to the sidechain and main chain crystalline packing ( Figure 9B).…”

“…The physicochemical properties of polypeptoids can be tailored by the N-substituent structures, enabling control over the hydrophilicity and lipophilicity balance (HLB), charge characteristics, [13,14] backbone conformation, [1][2][3][4][5][6][7][8][9][10][11][12] solubility, [15][16][17][18][19][20] thermal and crystallization properties of the polypeptoids. [21][22][23][24] Without extensive hydrogen bonding, polypeptoids are thermally processable similar to conventional thermoplastics, [20][21][22][23][24] whereas polypeptides undergo thermal degradation before they can be melt-processed due to the extensive hydrogen bonding interactions. While polypeptoids exhibited enhanced proteolytic stability relative to peptides, [25,26] they can be oxidatively degraded under conditions that mimic tissue inflammation, [27] suggesting their potential in vivo uses as biodegradable materials.…”

Synthesis of Amphiphilic Block Copolypept(o)ides by Bifunctional Initiators: Making PeptoMicelles Redox Sensitive

“…mp = 100.9 °C (5 °C min −1 ), 1 Sarcosine-N-Carboxyanhydride : The synthesis of sarcosine NCA was adapted from literature and modifi ed. [ 31 ] Sarcosine (15.16 g, 170.2 mmol, 1 eq) was weighed into a predried three-neck round-bottomed fl ask and dried in vacuo for 1 h. 300 mL of abs. THF were added under a steady fl ow of nitrogen and diphosgene (16.26 mL, 134 mmol, 0.8 eq) was added slowly via syringe.…”