Semicrystalline Long-Chain Polyphosphoesters from Polyesterification

Abstract

Semicrystalline aliphatic polyphosphoesters can be obtained in a one-step approach by polyesterification of readily available bio-based long-chain diols with dichloro­phosphorus compounds. Nonadecane-1,19-diol and tricosane-1,23-diol with respectively methyl­phosphonic dichloride or phenyl dichlorophosphate yield polymers (PPE19Me, PPE23Me, PPE19­(OPh), and PPE23­(OPh)) with molecular weights M n up to 3 × 104 g mol–1. DSC analysis of these polymers and a C12 analogue reveal significantly enhanced crystallinities and melting points (up to T m = 87 °C) with increasing methylene sequence length. DMA on injection-molded samples shows glass transitions at −19 °C (PPE19Me) and −12 °C (PPE23Me). Single crystals of PPE19Me accommodate a single C19 repeat unit, as concluded from a lamella thickness of only 3 nm thick determined by AFM. Hydrolytic degradation of solid polymer samples under ambient conditions occurred only to a minimal extent over three months by hydrolysis of very small amounts of in-chain anhydride defects.

A nucleation mechanism leading to stacking of lamellar crystals in polymer thin films

“…For our experimental studies, we mainly used one model polymer system, thin films of isotactic polystyrene (iPS) with various molecular weights (iPS7: weight‐average molecular weight M W of 7100 Da; iPS13: M W of 13 000 Da; iPS48: M W of 48 000 Da), synthesized by the group of Mülhaupt (Freiburg, Germany) . In addition, to generalize the results obtained with thin films of iPS, we have performed complementary experiments with thin films of two other polymers: the first was poly(2‐vinylpyridine)‐ block ‐poly(ethylene oxide) copolymer (P 2 VP‐ b ‐PEO; M W of 16 400 + 46 600 Da), synthesized by the group of Möller (Aachen, Germany), and the second was polynonadecane methyl phosphonate (PE19Me, M W of 10 850 Da), synthesized by the group of Mecking (Konstanz, Germany) . The polymer PE19Me was synthesized by polycondensation of long‐chain diols with dichlorophosphonic compounds, rather than traditional ADMET method …”

“…Thus, after quenching, no significant morphological changes in the crystal structures were observed by optical microscopy. However, P 2 VP‐ b ‐PEO and PE19Me had much lower T g . Consequently, it was unavoidable that some morphological changes at the growth front of (dendritic) crystals occurred during cooling.…”

“…In polymer crystallization, the formation of stacks of correlated lamellar crystals, i.e. an assembly of crystalline lamellae, all oriented parallel to each other, has been observed quite frequently . Surprisingly, although the lamellae in such stacks are separated by amorphous interlayers resulting from chain folding, the orientation of these lamellae was found to be in crystallographic registry .…”

Aliphatic Long-Chain Polypyrophosphates as Biodegradable Polyethylene Mimics

“…18 However, in such nonpolar PE mimics, degradation under physiological or environmental conditions is very slow, rendering them as too stable for certain applications, in which degradation is demanded. 19 Recently, Mecking and co-workers synthesized long-chain polyphosphoesters by polyesterification and reported that a low number of pyrophosphate linkages were formed during the process. These bonds—undesired in polyphosphoesters (PPEs)—were however responsible for a partial degradation of the materials at mild hydrolysis conditions.…”

“…Upon immersing polymer films in basic or acidic conditions, cleavage occurred selectively in anhydride groups, and the phosphoester bonds remained intact during the course of their study. 19 To date, no polypyrophosphates have been reported as degradable mimics for PE with a potentially very fast hydrolysis.…”